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Valuing a Test for Nitrogen Status in Rice
03 November 2005University of SydneySingh, Rajinder;Williams, Robert;Mullen, John;Faour, KhaledNitrogen is a crucial input for the efficient production of rice and is generally applied in two split treatments. The first treatment is given before flooding the rice paddocks at sowing time ie at the pre-flooding (PF) stage. The second treatment is applied within a week after the beginning of the panicle initiation (PI) stage. There is no pre-sowing test to estimate nitrogen requirements and farmers use cropping history to make this decision. Later in the season further nitrogen can be applied on the basis of existing Near Infra-red Reflectance (NIR) based nitrogen tissue test but yield potential has often been established by this time. A further source of yield risk is temperature prior to flowering and at high rates of nitrogen there is a potential for yield losses at low temperatures. The aim of one of the projects, funded by the Cooperative Research Centre (CRC) for Sustainable Rice Production, is to develop a nitrogen test for soils of rice paddocks. This would help determine the amount of nitrogen available in the soil and how much more nitrogen needs to be applied at the PF stage. The aim of this study is to first value the information that is provided to the rice growers at PF by the soil test on nitrogen availability and then measure returns to investment on research and extension to develop and promote this test. The problem is first presented in a decision tree framework. The Bayesian framework is then applied, where information provided by the test is used to revise perceived probabilities of yield outcomes under different nitrogen regimes. MaNage rice, a bio-economic model, is used to work out payoffs from different rates of nitrogen at PF on different nitrogen status soils. Finally, returns to investment on R&D are measured within a benefit-cost framework. The results reveal that the information provided by the soil test is valuable as the test helps farmers to use nitrogen more profitably. The outcome of the benefit-cost analysis shows that with the current accuracy levels the benefits from the new test are not sufficient to meet the costs involved on research. If the scientists were able to improve the accuracy of the test (ie at par with existing NIR tissue test), the returns to investment on the project would be quite significant.
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Spherical functions on homogeneous superspaces
17 February 2016University of SydneyZhang, Ruibin;Zou, Yi-MingHomogeneous superspaces arising from the general linear supergroup are studied within a Hopf algebraic framework. Spherical functions on homogeneous superspaces are introduced, and the structures of the superalgebras of the spherical functions on classes of homogeneous superspaces are described explicitly.
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Powering a Modern Life? Residents’ Experiences of the Electricity Supply in Tanjung Pinang
01 November 2019University of SydneyFord, MicheleAccess to an affordable and reliable electricity supply is vital not only for economic development but also for citizens’ quality of life. Indonesia has made significant progress towards near-universal electrification, but this achievement masks vast disparities in household access to electricity. Problems with affordability and reliability of supply are experienced even in Indonesia’s major cities but are far worse in remote areas and on the country’s many hundreds of inhabited small islands, which are not connected to a major grid. Drawing on Indonesian government data and a survey of householders (N = 360), this article measures variations in the quantity and quality of electricity supply in different areas in Tanjung Pinang, the capital of Riau Islands province (Kepri). As this article demonstrates, interruptions in supply have a serious impact on residents’ capacity to power a modern life. Akses terhadap listrik yang murah dan dapat diandalkan adalah sesuatu yang vital, tidak hanya bagi perkembangan ekonomi, namun juga bagi kualitas hidup para penduduk. Indonesia telah membuat kemajuan yang signifikan hingga mencapai tingkat elektrifikasi yang mendekati universal, namun pencapaian ini menutup ketimpangan akses rumah tangga terhadap kelistrikan. Permasalahan terkait keterjangkauan dan keterandalan penawaran listrik dialami bahkan di kota-kota besar di Indonesia, namun jauh lebih buruk di area-area terpencil dan di ratusan pulau kecil berpenghuni di seluruh Indonesia, yang tidak terkoneksi dengan jaringan listrik besar. Dengan menggunakan data pemerintah dari survey rumah tangga (jumlah sampel 360), tulisan ini mengukur variasi pada kuantitas dan kualitas penawaran listrik di berbagai daerah di Tanjung Pinang, ibukota dari provinsi Kepulauan Riau (Kepri). Seperti yang didemonstrasikan dalam tulisan ini, gangguan listrik memiliki dampak yang serius terhadap kapasitas warga untuk mulai menikmati kehidupan modern.
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Coordinated residential energy resource scheduling with vehicle-to-home and high photovoltaic penetrations
30 January 2020University of SydneyLuo, Fengji;Ranzi, Gianluca;Kong, Weicong;Dong, Zhao Yang;Wang, FanHome Energy Management System (HEMS) provides an effective solution to assist residential users in dealing with the complexity of dynamic electricity prices. This paper proposes a new HEMS in contexts of real-time electricity tariff (RTP) and high residential photovoltaic penetrations. Firstly, the HEMS accepts user-specified Residential Energy Resource (RER) operation restrictions as inputs. Then, based on the forecasted solar power outputs and electricity prices, an optimal scheduling model is proposed to support the decision-making of the RES operations. For the scheduling of Heating, Ventilating, and Air Conditioning (HVAC) system, an advanced adaptive thermal comfort model is employed to estimate the user’s indoor thermal comfort degree. For the controllable appliances, the ‘User Disturbance Value (UDV)’ metric is proposed to estimate the psychological disturbances of an appliance schedule on the user’s preference. The proposed scheduling model aims to minimize the future 1-day energy costs and disturbances to the user. A new biological self-aggregation intelligence inspired metaheuristic algorithm recently proposed by the authors (a Natural Aggregation Algorithm, NAA), is applied to solve the model. Extensive simulations are conducted to validate the proposed method.
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Hierarchical Energy Management System for Home Microgrids
30 January 2020University of SydneyLuo, Fengji;Ranzi, Gianluca;Wang, Shu;Dong, Zhao YangWith the spread of distributed energy resources, sensing infra-structure, and automation facilities, modern homes are becoming “home microgrids”. This paper intends to support this trend and proposes a two-stage hierarchical energy management system for smart homes by considering both day-ahead and actual operation stages. In the day-ahead stage, an efficient scenario analysis ap-proach is developed to account for the residential photovoltaic solar power uncertainty. The approach performs solar power scenario generation and reduction based on the Wasserstein dis-tance metric and K-medoids, respectively. This is then followed by the use of a stochastic day-ahead residential energy resource scheduling model. In the actual operation stage, a Semi-Scenario based Rolling Horizon Optimization (SSRHO) mechanism is proposed, based on which an actual operation model is estab-lished. Simulations are then conducted to validate the effective-ness of the proposed system
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A Multi-Stage Home Energy Management System with Residential Photovoltaic Penetration
30 January 2020University of SydneyLuo, Fengji;Ranzi, Gianluca;Wan, Can;Xu, Zhao;Dong, Zhao YangAdvances in bilateral communication technology foster the im-provement and development of Home Energy Management Sys-tem (HEMS). This paper proposes a new HEMS to optimally schedule home energy resources (HERs) in a high rooftop photo-voltaic penetrated environment. The proposed HEMS includes three stages: forecasting, day-ahead scheduling, and actual opera-tion. In the forecasting stage, short-term forecasting is per-formed to generate day-ahead forecasted photovoltaic solar pow-er and home load profiles; in the day-ahead scheduling stage, a Peak-to-Average Ratio (PAR) constrained coordinated HER scheduling model is proposed to minimize the 1-day home opera-tion cost; in the actual operation stage, a Model Predictive Con-trol (MPC) based operational strategy is proposed to correct HER operations with the update of real-time information, so as to minimize the deviation of actual and day-ahead scheduled net-power consumption of the house. An adaptive thermal comfort model is applied in the proposed HEMS to provide decision-support on the scheduling of the heating, ventilating, and air con-ditioning (HVAC) system of the house. The proposed approach is then validated based on Australian real datasets.
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Optimal Home Energy Management System WithDemand Charge Tariff and ApplianceOperational Dependencies
30 January 2020University of SydneyLuo, Fengji;Kong, Weicong;Ranzi, Gianluca;Dong, Zhao YangTwo-way communication facilities and advanced metering infra-structure enable residential buildings to be capable of actively participating in demand side management schemes. This paper proposes a new home energy management system (HEMS), which optimally schedules the operation of home energy resources, with the aim to minimize the home’s one-day electricity cost charged by the real-time pricing while taking into account the monthly basis peak power consumption penalty, charged by the demand charge tariff. To better ensure the user’s lifestyle requirements, the HEMS also models lifestyle-related operational dependencies of household appliances. Numerical simulations and case studies are conducted to validate the reasonability of the proposed method.
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Service Recommendation in Smart Grid: Vision, Technologies, and Applications
30 January 2020University of SydneyLuo, Fengji;Ranzi, Gianluca;Wang, Xibin;Dong, Zhao YangDriven by the energy crisis and global warming problem, smart grid was proposed in the early 21th century as a solution for the sustainable development of human society. With the two-way communication infrastructure available in smart grids, a current challenge is to interpret and gain knowledge from the collected grid big data to optimize grid operations. Service recommendation techniques provide promising tools to discover knowledge from the grid data, and recommend energy-aware products/services/suggestions to the smart grid participators. This paper is among the first to investigate the prospective of introducing service recommendation techniques into the smart grid demand side management (DSM). In the first part of the paper, the backgrounds of smart grid DSM and service recommendation techniques are reviewed, followed by the presentation and discussion of key technologies that can facilitate the development of smart grid recommender systems. An outline on potential application scenarios of smart grid recommender systems as well as future challenges are also provided.
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Household Appliance Commitment with Appliance Dependency Modelling
30 January 2020University of SydneyLuo, Fengji;Ranzi, Gianluca;Kolokotroni, MariaSmart home energy management is one of the main topics in demand side management. In the literature, many Home Energy Management Systems (HEMSs) are designed to optimally schedule the operation of household appliances. However, most of existing work ignores the lifestyle related requirements of the user on the appliances’ operational dependencies. In this paper, we propose a new household appliance commitment model that integrates both the operational constraints of individual appliances and the dependency constraints among them. In this sense, the proposed HEMS can more accurately reflect the end user’s lifestyle requirements. Several simulation scenarios are designed to validate the proposed HEMS.
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Risk and Financial Management of COVID-19 in Business, Economics and Finance
18 June 2020University of SydneyChang, Chia-Lin;McAleer, Michael;Wong, Wing-KeungThe SARS-CoV-2 coronavirus that causes the COVID-19 disease led to the most significant change in the world order over the past century, destabilizing the global economy and financial stock markets, the world’s economy, social development, business, risk, financial management and financial markets, among others. COVID-19 has generated great uncertainty, and dramatically affected tourism, travel, hospitality, supply chains, consumption, production, operations, valuations, security, financial stress and the prices of all products, including fossil fuel and renewable energy sources. This Editorial introduces a Special Issue of the Journal of Risk and Financial Management (JRFM) on the “Risk and Financial Management of COVID-19 in Business, Economics and Finance”. This Special Issue will attract practical, state-of-the-art applications of mathematics, probability and statistical techniques on the topic, including empirical applications. This paper investigates important issues that have been discussed in tourism, global health security and risk management in business as well as the social and medical sciences.
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Healthy power: Reimagining hospitals as sustainable energy hubs
17 November 2020University of SydneyGurieff, N.;Green, D.;Koskinen, I.;Lipson, M.;Baldry, M.;Maddocks, A.;Menictas, C.;Noack, J.;Moghtaderi, B.;Doroodchi, E.Human health is a key pillar of modern conceptions of sustainability. Humanity pays a considerable price for its dependence on fossil-fueled energy systems, which must be addressed for sustainable urban development. Public hospitals are focal points for communities and have an opportunity to lead the transition to renewable energy. We have reimagined the healthcare energy ecosystem with sustainable technologies to transform hospitals into networked clean energy hubs. In this concept design, hydrogen is used to couple energy with other on-site medical resource demands, and vanadium flow battery technology is used to engage the public with energy systems. This multi-generation system would reduce harmful emissions while providing reliable services, tackling the linked issues of human and environmental health.
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Insight into Three‐Coordinate Aluminum Species on Ethanol‐to‐Olefin Conversion over ZSM‐5 Zeolites
22 January 2021University of SydneyWang, Zichun;O'Dell, L. A.;Zeng, Xin;Liu, Can;Zhao,Shufang;Zhang, Wenwen;Gaborieau, Marianne;Jiang, Yijiao;Huang, JunCommercial bioethanol can be readily converted into ethylene by a dehydration process using solid acids, such as Brønsted acidic H‐ZSM‐5 zeolites, and thus, it is an ideal candidate to replace petroleum and coal for the sustainable production of ethylene. Now, strong Lewis acidic extra‐framework three‐coordinate Al3+ species were introduced into H‐ZSM‐5 zeolites to improve their catalytic activity. Remarkably, Al3+ species working with Brønsted acid sites can accelerate ethanol dehydration at a much lower reaction temperature and shorten the unsteady‐state period within 1–2 h, compared to >9 h for those without Al3+ species, which can significantly enhance the ethanol dehydration efficiency and reduce the cost. The reaction mechanism, studied by solid‐state NMR, shows that strong Lewis acidic EFAl‐Al3+ species can collaborate with Brønsted acid sites and promote ethanol dehydration either directly or indirectly via an aromatics‐based cycle to produce ethylene.
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Enhancing hydrogen production from the pyrolysis-gasification of biomass by size-confined Ni catalysts on acidic MCM-41 supports
22 January 2021University of SydneyYe, Mengjing;Tao, Yongwen;Jin, Fangzhu;Ling, Huajuan;Wu, Chunfei;Williams, Paul T.;Huang, JunHydrogen, currently produced from the reforming of fossil fuel resources, is a significant source for clean energy and the chemical industry. It is promising to develop a high-efficiency hydrogen production process from renewable biomass for sustainable development. This research reports that catalyst support acidity could strongly enhance the hydrogen production from the biomass gasification of wood sawdust. For minimizing the influence of the Ni particle size for the biomass gasification, the uniform Ni nanoparticles around 2–3 nm were loaded into one type of mesoporous support MCM-41 with various acidity. Ni/H-[Al] MCM-41 with a large amount of Brϕnsted acid sites contributed 2–3 times higher hydrogen yield (21.6 mmol H2 g−1 sample) than that on Ni/H-[Si]MCM-41 with a small amount of very weak acidic surface SiOH groups (9.8 mmol H2 g−1 sample) and that on nonacidic Ni/Na-[Si]MCM-41 (6.7 mmol H2 g−1 sample). The surface acid sites on supports could generate bifunctional catalysts and were proposed to show two functions for enhancing the hydrogen production: 1) help to crack and transfer the pyrolysis chemicals into smaller compounds for more efficient reforming on the Ni surface inside nanopores; 2) enhance the support and Ni interaction for better reduction property and surface activity of Ni nanoparticles and improve the reforming performance. The obtained Ni/MCM-41 catalysts were quite stable and no sintering has been observed after the gasification at 800 °C, and only a low coke deposition has been detected.
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Unravelling the effects of layered supports on Ru nanoparticles for enhancing N2 reduction in photocatalytic ammonia synthesis
22 January 2021University of SydneyLiu, Huimin;Wu, Ping;Li, Haitao;Chen, Zibin;Wang, Lizhuo;Zeng, Xin;Zhu, Yuxiang;Jiang, Yijiao;Liao, Xiaozhou;Haynes, Brian S.;Ye, Jinhua;Stampfl, Catherine;Huang, JunHarnessing the vast supply of solar energy as the driving force to produce ammonia from abundant nitrogen gas and water is beneficial for both relieving energy demands and developing sustainable chemical industry. Bulk carbon nitride (B-g-C3N4), exfoliated carbon nitride (E-g-C3N4) and graphite (g-C) supported Ru-K catalysts, denoted as Ru-K/B-g-C3N4, Ru-K/E-g-C3N4 and Ru-K/g-C, respectively, with the layered materials serving both as supports and light harvesters, were designed for photocatalytic ammonia synthesis. It was discovered that, besides the light harvesting properties of the catalysts which played roles in photocatalytic reactions, the structure of the supports influenced greatly the preferential locations of Ru species, which further exerted effects on the N2 activation process and ultimately impacted the ammonia production rate. The fine Ru nanoparticles uniformly and randomly dispersed on the monolayered E-g-C3N4 did not provide outstanding activity in ammonia photosynthesis; in contrast, Ru nanoparticles at the step edges of bulk g-C3N4 exhibited lower overall barriers for N2 activation and a much enhanced photocatalytic ammonia synthesis rate due to the synergy effects between metal and support as confirmed by density functional theory (DFT) calculations. The discovery of the relationship between reactivity and support geometry in this study will be important in guiding the rational predesign of efficient photocatalysts.
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Development of Fe-Promoted Ni–Al Catalysts for Hydrogen Production from Gasification of Wood Sawdust
01 February 2021University of SydneyDong, Lisha;Wu, Chunfei;Ling, Huajuan;Shi, Jeffrey;Williams, Paul T.;Huang, JunThe production of renewable hydrogen-enriched gas from biomass waste is a promising technology for the development of a sustainable economy and society. Until now, there are still challenges of the technology in terms of the efficiency of hydrogen production. A catalyst is known and has been tested to enhance hydrogen production from biomass gasification, in particular, using Ni-based catalysts, which have high reactivity for hydrogen production and are cost-effective. However, developing a Ni-based catalyst with high thermal stability and resistance of coke deposition on the surface of the catalyst is still a challenging topic. In this work, Ni–Al catalysts doped with low-cost Fe metal were investigated for hydrogen-enriched syngas production from gasification of biomass using a two-stage fixed bed reactor. NiO–Fe2O3–Al2O3 catalysts with various Ni/Fe molar ratios (9:1, 8:2, 6:4, 5:5, 4:6, 2:8, and 1:9) were studied, aiming to understand the influence of Fe addition on the production of hydrogen and the catalyst stability in terms of coke deposition on the surface. X-ray diffraction, temperature-programmed reduction, and transmission electron microscopy (TEM) analysis of the fresh catalysts showed that nanoparticles (mainly NiAl2O4 spinel phase and Al2O3, ∼5 nm) were identified in the catalysts. High dispersion of metal particles was obtained using a co-precipitation method of catalyst preparation. With the increase of Fe addition, hydrogen production was reduced from around 11 to 8 mmol of H2 g–1 of biomass. However, the addition of Fe to the Ni-based catalyst significantly reduced the amount of coke deposited on the surface of the catalyst. The H2/CO molar ratio was maximized to 1.28 when the Ni/Fe molar ratio was 1:1. In addition, sintering of metal particles was not observed through the TEM analysis of the fresh and reacted catalysts.
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Electrical and transient atomization characteristics of a pulsed charge injection atomizer using electrically insulating liquids
01 March 2021University of SydneyKourmatzis, Agisilaos;Shrimpton, JohnCharge injection atomizers are energy efficient devices that can be used in order to promote the atomization of dielectric liquids, and a potential application of such devices is fine spray delivery in small internal combustion engines. The operation of a pulsed charge injection atomization system operating at practical engine frequencies under a high voltage pulse train has not been well recorded in the literature. This initial investigation defines the electrical and transient global atomization performance of a charge injection atomizer operating under a steady flow regime, but with a typical high voltage pulse train. Results show that voltage-current characteristics follow similar trends to that of a steady flow, steady voltage system, and observation of the data also reveals that output current waveforms depend on the input pulse train frequency. No degradation in charging efficiency was observed at higher frequencies, which suggests that a charge injection atomizer can operate efficiently at practical engine speeds. Photographs also confirmed the high voltage pulse train injects charge that produces sections of primary atomization on the continuous liquid jet.
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Electrochemical CO2 reduction to ethanol: from mechanistic understanding to catalyst design
13 September 2021University of SydneyLi, FengwangThe electrochemical reduction of carbon dioxide (CO2) to chemicals is gaining great attention as a pragmatic solution for greenhouse gas mitigation and for the utilization of CO2 to produce useful fuels and chemical feedstocks using intermittent renewable energy sources. In recent years, strategies to design electrocatalysts for CO2 reduction to ethanol, a valuable liquid fuel, have been increasingly reported. The mechanistic understanding providing insights into steps of the reduction process has allowed for further development of highly efficient and selective catalysts. Several significant breakthroughs have been made; however, the door toward industrial-scale production of ethanol from CO2 is still wide open as most electrocatalytic systems reported so far are still suffering from low energy efficiency, inferior stability, and discouraging selectivity. Inspired by recent advances in the field, we herein provide a review of fundamental and material advances of the electrochemical CO2 reduction to ethanol. First, we discuss the pathways and the effects of reaction-environment factors on the formation of ethanol from both theoretical and spectroscopic points of view. We then give an overview of different strategies to design electrocatalysts for this reaction. Finally, we discuss the remaining challenges and propose promising future research directions, with the aim to bring this technology closer to practical applications.
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CO2 electrolysis to multicarbon products in strong acid
13 September 2021University of SydneyLi, FengwangCarbon dioxide electroreduction (CO2R) is being actively studied as a promising route to convert carbon emissions to valuable chemicals and fuels. However, the fraction of input CO2 that is productively reduced has typically been very low, <2% for multicarbon products; the balance reacts with hydroxide to form carbonate in both alkaline and neutral reactors. Acidic electrolytes would overcome this limitation, but hydrogen evolution has hitherto dominated under those conditions. We report that concentrating potassium cations in the vicinity of electrochemically active sites accelerates CO2 activation to enable efficient CO2R in acid. We achieve CO2R on copper at pH <1 with a single-pass CO2 utilization of 77%, including a conversion efficiency of 50% toward multicarbon products (ethylene, ethanol, and 1-propanol) at a current density of 1.2 amperes per square centimeter and a full-cell voltage of 4.2 volts.
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Molecular stabilization of sub-nanometer Cu clusters for selective CO2 electro-methanation
17 November 2021University of SydneyLi, FengwangElectrochemical CO 2 methanation powered by renewable electricity provides a promising approach to utilizing CO 2 in the form of a high-energy-density, clean fuel. Cu nanoclusters have been predicted by theoretical calculations to improve methane selectivity. Direct electrochemical reduction of Cu-based metal-organic frameworks (MOFs) results in large-size Cu nanoparticles which favor multi-carbon products. Herein, we report an electrochemical oxidation-reduction method to prepare Cu clusters from MOFs. This derived Cu clusters exhibit a faradaic efficiency of 51.2% for CH 4 with a partial current density >150 mA cm -2 . High-resolution microscopy, in-situ X-ray absorption spectroscopy, in-situ Raman spectroscopy, and a collective of ex-situ spectroscopies indicate that the distinctive CH 4 selectivity is due to the sub-nanometer size of the derived materials as well as stabilization of the clusters by residual ligands of the pristine MOF. This work offers a new insight into steering product selectivity of Cu by an electrochemical processing method.
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Tunable Metamaterials Fabricated by Fiber Drawing
22 December 2021University of SydneyFleming, Simon;Stefani, Alessio;Tang, Xiaoli;Argyros, Alexander;Kemsley, Daniel;Cordi, James;Lwin, RichardWe demonstrate a practical scalable approach to the fabrication of tunable metamaterials. Designed for terahertz (THz) wavelengths, the metamaterial is comprised of polyurethane filled with an array of indium wires using the well-established fiber drawing technique. Modification of the dimensions of the metamaterial provides tunability; by compressing the metamaterial we demonstrated a 50% plasma frequency shift using THz time-domain spectroscopy. Releasing the compression allowed the metamaterial to return to its original dimensions and plasma frequency, demonstrating dynamic reversible tunability.
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Energy justice issues in renewable energy megaprojects: implications for a socioeconomic evaluation of megaprojects
04 July 2022University of SydneySankaran, S.;Clegg, S.;M�ller, R.;Drouin, N.Purpose: The purpose of this paper is to investigate and discuss stakeholder issues faced by renewable energy megaprojects and in particular solar and wind power projects and their relevance to socioeconomic evaluation of megaprojects. Design/methodology/approach: The paper uses secondary data collected from the recent literature published on stakeholder issues face by mega solar and wind power energy generation projects around the world. The issues are then analysed across specific challenges in five continents where these projects are being developed. The paper then focuses on the literature on energy justice to elaborate the type of issues being faced by renewable energy megaprojects contributing to the achievement of UN Sustainable Goal 7 and their impact on vulnerable communities where these projects are situated. Findings: Renewable energy megaprojects are rarely discussed in the project management literature on megaprojects despite their size and importance in delivering sustainable development goals. While these projects provide social benefits they also create issues of justice due to their impact of vulnerable populations living is locations where these projects are situated. The justice issues faced include procedural justice, distributive justice, recognition inequalities. The type of justice issues was found to vary intensity in the developed, emerging and developing economies. It was found that nonprofit organisations are embarking on strategies to alleviate energy justice issues in innovative ways. It was also found that, in some instances, smaller local projects developed with community participation could actually contribute more equitable to the UN sustainable development goals avoiding the justice issues posed by mega renewable energy projects. Research limitations/implications: The research uses secondary data due to which it is difficult to present a more comprehensive picture of stakeholder issues involving renewable energy megaprojects. The justice issues revealed through thesis paper with renewable energy megaprojects are also present in conventional megaprojects which have not been discussed in the project management literature. Post-COVID-19 these justice issues are likely to become mor prevalent due to the pandemic's impact on vulnerable population exacerbating the issues and increasing their severity on these populations. Therefore it is becoming even more critical to take these into account while developing renewable energy megaprojects. Practical implications: Proper identification and response to energy justice issues can help in alleviating stakeholder issues in renewable energy megaprojects. Social implications: Contributes to the equitable achievement of the United Nations Sustainable Development Goal 7. Originality/value: This paper addresses a gap in the project management literature on the exploration of stakeholder issues on renewable energy megaprojects. It also brings out the importance of justice issues which can assist in expanding stakeholders issues faced by megaprojects as these issues have not received sufficient attention in the past in the project management literature.
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Scenario modelling of biomass usage in the Australian electricity grid
04 July 2022University of SydneyLi, M.;Middelhoff, E.;Ximenes, F.A.;Carney, C.;Madden, B.;Florin, N.;Malik, A.;Lenzen, M.Responding to the global crises - Covid19 and climate change - governments around the world are formulating green recovery plans to stimulate economic growth, boost clean energy technologies and cut emissions. Potential transition pathways for low carbon energy systems, however, remain as open questions. Generally, the simulation of biomass in the grid models is limited in their tempo-spatial resolution, transition pathways description, and/or biomass feedstock supply representation. This study aims to provide spatio-temporal highly resolved grid configurations featuring disaggregated biomass feedstocks, to assess Australia's potential energy transition pathways and 100% renewable electricity supply scenarios under various biomass bidding strategies and cost assumptions. We find that, as carbon prices increase, bioelectricity will prove to be a cost-effective flexible option compared to other low-carbon (such as CSP) and fossil-based flexible options (e.g. coal and gas), with its generation share reaching _9%-12% at higher carbon price scenarios. Biomass power plants can be well suited for operating in gap-filling mode to provide flexible power generation and to facilitate grid stability and load balancing. In light of the high biomass resource potential in Australia, keeping bioelectricity in the generation mix is beneficial for reducing system capacity and cost by 32% and 21%, respectively, under a future renewable-dominated Australian grid system.
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Elucidation of the high-voltage phase in the layered sodium ion battery cathode material P3-Na0.5Ni0.25Mn0.75O2
20 July 2022University of SydneyLiu, Jiatu;Didier, C;Sale, Matthew;Sharma, N;Guo, Z;Peterson, V E;Ling, Chris DThe P3-type layered oxide Na0.5Ni0.25Mn0.75O2 is a promising manganese-rich positive electrode (cathode) material for sodium ion batteries, with a high working voltage of 4.2-2.5 V vs. Na+/Na and a high capacity of over 130 mAh/g when cycled at 10 mA/g. However, its structural evolution during battery cycling – specifically, the nature of the high-voltage phase above 4 V – has never been fully understood, which has hindered efforts to rationally modify and improve its performance. In this work we use in situ neutron diffraction to show that the phase above 4 V is a modification of the intermediate O3 phase from which all sodium has been removed, and which consequently has a dramatically shorter interlayer distance. We label this fully Na-depleted phase O3s, such that the phase evolution with increasing voltage is P3O3O3s. Having elucidated its structure, we used first-principles calculations of the electronic structure as a function of sodium content to show that reversible oxygen redox plays a key role in the electrochemical activity of this O3s phase above 4 V. We also calculated the energies of oxygen/transition metal vacancies and found that the O3s phase should be relatively stable against their formation. The results will guide future research aimed at understanding and stabilizing the O3s phase, in order to improve the performance and cycling stability of this material in sodium ion batteries.
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Na2FeP2O7: A Safe Cathode for Rechargeable Sodium-ion Batteries
28 July 2022University of SydneyBarpanda, P;Liu, G;Ling, Chris D;Tamaru, M;Avdeev, Maxim;Chung, S-C;Yamada, Y;Yamada, AVying for newer sodium-ion chemistry for rechargeable batteries, Na2FeP2O7 pyrophosphate has been recently unveiled as a 3 V high-rate cathode. In addition to its low cost and promising electrochemical performance, here we demonstrate Na2FeP2O7 as a safe cathode with high thermal stability. Chemical/electrochemical desodiation of this insertion compound has led to the discovery of a new polymorph of NaFeP2O7. High-temperature analyses of the desodiated state NaFeP2O7 show an irreversible phase transition from triclinic (P-1) to the ground state monoclinic (P21/c) polymorph above 560 C. It demonstrates high thermal stability, with no thermal decomposition and/or oxygen evolution until 600 C, the upper limit of the present investigation. This high operational stability is rooted in the stable pyrophosphate (P2O7)4- anion, which offers better safety than other phosphate-based cathodes. It establishes Na2FeP2O7 as a safe cathode candidate for large-scale economic sodium-ion battery applications.
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Suppression of transients across the tap windings of an auto-transformer.
07 June 2013University of KwaZulu-NatalnanFor the energy transfer between the various voltage levels of the Eskom national grid, auto-transformers are mainly installed. These auto-transformers are interfaced with the distribution network.
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Fabrication of affordable and sustainable solar cells using NiO/TiO2 P-N heterojunction.
28 June 2018University of KwaZulu-NatalnanThe need for affordable, clean, efficient, and sustainable solar cells informed this study. Metal oxide TiO²/NiO heterojunction solar cells were fabricated using the spray pyrolysis technique. The optoelectronic properties of the heterojunction were determined. The fabricated solar cells exhibit a short-circuit current of 16.8 mA, open-circuit voltage of 350 mV, fill factor of 0.39, and conversion efficiency of 2.30% under 100mW/cm² illumination. This study will help advance the course for the development of low-cost, environmentally friendly, and sustainable solar cell materials from metal oxides.
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Modeling of fabricated NiO/TiO2 P-N heterojunction solar cells.
28 June 2018University of KwaZulu-NatalnanThis paper reports modelling and theoretical validation of a fabricated NiO/TiO2 P-N heterojunction solar cell. The solar cell equations were modelled and thereafter theoretical validation of the fabricated solar cells was performed. Modelling tools were used to validate the influence of NiO material features such as deposition temperature, voltage and defect densities on the performances of an ITO/TiO2/NiO heterojunction solar cell structure. The working points used included a temperature of 350 oC, illumination of 1000 W/m2 using an AM1.5 lamp, with voltage range of 0 to 1.5 volts. The output gave Voc of 0.1445 V, Jsc of 247.959195E-6 mA/cm2 and FF of 37.87 % and Voc 0.7056 and Jsc 28.366911 mA/cm2 when both contacts were added. This opens a new frontier for modelling of metal oxide based thin film solar cells especially NiO thin film solar cells. These findings enhance the quest to develop affordable and sustainable energy and encourage further research in solar cell technologies in low-income countries.
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From Scarcity to Abundance: The Changing Dynamics of Energy Conflict
11 February 2015University of PennsylvaniaKlare, Michael T.Energy security and geopolitics have played a pivotal role in international affairs for a very long time, ever since the development of oil-powered vehicles and weapons of war. Until recently, the geopolitics of energy have largely been governed by perceptions of scarcity—the assumption that oil and other energy reserves were relatively limited, and that competition over their exploitation would lead to recurring crisis and conflict. However, the recent utilization of advanced extractive technologies—including deep-sea drilling and hydraulic fracturing—have resulted in unexpected production gains and fostered a sense that abundance, rather than scarcity, will govern the future energy picture. This perception, in turn, has led to expectations that conflict over energy will diminish. But the deployment of the new technologies has engendered new conflicts of its own, as in the disputes over offshore oil and natural gas deposits in the Arctic Ocean and the East and South China Seas. Also, many nations view energy as a critical source of wealth and power, and so they continue to spar over the ownership and exploitation of valuable reserves. Accordingly, the prospects for relative abundance are not likely to eliminate the risk of conflict over critical energy supplies.
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Energy Re-Investment
01 January 2019University of PennsylvaniaOsofsky, Hari M.;Peel, Jacqueline;McDonnell, Brett H.;Foerster, AnitaDespite worsening climate change threats, investment in energy — in the United States and globally — is dominated by fossil fuels. This Article provides a novel analysis of two pathways in corporate and securities law that together have the potential to shift patterns of energy investment.The first pathway targets current investments and corporate decision-making. It includes efforts to influence investors to divest from owning shares in fossil fuel companies and to influence companies to address climate change risks in their internal decision-making processes. This pathway has received increasing attention, especially in light of the Paris Agreement and the Trump Administration’s decision to withdraw from it. But, alone, it will not be enough to foster transition to a cleaner mix of energy sources.Key to achieving this goal of energy reinvestment is a second pathway focused on fostering investments in new companies innovating in clean energy. This pathway — which has received far less attention — uses emerging legal mechanisms to support greater investment in entrepreneurial clean energy ventures. The Article’s analysis of this pathway looks beyond the well-established ways in which subsidies support fossil fuels and renewable energy. It instead examines the significance for energy reinvestment of changes in U.S. securities regulation permitting greater crowdsourcing of investment and in state laws allowing for new types of corporations.This Article is the first to examine how these two pathways can synergistically promote energy reinvestment. The first pathway moves money away from fossil fuels, while the second helps to spur needed reinvestment. The Article proposes strategies for deploying the tools in the two pathways together, taking into account the motivations and constraints of diverse investors and corporations.
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Taxing Local Energy Externalities
01 January 2020University of PennsylvaniaWiseman, Hannah JacobsThere is a fundamental problem of scale in the governance of industrial development. For some of the fastest-growing U.S. industries, the negative impacts of development fall primarily at the local level, and the benefits tend to accrue more broadly to states and the federal government. These governments accordingly have inadequate incentives to address the very localized negative externalities of development. Yet states also increasingly preempt most local control over some forms of development. This creates a regulatory void, in which state and federal regulations are inadequate, and local governments lack the power to use traditional Pigouvian tools such as regulation, taxation, and liability to address local harms. Without these Pigouvian sticks, local governments are also constrained in their use of Coasean bargaining, in which they could threaten regulation or taxation to bring industry to the table and negotiate for private solutions. This gap is particularly evident in the energy space, in which oil and gas and associated pipelines, wind energy, and solar energy have strong local effects, but local control is constrained to varying degrees. This Article explores the reasons for this governance gap, including federalism concerns, political economic factors, and views about the relative competency of local government, and it proposes solutions that take these drivers into account. The Article uses the areas of renewable energy, oil and gas production, pipelines, and natural gas export terminals to demonstrate the highly localized externalities of energy development, explore the Pigouvian and Coasean tools available to address these externalities, and analyze state preemption of local governments’ use of these tools. Based on the lessons from these industries, it argues that a combined system of taxation and negotiation incentives would best fill the regulatory void in local energy law while addressing the concerns that have created this void.
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Localizing the Green Energy Revolution
01 June 2021University of PennsylvaniaWiseman, Hannah JacobsThe United States is on the verge of a new industrial revolution. Renewable energy could replace more than 60% of our current energy generation infrastructure in fifteen years. This change is critical, yet it risks failure. The renewable generation already built in the United States consists primarily of large-scale projects connected to transmission lines in rural areas. The expansive new generation needed to reduce carbon emissions must also be predominantly large-scale, and rural, for reasons of efficiency. But a revolution that focuses nearly exclusively on “big energy” is likely to encounter obstacles, and it has downsides that could be mitigated with a stronger focus on small-scale energy. Many rural Americans—predominantly Republican—oppose Democratic policies, particularly climate policies. Even avowedly green liberal communities have mounted stiff opposition to renewable energy in some areas. Many landowners—particularly farmers—welcome the income from renewable energy leases, but residents often object to the blinking lights, landscape disruption, unsightly wires, and other impacts of these projects. Beyond facing political opposition, a projected buildout of more than 200,000 miles of new transmission lines to support new large-scale renewable projects threatens to create negative infrastructural path dependence. This could be analogous to the federal highway network expansion of the 1950s, which largely cemented U.S. reliance on cars rather than mass transit and divided communities. We need a nationwide network of new long-distance transmission lines to connect large renewable energy generation to population centers. But small energy projects could replace the need for some of these wires. Policymakers should place greater emphasis on “small” distributed energy in the form of solar and wind generation over or near parking lots, roadways, and buildings; community-scale renewables and microgrids; and energy efficiency projects, such as weatherization of apartment buildings. This effort is likely to be more politically feasible than a revolution focused too heavily on large-scale projects. And when targeted properly, small-scale clean energy can reduce the crushing energy burdens faced by low-income communities, whether rural or urban. For the energy transition to be feasible and less objectionable from a community and present-day environmental perspective, energy policies should also ensure that large-scale renewable generation is built in ways that reduce host community impacts. Renewable or clean energy policies should prioritize projects on polluted or abandoned brownfields, as New York requires; on marginalized farmlands; or offshore. Policies should also require large-scale renewable energy developers to negotiate with host communities and offer benefits—another strategy followed in New York.
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Appalachian Basin--Pennsylvania, West Virginia, and Ohio -- Oil and Gas Developments
01 January 2022University of PennsylvaniaPifer, Ross H.;Marie, Chloe J.This article addresses oil and gas case law developments that have occurred within the Appalachian Basin’s primary oil and gas producing states of Pennsylvania, West Virginia, and Ohio during 2021 by reviewing opinions issued by the highest appellate courts within each of these three states. The oil and gas law topics addressed by these state supreme courts during 2021 have ranged from those occurring upstream, such as leasing, to those occurring downstream, such as approval of a utility rate increase for the extension of a natural gas pipeline.
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Grid Reliability Through Clean Energy
01 January 2022University of PennsylvaniaWiseman, Hannah Jacobs;Klass, Alexandra;Macey, Joshua;Welton, ShelleyIn the wake of recent high-profile power failures, policymakers and politicians have asserted that there is an inherent tension between the aims of clean energy and grid reliability. But continuing to rely on fossil fuels to avoid system outages will only exacerbate reliability challenges by contributing to increasingly extreme climate-related weather events. These extremes will disrupt the power supply, with impacts rippling far beyond the electricity sector.This Article shows that much of the perceived tension between clean energy and reliability is a failure of law and governance resulting from the United States’ siloed approach to regulating the electric grid. Energy regulation is, we argue, siloed across three dimensions: (1) across substantive responsibilities (clean energy versus reliability); (2) across jurisdictions (federal, regional, state, and sometimes local); and (3) across a public–private continuum of actors. This segmentation renders the full convergence of clean-energy and reliability goals extremely difficult. Reliability-focused organizations operating within their silos routinely counteract climate policies when making decisions about how to keep the lights on. Similarly, legal silos often cause states and regional organizations to neglect valuable opportunities for collaboration. Despite the challenges posed by this disaggregated system, conceptualizing the sphere of energy reliability as siloed across these dimensions unlocks new possibilities for reform.We do not propose upending energy law silos or making energy institutions wholly public. Rather, we argue for calibrated reforms to U.S. energy law and governance that shift authority within and among the silos to integrate the twin aims of reliability and low-carbon energy. Across the key policy areas of electricity markets, transmission planning and siting, reliability regulation, and regional grid governance, we assess changes that would integrate climate and reliability imperatives; balance state, regional, and federal jurisdiction; and reconcile public and private values. We believe this approach to energy law reform offers a holistic and realistic formula for a cleaner, more reliable grid.
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Harrisburg's Objection to OCC's Motion for Standing
11 January 2022University of PennsylvaniananHarrisburg's objection to OCC"s motion for standing, filed January 11, 2022.
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Regional Cooperative Federalism and the US Electric Grid
02 February 2022University of PennsylvaniaWiseman, Hannah JacobsThe U.S. Constitution makes no direct mention of regional governing entities, yet they are an entrenched part of our federalist system. In the area of electric grid governance, the federal government enlists independent, private entities called regional transmission organizations (RTOs) to implement federal policy and achieve state energy goals. RTOs are the most prominent form of regional cooperative federalism, yet other policy spheres, such as opioid control, encompass a similar approach. This is a twist on the classic form of cooperative federalism, in which the federal government relies upon individual states to achieve federal mandates. The regionally governed electric grid represents a critical policy area. The availability of reliable electricity directly drives economic and human health outcomes, and populating the grid with clean sources of electricity while maintaining grid reliability is an urgent endeavor. The use of regional cooperative federalism in this area therefore calls for a fresh look at federalism principles. Many RTOs are geographically massive; the largest RTO covers all or part of the territories of fifteen states. Yet RTOs better encompass some of the core federalism principles ascribed to more decentralized control, including policy experimentation and innovation, efficiency, and accountability to stakeholders. Some RTOs have been particularly innovative in formulating new policies to address changing circumstances, such as demand for more renewable energy. But in the accountability sphere, other RTOs have struggled to address stakeholder needs. Regional cooperative federalism will be increasingly important in a world of complex policy issues that spill beyond local and state lines yet require locally tailored solutions. This Article constructs a normative framework for this under-recognized approach, using the attributes of federalism as guideposts, and suggests a path forward for productively expanding and improving this governance form.
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Climate change impacts on financial risk in hydropower projects
15 November 2004University of EdinburghHarrison, Gareth P;Whittington, Bert;Wallace, RobinLimiting the emissions of greenhouse gases from power generation will depend, among other things, on the continuing and increased use of hydroelectric power. However, climate change itself may alter rainfall patterns, adversely affecting the financial viability of existing and potential hydro schemes. Previous work developed a methodology for quantifying the potential impact of climate change on the economics of hydropower schemes. Here, the analysis is extended to examine the potential for changes in project risk. A case study is presented that indicates that the applied climate change scenarios alter not only the mean financial performance of the scheme but also the financial risk facing it. Given that investors must balance project risk and reward, this finding has implications for the future provision of hydropower.
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Social aspects of a solar-powered desalination unit for remote Australian communities
01 November 2010University of EdinburghWerner, M;Schäfer, AndreaThe technical, economic and environmental aspects of small-scale desalination units powered by renewable energies for remote areas have received considerable attention in recent years. However, social aspects of such units have often been neglected resulting in abandoned and dysfunctional systems. This paper considers the potential of the reverse osmosis solar installation (ROSI) to be integrated at a number of different sites in Central Australia. Performance is evaluated against attributes of social sustainability, such as the unit's capacity to meet community water needs (both quality and quantity), the human resources available to operate and maintain the unit and the community response to the unit. From this preliminary evaluation, a number of operation and management recommendations relating to membrane choice, recovery rate and maintenance provision are made to ensure the potential offered by ROSI is fulfilled in a socially sustainable manner. Areas requiring further research are also identified.
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Application of solar-powered desalination in a remote town in South Australia
15 November 2010University of EdinburghDe Munari, Annalisa;Capão, D.P.S;Richards, B.S.;Schäfer, AndreaCoober Pedy is a remote town in South Australia with abundant solar radiation and scarce and low quality water, where a reverse osmosis plant has been operating since 1967. This paper evaluates the feasibility of powering the plant with solar or photovoltaic (PV) panels whilst avoiding energy storage in batteries. Pilot tests were performed in October 2005 with a small scale PV-powered hybrid ultrafiltration-reverse osmosis (UF/RO) membrane filtration system. The performance of the system in Coober Pedy is presented over different operating conditions and two available brackish feed waters. The system has been shown to tolerate well the power variation during clear sky days due to direct use of PV panels, producing 764 L of water per solar day with average specific energy consumption of 3.2 kWh.m-3 when treating the groundwater with conductivity of 7.4 mS.cm-1. It has been concluded that a reverse osmosis plant utilising UF pre-treatment and powered by PV panels without battery storage is a promising alternative for Coober Pedy to overcome currently high energy costs for the existing RO plant.
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Potential of wind-powered renewable energy membrane systems for Ghana
15 November 2010University of EdinburghPark, G.L.;Schäfer, Andrea;Richard, B.S.Areas of the world that lack fresh water often have an ample supply of wind or solar energy, making renewable energy an attractive option as a power source for desalination systems. Particularly, wind energy is attractive because of its relatively low cost, high efficiency, and recent technological advancements in this area of research. To open system applicability to a broader range of geographical areas, the feasibility of substituting solar panels with a wind turbine on an existing membrane desalination systemthat has undergone testing in the Australian outback is examined. The use of wind turbines will provide greater scope for the system's implementation in various parts of the world according to the local wind or solar resources.Acomparison of several small wind turbines coupled with wind speed data from Ghana showed that a 1 kW FuturEnergy wind turbine would give the best performance for the lowest cost and is therefore the most appropriate for coupling with the membrane system. The predicted permeate production is 1.3 m3/d at a specific energy consumption (SEC) of 1.8 kWh/m3.
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Photovoltaic-powered desalination system for remote Australian communities
16 November 2010University of EdinburghRichards, B.S.;Schäfer, AndreaThis paper reports on the design and successful field testing of a photovoltaic (PV)-powered desalination system. The system described here is intended for use in remote areas of the Australian outback, where fresh water is extremely limited and it is often necessary to drink high salinity bore water. A hybrid membrane configuration is implemented, whereby an ultrafiltration (UF) module is used for removing particulates, bacteria and viruses, while a reverse osmosis (RO) or nanofiltration (NF) membrane retains the salts. The concepts of water and energy recovery are implemented in the design. Field trials, performed in White Cliffs (New South Wales), demonstrated that clean drinking water was able to be produced from a variety of feed waters, including high salinity (3500 mg/l) bore water and high turbidity (200 NTU) dam water. The specific energy consumption ranged from 2 to 8 kW h/m3 of disinfected and desalinated drinking water, depending on the salinity of the feed water and the system operating conditions. The optimum operating pressure when filtering bore water was determined to be in the range 6–7 bar.
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Setting the standard for research excellence
04 August 2016University of EdinburghTate, Dominic;Green, RobFeature article in CILIP Update about the Jisc pathfinder project LOCH (Lessons in Open Access Compliance)
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Power conversion systems for Ducks
13 October 2017University of EdinburghSalter, Stephen HughThis paper tries to define the problems of power conversion for a wave power device . It presents a little of the background theory; it discusses design principles, existing components and modifications to them; it tries to identify the main practical difficulties. Finally, it describes four possible solutions.
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Self-adjoint higher order differential operators with eigenvalue parameter dependent boundary conditions.
04 October 2016University of the WitwatersrandMöller, M.;Zinsou, B.Eigenvalue problems for even order regular quasi-differential equations with boundary conditions which depend linearly on the eigenvalue parameter λ can be represented by an operator polynomial (Formula presented.) where M is a self-adjoint operator. Necessary and sufficient conditions are given such that also K and A are self-adjoint.
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Hierarchical one-dimensional ammonium nickel phosphate microrods for high-performance pseudocapacitors
25 November 2016University of the WitwatersrandRaju, K.;Ozoemena, K.I.High-performance electrochemical capacitors will drive the next-generation portable, flexible and wearable electronics. Unlike the conventional all-carbon supercapacitors (electric double layer capacitors, EDLC) with high power but poor energy density, pseudocapacitors capitalize the high energy density inherent to reversible redox reactions and provide a facile means to enhancing the energy ratings of supercapacitors. The high length-to-diameter ratio and anisotropic character of 1-D architecture makes them suitable for use in energy storage. For the first time, we report 1-D microrod structures (∼ 36 nm width) of ammonium nickel phosphate hydrate (ANP mr) as a pseudocapacitor with high energy rating and power handling. To confirm the data, the ANP mr -based pseudocapacitor was subjected to various configurations (i.e., half-cell, symmetric, asymmetric, and flexible all-solid-state) and in each case it gave excellent values compared to any accessible literature to date. We clearly demonstrate that a flexible all-solid-state ANP mr -based pseudocapacitor achieved high areal capacitance of 66 mF cm ∼'2 with extra-ordinary energy (21.2 mWh cm ∼'2) and power (12.7 mW cm ∼'2) densities. This work opens doors for a facile, robust and scalable preparation strategy for low-cost, earth-abundant electrode materials for high-performance pseudocapacitors.
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Supergravity solutions with AdS(4) from non-Abelian T-dualities
15 February 2017University of the WitwatersrandZayas, L.A.P.;Rodgers, V.G.J.;Whiting, C.A.We present a large class of new backgrounds that are solutions of type II supergravity with a warped AdS(4) factor, non-trivial axion-dilaton, B-field, and three-and five-form Ramond-Ramond fluxes. We obtain these solutions by applying non-Abelian T-dualities with respect to SU(2) or SU(2)/U(1) isometries to reductions to 10d IIA of 11d sugra solutions of the form AdS(4) x Y-7, with Y-7 = S-7/Z(k), S-7, M-1,M-1,M-1, Q(1,1,1) and N(1,1). The main class of reductions to IIA is along the Hopf fiber and leads to solutions of the form AdS(4) x K-6, where K-6 is Kahler Einstein with K-6 = CP3, S-2 x CP2, S-2 x S-2 x S-2; the first member of this class is dual to the ABJM field theory in the 't Hooft limit. We also consider other less symmetric but susy preserving reductions along circles that are not the Hopf fiber. In the case of N(1,1) we find an additional breaking of isometries in the NAT-dual background. To initiate the study of some properties of the field theory dual, we explicitly compute the central charge holographically.
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LLM magnons
13 April 2017University of the Witwatersrandde Mello Koch, R.;Mathwin, C.;Van Zyl, H.J.R.We consider excitations of LLM geometries described by coloring the LLM plane with concentric black rings. Certain closed string excitations are localized at the edges of these rings. The string theory predictions for the energies of magnon excitations of these strings depends on the radii of the edges of the rings. In this article we construct the operators dual to these closed string excitations and show how to reproduce the string theory predictions for magnon energies by computing one loop anomalous dimensions. These operators are linear combinations of restricted Schur polynomials. The distinction between what is the background and what is the excitation is accomplished in the choice of the subgroup and the representations used to construct the operator.
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Carbon Encapsulated Ternary MnNiCo Oxide Nanoparticles as Electrode Materials for Energy Storage Applications
19 April 2021University of the WitwatersrandTarekegn Heliso Dolla;Isiaka A. Lawal;David Billing;K Pruessner;Patrick Ndungu;Dolla, TH;Lawal, IA;Billing, DG;Pruessner, k;Ndungu, PTernary transition metal oxides are promising advanced materials for use as electrode components in electrochemical energy storage systems. However, low electronic/ionic conductivity hinder practical applications. In this study, ternary Mn-Ni-Co oxide nanoparticles were encapsulated in carbon nanosheets, to improve the electrical conductivity and surface area. When tested as supercapacitor electrodes, the materials exhibited specific capacity of 91.2 mAh g(-1)at a current density of 1 A g(-1)in 2 M KOH. Moreover, after 3000 cycles the composite achieved a specific capacity of 74.6 mAh g(-1)at a current density of 6 A g(-1)and high capacitance retention of 96.4 %.
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Evaluation of a detailed radiation heat tranfer model in a high temperature reactor systems simulation model
31 August 2009North West UniversityVan Antwerpen, H.J.;Greyvenstein, G.P.Radiation heat transfer is a major mode of heat transfer in high temperature gas-cooled reactors (HTRs) because of the high operating temperatures. It is, however, a difficult phenomenon to calculate in full detail due to its geometrical complexity. One has to use either a numerical method or complex analytical view factor formulae. Except the difficulty of view factor calculation, a vast number of calculation elements are required to consider all interacting surfaces around a cavity. A common approximation in systems simulation codes is to connect only directly opposing surfaces with a view factor of one. The accuracy of this approximation was investigated with a finite volume, two-dimensional axial-symmetric reactor model implemented in the systems simulation code Flownex. A detailed radiation model was developed and also implemented in the Flownex reactor model. This paper also describes the analytical formulae for view factor calculation in this detailed radiation heat transfer model. The HTR-10 and the 268 MW version of the PBMR were used as case studies in which Loss-of-Flow events without SCRAM were simulated. In these simulations, the time to reach recriticality was used as an indicator of heat removal effectiveness. With the HTR-10, other non-linear phenomena in the reactor core constrained the solution process, so that the number of radiation elements had no effect on solution time, while with the 268 MW PBMR DLOFC, the use of a detailed radiation model increased solution time with 30%. With both the HTR-10 and the PBMR, the radiation model had negligible effect on the total heat resistance from the reactor, as indicated by the time elapsed until recriticality. For system simulation codes that focus on transient response of a plant, it is not considered worthwhile to use a detailed radiation model, as the gain in accuracy does not justify the increased solution time or the implementation and verification effort
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Developing esco procedures for large telecommunication facilities using novel simulation techniques
17 November 2009North West UniversityVan Rensburg, J.F.;Geyser, M.F.;Kleingeld, M.;Mathews, E.H.Peak electricity demand in South Africa will exceed the available operational generation capacity in 2007. The state utility, Eskom, is addressing this challenge, inter alia, with the implementation of a national Demand-side Management (DSM) initiative. Studies in South Africa have shown that 20% of the total municipal energy is utilised in commercial buildings. Telecommunication companies own and operate a large portfolio of diverse buildings within the municipal boundaries. Energy Services Company (ESCO) analyses on these buildings showed huge savings as well as load reduction opportunities. ESCOs however face major problems in evaluating DSM projects on telecommunication facilities. To address these problems a new ESCO procedure for telecommunications facilities was developed and successfully implemented. It was proven that the new ESCO procedure is successful in solving the unique problems in performing ESCO analyses for telecommunications facilities
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The application of system CFD to the design and optimization of high-temperature gas-cooled nuclear power plants
18 November 2009North West UniversityGreyvenstein, Gideon P.The objective of this paper is to model the steady-state and dynamic operation of a pebble-bed-type high temperature gas-cooled reactor power plant using a system computational fluid dynamics (CFD) approach. System CFD codes are 1D network codes with embedded 2D or even 3D discretized component models that provide a good balance between accuracy and speed. In the method presented in this paper, valves, orifices, compressors, and turbines are modeled as lumped or 0D components, whereas pipes and heat exchangers are modeled as 1D discretized components. The reactor is modeled as 2D discretized system. A point kinetics neutronic model will predict the heat release in the reactor. Firstly, the layout of the power conversion system is discussed together with the major plant parameters. This is followed by a high level description of the system CFD approach together with a description of the various component models. The code is used to model the steady-state operation of the system. The results are verified by comparing them with detailed cycle analysis calculations performed with another code. The model is then used to predict the net power delivered to the shaft over a wide range of speeds from zero to full speed. This information is used to specify parameters for a proportional-integral-derivative controller that senses the speed of the power turbine and adjusts the generator power during the startup of the plant. The generator initially acts as a motor that drives the shaft and then changes over to a generator load that approaches the design point value as the speed of the shaft approaches the design speed. A full startup simulation is done to demonstrate the behavior of the plant during startup. This example demonstrates the application of a system CFD code to test control strategies. A load rejection example is considered where the generator load is suddenly dropped to zero from a full load condition. A controller senses the speed of the low pressure compressor/low pressure turbine shaft and then adjusts the opening of a bypass valve to keep the speed of the shaft constant at 60rps. The example demonstrates how detailed information on critical parameters such as turbine and reactor inlet temperatures, maximum fuel temperature, and compressor surge margin can be obtained during operating transients. System CFD codes is a powerful design tool that is indispensable in the design of complex power systems such as gas-cooled nuclear power plants
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Optimisation of a storage facility used to effect power control in the PBMR power cycle
08 January 2010North West UniversityMatimba, A.;Mathews, E.H.;Pelzer, R.This article presents the optimization of a gas storage facility used to effect power control in South Africa's PBMR power cycle. It was shown in the article, a multitank storage facility to affect power control in the PBMR power cyclel, that a multi tank design with heat capacitance improves storage effictiveness, which could make the system cheaper. This storage facility is known as the Inventory Control System (ICS). The focus in this article is to determine an optimum number of tanks and heat capacitance that will achieve a spectfied performance for the lowest possible cost. Please note the values used in this exercise are not the actual valaes used by PBMR. However this article serves to demonstrate an approach to achieving an optimum solution for the ICS.
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DNA damage and repair detected by the comet assay in lymphocytes of African petrol attendants: a pilot study
03 February 2010North West UniversityKeretetse, G.S.;Laubscher, P.J.;Du Plessis, J.L.;Pretorius, P.J.;Van der Westhuizen, F.H.;Van Deventer, E.;Van Dyk, E.;Eloff, F.C.;Van Aarde, M.N.;Du Plessis, L.H.Petrol attendants are exposed to petrol volatile organic compounds (VOCs) which may have genotoxic and carcinogenic effects. The single-cell gel electrophoresis assay (comet assay) is a method highly sensitive to DNA damage induced by environmental and occupational exposure to carcinogenic and mutagenic agents. The aim of this study was to evaluate the level of exposure of petrol attendants to petrol VOCs and also to determine their effect on DNA damage and repair in lymphocytes of African petrol attendants. The exposed group consisted of 20 subjects, randomly selected from three petrol stations. A control group of 20 unexposed subjects was also chosen and matched for age and smoking habits with the exposed group. Sorbent tubes were used to assess personal exposure of petrol attendants. The comet assay was used to investigate the basal DNA damage and repair capacity in isolated lymphocytes of petrol attendants and unexposed subjects. Blood samples were taken from the petrol attendants at the end of their 8-h working shift and also from the unexposed subjects. The petrol attendants were found to be exposed to levels of petrol VOCs lower than the South African occupational exposure limit for constituent chemicals. A significant relationship was found between the volume of petrol sold during the shift and the average concentrations of benzene, toluene and the total VOCs measured. However, relative humidity had a negative correlation with the average concentrations of benzene, toluene, xylene and the total VOCs. Significantly higher basal DNA damage was observed with the exposed group compared to the unexposed group. The period of exposure influenced the level of DNA damage and the calculated repair capacity. Smoking and age had a significant influence on the level of DNA damage. DNA repair capacity was delayed in smokers of both exposed and unexposed group
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Oil crops in biofuel applications: South Africa gearing up for a bio-based economy
18 January 2011North West UniversityMarvey, B BLarge fluctuations in crude oil prices and the diminishing oil supply have left economies vulnerable to energy shortages thus placing an enormous pressure on nations around the world to seriously consider alternative renewable resources as feedstock in biofuel applications. Apart from energy security reasons, biofuels offer other advantages over their petroleum counterparts in that they contribute to the reduction in greenhouse gas emissions and to sustainable development. Just a few decades after discontinuing its large scale production of bioethanol for use as engine fuel, South Africa (SA) is again on its way to resuscitating its biofuel industry. Herein an overview is presented on South Africa’s oilseed and biofuel production, biofuels industrial strategy, industry readiness, challenges in switching to biofuels and the strategies to overcome potential obstacles.
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Simultaneous multi-wavelength campaign on PKS 2005-489 in a high state
05 September 2012North West UniversityAbramowski, A.;Büsching, I.;De Jager, O.C.;Venter, C.;Vorster, M.;H.E.S.S. CollaborationTeV γ-ray (H.E.S.S.), GeV γ-ray (Fermi/LAT), X-ray (RXTE, Swift), UV (Swift) and optical (ATOM, Swift) bands. This campaign was carried out during a high flux state in the synchrotron regime. The flux in the optical and X-ray bands reached the level of the historical maxima. The hard GeV spectrum observed with Fermi/LAT connects well to the very high energy (VHE, E > 100 GeV) spectrum measured with H.E.S.S. with a peak energy between ∼5 and 500 GeV. Compared to observations with contemporaneous coverage in the VHE and X-ray bands in 2004, the X-ray flux was ∼50 times higher during the 2009 campaign while the TeV γ-ray flux shows marginal variation over the years. The spectral energy distribution during this multi-wavelength campaign was fit by a one zone synchrotron self-Compton model with a well determined cutoff in X-rays. The parameters of a one zone SSC model are inconsistent with variability time scales. The variability behaviour over years with the large changes in synchrotron emission and small changes in the inverse Compton emission does not warrant an interpretation within a one-zone SSC model despite an apparently satisfying fit to the broadband data in 2009.
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An integral CFD approach for the thermal simulation of the PBMR reactor unit
15 November 2012North West UniversityKleingeld, Marius;Janse van Rensburg, Jacobus JohannesA CFD method was developed to conduct integral thermal reactor analysis for the complete Reactor Unit of the Pebble Bed Modular Reactor (Pty) Ltd (PBMR). The requirement was however also to include very detailed aspects such as leakage and bypass flow paths through the reflector blocks and sleeves. The aim was therefore to investigate the influence of leakage and bypass flow on the thermal performance of the Reactor Unit in an integral fashion. The focus of this paper is to discuss the methodology that was developed. The discussion will firstly highlight all the required inputs, elaborate briefly on the underlying theory and how this was implemented into the CFD modeling capability. Results will be discussed briefly, but the focus is on the methodology.
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CFD applications in the Pebble Bed Modular Reactor Project: a decade of progress
15 November 2012North West UniversityKleingeld, Marius;Janse van Rensburg, Jacobus JohannesOf all the systems and components that have to be designed for a nuclear plant, the Reactor Unit is the most significant since it is at the very heart of the plant. At Pebble Bed Modular Reactor (Pty) Ltd. (PBMR), the design of the Reactor Unit is conducted with the aid of extensive analysis work. Due to the rapid computational improvements, the analysis capabilities have had to evolve rather significantly over the last decade. This paper evaluates the evolution of RU Computational Fluid Dynamics (CFD) analysis in particular and presents a historical timeline of the analyses conducted at PBMR. The influence of advances in the hardware and software applications on the evolution of the analysis capabilities is also discussed. When evaluating the evolution of analysis, it is important to look not only at the advances in mesh generation and the representation of the geometry, but also at the improvements regarding the physics that were included in the models. The discussion evaluates the improvements from the pre-conceptual analyses, the concept design, the basic design and finally, the detail design. It is however important to note that the focus of this research was on establishing a methodology for the integrated CFD analysis of High Temperature Reactors. It is recognized however that results from this research can currently only be used to investigate and understand trends and behaviors rather than absolute values. It was therefore required to also launch an extensive V&V program of which the focus was to verify the approach and validate the methodology that was established. The final aim was therefore to combine the research into the methodology with that of V&V in an effort to determine uncertainty bands which would enable the researcher to supply absolute results with an uncertainty value attached.
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Pebble Bed Micro Model system identification
30 October 2013North West UniversityVenter, W.C.;Lamprecht, E.C.Linear system identification techniques will be applied to obtain mathematical models of a simulation of the Pebble Bed Micro Model (PBMM). The PBMM is a conceptual model of the Pebble Bed Modular Reactor (PBMR), a new high temperature gas nuclear reactor. The basis of the PBMR and PBMM is a three-phase Brayton Power Generation Cycle. The Brayton cycle will in this paper be simulated by the use of Flownex, a general thermal-fluid network analysis code solver. A description of the Brayton Power Generation Cycle, as well as description of the Flownex modelling program, will also be given.
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Environmental impact of an industrial compressed air system for solar power in South Africa
20 January 2014North West UniversityGouws, RupertAlmost 14% of the electricity generated by the national energy supplier (Eskom) in South Africa is sold directly to the mining sector and almost 20% is utilized directly by the compressed air systems of the mining sector. The industrial compressed air systems in South Africa therefore have a substantial impact on the environment in terms of emissions output. In this paper a solar powered compressor is installed parallel to an existing industrial compressed air system. The environmental (emissions) impact and energy consumption of the industrial compressed air system with the solar powered compressor is calculated and the results are provided. It is shown from the results that the solar powered air compressor improved the overall system efficiency and lowered the carbon footprint of the industrial compressed air system. The impact of the energy improvement on the amount of trees required to offset the calculated amount of CO2 is also provided.
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Factors influencing the performance and efficiency of solar water pumping systems: a review
30 June 2014North West UniversityGouws, Rupert;Lukhwareni, ThendoThe world is having an energy crisis and currently there is a strong drive towards renewable energy. A renewable energy option is solar energy, where by means of photovoltaic (PV) modules electrical energy can be produced. A residential as well as industrial application for these PV modules is solar water pumping systems. Disadvantages of solar water pumping systems are low performance and low energy efficiency. This paper provides a review on the factors that influence the performance and efficiency of solar water pumping systems, with a specific focus to South Africa. The principle factors discussed include: 1) environmental conditions, 2) PV panels, 3) controllers, 4) energy storages, 5) converters and inverters, and 6) pumps and motors.
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Efficiency and cost analysis of a designed in-line water heating system compared to a conventional water heating system in South Africa
06 August 2014North West UniversityGouws, Rupert;Le Roux, EstieIn this paper, the authors compares the efficiency and cost of a designed in-line water heating system with a conventional water heating system (geyser) in South Africa. The paper provides an overview on water heating systems and heating elements and provides the typical water consumption required by an average household in South Africa. A summary on the design of the in-line water heating system together with a system cost analysis is provided. The designed in-line water heating system takes the energy consumption, temperature and pressure into account during operation. The energy consumption and cost of the designed in-line water heating sys- tem is compared to a conventional water geyser. A cost analysis on the designed in-line water heating system, heat pumps and solar water heating systems are also provided. The energy consumption results showed that the conventional water geyser on aver- age consumes 2.5% more energy to heat one litre of water from 15 °C to 60 °C, than the designed in-line water heating system to supply one litre of water at 60°C.
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Modeling the flow and heat transfer in a packed bed high temperature gas-cooled reactor in the context of a systems CFD approach
22 August 2014North West UniversityDu Toit, C.G.;Rousseau, P.G.ABSTRACT Engineers are faced with two major challenges when carrying out the thermal-fluid design of a complex system consisting of many interacting components. The first challenge is to predict the performance of all the individual thermal-fluid components. The second challenge is to predict the performance of the integrated plant consisting of all its subsystems. The complexity associated with the thermal-fluid design of complex systems requires the use of a variety of analysis techniques and simulation tools. These range from simple one-dimensional models that do not capture all the significant physical phenomena, to large-scale three-dimensional computational fluid dynamics (CFD) codes that, for practical reasons, cannot simulate the entire plant as a single integrated model. In the systems CFD approach, a network code serves as the framework to link the models of the various components together and to control the solution. The models of the components can be of varying degrees of complexity. These can range from simple lumped models to complex fully three-dimensional CFD models. This paper gives a brief overview of the systems CFD (SCFD) approach and an overview of the model of the pebble bed nuclear reactor that was developed in the context of the SCFD approach.
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Hydrogen storage in aromatic carbon ring based molecular materials decorated with alkali or alkali-earth metals
22 September 2014North West UniversityBodrenko, Igor V.;Avdeenkov, Alexander V.;Bessarabov, Dimitri G.;Bibikov, Anton V.;Nikolaev, Alexander V.On the basis of first-principles calculations of molecular electron structure, we discuss the strategy of modifying the carbon-based materials in order to increase their capacity to bind with molecular hydrogen. In particular, we have studied hydrogen adsorption on molecular complexes having anionic aromatic carbon-based rings stabilized by cations of alkali (Li+, Na+, K+) or alkali-earth metals (Be2+, Mg2+, Ca2+). The adsorption depends more on the properties of the cation than on the ring itself. The interaction of the H2 molecule with an electrostatic field leads to the binding of the hydrogen molecule with the strongly polarized ionic molecular complex. The number of the adsorbed molecules is driven by two factors acting in opposite directions: the binding energy, which should be larger than a 4–5 kJ/mol threshold needed to keep hydrogen molecules attached, and the area around the cation (coordination sphere), which is determined by its radius. As a compromise between these factors, we propose several promising candidates for building blocks of hydrogen storage materials, including diboratabenzene lithium, C4B2H6Li2, and diboratabenzene potassium, C4B2H6K2, which can adsorb 6 and 12 H2 molecules, correspondingly. We also discuss the possibility of linking these molecular complexes in three-dimensional structures.
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Case study: the effects of a variable flow energy saving strategy on a deep-mine cooling system
19 March 2015North West UniversityDu Plessis, Gideon Edgar;Liebenberg, Leon;Mathews, Edward HenryCooling systems consume up to 25% of the total electricity used on deep level mines. These systems are integrated with the water reticulation system to provide chilled service water to the mine as well as cooling for mine ventilation air. Although there is definite potential for demand-side management on these systems, it is critical that the service delivery be maintained so as not to adversely affect productivity. An energy saving strategy based on variable water flow was developed for the unique demands of integrated mine cooling systems. The strategy is based on matching the evaporators with the demand of chilled water; condensers adapting to the heat load; and the bulk air cooler matching the demand of ventilation air requirements. In this paper, a case study is presented in which the savings and consequences of implementing the developed energy saving strategy are investigated. It is shown that a decrease of 31.5% in overall electrical energy usage is possible without affecting the service delivery or performance of the cooling system.
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Non-catalytic plasma-arc reforming of natural gas with carbon dioxide as the oxidizing agent for the production of synthesis gas or hydrogen
20 July 2015North West UniversityBlom, P.W.E.;Basson, G.W.The world’s energy consumption is increasing constantly due to the growing population of the world. The increasing energy consumption has a negative effect on the fossil fuel reserves of the world. Hydrogen has the potential to provide energy for all our needs by making use of fossil fuel such as natural gas and nuclear-based electricity. Hydrogen can be produced by reforming methane with carbon dioxide as the oxidizing agent. Hydrogen can be produced in a Plasma-arc reforming unit making use of the heat energy generated by a 500 MWt Pebble Bed Modular Reactor (PBMR). The reaction in the unit takes place stoichiometrically in the absence of a catalyst. Steam can be added to the feed stream together with the Carbon Dioxide, which make it possible to control the H2/CO ratio in the synthesis gas between 1/1 and 3/1. This ratio of H2/CO in the synthesis gas is suitable to be used as feed gas to almost any chemical and petrochemical process. To increase the hydrogen production further, the WatereGas Shift Reaction can be applied. A technoeconomic analysis was performed on the non-catalytic plasma-arc reforming process. The capital cost of the plant is estimated at $463 million for the production of 1132 million N m3/year of hydrogen. The production cost of hydrogen is in the order of $12.81 per GJ depending on the natural gas cost and the price of electricity. The purpose of this study is to demonstrate that plasma-arc reforming is competitive with SMR for synthesis gas production and to reduce CO2 discharge at the same time.
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Reactor technology options for distributed hydrogen generation via ammonia decomposition: a review
20 July 2015North West UniversityChiuta, Steven;Everson, Raymond C.;Neomagus, Hein W.J.P.;Van der Gryp, Percy;Bessarabov, Dmitri G.Hydrogen (H2) fuel obtained via thermo-catalytic ammonia (NH3) decomposition is rapidly attracting considerable interest for portable and distributed power generation systems. Consequently, a variety of reactor technologies are being developed in view of the current lack of infrastructure to generate H2 for proton exchange membrane (PEM) fuel cells. This paper provides an extensive review of the state-of-the-art reactor technology (also referred to as reactor infrastructure) for pure NH3 decomposition. The review strategy is to survey the open literature and present reactor technology developments in a chronological order. The primary objective of this paper is to provide a condensed viewpoint and basis for future advances in reactor technology for generating H2 via NH3 decomposition. Also, this review highlights the prominent issues and prevailing challenges that are yet to be overcome for possible market entry and subsequent commercialization of various reactor technologies. To our knowledge, this work presents for the first time a review of reactor infrastructure for distributed H2 generation via NH3 decomposition. Despite commendable research and development progress, substantial effort is still required if commercialization of NH3 decomposition reactor infrastructure is to be realized.
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Experimental performance evaluation of an ammonia-fuelled microchannel reformer for hydrogen generation
11 March 2016North West UniversityChiuta, Steven;Everson, Raymond C.;Neomagus, Hein W.J.P.;Bessarabov, Dmitri G.Microchannel reactors appear attractive as integral parts of fuel processors to generate hydrogen (H2) for portable and distributed fuel cell applications. The work described in this paper evaluates, characterizes, and demonstrates miniaturized H2 production in a stand-alone ammonia-fuelled microchannel reformer. The performance of the microchannel reformer is investigated as a function of reaction temperature (450–700 °C) and gas-hourly-space-velocity (6520–32,600 Nml gcat−1 h−1). The reformer operated in a daily start-up and shut-down (DSS)-like mode for a total 750 h comprising of 125 cycles, all to mimic frequent intermittent operation envisaged for fuel cell systems. The reformer exhibited remarkable operation demonstrating 98.7% NH3 conversion at 32,600 Nml gcat−1 h−1 and 700 °C to generate an estimated fuel cell power output of 5.7 We and power density of 16 kWe L−1 (based on effective reactor volume). At the same time, reformer operation yielded low pressure drop (<10 Pa mm−1) for all conditions considered. Overall, the microchannel reformer performed sufficiently exceptional to warrant serious consideration in supplying H2 to fuel cell systems
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A generic method for automatic translation between input models fordifferent versions of simulation codes
16 March 2016North West UniversitySerfontein, Dawid E.;Mulder, Eben J.;Reitsma, FrederikA computer code was developed for the semi-automatic translation of input models for the VSOP-A diffusion neutronics simulation code to the format of the newer VSOP 99/05 code. In this paper, this algorithm is presented as a generic method for producing codes for the automatic translation of input models from the format of one code version to another, or even to that of a completely different code. Normally, such translations are done manually. However, input model files, such as for the VSOP codes, often are very large and may consist of many thousands of numeric entries that make no particular sense to the human eye. Therefore the task, of for instance nuclear regulators, to verify the accuracy of such translated files can be very difficult and cumbersome. This may cause translation errors not to be picked up, which may have disastrous consequences later on when a reactor with such a faulty design is built. Therefore a generic algorithm for producing such automatic translation codes may ease the translation and verification process to a great extent. It will also remove human error from the process, which may significantly enhance the accuracy and reliability of the process. The developed algorithm also automatically creates a verification log file which permanently record the names and values of each variable used, as well as the list of meanings of all the possible values. This should greatly facilitate reactor licensing applications
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Sharp reduction in maximum fuel temperatures during loss of coolantaccidents in a PBMR DPP-400 core, by means of optimised placementof neutron poisons
17 March 2016North West UniversitySerfontein, Dawid E.In a preceding study, coupled neutronics and thermo-hydraulic simulations were performed with the VSOP-A diffusion code for the standard 9.6 wt% enriched 9 g uranium fuel spheres in the 400 MWth Pebble Bed Modular Reactor Demonstration Power Plant. The axial power profile peaked at about a third from the top of the fuel core and the radial profile peaked directly adjacent to the central graphite reflector. The maximum temperature during a Depressurised Loss of Coolant (DLOFC) incident was 1581.0 °C, which is close to the limit of 1600 °C above which the leakage of radioactive fission products through the TRISO coatings around the fuel kernels may become unacceptable. This may present licensing challenges and also limits the total power output of the reactor. In this article the results of an optimisation study of the axial and radial power profiles for this reactor are reported. The main aim was to minimise the maximum DLOFC temperature. Reducing the maximum equilibrium temperature during normal operation was a lesser aim. Minimising the maximum DLOFC temperature was achieved by placing an optimised distribution of 10B neutron poison in the central reflector. The standard power profiles are sub-optimal with respect to the passive leakage of decay heat during a DLOFC. Since the radial power profile peaks directly adjacent to the central reflector, the distance that the decay heat needs to be conducted toward the outside of the reactor and the ultimate heat sink is at a maximum. The sharp axial power profile peak means that most of the decay power is concentrated in a small part of the core volume, thereby sharply increasing the required outward heat flux in this hotspot region. Both these features sharply increase the maximum DLOFC temperatures in this hotspot. Therefore the axial distribution of the neutron poisons in the central reflector was optimised so as to push the equilibrium power density profile radially outward and to suppress the axial power peak near the middle of the core, while increasing the power density near the top and bottom of the core. This resulted in a huge reduction in the maximum DLOFC temperature from 1581.0 °C to 1297.6 °C, which may produce far reaching safety and economic benefits. However, it came at the cost of a 22% reduction in the average burn-up of the fuel. In a separate optimisation attempt a much smaller, but still significant, reduction in the maximum equilibrium temperature, from 1023 °C down to 988 °C, was achieved
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The case for nuclear electricity in South Africa – a political alignment framework
11 April 2016North West UniversityStoker, P.W.;Fick, J.I.J.;Stwayi, M.;Gumede, J.Energy is essential for economic development of South Africa. All areas for development and economic growth i.e. reducing poverty and improving quality of life require affordable access to reliable energy services. When the challenges of energy provision to the population of a state remain unresolved, the resulting misery often leads to conflicts and violence, which in turn affect development efforts and impact on regional and global stability. The Integrated Resource Plan 2010 (DoE 2010) allocates 9.6 GW electrical generation capacity to nuclear technology. At the date of writing this paper –almost 5 years later- this allocation has not yet been committed to a build program. This situation is perhaps not surprising, since the National Development Plan, generally viewed as a vision and master plan for South Africa's economic development, is not supportive of the nuclear option (NPC 2011). The plan calls for further investigation into the need for nuclear electricity, citing gas and shale gas as possible alternatives for base load power generation. Against this background, the paper presents a framework for moving towards political consensus on the generation of electricity using nuclear technology. The framework builds on the notion that a “political system” can be characterized as a Complex Adaptive System (CAS). It defines political consensus by applying seven criteria which should be met for successful consensus building. These criteria, originally developed by Innes, (Innes and Booher 2009) have been thoroughly tested, and are increasingly used as a strategy to achieve consensus amongst stakeholders on complex and controversial planning and policy tasks. (Innes and Booher 2009). This paper presents a set of principles on which a political alignment framework should be founded, for example: that South Africa's economic development vision and long term economic development plan should be elevated above party political considerations; that people power is the lifeblood of a democratic society. Give the people the power of knowledge, and allow them to make their own informed decisions - in this case regarding nuclear. A description is presented as to how the criteria for consensus building could be met in the South African political system. This description is informed by the development of nuclear lectricity in other political systems in both the eastern and western worlds. It further draws on the views of key political parties in respect of nuclear electricity, and proposes that political parties should implement within their own ranks, their own consensus building initiatives in respect of these national priorities. The paper concludes that if the consensus seeking framework is executed in an honest and transparent way, it could lead to consensus in respect of nuclear electricity, not only on a political but also at a national level
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Prototype monitoring system for power line inspection by means of a PandaBoard
27 July 2016North West UniversityGouws, Rupert;Visser, TjaartThe national energy supplier (Eskom in South Africa) supplies electricity through thousands-of-kilometers of overhead power lines. The current methods of inspection of these overhead power lines are infrequent and expensive. In this paper, the authors present the development of a prototype monitoring system for power line inspection in South Africa. The developed prototype monitoring system collects data (information) from the overhead power lines, is remotely accessible and fits into a power line robot. The prototype monitoring system makes use of a PandaBoard® (SBC) with GPS receiver and 5 MP camera to collect data. Hardware fatigue is the biggest problem faced on the overhead power lines and is captured by means of the 5 MP camera and is displayed on a website hosted by the PandaBoard® via Wi-Fi. The monitoring system has low power consumption, is light weight, compact and easily collects data. The data obtained from the prototype monitoring system was satisfactory and provides an improved solution for monitoring power lines for Eskom in South Africa
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Design and heat flow analysis of a commercial energy efficient in-line water heating system
27 July 2016North West UniversityGouws, R.;Le Roux, E.In this paper, the authors provide the design, heat flow analysis and pressure analysis of a commercial energy efficient in-line water heating system in South Africa. The designed commercial in-line water heating system captures the energy consumption, flow rate, temperature and pressure during operation and accordingly responds on these values to increase the energy efficiency of the system. The user is constantly aware of the energy consumption and cost during operation and can choose to switch to a more economical setting to conserve energy. A central processor with PID control was used to optimize the energy consumption of the in-line water heating system. An overview on the design and results of the heat flow analysis and pressure analysis are provided
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Improving the efficiency of single phase asynchronous machines
27 July 2016North West UniversityGouws, Rupert;Van Jaarsveldt, HeinoGlobally around 40% of the electricity supplied to the industrial and mining sectors is consumed by electric motorised systems and for South Africa around 60% of the electricity supplied to these sectors is consumed by asynchronous machines. The efficiency of these asynchronous machines can be improved by reducing their operating temperatures
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Using dynamic model of PEM-Fuel Cell supplying the load by the Z-source inverter with a novel control strategy
27 July 2016North West UniversityZabihi, Nima;Gouws, Rupert;Dobzhanskyi, OleksandrA new dynamic model is developed in this paper to connect PEM Fuel Cell (PEMFC) to a Z-source inverter (ZSI). This model is used to analyse the behaviour of a fuel cell by providing a polarization curve. A controller is designed based on an interpolation to spot parameters of PEM Fuel Cell such as temperature (or anode and cathode pressure). A current feedback is gained to regulate the output voltage through determination of physical parameters. The ZSI is used in the proposed model to generate AC power. In this research, to compensate the voltage drop of fuel cell the capacitor voltage of the Z-network is controlled using the state space averaging method to stabilize the AC output voltage of the ZSI. Simulation and experimental results verify the validity of the proposed controlling model
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Investigation and efficiency analysis: 405 km transmission line with series compensation
27 July 2016North West UniversityGouws, R.This article presents an investigative case study and efficiency analysis of the 405 km, 420 kV transmission line between Insukamini substation in Bulawayo, Zimbabwe and the Matimba thermal power station in South Africa (which is routed through Botswana)
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Thermal and efficiency analysis of a single phase induction motor with Peltier devices
27 July 2016North West UniversityGouws, R.;Van Jaarsveldt, H.We present the results obtained from the thermal and efficiency analysis of a single phase induction motor with Peltier devices. A single phase induction motor is completely simulated in SolidWorks® and Matlab® Simulink®. The cooling of the induction motor is done by means of Peltier devices and the corresponding power consumption and stator temperature is recorded. From the SolidWorks® simulation results it can be seen that the temperature of the induction motor under normal operating conditions is cooled from 68°C to 35°C. From the Matlab® Simulink® simulation results show that the efficiency of the induction motor is increased by an average of 3.73% from the normal operating condition to the cooled operating condition with the inclusion of the Peltier devices onto the system
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Prototype super-capacitor photovoltaic streetlight with xLogic SuperRelay functionality
29 July 2016North West UniversityGouws, Rupert;Van Niekerk, ElizbeIn this paper, the authors present and discuss the design of a prototype super-capacitor photovoltaic (PV) streetlight with xLogic SuperRelay (PLC) functionality. Deep-cycle batteries used in solar electrical systems, generally have low efficiencies, long charging times, are temperature sensitive and have a limited amount of charging and discharging cycles. This paper evaluated the effect of super-capacitors as an energy source for a PV streetlight in South Africa. An xLogic SuperRelay (PLC) is used to control the charging and discharging profiles of the super-capacitors and deep-cycle batteries. The following three design topologies are evaluated and presented: 1) deep-cycle batteries as an energy source, 2) super-capacitors as an energy source, 3) combination deep-cycle batteries and super-capacitors as an energy source. The experimental results obtained show that the deep-cycle batteries provide a constant supply to the load, while the super-capacitors charge and discharge with a linear curve. The results show that it is too expensive to replace deep-cycle batteries with super-capacitors, but a combination provides the most energy efficient solution
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Prototype line crawler for power line inspection
29 July 2016North West UniversityGouws, Rupert;Du Plessis, NicolaasIn South Africa, electricity is supplied through thousands-of-kilometers of overhead power cables, which is owned by Eskom the national energy supplier. Currently monitoring of these overhead power cables are done by means of helicopter inspection flights and foot patrols, which are infrequent and expensive. In this paper, the authors present the design of a prototype power line crawler (inspection robot) for the monitoring of these overhead power lines in South Africa. The designed prototype power line crawler is capable of driving on the wire, balancing on the wire and is capable of maneuvering past certain obstacles found on the overhead power cables. The prototype power line crawler is designed to host a monitoring system that monitors the power line as the inspection robot drives on it. Various experimental tests were performed and are presented in this paper, showing the capability of performing these tasks. This prototype inspection robot ensures a platform for future development in this area
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Energy management by means of PLC for a solar powered ultra-capacitor streetlight system
01 August 2016North West UniversityGouws, RupertThis paper presents the design of an energy management programmable logic controller (PLC) control program for a solar powered ultra-capacitor and battery powered streetlight system. A PLC is used to control the flow of energy between an ultra-capacitor bank and a deep-cycle battery bank for a solar powered streetlight system. The purposes are to increase the efficiency of the complete solar powered system and to prolong the lifetime of the battery bank, since deep-cycle batteries normally used in solar electrical systems, generally have low efficiencies, have a limited amount of charging and discharging cycles, have long charging times and are temperature sensitive. The designed operational diagram as well as a functional block diagram of PLC control program is presented. The results of five different scenarios pertaining to the functionality and use of the energy between the ultra-capacitor bank and deep-cycle battery bank are presented in this paper
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Analysis of a 405 km transmission line with series compensation
01 August 2016North West UniversityGouws, RupertThis paper presents an investigative case study and energy efficiency analysis of the 405 km, 420 kV transmission line between Insukamini substation in Bulawayo in Zimbabwe and the Matimba thermal power station in South Africa. Three scenarios were evaluated: 1) where a line to ground fault occurred on the secondary bus, 2) where an impedance fault occurred on the two transmission lines and 3) where the combination of the above two faults occurred. An analysis was made on the energy efficiency of the load with respect to the three scenarios by means of a simulation model
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Thermodynamical model for hydrogen storage capacity in carbon nanostructures
11 August 2016North West UniversityAvdeenkov, A.V.;Bessarabov, D.G.;Tokarev, A.;Bodrenko, I.V.;Bibikov, A.V.A simple thermodynamical model taking into account non-ideality and inhomogeneity of absorbed hydrogen molecular gas has been proposed to calculate hydrogen storage capacity in carbon nanostructures as a function of temperature and pressure. The model utilizing the effective interaction potential of the hydrogen molecule with the atoms of the considered material, is based on the experimental equation of state and a local density approximation for molecular hydrogen. We have applied the model for the search of the optimal geometry for hydrogen storage of such promising carbon materials as a set of graphene layers and bundles of carbon nanotubes. We demonstrate that the hydrogen storage capacity depends on the geometry of material and discuss the origin of this effect
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Performance evaluation of a high-throughput microchannel reactor for ammonia decomposition over a commercial Ru-based catalyst
11 August 2016North West UniversityChiuta, Steven;Everson, Raymond C.;Neomagus, Hein W.J.P.;Bessarabov, Dmitri G.In this work, the prospect of producing hydrogen (H2) via ammonia (NH3) decomposition was evaluated in an experimental stand-alone microchannel reactor wash-coated with a commercial Ruthenium-based catalyst. The reactor performance was investigated under atmospheric pressure as a function of reaction temperature (723–873 K) and gas-hourly-space-velocity (65.2–326.1 Nl gcat−1 h−1). Ammonia conversion of 99.8% was demonstrated at 326.1 Nl gcat−1 h−1 and 873 K. The H2 produced at this operating condition was sufficient to yield an estimated fuel cell power output of 60 We and power density of 164 kWe L−1. Overall, the microchannel reactor considered here outperformed the Ni-based microstructured system used in our previous work
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Air drying of fine coal in a fluidized bed
15 August 2016North West UniversityLe Roux, M.;Campbell, Q.P.;Van Rensburg, M.J.;Peters, E.S.;Stiglingh, C.The demand for energy has continued to rise worldwide in line with population growth. The majority of South Africa’s electricity is supplied by coal-fired power stations. The amount of fine coal (-2 mm) generated at coal processing plants has increased, due mainly to mechanized mining methods. Fine coal retains more water, which lowers its heating value. Drying the coal is costly and it is difficult to achieve the required moisture content. Consequently, coal fines are often discarded. An estimated 8% of the total energy value of mined coal is lost1. Fluidized bed technology is often used to dry coal thermally, but this method is expensive and has an adverse environmental impact. The objective of this study was to investigate the removal of moisture from fine coal (<2 mm) in a fluidized bed operated with dry fluidizing air at moderate temperatures as the drying agent. The effects of different air temperatures and relative humidity levels were investigated in a controlled environment. The study further investigated the influence of coal particle size on moisture removal. The drying rate was found to increase with increasing temperature. The relative humidity of the drying air had a more pronounced effect on the drying rate, even at temperatures as low as 25°C.. It became more challenging to remove moisture as the particle size decreased. The gain in calorific value was greater than the energy required to dry the coal samples, showing that a fluidized bed using moderately warm dry air is an energy-efficient drying technology. The energy efficiency of the fluidized bed compared favourably with other thermal drying methods
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Modeling hydrogen storage in boron-substituted graphene decorated with potassium metal atoms
17 August 2016North West UniversityTokarev, Andrey;Bessarabov, Dmitri G.;Avdeenkov, Alexander V.;Langmi, HenriettaBoron-substituted graphene decorated with potassium metal atoms was considered as a novel material for hydrogen storage. Density functional theory calculations were used to model key properties of the material, such as geometry, hydrogen packing, and hydrogen adsorption energy. We found that the new material has extremely high hydrogen storage capacity: 22.5wt%. It is explained by high-density packing of hydrogen molecules into hydrogen layers with specific geometry. In turn, such geometry is determined by the composition and topology of the material
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Model predictive control of an active magnetic bearing suspended flywheel energy
17 August 2016North West UniversityUren, K.R.;Van Schoor, G.;Aucamp, C.D.Flywheel Energy Storage (FES) is rapidly becoming an attractive enabling technology in power systems requiring energy storage. This is mainly due to the rapid advances made in Active Magnetic Bearing (AMB) technology. The use of AMBs in FES systems results in a drastic increase in their efficiency. Another key component of a flywheel system is the control strategy. In the past, decentralised control strategies implementing PID control, proved very effective and robust. In this paper, the performance of an advanced centralised control strategy namely, Model Predictive Control (MPC) is investigated. It is an optimal Multiple-Input and Multiple-Output (MIMO) control strategy that utilises a system model and an optimisation algorithm to determine the optimal control law. A first principle state space model is derived for the purpose of the MPC control strategy. The designed MPC controller is evaluated both in simulation and experimentally at a low operating speed as a proof of concept. The experimental and simulated results are compared by means of a sensitivity analysis. The controller showed good performance, however further improvements need to be made in order to sustain good performance and stability at higher speeds. In this paper advantages of incorporating a system model in a model-based strategy such as MPC are illustrated. MPC also allows for incorporating system and control constraints into the control methodology allowing for better efficiency and reliability capabilities
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Performance evaluation of a membraneless divergent electrode-flow-through (DEFT) alkaline electrolyser based on optimisation of electrolytic flow and electrode gap
02 September 2016North West UniversityGillespie, M.I.;Van der Merwe, F.;Kriek, R.J.A membraneless divergent electrode-flow-through (DEFT) alkaline electrolysis design and operating principle is investigated, which allows for the ohmic drop contribution and performance threshold limitations of a conventional membrane barrier to be overcome. Employing mesh electrodes of 30 mm diameter, operation of the electrolyser at an electrolytic flow velocity of 0.075–0.1 m s−1, resulted in an optimal electrode gap of ∼2.5 mm, while operating at greater velocities (>0.1–0.2 m s−1) allows for the employment of a smaller optimal gap of ∼0.8 mm. At an electrode gap of 2.5 mm and current densities of 3500 mA cm−2, hydrogen purity of 99.83% has been recorded. With pure nickel electrodes current densities of 101.19 mA cm−2 (at 1.80 VDC) and 326.33 mA cm−2 (at 2 VDC) have been achieved, while the use of superior catalysts, namely, RuO2/IrO2/TiO2 and Pt for the anode and cathode respectively, resulted in the current densities to increase to 219.99 mA cm−2 (at 1.8 VDC) and 474.40 mA cm−2 (at 2 VDC) at an electrode gap of 2.5 mm and a minimum flow velocity of 0.075 m s−1. The test rig is capable of generating hydrogen at a rate of 63.6 L/hr at normal temperature and pressure (NTP). The production rate follows current density linearly at high overpotentials
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Generalized double sinh-Gordon equation: symmetry reductions, exact solutions and conservation laws
05 September 2016North West UniversityMagalakwe, G.;Muatjetjeja, B.;Khalique, C.M.This paper aims to study a generalized double sinh-Gordon equation, which appears in several physical phenomena such as integrable quantum field theory, kink dynamics and fluid dynamics. Lie symmetry analysis together with the simplest equation method is used to obtain exact solutions for this equation. Moreover, we derive conservation laws for the equation by using two different approaches, namely, the direct method and the new conservation theorem due to Ibragimov
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Hydrogen production from ammonia decomposition over a commercial Ru/Al2O3 catalyst in a microchannel reactor: experimental validation and CFD simulation
11 October 2016North West UniversityChiuta, Steven;Everson, Raymond C.;Neomagus, Hein W.J.P.;Bessarabov, Dmitri G.In this work, an integrated experimental and CFD modelling technique was used to evaluate a microchannel reactor producing hydrogen from ammonia decomposition using a commercial Ru/Al2O3 catalyst. The microchannel reactor performance was first assessed in a series of experiments varying the reaction temperature (723–873 K) and ammonia flow rates (100–500 Nml min−1) at atmospheric pressure. A global rate expression based on Temkin-Pyzhev kinetics that accurately predicts the entire experimental operating space was established using a model-based technique with parameter refinement and estimation. The kinetic model provided the reaction source term for subsequent CFD simulations aiming to obtain a more fundamental understanding of the reaction-coupled transport phenomena within the microchannel reactor. The transport processes and reactor performance were discussed in detail using velocity, temperature, and species concentration profiles. Finally, the influence of mass transport limitations within the various regions of the microchannel reactor was evaluated and discussed by means of dimensionless numbers vis-à-vis Damköhler and Fourier numbers. Overall, results presented in this paper provide valuable data for the efficient design of ammonia-fuelled microchannel reactors for hydrogen generation aimed at portable and distributed fuel cell applications
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A modelling evaluation of an ammonia-fuelled microchannel reformer for hydrogen generation
14 October 2016North West UniversityChiuta, Steven;Everson, Raymond C.;Neomagus, Hein W.J.P.;Bessarabov, Dmitri G.;Le Grange, Louis A.Hydrogen production from an ammonia-fuelled microchannel reactor is simulated in a three-dimensional (3D) model implemented via Comsol Multiphysics™. The work described in this paper endeavours to obtain a mathematical framework that provides an understanding of reaction-coupled transport phenomena within the microchannel reactor. The transport processes and reactor performance are elucidated in terms of velocity, temperature, and species concentration distributions, as well as local reaction rate and NH3 conversion profiles. The baseline case is first investigated to comprehend the behaviour of the microchannel reactor, then microstructural design and operating parameters are methodically altered around the baseline conditions to explore the optimum values. The simulation results show that an optimum NH3 space velocity (GHSV) of 65,000 Nml gcat−1 h−1 yields 99.1% NH3 conversion and a power density of 32 kWe L−1 at the highest operating temperature of 973 K. It is also shown that a 40-μm-thick porous washcoat is most desirable at these optimum conditions. Finally, a low channel hydraulic diameter (225 μm) is observed to contribute to high NH3 conversion. Mass transport limitations in the porous-washcoat and gas-phase are negligible as depicted by the Damköhler and Fourier numbers, respectively. The experimental microchannel reactor yields 98.2% NH3 conversion and a power density of 30.8 kWe L−1 when tested at the optimum operating conditions established by the model. Good agreement with experimental data is observed, so the integrated experimental-modelling approach developed in this paper may well provide an incisive step toward the efficient design of ammonia-fuelled microchannel reformers
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Solutions of Two Nonlinear Evolution Equations Using Lie Symmetry and Simplest Equation Methods
25 October 2016North West UniversityMhlanga, Isaiah Elvis;Khalique, Chaudry MasoodIn this paper, we study two nonlinear evolution partial differential equations, namely, a modified Camassa–Holm–Degasperis–Procesi equation and the generalized Korteweg–de Vries equation with two power law nonlinearities. For the first time, the Lie symmetry method along with the simplest equation method is used to construct exact solutions for these two equations.
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Technology assessment of plasma arc reforming for greenhouse gas mitigation: a simulation study applied to a coal to liquids process
08 November 2016North West UniversityMapamba, Liberty S.;Conradie, F.H.;Fick, Johan I.J.Coal to liquids processes contribute significantly to coal rich countries like South Africa. However, their sustainability is affected by high greenhouse gas emissions and low carbon productivity. This paper explores the future possibility of applying plasma arc reforming to turn waste carbon dioxide into a useful chemical feedstock. This was achieved through a technology assessment that was performed by applying existing modelling techniques to an existing industrial liquid fuel from coal process. The approach was: 1) the selection of an appropriate plasma reforming technology, 2) evaluation of the potential impact on an industrial coal to liquids process and 3) assessment of commercial status of the chosen technology. Simulation results showed that carbon dioxide based plasma arc reformers are most compatible with coal to liquids processes. Plasma arc reforming of methane is capable of improving carbon efficiency of the coal to liquids process by up to 14% by carbon recovery from carbon dioxide. However, non-catalytic reforming of methane is not yet ready for commercial implementation, with a technology readiness level of 4. High electrical energy consumption and high technical risk in scale-up were identified as key barriers to technology commercialisation. The potential for success of plasma arc reformers would be enhanced by availability of low carbon electricity and characterisation of plasma reforming kinetics to minimise technical risk. This paper highlights the opportunity to derive value from intense, high purity waste carbon dioxide streams by the application of plasma arc reforming. It also identifies the areas technology developers should focus on to bring the technology to commercially readiness
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An integrated approach to sensor FDI and signal reconstruction in HTGRs. Part I. Theoretical framework
20 January 2017North West UniversityUren, Kenneth R.;Van Schoor, George;Du Rand, Carel P.;Botha, AnrikaSensor fault detection and isolation (FDI) is an important element in modern nuclear power plant (NPP) diagnostic systems. In this respect, sensor FDI of generation II and III water-cooled nuclear energy systems has become an active research topic to continually improve levels of reliability, safety, and operation. However, evolutionary advances in reactor and component technology together with different energy conversion methodologies support the investigation of alternative approaches to sensor FDI. Within this context, the basic aim of this two part series is to propose, implement and evaluate an integrated approach for sensor FDI and signal reconstruction in generation IV nuclear high temperature gas-cooled reactors (HTGRs). In part I of this two part series, the methodology and theoretical background of the integrated sensor FDI and signal reconstruction approach are given. This approach combines techniques such as non-temporal parity space analysis (PSA), principal component analysis (PCA), sensor fusion and fuzzy decision systems to form a more powerful sensor FDI methodology that exploits the strengths of the individual techniques. An illustrative example of the PCA algorithm is given making use of actual data retrieved from a pilot plant called the pebble bed micro model (PBMM). This is a prototype gas turbine power plant based on the first design configuration of the pebble bed modular reactor (PBMR). In part II, the described integrated sensor fault detection approach will be evaluated by means of two case studies. In the first case study the approach will be evaluated on real PBMM data and in the second case study the approach will be evaluated on a highly detailed Flownex® model of the new generation PBMR
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Techno-economic evaluation of a nuclear-assisted coal-to-liquid facility
26 January 2017North West UniversityChiuta, Steven;Blom, EnnisThe production of synthetic fuels (synfuels) in Coal-to-Liquid (CTL) facilities has contributed to global warming due to the enormous carbon dioxide (CO2) emission footprint of the process. This corresponds to inefficient carbon conversion, a problem growing in importance particularly given the severe consequences concomitantly posed by global warming and the rapid depletion of coal reserves. This paper seeks to address these simultaneous challenges of environmental and energy sustainability associated with CTL facilities. To reduce the environmental impact and improve the carbon conversion of CTL facilities, we propose and apply the concept of a nuclear-assisted synthesis gas (syngas) plant to a reference syngas plant in a CTL facility consisting of 36 dry fixed-bed gasifiers. In this kind of plant, a Hybrid Sulphur (HyS) plant powered by 10 high-temperature nuclear reactors (HTR's) splits water to produce nuclear hydrogen and oxygen. The nuclear hydrogen supplements the hydrogen-poor syngas from the Rectisol and the oxygen becomes part of the gasifier feed. The nuclear-assisted syngas plant concept that we have developed is entirely based on the premise that the water-gas shift (WGS) reaction is minimised by operating a dry fixed-bed gasifier under steam-lean conditions. A mass-analysis model of the syngas plant described in this paper demonstrates that the WGS reaction contributes 68% to the CO2 emission output. The consequent benefits of eliminating the WGS reaction include reductions in the CO2 emissions and gasification coal requirement of 75% and 40%, respectively, all to achieve the same syngas output as the conventional syngas plant. In addition, we have developed an economic model for use as a strategic decision analysis tool that compares the relative syngas manufacturing costs for conventional and nuclear-assisted syngas plants. Our model predicts that syngas manufactured in the nuclear-assisted CTL plant would cost 21% more to produce when the average cost of producing nuclear hydrogen is US$3/kg H2. The model also evaluates the cost of CO2 avoided, which at the average hydrogen cost is $58/t CO2. Sensitivity analyses performed on the costing model reveal, however, that the cost of CO2 avoided is zero at a hydrogen production cost of $2/kg H2 or at a delivered coal cost of $128/t coal. The economic advantages of the nuclear-assisted syngas plant are lost above the threshold cost of $100/t CO2. However, the cost of CO2 avoided in our model is below the threshold for the range of critical assumptions considered in the sensitivity analyses. Consequently, this paper demonstrates the practicality, feasibility and economic attractiveness of the nuclear-assisted CTL plant
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Validation of a transient thermal-fluid systems CFD model for a packed bed high temperature gas-cooled nuclear reactor
01 March 2017North West UniversityRousseau, P.G.;Du Toit, C.G.;Landman, W.A.This paper provides an overview of the theoretical basis for a new thermal-fluid systems CFD simulation model for high temperature gas-cooled reactors, contained in the Flownex software code. Flownex provides for detailed steady-state and transient thermal-fluid simulations of the complete power plant, fully integrated with core neutronics and controller algorithms. The reactor model is founded on a fundamental approach for the conservation of mass, momentum and energy for the compressible fluid flowing through a fixed bed, as well as the heat transfer in the pebbles and core structures. The time-wise integration of the resulting differential equations is based on an implicit pressure correction algorithm. This allows for the use of rather large time steps making it very suitable for simulating the slow transients that can be expected to follow incidents like reactor shutdowns. The paper also compares the Flownex results for four transient tests with the measured results from the SANA test facility as well as to the results of simulations with the Thermix/DIREKT code that were done at the Research Centre, Jülich. The Flownex results compare well with the Thermix/DIREKT results for all the cases presented here. Good comparison was also obtained between the simulated and measured results, except at two points within the pebble bed near the inner wall. The fact that quick computer simulation times were obtained indicates that the new model indeed achieves a fine balance between accuracy and simplicity. However, the discrepancies obtained at the two points near the inner wall, together with the fact that additional uncertainty was introduced in the original SANA test set-up by not being able to control the temperature of the outer wall, highlight the need for additional systematic tests to be performed in order to better validate the new model
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Impact of plasma arc reforming deployment on economic performance of a commercial coal to liquids process
13 March 2017North West UniversityMapamba, Liberty S.;Fick, Johan I.J.Coal remains integral to the supply of energy in many parts of the world despite the associated negative effects on the environment. Plasma arc reforming has the potential of making coal to liquids processes cleaner by reducing its greenhouse gas footprint. However, the chances of adoption without a clear understanding of how the process modification would affect economic performance are slim. In this study, financial models were built using an existing commercial coal to liquids process as a reference case. Economic analyses were done to evaluate the impact of deploying a plasma arc reformer on financial performance of a coal to liquids process. In building the financial models, the possibility of the introduction of a carbon tax was taken into consideration. The results show that deploying plasma arc reforming reduces the oil price required for break-even from $89/bbl. to $82/bbl., achieves a positive project NPV and exceeds the hurdle rate for similar projects. In the process, it reduces vulnerability to the introduction of a carbon tax. The requirement for extra low carbon electricity can be a hurdle to implementation, however the alternative carbon tax related charges are less desirable. Overall, it was concluded that the deployment of plasma arc reforming to coal to liquids processes is value adding. The project demonstrates that by implementing a cleaner production initiative it is possible to reduce greenhouse gas emissions of coal to liquids without significantly losing shareholder value
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Theoretical limit of reversible hydrogen storage capacity for pristine and oxygen-doped boron nitride
30 March 2017North West UniversityTokarev, Andrey;Bessarabov, Dmitri;Kjeang, Erik;Cannon, MarkTo achieve higher hydrogen storage capacity than that of compressed gas vessels, new advanced materials must be developed. Among the most promising are two-dimensional layered nanomaterials, such as graphene and boron nitride, storing hydrogen via physisorption which is potentially reversible at relatively low pressures. Unlike graphene, boron nitride is a polar material that makes it potentially more attractive for hydrogen physisorption. To quickly evaluate storage capacity of novel materials an efficient theoretical tool is proposed. A customized model combining quantum simulation with thermodynamic calculation is developed and applied for pristine and oxygen-doped boron nitride materials. It is shown that pristine boron nitride has a maximum reversible hydrogen storage capacity of 1.5 wt.% under 5 MPa at room temperature. Oxygen doping increases the capacity to 1.9 wt.% under the same conditions by deepening and widening the adsorption potential. Both gravimetric and volumetric storage properties are found to be strong functions of the interlayer separation distance of the material, with an optimum distance near 7 Å. The present results indicate that pristine and oxygen doped boron nitride materials have a suitable base configuration for potentially high reversible hydrogen storage
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Energy efficiency and the law: a multidisciplinary approach
06 April 2017North West UniversityDu Plessis, WillemienSouth Africa is an energy-intensive country. The inefficient use of, mostly, coal-generated energy is the cause of South Africa’s per capita contribution to greenhouse gas emissions, pollution and environmental degradation and negative health impacts. The inefficient use of the country’s energy also amounts to the injudicious use of natural resources. Improvements in energy efficiency are an important strategy to stabilise the country’s energy crisis. Government responded to this challenge by introducing measures such as policies and legislation to change energy consumption patterns by, amongst others, incentivising the transition to improved energy efficiencies. A central tenet underpinning this review is that the law and energy nexus requires a multidisciplinary approach as well as a multi-pronged adoption of diverse policy instruments to effectively transform the country’s energy use patterns. Numerous, innovative instruments are introduced by relevant legislation to encourage the transformation of energy generation and consumption patterns of South Africans. One such innovative instrument is the ISO 50001 energy management standard. It is a voluntary instrument, to plan for, measure and verify energy-efficiency improvements. These improvements may also trigger tax concessions. In this paper, the nature and extent of the various policy instruments and legislation that relate to energy efficiency are explored, while the interactions between the law and the voluntary ISO 50001 standard and between the law and the other academic disciplines are highlighted. The introduction of energy-efficiency measures into law requires a multidisciplinary approach, as lawyers may be challenged to address the scientific and technical elements that characterise these legal measures and instruments. Inputs by several other disciplines such as engineering, mathematics or statistics, accounting, environmental management and auditing may be needed. Law is often described as the catalyst for change, building bridges between different academic disciplines, and driving behavioural changes that are not only enforced by government, but that are also voluntarily adopted by the users themselves.
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Synthesis of a hybrid MIL-101(Cr)/ZTC composite for hydrogen storage applications
07 April 2017North West UniversityMusyoka, Nicholas;Bessarabov, Dmitri;Ren, Jianwei;Annamalai, Perushini;Langmi, Henrietta W.Metal–organic frameworks (MOFs) hybrid composites have recently attracted considerable attention in hydrogen storage applications. In this study a hybrid composite of zeolite templated carbon (ZTC) and Cr-based MOF (MIL-101) was synthesised by adding the templated carbon in situ during the synthesis of MIL-101(Cr). The obtained sample was fully characterized and hydrogen adsorption measurements performed at 77 K up to 1 bar. The results showed that the surface areas and the hydrogen uptake capacities of individual MIL-101 (2552 m2 g−1, 1.91 wt%) and zeolite templated carbon (2577 m2 g−1, 2.39 wt%) could be enhanced when a hybrid MIL-101(Cr)/ZTC composite (2957 m2 g−1, 2.55 wt%) was synthesized. The procedure presents a simple way for enhancement of hydrogen uptake capacity of the individual Cr-MOF and templated carbon samples
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Gas crossover mitigation in PEM water electrolysis: hydrogen cross-over benchmark study of 3M's Ir-NSTF based electrolysis catalyst-coated membranes
18 April 2017North West UniversityBessarabov, Dmitri;Krüger, Andries;Luopa, Sean M.;Park, Jiyoung;Molnar, Attila A.In this work we present some preliminary data, such as permeability (gas crossover) of oxygen and hydrogen as a function of current density and other operational variables, aimed at establishing baselines for unmitigated hydrogen crossover of 3M’s electrolyzer MEAs based on 3M’s NSTF low-PGM loading catalyst and several types of perfluoro sulfonic acid based PEM membranes, both of which are widely commercially available (such as Nafion™ membranes), and membranes made by 3M. Experimental challenges associated with ex situ and in situ gas crossover measurements will be also discussed
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The effect of acid demineralising bituminous coals and de-ashing the respective chars on nitrogen functional forms
13 June 2017North West UniversityPhiri, Zebron;Everson, Raymond C.;Neomagus, Hein W.J.P.;Wood, Barry J.An opportunity presented itself to compare changes in nitrogen functional forms brought by the acid treatment of South African bituminous coals and their respective chars. X-ray photoelectron spectroscopy (XPS) was used to determine functional forms of the raw coals, acid-treated coals, respective chars prepared at 740 and 980 °C in a bench-scale fluidised-bed (FB), and at 1000 and 1400 °C in a drop-tube furnace (DTF), as well as their corresponding de-ashed remnants. The XPS N 1s spectra for the raw coals were typically similar to previous widely reported bituminous coals, of which pyrrolic nitrogen was the predominant form of organically bound nitrogen, followed by pyridinic and quaternary nitrogen. In pyrolysed chars, quaternary nitrogen was the dominant form followed by pyridinic, pyrrolic and protonated-/oxidised heterocyclic nitrogen forms respectively. Nonetheless, XPS N 1s analysis for DTF severely pyrolysed chars (1000 and 1400 °C) prepared from high ash and vitrinite-rich coal, and also a char (1400 °C) from a relatively low ash and inertinite-rich coal, gave a spectra with only two sub-peaks corresponding to quaternary and pyridinic nitrogen. It seems that the HCl/HF/HCl sequential demineralising/de-ashing process had no effect on the nitrogen functional forms of raw coals and the entire chars prepared from the FB. De-ashing of DTF severely pyrolysed chars emanating from high ash and inertinite-rich coal exhibited no marked change to the nitrogen functional forms. However, acid treatment of DTF chars derived from a high ash and vitrinite-rich coal, a char from relatively low ash and inertinite-rich coal, which initially contained pyridinic and quaternary nitrogen resulted in additional nitrogen moieties of pyrrolic and protonated/oxidised nitrogen
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Power calculation accuracy as a function of wind data resolution
05 September 2017North West UniversityDe Klerk, Martinus Gerhardus;Venter, Willem ChristiaanWind power calculations are usually based on average wind data taken over one-hour intervals. The effect of the wind data resolution on the statistical techniques used to calculate the probable power output (PPO) is commonly overlooked. This effect is analysed in this paper by iteratively calculating and comparing the PPO of a wind turbine using data, averaged over different periods, obtained from Wind Association of South Africa. The power is calculated using both Weibull representation and direct polynomial substitution techniques in order to compare and verify the results. The results indicate a fairly linear relationship between the resolution used and the PPO error incurred. These results raise an interest to examine the effects of a fine resolution on the data in terms of data dependence, which may violate the criteria for the majority of statistical tests and procedures