There have been many studies in the energy field to achieve different goals such as energy security, energy independence and production of cheap energy. The consensus of the general population is that renewable energy sources can be used on a short-term basis to compensate for the energy requirement of the world. However, the prediction is that fossil fuels will be used to provide the majority of energy requirements in the world at least on a short-term basis. Coal is one of the major fossil fuels and will be used for a long time because there are large coal reservoirs in the world and many products such as hydrogen, ammonia, and diesel can be produced using coal. In the present study, the performance of a clean energy system that combines the coal gasification and alkaline water electrolyzer concepts to produce hydrogen is evaluated through thermodynamic modeling and simulations. A parametric study is conducted to determine the effect of water ratio in coal slurry, gasifier temperature, effectiveness of carbon dioxide removal, and hydrogen recovery efficiency of the pressure swing adsorption unit on the system hydrogen production. In addition, the effects of different types of coals on the hydrogen production are estimated. The exergy efficiency and exergy destruction in each system component are also evaluated. Although this system produces hydrogen from coal, the greenhouse gases emitted from this system are fairly low.

The global fossil reserves are dwindling and there is need to find alternative sources of energy. With global warming in mind, some of the most commonly considered suitable alternatives include solar, wind, nuclear, geothermal and hydro energy. A common challenge with use of most alternative energy sources is ensuring continuity of supply, which necessitates the use of energy storage. Hydrogen has properties that make it attractive as an energy carrier. To efficiently store energy from alternative sources in hydrogen, several methods of hydrogen production are under study. Several literature sources show thermochemical cycles as having high potential but requiring further development. Using literature sources, an initial screening of thermochemical cycles was done to select a candidate thermochemical cycle. The copper–chlorine thermochemical cycle was selected due to its relatively low peak operating temperature, which makes it flexible enough to be connected to different energy sources. Once the copper–chlorine cycle was identified, the three main copper–chlorine cycles were simulated in Aspen Plus to examine which is the best configuration. Using experimental data from literature and calculating optimal conditions, flowsheets were developed and simulated in Aspen Plus. The simulation results were then used to determine the configuration with the most favourable energy requirements, cycle efficiency, capital requirements and product cost. Simulation results show that the overall energy requirements increase as the number of steps decrease from five–steps to three–steps. Efficiencies calculated from simulation results show that the four and five–step cycles perform closely with 39% and 42%, respectively. The three–step cycle has a much lower efficiency, even though the theoretical calculations imply that the efficiency should also be close to that of the four and five–step cycles. The five–step reaction cycle has the highest capital requirements at US$370 million due to more equipment and the three–step cycle has the lowest requirement at US$ 275 million. Payback analysis and net present value analysis indicate that the hydrogen costs are highest for the three–step cycle at between US$3.53 per kg for a 5–10yr payback analysis and the five–step cycle US$2.98 per kg for the same payback period. / Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2012.

The global fossil reserves are dwindling and there is need to find alternative sources of energy. With global warming in mind, some of the most commonly considered suitable alternatives include solar, wind, nuclear, geothermal and hydro energy. A common challenge with use of most alternative energy sources is ensuring continuity of supply, which necessitates the use of energy storage. Hydrogen has properties that make it attractive as an energy carrier. To efficiently store energy from alternative sources in hydrogen, several methods of hydrogen production are under study. Several literature sources show thermochemical cycles as having high potential but requiring further development. Using literature sources, an initial screening of thermochemical cycles was done to select a candidate thermochemical cycle. The copper–chlorine thermochemical cycle was selected due to its relatively low peak operating temperature, which makes it flexible enough to be connected to different energy sources. Once the copper–chlorine cycle was identified, the three main copper–chlorine cycles were simulated in Aspen Plus to examine which is the best configuration. Using experimental data from literature and calculating optimal conditions, flowsheets were developed and simulated in Aspen Plus. The simulation results were then used to determine the configuration with the most favourable energy requirements, cycle efficiency, capital requirements and product cost. Simulation results show that the overall energy requirements increase as the number of steps decrease from five–steps to three–steps. Efficiencies calculated from simulation results show that the four and five–step cycles perform closely with 39% and 42%, respectively. The three–step cycle has a much lower efficiency, even though the theoretical calculations imply that the efficiency should also be close to that of the four and five–step cycles. The five–step reaction cycle has the highest capital requirements at US$370 million due to more equipment and the three–step cycle has the lowest requirement at US$ 275 million. Payback analysis and net present value analysis indicate that the hydrogen costs are highest for the three–step cycle at between US$3.53 per kg for a 5–10yr payback analysis and the five–step cycle US$2.98 per kg for the same payback period. / Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2012.

Production of hydrogen is primarily achieved via catalytic steam reforming, partial oxidation,and auto-thermal reforming of natural gas. Although these processes are mature technologies, they are somewhat complex and CO is formed as a by-product, therefore requiring a separation process if a pure or hydrogen-rich stream is needed. As an alternative method, supported metal catalysts can be used to catalytically decompose hydrocarbons to produce hydrogen. The process is known as catalytic cracking of hydrocarbons. Methane, the hydrocarbon containing the highest percentage of hydrogen, can be used in such a process to produce a hydrogen-rich stream. The decomposition of methane occurs on the surface of the active metal to produce hydrogen and filamentous carbon. As a result, only hydrogen is produced as a gaseous product, which eliminates the need of further separation processes to separate CO2 or CO. Nickel is commonly used in research as a catalyst for methane cracking in the 500-700C temperature range. To conduct methane catalytic cracking in a continuous manner, regeneration of the deactivated catalyst is required and circulation of the catalysts between cracking and regeneration cycles must be achieved. Different reactor designs have been successfully used in cyclic operation, such as a set of parallel fixed-bed reactors alternating between cracking and regeneration, but catalyst agglomeration due to carbon deposition may lead to blockage of the reactor and elevated pressure drop through the fixed bed. Also poor heat transfer in the fixed bed may lead to elevated temperature during the regeneration step when carbon is burned in air, which may cause catalyst sintering. A fluidized bed reactor appears as a viable option for methane catalytic cracking, since it would permit cyclic operation by moving the catalyst between a cracker and a regenerator. In addition, there is the possibility of using fine catalyst particles, which improves catalyst effectiveness. The aims of this project were 1) to develop and characterize a suitable nickel-based catalyst and 2) to develop a model for thermal catalytic decomposition of methane in a fluidized bed.

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Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2015-01-21T10:10:35Z No. of bitstreams: 0 / Made available in DSpace on 2015-01-21T10:10:35Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2015-01-21T10:10:35Z No. of bitstreams: 0 / Made available in DSpace on 2015-01-21T10:10:35Z (GMT). No. of bitstreams: 0 / Tendo em vista a Economia do Hidrogênio e sua infinidade de possibilidades, este trabalho estuda a geração de hidrogênio utilizando a energia solar fotovoltaica. Tendo em vista o consumo mundial de energia crescente, novos métodos de produção energética tem que ser levados em consideração, como o fato do hidrogênio ser um vetor energético de baixo impacto ambiental. Por outro lado, as reservas de combustíveis fósseis não serão capazes de satisfazer essa demanda em longo prazo e seu uso contínuo produz efeitos colaterais, como a poluição que ameaça a saúde humana e os gases de efeito estufa associados à mudança climática. No contexto do Brasil, a eletrólise da água combinada com as energias renováveis e células a combustível seriam uma boa base para melhorar o fornecimento de energia distribuída. Propõe-se, no presente trabalho, produzir hidrogênio por energia renovável, especificamente pelo acoplamento direto de um gerador fotovoltaico a um eletrolisador alcalino de água experimental, concebido localmente. Busca-se entender as características inerentes da interação desses dispositivos, encontrar as eficiências de cada etapa do sistema montado, assim como a eficiência global, adquirindo uma noção mais precisa e prática do uso da energia solar fotovoltaica na alimentação de um eletrolisador. Os resultados experimentais evidenciaram que a transferência da energia do gerador fotovoltaico ao eletrolisador depende fortemente das condições instantâneas climáticas e do modo como estes estão conectados. A interdependência entre variáveis foi reproduzida pelas investigações com destaque para: densidade de corrente no eletrolisador, potencial elétrico, irradiância solar, concentração do eletrólito, área do eletrodo e dimensões da célula eletrolítica. A eficiência do eletrolisador alcançada foi de 21%. A eficiência global (irradiância solar - hidrogênio) foi de 2%. O presente estudo dá subsídios para que seja dimensionado o acoplamento do sistema eletrolisador - gerador FV a partir de uma célula eletrolítica buscando-se minimizar perdas. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Production of hydrogen from biomass steam gasification can be enhanced by using calcium oxide sorbents for CO2 capture in the gasifier. Calcium looping suffers from two main drawbacks: the need for high-purity oxygen in order to regenerate the sorbent under oxy-fuel combustion conditions and the loss of sorbent reactivity over several cycles due to sintering of pores upon calcination at high temperatures. One method of addressing the issue of oxygen supply for calcination in calcium looping is to combine the calcium looping and chemical looping processes, where the heat produced by the reduction of an oxygen-carrier by a fuel such as natural gas or gasification syngas, drives the calcination reaction. The technologies can be integrated by combining an oxygen carrier such as CuO with limestone within a composite pellet, or by cycling CuO and limestone within distinct particles. The goal of this project is thus to investigate the different sequences of solids circulation and the cyclic performance of composite limestone-CuO sorbents under varied operating conditions for this novel process configuration. Using a thermogravimetric analyzer (TGA), it was found that using composite CaO/CuO/alumina-containing cement pellets for gasification purposes required oxidation of Cu to be preceded by carbonation (Sequence 2) as opposed to the post-combustion case where the pellets are oxidized prior to carbonation (Sequence 1). Composite pellets were tested using Sequence 2 using varying carbonation conditions over multiple cycles. While the pellets exhibited relatively high carbonation conversion, the oxidation conversion underwent a decrease for all tested conditions, with the reduction in oxygen uptake particularly drastic when the pellets were pre-carbonated in the presence of steam. It appears that the production of a layer of CaCO3 fills up the pellets pores, obstructing the passage of O2 molecules to the more remote Cu sites. Limestone-based pellets and Cu-based pellets were subsequently tested in separate CaL and CLC loops respectively to assess their performance in a dual-loop process (Sequence 3). A maximum Cu content of 50% could be accommodated in a pellet with calcium aluminate cement as support with no loss in oxidation conversion and no observable agglomeration.

The global consumption of fossil fuels continues to increase due to the rapid growth of energy demand, as a consequence of expanding population and human activities. Fast climate change is another inescapable issue caused by humans that need to be addressed. The development of solar energy conversion technologies is widely considered as one of the most promising solutions to sustainably maintain a modern lifestyle of the society and create a carbon-neutral social development operation mode. The solar energy is carried and delivered in the form of electromagnetic fields. Therefore, the efficiency of photon collection is the primary factor to create any solar energy conversion systems. Through the inspiration from nature, the functionalized disorder, with a specific design and engineering, can introduce unusual light-matter interaction behaviors, and thus offer a potential capability to achieve perfect light harvesting. In my thesis, we develop complex Epsilon-Near-Zero (ENZ) metamaterials that can be used either as light capturing networks or the photoactive media by turning the energy damping ratio between radiative and non-radiative channels. We successfully integrate it into thin-film photovoltaic modules with showing an excellent performance enhancement led by broadband light localization effect. Thanks to universal of such complex ENZ metamaterials, with combining a thin layer of dielectric, we further develop efficient hot-carriers driven plasmonic photo-catalysts for artificial green chemical fuel synthesis. The detailed theoretic analysis is presented in this work.

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