Modeling issues for solid oxide fuel cells operating with coal syngas

Fuel cells which directly convert the chemical energy into electricity are considered one of the most promising technologies to support energy needs in the near future. Solid Oxide Fuel Cells (SOFC) can run with alternative fuels such as synthesis coal gas due to their high operating temperature. Utilization of coal syngas in fuel cells would enable cleaner coal energy. A better understanding of the chemical and transport processes when running on syngas will allow researchers to find solutions to problems currently delaying the introduction of the technology into the market. A comprehensive modeling tool is developed for simulation of SOFCs operating on a wide range of fuel mixtures such as syngas, natural gas, etc. The new code takes into account the methane reforming and water gas shift reactions occurring on a common Ni-YSZ electrode using two alternative mechanisms namely, a global mechanism and a detailed surface mechanism. Simultaneous electrochemical oxidation of hydrogen and carbon monoxide at the anode-electrolyte active interface is accounted for using a new electrochemistry model. Model validation was performed by comparing the results with data published in the literature and available experimental data obtained at West Virginia University. Also, the associated numerical uncertainty was assessed and found that this was small in general, except for the ohmic heating. A parametric analysis considering the effect of temperature, fuel composition, and activation overpotential parameters for carbon monoxide oxidation was also performed. It was found that the increase of cell performance with temperature increase was caused by a decrease in all the overpotentials. The cell performance also increases when the concentration of the fuel in the anode stream increases. The operating temperature, as well as the composition of the fuel stream have a significant effect on the direction of the water gas shift reaction as well as on the current supported by hydrogen and carbon monoxide. However, when the ratio of hydrogen concentration to carbon monoxide concentration is kept constant, the splitting of the total current between these two fuels is not affected considerably. The cell showed one limiting current even when two fuels, hydrogen and carbon monoxide, are directly and simultaneously oxidized irrespective of the inlet composition. The new computational tool is applied to a more realistic case of planar SOFC with a surface of circa 100 cm2

Exhaust Gas Heat Recovery for an ORC: A Case Study

This work aims at developing a heat exchanger (HEX) sizing approach considering the need to maximize the heat recovery within the limitations of pressure drop and space. The application consists in the recovery of the energy contained in exhaust gases coming from an internal combustion engine (ICE). Two heat exchanger geometries are selected as case studies. The design approach involves the application of design of experiments (DOE) techniques and computational fluid dynamics (CFD) simulations. DOE techniques are used to observe the influence of some selected parameters (factors) in the design of the heat exchangers, and CFD simulations are carried out to determine the performance of the heat exchanger. The information obtained is used to determine local Nusselt number correlations that are used for the design of the heat exchangers

Advanced Exergy Analysis of an Integrated SOFC-Adsorption Refrigeration Power System

In this chapter, an exergy analysis applied to a solid oxide fuel cell (SOFC)/vapor adsorption refrigeration (VAR) system is presented. The influences of four significant parameters (current density, inlet fuel temperature, fuel utilization and steam-to-carbon ratio) on the exergy efficiency of both the SOFC stack and the SOFC-VAR system are investigated. In order to do so, a mathematical model is constructed in Engineering Equation Solver (EES) software to generate the simulations. The analysis shows that the calculated exergy efficiency is around 8% lower than the energy efficiency for both cases. Moreover, it is found that most of the causes of irreversibilities in the system are due to electronic and ionic conduction in the components. It is also shown that the exergy efficiency is substantially sensitive to fuel inlet temperature, which is evidenced by a bending-over behavior. Finally, in accordance with the calculated efficiency defects, the main exergy destructions are present in the heat exchangers, the SOFC, the afterburner and the generator

Caracterização do processo de pirólise de resíduos de polistireno expandido

From the different existing methods for plastic recycling, pyrolysis offers the possibility of solving mechanical recycling limitations, which requires large amounts of clean, separate and homogeneous plastic waste in order to be able to guarantee the quality of the final product. In pyrolysis, it is not necessary to classify or clean the different types of plastic waste and it is possible to process waste contaminated with food and chemical products, such as insecticides, herbicides and fertilizers, reducing classification and cleaning costs. Pyrolysis consists of the chemical decomposition of plastic materials by thermal degradation in the absence of oxygen. In this work the results obtained from the pyrolysis ofwaste expanded polystyrene (EPS) in a batch reactor, varying the pyrolysis temperature are presented. It was experimented with a mass of 500 g and temperatures of 350, 400 and 450 ° C. The results indicate that the highest conversion performance in to liquid hydrocarbon was obtained at a temperature of 450 ° C. The lowest yield of liquid hydrocarbon was obtained at the temperature 350 ° C.De los diferentes métodos existentes para el reciclaje de plástico, la pirólisis ofrece la posibilidad de resolver las limitaciones del reciclado mecánico, el cual necesita grandes cantidades de residuos plásticos limpios, separados y homogéneos para poder garantizar la calidad del producto final. En la pirólisis, no es necesaria la clasificación ni limpieza de los distintos tipos de residuos plásticos y es posible procesar residuos contaminados con alimentos y productos químicos, como insecticidas, herbicidas y fertilizantes, reduciendocostos de clasificación y limpieza. La pirólisis consiste en la descomposición química de los materiales plásticos por degradación térmica en ausencia de oxígeno. En este trabajo se presentan los resultados obtenidos de la pirólisis de residuos de poliestireno expandido (EPS) en un reactor tipo batch, variando la temperatura de pirólisis. Se experimentó con una masa de 500 g y temperaturas de 350, 400 y 450 °C. Los resultados indican que el mayor rendimiento de conversión en hidrocarburo líquido fue a una temperatura de 450 °C. El menor rendimiento de hidrocarburo líquido se obtuvo a la temperatura de 350 °C.Dos diferentes métodos existentes para a reciclagem do plástico, a pirólise oferece a possibilidade de resolver as limitações da reciclagem mecânica, na qual requerse grandes quantidades de resíduos plásticos limpos, separados e homogéneos para garantir a qualidade do produto final. Na pirólise, não é necessário classificar ou limpar os diferentes tipos de resíduos plásticos e é possível processar resíduos contaminados com alimentos e produtos químicos, como inseticidas, herbicidas e fertilizantes, reduzindo os custos de classificação e limpeza. A pirólise consiste na decomposição química de materiais plásticos por degradação térmica na ausência de oxigênio. Este trabalho apresenta os resultados obtidos da pirólise de resíduos de poliestireno expandido (EPS) em um reator tipo batelada, alterando a temperatura de pirólise. Os teste forem realizados com uma massa de 500 g e temperaturas de 350, 400 e 450 ° C. Os resultados indicam que a maior eficiência de conversão em hidrocarboneto líquido foi a uma temperatura de 450 ° C. O menor rendimento de hidrocarboneto líquido foi obtido a uma temperatura de 350 ° C

TRANSIENT ANALYSIS OF A COMPRESSED AIR ENERGY STORAGE SYSTEM

A transient energy analysis was performed in a Compressed Air Energy Storage (CAES) system. The aim is to perform a parametric analysis to determine the efficiency and output energy depending on some designparameters as the number of tanks connected in parallel, the insulation thickness, the storage time and the outflow. Mass and energy balanceswere carried out on every component of the system,the resulting equationsfrom the analysis weresolved numerically using the explicit Euler’s method. The system operating forashort storage timepresentsa higher efficiency (about 42.38%) with insulated tanks, however it is lower (about 23.54%) for long storage timeandnon-insulatedtanks. Nevertheless, when the system with insulated tanks reaches the steady state, i.e., for long storage time, its efficiency is almost half that onewith tanks without insulation, 11.5% and 23.54%, respectively. These results indicate that for short storage times is better to insulate the tanks and for longer storage times is more convenient no insulatio

Numerical Study on the Effect of Distribution Plates in the Manifolds on the Flow Distribution and Thermal Performance of a Flat Plate Solar Collector

Flow maldistribution represents a problem of particular interest in the engineering field for several thermal systems. In flat plate solar collectors, the thermal efficiency strongly depends on the flow distribution through the riser tubes, where a uniform distribution causes a uniform temperature distribution and therefore a higher efficiency. In this work, a Computational Fluid Dynamics (CFD) numerical analysis has been carried out using the commercial software FLUENT®, in order to determine the flow distribution, pressure drop and hence the thermal efficiency of a solar collector with distribution flow plates inside the manifolds. The obtained numerical solution for this type of thermal systems has been validated with experimental results available in literature for laminar and turbulent flow. Four distribution plate configurations were analyzed. Results show that using two distribution plates in each of both manifolds improves the flow uniformity up to 40% under the same operating conditions when distribution plates are not used. Besides, it is shown that there exists an increase in the overall pressure drop which is practically negligible for the tilt angles commonly employed in the installation of flat plate solar collectors in Mexico. The use of closed end distribution plates on the dividing and combining manifolds allows the thermal efficiency to become close to the ideal thermal efficiency which is obtained with a uniform flow distribution

Perspectives on Consumer Habits with Domestic Refrigerators and Its Consequences for Energy Consumption: Case of Study in Guanajuato, Mexico

This work presents the main behaviors shown in the habits of consumers of domestic refrigerators, which influences the energy consumption of this appliance. This study is based on a series of surveys answered by 200 consumers from four cities in the State of Guanajuato, Mexico. The questions were arranged with the aim of evaluating the general characteristics and usage habits such as refrigerator age, door opening frequency, damper position, load of food supplies, external and internal cleaning habits, and nearby heat sources, among other things. The randomly interviewed consumers were individuals between 20 and 60 years of age, who were interviewed using handmade surveys by experts in the field of refrigeration. In some cases, photographic evidence was gathered from the consumers’ refrigerators to represent the typical usage habits. In general, the results show that better usage habits are necessary from an energy point of view. Most consumers agree with adopting best practices for using their refrigerator

Multi-Objective Optimization of a Multilayer Wire-on-Tube Condenser: Case Study R134a, R600a, and R513A

This study presents the optimization of a multilayer wire-on-tube condenser exposed to forced convection, using the Optimized Multi-objective Particle Swarm Optimization (OMOPSO) algorithm. The maximization of the heat transfer and the minimization of the heat exchange area were defined as objective functions. In the optimization process, the variations of eight geometric parameters of the condenser were analyzed, and the Multi-objective Evolutionary Algorithm based on Decomposition (MOEAD), Non-dominated Sorting Genetic Algorithm-II (NSGAII), and OMOPSO algorithms were statistically explored. Furthermore, the condenser optimization analysis was extended to the use of alternative refrigerants to R134a such as R600a and R513A. Among the relevant results, it can be commented that the OMOPSO algorithm presented the best option from the statistical point of view compared to the other two algorithms. Thus, optimal designs for the wire-on-tube condenser were defined for three proposed study cases and for each refrigerant, providing an overview of compact designs. Likewise, the reduction of the condenser area was analyzed in more detail, presenting a maximum reduction of 15% for the use of R134a compared to for the current design. Finally, the crossflow condition was studied with respect to the current one, concluding in a greater heat transfer and a smaller heat exchange surface