Exergy analysis of solid-oxide fuel-cell (SOFC) systems
Department of Applied Mechanics, Thermodynamics and Fluid Dynamics, Norwegian University of Science and Technology, Trondheim, Norway Energy
(Impact Factor: 4.84).
04/1997; 22(4):403-412. DOI: 10.1016/S0360-5442(96)00119-3
The exergy concept has been used to analyze two methane-fueled SOFC systems. The systems include preheating of fuel and air, reforming of methane to hydrogen, and combustion of the remaining fuel in an afterburner. An iterative computer program using a sequential-modular approach was developed and used for the analyses. Simulation of an SOFC system with external reforming yielded first-law and second-law efficiencies of 58 and 56%, respectively, with 600% theoretical air. Heat released from the afterburner was used to reform methane, vaporize water, and preheat air and fuel. When these heat requirements were satisfied, the exhaust-gas temperature was so low that it could only be used for heating rooms or water. Because of heat requirements in the system, fuel utilization (FU) in the FC was limited to 75%. The remaining fuel was used for preheating and reforming. Reduced excess air led to reduced heat requirements and the possibility of a higher FU in the FC. Irreversibilities were also reduced and efficiencies increased. Recycling fuel and water vapor from the FC resulted in first-law and second-law efficiencies of 75.5 and 73%, respectively, with 600% theoretical air, vaporization of water was avoided and the FU was greater.
Available from: Sheng Wang
- "And the reformate are supplied directly into the SOFC. So researches on exergy analysis of SOFC were aimed at the whole SOFC power plant fed by various fuels    . The optional operational conditions and fuels were optimized. "
- "Many system studies on solid oxide fuel cell (SOFC) technologies and the integration of SOFC to gas turbines have been conducted in the last decade. These studies were based mainly on the analysis of the thermodynamic system using first law of thermodynamics in conjunction with a technoeconomical assessment, while some researchers applying the second law of thermodynamics to analyse the overall plant efficiency by calculating the exergy at each node of the thermodynamic system and the respective exergy destruction in each system component   . Literature available on SOEC modelling is limited, especially co-electrolysis modelling     . "
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ABSTRACT: A simple thermodynamic model of SOEC system was presented in this paper. We performed energy and exergy analysis on the SOEC system to determine its optimal operating conditions. Parametric studies have been carried out to determine the effects of key operating parameters on the SOEC system. For given operating conditions and set assumptions, it was found that the optimal voltage applied to the SOEC system is 1.37 V. At this optimal value, the SOEC system is capable of achieving 50% and 60%, respectively, in terms of energy and exergy efficiency. It also achieved 67% reduction in CO2 with maximum feedstock conversion of 63.5%. The corresponding energy and exergy required to convert one kg of CO2 is 16.4 kJ and 7.2 kJ, respectively.
Available from: Lydia Fryda
- "Exergetic analysis is commonly adopted      to evaluate the advantages of novel systems based on high-temperature fuel cells. The CHP system under study has a nominal output range of less than 1 MW e and integrates an atmospheric pressure SOFC with a novel allothermal biomass steam gasification process, called BioHPR . "
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ABSTRACT: This paper presents an exergetic analysis of a combined heat and power (CHP) system, integrating a near-atmospheric solid oxide fuel cell (SOFC) with an allothermal biomass fluidised bed steam gasification process. The gasification heat requirement is supplied to the fluidised bed from the SOFC stack through high-temperature sodium heat pipes. The CHP system was modelled in AspenPlus™ software including sub-models for the gasification, SOFC, gas cleaning and heat pipes. For an average current density of 3000 A m−2 the proposed system would consume 90 kg h−1 biomass producing 170 kWe net power with a system exergetic efficiency of 36%, out of which 34% are electrical.
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