Thermoeconomic analysis of two solid oxide fuel cell based cogeneration plants integrated with simple or modified supercritical CO2 Brayton cycles: A comparative study

Abstract

Two supercritical CO2 (sCO2) Brayton cycles for waste heat recovery in a solid oxide fuel cell (SOFC)-based plant are assessed and compared from thermodynamic and economic perspectives. One cycle considered is a simple sCO2 cycle with recuperation, while the other is the supercritical recompression CO2 (srCO2) cycle. To provide a fair comparison between the performances of the SOFC-sCO2 integrated plants, the flue gas is considered to exit at the same temperature in both cases, through a heating unit to generate hot air.The findings indicate that designing an efficient SOFC-sCO2 integrated plant for cogenerating electricity and a by-product, e.g., heat, is not solely a question of selecting the most efficient sCO2 layout as the bottoming power cycle. Rather, it is a tradeoff between the exergetic performance of the sCO2 layout and its potential to absorb heat from upper SOFC system. It is shown that, at the optimized condition, the capability of a simple sCO2 cycle for recovering heat from the SOFC is 30.86% higher than a srCO2 layout. However, the exergy efficiency of the SOFC-srCO2 integrated cogeneration plant is 0.64% higher than that of the SOFC-sCO2, with a corresponding increase in the average unit cost of products of 3.06%.