SOFC-based hybrid cycle integrated with a coal gasification plant

Application of large scale high temperature fuel cells on syngas fuel produced from coal would be a turning point in the power generation sector, dramatically improving the efficiency and the environmental performance of coal-fired power plants. The purpose of this study is the assessment of a system constituted by a SOFC-based hybrid cycle integrated with a coal gasification process. In this system, syngas produced in a high efficiency, dry feed, oxygen blown, entrained flow Shell gasifier is cooled, depurated from particulate and sulfur compounds and reheated; the clean syngas feeds a pressurized SOFC together with high pressure air generated by the compressor of a gas turbine. After combustion of unconverted syngas, fuel cell exhausts are expanded and cooled, providing heat to a bottoming steam cycle for an efficient energy recovery. A high integration between gasification and power islands is necessary in order to obtain an elevated efficiency: the heat recovery system from syngas cooling is carefully arranged to provide thermal power for clean syngas reheating, air preheating and steam generation. The paper presents a preliminary analysis of literature results and a discussion of the thermodynamic implications arising from the use of different primary fuels in a fuel cell-gas turbine cycle. Then the work presents a detailed thermodynamic analysis of the proposed IGFC layout, assessing the effect of SOFC operating pressure on power balance and net plant efficiency. A sensitivity analysis on the variation of fuel and air utilization in the fuel cell is also performed. Results show that the present innovative SOFC-based power system may achieve an efficiency gain of 7-11 percentage points, with respect to an advanced IGCC based on state of the art technology