Waste heat recovery and exergy-based comparison of a conventional and a novel fuel cell integrated gas turbine hybrid configuration

Abstract

In conventional gas-turbine cycles, a significant amount of heat is generated and gets unutilized, which results in lower thermal efficiency and higher exergy destruction. In this study, the available waste heat from the gas-turbine has been examined, considering the promising ways to utilize this waste heat. By integrating a waste heat recovery system, these losses can be overcome, and its exergy destruction can be minimized, and results in higher thermal efficiency. For this, a novel comparison has been made between simple gas-turbine without waste heat recovery, recuperated gas-turbine with single-stage recovery, and a solid oxide fuel cell recuperated gas-turbine with double-stage waste heat recovery hybrid system in terms of energy, exergy efficiency and exergy destruction. Using MATLAB, a detailed thermodynamic modelling has been done. The finding shows that a two-stage waste heat recovery system helps in reducing the temperature gradient at the inlet of fuel-cell, which makes the system more stable. At a pressure ratio of 10 and turbine inlet temperature 1250 K, maximum energy and exergy efficiency have been achieved for the proposed hybrid system, i.e., 65.33% and 61.639%, respectively. The waste heat recovery for recuperated gas-turbine is 119.462 kW, and for solid oxide fuel cell gas-turbine, is 1153.885 kW.