Comparative study of combined solid oxide fuel cell-gas turbine-Organic Rankine cycle for different working fluid in bottoming cycle

Abstract

Worldwide efforts are being made for evolving viable electricity generation alternative to the traditional fossil fuel based power generation systems and also to enhance the efficiency of existing power generation systems. Studies have been made for integrating fuel cell with gas turbine cycle and Organic Rankine cycle, but there exist possibility of further investigation by incorporating the measures to increase effective energy utilization in the cycle along with consideration of different working fluids in Organic Rankine cycle. In the present paper, a combined cycle system consisting of technologies namely solid oxide fuel cell, gas turbine and Organic Rankine cycle is studied. The considered combined cycle system employs Heat Recovery Steam Generator followed by Organic Rankine cycle as bottoming cycle for recovering the waste heat coming out from hybrid SOFC-GT system through a Heat Recovery Vapour Generator. The considered SOFC-GT system has methane gas being used as fuel which is reformed by both external and internal reformers with anode gas recycling. Here three different working fluids namely R141b, R245fa and R236fa are used in bottoming Organic Rankine cycle for comparing their effects on the cycle performance of proposed SOFC-GT-ORC combined cycle system based on first law of the thermodynamics. Results have been obtained from the computer simulation based on thermodynamic modeling of SOFC-GT-ORC combined cycle and the effects of gas turbine inlet temperature, cycle pressure ratio, fuel utilization factor and ORC turbine inlet temperature are investigated on the cycle performance. The study indicates that the efficiency is increased about 8%-12% by recovering SOFC-GT waste heat through ORC and R236fa is found to be the best in terms of power generation capacity and efficiency of SOFC-GT-ORC system. Outcome from this paper gives insight to the power sector professionals and research community working for evolving efficient and robust power generation alternatives based on the combination of direct energy conversion system and indirect energy conversion system.