Integration of solid oxide fuel cells into gas turbine power generation cycles. Part 1: Fuel cell thermodynamic modelling

Abstract

The development of a detailed thermodynamic model of a fuel cell is presented. This model predicts the performance of a gas turbine and fuel cell systems integrated together in hybrid power generation cycles. The achievement of this goal involved the independent modelling of each component (prereformer, internal reformer, active area, combustion zone and fuel preheating) using numerical methods in the form normally required by cycle calculations used in gas turbine design. The fuel cell model was based on the principle of operation of the Westinghouse tubular solid oxide fuel cell (SOFC) design, involving internal reforming and prereforming of methane. Its performance was examined under a wide range of operating conditions leading to exhaust temperatures in the range 370–935°C. Fuel cell system efficiencies as high as 56 per cent were predicted at low current densities (150mA/cm2), while the efficiency dropped to 38.7 per cent at high current densities (600mA/cm2) owing to the irreversibilities developed. Pressurized operation of the fuel cell was assessed in the range 1–25 atm; high-pressure operation leads to an increased power output, particularly at high current densities, but it also produces a significant decrease in electrical efficiency (from 55 to 37 per cent). Pressurized operation should only be contemplated when the fuel cell is integrated with a gas turbine, as shown in Part 2 of this paper, where the hybrid configuration will be shown to give an impressive 76.4 per cent maximum electrical efficiency.