Gas Turbine Cycles With Solid Oxide Fuel Cells—Part II: A Detailed Study of a Gas Turbine Cycle With an Integrated Internal Reforming Solid Oxide Fuel Cell

Abstract

In conventional energy conversion processes, the fuel combustion is usually highly irreversible, and is thus responsible for the low overall efficiency of the power generation process. The energy conversion efficiency can be improved if immediate contact of air and fuel is prevented. One means to prevent this immediate contact is the use of fuel cell technology. Significant research is currently being undertaken to develop fuel cells for large-scale power production. High-temperature solid oxide fuel cells (SOFC) have many features that make them attractive for utility and industrial applications. However, in view of their high operating temperatures and the incomplete nature of the fuel oxidation process, such fuel cells must be combined with conventional power generation technology to develop power plant configurations that are both functional and efficient. Most fuel cell cycles proposed in the literature use a high-temperature fuel cell running at ambient pressure and a steam bottoming cycle to recover the waste heat generated by the fuel cell. With such cycles, the inherent flexibility and shorter start-up time characteristics of the fuel cell are lost. In Part I of this paper (Harvey and Richter, 1994), a pressurized cycle using a solid oxide fuel cell and an integrated gas turbine bottoming cycle was presented. The cycle is simpler than most cycles with steam bottoming cycles and more suited to flexible power generation. In this paper, we will discuss this cycle in more detail, with an in-depth discussion of all cycle component characteristics and losses. In particular, we will make use of the fuel cell’s internal fuel reforming capability. The optimal cycle parameters were obtained based on calculations performed using Aspen Technology’s ASPEN PLUS process simulation software and a fuel cell simulator developed by Argonne National Laboratory (Ahmed et al., 1991). The efficiency of the proposed cycle is 68.1 percent. A preliminary economic assessment of the cycle shows that it should compare favorably with a state-of-the-art combined cycle plant on a cost per MWe basis.