EXAMINATION OF THE PERFORMANCE OF A COAL BASED GAS TURBINE FUEL CELL HYBRID POWER GENERATION SYSTEM WITH PRE-COMBUSTION CARBON CAPTURE AND STAGED COMPRESSION AND EXPANSION

摘要

In recent years there has been significant interest in different carbon capturing technologies that might be applied to fossil fuel power generation plants. These technologies are intended to reduce the amount of CO_2 that would normally be emitted into the atmosphere. In terms of system efficiency and operating costs carbon capture technology is expensive. The additional equipment that would be used to capture these emissions often requires an auxiliary heat source and they add to the complexity of the system. There has also been significant interest in coal based gas turbine solid oxide fuel cell hybrid power plants. A gas turbine fuel cell hybrid power plant can have a greater efficiency than a conventional gas turbine power plant because the heat that is normally unused in a standalone fuel cell is recovered in the hybrid system, and used to drive the turbine. It is thought that the increased system efficiency of the hybrid system might compensate for the increased expense of performing carbon capture. In order to provide some analytical insight on how to best use the heat that is generated from a solid oxide fuel cell (SOFC) in a coal fired power system, we examine several different configurations. In each system we assume that a 200 MW SOFC is driven by a coal derived syngas. Each system uses an isolated anode stream and assumes that carbon capture, has been performed upstream of the fuel cell thus providing a hydrogen rich syngas to the SOFC. This differs from hybrid systems which have been previously posed where an isolated anode stream was used as a means to isolate and capture CO_2 after the syngas has passed through the fuel cell and a post combustion process that is fed with pure oxygen producing an exhaust stream of water and CO_2. The configurations in this study are different in that the anode and cathode streams remain isolated so that the expansion leg of the heat engine cycle may be staged. By staging both the compression and expansion processes of the hybrid system we show that there is increased availability of useable heat over single staged systems. Maximizing this availability would give the hybrid system more energy to drive other auxiliary processes that are necessary for coal fired systems. These auxiliary operations could include fuel reforming or shift reactions, pre heating of coal for the gasification system, reheating the syngas after cooling for cleaning, or even heating steam in a bottoming cycle.