Assessment of Hot Gas Clean-Up Systems and Turbine Erosion/Corrosion Problems in Pfbc Combined Cycle Systems

Alternative methods of producing electricity from coal while maintaining acceptable environmental standards are currently being examined in detail. One such method involves the fluidized bed combustion of coal at elevated pressure, using an acceptor in the fluidized bed to remove the sulfur. Steam is raised using heat exchangers within and above the bed, and the hot combustion gases are expanded through a gas turbine. A serious limitation on this system is the ability to reduce the particulate loading in the combustion gases to a level at which a gas turbine having acceptable life can be constructed. The turbine may be either a new design or a modification of a currently available engine, and palliatives include lowering the turbine inlet temperature, lowering the gas velocity through the turbine, and “hardening” the turbine by the selection of appropriate materials or claddings for the vanes and blades. In this paper, the various degradation processes are considered, with emphasis on erosion, and the probable limits of particulate loading in the gas stream are estimated. These estimates are discussed in relation to existing hot gas particulate removal systems, and directions for further study are suggested.