Biomass externally fired gas turbine cogeneration

This paper is a presentation of a systematic study on externally fired gas turbine cogeneration fueled by biomass. The gas turbine is coupled in series with a biomass combustion furnace in which the gas turbine exhaust is used to support combustion. Three cogeneration systems have been stimulated. They are systems without a gas turbine, with a non-top-fired gas turbine, and a top-fired gas turbine. For all systems three types of combustion equipment have been selected; circulating fluidized bed (CFB) boiler, grate fired steam boiler, and grate fired hot water boiler. The sizes of biomass furnaces have been chosen as 20 MW and 100 MW fuel inputs. The total efficiencies based on electricity plus process heat, electrical efficiencies, and the power-to-heat ratios for various alternatives have been calculated. For each of the cogeneration system, part-load performance with varying biomass fuel input is presented. Systems wit CFB boilers have a higher total efficiency and electrical efficiency than other systems when a top-fired gas turbine is added. However, the systems with grate fired steam boilers allow higher combustion temperature in the furnace than CFB boilers do. Therefore, a top combustor may not be needed when high temperature is already available. Only one low-grade fuel system is then needed and the gas turbine can operate with a very clean working medium.