Why can the efficiency of the circulating fluidized bed boiler reach more than 90%, but the thermal efficiency of the whole plant is much lower than this value?

　　The thermal efficiency of the whole plant is determined by the efficiency of the boiler, steam turbine and generator. Due to the low efficiency of the current steam turbine, even if the boiler efficiency reaches more than 90%, a large amount of cold source loss will inevitably occur during the conversion of heat energy to mechanical energy. As a result, the thermal efficiency of the whole plant is at a relatively low level. Improving the steam parameters and reducing the heat loss of the cold source are the main means to improve the thermal efficiency of the whole plant.