Effect of pressure and turbine inlet temperature on the efficiency of pressurized fluidized bed power plants

The difficulties encountered in past and present efforts to operate direct coal-fired gas turbines are substantial. Hence the development effort required to assure a reliable, high-temperature pressurized fluidized bed (PFBC) combined cycle may be very expensive and time consuming. It is, therefore, important that the benefit of achieving high-temperature operation, which is primarily increased efficiency, be clearly understood at the outset of such a development program. This study characterizes the effects of PFBC temperature and pressure on plant efficiency over a wide range of values. There is an approximate three percentage point advantage by operating at a gas turbine inlet temperature of 870 C (1600 F) instead of 538 C (1000 F). Optimum pressure varies with the gas turbine inlet temperature, but ranges from 0.4-1.0 MPa (4-10 atm). An alternate PFBC cycle offering high efficiency at a peak temperature of about 650 C (1200 F) is also discussed.