Transitional behavior of combined-cycle power plants with circulating pressurized fluidized bed combustion

Combined cycle power plants with pressurized fluidized bed combustion (PFBC) are supposed to be promising concepts for future developments upon bituminous coal and lignite based power generation technologies of high efficiency and low emissions. The special attraction of the proposed PFBC concepts is due to the possibility to utilise coal directly in agas turbine process without an intermediate stage of coal gasification. Due to the complexity of PFBC power plants - in particular of the systems with circulating PFBC - the design as well as the operation of those power plants are affected by considerable uncertainty. In this context, mathematical modeling and computer-aided simulation can be useful to improve the process knowledge, to analyse the effect of process changes, to examine the influence of independent operation variables as well as to support the scale-up and the design of control systems. Within the contribution a mathematical model for the simulation of the steady-state as well as the transient behaviour of combined cycle power plants with PFBC consisting of comprehensive submodels for the gas turbine, the pressurized circulating fluidized bed combustion and the water-/steam process is roughly outlined. As an example for the simulations serves a PFBC power plant concept emerged from a draft study of the Vereinigte Energiewerke AG (VEAG), Berlin (Germany). On the basis of simulation results the principle transient behaviour of the above mentioned power plant is shown for set point changes of the independent operation variables fuel mass flow, split valve ratio, compressor inlet guide vanes position and feed water mass flow. Emphasis is laid on the discussion of the coupled interaction of the subsystems gas turbine, circulating fluidized bed combustor and water-/steam process.