Thermochemical analysis of ACFB-based gas and power cogeneration

A first- and second-law analysis is presented for a process developed for simultaneous generation of a fuel gas and electric power (gas and power cogeneration) based on atmospheric circulating-fluidized-bed (ACFB) combustion of coal. The mathematical model has a zone structure, multi-species equilibrium calculations for applicable zone conditions at high temperatures (50 gas-phase and seven solid-phase chemical species) and the concept of freezing of the gas composition at low temperatures. Our analysis shows that the process utilizes coal in a simple, effective and environmentally clean manner. The first- and second-law efficiencies of the process are, respectively, 35.0 and 27.6% for gas generation, 15.4 and 14.6% for power generation, 50.4 and 42.2% overall. The heating value of the gas is 11 MJ/Nm3 (medium). Desulphurization is achieved by using CaS-based sulphur capture during limestone addition to the gasifier bed. Results are compared with data from a 150 kg of coal/h experimental plant.