Combined cycle power plant with integrated CFB devolatilizer and CFB boiler

摘要

A high efficiency economical coal fired combined cycle power generation system and process is described. The system utilizes a circulating fluid bed ("CFB") coal devolatilizer which is fluidized with recycled coal volatiles. The devolatilizer is heated indirectly with hot bed material from a conventional CFB boiler burning the devolatilized coal (char). The CFB boiler is fluidized by gas turbine exhaust gas. The ratio of high efficiency/low capital cost Brayton cycle (gas turbine) power output to lower efficiency, higher capital cost Rankine cycle (steam turbine) power output is maximized by concurrently and/or successively preheating the gas turbine compressor discharge with; (1) gas turbine exhaust (recuperator), (2) hot coal volatiles exiting the devolatilizer, (3) coal char CFB boiler hot bed material (with either an external or internal heat exchanger), and (4) CFB boiler flue gas. The process and method described produces a thermally cracked, clean product gas with a high Btu content (500 BTU/SCF) and is, therefore, readily usable in gas turbines which are designed for natural gas without design modification. This high Btu product gas also reduces fuel gas cleaning volume and fuel gas sensible heat loss. The product gas yield and/or the devolatization reaction temperature is increased by either partially substantially or supplementing the fluidizing gas with steam and/or air or oxygen.