RESEARCH AND DEVELOPMENT OF CIRCULATING FLUIDIZED BED COMBUSTION COMBINED WITH COAL PYROLYSIS PROCESS

摘要

Circulating fluidized bed (CFB) combustion is one of effective technologies to convert coal to electric power. If coals which have high volatiles are directly burnt out, however, it is wasteful for the valuable volatiles. To more effectively utilize the high volatiles coals, it is reasonable to take volatiles out before combustion. A modified poly-generation process has been proposed which combines CFB combustion with coal pyrolysis [1]. In this process, a pyrolyzer is set on the downcomer below the cyclone. High-temperature ash from the CFB boiler via the cyclone is transported into the pyrolyzer to provide heat for the coal pyrolysis. The semi-coke produced in the pyrolyzer is returned to the CFB boiler for combustion. Thus, poly-generation of gas, tar, heat and power can be realized in a power plant using CFB boilers. Figure 1 shows a sketch of CFB combustion combined with coal pyrolysis. This poly-generation process has the following advantages: 1) It generates not only power but also tar and gas, which can be used as chemicals, liquid fuels, city gas or syngas, etc. Coals of high volatile content can be utilized more effectively; 2) It improves the system's thermal efficiency since the heat for the pyrolysis is provided by hot ash and the hot semi-coke is returned to the CFB boiler at the pyrolysis temperature; 3) It diminishes the probability of agglomeration between sticky char and pyrolyzer or pipe wall by adjusting the blending (ash/coal) ratio especially for caking coal; 4) It removes some of the sulfur compounds during the pyrolysis and yields high sulfur concentration pyrolysis gas to allow easier treatment and sulfur recovery and to reduce the burden of DeSO_x.