EFFECT OF VARYING COAL PROPERTIES ON IGCC PERFORMANCE USING CHAR COMBUSTOR FOR UTILISATION OF UNBURNT CARBON

摘要

Among the clean coal technologies, Integrated Gasification Combined Cycle (IGCC) is being considered the most promising because of higher thermal efficiencies and improved environmental performance. IGCC has the added advantage of removing sulphur pollutants in bed using sorbent as against expensive external post combustion flue gas desulphurisation systems. Coal reactivity, ash content and ash characteristics are the main parameters in selecting the appropriate gasification technology. Indian coals have washability index in the range of 15-43 and contain near gravity material between 18-27. This makes washing of coal exceedingly difficult and hence unwashed coal is to be used for power generation. Based on technoeconomic studies, air-blown pressurised fluidised bed gasification process initially with cold gas clean-up system has been selected for high ash Indian coals. The paper presents the performance of 100MWe IGCC plant using unwashed coal and washed coals with and without char combustor. A program is developed for optimising the Heat balances of IGCC power plant, which is used to estimate the overall efficiencies of the above alternatives. The CFBC boiler is sized to generate the process steam. The total steam generated in the boiler is equivalent to sum of the steam required for use in gasifier, steam turbine driven booster compressor, clean coal gas heater and HP heater. Thus by incorporating the CFBC combustor to bum unburnt carbon and coal fines, there is an increase of about 1 percent in the overall net efficiency of IGCC plant further lowering the cost of power generation and making it more competitive.