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Figure 3-3: BHEL's Bypass Over Fire Air (BOFA) SystemPlaten SHReheaterFinal SHLTSHBOFA nozzle at38.8 m elevationBOFA nozzle at31.8 m elevationRegularwind boxLTSHECOECOHot pry. AirSulphur content is high in imported coal as compared with Indian coal. BHEL hasmade provision for installing flue gas desulphurization (FGD) in all its 660 MW and 800MW projects. FGD retrofit is a distinct possibility in the future, as ambient air qualitynorms in the country get more stringent.BHEL has built fluidized bed combustion (FBC) boilers for alternative fuels such ashigh-sulphur coals, coal washery rejects, waste coal from steel plants, lignite, petcokeand biomass. FBC steam generators (both circulating and bubbling) work well withthese alternative fuels and produce lower NOx and SOx emissions owing to tighter insitu controls.BHEL's has built a pilot-scale FBC gasification test facility with the following parameters:Coal throughput: 18 t/dayGasifier diameter : 450 mmGasification media : Air/steam mixGasification temperature : 1,000ºCGasification pressure : 11 kg/cm 2Gas calorific value : 1,000-1,100 kcal/Nm 3FBC units have several advantages, such as:• Higher unit capacity;• On-bed sulphur removal option;• No tar or oil formation and easy gas cleaning;91