AIR GASIFICATION OF PEAT, WOOD AND BROWN COAL IN A PRESSURIZED FLUIDIZED-BED REACTOR .1. CARBON CONVERSION, GAS YIELDS AND TAR FORMATION

Fluidized bed air gasification of Finnish peat, sawdust and German brown coal were studied in a small pressurized fluidized-bed pilot plant operated at 0.4-1.0 MPa. The effects of air-to-fuel-ratio and other gasification variables on the conversion efficiencies and product yields are discussed in the article. Over 95% carbon conversion was achieved with all studied fuels under the best operating conditions. The lower heating value of the wet product gas ranged 3.5-5 MJ/Nm3. The highest heating value was achieved in low temperature gasification of wood, the light hydrocarbon gases representing nearly half of the gas heating value. The tar yields were dependent on the fuel type and on the freeboard temperature. The total yield of benzene and tars in wood gasification at 900-degrees-C was in the range of 3-4 wt% of dry ash-free fuel. In peat gasification the yield at the same freeboard temperature was only 0.7-1.2 wt% and in brown coal gasification below 0.5 wt%. The most stable components at higher freeboard temperatures were benzene and naphthalene. Toluene and phenol were almost completely decomposed when the temperature was raised above 850-degrees-C.