Catalytic hot gas cleaning of fuel gas from an air-blown pressurized fluidized-bed gasifier

Catalytic ammonia decomposition and tar reduction by a Ni catalyst were studied using a feed gas from a pilot-scale pressurized fluidized-bed gasifier. Tests were conducted in a tubular fixed-bed reactor with a space time of about 3 s at 800-900 degreesC and 12 atm. Ammonia removals of 35-95% and light tar conversions of 90-95% were observed. The amount of the light hydrocarbons was found to have a negative effect on the ammonia decomposition. An ammonia concentration in the fuel gas, gas residence time, and catalytic bed temperature also had a significant influence on the ammonia removal efficiency. After the catalyst, CO2 and CO approached equilibrium values,but the content of H-2 and H2O was lower because of reactions with tar. The heating value of the fuel gas remained the same; The gasification efficiency increased by about 10%, mainly because of catalytic tar cracking. Deactivation of the catalyst was not observed in the fuel gas containing 50-150 ppm H2S and about 10 g/Nm(3) tar.