Catalytic hot gas cleaning of gasification gas

Gasification gas containing dust can be efficiently purified from tars and ammonia with nickel monolith catalyst. Temperatures over 900°C and residence times of about 1 s (SV 2500 1/h) were needed at 5 bar pressure to obtain complete tar decomposition and 80% ammonia conversion with a feed gas from a pilot scale fluidized bed gasifier. At these conditions deactivation caused by carbon deposition or by H₂S can be avoided. Decline of catalyst activity was not observed during 100 h long test runs. Dolomites and limestones can be used as effective tar decomposing catalysts at lower pressures and around 900°C temperatures, where they stay in calcined form. Low-cost iron containing materials can in turn be applied for catalytic ammonia removal.