Kinetics of ammonia decomposition in hot gas cleaning

Reduction in the amount of ammonia in fuel gas from biomass gasification was studied. Experiments were carried out in a fixed-bed reactor dt 200-1000 degrees C, 21 atm. A kinetic model for ammonia decomposition was developed. The partial pressure of hydrogen in the fuel gas was a key factor to model ammonia decomposition. Activation energies in the empty reactor, on carbon, and in a sand bed were similar, 130-140 kJ/mol. The frequency factors for carbon and sand were 10 times as large as for the empty reactor. The activation energy for a Ni-based catalyst was 111-113 kJ/mol. Carbon deposit deactivated the Ni-based catalyst. High temperature was found to be essential for avoiding carbon fouling and for achieving high ammonia removal efficiency. Estimation of the ammonia reduction for fuel gas showed that a moderate amount of ammonia could be removed by use of the Ni-based pellets at 800 degrees C.