Destruction of N2O over different bed materials

Abstract

Since under fluidized bed conditions N2O is produced as a by product of the De-NOx process, the thermal decomposition of N 2O was investigated under conditions relevant to those in FBC installations. Laboratory experiments were made in a current of nitrogen using a fixed bed of pure quartz sand or sand with 10% (wt.) of the solids tested, CaO and Fe2O3. With a sand bed the decomposition was slightly faster than in the empty reactor and the reaction was first order with respect to [N2O]. Both fresh CaO and Fe2O3 strongly catalysed N2O decomposition. Their effectiveness diminished after they were heated to temperatures typical for FBC, but they still retained appreciable activity. This activity went down with increasing particle size. The flue gas components investigated were O2, water vapour and CO 2. Their presence appeared to interfere with N2O decomposition and increased with the concentration of the additive. The observations indicated that this could only be due to heterogeneous effects. Thus the effects of the bed solids and of the gas phase components are opposed. The effects associated with N2O decomposition have proved to be surprisingly complex and instead of supplying simple answers, this work uncovered more problems.