Group effects on fuel NO x emissions from coal

Abstract

The major component of NO x formed in the combustion of pulverized coal is the fuel NO x. Fuel NO x data for coal has been obtained from dilute streams of coal particles and this data is conventionally interpreted using single particle models. Recently the group combustion approach has been used to model the combustion of coal particles. Under this approach one looks at a collection of particles rather than looking at the behavior of an isolated particle. This becomes especially important when one considers fuel rich combustion zones as they exist in the vicinity of boiler burners. Under group combustion conditions of dense clouds, the cloud is oxygen deficient and hence fuel NO x is expected to be reduced. The present study uses a group combustion model to study fuel NO x emission from a spherical cloud of coal particles. The N evolution from coal was modeled by three methods: (i) finite first order kinetics, (ii) Fuel-N evolved with volatiles and (iii) Fuel-N evolution proportional to burn-out. The fuel N is assumed to evolve as HCN and is converted to NO or N 2, via competing kinetics, depending upon the availability of oxygen in the cloud. Of the three N evolution models used, the one using kinetics was found to show the least fuel-N to NO conversion efficiency, while the model based on the coal burn-out shows the maximum. Further it shows that the N to NO conversion was dependent on the local stoichiometry. Fuel rich combustion cloud inhibited the formation of fuel NO.