Evolution of nitrogen during char oxidation

This dissertation was directed at understanding the conversion of the nitrogen in coal char to nitrogen oxides (NO). The destruction of NO with char under inert conditions was studied in a laminar entrained-flow reactor modified by the addition of a solid distributor and a collection mesh to enable tests with chars produced in situ as well as extended reaction times. The comparison of the rate of NO destruction by a bituminous coal, the bituminous coal char and an activated carbon under inert conditions showed that the bituminous coal has a higher capacity for NO reduction just after injection than the char, a result that can be explained by the homogeneous destruction of NO by the volatiles released after coal injection. When devolatilization was completed, the reactivity of the char formed in situ was identical to that of the char produced ex situ.; The conversion of char-nitrogen to nitric oxides under oxidizing conditions for coal, ex situ char and activated carbon, decreased as the concentration of NO in the background was augmented, at rates that diminished as the oxygen concentration increases, independent of particle size. The steep reduction on NO production as the background NO concentration increases was explained by the reaction with NO in the gas phase of nitrogenous compounds produced during char oxidation, a conclusion supported by numerical simulation of the heterogeneous reactions, the reactions in the boundary layer and in the bulk and by the presence of low molecular weight hydrocarbons and HCN after coal injection.; The homogeneous reduction of NO was more important than the heterogeneous reduction on the char surface; and both processes could be approximated by a single particle model that only considers heterogeneous reactions, with the char-NO rate constant augmented to allow for the homogeneous reactions. This model was incorporated as a submodel into a comprehensive CFD code and used to simulate the conversion of char nitrogen to nitric oxide both in the laminar entrained-flow reactor and in a pulverized coal fired boiler. The model can be used to both predict furnace performance and guide the development of new control technologies.