Formation and reduction of NO x in pressurized fluidized bed combustion of coal

Abstract

This paper described an experimental and modelling study of NO x formation and reduction in pressurized fluidized bed combustion (PFBC) of coal. The aim was to evaluate the Thermal DeNO x process with NH 3 injection and staged combustion in PFBC as measures for the reduction of NO x emissions, and to develop a mathematical model for the emission of NO x . Experiments with NH 3 injection and staged combustion in a 1.6 MW PFBC test rig burning bituminous coal showed that both methods were able to reduce the emission of NO x by 50–70% under optimum conditions. Laboratory experiments were performed to elucidate the nitrogen chemistry under PFBC conditions and were used as input to the model. These experiments included an investigation of the release of nitrogen during devolatilization of coal and a kinetic study of important reactions for NO x formation and reduction catalyzed by char and bed material sampled from the test rig. The model is based on the two-phase theory of the bed and includes coal devolatilization, combustion of char and volatile matter, and NO x formation and reduction by homogeneous and heterogeneous reactions. The NO x emissions calculated with the model are in qualitative agreement with the emissions from the 1.6 MW test rig.