Trends in NOx Emissions during Pulverized Fuel Oxy-fuel Combustion

Abstract

This work presents the trends in NOx emissions during pulverized fuel (PF) oxy-fuel combustion using the coal combustion test facility (100 kW) at RWTH Aachen University. In this facility, three modes of pulverized coal combustion have been considered, namely, (1) firing in air (named as air mode), (2) firing in a mixture of oxygen and carbon dioxide (named as O2/CO2 mode) by varying the O2 concentration in the O2/CO2 mixture, and (3) firing in a mixture of oxygen and recycled flue gas (RFG) (named as O2/RFG mode). It was found that NOx emissions in the O2/CO2 mode were about 20% lower than those in the air mode. This causes high temperatures in the burner vicinity to form large amounts of thermal NOx in the air mode. On the other hand, NOx emissions in the O2/RFG mode are considerably reduced by approximately 50%. This is due to the fact that NOx contained in RFG is supplied back by a secondary stream to the flame, and thus, it is destructed by reduction gas in volatile matter. Moreover, in this investig...