N2O emissions from fluidised bed combustion.: The effect of fuel characteristics and operating conditions

Fluidised bed combustion (FBC) is a versatile and relative clean technology except with respect to nitrous oxide (N2O) emissions. The emissions of N2O from FBCs are very dependent on a number of operating conditions (temperature, sorbent addition, excess oxygen, etc.), fuel characteristics and many homogeneous and heterogeneous reactions that take place. This paper describes the results obtained during the study of the effect of coal type on N2O emissions from FBC. The combustion tests were performed in a circulating fluidised bed pilot plant, using two coals: a Spanish subbituminous (Puertollano) and a bituminous coal from Colombia (Carbocol). Using supporting laboratory-scale fluidised bed pyrolysis experimental data with these fuels the partitioning of fuel-N and the formation of the most important N2O precursors, NH3, HCN and char was followed. The pyrolysis tests results showed that the major part of the nitrogen remained in the char. Both coals a produced similar amount of HCN, but the amount of char-N was lower with Carbocol coal that with Puertollano coal. The combustion results showed that the conversion of fuel-N to N2O was higher on the tests with Puertollano coal than with Carbocol coal. For this it was concluded that the formation of N2O via char-N oxidation was the most important pathway. The temperature profile of the combustor and the sorbent addition strongly influence N2O emissions. (C) 2003 Elsevier Ltd. All rights reserved.