THE EMISSIONS OF SO_2, NO_x AND N_2O DURING THE COMBUSTION OF COAL BLENDS IN A FLUIDISED BED REACTOR

摘要

Combustion studies of five coals of different origins around the world (Colombia, Spain, South Africa and United States of America), were carried out in a laboratory scale fluidised bed combustor. Five blends prepared by mixing two coals, in three varying amounts, based on their petrological characterisation, were selected to study the possibility of reduction NO_x, N_2O and SO_2 emissions. Temperature, fuel ratio and N/C ratio were found to be most important parameters affecting NO_x and N_2O emissions among the single coals, while fuel-S content was the major factor in SO_2 emissions. The results showed that some blends had the opposite behaviour concerning the release of NO_x and SO_2 in relation to parent coals, and the emissions were higher than expected. The N_2O amounts observed were, however, in almost all blends tested, lower than predicted values. With some blends, the mixing levels intended to reduce SO_2 were not always found to correspond to those for simultaneous decrease of NO_x, raising difficulties in the optimisation of both emission levels. Most of the blends studied showed some evidence of interaction between the individual constituent coals. Varying the proportion of the blend components was observed to alter the temperatures at which interactions were stronger.