The effect of the coal blending method in a coal fired boiler on carbon in ash and NOx emission

This paper describes the numerical investigations of the influence of the blending method on the combustion characteristics and NOx emission in a 500 MW, tangentially coal-fired boiler. The in-furnace and out-furnace blending methods are simulated with the blend of 60% bituminous and 40% subbituminous coals on a weight basis. The simulation shows the blending method has a great effect on carbon in ash, but a little effect on NOx emission. The in-furnace blending method which burns bituminous coal at lower burners and subbituminous coal at upper burners gives the least carbon in ash. For two blending methods, carbon in ash is mainly attributed to the middle burner sets in the furnace. The field tests at a 500 MW coal-fired power plant showed that the in-furnace blending method substantially reduces in NOx and carbon in ash, compared with the out-furnace blending method.