Interaction of blended-coal combustion process:influence of coal blending methods on combustion characteristics

The experiment of the influence of out-furnace and in-furnace blending method on the combustion character- istics and NOx emissions were performed under high-volatile coal,low-volatile coal and their blended coal ( lean coal blended with bituminous of 0,25% ,50% ,75% ,100% ) in this paper. The results show that the combustion of blen- ded coal is impacted by two opposite effect:the promote function and the restrain function. The role of the two competi- tion determines the characteristics of blended-coal combustion. Under the out-furnace coal blending method,the pro- mote function is more obvious than the restrain function when the blending coal ratio is relatively small,which is in fa- vour of the blended-coal burnout. As further increasing the bituminous ratio,the restrain function becomes strong grad- ually,and more obvious than the promote function,which is not in favour of the blended coal burnout. NOx emissions of blended coal is in consistence with linear NOx ,and increase as increasing the blending ratios. Especially,the blended- coal burnout degree decreases significantly when the proportion of bituminous is more than 75% . The proportion of bituminous within 25% is beneficial to improve the coal burnout rate. The in-furnace method of blending coal weakens not only the promote function,but also the restrain function. The mixing of bituminous and lean coals is later at the large proportion of blending coal ratio,the burnout of blending coals is higher. NOx emissions of blended coal gradually decrease as increasing the delaying time. Bituminous are delayed to be mixing with lean coals at the in-furnace blend- ing method,which is in favor of the burnout and NOx reducing,while lean coals are delayed to be mixing with bitumi- nous,which is not in favor of the burnout,and NOx reducing is not obvious compared to the former.