氨煤混燃过程中单颗粒煤粉着火特性

Characteristics of single-coal-particle ignition in ammonia-coal cofiring process

开展绿氨与煤混燃有助于双碳目标下的火电降碳,在炉内掺烧技术逐步实现增大掺氨比过程中,煤粉颗粒着火特性是影响氨煤混燃机组宽负荷灵活运行的关键因素。针对氨与煤粉混合给料的掺烧技术路径,利用新型两级平焰燃烧器开展了氨煤混燃过程单颗粒煤粉着火特性研究。利用高速摄影和背光法,通过图像分析获得了不同工况(载气掺氨比、环境氧浓度)下准东煤粉颗粒着火模式和着火延迟时间。研究发现,非掺氨工况下颗粒着火过程由非均相着火模式主导,而掺氨可增大均相颗粒着火模式的煤粉颗粒比例。同时,增大掺氨比,煤粉在脱挥发分阶段破碎的比例增大。同时,通过构建含有氨总包燃烧反应的一维暂态煤粉着火模型,可较好复现氨对煤粉颗粒着火特性的影响:在中心还原气氛下影响较小;而中心氧体积分数为0.1、0.2时,掺氨显著降低单颗粒着火延迟时间,这主要是由于氨火焰提高了煤粉颗粒的加热速率。

The development of mixed combustion of green ammonia and coal in coal-fired power plants is beneficial to the carbon reduction of thermal power towards the goal of carbon neutrality.The ignition characteristics of coal particle is the key factor affecting the flexible operation of the units in the process of gradually increasing the ammonia mixing ratio in the furnace with the technology of mixed combustion.Based on the path of blended combustion technology for ammonia and coal powder mixed feed,a new two-stage flat flame burner was used to study the ignition characteristics of single particle coal powder during ammonia coal mixed combustion process.The ignition mode and ignition delay time of the pulverized Zhundong coal particles under different operating conditions(ammonia volume fraction of the carrier gas and the ambient oxygen concentration) were obtained from the image analyses with the high-speed photography and the backlight method.It is found that the ignition process of particles is dominated by the heterogeneous ignition mode dominates at the absence of ammonia,while ammonia cofiring increases the proportion of coal particles undergoing homogeneous ignition.Meanwhile,with an increase in the ammonia cofiring ration,the proportion of fragmented coal particles during the devolatilization stage increases.At the same time,by constructing a one-dimensional transient coal powder ignition model containing ammonia combustion reaction,the influence of ammonia on the ignition characteristics of coal powder particles can be well reproduced.The effect is relatively small under the central reducing atmosphere.When the central oxygen volume fraction is 0.1 or 0.2,the addition of ammonia significantly reduces the ignition delay time of a single particle,mainly due to the ammonia flame increasing the heating rate of coal powder particles.