深度空气分级下煤粉耦合氨燃烧及NO生成特性

Combustion and NO formation characteristics of pulverized coal co-firing with ammonia in a deep-air staging condition

氨作为一种富氢的无碳燃料,具有能量密度高、成本低、储运安全等优势,与煤粉耦合燃烧可降低煤燃烧过程中CO_(2)的排放。以某20 kW沉降炉(氨从煤粉火焰高温区喷入)为研究对象,在深度空气分级下对煤粉耦合氨燃烧特性及NO生成规律进行研究,通过Fluent数值模拟探究了氨掺混比例(0、10%、20%、30%)、氨燃烧区过量空气系数(1.08、0.96、0.84、0.72)、氨不同送入位置(0.5、0.6、0.7、1.0 m)对煤粉燃尽特性及NO生成特性的影响。结果表明:①与纯煤粉燃烧相比,煤粉中掺混氨后飞灰含碳量增加、NO生成量降低;氨掺混比例进一步提高会增加飞灰含碳量、降低NO生成量。考虑燃烧经济性和NO排放量,氨掺混比例维持在20%左右较为合适。②氨燃烧区过量空气系数大于1时,氧量过剩会导致反应NH_(3)+O_(2)→NO+H_(2) O+0.5H_(2)发生,生成大量NO;氨燃烧区过量空气系数小于1时,未完全燃烧的氨发挥还原作用,有利于反应NH_(3)+NO→N_(2)+H_(2)O+0.5H_(2)发生,抑制NO的生成。综合考虑,建议氨燃烧区过量空气系数维持在0.96左右,既可满足煤粉的高效燃烧,又可有效抑制煤粉耦合氨燃烧过程中NO的生成。③喷氨位置与煤粉火焰区距离越大,飞灰含碳量和NO浓度越高,建议喷氨位置尽量靠近煤粉燃烧火焰区。

As a hydrogen-rich carbon-free fuel,ammonia has the advantages of high energy density,low cost,and safe storage and trans⁃portation.Pulverized coal co-firing with ammonia can reduce CO_(2) emissions during coal combustion.Taking a 20 kW settling furnace(am⁃monia is injected from the high temperature zone of pulverized coal flame)as the research object,the coupled ammonia combustion charac⁃teristics and NO generation law of pulverized coal under deep air classification was carried out.By the numerical simulation,the effects of the ammonia co-firing ratio(0,10%,20%,30%),ammonia combustion zone excess air coefficient(1.08,0.96,0.84,0.72),and the am⁃monia injection location(0.5,0.6,0.7,1.0 m)on combustion characteristics and NO formation behavior in a 20 kW drop tube furnace with a deep-air staging condition(the ammonia is injected into the high temperature coal-flame zone)were investigated.The results show that compared with pure pulverized coal combustion,pulverized coal co-firing with ammonia increases the carbon content in fly ash and re⁃duces NO emissions.The carbon content in fly ash increases and NO emissions decrease with the further increase of the ammonia co-firing ratio.Considering the combustion economy and NO emissions,the ammonia co-firing ratio with approximately 20%is more appropriate.When the excess air coefficient in the ammonia combustion region is more than 1,the excess of oxygen promotes the reaction of NH_(3)+O_(2)→NO+H_(2)O+0.5H_(2),and amounts of NO are generated.When the excess air coefficient in the ammonia combustion region is less than 1,the incomplete-burning ammonia plays a reducing role,which is conducive to the reaction of NH_(3)+NO→N_(2)+H_(2)O+0.5H_(2),and the for⁃mation of NO is inhibited effectively.Considering comprehensively,it is suggested that the excess air coefficient in the ammonia combustion region is maintained at approximately 0.96,which can not only meet the high-efficiency combustion of pulverized coal,but also effectively inhibit the formation of NO during the ammonia combustion process.The farther the ammonia injection location is from the pulverized coal flame zone,the higher the fly ash carbon content and NO concentration is.It is recommended that the ammonia injection location should be as close as possible to the pulverized coal combustion flame zone.