氧分级对准东煤富氧燃烧NO_(x)生成与积灰特性的影响

Effects of staged oxygen on NO_(x) formation and ash deposition characteristics during oxy-fuel combustion of high-alkali coal

准东煤储量丰富,但由于其碱及碱土金属含量较高,会导致严重的换热面沾污问题,影响锅炉效率和运行安全。富氧燃烧有望实现准东煤的清洁利用,且分级条件下的富氧燃烧可进一步降低NO_(x)排放,但同时也会影响煤中矿物质演变。目前氧分级对高碱煤燃烧积灰的影响规律鲜有研究,氧分级对NO_(x)和积灰的耦合作用尚不明确。利用两段炉试验系统,研究富氧分级燃烧条件下高碱煤燃烧过程中的NO_(x)生成和积灰特性。试验结果表明,富氧条件下烟气中的NO体积分数远低于空气条件,富氧气氛下的NO体积分数仅为80×10^(-6)左右,而空气气氛下NO体积分数已超过170×10^(-6)。相同O_(2)体积分数下(21%),富氧条件下的灰沉积倾向弱于空气条件,富氧条件下为26.20 mg/g,而空气条件下为16.45 mg/g,证明了富氧燃烧的优越性。随着主燃区O_(2)体积分数的增加(25%~60%),准东煤的燃料N转化率及灰沉积倾向逐渐升高,积灰的整体结构更加致密,积灰颗粒之间的团聚和黏连现象严重,独立存在的灰颗粒数量明显减少,颗粒表面的凹坑不断发育,出现较多的孔隙结构,烧结现象逐渐加剧。该研究有利于加深对高碱煤富氧分级燃烧下的积灰和NO_(x)生成特性的认识,为促进高碱煤的安全清洁利用提供借鉴。

Zhundong coal is rich in reserves,but its high contents of alkali and alkaline earth metals can result in serious fouling on the heat exchange surface,influencing the boiler efficiency and the safe operation.Oxy-fuel combustion is promising to realize the clean utili⁃zation of Zhundong coal,and the oxy-fuel combustion under staged condition can further decrease NO_(x) emission,while it affects the evolution of mineral in coal as well.There is little research on the effect of staged oxygen on ash deposition caused by high-alkali coal,and the possible relationship between NO_(x) formation and ash deposition remains unclear.The characteristics of NO_(x) formation and ash deposi⁃tion under oxy-fuel combustion with staged oxygen were studied via a two-stage furnace.The experimental results show that the NO con⁃centration in flue gas under oxy-fuel condition is much lower than that in air.The NO concentration in oxy-fuel atmosphere is about 80×10^(-6),while the NO concentration in air exceeds 170×10^(-6).Under the same O_(2) volume fraction(21%),the ash deposition propensity under oxy-fuel condition is also weaker than that in air,which is 26.20 mg/g and 16.45 mg/g,respectively.The results indicate the superiority of oxy-fuel combustion.With the increase of oxygen content in the main combustion zone(25%-60%),the conversion ratio of fuel nitrogen and ash deposition propensity of Wucaiwan coal both gradually increases.The overall structure of ash deposit is more compact,the agglom⁃eration and adhesion between the accumulated ash particles are serious,the number of independent ash particles is significantly reduced.In addition,the pits on the particles surfaces develope,with more pore structures and more serious sintering observed.This reseach helps to better understand the ash deposition and NO_(x) formation characteristics during the oxy-fuel combustion with oxygen staged,which is also conducive to accelerating the safe and clean utilization of high-alkali coal.