H2O(g)对富氧燃烧超细颗粒物生成特性影响

为实现富氧燃烧技术的广泛推广,对煤粉燃烧在富氧气氛下的颗粒物排放特性进行了研究。在1800 K管式炉内进行煤焦燃烧试验,研究了富氧气氛下H₂O(g)体积分数(0、5%、10%、20%、30%)对煤焦燃烧超细颗粒物的影响;采用荷电低压撞击器(ELPI+)获得超细颗粒物质量和数量浓度粒径分布并进行分析。结果表明,H₂O(g)对超细颗粒物质量浓度和数量浓度粒径分布无影响,但会导致超细颗粒物的峰值波动。超细颗粒物总数量由最小粒径超细颗粒物决定,5种水蒸气浓度下EL?PI+第1级撞击器收集到的超细颗粒物数量占比均超过65%。超细颗粒物总质量由最大粒径超细颗粒物决定,5个水蒸气浓度下ELPI+第7级撞击器收集到的超细颗粒物质量占比均超过94%。低H₂O(g)浓度会抑制超细颗粒物生成,H₂O(g)体积分数为5%时的抑制作用最显著;高H₂O(g)浓度会促进超细颗粒物生成。这是因为一方面H₂O(g)与煤焦发生气化反应,使煤焦颗粒周围产生还原性气氛,促进矿物质还原为单质,进一步促进矿物质蒸发;另一方面气化反应是吸热反应,会降低煤焦颗粒燃烧温度,同时H₂O(g)加入也导致烟气热容增加进一步降低,煤焦燃烧温度抑制煤中矿物质的蒸发,导致超细颗粒物生成减少,是2种作用相互竞争的结果。此外,H₂O(g)的加入使超细颗粒物平均粒径增大,0~5%H₂O(g)时超细颗粒物平均粒径增大最迅速。

Effect of H2O(g)on the formation of ultrafine PM under oxy-fuel atmosphere

To extend the oxygen enriched combustion technology in a large scale,it is necessary to study the emission characteristics of par?ticulate matter in oxy-fuel combustion of pulverized coal.In this paper,the effect of H₂O(g)volume fraction(0,5%,10%,20%,30%)on the formation of ultrafine particulate matter(PM)under oxy-fuel combustion atmosphere was studied in a 1800 K drop tube furnace(DTF).Furthermore,the mass-based and number-based particle size distribution(PSD)were obtained and analyzed by a 14-stage elec?trical low pressure impactor(ELPI+).The results indicate that the mass-based and number-based PSD of ultrafine PMs remains almost unchanged in various H₂O(g)contents(0,5%,10%,20%,30%),while the peak of ultrafine particles fluctuates.The total number of ul?trafine PM is determined by the number of ultrafine PM with the smallest particle size.The number fractions of the ultrafine PMs collected by the first impactor of ELPI+are all higher than 65%under all H2 O(g)contents.The total mass of ultrafine PM is determined by the mass of ultrafine with the largest particle size and the mass fractions of the ultrafine PMs collected by the seventh impactor of ELPI+are all higher than 94%.Low concentration of H₂O(g)can inhibit the formation of ultrafine particles,and the inhibition effect is the most significant when the volume fraction of H₂O(g)is 5%;high concentration of H₂O(g)can promote the formation of ultrafine particles.Be?cause the gasification reaction of H₂O(g)with coal char produces a reducing atmosphere around the coal char particles,which promotes the reduction of minerals to elemental matter and further promotes the evaporation of minerals.On the other hand,the gasification reaction is endothermic reaction,which will reduce the combustion temperature of coal char particles.At the same time,the addition of H₂O(g)al?so leads to the increase of heat capacity of flue gas.The combustion temperature of coal char inhibits the evaporation of minerals in coal,resulting in the reduction of ultrafine particles,which is the result of the competition between the two kinds of interaction.In addition,the addition of H₂O(g)makes the average particle size of ultrafine particles increase,and the average particle size of ultrafine particles increa?ses the most rapidly when 0-5%H₂O(g)is added.