氨/煤气流床半气化燃烧及氮转化特性实验研究

An experimental study on the characteristics of ammonia/coal mild gasification-combustion and the Fuel-N transformation

氨气(NH_(3))作为零碳富氢燃料,在燃煤锅炉中掺烧NH_(3)是从燃烧源减少碳排放的有效途径,但会带来NO_(x)排放升高和煤粉燃尽变差等问题。为实现燃煤锅炉掺烧NH_(3)的低NO_(x)排放,在自行搭建的气流床半气化燃烧实验台上探究了气化炉掺烧20%的NH_(3)(G-20%NH_(3))和燃烧室掺烧20%的NH_(3)(C-20%NH_(3))中燃料氮的转化和NO_(x)排放特性。研究发现,气化炉内掺烧NH_(3)会降低炉膛温度,但对煤粉的气化反应影响较小,与纯煤工况相比,煤氮的转化率仅降低了3.64%,挥发分和固定碳转化率分别仅降低了0.70%和2.54%。在气化炉掺烧NH_(3)中,NH_(3)在气化炉中的转化率可达69.55%。气化炉内总燃料氮向N_(2)的转化率为68.88%,其中NH_(3)-N向N_(2)的转化率为67.73%。同时,气化炉掺烧NH_(3)促进了煤-N和NH_(3)-N向HCN的转化,转化率为0.36%。气化炉中煤粉的热解促进了NH_(3)的热解,相较于纯煤,气化炉掺烧NH_(3)使气化炉出口H_(2)体积分数升高了69.23%。掺烧NH_(3)降低了燃烧室燃烧初期的温度分布。相较于纯煤,气化炉和燃烧室掺烧NH_(3)使燃烧室的温度峰值分别降低了46℃和62℃。但是,掺烧NH_(3)推迟了气化半焦的燃烧,增加了燃尽区的温度。气化炉和燃烧室掺烧NH_(3)中燃尽区平均温度比纯煤工况分别升高了135.8℃和72.8℃,促进了煤粉的燃尽。其中燃烧室掺烧NH_(3)的促进效果更为显著,相较于纯煤,C-20%NH_(3)中飞灰含碳降低了1.8%。但气化炉掺烧NH_(3)更有利于降低NO_(x)排放,相较于C-20%NH_(3),G-20%NH_(3)的NO排放降低了23.51%。

Ammonia(NH_(3))is a carbon-free and hydrogen-rich fuel.NH_(3)co-firing in coal-fired boiler is an effective approach to reduce carbon emissions from the combustion source.However,it can lead to problems such as high NO_(x)emissions and poor coal burnout.To address the issues above,this paper investigated the Fuel-N conversion and NO_(x)emissions during co-firing 20%NH_(3)in gasifier(G-20%NH_(3))and in combustor(C-20%NH_(3))using a self-built mild gasificationcombustion experimental rig.The research found that the co-firing NH_(3)in the gasifier can decrease the gasifier temperature.However,it has little effect on the coal gasification reactions in gasifier.Compared with a pure coal condition,the conversion ratio of coal-nitrogen was only reduced by 3.64%,and the conversion ratio of volatile matter and fixed carbon decreased by only 0.70% and 2.54%,respectively.Besides,the conversion of NH_(3)in the gasifier can reach 69.55% during the condition of G-20%NH_(3).The 68.88% of total fuel-N was conversed to N_(2)in the gasifier,with NH_(3)-N converting to N_(2)was 67.73% in G-20%NH_(3).In addition,the NH_(3)co-firing in the gasifier promoted the transformation of coal-N and NH_(3)-N to HCN,with the value of 0.36%.Moreover,the coal pyrolysis in the gasifier promoted the NH_(3)pyrolysis.Compared with pure coal,the NH_(3)co-firing in the gasifier increased the H_(2)concentration at the outlet of the gasifier by 69.23% than that of pure coal.The NH_(3)co-firing also decreased the temperature during the preliminary stage of combustion.Compared with pure coal,the NH_(3)co-firing in the gasifier and combustor decreased the temperature peak by 46℃ and 62℃,respectively.Simultaneously,the NH_(3)co-firing delayed the occurrence of temperature peaks.Additionally,the NH_(3)co-firing delayed the gasified char combustion in the combustor.The average temperature in the burnout zone increased by 135.8℃ and 72.8℃ during G-20%NH_(3)and C-20%NH_(3),respectively,compared to PC.It was more conducive to the burnout of pulverized coal.The NH_(3)-cofiring in combustor had more significant promoting effects on the burnout of pulverized coal,in which the unburned carbon in fly ash decreased by 1.8% compared PC.However,the NH_(3)co-firing in gasifier was more effective in reducing NO_(x)emissions.During the G-20%NH_(3),NO emissions were decreased by 23.51% compared to C-20%NH_(3).The study offers some innovative ideas and data reference for the development of low NO_(x)emission technology for NH_(3)co-firing in coal-fired boiler.