生物质热化学转化过程(热解与气化)含N污染物是大气PM2.5的重要成因,研究其形成对大气污染防控具有重要意义。本文综述了国内外关于生物质热解与气化含N污染物形成机理及其影响因素的研究进展。现有研究结果表明:热解与气化过程含N污染物形成路径相似,但其种类及含量有明显差异,其中,热解主要为NH3与HCN,气化主要为NH3。从影响因素上看,燃料N赋存、温度、热解升温速率、气化反应气氛、燃料理化特性及反应添加物对含N污染物均有一定影响。升温速率快、燃料含N高、参与反应水蒸气浓度高等,均会造成含N污染物的增加,温度对两过程含N污染物的影响规律具有相似性,高温有利于降低其含量。从含N污染物三相分布特征来看,主要以气相形式存在,热解基本在50%左右,气化可高达90%,因此,控制并降低气相含N污染物形成是生物质热化学转化过程减少污染的重要方向。同时,本文基于研究结论的对比,指出国内外目前研究现状的不足。
To investigate the formation of nitrogenous pollutants( NPs) during biomass thermo-chemical conversion( pyrolysis and gasification) is significant for the control of air pollution as these NPs are an important factor for the formation of PM2.5. Research progress on the formation mechanism and influence factors of NPs during two processes are reviewed. Consistent conclusions from the literature can be summarized as follows: 1)NPs formed from two processes resemble in their formation paths but differ in their types & components. Either NH3 or HCN is confirmed to be main NPs for pyrolysis while NH3 is dominant for gasification. 2) Comparing the influence factors,it is demonstrated that the increase of any factor such as the heating rate,the content of fuel nitrogen and the concentration of steam involved will enhance the formation of NPs for two processes.Meanwhile,the effect of temperature on the selectivity of NPs towards two processes are similar as well as higher temperature is inclined to decrease the amount of NPs. 3) Comparing the results of nitrogen distribution,it is found that the percentage of NPs in gaseous phase are approximately 50% for pyrolysis and as much as 90% for gasification. Therefore,to control the formation of NPs in gaseous phase is effective to reduce the pollutantsduring biomass thermo-chemical conversion. Meanwhile, based on the current conclusions obtained, the deficiencies of formation mechanism are summarized as well as the prospective developments are proposed for further research.