Release characteristic of NOx precursors during the pyrolysis of nitrogen-rich biomass
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摘要: 利用热重分析-傅里叶红外光谱联用(TG-FTIR)和水平管式炉-X射线光电子能谱(XPS)研究了两种富氮生物质原料(大豆秸秆(SBS)和纤维板(FB))热解过程中NOx前驱物(NH3、HCN和HNCO)的释放特性,考察温度、升温速率及燃料含N物质结构对其NOx前驱物释放行为的影响。结果表明,燃料中的N来源不同(天然固有与人工添加)造成其转化差异:SBS释放的NOx前驱物主要为NH3而FB为NH3、HCN(快速)和HNCO(慢速);FB气相N主要随挥发分析出,而SBS则相反,在二次反应阶段析出;两种燃料中N的转化随温度变化,低温下富集于半焦N,600℃以上时更多向非半焦N转移,NOx前驱物以NH3为主,高温及高升温速率利于HCN生成,若以减排NOx为目的,热解温度控制在600℃为佳;两种燃料中N的结构均为胺类N(N-A),热解时部分N-A向半焦中杂环N转化,同时伴随杂环N分解;高温下吡啶N和吡咯N分解分别主要产生HCN和NH3。Abstract: The release of NOx precursors (NH3, HCN and HNCO) in the pyrolysis of two nitrogen-rich biomass materials, viz., soybean straw (SBS) and fiberboard (FB), were investigated by thermogravimetric-Fourier transform infrared spectroscopy (TG-FTIR, for slow pyrolysis) and horizontal tubular reactor-X-ray photoelectron spectroscopy (HTR-XPS, for rapid pyrolysis); the effects of final temperature, heating rate and nitrogen form in biomass on the release characteristic were considered. The results indicate that the evolution pathway is related to the form of nitrogen in biomass; nitrogen in SBS (SBS-N) is mainly converted to NH3 during the secondary cracking reaction, whereas nitrogen in FB (FB-N) is transformed to NH3, HCN (rapid) and HNCO (slow) during the primary pyrolysis reaction. Nitrogen in biomass (fuel-N) is inclined to convert to nitrogen in char (char-N) at low temperature and to nitrogen in tar (tar-N) or NOx precursors at high temperature (>600℃), which suggests that a pyrolysis temperature below 600℃ can suppress the release of NOx precursors. SBS-N and FB-N are characterized by protein and amide, respectively, which are partly converted to pyrrolic-N and pyridinic-N in char, forming preferably NH3 and HCN, respectively.
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Key words:
- soybean straw /
- fiberboard /
- pyrolysis /
- NOxprecursor /
- form of nitrogen
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图 9 FB与SBS快速热解N产物分布随热解温度变化
Figure 9 Nitrogen distribution in various products during the rapid pyrolysis of SBS (a) and FB (b)
Figure 9 : NOx precurrsor; : other-N; : char-N
表 1 豆秸与纤维板的元素分析与工业分析
Table 1 Ultimate and proximate analysis of soybean straw (SBS) and fiberboard (FB)
Sample Ultimate analysis w/%(dry-ash free basis) Proximate analysis w/%(dry basis) C H N S O* V FC A SBS 46.74 6.59 1.40 0.06 45.21 77.77 16.91 5.32 FB 44.79 6.16 7.49 0.01 41.55 83.56 16.13 0.30 *: calculated by difference -
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