基于炉内含氮污染物控制的生物质分级气化理论

Low-tech combustion of biomass wastes from agriculture and industry is one of those sources of atmosphere nitrogen oxide thus has been drawn attention from environmental supervision departments. Clean and high-efficiency biomass thermal conversion technologies like gasification are of particular important nowadays in China which facing serious haze pollution problem. Based on the staged conversion principle, the optimal conditions of various reaction kinetics are to be gained through the study on pyrolysis, gasification, char gasification, pollutant inhibition, volatile oxidation etc. To inhibit the generation of particulars and tar, and improve the efficiency of gasification through staged control, directional adjustment the transformation way of fuel N, Wood dust and high fiber board etc with high N biomass are to be studied, especially on the key scientific problems so as to establish the staged biomass gasification theory based on the control of nitrogenous pollutants inside Gasfier: controlling migration and transformation of gas phase containing N component in pyrolysis and gasification process, mechanism of the release and inhibition of tar and particulars, controllable conversion and gasification of fuel N reduction and decomposition mechanism of nitrogen oxides, coupling control of biomass high efficiency gasification and low N pollutants emission. The research would provide a theoretical basis for utilizing high N biomass gasification and reference for the control of nitrogen oxides and its precursors in the gasifier. The realization of the expected goal will provide basic data for efficient and clean utilization of straw and industrial wastes.

在霾污染日趋严重的背景下，秸秆露天焚烧及普通锅炉燃用高含N工业生物质废弃物导致的污染问题引起环境监管部门的重视，迫切需要与秸秆管控措施结合，发展高效清洁的生物质气化技术。本项目利用分级转化原理，通过对热解、半焦气化、污染物抑制、挥发分氧化等研究，得到各反应的最优动力学条件，通过分区控制定向调控燃料N转化途径，同时抑制颗粒物及焦油的生成，并提高气化效率。项目以砂光粉、高纤维板等高含N生物质为对象，研究热解气化过程气相含N组分的可控迁移与转化、考察焦油与颗粒物释放及抑制机理，阐明燃料N的可控转化与气化气还原分解氮氧化物机理、生物质高效气化与低N污染排放耦合控制等关键科学问题，建立基于炉内含N污染物控制的生物质分级气化理论。研究不仅为高含N生物质气化利用提供理论基础，也为炉内氮氧化物及其前体物的控制提供参考依据，具有重要的科学意义。预期目标的实现将为秸秆和工业废弃物的高效清洁利用提供基础数据。

为解决富氮生物质热能利用导致的氮污染问题，迫切需要发展高效清洁的热解气化技术。本项目重点关注富氮生物质热解气化过程含氮组分的可控迁移与转化，以其建立低氮污染物排放的生物质高效清洁分级气化理论。主要研究内容：（1）热化学预处理与转化过程含氮污染物的迁移演化规律和机理；（2）基于生物质碳/氮组分调控的改性高值燃料的制备方法与理论；获得如下主要结论：（1）解析了水热碳化过程固相碳/氮组分迁移路径：一方面，不稳定碳结构（-C-H、-C-O）热裂解并以可溶性中间体富集在液相，进而通过缩聚、聚合、成环反应形成类煤结构；另一方面，不稳定氮结构经水解、脱氨反应以无机氮离子和可溶性有机氮富集于液相（去除机制），较稳定燃料氮经环化、缩聚反应转化为固相更稳定氮官能团（稳定机制）；（2）明确了热解过程燃料氮到NOx前驱物的迁移演化，确定了NOx前驱物种类（NH3和HCN）和产率水平：20-45wt%，高温快速热解是决定因素；明确了以蛋白质氮/无机氮为体系的燃料氮类型及其热稳定性；揭示了不同热解阶段燃料氮经半焦氮/焦油氮到NOx前驱物的演化路径，其转化水平与热解阶段和燃料类型相关；（3）探究了多类单一或耦合热化学手段对富氮生物质源端提质降氮的规律和潜力。对固体燃料而言，水热碳化、与煤共水热碳化方式可有效实现固相氮去除和碳改性（能量密度提升20-40%，氮组分去除55-75%）；对燃气而言，湿法烘焙+热解、分级热解、与煤共热解、还原性气氛气化等方式可有效调控气相氮污染物，燃气热值提高10-20%，氮污染物含量低至30 ppmv。基于上述研究结论，本项目提出了几类针对含氮污染物源端调控的富氮生物质高效清洁热解方法，形成了符合低氮污染物排放和高值热属性的碳化-热解-气化耦合工艺路线。为富氮生物质的高效清洁利用提供了有效基础数据和理论。