生物质气化燃气临氧高温过滤净化过程的机理研究

The purification technologies of biomass gasification gas (BGG) are relatively backward in our country, and there has grown up an urgent need for an integrated high temperature syngas cleaning technology with low cost. This program focuses on the cleanup mechanism of integrated hot gas filtration for tar removal and particulate abatement in the presence of oxygen without any catalyst at 300~500℃. . Firstly, based on the special oxidation characteristics of BGG gas at high temperature, a new calculation method for the safe oxygen content of BGG gas would be built up in this study, in order to determine the suitable operation conditions of hot gas filtration in the presence of oxygen. Secondly, using a variety of in-situ analysis techniques, it will be investigated respectively that the high temperature oxidation pyrolysis mechanism of solid particles (PBG) and tar (TBG) model compounds produced by biomass gasification under the simulated BGG gas atmosphere, to explore the main factors restricting the BGG gas filtration efficiency at high temperature. Thirdly, we plan to build a novel experimental equipment for hot gas filtration with high precision, using the self-made modified ceramic fiber composite membranes. Based on the reaction, material, and heat balance calculation of the real biomass gasification-purification system, this program will emphatically explain a series of engineering thermal physics problems in the process of hot BGG gas filtration with an appropriate amount of oxygen, such as gas-solid flow, mass and heat transmission, selective oxidation reaction, and so on. On the basis of these factors, it will be determined that the empirical equation and the the predicting model for the interactional condition of high-temperature filtration conditions and characteristics of BGG gas. Finally, the integrated hot gas filtration for tar removal and particulate abatement would run continuously at the optimum condition for more than 100 hours, in order to investigate the main factors affecting the thermal chemical stability of ceramic filter materials and the regeneration/corrosion mechanism of the filter materials at the high temperature. . As a result, this work will provide the theory basis and the technical standard for the application and development of high temperature purification and conditioning of syngas produced by biomass gasification.

本项目提出了在300~500℃且不添加催化剂的条件下，通过优化临氧高温过滤条件，实现生物质气化燃气除尘除焦一体化的新思路。首先，通过对燃气高温氧化特性的研究，建立适用于生物质燃气安全含氧量的计算方法，并确定适宜的高温临氧操作范围；进而，采用多种原位在线分析技术，分别研究气化固体颗粒物和焦油模型化合物在模拟生物质燃气中的高温氧化热解机理，并探索制约燃气高温除尘除焦效率的主要影响因素；其次，通过对真实生物质气化-净化系统的精准实验监控和反应/物料/热量平衡计算，阐释临氧高温除尘除焦一体化过程在气固流动、质量和热量传输、选择性氧化反应等工程热物理方面的基本原理，建立描述高温过滤条件与生物质燃气特性之间相互影响规律的经验关系式和预测模型；最后，根据长时间连续实验结果，分析影响陶瓷高温过滤材料热化学稳定性的主要因素和过滤材料的再生/腐蚀机理，从而为该技术的工程应用与开发提供理论依据和技术标准。

生物质气化技术是一种重要的生物质能源化利用方式，可将低品位的生物质废弃物转化为高附加值的燃气产品。气化燃气中的含碳固体颗粒物（carbonaceous flyash particles，简称CFPs）和焦油（tar）是生物质气化过程中产生且不可避免的杂质副产物，采用高温过滤虽能有效拦截CFPs固体颗粒物和部分重组分焦油类物质；但传统工艺中，CFPs颗粒物和焦油组分易发生结焦、烧结和腐蚀等问题。CFPs粉末不断地粘附在除尘管表面易引起压降骤增、除尘管堵塞和滤芯断裂等问题，导致反吹再生难以实现。. 本研究提出了在300-500℃且不添加催化剂的条件下，通过优化临氧高温过滤条件，实现生物质气化燃气除尘除焦一体化的新工艺。通过对燃气临氧氧化特性的研究，确定适宜的临氧高温过滤条件：含氧量≤4%，温度≤450℃，过滤速率≥0.53cm/s。进而，考察了高温过滤条件与生物质燃气特性之间的相互影响规律，证实：在2%氧含量和350-400℃的过滤温度下，CFPs颗粒物的选择性氧化速率显著高于可燃气体组分。CFPs恒温热解机理研究表明，在无氧燃气气氛下，CFPs以脱氢脱氧的芳香化缩聚反应为主，易形成焦油类的大分子稠环芳烃；而在临氧燃气气氛下，CFPs表面的有机基团易与O2发生选择性氧化反应，生成表面含氧官能团，抑制了芳香环缩聚反应，有利于降低焦油产率和形成疏松多孔的积灰层。连续100h的生物质燃气高温过滤中试试验，证实在含氧量为1-2%的临氧高温过滤条件下，过滤压差大幅降低至<2000Pa，并能长时间稳定运行；其除尘率高达99%、除焦率也达92%，实现了除尘除焦一体化；可连续生产出媲美于天然气品质的绿色清洁燃气，为该技术的工程应用提供了理论依据和关键技术参数。