焦炉气甲烷化及沼气原位提纯耦合新工艺与原理

The upgraded biogas with methane content higher than 90% can be used as natural gas or vehicle fuels, which will increase its utilization efficiency. However, the biogas upgrading is generally performed outside the anaerobic reactor and the cost is relatively high. Coke oven gas contains mainly H2 and CH4, and small amount of CO and CO2. Based on the research result that H2, CO2 and CO could be converted to methane in anaerobic reactor, the present project proposes an innovative process for simultaneous coke oven gas biomethanation and in-situ biogas upgrading in anaerobic reactor. In the project, the mass transfer characters and conversion efficiency of hydrogen provided by hollow fiber membrane will be studied, including the role of active components in mass transfer. Moreover, the biofilm attached on the hollow fiber membrane and membrane fouling will be analyzed, and the methods to increase the methane content will be investigated. The project will also study the effects of coke oven gas addition on the organics degradation, changes of buffer system and microbial activity in the anaerobic reactor, and the qualitative and quantitative changes of methanogens will be characterized. The biochemical reactions and dynamics will be explored, and the mathematic model for mass transfer and biochemical reactions will be established. The study will provide theoretical and technical solutions for the application of the proposed process.

厌氧消化产生的沼气提纯后甲烷含量达到90%以上，可以替代天然气从而提高利用效率，然而目前沼气提纯均在厌氧反应器外进行的，成本较高。焦炉气主要成分为H2和CH4，和少量CO、CO2等气体，研究发现某些厌氧微生物可以实现H2，CO2和CO向甲烷的转化。本申请在前期可行性研究的基础上，提出一种利用厌氧微生物实现焦炉气甲烷化和沼气提纯的耦合工艺，以传质理论和生化反应动力学为基础，探索采用中空纤维膜实现焦炉气向厌氧反应器的高效扩散，研究各反应组分在各相中的传质-反应规律和过程参数对气体传质效果的作用，分析中空纤维膜表面生物膜特性和膜污染成分，探讨提高甲烷浓度的工艺策略；深入研究焦炉气加入后对厌氧过程有机物降解、缓冲体系和微生物活性的影响，从分子水平上研究系统内不同产甲烷菌群定性和定量的变化，探究反应系统的微观生化机制和动力学，构建耦合工艺的传质-生化动力学模型，为该工艺的应用提供理论基础和技术支撑。

本课题提出将焦炉气作为廉价的外加氢源，通入正在运行的处理有机废弃物的厌氧反应器中，焦炉气中的CO和CO2可在厌氧微生物作用下与H2结合转化为CH4，剩余的H2和厌氧反应器产生的沼气中的CO2结合生成CH4，该工艺不仅实现焦炉气的甲烷化，同时也能够实现沼气原位提纯。课题研究发现非限制性气液传质条件下，氢气分压增加或混合不会有利于较高的氢气消耗速率，由于限制因素是微生物的活动，而不是氢的传输速率。增加微生物浓度可能导致更高的氢气消耗速率。利用中空纤维膜向厌氧反应器中通入模拟焦炉气，通入一定量的模拟焦炉气后，甲烷浓度从65%提高到90%左右，然而进一步增大模拟焦炉气进气量（2900 mL/L·d）后，pH突增至9.0，随即反应器崩溃。进一步在维持进气量为2900 mL/L.d条件下将pH控制在8.0，此时甲烷浓度可高达98-99%。从现有的研究结果来看，控制pH值条件下通入模拟焦炉气可以获得纯度很高的甲烷，且CO的存在对产甲烷过程没有明显毒害作用。高温和超高温条件下，测试范围CO的加入对体系的耗氢产甲烷性能均无抑制，并且能够转化利用。经过CO长期驯化的混合菌群体系，延迟期大大缩短，古菌群落的多样性随着温度的升高而降低，在超高温条件下，Methanothermobacter占古菌群落的97%以上，均具有将CO甲烷化的潜力。

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