二氧化碳置换模拟移动床吸附浓缩低浓度煤层气甲烷的研究

For the enrichment of the low-concentration coal bed methane, the separation of CH4/N2 is very difficult due to the similarity of two gases in physicochemical properties, and the available adsorbents have a poor adsorption CH4 capacity. Therefore, the objectives of this work are to develop the advanced adsorbent materials and the novel CO2 displacement simulated moving bed process. In the proposed gas-phase simulated moving bed process, the separation of CH4/N2 is enhanced significantly by the synergistic action of CO2 displacement and countercurrent flow between adsorbents and gas phase, being a promising technology for the enrichment of the low-concentration coal bed methane with low energy consumption and high efficiency. To reach this major goal, several intermediate milestones must be achieved: (1). the novel adsorbent materials with high CH4 adsorption capacity and high CH4/N2 selectivity are prepared by the microspore structure adjustment and surface chemical modification. (2) CO2 displacement mechanism for the remained CH4 and N2 in the column packed with the prepared adsorbent materials is investigated experimentally and theoretically. A rigorous mathematical model is developed to demonstrate the significant enhancement for the enrichment of the low-concentration coal bed methane. (3) According to the research on CH4 capture，CO2 displacement and adsorbent regeneration in a packed column, a novel CO2 displacement simulated moving bed process (multi -column system) is developed for the enrichment of the low-concentration coal bed methane. A rigorous mathematical model of multicomponent, non-isothermal adsorption system is used to design the separation zone of CH4/N2 and to optimize the operation conditions in order to maximize the methane purity, recovery and productivity and minimize the cost and energy consumption. The feasibility and efficiency of the proposed adsorption process are demonstrated by experiments and simulation. The set-up theoretical system for the design and optimization of the gas-phase simulated moving bed will provide a strong technical support on the low-concentration coal bed methane utilization.

针对煤层气中CH4/N2难以分离以及现有材料吸附甲烷容量低，设计和制备高效超级活性炭材料，建立二氧化碳置换模拟移动床吸附浓缩煤层气甲烷新方法。该方法通过多塔内吸附剂固定相与气相逆流流动和二氧化碳置换协同作用强化CH4/N2分离，解决低浓度煤层气甲烷浓缩过程的高能耗和高费用问题。研究重点聚焦：①通过材料孔道结构调控、表面/骨架化学修饰和官能团负载等方法，设计制备高效超级活性炭；②建立非线性多组分填充塔内竞争吸附数学模型，结合实验，探讨超级活性炭填充塔内CO2置换强化CH4/N2分离的机理；③在单塔低浓度CH4吸附、CO2置换与吸附剂再生研究基础上，建立多塔模拟移动床吸附分离CH4/N2的流程构态。建立非线性、非平衡和多自由度的吸附分离过程数学模型，开发模拟优化软件包，确定分离区，优化操作条件， 进行实验验证，形成模拟移动床分离过程优化设计的理论体系，为煤层气资源开发与应用奠定工程基础。

甲烷是一种优质燃料，在自然界中储量大、热值高，在能源体系中占有重要地位。但甲烷又是重要的温室气体，其温室效应是二氧化碳的21倍。因此，从煤层气、页岩气等低品质甲烷气中分离提纯甲烷对改善能源结构和保护大气环境，具有重要的现实意义和战略意义。目前，制约低浓度甲烷利用的重要因素是CH4含量低，如果将CH4浓度提高至80％以上，就能用作化工原料或高能燃料；如果CH4含量达到95％，就可直接并入天然气管网输送。低浓度甲烷气中除了含有一定量CH4外还含有大量的CO2和N2及少量氧气。CO2, O2和CH4分子物理性质差别大，易于分离，但是，CH4和N2因两者动力学直径相近，物理性质也相似，成为最难分离的体系。.在NSFC-山西煤基低碳联合基金资助下，针对低品质甲烷气规模化除氮气浓缩甲烷所存在的共性基础科学问题，我们研制高效活性炭，阐明碳材料微观结构与吸附分离CH4/N2性能的关系，基于单塔吸附分离CH4/N2和真空解吸/置换解吸过程研究，创新地研发多塔串联操作的模拟移动床吸附分离CH4/N2工艺。本课题制备的高效活性炭对低浓度甲烷氮气体系的分离系数达到了4.5，较国内外现有的吸附材料（分离系数2-4）获得了很大的提升，解决了低浓度甲烷与氮气吸附分离缺乏高性能吸附分离材料的核心问题。提出置换解吸新概念，并引入到传统真空变压吸附工艺中，形成CO2置换真空变压吸附新工艺，显著提高低浓度甲烷浓缩效率，10%-30% CH4低浓度甲烷气能够连续浓缩到80%以上甲烷纯度。进一步创新地开发了气相模拟移动床吸附分离甲烷与氮气新工艺，自制多塔模拟移动床装置，以研制的高效活性炭填充吸附塔，实验验证了该工艺能够连续浓缩低浓度甲烷气（30% ~50% CH4），得到高纯度甲烷产品气，产品气中甲烷纯度达到100%，可以直接并入天然气管道输送或用作化工原料。本课题研发新型高效活性碳和新颖模拟移动床吸附分离工艺，解决规模化浓缩低品质甲烷气的高能耗高费用问题，对缓解国民经济发展能源供需矛盾、改善能源结构、减少瓦斯灾害、改善大气环境等提供新的解决方案与技术支撑。