Abstract: The production of compressed natural gas (CNG) from anaerobic fermentation gas is an important way for large scale use of biomass resources. A discrete simulation model for hollow fiber membrane is established by the finite element method in the process software UniSim Design, which is suitable for membrane separation with high permeation stage cut to purify bio-methane. The key operation condition, membrane feed pressure, which affects membrane process capacity, methane recovery ratio and CNG specific energy consumption, is studied by simulating the single-stage separation process of polyimide membranes. In this system, process capacity and methane recovery ratio are improved by increasing membrane feed pressure, but the lowest specific energy consumption is 0.46 kW·h·m^-3 at membrane feed pressure of 2.70 MPa. After analyzing the change of methane content in permeate, a single-stage two-step membrane process is developed, with the advantages of compact process structure, low equipment investment, high methane recovery ratio and high production profit. For processing 1000 m³·h^-1 feedstock, the methane recovery ratio is higher than 95%, with 500 m³·h^-1 CNG yielded. The overall investment is 3.8×10⁶ CNY, annual operation and depreciation cost is 1.5×10⁶ CNY, and the annual gross economic profit can be 2.5×10⁶ CNY at least.

Key words: methane, membrane, compressed natural gas, finite element model, process design, carbon dioxide

摘要： 以厌氧发酵生物气为原料生产压缩天然气是大规模利用生物质资源的重要途径。首先，在过程模拟软件UniSim Design中基于有限元方法建立了中空纤维膜的离散数值计算模型，适合于模拟渗透切割比非常高的生物甲烷膜分离过程。以单级聚酰亚胺膜分离系统为例研究了关键操作条件——膜的进料压力对处理能力、甲烷收率及压缩天然气生产单耗的影响。目前的评估体系下，提高进料压力有利于提高处理能力和甲烷回收率，而压缩天然气生产单耗在2.70 MPa时最低，为0.46 kW·h·m^-3压缩天然气。通过分析渗透气的甲烷浓度变化趋势，开发了一级二段气体膜分离系统，兼具流程简单、设备投资低、甲烷收率高、产值高的优点。以处理1000 m³·h^-1生物气为例，甲烷收率达95.0%，压缩天然气产量500 m³·h^-1。对应地，装置总投资为3.8×10⁶ CNY，年运行费用及设备折旧为1.5×10⁶ CNY，年经济效益（毛利）超过2.50×10⁶ CNY。

关键词: 甲烷, 膜, 压缩天然气, 有限元模型, 过程设计, 二氧化碳