Direct utilization of “low-grade” biogas, as an important sustainable energy resource, provides a viable approach to avoid the energy-intensive upgrading step that is often required to separate CO₂ from CH₄ in order to produce a pipeline-grade fuel gas. This study investigated dual, onboard storage and separation of biogas in an adsorbed gas system (AGS) over two highly porous carbon sorbents, Br-318 and Nuchar, in the pressure range of 0–55 bar. The AGS was pressurized with a 50/50 vol % CH₄/CO₂ feed, and working capacities as a function of charge–discharge pressures and temperatures were determined and compared with those obtained from the pure CH₄-pressurized AGS. Also, the outlet composition of the discharged gas during depressurization was determined experimentally as a function of vessel void fraction. Both sorbents exhibited an acceptable storage and separation performance; but Br-318 outperformed Nuchar by displaying a 20% higher storage capacity at a 40% void fraction. This, however, only improved the purity of delivered CH₄ by 10% at elevated temperatures. As the void fraction of the Br-318-filled AGS decreased from 40 to 10%, the weight of biogas stored increased by 35.3% and the purity of CH₄ at the outlet increased to 89%. Analysis of the temperature profiles indicated large temperature fluctuations of 52.0 and 40.3 °C during charge and discharge steps, respectively, necessitating a proper thermal management to maintain the vessel’s temperature. Additionally, cyclic test results showed capacity losses of 7.4 and 5.7% for Br-318 and Nuchar, respectively, after the fourth cycle, highlighting the importance of consistent regeneration to maintain the storage/separation performance of the biogas-filled AGS. Lastly, the biogas-filled vessel demonstrated an increased gas storage performance compared to the pure CH₄-filled vessel by exhibiting 61.8% higher storage capacity under the same conditions.

中文翻译：

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碳基吸附气体系统中沼气的双重、机载储存和分离分析


直接利用“低品位”沼气作为一种重要的可持续能源资源，提供了一种可行的方法，可以避免通常需要将 CO₂ 与 CH₄ 分离以生产管道级燃气所需的能源密集型升级步骤。本研究调查了在 0-55 bar 的压力范围内，通过两种高多孔碳吸附剂 Br-318 和 Nuchar 在吸附气体系统 （AGS） 中对沼气进行双重、机载储存和分离。用 50/50 vol % CH₄/CO₂ 进料对 AGS 加压，确定作为充放电压力和温度函数的工作容量，并与从纯 CH₄ 加压 AGS 获得的工作容量进行比较。此外，通过实验确定减压过程中排出气体的出口组成与容器空隙分数的函数关系。两种吸附剂都表现出可接受的储存和分离性能;但 Br-318 的性能优于 Nuchar，在 40% 的空隙率下显示出 20% 的存储容量。然而，这仅在高温下将交付的 CH₄ 的纯度提高了 10%。随着 Br-318 填充的 AGS 的空隙率从 40 降低到 10%，储存的沼气重量增加了 35.3%，出口处 CH₄ 的纯度增加到 89%。温度曲线分析表明，在充注和卸料步骤期间，温度波动分别高达 52.0 °C 和 40.3 °C，因此需要适当的热管理来维持容器的温度。此外，循环测试结果显示容量损失分别为 7.4 和 5。第四次循环后，Br-318 和 Nuchar 分别为 7%，突出了持续再生对于维持充满沼气的 AGS 的储存/分离性能的重要性。最后，与纯 CH₄ 填充容器相比，沼气填充容器的储气性能更高，在相同条件下的存储容量提高了 61.8%。