Abstract The transport sector represents one of the major cause of air pollution and greenhouse gases emissions. For this reason, several measures have been taken: penalty and incentive schemes have been introduced worldwide to increase renewable energy sources and alternative fuels use. It is widely accepted that natural gas (NG) is a good alternative fuel, especially in its liquid form (LNG), and it can be produced using biogas as methane source to obtain renewable liquefied biogas (LBG). However raw biogas contains several impurities and it needs to be pre-treated. At present, several technologies allow biogas purification. In particular cryogenic separation represents a promising solution for simultaneous purification and liquefaction. It can achieve impurities removal and methane liquefaction by means of a single plant. In this work, a novel cryogenic separation process, based on CO2 cold recovery, is presented. The proposed plant is optimized and a sensitivity analysis is also performed. Results indicate that the proposed plant represents a valid option for LBG production. Indeed the specific energy consumption is 1.574 kWh kg−1 for a CO2 content in inlet biogas of 50%. Furthermore the energy use and operative costs are compared with those of standard technologies and they result respectively 23% and 22% lower, taking into account the influence of CO2 as by-product.

中文翻译：

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沼气中二氧化碳分离甲烷液化低温技术的理论评价与优化

摘要 交通部门是造成空气污染和温室气体排放的主要原因之一。出于这个原因，已经采取了一些措施：在世界范围内引入了惩罚和奖励计划，以增加可再生能源和替代燃料的使用。人们普遍认为，天然气（NG）是一种很好的替代燃料，特别是其液态（LNG），它可以使用沼气作为甲烷来源进行生产，以获得可再生的液化沼气（LBG）。然而，原沼气含有多种杂质，需要进行预处理。目前，有几种技术可以净化沼气。特别是低温分离代表了同时纯化和液化的有前途的解决方案。可通过单台装置实现除杂和甲烷液化。在这项工作中，提出了一种基于 CO2 冷回收的新型低温分离工艺。拟建的工厂经过优化，并且还进行了敏感性分析。结果表明，拟议的工厂代表了 LBG 生产的有效选择。实际上，当入口沼气中的 CO2 含量为 50% 时，单位能耗为 1.574 kWh kg-1。此外，与标准技术相比，能源使用和运营成本分别降低了 23% 和 22%，考虑到了副产品 CO2 的影响。574 kWh kg-1 对于入口沼气中 50% 的 CO2 含量。此外，与标准技术相比，能源使用和运营成本分别降低了 23% 和 22%，考虑到了副产品 CO2 的影响。574 kWh kg-1 对于入口沼气中 50% 的 CO2 含量。此外，与标准技术相比，能源使用和运营成本分别降低了 23% 和 22%，考虑到了副产品 CO2 的影响。