Abstract In the energy transition towards a zero-carbon energy sector, natural gas grows much faster than either oil or coal, since it is an environmentally-friendly fuel supported by the continuing expansion of LNG, increasing the availability of gas globally. In recent years, the substantial growth in the world energy demand has increased the interest in the exploitation of natural gas reservoirs previously deemed undesirable due to their high acid gas content. Existing technologies for natural gas purification, such as chemical absorption with alkanolamine solvents, may be not suitable for treating highly contaminated natural gas due to the required higher solvent circulation rate and, consequently, to the energy demand for solvent regeneration. Over the last decades attention has been devoted to the study and development of low-temperature CO2 removal processes. With these new technologies, CO2 is separated as a high-pressure liquid making it easier to be pumped underground for sequestration or utilization in Enhanced Oil Recovery (EOR) projects. The aim of this work is to analyze natural gas purification technologies and liquefaction schemes for the production of LNG starting from the same acid natural gas stream. In particular, two CO2 removal technologies are considered to bring CO2 concentrations down to levels suitable for LNG production: the conventional chemical absorption technology with activated-MDEA (aMDEA) as solvent and the recently patented Dual Pressure Low-Temperature (DPLT) distillation technology. Different commercial technologies are taken into account for the liquefaction of the purified natural gas: Propane-Mixed Refrigerant (C3MR), Mixed Fluid Cascade (MFC), and Single Mixed Refrigerant (SMR). However, since these liquefaction processes are designed for a sweet gas obtained using a conventional acid gas removal technology, some adjustments have been made for their application to a low-temperature sweet gas. The choice to compare a conventional technology with a novel low-temperature one has been made to understand if the synergy between a CO2 removal technology operated at low-temperature and the downstream liquefaction process is advantageous, despite the need for refrigeration also in the CO2 removal step. The different process schemes resulting from the combination of the two CO2 removal technologies with the liquefaction ones have been simulated in Aspen HYSYS® V10 and their performances are assessed and compared by means of energy and exergy analyses, respectively based on the “net equivalent methane” approach and on the exergy efficiency concept. Results suggest that, although the aMDEA absorption process and the DPLT distillation one with downstream NGLs recovery have about the same specific energy consumption when applied to the natural gas stream taken into account in this work considering the CO2 removal step only, the overall process (including the liquefaction of the purified natural gas stream) involving the DPLT distillation technology is characterized by lower consumptions and a higher exergy efficiency.

中文翻译：

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LNG 生产链中酸性气体脱除过程的能量和火用分析

摘要 在向零碳能源领域转型的过程中，天然气的增长速度远远快于石油或煤炭，因为它是一种环保燃料，受到 LNG 持续扩张的支持，增加了全球天然气的供应量。近年来，世界能源需求的大幅增长增加了人们对开采天然气储层的兴趣，这些天然气储层以前因酸性气体含量高而被认为是不可取的。现有的天然气净化技术，例如用烷醇胺溶剂进行化学吸收，可能不适合处理高度污染的天然气，因为需要更高的溶剂循环速率，因此，溶剂再生需要能源。在过去的几十年中，人们一直致力于研究和开发低温 CO2 去除工艺。借助这些新技术，CO2 被分离为一种高压液体，从而更容易被泵送到地下进行封存或在提高石油采收率 (EOR) 项目中加以利用。这项工作的目的是分析从相同的酸性天然气流开始生产 LNG 的天然气净化技术和液化方案。特别是，两种 CO2 去除技术被认为可以将 CO2 浓度降低到适合 LNG 生产的水平：以活性 MDEA (aMDEA) 作为溶剂的传统化学吸收技术和最近获得专利的双压低温 (DPLT) 蒸馏技术。纯化天然气的液化考虑了不同的商业技术：丙烷混合制冷剂 (C3MR)、混合流体级联 (MFC) 和单一混​​合制冷剂 (SMR)。然而，由于这些液化工艺是为使用传统酸性气体去除技术获得的脱硫气体设计的，因此已经对其应用于低温脱硫气体进行了一些调整。选择将传统技术与新型低温技术进行比较是为了了解在低温下操作的 CO2 去除技术与下游液化过程之间的协同作用是否有利，尽管在 CO2 去除过程中也需要制冷步。在 Aspen HYSYS® V10 中模拟了将两种 CO2 去除技术与液化技术相结合所产生的不同工艺方案，并分别基于“净当量甲烷”通过能量和火用分析来评估和比较它们的性能方法和火用效率概念。结果表明，尽管 aMDEA 吸收过程和带有下游 NGL 回收的 DPLT 蒸馏过程在应用于本工作中仅考虑 CO2 去除步骤的天然气流时具有大致相同的比能量消耗，但整个过程（包括涉及 DPLT 蒸馏技术的纯化天然气流的液化）的特点是消耗量低和火用效率高。