Abstract:

The fracturing flowback fluid produced during the hydraulic fracturing process of shale gas has the characteristics of complex composition of pollutants, high concentration of total dissolved solids and heavy metals. The "dual carbon" target has prompted the fracturing flowback fluid treatment industry to urgently transform its carbon emission reduction. Membrane technology, as one of the key low-carbon technologies for energy conservation and emission reduction, has the potential to reduce industrial energy consumption by up to 90%. This study focused on the integrated membrane process of "pretreatment-tubular ultrafiltration-nanofiltration-electrodialysis-reverse osmosis-mechanical vapor recompression" for treating the fracturing flowback fluid, and conducted a comprehensive life cycle assessment (LCA) and analysis of each treatment process from the perspectives of pollution reduction and carbon reduction. The results revealed that the carbon footprint of the integrated membrane treatment process amounted to 86.7kgCO₂eq. In terms of the global warming impact category, the carbon footprint contribution of pretreatment, tubular ultrafiltration membrane and mechanical vapor recompression was 90.7%, which was primarily attributed to reagents utilized in the pretreatment process while substantial electricity consumption was resuled from high-frequency operation of the processes. For the greenhouse effect and other typical indicators, the sensitivity of influencing factors was as follows: electricity > sodium carbonate > sodium hydroxide. Therefore, reasonable and efficient operation of the equipment could save energy loss and ensure low-carbon operation. This study clarified that pretreatment, tubular ultrafiltration and mechanical vapor recompression process were the keys of pollution and carbon reduction that should be focused on for the treatment of fracturing flowback fluid.

Key words: fracturing flowback fluid, membranes, waste water, environment, life cycle assessment (LCA), carbon footprint

摘要：

页岩气从水力压裂开采过程中产生的压裂返排液具有污染物种类复杂、总溶解性固体和重金属浓度高等特点。我国“双碳”目标的提出促使压裂返排液处理技术亟需低碳减排转型。膜分离技术作为一种节能减排关键低碳技术之一，可减少工业领域90%的能耗。本研究基于“预处理-管式超滤-纳滤-电渗析-反渗透-机械蒸汽再压缩”膜集成工艺处理压裂返排液，采用全生命周期评价对其物耗、能耗、碳足迹及环境影响评价进行分析，结果表明：该集成处理工艺的碳足迹为86.7kg CO₂ eq；对于温室效应影响类别，预处理、管式超滤膜、机械蒸汽再压缩的碳足迹贡献为90.7%，其原因是预处理阶段所投加的大量药剂以及管式超滤膜和机械蒸汽再压缩系统高频率运行所消耗的大量电能。针对温室效应指标及其他典型指标，其影响因素敏感性大小为：电力>碳酸钠药剂>氢氧化钠药剂，因此管式超滤膜和机械蒸汽再压缩系统的合理高效运行可节约电力损耗，保证该系统的低碳高效运行。本研究明确了预处理、管式超滤、机械蒸汽再压缩单元是压裂返排液处理工艺应重点关注的减污降碳环节。

关键词: 压裂返排液, 膜, 废水, 环境, 生命周期评价, 碳足迹