正渗透处理页岩气返排液过程中膜污染机制与控制研究

Shale gas is a clean and abundant unconventional gas resource. The drilling and completion of wells require large quantities of fresh water, and a large percent of which returns to surface as flowback water. High salinity and complexity of the flowback water make it difficult to treat. Forward osmosis (FO) technology is a newly emerging technology for the treatment of shale gas flowback water. However, membrane fouling remains a key limiting factor for the widespread application of FO process. This project tries to employ FO membranes to treat the flowback water of shale gas in China which is characterized with high total dissolved solids and high organics. Firstly, FO membrane fouling experiments for treating flowback water from different shale gas wells at various phases will be carried out to identity major membrane foulants, to analyze the spatial and temporal variations of the major membrane foulants, and to search for universal membrane foulants. Secondly, the deposition and removal of the major foulants on membranes will be investigated. The interaction between major foulants and FO membranes will be analyzed by XDLVO theory, the relation between foulant-membrane interaction and membrane fouling will be evaluated to illustrate mechanisms of FO membrane during filtration of flowback water. Then, the key influencing factors of membrane fouling will be determined by reducing the concentrations of major membrane foulants, decreasing the deposition of foulants on membranes and increasing the removal of foulants. Thus, specific methods will be proposed to control the fouling of FO membrane. This study can provide theoretical and technical supports for the widespread application of FO membranes in shale gas flowback water treatment.

页岩气是一种清洁、大储量的非常规天然气资源，在其开采过程中消耗巨量淡水的同时会产生大量的返排液。返排液中盐度高、成分复杂，这增加了其处理难度。正渗透技术是处理页岩气返排液的新兴技术，然而，膜污染是其应用的主要限制因素。本项目拟针对我国高盐、高有机物的页岩气返排液，通过开展多口页岩气井不同阶段返排液的正渗透膜污染实验，识别页岩气返排液中的关键膜污染物质，分析其普适性与时空变化规律；明确关键膜污染物质在膜上的沉积规律，利用XDLVO理论解析污染物与膜之间的微观界面相互作用，探索其与膜污染之间的关系，阐明主要膜污染物质的正渗透膜污染机制；明确膜污染的关键影响因素，提出通过减少进水中关键膜污染物质含量、调控关键污染物-膜之间相互作用和去除沉积在膜上的关键污染物的措施来控制膜污染。本项目的研究成果将为正渗透技术在我国页岩气返排液处理中的推广应用提供理论依据和技术支撑。

伴随着页岩气产业的快速发展，开采过程中产生了大量水质成分复杂的返排液，由此造成的环境污染及其有效的管理和处理问题已经引起广泛关注。本项目聚焦于正渗透技术在页岩气返排液的应用，通过分析国内外页岩气返排液的水量与水质特性,综述了膜技术在页岩气返排液处理中的应用现状、挑战及前景，提出了基于膜技术、高选择性的吸附和分离等技术的水资源和有价值元素的回收利用的策略，评估了页岩气返排液中稀土元素的含量及回收潜能。考察了超滤作为正渗透预处理时超滤膜的污染特性，研究了不同膜工艺的出水或浓水作为反冲洗用水时超滤膜的污染特性；采用重力驱动膜过滤系统应用于页岩气返排液的长期处理，处理出水作为后续正渗透工艺的进水，考察了过滤水头和膜结构对过滤性能的影响，探讨了稳定通量的形成机制。系统研究了肥料驱动正渗透处理页岩气返排液时汲取液类型和运行模式对膜性能的影响，评估了正渗透稀释的肥料汲取液用于植物灌溉的可行性，并阐述了不同灌溉用水对植物生长特性差异的原因。本项目的研究成果将为正渗透技术在我国页岩气返排液处理中的推广应用提供理论依据和技术支撑。