Integration of Ejector-Based Flare Gas Recovery and Desalination Processes for Produced Water Onsite Treatment in Shale Gas Production

Flaring is a major concern in the oil & gas industry because it wastes valuable raw materials/energy and emits a substantial amount of air pollutants. Also notable, the produced water treatment during oil and gas production is troublesome due to its large processing volume, high salinity, and expensive disposal cost. Thus, the on-site integration of flaring gas recovery and desalination processes for handling produced water could not only monetize flare emission sources, but also generate freshwater for versatile usages. In this paper, a novel process integrating the ejector-based flare gas recovery process with the thermal vapor compression (TVC) based desalination process (EFGR-TVC) has been developed. It replaces the compressor by an ejector in the flare gas recovery system to power the TVC desalination process more efficiently. The proposed study includes three progressive stages of work: (i) creating a process simulation for the EFGR-TVC process; (ii) operating sensitivity analysis; and (iii) performing an economic evaluation and comparison. In the first stage, rigorous modeling and simulation are conducted for the newly developed EFGR-TVC process. In the second stage, critical design variables affecting the thermal efficiency as well as the system performance are examined, i.e., the sensitivity study for energy intensity (EI) and specific area (SA) for heat transfer with feed water salinity (X), compression ratio (CR), and motive pressure (Pm) will be investigated. In the third stage, fixed and operating costs are examined and compared with the compressor-based TVC process. The simulation results have shown that the replacing the compressor by an ejector in the flare gas recovery system to power the TVC desalination process will be more efficient and economical at normal operating conditions. The EFGR-TVC process could save about 33% capital cost and 16% operating cost per year compared with the compressor-based flare gas recovery TVC process. This study provides a valuable conceptual design to help the oil & gas industry solve both flare emission and produced water treatment issues simultaneously and cost-effectively.