Comparison of DCMD and VMID for Treatment of Produced Water from Unconventional Gas Extraction

Unconventional gas extraction by hydraulic fracturing generates a huge amount of high salinity wastewater that needs to be treated to enable its reuse and to reduce the amount of wastewater that has to be disposed. Membrane distillation is a technology with a small economic footprint that can utilize low quality waste heat to obtain almost pure water from high salinity solutions. This study compared the energy requirements of direct contact membrane distillation (DCMD) and vacuum membrane distillation (VMD) to concentrate saline wastewaters. Based on the fundamental heat and mass transfer in membrane distillation, APSEN Plus simulations were developed to simulate DCMD and VMD processes with heat recovery. The effect of heat recovery on the gain output ratio (GOR) and specific electrical energy consumption (SEEC) of both process was studied. While DCMD can recover a significant amount of energy from the permeate stream, VMD offers no heat recovery. Moreover, it was found that DCMD becomes more efficient with an increasing driving force (i.e., temperature difference between feed and permeate), whereas VMD showed a decrease in efficiency at high vacuum conditions.

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