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Direct contact membrane distillation (DCMD) has immense potential in the desalination of highly saline wastewaters where reverse osmosis is not feasible. This study evaluated the potential of DCMD for treatment of produced water generated during extraction of natural gas from unconventional (shale) reservoirs. Exhaust stream from Natural Gas Compressor Station (NG CS), which has been identified as a potential waste heat source, can be used to operate DCMD thereby providing economically viable option to treat high salinity produced water. An ASPEN Plus simulation of DCMD for the desalination of produced/saline water was developed in this study and calibrated using laboratory-scale experiments. This model was used to optimize the design and operation of large scale systems and estimate energy requirements of the DCMD process. The concept of minimum temperature approach used in heat exchanger design was

A B S T R A C THydraulic fracturing used for natural gas extraction from unconventional onshore resources generates large quantities of produced water that needs to be managed efficiently and economically to ensure sustainable development of this industry. Membrane distillation can serve as a cost effective method to treat produced water due to its low energy requirements, especially if waste heat is utilized for its operation. This study evaluated the performance of commercially available hydrophobic microfiltration membranes in a direct contact membrane distillation system for treating very high salinity (i.e., up to 300,000 mg/L total dissolved solids) produced water. Polypropylene and polytetrafluoroethylene membranes yielded the highest permeate flux with membrane distillation coefficient of 5.6 l/m 2 /hr/kPa (LMH/kPa). All membranes showed excellent rejection of dissolved ions, including naturally occurring radioactive material (NORM), which is a significant environmental concern with this high salinity wastewater. Analysis of membranes after extended testing with actual produced waters revealed unevenly distributed inorganic deposits with significant iron content. A key finding of this study is that the iron oxide fouling layer had negligible effect on membrane performance over extended period of time despite its thickness of up to 12 µm. The results of this study highlight the potential for employing membrane distillation to treat high salinity wastewaters from unconventional gas extraction.

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The Unites States natural gas (NG) pipeline system is a complex network that relies on about 1800 compressor stations (CS) to maintain the pressure in the network. Concurrently, about two-thirds of the fuel energy to CS is lost as waste heat mainly in the form of hot flue gases. However, to date, there has been little emphasis on quantifying available waste heat at NG CS. We determine the quantity, quality, and spatial distribution of waste heat available at existing NG CS using thermodynamic analysis, installed capacity of NG CS reported by the U.S. Energy Information Administration (EIA), and load factors. The uncertainty in operating hours of CS is addressed by the concept of load factor and statistical Monte Carlo simulations. The analysis indicates that an average of 610 TJ/day is available in the U.S. at temperatures above 645 K. Recovering available waste heat from NG CS has the potential to avoid emissions of 47 000 metric tonnes of CO2-equiv/day at the national level. The large quantity of available waste heat highlights the critical need for development of waste heat recovery technologies. The insights from this work are helpful in identifying regional opportunities and constraints for feasibility of waste heat end-uses.