Distillation for hydraulic fracturing flowback treatment: Hydraulic fracturing (fracking) injects a high-pressure water and sand mixture underground to crack rock. It frees natural gas or oil trapped in rock, most commonly shale. Shale formations are generally 4,000 to 14,000 feet beneath the ground, well below drinking water aquifers that are commonly 250 to 1,100 feet deep. Despite what some think, hydraulic fracturing poses minimal risk to drinking water aquifers because of the distance between them and the activity.
The earliest stage in the excavation process is to drill a horizontal well, which is rotated sideways at the depth of the shale to drill through the stone. The completion phase, in which fracking occurs, follows drilling. During this phase, a steel casing is inserted downhole and cemented into position. A perforating gun is inserted into the drilled well where explosive charges are precisely detonated to add little holes through the casing cement into the rock.
After detonation, a high-pressure frack pump injects water and sand with about 1 percent chemical additives into the well. The chemicals in the mixture often include acids, chloride, polyacrylamide, ethylene glycol, sodium or potassium chlorate, citric acid, isopropanol, and other chemicals. The high-pressure pumps crack the shale rock further, and the sand and chemical additives keep the fissures propped open so that the natural gas or oil can be discharged.
After this, the area that was hydraulically fractured is plugged, and the process continues down the length of the horizontal well. Next, the plugs are drilled away, and hydraulic fractured fluid is extracted and natural gas or oil is brought to the surface for use.
This initial procedure may take up to four months, but the well can be produced for up to 35 years. However, public concern has arisen over the management of fracking fluids. Properly disposing of hydraulic fracturing fluid is an expensive process for energy companies and a public environmental pollution concern. This column examines options for handling these fluids.
Membrane distillation
Membrane distillation (MD) is a cost-efficient desalination process involving the evaporation and condensation of volatile components through a membrane that is porous and separates the volatile components from water. It can treat salinity that is too high for traditional desalination. Then the water can be further processed at a treatment facility. After this, the water can be recycled and used in other industrial applications. With MD, deep injection may be unnecessary.
Vapor compressor-driven MD system
A vapor-compressor-driven, MD system concentrates produced water from the fracking process to reduce costs and enable water reuse. MD combined with vapor compression can manage the high-salinity produced waters associated with unconventional gas production.
Tests yielded noticeably decisive results such as: more than 90 percent process uptime without visible reduction in functioning or demand for cleaning, reliable achievement with brine concentrations approaching saturation, lower energy use compared to established technology, and high distillate quality.
As the cost of brine concentration decreases, treatment options that are more fitting than trucking water to treatment facilities and deep-well disposal will evolve. The treated water from this process can be reused and will decrease the quantity of clean water needed per well, further reducing costs and minimizing potential environmental harm.
Thermal distillation & crystallization
Fracking creates higher concentrations of total dissolved solids (TDS) in flowback water, the solution that flows up to the surface during and after fracking. It contains chemicals that typically cannot be removed with membrane technology. However, they are treatable by distillation and crystallization.
Distillation and crystallization are established technologies that rely on evaporating the wastewater to separate the water from the TDS. The vapor stream moves through a heat exchanger to condense the gas and produce distilled/purified water. Distillation can withdraw up to 99 percent or 990,000 parts per million (ppm) of the TDS and can reduce handling and removal costs by up to 70 percent for treating water from shale oil development.
As with reverse osmosis, distillation requires energy. Thermal distillation can treat flowback water having up to, and in some cases even surpassing, 110,000 ppm of TDS, but the most state-of-the-art technology has maximum flow rates of approximately 300 cubic meters (m3), 79,250 gallons per day (gpd), which requires building large storage containments or using multiple storage units. For instance, flowback water from gas sites can produce at rates of more than 300 m3, more than 79,250 gpd.
Developments include mechanical vapor recompression schemes to concentrate flowback water, which can be less expensive than traditional distillation because the high-temperature compressed vapor preheats the influent.
Water evaporation to create dry mineral crystals improves water rehabilitation and creates salt products for reuse as industrial feedstocks. Crystallization is viable for treating flowback water with TDS concentrations as high as 290,000 ppm, but it requires high energy and substantial capital investment.
Known in the industry as “Wastewater Dan,” Dan Theobald, proprietor of Environmental Services, is a professional wastewater and safety consultant/trainer. With more than 24 years of hands-on industry experience operating many wastewater treatment processing units, he is anxious to share his knowledge with others.
