A company, Purestream Technology, is employing a combination of proprietary elements, called Induced Gas Flotation (IGF) and Accelerated Vapor Recompression (AVARA), to provide a comprehensive wastewater treatment regime for production, frac, and flow-back water for the oil and gas industry. The system is integrated on a mobile platform that can be easily adapted on site from wellhead to wastewater treatment facility.
The IGF module takes care of total suspended solids (TSS) and hydrocarbon recovery, while the AVARA module handles produced water purification, fresh water recovery, and brine concentration. Both modules are described as thermally efficient processes, cost effective with reduced air emissions, allowing for recapture of sour gas/b-valve gas. Waste heat from power generation can be used to help fuel the processes.
In the Level 1 IGF system, the wastewater input stream containing hydrocarbons and other suspended solids is routed through the IGF separator, where suspended solids and hydrocarbons are mechanically skimmed from water and isolated. The IGF process involves introducing gas into the wastewater stream via an educator, which coalesces the oil/solids; releasing the water in a separation vessel; skimming the “floated” oil and solids from the surface of the vessel; and discharging clarified effluent from the bottom of the vessel.
The IGF combines all of these actions in a said-to-be-unique vertical design by using finely dispersed gas to reduce the apparent density of the oil and solids, increase their droplet size, and greatly increase buoyancy through coalescence. The vertical annular riser eliminates the potential for short-circuit flow found in some horizontal designs and combines “column flotation” technology with its down-flow design, which promotes flotation of oil at the surface. The resultant water stream is polished by IGF, effectively removing 97 percent of TSS. Valuable hydrocarbons are recovered and isolated to on-site storage tanks and made available for future sales.
The Level 2 AVARA system utilizes a thermal membrane to separate produced water from the condensing chamber. Steam is then pulled from the evaporation side of the membrane and compressed by a blower into the condensing side of the membrane, utilizing a unique, state-of-the-art technology designed specifically to minimize fouling issues. As it is compressed, the steam condenses onto the thermal membrane and releases energy through the membrane into the evaporation side. This, in turn, increases evaporation, creating a loop that cycles the energy while evaporating water.
The resulting distilled water can be put to beneficial use for field operations, with non-detectable levels of total dissolved solids (TDS) and TSS. This system can also capture vent or flared gas to utilize as a fuel for the heat and energy required to operate. Large volumes of water are processed with very net little energy cost, according to Purestream, since the energy expelled during the condensing phase feeds the evaporation phase.
The integrated unit is configured via trailer mount or single container, providing accessibility to the oilfield operations. AVARA can be site-customized to process from 100 bbl/day to 100,000 bbl/day. The final output stream is said to be clean enough that it can be run through final process to create potable water.
Purestream points out that, where feasible, reusing flow-back water and produced water has both environmental and economic benefits. It reduces demand for fresh water and reduces produced water disposal volume. It also reduces truck traffic for hauling water, which can be a significant savings. A 20,000 cu-m frac with 50 percent flow back would otherwise require 300 truck trips for disposal, the company says.
Of course, reuse doesn’t always make sense. It depends on a number of considerations, including economic (water quality, chemicals, energy cost, transportation, storage), logistical (centralized versus mobile, trucking versus piping, disposal options), and regulatory (improved permitting time, lined versus unlined pits).