May 6, 2014 9:59 pm
In a little more than a year, Boston-based Gradiant’s humidification-dehumidification (HDH) technology has gone from a lab at MIT to being selected as GWI-WDR’s Technology Idol to commissioning its first commercial installation, which was then selected as GWI’s Industrial Water Project of the Year. That installation has also validated Gradiant as a legitimate, revenue-generating oilfield service company.
Gradiant’s technology is based on a carrier gas extraction (CGE) process, which recirculates air through a humidifier and multistage bubble column dehumidifier in a closed loop. As saline feedwater enters the unit, it is preheated in the dehumidifier before being heated an additional 10-15°C (18-27°F) using a natural gas-fired boiler. Some of the feedwater is evaporated as it is sprayed over a packed bed and condensed as distillate in the dehumidifier. Meanwhile, the non-evaporated portion of the feed is removed as saturated brine and the now re-humidified air is then returned to the dehumidifier column to continue the process.
Last week, WDR visited the company’s first installation near Midland, Texas, in the Permian Basin’s Spraberry-Wolfcamp play (see following story). The system was installed and began operating late last year, and has now been in continuous commercial operation for the last four months, producing 500 bbl/d of distillate and 3,500 bbl/d of pretreated water, which is returned to the client for reuse.
According to Prakash Govindan, Gradiant’s chief technology officer, the company’s client—one of the largest independent oil and gas companies operating in the region—diverts up to 4,000 bbl/d of produced water from a nearby disposal well to Gradiant’s site for treatment. “Not only does our client save money on disposal costs for every barrel sent to us, they are able to reuse both the treated water and the brine we produce,” said Govindan.
He noted that Gradiant operates as a service company, owning and operating all of the equipment and charging a fixed tariff for all water that passes through their facility, based on the level of treatment provided.
The feedwater, which has a total dissolved solids (TDS) ranging from 95,000 to 140,000 mg/L, first undergoes chemical softening before it is conditioned with polyaluminum chloride (PAC) and clarified in a lamella settler. While the sludge is dewatered for disposal in a landfill, 500 bbl/d of the pretreated effluent is sent to the HDH system for distillation, and the remainder is pumped to ‘clean brine’ tanks for reuse as drilling fluids.
The HDH system produces distillate with a TDS of less than 100 mg/L, which can be reused in hydraulic fracturing. It usually operates at a volumetric recovery of 70 percent in the process of producing 10-pound brine, although its design flexibility allows it to be operated at a recovery of more than 85 percent when operating in a ‘salt production mode’.
A proprietary algorithm, which relies on sensors located at all relevant thermodynamic points in the system, monitors the humidity, temperature, concentrations and flow rates of all fluids and continuously optimizes the system to run at peak thermal performance.
Based on the performance of the distillation system, Gradiant has received a contract to install seven more modular HDH units at the site to treat the full 4,000 bbl/d pretreated effluent. The expanded capacity is expected to be operational later this summer.