By Art Haddaway, Industrial WaterWorld Editor
Industrial desalination has come a long way in the last several years, particularly with respect to the field of oil and gas. Ongoing developments with innovative trends and technologies across the nation -- both onshore and offshore -- have brought large-scale improvements to the industry. These advancements are paving the way for oil and gas desalination processes to be more water-conscious, cost-competitive and energy-efficient.
In the United States, industrial desalination is growing more prominent and is an essential component for reusing and repurposing saline water for critical processes, as well as providing sustainable sources of fresh water for various applications. According to the Congressional Research Service (CRS), approximately 2,000 desalination plants larger than 0.3 million gallons per day are in operation around the country, representing more than 2.4 percent of freshwater use. Further, it noted that the industrial sector accounts for about 18 percent of total U.S. desalination capacity.
As the industrial desalination industry continues to expand, the demand for new technologies used to produce high-quality water supplies and to reclaim contaminated supplies -- including from oil and gas development -- continues to grow, the CRS explained. These technologies encompass membrane treatment such as reverse osmosis (RO), as well as thermal techniques such as distillation, and deal with unconventional extraction methods, like hydraulic fracturing; conventional exploration, such as oil wells; and enhanced oil recovery (EOR), including chemical injection.
"There's a lot of work going on with the desalination industry for applications --both membrane and thermal -- and new ideas of how to use low energy or renewable energy to improve operations and reduce costs," said Leon Awerbuch, a director at the International Desalination Associate (IDA) and chief executive officer of Leading Edge Technologies (LET). "Many companies today are looking for ways to recover this water and minimize disposal -- to find an economic solution to deal with water being produced from their oil and gas operations."
While it's imperative that the industrial sector adopt new desalination technologies and replace older systems with more advanced solutions, plants also face ever-increasing financial, environmental and regulatory challenges. The CRS indicated that from construction to operation, the costs of current desalination systems are increasing, requiring federal and state permits; processes are becoming more energy-intensive, raising concerns about climate change and greenhouse gas emissions; and existing technologies are having a larger environmental impact, potentially threatening public health and aquatic wildlife -- especially as it relates to disposal.
Awerbuch explained that reducing costs, reusing water and minimizing discharges are the three most important factors when dealing with all aspects of the desalination process, including the rejection of brine on the ground. "There's a shortage of water in the first place. The permit to obtain the water is of significant cost to the developer of oil and gas companies," he said. "You then have highly concentrated brine in the flowback of produced water, and therefore you need to dispose of it -- that disposal costs a lot of money, even if you reject it without having environmental problems."
Accordingly, it's important that industrial desalination processes recognize these challenges and ultimately establish some effective solutions they can bring to the table. As Awerbuch previously mentioned, there is much research and development underway with regard to membrane and thermal technologies and enhancing or replacing current systems. Further, other prospects involving, for example, nanofiltration (NF), vapor compression and humidification and dehumidification are a possibility but often vary based on the type of oil and gas application, its location, amount of effluent discharged, condition of regulations, and mainly operational costs.
"Although desalination costs have dropped in recent decades, significant further decline may not happen with existing technologies," the CRS indicated. However, "emerging technologies (e.g., forward osmosis [FO], capacitive deionization and chlorine-resistant membranes) show promise for reducing desalination costs. Research to support emerging technologies and to reduce desalination's environmental and human health impacts is particularly relevant to future adoptions of desalination and membrane technologies."
When incorporating desalination technologies, there is a particularly strong focus on addressing zero-liquid discharge (ZLD), pretreatment, pressure recovery, and low-temperature sources of energy, to name a few. Moreover, optimizing costs, improving yields and complying with water quality and effluent regulations is of great concern.
Awerbuch noted that in addition to advancements in RO and NF, there is much research and development occurring with membrane pretreatment such as ultrafiltration and microfiltration for total dissolved solids (TDS) below 70,000 ppm, as well as thermal approaches such as mechanical vapor compression (MVC) and multi-effect distillation (MED) for TDS ranges of 100,000 to 250,000 ppm. "The LET patented technology of combining an NF softening membrane with an MVC or MED process allows recovery of a significant amount of distillate and at the same time concentrates the brine without risk of scaling in the evaporators," he said.
"This approach offers the advantage of lower capital and operating costs," continued Awerbuch. "The softening NF membranes are characterized by the ability to reject, in simple terms, over 98 percent of sulfate, over 60 percent of barium, calcium and magnesium ions, and only 10 to 40 percent of chloride ions from the solution at high fluxes and low driving pressure. The idea is based on successful demonstration of this process by LET of softening seawater for improving efficiency and output of thermal desalination plants."
With regard to unconventional gas extraction, Awerbuch explained that many production firms face problems obtaining the needed water for fracking and disposal of the flowback water. In many areas, the amount of clean water is not available, while disposal of the contaminated produced or flowback continues to be a significant issue. As a whole, he noted that this water can be sourced for the fracking job, reused as fracking makeup water, recycled to upgrade the flowback water to required specifications for the makeup water, or disposed of on or off site via transportation or other methods.
"The best solution to this combined water supply and wastewater disposal problem is to treat and recycle the flowback water, over and over again, as frack water," he said. "Treatment of the flowback water to remove suspended solids and scale forming impurities renders it suitable for recycle." This is especially relevant for the Marcellus Shale of the Northern Appalachian region, estimated to contain around 170 trillion cubic feet of natural gas, where a high occurrence of horizontal drilling with high-pressure water and sand produce a large amount of produced and flowback water.
Devesh Sharma, a director at IDA and managing director of Aquatech, serves the Marcellus Shale play in Pennsylvania and explained that the company operates a division, Aquatech Energy Services, which focuses on working with oil and gas producers to deliver water treatment and management services across national and international shale plays. The company operates central facilities where producers can send their water for treatment or disposal, as well as satellite facilities using mobile units to treat water on a well pad. Additionally, Aquatech offers water logistics services to different parts of the state, contributing to the wastewater recycling business "by taking one customer's wastewater, moving it, treating it, and turning it into another client's source water for their next frack," he said.
"Although finding the right technology is important, packaging these technologies with a customer-focused service offering is fundamental, as the dominant money spent in this market is still simply trucking the water to and from a well site," said Sharma. "This could be to a disposal well or a central facility. So, treatment only makes sense when it can cost-effectively reduce or eliminate volumes of water to be trucked off site or, more importantly, assist a gas producer in reusing water for the next frack. Aquatech's water management service offering is packaged to target reduction of trucking costs by bringing recycle and reuse options closer to where the wastewater is produced."
In relation to EOR, Sharma also noted that certain desalination methods exist to improve yields from oil wells, as demonstrated in Western Canada, where steam is used as a predominant form of oil extraction to flood wells. "Recycling the produced water to put back into the ground as steam is an important issue for these oilfields," he said. Aquatech's evaporation technology, for example, has been the staple of many steam-flood projects in Western Canada and in the Middle East. Sharma added that other emerging trends include "smart water" plants that condition water to a particular TDS and sulfate level.
Compared to traditional processes, new and advanced desalination technologies are ideally designed to extract the highest possible amount of saline and polluted water in the system, as Thermal Purification Technologies Limited (TPTec) also demonstrates. A clean-tech startup, TPTec's thermal technologies are built with advanced thermodynamics to ultimately establish simple and robust facilities that can repurpose existing waste or low-value streams to purify challenging feeds -- all with a minimum of residual effluents, said Espen Mansfeldt, chief executive officer.
"The key challenge today is to use existing waste or low-value streams from oil and gas exploration (and other industrial processes) to reduce the amount of effluent generated," said Mansfeldt. "Increasingly, the industry is facing restrictions (or higher costs) on the discharge. Therefore, developing new, efficient and robust technologies to reduce effluents -- including full separation of water and solids -- is a clear priority."
He indicated that TPTec has already developed two full-scale facilities and are now available for commercialization. The first was built in El Gouna, Egypt, with a capacity of 500 m3/day and features LTDis (low-temperature distillation) technology, which uses direct evaporators and condensers to clean challenging feeds (see Fig. 1). The second was built in Würenlingen, Switzerland, with a capacity of 20 tons/day of sewage sludge and features LTDry (low-temperature drying), which was built on the same principles as LTDis, where the dry material is used as a carrier for the process to take place.
"The oil and gas market particularly needs robust (no sensitive membranes or tube bundles) and flexible (mobile, part load tolerant, capable of handling variations in the feed) solutions. Either alone or in combination, the technologies offer an ideal route to ZLD," said Mansfeldt. "LTDis can handle feedwater with high levels of dissolved solids (up to and into precipitation, typically at 300,000 to 330,000 ppm) plus significant levels of hydrocarbons. As there is often low-grade heat (40-100°C) available (flare gas, steam production, diesel gensets, etc.), robust thermal technologies are particularly well-suited for this market."
Awerbuch added that other companies such as Oasys, Memsys, Trevi, Hydration Technology Innovation, and more, for example, are targeting highly advanced desalination-centric technologies in an effort to expand their services and ultimately contribute to the ongoing development of oil and gas desalination.
One example of a breakthrough in this field is a process invented by engineers at the University of Colorado Boulder that can simultaneously remove both salts and organic contaminants from oil and gas wastewater, all while producing additional energy.
The new technology, called microbial capacitive desalination, produces advanced microbes to consume energy-rich hydrocarbons contained in the effluent that ultimately releases their embedded energy, which is then used to produce positively- and negatively-charged electrodes, similar to a battery. "Because salt dissolves into positively- and negatively-charged ions in water, the cell is then able to remove the salt in the wastewater by attracting the charged ions onto the high-surface-area electrodes, where they adhere," a press release noted.
The researchers have co-founded the start-up BioElectric Inc., and are in the process of scaling up the technology to eventually commercialize it and provide a viable solution for oil and gas companies.
