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Multi-level approach to successful water treatment

Upstream and downstream facilities all use water, and may need different methods to handle treatment of used water.

Multi-level approach to successful water treatment

The underlying principle in the Water-Energy nexus is that it takes water to produce energy, and vice versa. As a result, there are many opportunities for water treatment in Oil and Gas facilities – both upstream and downstream. They include water treatment for steam generators, pilot plants, produced water treatment, temporary mobile water treatment until wells are proven, and potable water treatment for remote camps. 

Determining the optimal water treatment programs for each of these needs is based on several criteria, starting with each customer’s specific goals such as increasing energy efficiency or reducing costs, and then ranging from solutions to deal with specific water quality issues to addressing logistical challenges that might dictate the need for temporary mobile solutions.

Culligan Matrix Solutions has worked extensively with oil & gas companies to devise solutions that meet a wide variety of needs. Following are some examples of how the combination of experience and innovation has helped these companies achieve their goals.

Higher water quality for higher pressure steam generation
Steam Assisted Gravity Drainage (SAGD) is an enhanced oil recovery process employed to produce heavy crude oil and bitumen, widely used in western Canada and other parts of the world. In a SAGD process, two parallel horizontal wells are constructed a few meters above each other. Steam is then generated and pumped into the upper well to soften or reduce the viscosity of the crude oil. This allows the oil and condensed steam to drain to the lower well.

The steam and the gases flow to the upper well due to the lower density. The condensed steam and crude oil are pumped back up to the surface. The crude oil or bitumen is then separated from the water. This water is treated, topped up with new water, and returned to the steam generators. Treated water is essential for proper operation of steam generators. Conventional steam generators employ low pressure, low quality saturated steam. This type of boiler water treatment includes chemical treatment or softening.

An alternative is the implementation of packaged high pressure boilers, which require higher water quality. This type of treatment may require ultra softening (less than 1 ppm of hardness) and/or membranes.

Culligan designed and installed a PLC controlled water treatment system for the high pressure steam generators in a pilot plant. The system included two pre-filters to reduce sediments in the raw water supply. The 50 gpm duplex alternating softener system was used to provide ultra soft water to the steam generators. The ultra softener system featured primary and polishing softeners in series to meet the customer’s water quality specification for the steam generators. 

Generate multiple savings
In other oil and gas applications, naturally occurring minerals such as Calcium, Magnesium and Silica can cause scale in steam boilers and other types of equipment used in refinery operations. Scale deposits in steam boilers can reduce equipment efficiency and increase energy, chemical, disposal and maintenance costs. 

Hot lime softening is a traditional treatment technology used to remove hardness and alkalinity from boiler feed water. However, the process used by a refinery posed several challenges: 
• First, the refinery was looking to increase the energy efficiency and reduce costs associated with boiler blow down requirements.
• Second, the refinery wanted to lower the hot process softener maintenance and the associated equipment plugging and cleaning that was required.
• Third, the refinery wanted to eliminate handling of lime slurry and related waste disposal costs.
• Finally, the refinery sought to reduce the boiler treatment chemicals associated with the current process.

Culligan proposed a skid mounted water treatment system to achieve these goals. The solution included multi-media filters, a chemical treatment system, a re-pressurization system, reverse osmosis membranes and a polishing softener.

The first component of the solution is the multi-media filters. The feed water is first passed through two multi-media filters. The multi-media filters contain layers of media that remove suspended solids and prepare the feed water for further treatment down the process.

The second component of the solution is a chemical treatment system. Chemical are added to the water to remove silica, which scales reverse osmosis membranes. Furthermore, chemical treatment was also used to reduce free chlorine, which can damage the reverse osmosis membranes.

The third component was a re-pressurization system that increased the feed pressure to approximately 300 psig before the feed water enters the reverse osmosis membranes. The application of pressure to the influent water forces the water through the semi-permeable membrane.

The fourth component was the reverse osmosis (RO) membranes. Osmotic membranes perform the best level of filtration and are barriers to salts and to organic substances including micro-contaminants. Reverse osmosis also eliminates the need for chemical regenerants used in the previous hot lime softening process. 

The fifth component of the system is a polishing softener – the final step before the water enters the boilers.

This solution helped the facility increase equipment and process efficiency, reduce boiler treatment chemicals, reduce maintenance costs and minimize waste.

The most significant benefit was the reduction in boiler blow down as a result of the increase in the cycles of concentration from 7.5 cycles to 65 cycles. The energy savings as a result of the reduction in boiler blow down was approximately $165,000 per year. The reduction in boiler chemicals helped the company save approximately $36,000 per year. Furthermore, maintenance and waste disposal savings were approximately $20,000 and $4,300 per year, respectively. The net annual savings from the Culligan solution was approximately $200,000 for this application alone. 

Going mobile
Mobile water treatment systems are an ideal solution for fast response, emergency situations, supplemental, or temporary requirements. They are often used to assist oil and gas customers during plant start up and maintenance outages when the plant's water treatment system is unavailable or cannot meet the water production requirements. Examples include situations where wells are not proven and the evaporators are not on-line; in these scenarios, a temporary water treatment trailer is an ideal option.

Mobile plants fulfil a variety of needs and address a myriad of situations such as peak demand, capacity expansion, equipment breakdown, emergency rentals, plant commissioning, and wastewater minimization – any circumstance where production demand for clean water exceeds existing system capacity.

Culligan’s mobile water treatment fleet provides comprehensive multi-level water purification, monitoring, and control in a single solution for oil and gas facilities. The modular system is designed to accommodate a wide variety of feed sources (i.e., brackish water, surface water and seawater). It can be operated in a rugged environment and can be installed quickly to seamlessly provide large quantities of water on demand.

These systems utilize varying technologies depending on the customer's feed water conditions, desired application and final product water quality requirements. Pre-treatment including clarification, multi-media filtration, carbon filtration and softening, is used to prepare feed water for further use. In some cases, anti-scalants and chemicals may be used to address specific feed water conditions and operational circumstances.

The standard mobile offering includes reverse osmosis, which provides an advanced level of filtration and is an effective barrier to salts, micro-contaminants, and organic substances, making it ideal for applications where high-purity water is needed. Culligan’s mobile units are available as containers that can be dropped off at the customer site as well as skid-mounted systems. A standard container produces 200 gpm, and the capacity is scalable to meet the customer's needs.

Effective water treatment programs are essential aspects of oil & gas exploration and refinery operations. Devising successful solutions depends on a relationship between the oil & gas company and a water treatment partner that is rooted in a clear understanding of the company’s goals, the ability to accommodate specific site and water quality requirements, and ready access to the most appropriate – and often multi-level – technologies.