On offshore oil and gas platforms and vessels, a supply of fresh water is essential, not only for drinking but also to keep critical machinery and equipment operational. Rig managers, water quality managers and design engineers face several challenges when it comes to finding the right desalination solution for generating potable and ultra-pure water. Before selecting a system, consider the following factors:
- Type of technology
- Application requirements
- Supplier attributes
- System capabilities
What is desalination?
Desalination is a process that purifies seawater by removing salt and other minerals, making it suitable for human consumption (potable) and various industrial uses such as ultra-pure applications.
Ultra-pure water is water that has been treated to the highest levels of purity for all contaminant types, including organic and inorganic compounds, dissolved and particulate matter, volatile and non-volatile, reactive and inert, hydrophilic and hydrophobic, and dissolved gases. A typical ultra-pure water system has three stages:
- Pretreatment stage to produce purified water
- Primary stage to further purify the water
- Polishing stage, the most expensive part of the treatment process
Many technical applications on offshore rigs such as turbine wash, water-based hydraulic fluids, boiler feed, turbine cooling and power augmentation require ultra-pure water.
Desalination technologies for ultra-pure water
Reverse osmosis (membrane-based)
Reverse osmosis (RO) is a popular technology used for desalination. Seawater is passed through semi-permeable membranes to remove salt and minerals. The water is then treated by electrodeionization. In this stage, the water produced is sent to gas-liquid separation membranes that allow gas, but not liquid, to pass through before the water is sent to an electrodeionization water treatment module. This module utilizes electricity and ion exchange resin to deionize the water to further reduce dissolved ions (impurities) and produce ultra-pure water.
Environmentally friendly, an RO system replaces single-use ion exchange media and devices that use salt for regeneration of the media. Unlike ion exchange technology, there is no need to purchase and ship materials back and forth and there is less waste to dispose of.
Most ion exchange systems are comprised of pressure vessels filled with ion exchange resin operated on a cyclic basis. Water flows through the resin until the resin is considered exhausted when water leaving the exchanger contains more than the desired maximum concentration of the ions being removed. Resin is then regenerated by sequentially backwashing the resin bed to remove accumulated solids, flushing removed ions from the resin with a concentrated solution of replacement ions, and rinsing the flushing solution from the resin. Production of backwash, flushing, and rinsing during regeneration of ion exchange media limits the usefulness of ion exchange for a number of applications as it creates a waste stream that must be disposed of.
Advantages of membrane-based desalination technology
Using membrane-based desalination technology carries many advantages including:
- Consistent high-quality water production
- Minimal operator intervention
- Plug and play system
- Many configurations to fit specific applications
- Global availability of parts and service providers
The chart below shows contaminant removal achieved with various membrane filtration systems.
What to consider before contacting a supplier
Before contacting a desalination system supplier, it’s advisable to have the scope of the requirement in perspective. Prepare a list of key specifications and priorities. Detail the conditions, resources and primary objectives for application of the system for the supplier. It’s also important to prepare questions and concerns that the experts in the technology can address. Tapping the knowledge base of a qualified, experienced supplier can be invaluable to the ultimate success of the project. Be prepared to answer these questions about your application:
- What is the seawater inlet quality in TDS (total dissolved solids)?
- What is the seawater inlet quality in TSS (total suspended solids)?
- What is seawater minimum and maximum inlet temperature range?
- How much fresh water is required per day?
- What is the quality of the freshwater required?
- What is the available voltage and amperage?
- Where will the system be located?
- What is the minimum and maximum ambient temperature?
- What are the required area classifications?
- Are there any space constraints?
Selecting a desalination system supplier
When selecting a desalination system, choosing the right supplier is critical for reliable, cost-efficient operation. Downtime is not an option on a remote vessel. Important factors to consider include:
- Reputable company
- Application engineering
- Design and packaging expertise
- Vertical integration to allow for proper material selection
- Experience with successful system installations operating in similar applications
- Global presence to allow for parts and service availability
Well-known for its engineering excellence, product quality and premier customer service, Parker Hannifin has been providing desalination and water purification systems to the oil and gas, marine, defense, disaster relief, and power generation markets for over 35 years.
Parker specializes in vertical system integration, meaning that all system parts and components are manufactured by Parker. The advantages of partnering with a one system solution provider include improved efficiency, immediate parts availability, design expertise, and lower overall system cost. With locations in 50 countries, 13,000 distribution outlets, and 24/7 worldwide support, global parts availability and service is guaranteed.
Ultra-pure RO water generation system
The Parker Ultra-Pure Water Generation System, designed for offshore, upstream oil and gas installations, uses RO technology to produce an endless supply of ultra-pure, high-grade water for a variety of critical applications. Features include:
- Compact footprint
- Modular design for easy maintenance and expansion
- Low operating expenditures
- ATEX, CLASS I Div. II., ABS Type Approved - Compliant with IEEE, NEC, UL,
- NORSOK Explosion proof ratings: - NEC class 1, division 1 - NEC class 1, division 2 - IEC 60079 zone 2, group IIA
- The entire system, from frame to membranes, contains Parker parts, guaranteeing high-quality and reliability
- Worldwide parts availability
- Uses advanced membrane filtration technology that maximizes system recovery and minimizes discharge
- Media filter, carbon filter, de-chlorination pretreatment
- 2nd pass system for turbine/boiler water requirements
- Re-mineralizer post-treatment for pH neutralization
- Chlorination post treatment
- Ultraviolet light germicidal systems
- Status and alarm signal for remote monitoring
Selecting the right desalination system for an offshore installation can be challenging. It’s important to not only look at the capabilities of the system but to also consider the supplier and its reputation, level of experience, design expertise, global presence, and support services. That’s the formula for success.
This post was contributed by the Parker Water Purification Team.