Desalination

The US Department of the Navy announces new technology and modifications to existing reverse osmosis technology to reduce operational and maintenance cost for desalination and potable water treatment.

Desalination Technology Increases Naval Capabilities, Meets Humanitarian Needs

Released: 9/23/2009
Point of Contact:
Public Affairs
Office of Naval Research
Corporate Communications Office
Phone: 703-696-5031
Fax: 703-696-5940
E-mail: onrcsc@onr.navy.mil

ARLINGTON, Va.—The next generation of technology to turn saltwater into a fresh resource is on tap for the Navy. The Office of Naval Research (ONR) is sponsoring the development of an innovative solution for generating potable water at twice the efficiency of current production for forces afloat, Marine Corps expeditionary forces and humanitarian missions ashore.

"Saving energy and producing clean water is a tactical issue for the Navy," said Dr. J. Paul Armistead, an ONR program officer with interests in water purification. "We plan to build prototype desalination units that will use 65 percent less energy and be 40 percent smaller by weight and by volume relative to current Navy reverse osmosis systems. They should require roughly 75 percent less maintenance."

Delivering drinkable water for ships at sea and Marines ashore for less cost and less energy became an ONR priority in 2004 under the Expeditionary Unit Water Purification Program, or EUWP.



(Read a transcript | Download a fact sheet)

Before the advent of modern desalinization plants, mariners relied on the fresh water they collected from rain and stowed while at sea. Today, Sailors and Marines benefit from high-tech, Reverse Osmosis (RO) desalinization plants aboard most U.S. Navy ships.

It takes energy to make water, and that energy comes from burning fuel to spin turbine generators that produce electricity necessary for ship systems, including RO plants. A more efficient desalinization plant translates into a more efficient ship, which uses less fuel, extends combat capability and reduces its carbon footprint.

Since its inception, the EUWP program has produced advances in desalinization capability. The first generation EUWP technology demonstrator was designed as a deployable high water production unit more easily transported by the military and used for a variety of missions.

In fact, the EUWP Gen 1 demonstrator has been used in a number of humanitarian missions. In 2005, it was deployed in support of the Navy´s response to Hurricane Katrina where it delivered safe drinking water to Gulf Coast residents being treated at a hospital in Biloxi, Miss. In this case, the EUWP Gen 1 was trucked in and set up on the shores of the Gulf of Mexico, approximately four blocks from the hospital. The Gen 1 unit desalted and purified about 100,000 gallons of water per day from the turbid Gulf of Mexico, replacing the daily caravan of 18 tankers needed to keep the hospital running.

The second generation EUWP Gen II technology demonstrator, built with shipboard constraints imposed on the design, is a larger, more stationary demonstration unit, and has potential for use by isolated communities. It has been tested successfully at the Seawater Desalination Test Facility at the Naval Facilities Engineering Service Center in Port Hueneme, Calif.

Armistead anticipates increased capabilities from the newer demonstration unit. "From current Navy desalination systems we only get 20 percent product water," he said. "That means for 1,000 gallons of feed water, we would get only 200 gallons product water. These new systems will likely double that."

Michelle Chapman, a physical scientist with the U.S. Bureau of Reclamation, is a member of the ONR team managing the research program. She highlighted the program´s success by noting its benefits to the public at large. "Several of the projects we have funded have turned into patents for commercially available products and processes that are available for use in water desalination systems for communities where freshwater sources are not available," Chapman said.

Based on the successes in the EUWP program, the Advanced Shipboard Desalination, Future Naval Capability Program will begin in 2010. Navy Surface Warfare Center Carderock Division, Ship Systems Engineering Station (NSWCCD-SSES), is a partner in this effort. According to Dave Nordham, a NSWCCD-SSES mechanical engineer, "Any sort of technology advancements we find for ships are directly applicable ashore and can be utilized by ever-increasing drought ridden areas."

Key partners in the EUWP program include NSWCCD-Philadelphia, U.S. Army Tank Automotive Research Development and Engineering Command, U.S. Bureau of Reclamation and the Naval Facilities Engineering Service Center´s Seawater Desalination Test Facility at Port Hueneme, Calif.

---

About The Office of Naval Research

The Department of the Navy´s Office of Naval Research provides the science and technology necessary to maintain the Navy and Marine Corps´ technological advantage. Through its affiliates, ONR is a leader in science and technology with engagement in 50 states, 70 countries, 1,035 institutions of higher learning, and 914 industry partners. ONR employs approximately 1,400 people, comprising uniformed, civilian and contract personnel.

Pitfalls In Specifying Reverse Osmosis Equipment In Industrial Applications

Applications

This discussion is the first of several which address pitfalls in selecting or purchasing reverse osmosis machines.

Raw Water Temperature

The density of water changes with temperature; its maximum density is reached in the form of ice at 32° F and its density decreases almost linearly as its temperature increases. Since reverse osmosis involves the passage of water molecules through a semi-permeable membrane, the "thicker" or more dense the water, the slower the passage.

In reverse osmosis applications, most feedwater temperature fluctuates based on ambient temperature, often ranging from 40° F to 70° F if sourced from lakes, rivers or streams. Well water in much of the world maintains stable year-around temperatures of ~ 55° F. In arid or tropical areas, the temperature of well and surface waters will be significantly higher.

Confusion and potential misapplication of RO equipment ensues because many years ago, manufacturers of RO membranes selected 77° F as the standard or "normalized" temperature at which to rate the flow capacity of their membranes. However, very few real world applications use a feedwater which is consistently at 77° F. For example, technical specifications from most RO manufacturers list a 100 gallons per minute (gpm) RO with small print at the bottom of the page indicating this is at 77° F. However, if the raw water fluctuates as described above, the "100 gpm" RO output will be approximately 52 gpm at 40° F and 88 gpm at 70° F. Obviously if the system is selected based on output at 77° F, there will be a deficit, equal to 50% during some months of the year. While your vendor should point this out, not all may be aware, or they may fear that sizing the machine correctly for the lowest possible feedwater temperature will make them uncompetitive since it requires a larger machine with more membranes.

In the above example, the machine must be sized for the lowest temperature, requiring one rated for ~190 gpm at 77° F in order to produce 100 gpm at the low temperature of 40° F. When the feedwater reaches 70° F, this machine will be producing about 165 gpm. This presents the following critical design considerations:

1. The RO product water storage tank should be designed with enough capacity to avoid turning the RO on and off due to high water more frequently than ~ 30 mins when operating at the peak feedwater temperature.
2. Piping design and sewer capacity must be capable of handling a reject (wastewater) stream ranging from 33 gpm to 55 gpm.
3. Pretreatment equipment (e.g., softener, depth filter, iron filter, carbon filter) must be capable of treating the range of feedwater demanded by the RO, ranging from 133 gpm to 220 gpm.
4. Incoming raw water supply must be capable of supporting a flow of 133 to 220 gpm at the minimum dynamic pressure required (typically 35 psi).
5. Integration of a variable frequency drive RO pump in the initial design can help modulate the flow since pump output is adjustable.
   

Temperature is one of several very important considerations involving RO equipment and ancillary equipment design. The following chart provides temperature correction factors for a wide range of feedwater temperatures.

Enlarge image.

Advantages of Combining Chemical Water Treatment With Equipment

Most companies in the business of treating boilers and cooling towers offer chemical treatment alone. The possibility of removing dissolved minerals as part of the treatment program may not be presented to their customers since it often drastically reduces chemical consumption. However, removing dissolved minerals such as calcium (hardness) feeding a boiler will not only decrease chemical consumption (in the form of scale inhibitors) but will save energy by reducing blow down. Specifically, boilers evaporate water into steam, leaving dissolved minerals behind in the boiler where they will form damaging scale if allowed to accumulate beyond a certain concentration. Chemical scale inhibitors minimize scaling to a point. However, as the mineral concentration increases, scaling will occur even with proper chemical treatment so water from the boiler is periodically dumped to sewer (blown down) to allow feed water with lower mineral concentration to enter (make-up water). Blown down water is typically 212° to 250° F, so in addition to the cost for water and sewer fees, the energy cost can be very high. When scaling minerals are removed, the need for blowing down the boiler is greatly reduced, significantly saving energy as well as water and sewer costs.

Treating boiler make-up water with reverse osmosis can reduce blow down significantly more since 98% or more of all dissolved minerals are removed. Depending on the size of boiler and operating pressure, amount of condensate returned and mineral content of the feed water, savings can be in the hundreds of thousands of dollars annually. View Reverse Osmosis Savings Article.

Utilization of side stream filters on cooling tower recirculation loops frequently remove many pounds of suspended particles daily. Since suspended solids react with chemicals such as corrosion inhibitors and biocides, filtration sharply reduces the use of these chemicals. Towers also require blow down to keep the dissolved mineral concentration within certain limits or scaling will occur (as water evaporates from the tower, the minerals are concentrated in the sump). Mineral reduction upstream of the tower can often lower the blow down as well as the chemicals required. Recovery and reuse of tower blow down water using treatment equipment is another option.

By offering water treatment equipment as well as chemicals, the WaterProfessionals® are well positioned to thoroughly assess your water treatment requirements. Equipment technologies offered include reverse osmosis, delakalization, softening, ultrafiltration, nanofiltration, sand and multimedia filtration. Many customers opt to have the WaterProfessionals own and operate the equipment 24/7 and administer chemical treatment on their premises. Learn more.