US Navy aims for more energy-efficient desalination

The US Navy hopes to find a way to make saltwater fresh that uses significantly less energy than current desalination technologies.

The Office of Naval Research (ONR) is sponsoring the research to help ensure freshwater supplies 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 J. Paul Armistead, an ONR programme officer with interests in water purification. “We plan to build prototype desalination units that will use 65 per cent less energy and be 40 per cent smaller by weight and by volume relative to current Navy reverse osmosis systems. They should require roughly 75 per cent 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 Programme, or EUWP.

Before the advent of modern desalination technologies, mariners relied on the freshwater they collected from rain and stowed while at sea. Today, most US Navy ships rely on high-tech, reverse osmosis desalination for their water supplies.

The energy for converting saltwater to fresh on ships comes from burning fuel to spin turbine generators that produce electricity for ships’ systems. More efficient desalination would therefore mean more efficient ships, which would reduce fuel consumption, extend combat capability and lower the Navy’s carbon footprint.

Since its inception, the EUWP programme has produced a number of advances in desalination technology. The first-generation 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 demonstrator has already 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, Mississippi. The device was trucked in and set up on the shores of the Gulf of Mexico, approximately four blocks from the hospital. It 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 technology demonstrator is a larger, more stationary unit with the 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, California.

Armistead said he anticipates increased capabilities from the newer demonstration unit.

“From current Navy desalination systems we only get 20 per cent 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 US Bureau of Reclamation, is a member of the ONR team managing the research programme. She noted the programme has generated benefits for 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 programme, the Advanced Shipboard Desalination, Future Naval Capability Programme 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 utilised by ever-increasing drought ridden areas.”