Reverse Osmosis

In 1954, the U.S. Navy launched the Nautilus, the first nuclear powered submarine. Using nuclear power to generate steam to drive a submarine’s propulsion system allows the vessel to stay under water for long periods of time without refueling. Nuclear power is now the primary method of generating power for propulsion for the U.S. Navy’s fleet of fast attack and ballistic missile submarines.

Supporting the nuclear submarine fleet is a research and development facility located in the upstate New York town of West Milton. Known as the Knolls Atomic Power Laboratory and run by the defense contractor, Lockheed Martin, the laboratory is engaged solely in research and development for the design and operation of improved naval nuclear propulsion plants and reactor cores.

A chief requirement in testing the submarine nuclear propulsion systems includes generating steam to run turbines. It is necessary to use extremely high-purity boiler make-up water in making this steam to avoid the problem of scale build-up on the turbines due to the heavy metals, calcium and salts that are present in untreated feed water. When scale builds up on the turbines, they begin to operate inefficiently.

Due to the high maintenance and monitoring costs to produce process water for nuclear submarine reactor research, a U.S. Navy laboratory decided to replace a mixed bed deionization system with a dual-pass reverse osmosis (RO) system from ITT Industries’ Aquious unit.

Navy Lab Sought Cost-effective Replacement

When the laboratory initially contacted ITT Industries’ Aquious unit, they were processing raw water from the municipality through a mixed bed deionization unit. Mixed bed deionizers produce water containing the lowest ionic concentrations and are most commonly used when ionic contamination is such that other filtration systems alone cannot be relied upon to produce water of acceptable quality. Additionally, deionizers are often used in industrial applications involving reclamation of heavy metals.

While circumstances vary, it is generally not economical to use deionization alone to produce large volumes of purified water. If deionizers are operated to exhaustion, ions previously removed may be released, possibly at concentrations exceeding that of the incoming water.

The customer found that although the mixed bed deionization unit was producing high quality process water, the costs for maintaining the system—both in terms of changing the resins needed for the process as well as monitoring the system—were very high. The Aquious Water Equipment Technologies unit was charged with the task of designing a low-operating cost water filtration system that allowed for more automatic operation and remote monitoring while providing the high quality water required to test the nuclear propulsion systems.

Dual-pass RO System Provides Solution

With a required flow at the laboratory of 25 gpm, Aquious Water Equipment Technologies designed a dual-pass RO system. Installed in the boiler room of the facility, the system takes the municipal city water and runs it through a set of RO membranes. It then takes the product of that first pass and runs it through a second set of membranes.

According to Tom Morgan, a filtration system engineer with Aquious Water Equipment Technologies, “With the first RO pass, we are removing 98% of heavy metals, calcium, magnesium and salts. On the second pass, we are taking out another 98% of the contaminants from the first pass. At the end of the dual-pass process, the quality of the water is one level under deionized water, but certainly pure enough for the requirements of the laboratory.”

Aquious delivered two, dual-pass systems mounted on a skid. Having a redundant system—each capable of producing 25 gpm—allowed the laboratory to provide for system downtime. The customer required a great deal of instrumentation, and all of the system’s controls were designed to be integrated into a single package.
The customer also asked for a high degree of automation.

“They wanted to sit at their desks and see all of the operating parameters, pressures, flows and water quality readings,” Morgan said. “They wanted to be relieved from the time-intensive operation of the mixed bed deionization system and be able to just push a button to switch machines, adjust valves and otherwise operate the filtration system from the desktop.”

The cost savings from using the RO system were immediate. The mixed bed deionization unit had been producing process water at a cost of approximately $50 per 1,000 gal. Including energy consumption, consumables and maintenance, the RO system provided by ITT is producing process water at approximately $6 per 1,000 gal. Additionally, the membrane filters that form the heart of the RO system only need to be replaced every three to five years, greatly lowering total lifecycle costs.