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A Low Pressure Electrolyzer (LPE) is being developed to provide metabolic oxygen aboard US nuclear submarines. The system is derived from a more complex system already developed for the Virginia Class of attack submarines. The LPE generates up to 250 standard cubic feet per hour (SCFH) of oxygen at ambient pressure through electrolysis of water utilizing SPE® (Solid Polymer Electrolyte) technology. The hydrogen is generated at pressures suitable for disposal overboard. The system operates unattended which minimizes crew workload, and can safely shut down without crew intervention. Generating oxygen at ambient pressure significantly reduces risk to personnel and greatly simplifies the system. Reliability, maintainability, safety, and ease of operation are major system design drivers.

Submarines, aircraft, and manned space vehicles require oxygen for human respiration. On-board generation through the electrolysis of water is a practical means of obtaining this oxygen. Proton exchange membrane ceils have been in production for many years. Existing system designs are based on maintaining the oxygen and hydrogen sides of the cells at nearly equal pressures. Recent technical advances allow high differential pressure cell stacks, which permit direct discharge of one gas at low or ambient pressure while supplying the other gas at high pressure. This capability simplifies system and component designs and results in improved reliability, safety, and operability. This paper updates the development status of high differential pressure SPE® electrolysis cells and provides test results from prototype assemblies.

Submarines, aircraft, and manned space vehicles require oxygen for human respiration. Onboard generation through the electrolysis of water is a practical means of obtaining this oxygen. Proton exchange membrane cells have been in production for many years. Existing system designs are based on maintaining the oxygen and hydrogen sides of the cells at nearly equal pressures. Recent technical advances allow high differential pressure cell stacks, which permit direct discharge of one gas at low or ambient pressure while supplying the other gas at high pressure. This capability simplifies system and component designs and results in improved reliability, safety, and operability. This paper updates the development status of high differential pressure SPE ® electrolysis cells and describes systems for applying this technology to submarine and aircraft applications.

The Water Reclamation and Management System (WRM) for the Environmental Control and Life Support System (ECLSS) has changed dramatically since Space Station Freedom (SSF) Restructure. What was two separate processors: the Potable Water Processor (PWP) and the Hygiene Water Processor (HWP), is now one combined system called the Water Processor (WP). This combined system is required to process the waste hygiene, handwash, and laundry waters, the Temperature and Humidity Control (THC) condensate, Shuttle fuel cell water, and the urine distillate, to produce potable quality water. The WP is composed of four major functions: waste water collection and storage, processed water storage and delivery, contaminant removal, and microbial separation between the waste and processed water. The two water storage and delivery functions are accomplished using vented bellows tanks and pumps.

In 1979, a test was initiated to evaluate the use of dissimilar metals in close conjunction with each other, including aluminum, stainless steel and an Al-Ti-Al laminate heat exchanger, in a closed deoxygenated water coolant loop over an extended vehicle life. The closed, sealed loop contained distilled, deoxygenated water initially supplied at <0.3 ppm by weight dissolved oxygen. The system involved a variety of dissimilar metals, including 300 series CRES, 6061 aluminum alloy, gold-nickel braze alloy and thermometer bi-metallics. Coatings were also used to provide added protection to the aluminum. A stainless steel to aluminum transition tube was sandblasted, passivated, alodined and coated with P.D. George epoxy coating No. 923. The heat exchanger was of plate fin construction with parting sheets made of an Al-Ti-Al laminate designed to prevent through wall pitting in case corrosion attack initiated.

The Water Recovery and Management (WRM) Subsystem on Space Station Freedom is part of the Environmental Control and Life Support System (ECLSS). The WRM provides water to the crew for drinking, food preparation, washing, and bathing. Water is also provided for equipment use such as electrolysis in order to generate crew metabolic oxygen. In addition, any excess water is made available for experiment uses. The primary function of the WRM is to collect waste water, process it to remove contaminants, store the recovered water for reuse, and finally, to distribute it to users within the habitable modules of the Space Station. The WRM is divided into two separate collection/distribution loops: one is used to recover condensate to potable standards for crew consumption, and the other is used to recover waste hygiene water back to hygiene standards for crew bathing and equipment use.

Recent development of the solid amine/water desorbed (SAWD) CO2 control system technology has resulted in two preprototype systems. The SAWD I system was developed under NASA Contract NAS9-13624 and is currently under test in the NASA Johnson Space Center, Crew Systems Division Advanced Environmental Control Systems (ECS) Laboratory. The SAWD II system is being developed at Hamilton Standard Division of United Technologies (HSD) under NASA Contract NAS9-16978. This paper reviews the development history of solid amine CO2 control systems and describes the SAWD I and SAWD II systems. In the development of the SAWD II system, special attention was given to reducing its power requirements and to designing the system to be compatible with zero-gravity operation. Energy saving features are discussed, and the zero-gravity solid amine canister test program and selected design are described.

Maintaining the ambient CO2 partial pressure as low as practical within available space and power limitations is desirable for the extended submerged operations of modern nuclear submarines. Existing liquid amine systems are designed to control CO2 partial pressure to a minimum of 0.5 percent. Advanced technology utilizing commercially available solid amine resin is being developed for an improved CO2 removal system capable of 0.2% CO2 partial pressure. The solid amine is regenerated by heating it with atmospheric pressure steam. Amine bed dynamics during the regeneration process allow the CO2 to be highly concentrated. The major components in this system's conceptual design include four beds of solid amine resin, a process air fan, a steam generator for amine regeneration, a condensing heat exchanger, and a CO2 compressor. A sequencing controller provides continuous system operation by cycling the solid amine beds between CO2 absorption and regeneration.