Closing the Loop on Aqueous Cleaning at Hamilton Standard

by: Robert W. Jenkins
Pages: 18 - 22; November, 1995

Hamilton Standard, a division of United Technologies Corporation, is a manufacturer of a variety of aerospace components, including environmental control systems, propeller systems and jet engine controls. The Hamilton Support Systems (HSS) business unit, based in East Windsor, CT, overhauls and repairs all Hamilton Standard products and is an FAA repair station. HSS manufactures ground support equipment, principally component test stands.

As an overhaul shop, HSS must maintain the capability to clean a variety of part configurations. Parts such as jet fuel control housings or valve bodies have intricate passages and many internal features, while propeller hubs, jet engine disks or stators are larger in size and have many external features.

Prior to 1993, HSS used traditional vapor degreasers using 1-1-1 trichloroethane and perchloroethylene to remove soils ranging from baked-on carbon and grime to machine coolants, cutting oil, fingerprint oil and preservatives. Due to tightened environmental standards, product labeling laws and the Montreal Protocol, HSS decided to eliminate the use of ozone-depleting chemicals in its plants. In 1993 HSS procured and installed six cabinet type spray washers and four ultrasonic cleaning systems using aqueous cleaners to replace the vapor degreasers.

Waste generation was a major consideration during the switch to water-based cleaning. Local regulations required that no cleaning baths or rinses should be discharged to the town sewer. To minimize the effect of this regulation, all spray washers and ultrasonic cleaners were equipped with oil skimmers, coalescers or water conditioning systems to extend the life of the cleaning baths and rinses.

In spite of the steps taken, HSS was not prepared for the dramatic increase in the amount of water-based waste generated by these new cleaning systems. Prior to the introduction of water-based cleaning, HSS generated approximately 2,200 gallons per month of non-hazardous water-based waste. This waste was composed mainly of machine coolant, wet dust collector waste and vacuum furnace cooling water. After installation of the aqueous cleaning systems, generation of water-based waste jumped to 4,700 gallons per month. At that time, the only disposal option available to HSS was removal by a licensed waste handler at a cost of approximately $0.37 per gallon. Clearly, some kind of in-house treatment was required to reduce disposal costs and allow for recovery and re-use of the water.

Four treatment technologies were considered for the water-based waste: resin columns, atmospheric evaporators, membrane systems and vacuum distillation. Each method has advantages and disadvantages which will be discussed briefly.

Mixed bed resins are very effective for on-line treatment of spray washer and ultrasonic cleaner rinse tanks, and are used on several HSS cleaning systems. For lightly contaminated rinsewater, a 0.9 cubic foot mixed bed resin bottle is capable of providing 50,000 ohm quality water at two gallons per minute. HSS found that by cycling the rinse through the resin column for an hour in the morning and by treating city water make-up, effective rinsing was maintained. The disadvantage is that as contaminant loading increases, efficiency of the resin decreases, and bottles have to be replaced more frequently. Therefore this type of system is not appropriate for treatment of large amounts of heavily contaminated aqueous waste.

Atmospheric evaporators provide volume reduction by boiling waste water and allowing the vapor to escape into the atmosphere. This system can treat any kind of water-based waste and can be sized for whatever volume is required. Disadvantages are that the system is energy intensive, does not allow recycling of water and air emission permits may be required.

Membrane systems, such as micro- or ultrafiltration, are very effective in removing solids or molecules such as oil and grease from waste streams. Soap, however, tends to foul the membranes. Also, each membrane must be designed for a specific waste stream and typically must be replaced if the process changes or a different waste is to be treated.

Vacuum distillation is a process in which water-based waste is boiled in an enclosed vessel under vacuum. Low surface tension of the liquid in the vessel allows the liquid to be boiled between 50 and 90°F. The vapor is then condensed to a pure distillate, leaving contaminants or reclaimed chemicals behind. The system is flexible in that it can treat many different waste streams. Carryover of contaminants is also minimized and energy efficiency is increased because the liquid is boiled at such a low temperature. Moreover, systems can be sized to provide whatever capacity is required. Further, vacuum distillation allows for recycling of process chemistry and provides a source of distilled water which can be re-used in the factory.

After considering the various treatment options available, HSS elected to procure a vacuum distillation system for treatment of the water-based wastes. Vacuum distillation was chosen primarily because HSS desired to treat many types of water-based waste streams, including aqueous cleaners, machine coolant, wet dust collector waste, vacuum furnace and cooling tower water and air compressor condensate. The system would be required to provide 1,000 gallons of clean distilled water in a 24 hour period and provide a minimum of 90 percent volume reduction of wastewater. The system would have to run continuously with minimal operator intervention. HSS determined that the successful treatment system supplier would be required to design, build and install a complete turnkey system, including transfer pumps, holding tanks and interconnecting wiring and piping.

HSS ultimately procured its vacuum distillation system from Calfran International of West Springfield, MA. Calfran proposed a vacuum distillation system, sized for 1000 gal/24 hr (Figure 1).

Figure 1
Cold Vaporization Process

The system consists of a PVC reaction vessel, holding tanks for liquid waste, distillate and concentrate, vacuum pump, heat and cold source, transfer pumps and interconnecting wiring and piping. The system operates under a vacuum of 10-20 mm hg. Wash and rinses from the cleaning equipment are drained, cleaned and replaced on a two-week to two-month frequency depending on the cleanliness required of the parts and the number of parts processed through the equipment. The waste is drained from the equipment into a 300 gallon tote container, which is then transferred to a central treatment area in the shop. The totes are then drained to a waste holding tank. Waste is drawn into the reaction chamber and is boiled at 50°-90°F. Additional waste is introduced to the reaction vessel as the liquid boils away. The vapor passes through a mist eliminator and is condensed on the cooling side of the vessel. Distillate is then transferred to a holding tank for later use in the factory as make-up for the aqueous cleaners. Concentrate is periodically bled from the reaction chamber and transferred to a concentrate holding tank for off-site disposal. The whole system is balanced using a series of level controls and solenoid valves.

Traditional vacuum distillation systems use a refrigeration package to provide cooling for the distillate. Heat rejected from the condenser is used to boil the waste. In the HSS plant, however, factory steam and chilled water are used allowing elimination of a refrigeration package.

HSS has been tracking waste generation data for several years. For the five months prior to the change-over to aqueous cleaning, water-based waste, generated and disposed off-site, averaged 2,200 gallons per month (Figure 2). After implementation of aqueous cleaning in June 1993, the amount generated and disposed off-site rose to an average of 4,700 gallons per month. The Calfran unit became operational in March, 1994. For the six months ending January 1995, the average waste generated was 5,950 gallons per month. Of that, however, 3,235 gallons per month were distilled by the Calfran unit and re-used in the shop. As a result, the amount required to be disposed off-site was reduced by 2,000 gallons per month, at a cost savings of about $740 per month. As time passes, it is expected that cost savings will grow as HSS increases the scope of waste water distillation and recycling.

Figure 2
Water Based Waste Generated at HSS

Once the Calfran unit became operational, HSS took the additional step of integrating vacuum distillation with an existing ultrafiltration treatment process for fluorescent penetrate inspection (FPI) rinse water (Figure 3). The system is configured so that permeate from the ultrafiltration system may be cycled through the vacuum distillation system and subsequently used as make-up for the FPI area. The proportion of permeate actually recycled depends on the volume of other aqueous waste that needs to be processed. The process and flow balances are still being developed, but HSS is considering increasing operation of the vacuum distillation system from eight to 24 hours per day to accommodate additional volume.

Figure 3
Integrated Treatment and Recycling System

Overall, HSS has found vacuum distillation to be a flexible and effective method for reducing disposal costs of water-based waste. HSS continues to explore factory applications for vacuum distillation and strives to increase the proportion of waste water processed, further reducing the amount to be disposed off-site. Other potential applications include treatment of floor scrubber wash water and vapor blast water. These other waste streams would require filtration prior to distillation due to high solids content. HSS also searches for opportunities to reduce the total amount of waste generated, recognizing that source reduction of waste, pollution prevention and recycling not only is good for the environment, but has a beneficial effect on the bottom line.

About the Author

Robert Jenkins has been employed by Hamilton Standard for nine years and is currently Supervisor of Facilities Engineering. He is leader of a cross-functional team that replaced vapor degreasing with aqueous cleaning plant-wide. Robert holds a BSME from Lehigh University and a MBA from the University of Hartford (CT).

Grateful acknowledgment is made to Phylis Warner and Jon Becker for their assistance in the preparation of this article.