DryWash™
Hughes Environmental Systems, Inc.,
and Global Technologies, LLC
From industrial laundries that service military installations to retail dry cleaners that cater to the public, the garment-cleaning industry affects billions of people and generates nearly $20 billion in worldwide revenue each year. Unfortunately, the most commonly used dry-cleaning solvent, a chlorinated organic liquid known as perchloroethylene (perc), poses serious health and environmental hazards, and the costs of environmental compliance for perc have skyrocketed to the point that many cleaners cannot afford to operate. As a result, the dry-cleaning industry is searching for a viable alternative.
Los Alamos National Laboratory, Hughes Environmental Systems, Inc., and Global Technologies, LLC, have developed an innovative dry-cleaning process that offers such an alternative. This process, called DryWash™, cleans with liquid carbon dioxide (CO2) that is applied through high-pressure fluid jets. As an odorless, nonflammable, nonhazardous solvent, CO2 effectively removes oils, sweat, and dirt from a wide variety of fabrics. In addition to its environmental and performance benefits, DryWash™ also reduces dry-cleaning costs by lowering energy consumption, run times, and labor costs.
The Invention — Characteristics and Advantages
Carbon dioxide has been used in the past to clean a variety of electronic, mechanical, and optical equipment, but DryWash™ is the first process that uses CO2 as a cleaning solvent for fabrics. In the DryWash™ system, liquid CO2 at 54°F-58°F and 700 pounds per square inch--a pressure comparable to that used for soft-drink units at restaurants--is pumped from a storage tank into the cleaning vessel, and a recirculating loop is established.
During the cleaning cycle, the CO2 must remove CO2-soluble soil, water-soluble soil, and pigment soil (insoluble in both CO2 and water). The CO2-soluble soils, including body oils, dissolve in the nonpolar, liquid CO2 and are carried from the cleaning vessel. The water-soluble soils, such as salts, are usually removed by agitation. The most difficult to remove are the pigment soils, which are chemically bound to garments or mechanically trapped between adjacent fibers of the fabric.
The design of the cleaning vessel makes DryWash™ particularly effective at removing pigment soils. The garments are held in a perforated basket inside a stationary cleaning vessel. To get mechanical action equivalent to that of the rotating basket found in conventional dry-cleaning equipment, DryWash™ uses a process called hydrodynamic agitation, in which nozzles located on the inside periphery of the basket spray high-speed jets of liquid CO2. The jets create a vortex that causes the clothes to spin around inside the basket. As the outermost garments pass through the fluid jets, they momentarily stretch slightly, and once they have moved away from the jets, they relax to their original size. This stretch-relax cycle effectively dislodges particles. The layer of peripheral fluid immediately carries the dislodged particles out through the drain without penetrating the bulk of the load, minimizing the amount of soil that is redeposited on other garments.
At the end of the cleaning cycle, the liquid CO2 drains from the cleaning vessel and is converted to a gas in the still. The dirt carried from the garments (the only waste generated in the DryWash™ process) collects at the bottom of the still, and the clean, gasified CO2 is then recondensed for the next cycle. Because CO2 has a low surface tension and evaporates rapidly, only a short, "cold" (54°F-58°F) drying cycle is necessary.
DryWash™ offers numerous benefits. It is
- Environmentally friendly —Carbon dioxide is a nonflammable, nontoxic, inexhaustible solvent that will not deplete the ozone or pollute the ground water. As a result, DryWash™ helps the dry-cleaning industry comply with federal and state environmental regulations because the process minimizes wastes and emissions.
- Effective —The DryWash™ process greatly reduces pigment-soil redeposition (graying), fading, and dye transfer. Because CO2 is a gentle solvent, it can effectively clean materials that perc often damages, such as leathers, furs, and accessories with sequins. In addition, the low temperatures of DryWash™’s drying cycle minimize heat-set stains and wrinkles.
- Efficient —Because of its short drying cycle, the DryWash™ process is complete in half the time required for conventional dry-cleaning processes.
- Inexpensive to operate — At 15-40¢ per pound, CO2 is a cheaper solvent than perc ($5-$7 per pound), and DryWash™ minimizes the costs of environmental compliance, such as hazardous waste disposal and new emissions-control equipment. In addition, DryWash™ dramatically reduces the need for costly finishing labor and nearly eliminates liability costs associated with damaged garments.
Applications
DryWash™ offers an efficient and environmentally friendly replacement for the hazardous dry-cleaning methods currently used. The process can be used to clean almost all types of fabric encountered in the drycleaning industry, including some that cannot be cleaned by current perc technology. DryWash™’s benefits have the potential to affect billions of people worldwide who rely on retail dry cleaners or industrial laundries at hotels, military installations, hospitals, nursing homes, and corporate facilities.
In the future, the DryWash™ system and fluid jets could be used by industries to wash dishes and to degrease and decontaminate machined parts. Eventually, small-scale versions of DryWash™ may be available for laundry or dishwashing in the home.
Staff Who Worked On the DryWash Project
Shown above are the LANL researchers who worked on the DryWash™ process:
(back row, left to right) Jerome Barton, W. Kirk Hollis, Dennis L. Hjeresen, Matthew Roepcke;
(front row, left to right) Craig M. V. Taylor, Leisa B. Davenhall, Leah D. Bustos, and L. Dale Sivils. The former principal investigator of DryWash, W. Dale Spall, is not pictured.
Operated by the