Drycleaning Equipment & Drycleaning Operations

In early drycleaning operations, solvent was applied to the garment with a brush on a table. The garments were then rinsed in tubs filled with solvents and were hung to dry in a warm room.

In the late nineteenth century washing machines were utilized in drycleaning but dryers or “tumblers” were not utilized until the 1920s. This marked the introduction of transfer machines or “first-generation machines” which were actually two or three machines including a washer (where the garments were washed), an extractor (where the solvent was extracted from the garments by centrifugal force), and a tumbler (where the garments were dried). Later transfer machines incorporated the extractor into the washing machine.

In a transfer machine operation, the clothing is physically “transferred” from the washer to the tumbler. This clothing transfer results in solvent vapors escaping to the atmosphere.

In the late 1960s “dry-to-dry” machines were developed: washing, extraction and drying of garments occur in the same machine. The garments go into the machine dry and come out dry, hence the name “dry-to-dry”.

The earliest dry-to-dry machines are also known as “second-generation machines”. A number of improvements have been incorporated into dry-to-dry machines over the years to improve solvent mileage – the pounds of clothing cleaned per gallon of solvent. It is estimated that PCE transfer machines used approximately 82 pounds of solvent to clean 1,000 pounds of clothing compared to 34 pounds of PCE used by second-generation machines.

The latest PCE drycleaning machines, known as “fifth- generation machines” use approximately 10 pounds of PCE to clean 1,000 pounds of clothing.

The Clean Air Act Amendments of 1990 identified PCE as a hazardous air pollutant.

In 1993, the EPA Air Office published the final air standard for perchloroethylene drycleaners.

These air regulations have had a greater impact than any previous regulations with regards to changes in drycleaning equipment, practices and solvent usage. Transfer machines are no longer being manufactured. New PCE drycleaning machines have refrigerated condensers, carbon adsorption units, inductive fans and lockout devices, which prevent operators from performing certain operations until PCE concentrations in the air in the machine drum are below certain levels. Drycleaning operations in the United States have changed dramatically in the last ten years.

Coin-operated drycleaning machines were introduced in 1960 by Whirlpool. These are small (clothing capacity 8 – 12 pounds) dry-to-dry machines that use PCE or Freon 113. Most of these machines were manufactured in Europe and they are no longer being manufactured. However, they are still being used in the United States, primarily in laundromats.

Filtration is one of the processes used to purify spent solvent in drycleaning operations. A wide variety of filter types have been used in drycleaning operations, including powder filtration, cartridge filters and spin disc filters.

Another process used to purify spent solvent is distillation. This process vaporizes the spent solvent in the distillation unit or “still” by heating with steam. The solvent vapors are routed to a condenser leaving nonvolatile residues and impurities behind in the distillation unit. The solvent vapors are cooled in the condenser. The liquid resulting from condensation is a mixture of solvent and water. The solvent is recovered by gravity separation in a water separator.

The distillation unit is incorporated into modern drycleaning machines. In some older operations it is a separate piece of equipment.

A variety of wastes are generated during the drycleaning process. In chlorinated solvent drycleaning operations, most of these wastes are hazardous. Discharges of these wastes have caused soil and groundwater contamination at drycleaning sites.

Contact water is any water that has come into contact with drycleaning solvents or drycleaning solvent vapors. Contact water contains some level of dissolved solvent. Several types of contact water are associated with drycleaning operations.

The waste product generated from the distillation process is known as either still bottoms or cooked powder residues (from powder filtration systems). Still bottoms contain grease, oil, detergent, dyes, sizing, waxes, filter materials and other non-volatile residues.

Distillation residues can contain up to 75% solvent by weight. Not all drycleaners perform distillation. This is particularly true of many petroleum solvent drycleaning operations, which purify solvent by filtration alone. If these operations use a powder filtration system the filter waste generated, known as “muck”, can contain considerable solvent.

A considerable amount of solvent is lost to the atmosphere as vapors in PCE transfer machine operations and even from first generation (vented) dry-to-dry machines. Based on emission factors (pounds of PCE per 100 pounds of clothing cleaned) the Center for Emissions Control estimates that approximately 53% of PCE losses for transfer machine operations were through the machine vents and in clothing transfer. This figure is estimated to be approximately 25% for vented dry-to-dry machines.

(The information in this newsletter has been gleaned from an EPA sponsored site http://www.drycleancoalition.org and enhanced with pictures.)