Vapor Degreasing Process

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Vapor Degreasing Process

What is solvent degreasing

Solvent degreasing involves the use of a solvent to remove water-insoluble soils,

e.g. oils, greases, waxes, tars, etc., from surfaces prior to processes such as painting,

plating, repair, inspection, assembly, heat treatment or machining. Solvent degreasing

does not constitute a distinct industrial sector. It is a process used by many industries,such as automobile, auto parts, aerospace, furniture, appliance, primary metals and

electronics.

Vapor degreaser

Solvent degreasing involves the exposure of a workpiece to pure solvent vapors

released by a boiling solvent. The acting principle behind the vapor degreaser process isthat the solvents will dissolve the contaminants on the workpiece and remove them by

dripping off the part. A basin of solvent is set up with a heating coil to bring the solvent

to boil. As the solvent evaporates it rises to the fill-line in the chamber, above which is air

with a much lower density than the solvent. This contains the vaporized solvent in aclosed space where the workpiece is placed. The solvent condenses on the more frigid

workpiece and the now liquidsolvent dissolves the greases on the part. With theimpurities contained in the liquid beads, the solvent runs off the part. The degreaser are

primarily designed for use with n-propyl bromide and chlorinated solvents, includingtrichloroethylene, methylene chloride, and perchloroethylene. Although these systems

can also be used with Fluorinated fluids like HFE, HFC and their azeotropes.

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Pollution in degreasing

Chlorinated solvents have traditionally been used for degreasing because (1) they

quickly dissolve organic soils such as oil, grease, and dirt from parts and (2) residualsolvent on parts evaporates rapidly, leaving them clean, dry, and ready to be finished.Today, however, use of most chlorinated solvents is being phased out by increasingly

stringent state and federal air regulations.

Some solvents used in metal finishing, such as 1,1,1- trichloroethane (TCA), are ozone-

depleting and global warming compounds. Other solvents, such as perchloroethylene(PERC) and trichloroethylene (TCE), are subject to increasingly stringent regulations

because of the risks they pose to human health.

Degreasing regulation:On December 2, 1994, the Environmental Protection Agency (EPA) published the

National Emission Standards for Hazardous Air Pollutants " for Halogenated SolventCleaning (59 CFR 61801). The law falls under the authority of Section 112 of the 1990

Clean Air Act Amendments. You can find the regulation in 40 Code of Federal

Regulations Part 63, Subpart T.The regulation focuses on "reducing the emissions of selected halogenated solvents used

in parts cleaning. The compliance methods center around best operating practices and

pollution prevention techniques.

Owners and operators of degreasers using the following chlorinated solvents: methylenechloride; perchloroethylene; 111 trichloroethane; trichloroethylene; chloroform; carbon

tetrachloride. Suspected ozone depleting solvents like freon, 111 trichloroethlene, carbon

tetrachloride, chloroform and some others are severely restricted under other Clean Airprovisions.

EPAs Vapor Degreaser Maximum Available Control Technology (MACT) Standard:

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New technology:Seven available cleaner technologies for cleaning and degreasing are evaluated:1. Add-on controls to existing vapor degreasers

2. Completely enclosed vapor cleaner

3. Automated aqueous cleaning

4. Aqueous power washing

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5. Ultrasonic cleaning

6. Low-solids fluxes7. Inert atmosphere soldering.

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Convert from perchloroethylene vapor degreasing to water-based cleaning

systems.

All companies using processes whereby VOCs are emitted are called upon to

reduce the quantity of VOC emissions by prevention or treatment.

Many users of cleaning processes involving volatile solvents are now faced with the

decision of investing into an exhaust air treatment system or switching to a different

cleaning method.

The principal criteria to be considered in the decision for or against using solvents

that cause VOC emissions are the ecological and economical problems of exhaust air

treatment and the technical requirements that must be met by technologically advanced

cleaning systems.

Numerous aqueous, or water-based, cleaning chemicals are now available that are

significantly less toxic than chlorinated sol- vents. Because organic soils are less soluble

in water than in chlorinated solvents, chemical and physical mechanisms such as

surfactants, emulsifiers, agitation, sprays, and ultrasonics are often used to enhance

cleaning effectiveness.

Water-based cleaning systems have been used successfully for a wide range of

cleaning tasks. Water-based cleaning methods, washing solutions generally produced

through dilution with water, emit little or no organic substances and are hence

particularly sustainable in both economical and ecological terms. The machine-supported

aqueous cleaning systems that are now widely used produce much better cleaning results

and are hence increasingly used for cleaning tasks accompanying production.

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In the early 1990s, there were as many as 3,000 vapor degreasers in the South

Coast Basin. Most of these vapor degreasers used 1,1,1-trichloroethane (TCA), a

chlorinated solvent. In 1996, TCA production was banned because the solvent contributes

to stratospheric ozone depletion. Many of the companies using the solvent converted their

operations to water-based cleaning and more traditional VOC solvents. Some of the

companies continued to use vapor degreasers with other halogenated solvents. By 2002,

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there were only about 250 companies using vapor degreasers and most of these

companies were using perchloroethylene (PERC). The results of the project indicate that

water-based cleaners are a viable alternative to PERC vapor degreasing. The water-

based cleaners offer an overall advantage from the human health and environmental

standpoint and, in most cases, they are less costly or about the same cost as PERC vapor

degreasing. Four of the companies that participated in the project converted to water-

based cleaners. Acetone is also a viable alternative to PERC vapor degreasing for certain

types of operations. Acetone is not classified as a VOC and it is relatively low in toxicity.

One of the companies that participated in the project converted to acetone handwipe

cleaning.

Ultrasonic cleaning can also replace vapor degreasing.

Ultrasonic cleaning is a technology that uses high frequency sound waves

(ultrasonic: above the range of human hearing) to agitate an aqueous or organic medium

(cleaning chemistry) that in turn acts on contaminants adhering to substrates like metals,

plastics, glass, rubber and ceramics. Contaminants can be dust, dirt, oil, pigments, grease,

polishing compounds, flux agents, fingerprints, soot wax and mold release agents,

biological soil like blood, and so on.

Ultrasonics is an environmentally friendly and a technically feasible alternative to

solvents that are ozone depleting and have other undesirable characteristics. Reduced

emissions, biodegradable waste and a safer environment for employees are among the

benefits.

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Reference

www.epa.gov/region9/waste/p2/projects/metal-dgrease.pdfhttp://www.epa.gov/ttn/atw/degrea/halopg.html#RULE

http://www.dtsc.ca.gov/PollutionPrevention/upload/Alternatives-to-PERC.pdf http://www.packaging-int.com/article/water-based-cleaning-technology.html

http://www.ultrawave.co.uk/pages/Why-Use-Ultrasonics-53.php