This is a short synopsis (Below this synopsis is a more detailed version.) of what a vapor degreaser (VD) is, the various types of VDs and what solvents are used in VDs. There are two types of VDs. One is a vapor immersion unit which usually has two solvent-filled sumps (the boil sump and the cold sump which is filled with clean, distilled condensate solvent and is often used for rinsing). An ultrasonics-equipped degreaser is a version of a vapor immersion type degreaser. The other type of degreaser is a vapor/spray unit in which the solvent is boiled in the very bottom of a one-sump degreaser. There is a perforated metal stand just above the boiling solvent. A metal basket filled with dirty parts is usually placed on this stand. The basket or parts are not immersed in solvent. Instead the vapor made by the boiling solvent encompasses the parts completely and removes the oils and soils. The oils and soils, now diluted into the condensing liquid, will drip back into the boiling solvent below. There is a manual spray wand, which is sprayed under the cooling coils, directly on hard-to-remove soil.

Near the top of the either type of degreaser is a set of cooling coils, that catches the vapor before it escapes from the unit. It cools and condenses it back to its liquid form and flows it back to a clean condensate tank and finally it goes back to the boil sump or the rinse tank. Since oil and grease boil at a higher temperature than for chlorinated solvents, the vapor caused by the now oil mixed solvent, only vaporizes the clean chlorinated solvent not the dirty oil, if the temperature settings are correctly set. Therefore only clean vapor is used to clean parts.

There are 3 standard chlorinated degreaser type solvents - trichloroethylene(TCE), methylene chloride and perchloroethylene (perc). There are other new VD solvents which are more expensive but have certain characteristics which require their use in some cleaning situations. By the way, chlorinated solvents (and the newer vapor degreaser solvents) have no flash point so they are not flammable. Non vapor degreasing solvents like acetone, xylene, methyl ethyl ketone, alcohols, etc. should not be used in heated tanks that are not explosion proof like VDs. All are flammable.

Editor's note. I believe, in spite of the somewhat bad and unjustified environmental reputation that vapor degreasers have acquired in the late 80s and early 90s, there is no better method of cleaning metal (and other) parts of oil, grease, wax, flux, etc. With updated equipment and careful operation, there should be no environmental damage done. My company also sells aqueous washers and other types of parts washers but I am sold on vapor degreasing. Rod Murphy 4/11/00

Nothing written or implied in this booklet should be considered as recommendations or in any way are the writers or editors of this booklet liable for any damages.

Some Ideas on Basic Vapor Degreaser Use

The minimum that equipment for vapor degreasing must provide is: adequate space for effective cleaning; allowing sufficient contact with the solvent (vapor and/or liquid) to remove soils, and capability to recycle the solvent for extended use.

The design of vapor degreasing equipment is determined by the size, shape, and specific heat of the parts to be cleaned; volume and rate of production; and the type and amount of soils to be removed. These considerations in turn influence the cleaning cycle selected and the method of moving parts through the cycle. Federal, state, and local emissions and other regulations are a further influence, as is on-site availability and economy of a heating source.

Basic Degreaser Design
VDs vary in size and type from small, manually operated machines to automated, conveyorized systems. The simplest VD is a rectangular tank with a sump of boiling solvent in the bottom. The cleaning space, or vapor zone, is just above the boiling solvent.
To confine solvent vapor to the tank and prevent vapor loss to the atmosphere, a refrigerant or water cooled external jacket or internal coils are located above the vapor zone. Clean vapor condensate is collected in a trough, passed through a water separator to remove excess moisture, and returned to the boiling sump. Degreasers commonly are designed with larger condensers than actually required, in order to minimize solvent loss and prevent vapor contamination of the air in the work area.

Buying a Vapor Degreaser
The number of vapor degreaser manufacturers has waxed and waned in this new era of mergers, federal and regional emissions and other pertinent regulations. Some of the older well known names, BRANSON, BARON BLAKESLEE, FINISHING EQUIPMENT remain in the business; some with different ownership. Other firms discontinued making VDs; TALLY, CREST. And some have gone out of the business; LENAPE and DELTA. There are also a few new VD manufacturers. And there are some import manufacturers like FLONIC.

In the USA there are a few wholesale dealers specializing in used vapor degreasers. Such dealers can provide late model, good condition VDs with EPA required retrofits at half the cost of a new degreaser or less. Some specialty dealers are veterans in the business and can provide helpful advice also.

Freeboard Function and Design
The sides of the VD tank extend above the condenser (cooling coils), and this area is called freeboard. Its purpose is to shield the vapor zone from air currents that could cause turbulence and resultant vapor loss. Since excessive solvent vapor loss also contributes to atmospheric contamination, freeboard height is subject to federal and state and regional regulations; EPA requires that the freeboard height be at least the same as the width of the tank (narrowest dimension) or "100% freeboard".

Storage Tank
Most degreasers have a separate storage tank for clean, distilled solvent, This provides a supply of contaminant-free solvent for immersion degreasing or spraying.

Sizing the Equipment
Equipment sizing for an open-tank degreaser represents a balance between process requirements and solvent conservation. There must be sufficient working area in the vapor zone to avoid a piston action that will pump solvent vapors out of the machine as work is immersed and removed. An open-tank degreaser requires at least 50 percent greater working area than the dimensions of the largest workload. Beyond satisfying this requirement, tank size should be kept to a minimum to avoid excessive vapor loss through evaporation.

To further control vapor loss, environmental regulations as well as economic considerations dictate a freeboard design with an adequate ratio of freeboard height to tank width, federal and state regulations require that the freeboard height be at least equal to the width of the tank, i.e.100% freeboard. In 1994 the Environmental Protection Agency (EPA) promulgated a complicated set of related regulations called NESHAPS.

Heat Requirements
Heat input requirements for vapor degreasing are determined by the weight and specific heat of the work (which has to be heated to the solvent boiling point), radiation losses from the tank walls, solvent distillation, and the solvent used.

Heating the Work
The number of BTUs required hourly to maintain the solvent at boiling temperature can be calculated by multiplying the pounds/hour of work to be cleaned by the specific heat of the metal and the difference between ambient temperature and the boiling point of the solvent in degrees Fahrenheit. A safety factor of 50 percent is usually added.
For large workloads, added heating coils can be provided to minimize temperature swings. It is important to maintain a constant vapor level to minimize vapor loss; therefore sufficient heat input should be available to raise the workload surface temperature to the vapor temperature as quickly as possible.

Radiation Losses
If radiation losses from bare tank walls become excessive, it can be reduced by insulating the tank walls. Radiation losses will vary with the boiling point of the solvent. High heat perc degreasers should be insulated on the outside for operator safety and to reduce radiation loss.

Heating for Solvent Distillation
The heat required to produce clean distillate for spraying or multiple immersion chambers should be included in determining total heat input required.

Heat Sources
Heat input for vapor degreasing can be supplied by electricity, steam, and gas or by a heat pump. Most systems recently manufactured use electricity.

Electricity
Immersion heaters with a heat density of about 20 watts/sq. in. are generally used in electric heating installations. It is important that the liquid solvent level be kept above the immersion heater, since an exposed heating element will elevate surface temperature and result in solvent decomposition and burnout of the heating element. A low-liquid-level shutoff will provide warning.

Steam
Immersed steam coils are generally used to supply heat to the solvent; other methods include plate coils or steam-jacketed tank bottoms. Steam pressures required to achieve the boiling point for clean solvent range from 5-15 psig for TCE and 50-65 psig for perc. As the contamination level of the solvent increases, its boiling temperature increases accordingly, as does the steam pressure required to maintain the same rate of distillation.

Hot Water
Pressurized hot water pumped through immersion coils is another heat source for VDs. Water temperatures and pressures commonly used are 250°-300° F (121°-1490° C) at 25-70 psig for trichlorethylene, and 300°-325° F (149°-1630° C) at 70-105 psig for perc.

Gas
Gas heating is less commonly used for vapor degreasing tanks. Immersion coils are employed, and fuel input is generally sized at twice that required for steam to allow for combustion inefficiency and flue stack losses.

Operating and Heat Safety Controls
In addition to operating controls specific to the heating system selected, certain safety controls are common to all heating methods. A coolant flow switch and temperature control are required to shut off the heat source if coolant flow is insufficient. A sump thermostat should be set to cut off heat supply if the sump temperature exceeds recommended maximum for the solvent used. Further protection against inadequate cooling is provided by a vapor thermostat, discussed under Vapor Control. All shutoff controls should require manual resetting. See "Sizing the equipment" above for information on EPA regulations (NESHAPS) requiring these safety controls plus some other things.

Heat Safety Controls
Steam: A pressure regulator is required that is suitable for the solvent used. A pressure gauge and relief valve should be installed on the low-pressure side. Steam traps should be provided to receive condensate from the steam coils and return it to the boiler.
Gas: Automatic pilot protection should be provided to shut off all gas within 45 seconds of pilot failure. Dissolved oil and grease raise the boiling point of the solvent, and this temperature rise should be limited by a thermostat. Thermostatic protection against low liquid level, which might expose the gas immersion coil, also is required. Open flame gas heated degreasers could be dangerous if exposed to chlorinated solvent vapor.
Electric: A low-liquid-level device, either thermostatic or of the mechanical float type, is required to prevent solvent decomposition due to exposed heating elements.

Warning
An exposed gas or electric heating element will result in excessive surface temperature of the heating element, with consequent solvent decomposition and the formation of toxic gases. The reaction also can result in an acid degreaser and an attendant danger of fire. To insure a minimum level of solvent, a low liquid level shutoff should be used.

Sump Thermostat
A sump thermostat set to the recommended limit for the solvent used should be coupled to a shutoff valve with manual reset. Recommended sump thermostat settings are for methylene chloride; 195° F (91° C) for TCE and 260° F (127° C) for perc.

Vapor Control
Control of the vapor level is the key to successful degreaser operation. Vapor control is accomplished by the flow of cooling water through coils inside the tank or through a jacket around the outside of the tank.

Cooling Coils
Cooling coils are positioned to control the vapor level, allowing clearance below the work and a vapor layer above the work. Cooling refrigerant or water temperature above the vapor line should be higher than the dew point of the surrounding air to avoid condensation of atmospheric moisture. This can be helped by directing refrigerant or water flow through the cooling coil from the bottom to the top.

Waterjacket
In addition to or instead of cooling coils, a cooling jacket around the outside perimeter of the degreaser tank can be used to coot the wall below the freeboard and condense the solvent.

Vapor Thermostat
Should the vapor level rise above the cooling coils, this sensor will respond to the temperature of the vapor and shut off the heat source. The thermostat should require manual resetting. Typical settings are methylene chloride; 160° F (71° C) for TCE and 180° F (820° C) for perc. Required by NESHAPS.

Water Separation
Water contamination of the solvent may originate from condensation of atmospheric moisture, from the surfaces of parts being cleaned, or from leakage of condenser water or steam lines.

Caution
Excess water in a chlorinated solvent can cause corrosion of parts and equipment. In particular, 1,1,1 trichloroethane is subject to hydrolysis in the presence of excessive water, resulting in the formation of acidic materials. The acidic solvent is corrosive and may cause equipment damage. To avoid this, guidelines for the design and operation of a water separator should be carefully followed.

Water in the solvent is usually evidenced by spots appearing on metal being cleaned. These may be rust-colored if some corrosion has already occurred. After the solvent evaporates, spots may be visible on the cleaned work. Another indication of excess water is the formation of a dense white fog in the vapor zone, called ghosting. The density of the cloud varies directly with water concentration. A properly designed water separator located on the condensate return line will keep solvent moisture content at a low level. Water-contaminated solvent enters the separator through a pipe below the liquid level. Above, the solvent water interface, water flows out. Solvent, since it is heavier than water, is drawn off through a pipe below the interface. Since the separation is accomplished by gravitational settling of vie heavier solvent, the separator should be designed to provide adequate retention time. A minimum retention time of five minutes is recommended for chlorinated solvents. In addition, a deep tank is more efficient than a shallow design because it minimizes the area of the solvent-water interface. Since water is not as soluble in methylene chloride, perc or TCE, the water separator for methylene chloride, perc or TCE may be somewhat smaller. Separation is further improved by lowering the temperature of the condensate in a heat exchanger either before it enters the water separator or in the separator. Water separators operate most efficiently when the solvent temperature is below 100° F (38° C) for TCE and perc.

Construction Materials
While stainless steel is the preferred material of construction for degreaser tanks, resin-coated mild steel is satisfactory. Metal accessories preferably should be stainless steel, brass or bronze. Aluminum or magnesium should not be used as materials of construction. Zinc-plated or galvanized steel is not suitable for use with chlorinated solvent.

Caution
Do not use aluminum as a construction material. Chlorinated solvents may react with aluminum when in constant contact, resulting in solvent decomposition and consequent equipment damage from the acidic products of decomposition.

Warning
In a closed system, methylene chloride may react with aluminum components and decompose. The resultant generation of heat, pressure and explosive gases may rupture the equipment with explosive-like force, causing injury to nearby personnel. Do not use aluminum piping, pumps or other components.

Materials Handling
Vapor degreasing, is adaptable to a wide range of part sizes and production requirements, from large parts lowered by hoist to batch cleaning in racks or baskets to high volume automated installations.

Manual Operation
Large, heavy parts, and assemblies are commonly handled by hoists, which should be limited to a maximum vertical travel of 11 ft/min. (Required by NESHAPS) to avoid vapor disturbance. Part size must also be considered in relation to tank area, with sufficient clearance to avoid a piston action as the part is lowered and raised. The part area should not exceed 50 percent of the tank area.
Batch production is handled in racks or baskets, with the same caution about overall basket size to avoid pumping. Since the rack or basket must be heated along with the work, weight should be kept to a minimum.

Automated Systems
Monorail conveyors are particularly suited to high-volume applications where parts can be suspended from hooks or hangers. Vertical travel should be restricted to a maximum speed of 11 ft/minute. The system should be designed so that the conveyor travels above the vapor zone; automatic lubrication should be provided as alternative.

Crossrod conveyors are used to degrease small parts in baskets, which can he designed to rotate to facilitate drainage. The crossrod conveyor incorporates two parallel strands of chain connected at intervals by rods, from which the baskets are suspended.
Ferris wheel or Carousel. As the name implies, this design rotates the work in a number of baskets attached to a wheel-like assembly. The design is enclosed except at the operator station where work is loaded and unloaded. Variations of immersion and spray can be included in the cleaning cycle, as well as rotation of the baskets.

Vibra conveyor: This high-capacity design is particularly effective in cleaning small metal parts such as fasteners, screw machine products and small die castings. A combination of solvent action and vibration is responsible for its effectiveness in cleaning hard-to-remove solids. The parts are directed to the bottom of a spiral elevator which is actuated by a vibrator drive. The vibrating action moves the parts upward along the spiral through solvent and vapors where soil is flushed away and the parts dried.
Elevator conveyors are batch-type, and incorporate a platform - usually made of open rollers - to lower and raise the work. The design can be adapted to provide closed operation. Care should be taken to provide sufficient clearance between the elevator platform and the tank walls to avoid pumping.

Degreaser Installation
Location of a VD usually is dictated by its position in the production sequence, but available space or environmental problems within the plant may influence this decision. Consideration also should be given to proximity of other processes, such as paint finishing where solvent vapors could have an effect on the work.

Space Requirements
Because of the short cycle time involved in vapor degreasing and the compact design of the equipment, VDs require a minimum of space. Ceiling height ordinarily is not a problem. Where parts with long vertical dimensions must be cleaned and ceiling height is a restriction, the degreaser can be installed in a pit.

Clearance
There should be sufficient clearance around the machine to allow access to cleanout doors and to permit removal of heating elements.

Elevation
For a manually operated, open top degreaser, the top of the tank should be 48" above floor level or the operating platform; or a railing provided at this level. The 48"inch height is considered adequate to protect against accidental falls and to provide a safe breathing zone.

Locating a Degreaser in a Pit
Degreasers installed in pits require clearance similar to those at floor level for access and maintenance. A 48"inch high rail should surround the pit, and the open tank area covered by grating.

Warning
Solvent vapors are heavier than air, and presents a hazard in a pit or other low-lying area. Exposure to high concentrations of chlorinated solvent vapors causes depression of the central nervous system, which can result in unconsciousness or death. Safe entry procedures must be followed if it becomes necessary to enter a pit where high concentrations of solvent vapor may be present.

Drafts
Until EPA's NESHAPS, normal air circulation was considered beneficial in dissipating the small quantities of solvent vapor usually encountered in degreaser operation. Accordingly, former recommendations for degreaser location was where there is sufficient ventilation to maintain vapor concentration in the air below accepted Time-Weighted Average (TWA) values. Since the 1994's NESHAPS, required design of VDs has been tightened so that solvent emissions should be minimum. However, cross-drafts can scoop solvent vapors from the degreaser, and cause excessive vapor loss. The degreaser should not be located where it can be affected by drafts from windows, doors, fans, unit heaters, ventilators, or adjacent spray booths. If necessary, the tank should be enclosed with walls.
Avoid open flames and hot surfaces!

Caution
Do not install a VD near gas heated ovens, space heaters, open flames or hot surfaces above 750° F (399° F); or near welding or heat treating operations. Solvent vapors may decompose upon contact with hot surfaces or open flames, producing acidic products which can cause corrosion of surrounding structures.

Warning !
Arc welding should not be attempted near VD. Ultraviolet radiation from the arc welding may cause decomposition of solvent vapors and the generation of a strong disageeable odor together with the localized formation of toxic gases, These gases could cause personal injury to the welder.

Gas-heated Degreasers
Gas-heated degreasers must not be located in a room where the general mechanical exhaust system produces a negative pressure unless a powered exhaust device is provided to remove all products of combustion. Open flame gas jets are a possible danger when exposed to chlorinated solvent vapors.

Degreaser Operation

Before attempting startup or operation of vapor degreasing equipment, an operator should be thoroughly familiar with the operation, control and maintenance of that particular machine. The manufacturer's operating instructions should form a part of his training, and the operating instructions should be permanently positioned in a conspicuous location on the machine.

The operator should be equally familiar with recommended safety practices as well as the hazards related to the solvent being used. Operating temperatures and pressures and thermostat settings for VDs and stills are available from degreaser manufacturers, used equipment dealers and chemical distributors.

Degreaser Startup
The following general procedure is recommended when starting the VD:

1. Turn on condensing water, and check to make sure that it is flowing properly.
2. Turn on self-contained, refrigerated units and the chiller goes on before anything else automatically.
3. Actuate all control devices and check periodically to insure proper operation. This includes the automatic heat shutoff thermostat above the condensing zone, maximum surface temperature controls on heating elements, and maximum solvent temperature control in cleaning compartments. Usually all these safety controls go on when the main switch is thrown.
4. Add solvent in all compartments as necessary.
5. Check to make sure that degreaser covers, which should have been in place during idle period, remain so during startup.
6. Turn on heat supply and, if degreaser is steam-heated, check settings to conform with those recommended for the solvent used. Electrically heated units go on with main switch.
7. As degreaser reaches operating temperature, adjust heat so that upper level of vapor zone is at the midpoint of the condenser coils. Maximum operating efficiency and minimum solvent loss are obtained when vapor generation is balanced by condensation from the work load and condensing coils.
8. When the vapor zone has reached the condenser coils, check to insure that condensed solvent is flowing to the water separator, and through it to the proper degreaser compartments. The ideal is when the solvent is dripping heavily from the cooling coils back into the underneath trough.
9. Check all thermometers and gauges to insure that readings are in the proper operating range.
10. Start cleaning cycle.
11. Check water flow through condenser, and cooling water temperature, which should be 90°-120° F (32°-49° C) at the discharge outlet of the water coils. This range will provide effective cooling and minimize atmospheric condensation. Refrigerated units have settings (e.g.TCE at approx. 50°F.).

Solvent contamination level
The solvent contamination level in the degreaser sump should never be allowed to exceed 25% and should be maintained below this level. 15% contamination is an even better Preventive Maintenance target to change solvent.

A VD delivers its greatest output and economy when the solvent is clean, because the effectiveness of the process depends on the ability of the unit to provide a constant supply of clean solvent vapor. As contamnination increases cleaning efficiency is reduced.
Excessive solvent contamination will lead to solvent breakdown, insufficient vapor generation, sludge formation and the baking of sludge on the tank bottom and heating element. In addition, the boiling temperature of the oil-solvent mixture rises to a level where it reduces cleaning effectiveness.

Maximum recommended sump temperatures are approximately 193° F (89° C) for TCE, and 256° F (124° C) for perc.

Water contamination
Sources of water entry into a degreaser should be identified and eliminated so far as possible to avoid equipment corrosion, spotting of work, and increased solvent consumption. For a more detailed discussion of moisture removal, see Water Separation.

Adding solvent to the degreaser
When solvent is added to the degreaser, care should be taken to avoid agitating the vapor zone. Pumping the solvent into the degreaser, rather than pouring directly from drums, will minimize disturbance, Makeup solvent ordinarily is added to the clean rinse compartments or the condensate tank.

Shutting down the degreaser
When not in production, degreasers normally are shut down for economy. Some low boil solvents may evaporate without on demand refrigeration. The following steps are a guideline:

1. Stop degreaser operation and remove work.
2. Shut off heat supply.
3. Allow vapor level to drop below condenser area.
4. Shut down water supply to condenser.
5. Turn off control devices and auxiliary equipment.
6. Cover open-tank degreasers.

Warning !
As previously stated, exposure of the heating element during distillation will result in excessive surface temperature of the heating element and the production of toxic gases. In addition, the high temperatures will damage the solvent to the extent that the reaction can result in an acid degreaser with the consequent danger of fire and injury to personnel.
Internal distillation.

When permitted by production schedules, the degreaser itself can be used to reclaim solvent on a batch basis. Distillation is accomplished by boiling the sump, and the distillate is collected in a separate receiver.

Liquid levels must be monitored when using the degreaser as a still to avoid exposure of the heating element and consequent overheating of the element. The liquid level must be kept at least 1.5" above the heating element.

If solvent vapors are still present when this level is reached, the remaining concentrate may be removed to a drum and added during the next cleanout period. Fines, chips, and sludge should be removed with a hoe or similar tool and disposed of in compliance with regulations.

Warning !
Fire Hazard
As the liquid becomes concentrated during distillation, afire hazard exists in electrically and gas-heated degreasers if the temperature of the oil contaminants reaches its flashpoint. To avoid this, bottom thermostats should be set to the proper temperature for the solvent used, and should be tested frequently. Thermostats on gas and electric degreasers should be set to shut off at 195° F (91° C) for TCE and 260° (127° C) for perc.

Caution !
Do not inject steam into the boiling chamber, as excessive water may cause equipment damage. Vapor thermostat setting should be 160° F (71°C) for TCE and 180° F (82° C) for perc.

External Distillation
An external solvent recovery still combines a heat source to vaporize the contaminated solvent, a condenser and a water separator. The unit should be equipped with the same safety and operating controls as the degreaser, and similar operating practices should be followed.

A separate solvent recovery still offers a number of cost-saving advantages. The degreaser can operate for extended periods without shutdown for cleanout. Degreasing efficiency is enhanced because the solvent is maintained relatively free of contaminants. Operating temperatures generally are lower because of less contamination, which reduces energy requirements. In addition, the external still offers a higher rate of solvent recovery than is obtainable with distillation in the degreaser.

A solvent recovery still may be connected directly to a large degreaser, or operate independently as a free-standing unit processing solvent in batches that are collected from a number of degreasers.

Where the still is connected to a single degreaser, it operates continuously. The unit receives solvent from the most heavily contaminated section of the degreaser, and returns distillate to the degreaser rinse compartment or to a storage reservoir. Solvent level in the still is maintained by an automatic level control switch which actuates a transfer pump.
Solvent contaminants are accumulated in the still and periodically it is necessary to shut down the unit for concentration and disposal of the soils. Concentration will recover a substantial portion of the solvent contained in the sludge. Additional solvent can be recovered by steam sweeping, which is the injection of live steam into the boiling chamber above the solvent toward the end of distillation. The steam forms a lower-boiling azeotrope with TCE and perc which allows maximum solvent recovery.

Caution!
Do not use steam sweeping with 1,1,1-trichloroethane. This may cause a hydrolytic reaction which will result in solvent breakdown, formation of corrosive acids, and lead to equipment damage.

Warning!
Fire/Toxic Gas Hazards Residue concentrations may present a fire hazard, or danger from toxic gases, or both. They must be handled and disposed of in accordance % with proper safety procedures to avoid fire or toxicity hazards to personnel.

Residue concentrations for degreaser sumps or external stills should be handled and disposed of in accordance with local and state regulations concerning hazardous wastes. Handling and removal should follow established safety procedures. Residues should be cooled to room temperature; if removed while hot, ventilation should be adequate to minimize atmospheric contamination and resultant toxicity hazards.
For additional information, refer to Disposal of Solid Wastes, in the following section Cleaning the Degreaser.

Operation of an External Still
Basic procedure for startup and operation of an external still is similar to that for a degreaser, following these steps:

1. Open the valve to supply condensing water or turn on refrigerated unit's main switch.
2. Check settings of control devices, then actuate. Set thermostat settings for chlorinated solvents.
3. Close drain valve.
4. Fill still with solvent to operating level.
5. Check water flow through condenser, and cooling water temperature which should be at 90°-120° F (32°-49°C) at the discharge point.
6. Concentration of contaminants will raise the boiling point of the solvent.
7. When solvent temperatures approach the level of the still sump thermostat settings for the solvent being distilled, distillation normally will end.
8. For TCE and perc only, initiate steam sweeping by closing the steam coil inlet valve and slowly opening the steam injector valve. Be careful to avoid foaming of the concentrated material. Optimum solvent recovery is achieved when the flow of distillate ceases. Close steam injector valve.
9. Shut off heat supply.
10. Deactivate control devices.
11. Cool residue, and dispose of in accordance with applicable environmental regulations. (See Disposal of solvent wastes)

Degreaser Maintenance and Cleaning

Degreaser maintenance includes both regularly scheduled procedures to keep the degreaser at optimum operating efficiency, and the periodic major cleanouts required to maintain contamination at an acceptable level.

Routine Maintenance
A good routine maintenance program anticipates problems and helps to prevent major work stoppages. Routine maintenance is basically good housekeeping, and pays dividends in reduced solvent losses and faster, more effective cleaning.

Warning
Fire/Explosion Hazard Excessive amounts of aluminum or zinc chips or fines can, under certain circumstances, cause a violent chemical reaction which may further result in ignition of the oils in the degreaser sump. Nearby personnel would be subject to injury from either or both occurrences. To prevent this, fines and chips should be removed daily.

Some recommended procedures follow. Most of these should be performed daily; checking of temperatures, liquid flows, and steam pressure (where used) even more frequently.

1. Insure that all compartments of the equipment are maintained at proper operating levels.
2. Clean liquid-level sight glasses and porthole glasses.
3. Check solvent pumps, gasketed closures, transfer lines, and other connections for leaks.
4. If steam is used for heat input, check steam pressure and steam traps.
5. Check sump temperature to determine contamination level.
6. When starting up for the day, check the time required for the vapor level to rise to the midpoint of the condenser coils and hold steady. As work is introduced, observe whether the vapor zone maintains its level or drops substantially. Excessive heating time or vapor level drop may indicate need for degreaser cleanout.
7. Check condensate trough.
8. Check solvent flow from the water separator back to the degreaser. Reduced flow may indicate not only a blockage but also diminished vapor generation.
9. Check water drain on water separator.
10. Check temperature of condenser coolant (water cooled units) at exit point; maintain between 90° and 120° F (32°-49°C)
11. Since solvent vapors remove lubricant from conveyors, lubricate frequently.

Safety procedures for entering a degreaser
The following procedures must be observed when it is necessary to enter the degreaser:

1. The entire system must be drained.
2. All access ports must be removed or locked in an open position.
3. All solvent vapors must be expelled.
4. Purge the degreaser with forced air directed toward the bottom of each compartment.
5. Using proper instrumentation, measure the air quality inside the degreaser.
6. The person entering the degreaser must wear a harness and lifeline and NIOSH/ MSHA-approved self-contained breathing apparatus of a pressure-demand type with full facepiece
7. A second person should hold the free end of the lifeline, must be similarly equipped for degreaser entry, and must be able to communicate at all times with the first person when the first person is inside the degreaser.
8. A third person must be within audible hailing distance. The second person should not enter the degreaser unless absolutely necessary to remove the first person, and must not enter before the third person has been alerted. The third person must not enter the degreaser.
   

Internal cleaning procedures

1. Brush out the condensate trough and check to make certain that there are no obstructions to condensate
   flow.
2. Brush cooling coils, walls, and compartment floors to remove accumulated rust and scale. Take care to avoid damaging corrosion-resistant finishes.
3. Brush down rusted areas; inspect and lubricate conveyor system or internal drive mechanism as required.
4. Scrape and brush heating elements free of all caked sludge to assure efficient heat transfer. Further equipment cleanout should include:
5. Clean out condensate lines from the collection trough outlet to the water separator, and from the water
   separator to the discharge point in the degreaser.
6. Clean out the water separator and remove any sludge that may have accumulated in the bottom.
7. Clean strainers, filters, sight glasses, and porthole glasses before reassembly.
8. Clean and check controls, indicators and regulators before reassembly. Adjust if necessary.
9. While unit is down, it may be a good time to perform other maintenance, including a check of doors, pipe fittings, gauges, and other trouble spots for leaks. Solvent-resistant gaskets and sealing compounds should be used to help prevent solvent loss.
10. Reconnect heat input.
11. If manual cleanout is insufficient, the degreaser may be cleaned with a hot solution of soda ash and water.
    Fill the unit with water to a level about 4 to 6 inches above the heating element, and add one pound of soda
    ash per five gallons of water in the degreaser. Heat this solution for one-half hour. The sides and all
    compartments should be thoroughly washed, after which the unit should be drained, rinsed well, and dried.
12. Turn on water supply to condensers and beat exchangers and inspect for water leaks. Repair any leaks.
13. Fill all compartments to normal levels with solvent, and start the degreaser.
    

Treating an acid degreaser
Treatment of an acid degreaser consists of neutralizing the acid solvent, draining the degreaser, cleaning the unit manually, and neutralizing with a heated soda ash solution.

Warning !
Fire/Explosion Hazard An acid degreaser presents the potential of fire and explosion with consequent personal injury. A continuing acid reaction results in the formation of toxic gases including hydrogen chloride, and possible violent exothermic reaction with iron oxides and aluminum when present in the sump. The acid degreaser should be neutralized immediately, following recommended procedures.

The following steps should be employed:


1. Turn off heat.
2. Add soda ash to sump in a solution of one pound of soda ash to 5 gallons of water, and agitate as much as possible while solvent is cooling.
3. When solvent is cool, remove from degreaser.
4. Following the procedure outlined in the previous section, remove as much sludge as possible from outside of the degreaser.
5. If it is necessary to enter the degreaser, the safety precautions outlined in the previous section must be observed.
6. Fill the degreaser with water to a depth of 4-6 inches above the heating elements, and add soda ash at the rate of one pound per 5 gallons of water in the sump.
7. Heat the soda ash solution and boil if possible. Wash all parts of the degreaser that were in contact with the acid solvent.
8. Drain degreaser and dry completely.
9. Add fresh solvent.
10. Determine cause of acid generation and take action to prevent future occurrence.
    

Disposal of Solvent Wastes
Sludge from a VD or from a solvent still may be stored in drums until ready for disposal. Drums should not be tightly sealed, especially those that contain sludge with aluminum residues. Prior to disposal, drums should be stored outdoors and away from any combustible materials or source of combustion. Solvent wastes normally consist of chlorinated solvent, oil, tar, metal particles, buffing compounds, and other contaminants. Chlorinated solvents are considered hazardous wastes under the Resource Conservation and Recovery Act. Therefore any waste containing chlorinated solvents must be disposed of by approved incineration. Before disposing of wastes containing chlorinated solvents, every effort should be made to recover as much of the solvent as possible by distillation. A solvent recycling firm should be considered. It is the responsibility of the generator of any waste to ensure that disposal is carried out in accordance with the Clean Air Act, Clean Water Act, the Resource Conservation and Recovery Act, and all relevant state or local laws and regulations regarding disposal.

Warning !
Do not add dry soda ash to an acid degreaser. This may cause flashing from the degreaser, and consequent injury as nearby personnel are exposed to the eruption of hot solvent and corrosive acid. Soda ash must always be added in a water solution.

Warning !
Do not add soda ash solution to boiling solvent or to solvent that is above the azeotropic temperature of 149' F (65' Q. This may cause flashing from the degreaser, with a consequent eruption of hot solvent. Allow solvent to cool, or carefully dilute with water to reduce temperature.

Warning !
Explosion Hazard
Do not add sodium hydroxide (NaOH) or other strong alkalies to an acid degreaser This can result in a violent chemical reaction and there is even the possibility of an explosion, with consequent danger of injury or death to nearby personnel. Use only a soda ash or sodium bicarbonate solution.

Corrective Action
Water separator: Insure that separator is clean and that water flow through separator is unhindered.
Condensing coil: Check temperature of discharge water. It should range between 90° and 120° F (32°-49° C) to avoid condensing atmospheric moisture.
Water on incoming work: Determine whether parts entering degreaser are wet or carrying water-based cutting, oils.
Collection trough: Check installation and performance.
Freeboard chiller: Freeboard refrigerated chillers should have separate collection trough and water separator.

Poor Cleaning Action
Ineffective cleaning of the work generally is a result of insufficient contact with the solvent and/or solvent vapor. Following are some common contributory conditions:

Cause: Vapor immersion and/or rinse cycle too short.
Correction: Leave work in vapor zone until all condensation stops.

Cause: Vapor level too low for adequate cleaning; and rinse.
Correction: Check heat input to insure sufficient vapor generation.

Cause: Vapor level collapse because of too heavy a load. If temperature of work increases, oils may bake on parts.
Correction: Follow degreaser equipment manufacturer's guidelines on loading.

Low Acid Acceptance
Solvent stabilizers are effective in the industry in resisting acid formation and solvent decomposition, even after repeated distillation. However the original acid acceptance of solvents will gradually decline, depending on production volume and the type of work being cleaned. Periodic addition of make-up solvent restores acid acceptance.
Occasionally a degreaser becomes acid, creating a situation that requires immediate action and which could result in a safety hazard.

Troubleshooting Vapor Degreaser

High solvent consumption -excessive vapor odors
These problems usually are related: excessive vapor odor is an indication of vapor loss to the atmosphere. If the cause of pronounced vapor odors is located and corrected, solvent consumption will be reduced. A detection meter will help locate the source of vapor loss.

Cause: Solvent dragout.
Correction: Rack parts for complete drainage; eliminate pockets and recesses.

Cause: Vapor level too high.
Correction: Check vapor thermostat and sump temperature; check and adjust heat input to maintain vapor level at midpoint of condenser coils. (Refer to recommended vapor thermostat and sump temperature.)

Cause: Entry and removal; rates too fast.
Correction: Entry and exit rates should not exceed 11 ft/minute. Faster speeds pull vapors out of degreaser.

Cause: Insufficient clearance between basket and degreaser walls; causes piston effect as work is lowered and raised.
Correction: Work should not exceed 50 % of degreaser surface area.

Cause: Solvent loss from spraying,
Correction: Keep nozzle at least 6 inches below vapor level; use only enough pressure to wash the work.

Cause: Drafts which sweep vapor from degreaser.
Correction: Avoid open doors and windows; shield degreaser from other drafts such as exhausts.

Cause: Solvent evaporation from open tank.
Correction: Cover degreaser when idle or shut down. Cover water separator if open-tank construction.

Cause: Leaks.
Correction: Locate source with detection equipment. Check valve packing nuts, pump packing, sight glasses, piping, and gaskets.

Cause: Insufficient freeboard height allows vapors to escape to atmosphere.
Correction: Freeboard height should be at least 100 percent of tank width.

Cause: Insufficient condensation.
Correction: Insure that water is flowing through cooling coils before turning on heat input
to sump; confirm that water temperature at condenser outlet is between 90°-120° F
(32°-49°C).

Cause: Vapor level collapse. Too heavy a load will cause vapor collapse, creating
air-vapor mixture that is pushed out of degreaser.
Correction: Check equipment rating; do not overload degreaser.

Cause: Insufficient cycle time; work emerges dirty and wet, carrying solvent into
atmosphere.
Correction: Wait until all condensation stops before removing work from degreaser.

Cause: Absorbent materials.
Correction: Do not use degreaser to clean clothing or leather goods; do not use wood or other absorbent materials in baskets.

Cause: Excessive moisture. Water in sump forms azeotrope with TCE and
perc which has a lower boiling point than solvent, causing vapor loss to
atmosphere.
Correction: See following section on moisture contamination.

Moisture Contamination
Excessive moisture in the solvent can cause spotting and corrosion of the work as well as damage to the equipment.

Caution
In the presence of excess water, 1,1,1-trichloroethane (EPA restricted along with Freon) is subject to a hydrolytic reaction that results in solvent decomposition and the formation of acidic material. This is highly corrosive and may cause equipment damage. The degreasing operation should be continually monitored for signs of excessive moisture.
Indications of water contamination

Following are some indications of excessive moisture and the corrective action to be taken.
Water spots, equipment rust: Excessive water in the solvent will spot or corrode the work; rust will develop on degreaser walls around cooling coils and condensate trough.
Ghosting: A dense white cloud develops in the vapor zone. Density increases with water concentration.

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Bibliography
"The Design, Operation & Maintenance of a Detrex Degreaser" Detrex Chemical , Detroit, MI 1952
"Vapor Degreasing" PPG Industries, Pittsburgh, PA 1986
" The ABC's of Vapor Degreaser Conversion" Ibid 1985
"Vapor Degreasing with Freon TF Solvent" Dupont, Wilmington, DE 1983
":Solvent Emission Reduction" Ibid 1988