Vapor Degreasing: Operational Details

• General Start-up and Shut Down Procedures
• Recommended Operating Procedures
• Solvent Handling
• Changing the Cleaning Fluid in the System
• Acid Acceptance Testing

General Start-Up and Shutdown Procedures

To minimize solvent losses during start-up, it is recommended that the following procedures be used:

1. Activate condenser cooling system and check to ensure that it is operating properly.
2. Activate, where provided, any auxiliary emission control equipment.
3. Check and adjust solvent levels in all compartments.
4. Activate heaters.
5. Wait until stable vapor blanket has been established before activating spray pumps.
6. Wait until stable vapor blanket has been established before introducing work into the unit.

To shut down the unit, use the following procedure:

1. Stop work processing and clear the machine of all work.
2. Deactivate the heaters.
3. Activate sump cooling coils, if available.
4. Allow vapor blanket to collapse completely.
5. Keep the condenser cooling system ON.
6. Close cover on open-top units.

Here’s an important money-saving tip: if the degreaser contains cleaning fluids, never turn the cooling system off. Make sure the system is on 24-hour electrical service, and put the system into “stand-by” mode at the end of the day which turns off the heat but not the condensing coils. This will keep the vapor barrier intact, keeping the solvent in the machine. It also will avoid big (and expensive) surprises when work resumes.

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Recommended Operating Procedures

Good work practices play an important role in using a vapor degreaser effectively. Failure to define good work practices and failure to train workers in those practices can reduce or eliminate the many benefits expected from selecting MicroCare fluids and state-of-the-art equipment. That's why every MicroCare customer will enjoy the industry-leading product stewardship program to ensure they use these cleaners wisely and cost-effectively.

There are some useful and simple work practices that can play a major role in helping a cleaning system to operate at its peak:

System Location

Airflow across the top of a vapor degreaser is the single most common cause of extraordinary solvent losses. Do not ventilate the degreaser. Do not put a fan on the wall to blow vapors away from workers. Do not use the machine under a ventilation hood. Rapid airflow will cause the machine to work less effectively and cause wasteful and unnecessary unexpected solvent losses.

When excessive air movement is a problem with existing equipment, and the equipment cannot be moved, consider the installation of baffles or partitions on the windward side to divert the draft away from the cleaning unit. Finally, always keep the lid closed with the system is not being used.

Workload Size

The processing of workloads that exceed the cleaning system's design capabilities will expel solvent vapors from a cleaning system. This can be caused by one, or both, of two common effects:

A basket that is too large in physical size can displace vapor from the cleaning unit by the piston effect. This causes solvent to be ejected from the machine as the mass of cleaning materials descends into the cleaning vapors. To avoid losses by this mechanism, the area of the workload should not be greater than 75% of the horizontal cross-sectional area of the sump into which it is being introduced.

[Schematic, right] The rapid addition of parts into the vapor layer displaces those vapors, forcing them up and out of the machine (left illustration). Similarly, when removing the parts the basket acts as a piston and pushes some vapors out of the tank while also pulling a cloud of solvent vapor behind it. The only way to defeat the piston effect is to move the parts very slowly, usually with an automatic hoist.

The introduction of a workload that is too heavy will result in a collapse of the vapor blanket in a process called work shock. The infiltration of air into the cleaning unit will increase solvent losses until the vapor blanket is re-established. If this condition is encountered on a regular basis, the equipment manufacturer should be consulted to determine if a hoist might ameliorate the problem or if additional heating can be incorporated into the unit. If not, the purchase of a new machine with larger work-handling capabilities should be considered.

Work Positioning

Work being cleaned in the cleaning system, whether contained in baskets, suspended from hooks, racks, or conveyed on a belt, always should be positioned in a manner that permits maximum drainage to minimize drag-out losses of solvent. Drag-out is the solvent lost as the parts are removed from the cleaning system; the schematic highlights the drag-out issue.

Retention of solvent in pockets and recesses can result in excessive solvent drag-out. Try to position the products in such a manner as the solvent can drip from the parts back into the cleaning system. If this is not feasible, slow the extraction of the parts and consider using superheat.

As the drawing on the right shows, drag-out is extremely sensitive to operator training, good cleaning procedures and useful machine features. A good vendor should be able to document incremental operating costs and drag-out losses on a feature-by-feature basis. Furthermore, they should be able to highlight specific environments (e.g., types of contamination, cycle times) which will reduce solvent losses.

Vapor Dwell Time

The workload should be retained in the vapor zone after the final cleaning step until its temperature equilibrates with that of the vapor zone and vapor condensation on the part stops. Work withdrawn earlier will emerge wet with solvent condensate. Insufficient dwell times are encountered most frequently in open-top units where work is manually moved into and out of the unit. Use of a programmed work transporter (e.g., an automated hoist) can help eliminate excessive drag-out due to insufficient dwell time.

Spraying and Spray Wands

Spraying is not recommended. If required, MicroCare recommends that spray bars be installed inside the cleaning system, so the spraying can be done deep within the vapor zone to minimize solvent losses.

If manual spraying is used, technicans need to be extremely careful to avoid rapid movements or spraying the liquid solvent ricochet into the freeboard zone that might cause excessive solvent losses. Should they spray cold solvent into the vapor zone, the subsequent temperature change may collapse the vapor blanket. The use of warm solvent having a temperature no more than 3°C (5°F) below the solvent's normal boiling point will minimize the loss of solvent.

Work Scheduling

The expulsion of air from a vapor degreaser during start-up always results in some solvent vapor carryout. When work is being processed on an intermittent basis, emissions caused by frequent activation and deactivation of the cleaning system can be minimized by deferring cleaning until all of a day's production is accumulated for processing with only one start-up of the cleaning equipment.

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Solvent Handling

Here are crucial tips for minimizing solvent loss during normal operation of the machine:

• The addition of solvent to the degreaser/defluxer should be done with care to minimize disturbance of the vapor/air interface. Ideally, the solvent should be pumped into the degreaser through a liquid-submerged fill connection.
• Make-up solvent (topping off the machine to replace lost solvent) should be added to the rinse sump.
• Cold solvent should not be added to operating degreaser; its introduction can collapse the vapor blanket. The cold solvent will cause the vapor blanket to collapse.
• The addition of solvent to an open-top degreaser by pouring from drums or buckets should be avoided. The turbulence of such pouring destabilizes the vapor/air interface.
• Any drums containing solvent should be kept tightly sealed between transfer operations to prevent unnecessary evaporation losses. Drums should be stored with the bung end up to eliminate the possibility of incurring a major spillage of solvent through a leaky bung. Take great care when moving drums of solvent; automated systems (fork lifts, etc.) are recommended. Do not pressurize the drums of solvent in an attempt to expedite unloading.

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Changing the Cleaning Fluids in the System

The MicroCare cleaning fluids are extremely stable and can be used for weeks or months inside a well-tuned vapor degreaser.

 

Since the solvent is constantly being distilled and recycled, it remains clean and pure indefinitely. While the Bromothane^™ products have a requirement to perform acid acceptance tests on a weekly basis (the other products can skip this step), overall the maintenance is pretty minimal.

The real issue is not the solvent – which remains clean and pure indefinitely – but the collection of debris at the bottom of the sump. After a while the debris accumulates and the machine becomes too dirty to operate efficiently. This is when a system clean-out becomes necessary. In a busy machine, this might occur twice to four times a year.

In a standard degreaser, the contamination accumulates in the boil sump. This is the first chamber in the cleaning cycle and is the location into which the dirty parts are placed when they first go into the machine. It is here where the worst contamination will aggregate.

 

In general, watch for a change in the color of the solvent in the boil sump (the rinse sump fluid will always be clear and colorless). It will be time to change the solvent in the boil sump when it accumulates a high concentration of dissolved contamination, to the point of tinting the solvent yellow or beige. Additionally, at the bottom of the boil sump will be a large collection of insoluble junk – like solder balls, metal filings, labels and chewing gum – which will need to be removed. It's time to clean the machine.

Cleaning a degreaser normally involves a process called a boil-down. This simply involves distilling (boiling) all the solvent out of the system and rather than returning it to the rinse sump recapturing it in a pail or a drum for re-use. When the last few liters of solvent remain at the bottom of the boil sump, the heat is turned off. Any residual waste solvent and the solid contamination is cleaned out by hand and disposed of as a hazardous waste. The whole process may take a day on a big and dirty machine.

In more sophisticated machines, a recirculating pump is installed on the boil sump to refresh the solvent in the boil sump and to remove particulate. This will extend the periods between boil-downs.

Once the machine is ready to be returned into service, the old (but clean) solvent that was recaptured during the boil-down process is dumped back into the machine.

Check with the machine manufacturer for their thoughts and recommendations.

Details of the Solvent Boil-Down Process

It is easy to recycle the MicroCare cleaning fluids easily and inexpensively.

During the cleaning process with a vapor degreaser, the soils that are removed from the parts accumulate in the boil sump of the degreaser. Ultimately, this dirty solvent must be discarded. But before the solvent is disposed a substantial quantity of the solvent may be reclaimed in a simple "boil down" process that substantially reduces solvent losses and costs.

The recovery procedure described here should be conducted on a regularly scheduled basis, typically quarterly or semi-annually. Be advised that the machine must be taken out of production during the boil-down process; cleaning cannot be performed while the reclamation process is underway.

Here are the steps to follow:

1. When the solvent in the boil sump is too dirty for normal operations to continue, turn the ultrasonics off. Empty the condensate (and the "rinse" sump in a multi-chamber system) into a clean, solvent-safe container (pail or drum).
2. Continue to operate the boil sump. As the dirty solvent boils in the boil sump the solvent vapors will be captured and distilled by the cooling coils. The clean, nearly-pure distillate should be reclaimed into the solvent-safe container.
3. Gradually the solvent and contamination remaining in the boil sump will concentrate and become viscous and syrupy.
4. Before the residues become too thick, the high-temperature safety controls in the boil sump will detect the rising temperature and shut off the heaters. At this point, about 50% of the material in the sump will be solvent.
5. Manually raise the boil sump temperature by another ten degrees and continue to boil the system until the safety controls shut off the system again.

   SPECIAL NOTE: Workers should be aware that this operation requires constant attention. It is advisable to monitor the boil sump temperature with a thermometer. Importantly, under no circumstances should the boil sump be allowed to boil dry as damage to the equipment will result. The equipment should never be left unattended during this process.

6. The "bottoms" then is collected for disposal by draining the boil sump. The boil sump should then be cleaned with wipes and elbow grease. Wear gloves and take precautions to avoid exposures to high concentrations of the vapors.
7. Once the boil sump is clean and dry, close all the drain valves and add fresh solvent to the clean solvent collected during the boil-down. Add enough solvent that the normal operational levels are re-established.
8. Return the temperature controls on the boil sump back to their original and correct settings.

If the facility has collected contaminated cleaning fluids over a period of time and would like to reclaim it all at once, this procedure can be extended simply by adding more of the dirty solvent to the boiling chamber during the boil down process.

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Acid Acceptance Testing Procedure

Certain solvents degrade in the presence of water, in a process call hydrolysis, which creates acids in the solvent. Among the MicroCare product line, the only products that behave in this manner are the Bromothane^™ products. With the industry-leading Product Stewardship program from MicroCare, managing this situation is simple and safe.

The object of the testing process is to compute the number of gallons of BromoBooster^™ required to bring the solvent back into an acceptable degree of acidity. All that is needed is a Bromothane^™ test kit, some eye-hand co-ordination and a little patience. It's actually pretty simple and very interesting.

Here's a summary of the acid acceptance test procedures:

Setting Up the Test

The acid acceptance test is a simple chemical test which determines (a) if there is a need to add BromoBooster^™ and (b) how much BromoBooster^™ to add. The entire test takes about 15 minutes to perform. MicroCare recommends testing weekly, and keeping a log book of the results.

Begin the test by collecting a small sample of the solvent from the degreaser. It is recommended the sample be collected from the water separator, the spray wand or the rinse sump (which is the cleanest solvent). Using solvent from the boil sump – which is where all the contamination is concentrated – can produce inconsistent results. Make sure the sampling jar for the solvent is clean and water-free. Typically, a sample of 200 mL (about half a pint) is sufficient. Let the solvent cool to room temperature.

Conducting the Test

To begin the test, use the eye dropper provided in the kit and remove 1.5 mL of solvent from the sample jar. Carefully deposit the sample into the snap-lid container.

It's important that technicians MUST use the eye dropper supplied with the kit only. MicroCare has tried several other "graduated" eye droppers and they ALL measured different quantities of liquid. Different eye droppers will yield different results. Since the test is calibrated for exact quantities of solvent and test solutions, use the eye dropper provided with the kit.

Similarly, technicians need to be very precise in obtaining 1.5 mL – the whole test is calibrated to a 1.5 mL sample. This is complicated by the fact that the solvent has some surface tension. This means the solvent will "crawl" slightly up the inside wall of the eyedropper, creating a curved bubble near the top of the eye dropper. The bubble is the solvent-air interface and is called the "meniscus" (red arrow, photo left). Take the measurement of 1.5 mL from the BOTTOM of the meniscus. Practice this a few times until the sample is precisely 1.5 mL in the snap-lid container.

Adding the First Drops of the Test Solution

The next step is to add Solution A to the sample. This is the yellow liquid in the bottle with the red label. Supplement the sample of Bromothane^™ with 2.0mL of Solution A; at that point there should be 3.5 mL of liquid in the snap-lid container. Hold the Solution A bottle at approximately a 45° angle to provide the maximum consistency between drop sizes. Add Solution A slowly, because if too much Solution A is added the technician will have to throw out the sample and start again. Do not shake the container during the addition of Solution A.

Again, the liquid forms a meniscus in the plastic snap-lid container. For maximum precision, the BOTTOM of the meniscus should just touch the 3.5 mL graduation mark on the snap-lid container.

Once the proper amount of Solution A has been added, tightly cap the bottle of Solution A. Snap down the lid on the snap-lid container and lock the safety tab in place. Shake the container for 10-20 seconds to thoroughly mix the contents. Let the sample rest for 10 minutes. Take a break!

It's funny how very sensitive this test can be, and this ten-minute break is a good example of how slight variations in procedures can produce unusual results. If the "resting period" is too short, erroneous readings will be the result. If the break is more than half an hour, again the results may be flawed. So don't short-change the ten minutes, but don't wait too long either. Be as consistent as possible between weekly tests.

Monitoring for the Color Change

The technician should now be ready to finish the test. Take the bottle containing Solution B – the green labeled bottle – and start adding liquid to the test sample. Add the liquid drop-by-drop. Count each drop until the solution turns bright blue.

Here's a few tips for adding Solution B.

• Hold the bottle at approximately a 45° angle to provide the maximum consistency between drop sizes.
• The color change happens quickly. After each drop, close the lid on the snap-lid container and give the mixture a brief shake.
• Do not use a thumb to seal the top of the test mixture in place of the snap-lid: the contamination on a person’s fingers could affect the test results.
• Typical results are between 23 and 33 drops. If the number of drops is 40 or more, either something is wrong with the test, or the solvent is literally "off the charts" with acidity.
• Always record the results into a log book.
• Discard the sample in a manner approved by company management.

Determining the Quantity of BromoBooster^™ to Add

The Test Kit instruction package includes this conversion table:

Bromothane™ S		Bromothane™ E
# Drops	Factor	# Drops	Factor
< 15	Normal	< 30	Normal
20	0.031	32	0.033
30	0.052	35	0.039
35	0.063	39	0.046
>50	Replace Solvent	>50	Replace Solvent

The object of this process is to compute the number of gallons of BromoBooster^™ required to bring the solvent back into an acceptable degree of acidity. To perform this task, multiply the factor from the table above by the number of gallons of solvent in the degreaser.

Example:

Suppose the degreaser holds 150 gallons of Bromothane^™ S, and the test results show that it took 30 drops of Solution B to turn the sample blue.

The factor from the Bromothane^™ S table for 30 drops is 0.052.

Multiply 150 by 0.052 and get 7.8.

So add 8 gallons of BromoBooster^™ and the system will be in fine shape.

Adding BromoBooster^™ to the Degreaser

When adding stabilizer, allow the system to cool to room temperature before adding the solvent. Don't just dump the BromoBooster^™ into the machine. After the degreaser has cooled, add the BromoBooster^™ and any fresh solvent into the "condensate" or "rinse" sump. This will allow for faster mixing throughout the system. In addition, it will be safer.

Remember that BromoBooster^™ is flammable (although Bromothane^™ solvents are not). By adding the flammable BromoBooster^™ to the largest, cleanest volume of solvent the solvent will quickly dilute the flammable stabilizer and inert it.

After adding the booster, run the machine for two hours to allow the mixture to stabilize. Then, do ANOTHER acid acceptance test to be sure all the measurements were correct. If all is well, then go ahead and return the machine to production.

Please note: the Bromothane^™ Acid Acceptance Test is designed only for Bromothane^™ solvents and the stabilizer package used by MicroCare. MicroCare cannot predict its accuracy or effectiveness on solvents and stabilizers from other companies.

Click here for these instructions in pdf format.

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