What Work Practices Are Recommended
to Optimize Cleaning, Lower Costs and Minimize Emissions?

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 Bromothane™ and state-of-the-art equipment. That's why every Bromothane™ customer will enjoy our unique, free-of-charge, product stewardship program to help make sure you have the tools and the training to use this solvent wisely and cost-effectively.

Here are some useful and simple work practices that can play a major role in helping your cleaning system to operate at its peak, while eliminating solvent waste, improving the safety of your facility and protecting the environment through reduced solvent losses.

System Location

Here's the prime directive of vapor degreasing: Airflow across the top of a vapor degreaser is the single most common cause of extraordinary solvent losses. Do not ventilate your degreaser. Do not put a fan on the wall to blow vapors away from your workers. Do not use the machine under a ventilation hood. Bromothane™ solvents have been formulated to be safe in vapor degreasers, including a safety allowance for the normal exposures to solvent vapors in a properly configured cleaning system. So, the solvent is generally safe, the people don't need the extra protection, and the rapid air flow will cause the machine to work less effectively. Potentially, excess ventilation can cost you a lot of money through unexpected solvent losses.

Similarly, keep the cleaning systems out of drafts as much as possible. Airflow turbulence across the top of the vapor blanket caused by drafts (velocity >40 ft/min) disturbs the vapor blanket and will increase your solvent losses. Look for drafts from adjacent windows, doors, room heaters, air conditioning, ventilators or spray booths. Eliminating these drafts will greatly diminish the rate at which solvent vapor is emitted to the atmosphere.

When excessive air movement is a problem with existing equipment, consider the installation of baffles or partitions on the windward side to divert the draft away from the cleaning unit.

Do not use open-top equipment -- that's old technology. Every machine today must have a tight, sliding closure. However, just in case the application requires open-top equipment, problems with drafts can be avoided or corrected by using hooded enclosures in conjunction with automated work-handling facilities.

If you remain concerned about aromas and vapors, buy a set of inexpensive halogen monitors and track the exposure levels until a comfort level is achieved with this new technology.

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 workload 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 50% of the horizontal cross-sectional area of the sump into which it is being introduced.

  Figure 59-1: the Piston Effect

  [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 cold and too massive will result in a collapse of the vapor blanket in a process called work shock. The infiltration of air into the cleaning unit will cause excess 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 and condensing facilities can be incorporated into the cleaning unit. If not, the purchase of a new machine with larger work-handling capabilities should be considered.

Start-Up and Shutdown Procedures

To minimize solvent emissions 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. Also 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 where provided.

4. Allow vapor blanket to collapse completely.

5. Deactivate condenser cooling system.

6. Close cover on open-top units.

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.

Also, a reduction in vapor emissions can be achieved by consolidating operations with several open-top units into a single, enclosed unit designed for continuous work transport.

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.

Figure 59-2: Positioning of Parts

[Schematic, right] The proper positioning of parts prior to cleaning allows the solvent to drain off the parts are the basket is being removed from the system. This will eliminate drag-out losses and deliver a big boost to cleaning efficiency.

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.

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 dragout due to insufficient dwell time.

Spraying and Spray Wands

Spraying is not recommended. However, if required, spraying should be done deep within the vapor zone to avoid excessive disturbance of the vapor/air interface. Care also should be taken in spray-lance handling to avoid having the liquid solvent ricochet into the freeboard zone or out of the machine.

Technicans need to be extremely careful when using spray lances or spray wands. 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 potential for vapor blanket collapse and the loss of solvent that accompanies vapor blanket reestablishment.

Solvent Handling

Here are some subtle but 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.

  Figure 59-3: Adding Solvent to the System

  [Schematic, above] There are two ways to add solvent to a degreaser: dumping it in through the top like a ninny (left hand illustration), or carefully pumping it in from a stable and secure position using the appropriate tools, like drum pumps (right hand example). Here at MicroCare, we strongly recommend the safe and secure method.

• Makeup solvent should be added to a rinse compartment or, preferably, to the degreaser/defluxer's condensate collection tank. Cold solvent should not be added to a boiling sump; its introduction can stop boiling activity and collapse the vapor blanket.

• The addition of solvent to an open-top degreaser/defluxer by pouring from drums or buckets should be avoided. The turbulence of such pouring destabilizes the vapor/air interface. The cold solvent could cause the vapor blanket to collapse.

• Solvent handling in open-top containers should be avoided because it offers the opportunity for solvent evaporation and spillage.

• 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.

Cleaning Equipment Considerations

There have been many advances in containment technology that have been employed by manufacturers who produce new and retrofitted equipment. It is recommended that the user consult their equipment supplier for suggestions about features which can reduce solvent consumption in their equipment. Features that are commonly available are as follows:

• Higher freeboard ratios that exceed 1.5

• A second set of low temperature (-29°C / -20°F) condenser coils to reduce vapor losses

• Sliding covers optionally sealed and power operated to contain solvent vapors during a loss of power

• Gaskets for water separators

• Super-heated vapor zones that minimize losses from solvent drag out

• Automated hoist systems that control vapor dwell times in the degreaser.

All of these subsystems add to the cost of the equipment, but can pay for themselves almost instantly in reduced solvent losses. For your convenience, a handy spreadsheet is available on this web site. It facilitates the easy computation of your total cost-per-part-cleaned under different equipment configurations.

System Maintenance and Leak Checking

In general, the boil sump on a busy machine will need to be cleaned quarterly. A typical boil-down cleaning process will take the machine off-line for about one day.

The importance of a good maintenance program cannot be stressed too strongly. All solvent-containing equipment should be checked regularly for leaks from pump seals, valves, pipe joints, gasketed covers, sight glasses, and filter housings. The detection and repair of leaks at an early stage are essential elements of a good emission control program. From an industrial hygiene standpoint, prompt correction of leaks is needed to ensure worker safety.

In addition to being a good industrial hygiene practice, monitoring of the work area for vapor concentration on a regular basis can be useful in detecting equipment malfunction and/or poor work practices.

Updated: Dec. 21, 2004
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