Every vapor degreaser has a water separator or should have one if it is properly designed. Vapor degreasers use cooling systems to condense and confine solvent vapors, keeping the solvent inside the degreaser and purifying it through the process of distillation.
All the solvent within a vapor degreaser eventually flows through the water separator. To describe the mass flow of solvent in a vapor degreaser, here is a description using a two-sump vapor degreaser as an example. In an immersion vapor degreaser such as the Baron Blakeslee MLR / MSR models (https://www.baronblakeslee.net/vapor-degreasers/m-series-precision-equipment/) there are two sumps which contain liquid solvent, as well as a zone of saturated solvent vapor that fills the tank area above the two sumps.
The sump on the left is the boil sump, which contains electric heaters to boil and vaporize the solvent. The sump on the right is the immersion sump which contains a recirculating filtration system and possibly ultrasonic transducers (MSR models). In the vapor degreaser, solvent liquid is boiled in the boil sump to generate vapor. The vapor rises within the tank and condenses on the primary refrigeration coils (the primary coils are the evaporator side of a direct expansion R-448A refrigeration system), and the phase changes from vapor to liquid.
The condensed drops of liquid solvent fall by gravity from the surface of the primary condensing coils into a trough below, and then flow into the water separator. Solvents used in the vapor degreasing process are less dense than water, and accumulated water floats to the top of the solvent in the water separator, allowing the water to be easily drained from the degreaser by a manual valve. Solvent from the water separator flows into the distillate receiver, which is a tank that accumulates distilled solvent that may be sprayed onto parts by using the manual spray wand system that is a standard feature on all M Series vapor degreasers.
Solvent from the distillate receiver then flows back into the vapor degreaser, spilling into the ultrasonic immersion sump. The solvent then flows across the weir dividing the immersion and boil sumps, which completes the solvent circulation cycle. The continuous process of solvent boiling and condensing creates a mass flow of solvent through the degreaser, which continuously purifies the contents of the immersion sump through the process of solvent distillation and dilution of contaminants in the ultrasonic immersion sump.
All soluble contaminants are pushed by the flow of distilled solvent into the boil sump, where they remain, and cannot escape. Insoluble contaminants, and particulate are removed from the process by the recirculating filtration system in the ultrasonic immersion sump.
M Series vapor degreasers also feature a secondary sub-zero freeboard refrigeration system, with the evaporator coils of an R-448A refrigeration system mounted above the R-448A refrigerated primary condensing coils. So, M Series vapor degreasers have two (2) refrigeration systems. The purpose of the R-448A sub-zero freeboard refrigeration system is to cool the air above the zone of solvent vapor, and to dehumidify the process tank which enhances the removal of water from the process.
The evaporator coils of the sub-zero freeboard refrigeration system operate at approximately -20OF (-29OC), which creates a heavy, dense blanket of very cold air that lays atop the solvent in the degreaser tank. This heavy, dense blanket of very cold air suppresses the solvent vapor and greatly reduces evaporation of solvent. The density of the very cold air blanket also minimizes the effect that drafts in the room can have in respect to blowing vapor out of the tank. Moisture in the air will freeze on the freeboard refrigeration coil surfaces, and to maintain efficiency, those coils must be defrosted, and when that water melts it accumulates in the water separator.
Water is less dense than the halogenated hydrocarbon solvents used in vapor degreasing, and therefore water floats on the surface of the solvent which accumulates in the water separator. The water may be removed from the separator by opening a valve, and the water drains from the system via gravity. Emptying the water separator of a degreaser is very important, for several reasons. Certain solvents like n-propyl bromide (nPB, 1-Bromopropane), trichloroethylene (TCE, “trike”) and perchloroethylene (PCE, “perk”) can hydrolyze to form their corresponding acids in the presence of water.
In the case of nPB, hydrobromic acid forms, and TCE & PCE form hydrochloric acid. Acidic solvent can cause corrosion inside the vapor degreaser, and damage like weld failures or leaks may occur as a result. Parts may also be damaged by the acidic solvent liquid and vapor. An acidic condition in a vapor degreaser is evident when the solvent turns very dark in color, even black, in the boil sump, and the solvent may fume, evolving acidic vapors.
Generally, in an acidic degreaser, corrosion in the form of brown rust may be seen inside the degreaser, or surfaces may appear green or orange inside the degreaser. Usually, corrosion begins inside the water separator, and a band of rusty residue will be observed at the water line atop the solvent layer in the separator. The types of reaction products formed in an acid condition are: 1. Irritating, corrosive and toxic fumes, as well as sharp, pungent odors of solvent. 2. Black, gummy residues composed of carbon, polymers, metal organic compounds, and if aluminum is present, aluminum chloride.
If a degreaser becomes acidic, the acidic solvent must be drained and properly disposed of as waste, then the machine must be thoroughly cleaned out and neutralized to prevent the acidic condition from reoccurring. There are specially trained contractors who perform the clean-out and neutralization services who are trained in confined space entry, etc.
Properly formulated, vapor degreasing grades of nPB, TCE & PCE are “stabilized”, blended with chemicals like butylene oxide, etc, that inhibit the hydrolysis reaction. However, the water separator must be drained frequently to reduce the stress on the solvent stabilizer package. Stabilized, vapor degreaser grade nPB, TCE & PCE solvents require “acid acceptance” testing to monitor stabilizer content.
The acid acceptance test kit is specific to the solvent formulation and is available from the solvent supplier. Do NOT use non-stabilized solvents or your degreaser will become acidic! If your solvent supplier does not have acid acceptance test kits available for the nPB, TCE or PCE you are using, it is time to find a supplier who does!
There are a variety of fluorinated solvent blends on the market now, which generally tend to have more favorable environmental health and safety characteristics, (such as higher operator exposure limits, higher TLV) than the traditional solvents like nPB, TCE & PCE. The active ingredient in all these fluorinated degreasing solvents is a chlorinated solvent called trans-1,2-dichloroethylene (sometimes referred to as “trans”, or “trans DCE”) to perform the actual cleaning. In general, fluorinated solvent blends tend to be more stable than nPB, TCE & PCE in respect to hydrolysis & acidification in the presence of water.
Generally, manufacturers of fluorinated solvents do not require acid acceptance testing to be conducted, and do not require the use of stabilizers or additives, for these products. In the case of the fluorinated solvents, water should still be emptied from the water separator daily to prevent water from accumulating within the vapor degreaser. Excess water in a vapor degreaser can make the vapor look hazy, white, cloudy, foggy, which indicates an aerosol of water in the solvent vapor. Water droplets suspended in the solvent vapor can cause water spotting on parts which can translate to quality defects. Emptying the water separator daily will remove the water from the process and prevent nuisance water spotting of parts.
Maintaining a water separator literally only takes a minute. The accumulated water should be drained from the separator at least daily, or after each shift, depending on the relative humidity in the area. Water is drained by opening a manual valve, and the process is very easy and again, takes only a moment to do. The water separator should be drained of water when the degreaser is completely up to temperature with solvent boiling and condensing, which is why it is generally suggested to perform this operation at the end of each day or shift.
Water collected from the separator is wastewater and must be disposed of in accordance with applicable regulations. In most vapor degreasers, only a relatively small amount of water accumulates daily, so the volume of water that must be dealt with is minimal, typically an ounce or so per day, maybe less. Most solvents can be recycled almost indefinitely with proper care in distillation and water removal. The solvent should be periodically checked for proper pH levels, acid acceptance or the contamination introduced into the solvent and water in system (either by condensation or by parts).
Contact your solvent supplier for proper chemical monitoring requirements.
Proper maintenance of a water separator saves money and maximizes productivity. Protect the investment in your vapor degreaser by spending a minute a day emptying the water separator!