As a member of the Fabricare Group on Yahoo, I have noticed many requests for information on how to recover from the day-to-day disasters which occur during the course of running a dry cleaning operation. With this in mind let’s start with that perennial favorite, the dreaded still boil over.
What Is A Still Boil Over?
A still boil over occurs when the nasty witche’s brew in the still is forced up the still riser (large pipe between the still and condenser) into the condenser and from there to the water separator. The still is chock full of detergent and other nasties that prevent the separation of the solvent and water mixture; hence the performance of the water separator becomes non-existent. Solvent and water in the form a dirty looking, milky liquid wind up contaminating the separator, solvent lines going all the way to the distilled solvent storage tank (rinse tank) and the storage tank itself.
However, before treating the symptom, let’s discuss what caused the condition:
1. Overfilling The Still – I’ve found the most common cause of a boil over is overfilling the still. Despite the fact that all new machines have a float type switch in the still it is possible, if it is not set correctly, to pump enough solvent into the still to cause a boil over. Solvent expands when heated. What would be a safe level with cool solvent becomes a problematic high level when heated to boiling. There is a “Catch 22” to recovering from overfilling the still and that is the behavior of the still safety float switch and its associated circuitry. In the infinite wisdom of the machine designers, once the safety switch activates, it shuts off the pump to prevent further filling of the still which is good. Unfortunately, it also shuts off the steam valve supplying heat energy to the still thereby preventing further distillation. The only way to remove solvent from the still, thereby lowering the level, is to drain the liquid contained inside the still, a torturous and hazardous job; or of course, to distill, DUUUH! (Do you see the hole in the fabric of this logic?) The happy news is that the still float switch is easily fooled, so distillation can be used to recover from the problem.
2. Excessive Moisture – Coming in with a close second is excessive moisture (water) in the still. Free water turns to steam at temperatures below the boiling point of solvent. This steam in the still liquid agitates the witches brew inside the still, causing violent bubbling and foaming, forcing raw still content up the still riser contaminating the condenser. In addition, perc and water mixed in the proper proportions form what is known as an azeotrope (I don’t know about the lighter than water solvents). I won’t begin to try to explain the many queer and amazing qualities of a perc/water azeotrope other than it reduces the boiling temperature of perc from 260 degrees F to around 190 degrees F. Since the temperature of the still is set by steam pressure (the still steam pressure regulator doesn’t know that there is water in the still) hence, with the reduction of 70 degrees in the boiling point you get a geyser of frothing perc, nasties and water vomiting up the still riser like “Old Faithful.” The source/sources of this contaminating moisture could be a leaky or partially open steam sweep valve, excessive “wet side” spray (slop) pre-spotting, wet garments in the dry cleaning load, let you imagination be your guide.
3. High Distillation Temperature – Last but not least in this species of screw ups is excessive distillation temperature. You’ll no doubt remember from past articles that steam temperature is a function of steam pressure. So overheating the still can be caused by either:
A. The failure of the still steam regulator.
B. Someone fiddling with the adjustment or a regulator bypass valve being open (if there is one installed).
In either case you should have a pressure gage that indicates the steam pressure of the steam entering the still. The setting of the steam pressure for proper distillation varies by machine manufacturer and also by solvent type so I can’t give a recommendation, but your equipment distributor or manufacturer will know, and if asked nicely might tell you. Keep in mind when reading the steam pressure the still must have at least 10 gallons of boiling solvent in it before an accurate pressure reading or any regulator adjustments are made.
The Road To Recovery
Recovery from any of these situations requires the patience of a saint and a surgeon’s hand on the steam pressure regulator. First, the cause must be determined and rectified. Next, the water separator should be drained and the contaminated mixture either disposed of, or stored in a covered bucket; more of what to do with the stored contaminated solvent at the end of this article. You need to have a clean tank to store the newly distilled solvent. So, if the distilled solvent storage tank (rinse tank) is contaminated, and it probably is, it must be pumped free of contaminated solvent to either another tank or to the basket for later distillation. After these steps are accomplished adjust the still pressure regulator to around 25-30 psi. This will allow the solvent to cook off at a more controlled rate.
If excessive moisture is the culprit, you will see a foggy or streaky whitish film on still sight glass (the round porthole looking glass in the still) until the moisture is cooked off, at which time the sight glass will clear. At this point it is usually safe to slowly, step by step, raise the still steam pressure and watch the results. You will need to repeat this process for the remaining contaminated solvent. Shut the steam off to the still for about 5 minutes before refilling with contaminated solvent. Be sure to remember to deal with about 10 gallons at a time and start with the lower steam pressure until the moisture cooks off.
If overfilling was the cause of the problem, after the solvent is cooked off down to a safe level the steam pressure can be raised slowly back to normal. Follow the same procedure as in the preceding paragraph but you will probably be back in bus,iness in a lot less time.
No matter what the cause, if your filters are contaminated they also must be drained to the still and refilled with clean solvent; be sure to complete steps in the next paragraph, cleaning the piping before refilling the filters.
After you are done distilling and you have sufficient solvent in the rinse tank, pump a few gallons of clean solvent from the rinse tank to the still. Also, if the filters were contaminated, pump clean solvent from the rinse tank to the filters. If you are using a spin disk, go through the spin cycle. Inject a lot of detergent into the solvent before sending it to the filters then drain the filters to the still. I know this sounds like a lot of extra work but it will prevent clogging the fabric on the spin disks with slime and will “dry out” the cartridges somewhat. Now remember the contaminated solvent from the separator sitting in a bucket somewhere. After a day or so the water and impurities will separate and the solvent or water (depending on the solvent) can be skimmed off; solvent can be distilled for reuse.
That’s it for now…more to come next month.