19
Manual on Vapor Degreasing
20 Manual on Vapor
Degreasing
TABLE 7. Recommended maximum boiling temperature.
Solvent Methylene chloride Perchloroethylene 1,1,1 -Trichloroethane Trichloroethylene Trichlorotrifluoroethane
Recommended M a x i m u m Boiling T e m p e r a t u r e
°F 110 260 175 195 125
°C 43 127 79 91 52
5. Drain residues (if still hot or w a r m , provide additional ventilation).
6. Ventilate equipment thoroughly to remove residual solvent (liquid a n d vapor) as completely as possible.
7. Carefully remove t h e r m o m e t e r s a n d safety devices t o avoid damage.
8. Disconnect heat-supply service connections.
9. Remove cleanout p o r t s and heating elements.
10. Remove all dirt, sludge, and metal chips possible from the b o t t o m of each c o m p a r t m e n t w i t h o u t entering the machine.
11. Lock off all p o w e r to conveyor and p u m p s , and disconnect or lock closed solvent lines from storage.
12. When the unit is a e r a t e d thor- oughly by forced ventilation (fan, com- pressed air, or b l o w e r exhausting outside the building), m a i n t e n a n c e personnel may enter the unit (ASTM D 4276)^ to complete the cleaning. The m a n entering the unit m u s t w e a r a h a r n e s s a n d lifeline in addi- tion to approved r e s p i r a t o r y protection, such as a hose m a s k o p e r a t i n g from a remote source of c o m p r e s s e d air or a self- contained b r e a t h i n g a p p a r a t u s . A second person m u s t be in a t t e n d a n c e outside the degreaser at all times with supplied air b r e a t h i n g a p p a r a t u s as an added safety precaution. Continue ventilation of the unit while m a i n t e n a n c e personnel clean the unit interior. They shall, as follows:
(a) B r u s h out the condensate trough and check to m a k e sure t h e r e a r e no o b s t r u c t i o n s to c o n d e n s a t e flow. Use non-ferrous m a t e r i a l s such a s nylon, b r a s s or equivalent. Do not b r u s h stain- less steel e q u i p m e n t with steel w i r e b r u s h e s .
(b) B r u s h condensing coils, walls.
overhead, and c o m p a r t m e n t floors to remove all a c c u m u l a t e d residue, scale, and so forth.Take care to avoid damag- ing corrosion-resistant finishes. B r u s h down r u s t e d areas, inspect and lubri- cate conveyor system or internal drive system, a s r e q u i r e d .
13. S c r a p e a n d b r u s h heating ele- ments free of all caked sludge to e n s u r e efficient h e a t transfer. Inspect and re- place faulty elements. Chemical cleaning with aqueous, h o t alkaline solutions, or with formulated organic solvent carbon remover is often practiced. These aggres- sive chemicals should be flushed out im- mediately after use. These liquids should be disposed of in accordance with federal, state, and local regulations. (See section on "Chemical Hazards, Effects of Alkalies").
14. Clean out condensate lines from the collecting t r o u g h outlet to w a t e r sepa- r a t o r a n d from w a t e r s e p a r a t o r to dis- charge point in the degreaser. These lines can be blown out with c o m p r e s s e d air;
short r u n s may b e b r u s h e d out.
15. Clean out the w a t e r separator, removing any sludge t h a t may have accu- mulated on the b o t t o m .
16. Clean a n d check controls, indica- tors, and r e g u l a t o r s before reassembly.
17. Clean s t r a i n e r s , filters, sight glasses, p o r t h o l e glasses, and so forth before reassembly.
18. With the cleaning operation com- pleted, carefully r e a s s e m b l e the various components and m a k e all joints a n d con- nections leak-proof. Most c o m m o n pipe dopes will affect a d e q u a t e seal at pipe fittings, b u t Teflon® t a p e is preferred. Do
®Trademark of E. I. DuPont de Nemours &
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not use excessive quantities of pipe dope on fittings. The joining surfaces of clean- out p o r t s should b e clean a n d dry. Re- place w o r n a n d t o r n gaskets. Lead, poly- tetrafluoroethylene (PTFE-TEFLON), and plant fiber c o m p r e s s e d sheet are effective gasketing materials, p a r t i c u l a r l y w h e r e flanges are rough and thicker gaskets are required. In all instances, as thin a gasket as possible should b e used. W h e r e com- pressed cork or p a p e r gaskets a r e used, a coating of g r a p h i t e and glycerin or ethyl- ene glycol will do m u c h to prevent gasket bonding to the metal surface. Such bond- ing usually r e s u l t s in b r e a k i n g the gasket during t e a r d o w n a n d often necessitates scraping to remove adhering gasket material.
19. After assembly is complete, t u r n on coolant supply to c o n d e n s e r s a n d h e a t exchangers to inspect for leaks. W h e r e steam heat is used, apply s t e a m p r e s s u r e to the heating coils a n d check for leaks (turn off s t e a m and allow to cool before adding the solvent).
20. Fill all c o m p a r t m e n t s to n o r m a l operating level and s t a r t unit in pre- scribed m a n n e r .
2 1 . Check all solvent lines, valves, fittings, gasketed closures, and p u m p s for leaks and adjust as necessary. Refer to s t a r t u p p r o c e d u r e when degreaser is ready to be p u t back into operation.
Routine Maintenance
The following points a r e r e c o m m e n d e d in the routine m a i n t e n a n c e of the equipment:
1. Keep all c o m p a r t m e n t s of the equipment filled to the p r e s c r i b e d operat- ing levels.
2. In s t a r t i n g the e q u i p m e n t each day, observe w h e t h e r excessive time is required for v a p o r s to rise a n d hold steady at the midpoint of the condenser coils. Also observe w h e t h e r the vapor level drops a b n o r m a l l y w h e n w o r k is p u t through. If either of the above occurs, the unit may r e q u i r e cleaning, w h e t h e r nor- mally r e c o m m e n d e d cleanout tempera- t u r e s have been reached or not.
3. Keep liquid level sight glasses a n d p o r t h o l e glasses clean.
4. Check solvent p u m p s , gasketed closures, t r a n s f e r lines, a n d so forth daily
for leaks. Repair of leaks at an early stage will result in solvent savings a n d safety.
5. Frequently check the t e m p e r a t u r e of discharging condenser coolant. Main- tain the condenser coolant flow so maxi- m u m outlet t e m p e r a t u r e is in the range of 100 to 120°F (38 to 49°C) for perchlo- roethylene, 1,1,1-trichloroethane a n d trichloroethylene, and less t h a n 75°F (24°C) for methylene chloride a n d tri- chlorotrifluoroethane.
6. If the w a t e r d r a i n outlet on the w a t e r s e p a r a t o r is valved, open the valve frequently a n d allow a c c u m u l a t e d w a t e r to d r a i n out.
7. Periodically check solvent flow r e t u r n i n g to the d e g r e a s e r from the w a t e r s e p a r a t o r . Diminished solvent flow t h r o u g h the s e p a r a t o r may indicate the following:
(a) p a r t i a l block in the distillate line from the collecting trough,
(b) r e d u c e d r a t e of vapor generated due to sludging of heating elements,
(c) excessive contamination, or (d) reduced heat input.
8. Inspect the c o n d e n s a t e collecting trough frequently. If the t r o u g h is over- flowing, a block may have developed in the distillate line b e t w e e n the c o n d e n s a t e trough outlet a n d the w a t e r s e p a r a t o r .
9. When s t e a m is u s e d for heating, check the s t e a m p r e s s u r e gages fre- quently to e n s u r e continued operation within the r e c o m m e n d e d p r e s s u r e range.
Also check s t e a m t r a p s frequently.
10. Keep the conveyor m e c h a n i s m well l u b r i c a t e d at all times.
11. Check the t e m p e r a t u r e of the boiling solvent in the d e g r e a s e r regularly to d e t e r m i n e the c o n t a m i n a t i o n level and, thus, when to clean the degreaser.
Acid D e g r e a s e r s
An "acid d e g r e a s e r " is the result of decom- position of the degreasing solvent to acid p r o d u c t s . An acid d e g r e a s e r may b e recog- nized by the p r e s e n c e of a variety of symp- toms including a strong acid odor, dense white acrid smoke in the vapor zone, pit- ting and r u s t i n g on p a r t s after degreasing, and loss of acid acceptance.
If a d e g r e a s e r is d e t e r m i n e d to have 21
Manual on Vapor Degreasing
22 Manual on Vapor
Degreasing
"gone acid," the following steps should b e taken immediately:
IMMEDIATE ACTION FOR HANDLING AN ACID DEGREASER/STILL