Handbook of Solvents - George Wypych - ChemTech - Ventech!

890 Kaspar D. Hasenclever
Computer control:
All the processes are computer controlled. Drying/Recovering, Distilling/Filtration operate
according to fixed programs; the cleaning cycle can be varied with regard to the requirements
of the garment. The most common program works as follows:
Loading the machine, closing the door, starting computer control:
1 min pumping solvent from working tank into cylinder up to low dip
level (3 l/kg);
3 min pre-cleaning by rotating the cage in the cylinder;
1 min pumping the solvent from the cylinder into the distillation vessel;
1 min spinning;
2 min pumping solvent from working tank into cylinder up to high dip
level (5 l/kg); addition of detergent (2-5 ml/l of solvent);
8 min cleaning by rotating the cage in the cylinder together with filter
action;
1 min pumping the solvent from the cylinder back to the working tank (the
solvent in working tank is filled by overflow from clean tank);
3 min spinning
8 min drying /recovering solvent with recovery system
5 min drying/recovering solvent with charcoal filter.
After the sensor has indicated that the load is free of solvent residue, opening the door and
unloading the machine. After the cleaning process, the garment is controlled for cleaning
quality and can be finished or if necessary, it undergoes spotting/recleaning before finishing.
14.7.1.7 Recycling of solvents in dry cleaning
The recycling of solvents in dry cleaning is very important, because solvents are too expensive
for single use. Three different systems are used for the cleaning of the solvent in order
for it to be recycled:
• Filtration
• Adsorption
• Distillation
Filtration is a simple physical process, separating insoluble parts from the solvent. It is
done during the cleaning cycle.
Adsorption is mainly used together with hydrocarbon solvents, because their high
boiling temperature is insufficient to separate lower boiling contaminants from the solvent.
Adsorption systems use charcoal or bentonites. The solvent is pumped to filters where contaminants
with higher polarity than solvent are adsorbed by the adsorbing material. The adsorbing
material can adsorb contaminants in a quantity of about 20% of its own weight.
After being saturated, the adsorbing material must be replaced and changed to fresh material.
The charged adsorbing material is disposed according to regulations, which is cost intensive.
Distillation is the best cleaning method if the boiling point of solvent is significantly
lower than the boiling point of possible contaminants. With dry cleaning machines using
TCE, distilling is the normal recycling method. The boiling point of TCE is 122°C, which
makes steam heating possible, so that the process can be done safely and cost effectively.
The distillation residue consists of removed soil and detergents. Its quantity is much lower