Recovery of Solvent

Solvent can be recovered from the soils removed in cleaning parts and from solvent vapors in air. Used solvent may be transferred to a still and recovered by distillation with or without steam. Also, the solvent may be recovered by using the degreaser as its own still and drawing off the distillate to storage.

Distillation in the degreasing unit may be accomplished by operating the degreaser with the solvent return line closed. After being passed through the water separator, the distilled solvent may be collected in a clean drum or tank, leaving the sludge behind in the boiling compartment. Some degreasers have built-in tanks for this purpose. As the concentration of high boiling oils in the sludge increases, the amount of solvent recovered decreases sharply until it is no longer profitable to continue distillation.

At no time during distillation should the heating element be exposed. Such exposure may be detected by the copious white fumes generated. The high surface temperature developed by an exposed heater destroys the heater, deteriorates the solvent, and, in extreme cases, may cause a flash fire.

Solvent Still. The use of a special still for solvent recovery is usually justified when large amounts of soil must be removed from the solvent daily, when cleaning requires immersion in a solvent with very little contamination, or when downtime for maintenance must be held to an absolute minimum.

A still may be plumbed directly to a degreaser. A solvent level detector in the still senses when a pump drawing solvent from the degreaser should be turned on and off, in this arrangement. Alternatively, dirty solvent from multiple degreasers may be recovered in a centralized still or by a service company.

Solvent vapors captured in ventilation air streams may be recovered by adsorption on activated carbon. When the carbon becomes saturated with solvent, the solvent can be revaporized with steam, condensed to a liquid, separated from the steam condensate, and collected for reuse.

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