The conventional industrial practice for capturing solvents contained in low concentrations from large volumes of gas or air consists of blowing the gas through a battery of large vessels containing beds of adsorptive activated granular carbon.

Since both the carbon and the solvent are relatively costly and the solvent is usually highly flammable, one-time use and disposal is uneconomical. It is, therefore, necessary to regenerate the carbon’s adsorptive power and recover the solvent. Conventional practice of recovery/regeneration consists of isolating the "oldest" of the carbon beds from the gas stream and steaming it with low-pressure steam at about one pound gauge pressure. Thus the solvent is driven off by the steam displacing the solvent from the pores of the carbon. At the end of the steaming cycle, reverse gas flow through the bed both cools and dries it for reuse. For solvent recovery, the mixed vapors leaving the bed are totally condensed and subcooled to about 100 F so that the two resulting immiscible liquids can be gravimetrically separated in a settling vessel conventionally called a "decanter." This conventional scheme results in the consumption of considerable quantities of energy.

Units: Dual