Distillation is used to separate liquid organic wastes, primarily spent solvents, for full or partial recovery and reuse. Both halogenated and nonhalogenated solvents can be recovered via distillation. Liquids to be separated must have different volatilities. Distillation for recovery is limited by the presence of volatile or thermally reactive suspended solids. If constituents in the input waste stream form an azeotrope (a specific mixture of liquids exhibiting maximum or minimum boiling point with the individual constituents), the energy cost to break the azeotrope can be prohibitive.
Batch distillation in a heated still pot with condensation of overhead vapors is easily controlled and flexible, but cannot achieve the high product quality typical of continuous fractional distillation. Small, packaged-batch stills treating one drum or less per day are becoming popular for on-site recovery of solvents. Continuous fractional distillation is accomplished in tray columns or packed columns ranging up to 40 ft in diameter and 200 ft high. Each is equipped with a reboiler, a condenser, and an accumulator. Unit capacity is a function of the processed waste, purity requirements, reflux ratios, and heat input. Fractional distillation is not applicable to liquids with high viscosity at high temperature, liquids with high solid concentrations, polyurethanes, or inorganics.
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