1. Solid-state adsorption method
Use as solid adsorbent are molecular sieve, activated carbon and activated carbon fiber.
Because of its small microhole, expensive price, and gas drying, molecular sieve is less used for solvent recovery and production, and is mostly used for gas purification.
Activated carbon is a large number of adsorbent used for solvent recovery, which has been flourishing since the early 20th century. Activated carbon traps the solvent gas from the solvent air mixture gas with better effect, and it is easy to be used for water steam desorption and regeneration. For unoxidized solvent gas, such as alkane solvents, can be desorbed by the alcohol recovery machine, for easily oxidized solvent gas, can be desorbed by hot inert gas such as pure nitrogen. At present, the use of granular activated carbon recovery solvent is still the mainstream of domestic solvent recovery. The remove solvent needs to be distilled or membrane separated to achieve a pure solvent. Distillation and purification is generally one solvent with one tower.
2. Absorption method
According to principle of homogeneous solvent, the solvent air mixture gas is introduced from the bottom into the equipment. Through the packing layer of the oily liquid(such as waste oil or diesel oil) with little viscosity on the top, the air and liquid are backward convection, and the solvent molecule is absorbed and dissolved by the oil liquid. By adjusting the height of the packing layer and the flow of the oily liquid, the final exhaust gas can meet the environmental requirements.
An oily liquid that absorbs the solvent can be used directly as a fuel(such as heavy oil for boiler combustion), or to separate the solvent from the oily liquid by fractionation.
3. Freezing condensation method
In some mixed gases, the solvent gas is single and the concentration is high(for example, when gasoline tanks at gas station are filled with oil in summer, only gasoline vapor is discharged from the gas outlet), and its saturated vapor pressure varies greatly with temperature. In this case, method of freezing and condensing can be adopted, that is, the mixed gas will be cooled and condensed through a coiled tube or shell-and-tube condenser, and the solvent will be separated from mixed into a liquid, Freon and other refrigerants can be used for cooling. Liquid nitrogen evaporation refrigeration can also be used, and different refrigerants can be used according to the needs of recovery and conditions. The solvent recovered by this method is of high purity and can be used without other treatment. However, this method is not suitable for the following situations: 1) the amount of exhaust gas is large and the amount of solvent is low; 2) the saturated vapor pressure does not change much with temperature; 3) the mixed gas contains a variety of solvent gases, and their saturated vapor pressure changes with temperature differently, etc.
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Solvent Recovery - Solvent Recycling - Solvent Distillation
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