Air Gas Liquid Drying System
System Operation
Desiccant systems for liquid dehydration have two basic cycles— adsorption (where water is removed by passage of the liquid through the desiccant material) and reactivation (where the water is stripped from the desiccant by the application of heat). The operations are described below.
Adsorption.
The removal of dissolved water from liquids is accomplished by passage of the liquid through a freshly reactivated packed column of granular desiccant material.
Continuous operation is accomplished by the use of dual adsorbers, with one tower on the process stream while the other is being reactivated.
Reactivation.
The flow diagrams show typical valving arrangements for the Process Systems type "IH" dryer and Convection type dryer.
Reactivation is accomplished in the following steps:
- Drain the tower of liquid product.
- Heat the desiccant to release water.
- Remove released water from the tower.
- Cool and refill.
Before reactivating a tower, the single volume of process liquid must be emptied. Low volatility liquids can be drained or pumped into a storage tank. Many highly volatile liquids (e.g., propane) can be pumped or pressurized (by heating) back into the process line.
Heating of the desiccant in the type "IH" dryer is accomplished with internal heaters (electric or steam) in conjunction with the use of a dry nonreactive purge gas and in the Convection dryer by passing a hot gas stream through the bed. During reactivation the residual process liquid and adsorbed water are vaporized as reactivation temperatures are attained.
The reactivation gas flow provides the means for removing product and water vapors. Some highly volatile liquids can be vaporized to provide the source for the reactivation gas. A vaporizer for this purpose can be provided as an accessory.
Before placing a reactivated tower in service, the bed should be cooled (i.e., by radiation or by continued circulation of cool regeneration gas). Many liquids are sufficiently stable so that cooling of the desiccant can be accomplished by quenching or self-refrigeration at the time of filling.
Designs
Process Systems liquid dryers are offered in two basic designs, internal heat reactivation (IH type) and external heat reactivation (Convection type). Typical flow diagrams for each are shown on the facing page.
Reactivation system alternatives include:
I. Type of Reactivation System
- A. Open (once through)
- B. Closed (recirculated high or low pressure)
- C. Open Heating, Closed Cooling
II. Heat Source
- A. Electric
- B. Steam
- C. Electric and Steam Combination
III. Reactivation System Components
- A. Heater only
- B. Heater and Blower
- C. Heater and Cooler
- D. Heater, Cooler, and Blower or Pump
IV. Reactivation Flow Configuration
- A. Cocurrent or Countercurrent Heating, No Cooling
- B. Cocurrent Heating and Cooling
- C. Countercurrent Heating and Cooling
- D. Countercurrent Heating, Cocurrent Cooling
Applications
Process Systems applies 30 years of experience in adsorption systems to the design of liquid dryers. Process Systems is capable of designing liquid dryers for many diverse applications.
A partial list of typical liquids dried by Process Systems includes:
- •Aromatics—Benzene, Toluene, Xylene
- •Saturated Hydrocarbons—Propane, Butane, Pentane, Hexane
- •Unsaturated Hydrocarbons—Butadiene, Butene, Propylene-Propane Mixtures
- •Chlorinated Hydrocarbons—Methylene Chloride, Trichloroethylene, Trichloroethane
- •Miscellaneous Liquids—Ethanol, Vinyl Chloride, Acetone, Tetrahydrofuran, Dimethylacetamide, Methyl-Ethyl-Ketone, Ethylene Dichloride, Normal Paraffins, Kerosene