Process Description for Molecular Sieve Dehydration Plant
Solvent (Ethanol, IPA, Acetonitrile) containing maximum 15% v/v moisture is pumped from solvent feed tank to dehydration plant. Solvent is preheated in Feed preheater with the help of product vapors and then fed to top of Evaporator Column.
The objective of the Evaporator Column is to evaporate solvent and to recover the solvent from purged steam of mole sieve. The Evaporator Column operates under pressure. Energy is supplied to the Evaporator Column through Evaporator Column Reboiler with steam condensing on shell side (thermic fluid can also be used as energy source). The steam condensate can be recycled back to the boiler.
Overhead feed solvent vapors from the Evaporator Column are then passed through Superheater where solvent vapors are superheated. Energy for superheating is supplied by steam condensation on shell side of the Superheater.
Superheated hydrous solvent vapors are sent to twin Adsorbent Beds. The twin Adsorbent Beds operate in cyclic manner. Twin beds are provided to allow for bead regeneration in continuous operation. While one bed is in dehydration mode, the other is in regeneration mode. Depending on feed and product specifications, dehydration-regeneration exchange takes place approximately every few minutes. The feed solvent vapors are passed through the bed under dehydration mode. The Adsorbent Bed will absorb moisture present in feed vapors and dehydrated product solvent vapors are obtained from bottom of the bed.
The product solvent vapors are then passed through Regeneration Preheater and Feed Preheater for heat recovery. The Product solvent vapors are then passed through Product Condenser where product vapors are condensed with the help of cooling water. Condensed product solvent is collected in product receiver. The Product solvent from Product Receiver is pumped to Product Cooler where it is cooled with the help of cooling water and then sent for anhydrous solvent storage.
During regeneration mode, vacuum is applied to the bed under regeneration. A small amount of product solvent vapors are purged through the bed in regeneration mode under high vacuum, to prepare the desiccant for cycle changeover when this bed goes online. The purged solvent vapors act as carrier for removal of moisture from the bed. These solvent vapors along with moisture are obtained from the top of bed. These solvent-water vapors (regeneration stream) are condensed in Regeneration Condenser, which is attached to Vacuum Eductor.
Vacuum is pulled in the system with the help of Vacuum Eductor. Regeneration stream is used as motive fluid for Vacuum Eductor. The regeneration stream coming from the Regeneration Condenser is pumped, preheated in Regeneration Preheater and fed to the Evaporator Column for recovery of solvent. Moisture present in feed solvent is removed from the bottom of the Evaporator Column in the form of spent effluent containing less than 1000 ppm of solvent.
After one cycle is over, the beds are interchanged, that is, the bed on dehydration mode will be switch over to regeneration mode and the bed on regeneration mode will be switch over to dehydration mode, with the help of automation system.
Salient Features of PAL ENGINEERINGS Dehydration System-
- 1. Energy efficient process with a very less steam consumption as compared to conventional distillation process.
- 2. The plant is fully automated, virtually eliminating human error.
- 3. The plant can suitably be operated up to 60 % turndown.