Distillation & Solvent Recovery Vacuum
Distillation and solvent recovery run under vacuum to lower boiling points. The gas reaching the pump is often a condensable solvent vapour with some air in-leakage.
A liquid ring pump condenses part of the vapour in the ring and handles the rest reliably; closed-loop versions reuse the sealing liquid. Two-stage or cone types reach the deeper vacuum some columns need.
The pump is normally installed downstream of the column condenser and receiver, where it removes non-condensables and the solvent vapour that escapes condensation. An upstream knock-out vessel protects against liquid slugs, and improving condenser duty can reduce the vapour load presented to the vacuum pump.
The seal liquid must be chemically compatible with the process and easy to separate from the recovered solvent. A closed loop uses a gas-liquid separator, circulation pump and cooler to control both temperature and solvent buildup. Wetted materials may range from cast iron to 304, 316 or duplex stainless steel according to solvent composition and chlorides; mechanical seals and an explosion-protected motor should be specified when the process and hazardous-area classification require them.
The vapour pressure of the circulating liquid at operating temperature sets a practical limit on attainable vacuum and useful capacity. Solvent condensation adds heat and changes the seal-liquid composition, so selection should use the equilibrium gas load and the hottest stabilized loop condition. Check cavitation margin, condenser performance and purge or make-up requirements as one system.
Pumps for this duty: