Pumping of condensable vapours and exhaust vapour condensation

Abstract

The use of chemically resistant oil-free diaphragm pumps to pump condensable vapours allows the recovery of these vapours on the high pressure side. Due to their limited ultimate pressure they mainly replace water jet pumps and thus drastically reduce water consumption and pollution. In addition they raise the efficiency of evaporators and, as a consequence, diminish the pollution of air. The combination of this type of diaphragm pump with an oil-sealed rotary vane pump (“HYBRID” pump) combines the advantages of both pumps, i.e. low ultimate pressure and high resistivity to chemicals. Thermodynamic considerations lead to this set-up, in which the dry pump evacuates the oil reservoir of the rotary vane pump and thus the oil is permanently distilled. Due to the elevated temperatures of the oil (50–70°C) and the reduced pressure (≈ 50 mbar) condensation is avoided or significantly reduced, thus enhancing oil lifetime and maintenance intervals.