Vacuum systems for vinyl chloride extraction during PVC manufacture
PVC can be made from vinyl chloride (VC) using one of three methods: in a one- or two-stage process as substance that is formed during polymerisation, through an aqueous phase as emulsion that is formed during polymerisation or through intermittent suspension polymerisation.
In the case of suspension polymerisation, vinyl chloride is extracted from the PVC. This is performed in reactors equipped with agitators. The resulting polymerisate is then available in the form of beads or granules.
The vinyl chloride evacuated out of the reactors was to be stored in its compressed state in a so-called gasometer under positive pressure at a leading European manufacturer of PVC resins, source chemicals and special chemicals. The vinyl chloride is then circulated in the reactors. The objective was to have evacuation durations under five minutes. Plus it should be possible to have two reactors evacuated at the same time.
HERMETIC-Pumpen selected liquid ring vacuum pumps with an extraction capacity of 1800 m³/h and a motor capacity of 75 kW. The only possible configuration was a hermetically sealed version with a magnetic coupling due to the harmful properties of vinyl chloride.
Two operating pumps and one reserve vacuum pump for the HERMETIC-Pumpen vacuum system ensure that the two reactors can be evacuated concurrently at any given time. The configuration was selected so that replacement with the reserve vacuum pump of one or the other operating pump was ensured with the aid of an isolation valve.
Hermetically sealed centrifugal pumps and pumps from HERMETIC with a magnetic coupling ensure that the system is supplied with operating liquid.
The monitoring of fill levels and flow rates enables automation so that the vacuum system can be remotely controlled and operate in batch mode.