High efficiency devolatilization

Vacuum technology plays a special role in Gneuss‘ melt degassing processes. Not only is the reliable, process-constant and energy-saving generation of the required vacuum important, but also the separation of foreign substances or water from the degassed vapours. Depending on the specific requirements, different partial pressure drops are needed. As it is inevitable that monomers, oligomers or other solid components or sublimates are sucked in during polymer degassing, the use of efficient separation systems is essential to protect the pumps.

Due to their large surface area, OMNI MRS extruders can in most cases operate at an absolute pressure of 25 mbar. This allows the use of robust water ring pumps, which generate the vacuum by means of a rotating impeller running in a liquid ring. Water ring technology eliminates the need for additional separation systems; gases and volatiles are condensed and released into the process water stream. The circulating liquid is cleaned by a belt filter, minimising maintenance of the entire system. The combination of the water ring pump and the belt filter means that even sticky monomers and oligomers, or even hard impurities and foreign matter, cannot damage the system.

The circulation of process water generates heat which must be removed by a heat exchanger. Thanks to the intelligent design of the robust Gneuss vacuum system, the heat exchanger can be easily cleaned during operation if necessary.

While the MRS extruder operates with the low-maintenance 25 mbar liquid pump system as standard, special effects can be achieved by combining the extruder‘s intensive surface exchange with a lower vacuum (e.g. 1 mbar). During the degassing process on the high-performance OMNImax and OMNIboost recycling systems, in addition to water vapour and ethylene glycol, a large amount of monomers, dimers, waxes or other sticky substances are extracted which quickly block the conventional, closely intermeshing vacuum generation systems. The focus must therefore be on separating these substances between the degassing dome and the vacuum generator.

Gneuss has developed vacuum technologies that are optimally adapted to the respective processes.
During degassing, a large proportion of the gases consists of water vapour, sometimes up to 1 % of the throughput and more. For a 1000 kg/h system this means 10 l/h of water or 10 m³/h of water vapour (under standard conditions) to be extracted.

With a lower vacuum, this gives a theoretical suction capacity of 10,000 m³/h, which would require a very large system size. For this reason, robust cold trap technology is used for vacuum degassing. This is cooled by a very cold circulating medium so that the extracted water vapour passes into the solid phase (resublimation). The ice deposited on the heat transfer surfaces (as well as any other products that are also removed) can then be removed by either mechanical cleaning during the process or by thawing.

The reduced pumping volume, consisting of residual gas and any polymer filaments or droplets due to high flow velocities, is then passed through a safety filter before the residual gas flow is fed to the pumps.
The use of sublimators in Gneuss vacuum technology drastically reduces pump volume, allowing the use of smaller pumps and lower energy consumption. It also increases the reliability of the vacuum generators used.