Finvac vacuum drying upgrades11 March 2010
Vacuum dryers have been around for just over fifty years but recent research into vacuum drying processes has shown some disadvantages in vacuum drying techniques commonly used today.
In most cases high vacuum, low temperature drying is created by a mechanical vapour recompression unit (turbo) between the condensers and the liquid ring vacuum pump. This kind of structure is beneficial only if cooling water below 10ºC is available (ref: Everest Transmission 2005). Cooling water of a higher temperature makes condensers obsolete and causes all the water vapour from the leather to enter the vacuum pump, increasing the liquid ring pump size and causing much higher power requirements.
Liquid ring pumps are used for creating and maintaining the vacuum. There are two main choices for sealing the liquid ring pump, either water or oil. By using oil instead of water it is possible to achieve higher vacuum with the same working temperature. However, if the pump is serviced by oil there’s a huge risk of running the pump at too high a vacuum. In such a situation the condenser stops working and all the water vapour is sucked into the liquid ring pump and gets mixed with the oil causing the resulting oil to leak into the sewer with drain water. Other disadvantages are that the gaseous volume in the liquid ring pump increases and more electricity is needed for running the pump.
Finvac Dryers Ltd have created two alternative solutions to avoid these problems. Finvac AV is new vacuum drying technology using a heat pump to recycle energy back from condenser to the heating table. The condenser temperature is lowered to +2ºC (vacuum 96%) can easily be achieved. The main benefits of AV technology are: effective low temperature drying of leather, steam or water cooling are not needed during operation. Finvac SC is a cost effective technology using spray condensing instead of a tube condenser. SC technology is highly advantageous especially if a cooling tower is used as it minimises the temperature difference between the cooling water and the vacuum system. By combining a jet booster with SC technology, it is possible to maintain a vacuum up to 97% already with as warm as 20ºC cooling water.