Many technologies have been used to provide vacuum for chemical and pharmaceutical processes. Some examples include steam jet ejector systems using the Venturi effect to draw a vacuum, liquid-ring vacuum pumps using water as a sealant and rotary vane vacuum pumps using a once-through sealing system. Each of these technologies continues to have a place in chemical and pharmaceutical applications, but dry screw vacuum technology is preferred in most chemical and pharmaceutical applications since no operating fluid is required to compress the process gas.
In a screw vacuum pump, two interlocking screw-shaped rotors rotate in opposite directions. The process vapors are drawn in, trapped between the cylinder and screw chambers, compressed, and transported to the gas outlet.
During the compression process the screw rotors do not contact each other or the cylinder. Precise manufacturing and minimal clearance between the moving parts enable this and guarantee an ultimate pressure of Advantages of Dry Screw Vacuum Pumps:
- dry compression, no contamination or reaction possible between process gas and operating fluid
- ultimate vacuum
- energy efficient
- can be designed for nearly all process gases thanks to material selection and temperature regulation
Disadvantages of Dry Screw Vacuum Pumps:
- sensitive to particles entering the system
Dry screw vacuum pumps should not be confused with oil-lubricated screw vacuum pumps. Oil-lubricated screw vacuum pumps use the same principle of two interlocking screw rotors rotating to move the gas through the pump, and are “dry” in the sense that they do not use water as a sealant. They do use oil as a recirculating operating fluid/sealant in the pumping chamber and, therefore, have the same potential issues in chemical applications as other pumps using operating fluids/sealants (recirculating oil-sealed rotary vane, liquid ring, etc.).
These issues include contamination of the process vapors with the sealant, contamination of the sealant with process material due to condensation, absorption, reaction, etc., leading to reduced capacity and vacuum capability, as well as oil breakdown/degradation.
Since dry screw vacuum pumps do not use any sealant in the pumping chamber, they should not experience these issues.
The choice of vacuum technology has been driven by influences including rising energy costs, environmental regulations and increasing costs of water treatment and hazardous waste disposal. As a result, the market has been driven to seek vacuum technologies that will provide high efficiency while minimizing waste streams.
Dry screw vacuum pumps can be a good choice in that they can provide high efficiency while reducing additional waste streams through the elimination of operating fluids, whether they be steam, water or oil. As stated above, dry screw pumps are frequently integrated into custom-designed vacuum systems incorporating components to optimize the operation and capability of the vacuum pump with regard to flow capacity and vacuum level, and to protect the pump and components.