Vacuum ejectors or vacuum jets extend the operating range of process vacuum systems that is beyond what can be achieved by liquid ring vacuum pump-based systems alone. Utilizing the venturi principle, the motive fluid entrains the process stream (non-condensables and condensables) discharging either into a condenser or the liquid ring vacuum pump.
The motive fluid can either be pressurized steam or atmospheric air. Steam is useful as it can be condensed and removed from the process thus keeping the backing pump size smaller. However, the cost of steam utility may be a cause for a different motive fluid source. Alternatively, we utilize atmospheric air to compress the process to a higher absolute pressure. Because we use atmospheric air, there is no added utility cost. However, because we will still be operating under vacuum, any non-condensable introduced into the process will expand. This causes the backing vacuum pump to increase in size. The added vacuum pump size must be analyzed against the added utility of a steam jet to determine which route is best suited to the application.
Advantages include the following
- No moving parts
- Low cost
- Reduces load on other stages of compression (as a result, helps pull a deeper vacuum)