Steam Ejectors are the simplest means available today for vacuum – raising applications. The Steam Ejectors utilizes high pressure steam to compress low pressure vapours or gases.
This creates a vacuum in a vessel or chamber to which the ejectors is connected. The fundamental operation of an ejector is shown in the illustration:
Steam at pressure Pi expands through a nozzle and exits at very low pressure (Px) and at very high velocity. The low pressure induces a flow of load vapours at a pressure (P1) into the ejector. The two streams i.e. the low pressure, high velocity steam from the nozzle, together with the slower, entrained load vapours, will mix as they converge into the throat of the ejector. Upon leaving the throat, the gases slow down and regain pressure to a pressure P2.
The load gases have been compressed from their original pressure P1 to a new pressure, P2. We define the compression ration for this ejector as P2/P1.
If Ws kg/hr motive steam are required to entrain and compress Wl kg / hr of load vapours, we define the entrainment ratio for this ejector as Wl/Ws. These ratios are computer calculated and are the key parameters in ejector design.
Multi Stage Ejectors Sets
In practice, for suction pressure below 100 mbar absolute, more than one ejector will be used, usually with condensers between the ejector stages. Condensing of motive steam greatly improves Ejector Set efficiency. We supply both barometric and shell-and-tube surface condensers for this purpose.