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 EJECTOR
SETS
In practice, for suction pressure below 100 mbar absolute, more than
one ejector will be used, usually with condensors between the ejector stages.
Condensing of motive steam greatly improves Ejector Set efficiency. We supply
both barometric and shell-and-tube surface condensors for this purpose.
APPLIED VACUUM have
been involved in designing, fabricating and commissioning multi-stage Ejector
Sets since the mid 1970's. Our computerised designs yield steam and cooling water
efficiencies which are comparable to those offered by manufacturers worldwide. We
have supplied Multi - stage Ejector sets fabricated in Carbon Steel, Stainless
Steel, Titanium, PTFE, Carbon and others. The
Ejector Sets operate in a range of suction pressures down to 0,3 mbar absolute,
and carry loads of up to 1000 kg/hr.
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