The high pressure motive steam expands through a specially designed
nozzle that converts the pressure to a high velocity jet of steam at
the exit of the nozzle. The high velocity steam entrains and mixes with
the suction gas.The combined flow passes through the venturi tail
where the gas is compressed to an intermediate pressure between the
suction and motive pressures.
A single stage ejector is capable of providing a suction pressure of 50
Torr when discharging to atmospheric pressure. However,at a pressure
of approximately 100 Torr or lower, & where cooling water is available,
a multistage ejector system with a condenser between the stages is
often used to lower overall steam usage At pressures below 50 Torr
condensers are almost always used between the ejector stages to
lower motive steam consumption.
Barometric installation is required for gravity draining of the condensate
from interstage condensers. Based on water drainage,barometric height
is 34 feet. However, a minimum of 38 feet is recommended to account
for barometric pressure fluctuations, tail pipe pressure losses, and
vena-contracta losses at the drain connection of the condenser. If
barometric installation is not possible specially designed low level
operating systems are available from Crystal.
APPLICATION
Steam jet vacuum ejectors provide a low cost solution for most
applications requiring a vacuum. Applications for which vacuum ejectors
can be used to provide the vacuum include metal degassing, freeze
drying and vacuum drying operations, vacuum distillation, desalination
refrigeration, crystallization, and removal of air from turbine condensers.
Since steam jet ejectors have no moving parts , they may provide a
reliable alternative to maintenance intensive mechanical pump systems
where downtime could be costly. Steam jet ejectors can also be
constructed of exotic metals at affordable prices, and they can be
provided within reasonable delivery times.
CONSTRUCTION
The standard construction materials are steel and stainless steel. The
ejectors can also be machined or fabricated in a variety of corrosion
resistant materials such as titanium, Hastelloy, brass, Inconel, Teflon,
graphite, Haveg, and FRP.
Suction and discharge connections are normally flanged. Motive steam
inlet connections are threaded for small ejectors and flanged for larger
fabricated ejectors.
OPERATION
Steam jet vacuum ejectors are compressors that
utilize pressure steam as the motivating fluid to
compress gas to atmospheric pressure from a
subatmospheric pressure (vacuum)at the inlet of
the system. Since the compression of a single
ejector is limited, jet ejectors are commonly
staged by connecting the ejectors to series
to produce a lower pressure (higher vacuum) at the inlet of the system. Ejectors
are also referred to as boosters, high vacuum ejectors, and low vacuum ejectors,
respectively.
