Heat transfer solutions Thermocompressors
6
Please note that for clarity welds are not shown
Low pressure water vapour inlet
Diffuser
High pressure steam inlet
Intermediate pressure outlet
Diffuser
Nozzle
Typical example of the final design of an SJT Steam Jet Thermocompressor
High pressure motive steam enters the SJT Steam Jet Thermocompressor and passes through the nozzle where the high pressure steam energy is converted into kinetic energy. On leaving the nozzle at high velocity, the steam enters the suction chamber where it is brought in contact with the suction stream. There is then an exchange of momentum between the motive and suction streams, resulting in an acceleration of the suction vapours, giving rise to their subsequent entrainment. A uniform mixture results at the narrowest part of the diffuser (called the throat) and finally the reconversion of the velocity energy into pressure energy occurs in the diverging section of the diffuser. An SJT Steam Jet Thermocompressor is a type of Ejector that uses high pressure (HP) steam to entrain low pressure water vapour (LP) and discharges at a pressure (P d ) that lies somewhere between the HP and LP pressures.
6.3 3
Understanding SJT Steam Jet Thermocompressor discharge pressures
An SJT Steam Jet Thermocompressor can be represented by the adjacent diagram:
Motive
Discharge
Suction
10.3.4
The SJT Steam Jet Thermocompressor is designed to 'match' a specific discharge pressure. For example the following SJT is designed to discharge against a backpressure of 18.5 bar g. However, if the unit is allowed to discharge to atmosphere, the actual discharge pressure is atmospheric pressure, even though it was designed to discharge at a higher pressure.
Where: P d = Discharge pressure
Actual P d = 0 bar g
Continued on next page
TI-P493-02 TES Issue 3
Page 3 of 11
SJT Steam Jet Thermocompressor
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