Heat transfer solutions Thermocompressors
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Types of thermocompressor There are two types of thermocompressor; Sonic and Subsonic. Although they look similar, they behave differently and must be controlled differently. Compression ratio In order to determine what type of design the Thermocompressor will be, we need to calculate the 'Compression ratio'.
Discharge pressure (P d ) Suction pressure (P s )
Compression ratio (K) =
Is K > 1.8
Subsonic design
Sonic design
For Example: - The discharge pressure = 2.5 bar g = 3.513 bar a - The suction pressure = 1.2 bar g = 2.213 bar a - The Compression ratio (K) = 3.513 = 1.59 2.213
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Subsonic designs: - Compression ratio (K) is less than 1.8
Sonic designs: - Compression ratio (K) greater than 1.8 - With a sonic design, the Motive (HP) steam flowrate is 'fixed' - The Suction (LP) steam flowrate can operate with full turndown (100% to 0%)
- With a subsonic design, the Motive (HP) steam flowrate can be varied to 'save' steam when process conditions become more favourable - The Suction (LP) steam flowrate can operate with full turndown (100% to 0%) - Spirax Sarco offer a special design called a 'Variable Orifice' thermocompressor which has integrated Motive steam control.
10.3.6
Therefore the subsonic design will provide the optimum performance and effectiveness for the given application.
TI-P493-02 TES Issue 3
Page 5 of 11
SJT Steam Jet Thermocompressor
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