Thermocompressor (Steam Jet Thermocompressor)



Steam is the common source of heat in most of the process industries. This steam is mainly produced from fossils and are fast depleting in nature. The generation cost of steam is also increasing drastically day by day. It is therefore an impressive that the process industries focus on steam utilization and initial action to minimize or optimize the use of steam.    

Aricle written By : Rayyan Shaikh

One of the Direct ways of reducing steam consumption is to maximize the use of low pressure flash steam. Thermocompressor offer an energy efficient solution to recover or reclaim low grade or low pressure steam.

A large number of industries vent low pressure steam to the atmosphere as this steam is at low temperatures and therefore can not be useful redeployed in the process. However  with thermocompressor technology one can very easily increase the pressure and temperature of flash steam. As a consequence energy consumption reduces by a significant amount.

What is Thermocompressor ?

Thermocompressor is a fluid jet device that compresses the low pressure steam resulting to a high pressure steam by using the principle  of energy conservation. High pressure motive steam is passed with supersonic speeds through a converging diverging nozzle where it meets the slow moving low pressure steam (through suction inlet)  resulting entrainment and mixing. This mixed jet is then allow to pass through a diffuser (where due to geometry velocity decreases results in increase in pressure energy as per Bernoulli’s principle) at which the kinetic energy is converted into pressure energy. Thus  the discharged steam, which having comparatively higher pressure energy is again put back back into the process for more higher pressure.

The name thermocompressor is derived from the process of using thermal energy or enthalpy of steam to achieve compression.

So Simply thermocompressor is a device which is used to reuse low pressure steam and get it to converted into high pressure steam as a result,  reduces capital cost of company by reducing the consumption.


Figure 1 : Steam Thermocompressor Schematic

Thermocompressor consist of the main parts.

  1. Nozzle
  2. Suction chamber
  3. Mixing Chamber
  4. Diffuser

Thermocompressor have three connection.

  1.  The high pressure steam that enter in the nozzle called motive steam.
  2. The flash steam or LP(low pressure) steam that is recoverd/compressed is know as  the suction steam
  3. The resultant steam that exits the thermocompressor from the diffuser is termed as the discharge steam.
 Figure 2 : One of the arrangement of thermocompressor (Steam Balancing)

 At first the motive steam comes into the suction chamber at very high speed. This create low pressure zone in control chamber cause of this low pressure steam or flash steam is sucked in suction chamber. Both steam mixes together in the mixing chamber and allow to flow through diffuser, where the velocity falls and pressure rises. As a result intermediate pressure steam is obtained.

Working : 

Figure 3 : Thermocompressor operations on a Mollier Diagram
  • High pressure steam called motive steam in expand in the nozzle-process 1-2, this being a isentropic (entropy =constant)  process.
  • Due to frictional losses in the middle the actual process of expansion achieved is represented by process 1-2′.
  • The high velocity of motive steam after the nozzle entertains the low pressure steam ( suction steam).
  • Process 2′-4 and 3-4 represent the mixing process of the motive steam and entrained suction steam.
  • Process 4-5 represents the process in the diffuser.
  • Velocity head of the mixture is converted to pressure head in the diffuser.
  • Due to frictional  losses the actual process Achieved  is 4-5′.


  • No condensation losses take place
  • Thermal efficiency of system is extremely high
  • Entrainment of low pressure steam results in substantial saving
  • No moving parts results minimal maintenance cost 
  • No major operational charges
  • Compact in Size
  • Insensitive to fouling
  • High operational reliability
  • Low investment.


  • Thermocompressor has a wide potential scope from industrial view point.
  • When ever low pressure steam is being vented or being condensate, thermocompressor can be used.
  • Paper industry, solvent extraction plant, tobacco plant textiles, rayon, rubber , sugar dairy, refinery, chemical plants, flash steam recovery, distillery , cogeneration plant.

Content source : Inveno; Wikipedia

Image source : Inveno

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