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Thermocompressors

Principle of Operation of Thermocompressors

The Thermocompressor is an ejector used when both motive and suction gases are steam. Thermocompressors have automatically-controlled spindles. They are used when pressure suction or discharge conditions vary and it is necessary to control discharge pressure or flow. Thermocompressor spindles are designed to act as temporary valves and provide tight shut-off. Thermocompressors are available in materials to fit operating conditions or as specified by the customer.

Figure 426 Thermocompressor with actuator, stuffing box, spindle, nozzle, and diffuser
Figure 426 Thermocompressors are used when pressure, suction, or discharge conditions vary and the necessity to control discharge pressure or flow
Figure 439 Jet Compressor are used in applications operating over a range of pressures and differential pressures

Fig. 426 Thermocompressors have automatically-controlled spindles. The spindle can be operated with a diaphragm, piston, or motor actuator using any standard instrument signal, either electric or pneumatic. The Fig. 439 Thermocompressor is the threaded-connection version of the Fig. 426.

Fig. 426 and Fig. 439 Thermocompressors are Automatic Jet Compressors that can be used in applications operating over a range of pressure and differential pressure. Thermocompressors may be utilized wherever available energy is being lost through reducing valves; such as high pressure steam reduced and desuperheated for process use and mixing of gases without use of mechanical compressors. Diaphragm and piston operators use any standard split or full range, electric, electronic, or pneumatic instrument signal. The control can be activated by temperature, pressure, flow, or suction to motive gas ratio.

  • Watchcase vulcanizers used in making rubber tires and tubes.
  • Steam Jet Compressors are used for recirculating in connection with a Yankee Dryer for paper.
  • Jet Compressors are used to boost the pressure of flash steam from a condensate receiver.
  • Recirculating in Yankee Dryers with diaphragm operated make-up valve.
  • Used in dryer bank application. As part of a steam and condensate system in paper mill industry.
Thermocompressor recirculation in watchcase vulcanizers
Fig. 426 Thermocompressor application in watchcase vulcanizers.
Watchcase vulcanizers used in making rubber tires and tubes offer an excellent example of Fig. 426 Steam Jet Compressors engaged in recirculation. Here, a constant circulation of steam is necessary to avoid air and condensate pockets and resulting undercured spots in the product. The compressor discharges at a velocity sufficient to maintain proper recirculation of the steam and to accelerate removal of condensate which would otherwise lower the efficiency of the operation. Only enough live steam is required to make up for that which has been condensed.
Thermocompressor recirculation in yankee dryer paper machine application
Fig. 426 Steam Jet Compressors Used for Recirculating in Connection with a Yankee Dryer for Paper.
Regulation here must be precise to maintain proper steam temperature on the drying rolls used for tissue paper. Pressure difference between suction and discharge must be maintained at a level high enough to overcome the combination of the pressure drop within the roll, the centrifugal force of the condensate to be removed, and the pressure losses in the piping and condensate separator or flash tank. Automatic regulation is by means of an air-operated pressure controller and diaphragm or piston operator. This same system is also being used for banks of dryer rolls on newsprint and board machines.
Thermocompressor using high pressure steam to entrain flash steam
Fig. 426 Jet Compressors Used to Boost the Pressure of Flash Steam From a Condensate Receiver.
Normally, this steam would be at atmospheric pressure. The two compressors use high pressure steam to entrain the flash steam and discharge at an intermediate pressure into a main which distributes the supply throughout a plant. An air operated pressure controller is affected by the pressure in the main and causes an increase or decrease in the pressure in the air line to the control mechanism on the compressor. A pressure relief valve acts as a guard against the building up of pressure in the receiver. The control system operates the two units in sequence and allows operation at a satisfactory entrainment ratio with varying capacities. The first one operates up to its full capacity before the second begins to operate. Upon load decrease, the second unit shuts down completely before the first unit begins to reduce.
Thermocompressor installed in parallel with diaphragm operated make-up valve
A Fig 426 Thermocompressor Installed in Parallel with Diaphragm Operated Make-up Valve.
Typically, a pressure controller is used for control and set for desired steam pressure and operates the spindles in sequence by split ranging the valve positioners.The Thermocompressor is sized to pass the steam required for heating the dryer under load. The make up valve is sized to provide additional steam required for warm up. Valve operators are arranged to close the steam valve in the event of failure of the control system by means of springs. This protects the dryer from over pressure. The Thermocompressor is designed to provide the necessary quantity of recirculated steam to “sweep” out the condensate and overcome the consequent pressure drop through the drainage system. It is not necessary to control the pressure drop by means of a blow thru valve since the characteristics of the Thermocompressor are such that sufficient recirculation will be provided with the varying steam pressures. When Thermocompressors are not used, it is sometimes necessary to desuperheat the steam down stream of the dryer pressure control valve. When a Thermocompressor is used, the moisture in the steam entrained from the separator reduces the temperature of the steam supplied and eliminates the need for a desuperheater unless the motive steam contains high superheat.
Thermocompressor used in dryer bank application in paper industry
Thermocompressor Used in Dryer Bank Application
Many paper machines operate with several banks of dryers 4 feet and larger in diameter depending on the number of dryers and the type of machine. These are manifolded with anywhere from 2-25 dryers operating at a given steam pressure. The problem of removing condensate is much simpler than in the Yankee Dryer due to the smaller diameter. Standard practice has been to blow thru steam from one bank of dryers to the next bank – operating at a lower pressure with each succeeding bank dropping in pressure. This continues to the wet end where either the first dryers condense the steam or it is discharged to a surface condenser before returning to the boiler. This type of system has been quite successful but limits the flexibility in adjusting the dryer pressures. It is possible to apply thermocompressors to any given bank of dryers either eliminating or reducing blow thru to subsequent banks and allowing complete flexibility in the dryer temperature.
In this type of application, the amount of blow thru required for condensate removal is low and only sufficient steam for good drainage is applied through the Thermocompressor. The remaining steam is added through the steam control valve. Dryer pressure is controlled by the main steam valve with the Thermocompressor allowed to run at the smaller flow. A diaphragm head may be utilized on the Thermocompressor which would normally remain wide open but will provide a fail safe feature should the control system fail. As a wide range of pressures is to be encountered on the same bank of dryers, it may be necessary to adjust the spindle position on the thermocompressor to obtain optimum drainage. Typically, the Thermocompressor would be wide open at high dryer pressures and partially throttled for extremely low dryer pressures. It is necessary to provide this adjustment either by hand control by the operator or by means of automatic control, separate from the dryer pressure control.

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