Jet Compressors & Thermocompressors

Type 426 Variable Area Nozzle Thermocompressor Jet Compressors are used in the process, pulp and paper, petroleum, power, gas and many other industries to circulate steam or gas, boost or recover low-pressure steam, and to mix, transfer, and compress gases. Jet compressors use a jet of high pressure gas to entrain a low-pressure gas, mix the two thoroughly, and discharge the mixture at an intermediate pressure. Gases can be steam, air, propane, or other mixture - basically any gas. When both motive and suction gases are steam, the compressor is generally referred to as a Thermocompressor.

Compared with other types of compressing equipment, Jet Compressors offer definite advantages:

Two different types of jet compressor are available:

Variable Area Nozzle Compressor - this type of Jet Compressor is used when motive, suction, or discharge conditions vary and it is necessary to control the discharge pressure or flow. Control of this compressor is accomplished by a spindle which regulates the motive gas flowing through the nozzle, however unlike a control valve where energy is lost, the spindle can reduce flow without reducing the available energy. Control of the spindle can activated by temperature, pressure, flow or suction to motive ratio and variation of the spindle travel can be achieved with any suitable actuator.

Fixed Nozzle Compressor - this type of Jet Compressor has no regulating spindle, and are generally used where operating conditions are stable. These compressors will accept some level of variation however the operating envelop is much smaller than that of the Variable Area Nozzle Compressor.

Typical applications

While there are numerous applications for Jet Compressors a few of their primary applications can seen below:

Gas Compressing

Fixed Nozzle Jet Compressors make it possible to mix natural gas or L-P gases in desired proportions without the need for any complicated apparatus. In many installations jet compressors are used when the necessity arises for producing a gas of a specific heating value and density to substitute for another commonly used gas. The compressors will operate at peak load conditions or to provide emergency supplies in case of emergency breakdowns. Using jet compressors propane, butane or natural gas can be mixed with air in a specific proportion to obtain the desired heating value. In gas mixing applications automatic spindle control is not important as these units are designed for a constant mixing ratio. Therefore once correctly adjusted the fixed nozzle compressor will perform consistently time after time. To obtain a system with enough flexibility to match load variations, multiple units are usually installed and used in parallel operation.

Type 420 Fixed Nozzle Compressor Gas Compressing Application

The compressors in this application do not have regulating spindles, but the set of units is sized so that 15 variations of capacity are available and each unit is designed to handle double the capacity of the preceding unit. Each gas compressor is operated either wide open or is shut off by means of a valve. A check valve should be installed on the suction side of each compressor to close automatically in order to prevent back flow of gas in to the intake manifold when a compressor is shut off.

Recirculating Steam

In a recirculating operation, the jet compressor entrains steam which would normally be wasted, it does this by using higher pressure steam as the motive force to entrain the low-pressure steam, and then discharge at an intermediate pressure to the system pipe work. Typical systems could be a tire vulcaniser, a paper mill Yankee Dryer (both illustrated below), drying roll, or any type vessel where it is difficult to remove condensate such as for instance, a heat exchanger. Process plants where heating is accomplished by condensing steam may find condensate removal to be a problem, to help over come this many plants use jet compressors instead of reducing valves as the jet compressor increases the velocity of steam flow through the system and carries condensate with it. In this application, without a compressor condensate must be removed by an often impractical method of blowing down the system.

Jet compressors recirculates with out loss of heat or energy, by using exhaust steam which might otherwise be wasted the compressor improves heat transfer rates and increases the heating or drying capacity of the system. Energy normally lost in a reducing valve is used to circulate the steam through the system. The jet compressor increases flow velocity and sweeps condensate along with the steam.

Jet compressors used in recirculation of steam are usually automatically controlled to allow for accurate control of the downstream pressure. Control is no more complex than that required for a reducing valve, namely control by pressure and temperature. Essentially, controls should provide for a variable throttling range and a reset feature. The jet compressor will desuperheat to some extent. However, where steam pressures and temperatures are higher than is desired, additional desuperheating equipment should be used. For information on desuperheaters please look here .

Type 426 Variable Area Nozzle Recirculating Steam Application

Shown above, Watchcase vulcanisers are being used in making rubber tires and tubes, this offers an excellent example of Type 426 Steam Jet Compressors engaged in a recirculation duty. Here a constant circulation of steam is necessary to avoid air and condensate pockets, resulting in under cured spots in the product. The compressor discharges at a velocity sufficient to maintain proper recirculation of the steam and to accelerate removal of condensate that would otherwise lower the efficiency of the operation. Only enough live steam is required to make up for the lost steam that has been condensed through the process.

Type 426 Variable Area Nozzle Yankee Dryer Application

In this application, Type 426 Steam Jet Compressors are used for recirculating in connection with a Yankee Dryer for paper manufacture in Paper mills. Regulation here must be precise to maintain proper steam temperature on the drying rolls used for tissue paper. Pressure difference between the 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 flash tank.

Reducing and Compressing

Jet compressors can be used to advantage in plants by compressing steam or reducing pressure. For instance, a plant may have been built originally to provide steam at certain pressures. Over a time conditions might change to an extent where the available pressures no longer provide a sufficiently wide range, a Jet Compressor can be used to correct the condition.

In cases where steam pressure is too high, the jet compressor can mix the high-pressure steam with exhaust steam and produce the required discharge pressure. In such operations, the cost of a jet compressor plus steam saving should be compared with the cost of a pressure reducing valve. Where steam pressure is too low, and high-pressure steam is available for operating the unit, the compressor can mix the two and boost the low-pressure steam. Low-pressure steam can be flashed-off condensate, steam from a low-pressure main, exhaust from a turbine, or from any other source.

Type 426 Variable Area Nozzle in a Steam Compressing or Booster Application

Here, two Type 426 Variable Area Nozzle Jet Compressors are used to boost the pressure of flash steam from a condensate receiver which normally 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 pipeline 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 airline 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. When the load starts to decrease the second unit shuts down completely before the first unit begins to reduce.

Registered Address - Venturi Jet Pumps Ltd, Venturi House, Edensor Road, Longton, Stoke on Trent, Staffordshire, ST3 2QE, United Kingdom
Tel. : +44 (0) 1782 599800, Fax. : +44 (0) 1782 599009
Company Registration Number - GB 3654492