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How an air ejector works in a boiler feed system

The air ejector draws out the air and vapours which are released from the condensing steam in the condenser. If the air were not removed from the system it could cause corrosion problems in the boiler. Also, air present in the condenser would affect the condensing process and cause a back pressure in the condenser.



The back pressure would increase the exhaust steam pressure and reduce the thermal efficiency of the plant. A two-stage twin-element air ejector is shown in Figure .

In the first stage a steam-operated air ejector acts as a pump to draw in the air and vapours from the condenser. The mixture then passes into a condensing unit which is circulated by feedwater. The feedwater is heated and the steam and gases are mostly condensed.

The condensed vapours and steam are returned to the main condenser via a drain and the remaining air and gases pass to the second stage where the process is repeated. Any remaining air and gases are released to the atmosphere via a vacuum-retaining valve.
The feed water is circulated through U-tubes in each of the two stages. A pair of ejectors are fitted to each stage, although only one of each is required for satisfactory operation of the unit.

Feed system air ejector

Fig:Feed system air ejector


Summarized below more guidance for marine feed system:
  1. Open feed system for an auxiliary boiler - how it works
  2. In open feed system for an auxiliary boiler , the exhaust steam from the various services is condensed in the condenser. The condenser is circulated by sea water and may operate at atmospheric pressure or under a small amount of vacuum. The condensate then drains under the action of gravity to the hotwell and feed filter tank....


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  3. Closed feed system for an auxiliary boiler - operating principle
  4. A closed feed system for a high pressure watertube boiler supplying a main propulsion steam turbine is shown in Figure above. The steam turbine will exhaust into the condenser which will be at a high vacuum.

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  5. How De-aerator works in a boiler feed system
  6. The de-aerator completes the air and vapour removal process begun in the condenser. The condenser is a heat exchanger which removes the latent heat from exhaust steam so that it condenses and can be pumped back into the boiler

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  7. Heat exchangers in a boiler feed system /steam turbines
  8. The gland steam condenser, drains cooler and low-pressure feed heater are all heat exchangers of the shell and tube type. Each is used in some particular way to recover heat from exhaust steam by heating the feedwater which is circulated through the units.

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  9. Auxiliary Feed systems for boilers and steam turbines
  10. Where, for instance, steam-driven deck auxiliaries are in use, a separate auxiliary condenser operating at about atmospheric pressure will condense the incoming steam . An extraction pump will supply the condensate to an air ejector which will return the feedwater to the main system at a point between the gland steam condenser and the drains cooler.....

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    Boiler feed operation and maintenance
    Extraction pumps should be checked regularly to ensure that the sealing arrangements are preventing air from entering the system. It is usual with most types of glands to permit a slight leakage of water to ensure lubrication of the shaft and the gland.

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  11. Function of High pressure feed heater
  12. The high-pressure feed heater is a heat exchanger of the shell and tube type which further heats the feedwater before entry to the boiler. Further heat may be added to the feedwater without its becoming steam since its pressure has now been raised by the feed pump.....

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  13. Sea water circulation of coolers for lubricating oil, piston cooling, jacket water, charge air, turbo-charger
  14. The usual arrangement for motorships has been to have sea-water circulation of coolers for lubricating oil, piston cooling, jacket water, charge air, turbo-charger oil , fuel valve cooling, plus direct sea-water cooling for air compressors and evaporators.....

  15. Feed extraction pump - working procedure
  16. The extraction pump is used to draw water from a condenser which is under vacuum.The pump also provides the pressure to deliver the feed water to the de-aerator or feed pump inlet.

  17. How an air ejector works in a boiler feed system
  18. The air ejector draws out the air and vapours which are released from the condensing steam in the condenser. If the air were not removed from the system it could cause corrosion problems in the boiler. Also, air present in the condenser would affect the condensing process and cause a back pressure in the condenser.....

  19. Function of condenser in a feed system for boiler and steam turbine
  20. The condenser is a heat exchanger which removes the latent heat from exhaust steam so that it condenses and can be pumped back into the boiler. The feed system completes the cycle between boiler and turbine to enable the exhausted steam to return to the boiler as feedwater.



Marine machineries - Useful tags

Marine diesel engines ||Steam generating plant ||Air conditioning system ||Compressed air ||Marine batteries ||Cargo refrigeration ||Centrifugal pump ||Various coolers ||Emergency power supply ||Exhaust gas heat exchangers ||Feed system ||Feed extraction pump || Flow measurement || Four stroke engines || Fuel injector || Fuel oil system || Fuel oil treatment ||Gearboxes || Governor || Marine incinerator || Lub oil filters || MAN B&W engine || Marine condensers || Oily water separator || Overspeed protection devices || Piston & piston rings || Crankshaft deflection || Marine pumps || Various refrigerants || Sewage treatment plant || Propellers || Power Plants || Starting air system || Steam turbines || Steering gear || Sulzer engine || Turbine gearing || Turbochargers || Two stroke engines || UMS operations || Drydocking & major repairs || Critical machinery || Deck machineries & cargo gears || Control and instrumentation ||Fire protection ||Engine room safety ||






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