FUNCTIONAir ejector units are generally of the steam jet type. Although electrically powered units offer the advantage of ease of installation and slightly improved operating efficiency their maintenance requirements has ensured that the most common type on larger installations are steam powered Their primary function is to remove non- condensible gases from the condenser
After passing through the nozzle the high velocity stream jet entrains air and vapour , compresses it, and the mixture passes to a condenser section were it is cooled. The air with any uncondensed steam and vapour passing to the second stage were further compression of the air takes place.
Depending upon the number of stages of the air ejector, the air is now discharged to atmosphere or to a final stage and then to atmosphere.
The condensers are of the surface type and are cooled by condensate, in this way acting as a feed heater.
Either, two complete units or two ejectors mounted on one condenser are used , nozzle diameters are very small typically 1.2 to 4.7 mm and are liable to wear, abrasion and blockage.
When manouevring or at rest provision must be made to ensure that there is adequate flow of condensate through the condenser to provide cooling . This is achieved by means of a recirculating v/v which leads condensate from the outlet of the air ejector condenser outlet ( and other low pressure feed heaters such as an evapourator ) back to the main condenser. The opening of this v/v should be limited as it leads to a loss of plant efficiency.
The position of the cooler can vary; either as shown, incorporated into the tank or on the suction side of the pump.