The Steam Condensate System
6. Steam Turbine Condenser
Expanded steam from the low pressure turbine is drawn into the tube condenser by a vacuum which is maintained at 28"- 29"Hg where it is condensed by water which has been cooled in the cooling tower.
7. Air Ejector
The air ejectors are used to create the initial vacuum in the condenser and maintain a vacuum of 28-29"Hg for optimum steam evaporation. The ejectors draw the air out of the condenser by passing high pressure steam through a vortex piping arrangement thus causing the vacuum.
8. Condensate Pump
This pump draws the water from the bottom of the condenser or hotwell and pumps it up to the deaerator.
9. Tray Deaerator
This is a pressure vessel with a horizontal and vertical section somewhat like a comic strip submarine shape. It effectively removes the air and oxygen from the feed water (condensate) which would otherwise damage the inside of the boiler tubes by corrosion.
There are several types of deaerators; we will look at the tray type which is a vessel having a horizontal section with a vertical dome. The bottom horizontal section is used to collect and store the deaerated water; the vertical section has perforated trays set at intervals along its upper length. The condensate enters at the top of the vertical section cascading down through the trays, meeting steam injected from the sides and gathers at the bottom section where it is heated by steam coils or sprays. The air is vented from the very top of the deaerater vertical domed section.
10. Boiler Feed Pump
This pump takes the water from the deaerator and pumps it through a series of feed heaters into the boiler economizer (see boiler auxiliaries article) and into the boiler top drum through the feed water control valve.
The water used to condense the steam to condensate is now pretty hot itself, so it needs to be cooled down before being used again. The cooling tower is used for this purpose. It is a vertical hyperboloid concrete structure with a honeycombed interior usually of plastic and the water enters at the top cascading down through the plastic sections. It draws in air from the bottom, which rising up through the tower mixes with the water thus cooling it helped by evaporation, the resultant plume rising out of the top of the tower.
12 Cooling Medium Pumps
These pumps circulate the cooling medium from the main vacuum condenser and LO cooler to and from the cooling tower.