Deaerator
Deaerator
The information is given under the following heads
What Deaerator means
Position in Boiler/TG cycle
Construction details[[1]]
Mounting arrangement
Controls and monitoring
References
External links
What Deaerator means
‘’Deaerator’’ as the name implies indicates equipment for air removal. In industries it is removal of all gases (also emanated by the use of water treatment chemicals as well[[2]]from water to make it non corrosive. With reference to Thermal Power Station, this word deaerator, in usage, generally implies not only to deaerator but also the Feed water tank below where deaerated water is stored and fed to Feed pumps. The description herein is mainly with reference to its use in Thermal Power Stations [[3]] of an Utlity.
Position in the Turbine cycle
The schematic diagram shows its position in the Turbine cycle diagram. [[4]]
![[4]](https://en.wikipedia.org/wiki/Image:Dores-Turbine_Cycle_diag1.jpg){kind=link}
Construction details
The sketch[ [5]] shows the construction of a typical deaerator. The actual construction details may vary from manufacturer to manufacturer depending on their own design and the requirement of the system to which it is attached.
![[5]](https://en.wikipedia.org/wiki/Image:Dores-Deaerator_diag1.jpg){kind=link}
The Feed tank is generally a horizontally mounted cylindrical steel vessel with dished ends with a dome on the top and with internal and external fittings. The size of the same depends on the unit capacity it is associated with. The cylindrical vessel portion acts as storage for Boiler feed water supplying to the suction of the Boiler Feed pumps from a pipe connected to the bottom of the tank, generally in the mid portion.
At the top and in the mid portion of the cylindrical tank an inverted domed vessel of sufficient size as dictated, is attached which is called Deaerator. This portion has internals something like a perforated tray to breakdown the down flow feed water from the top into fine globules to separate dissolved gases from the steam, which is fed at the lower level of the dome and passes upwards to give good intermixing. That means this dome acts as an deaerator and normally known by this name. Therefore a small vent pipe at the topmost point of this dome is provided for venting out the dissolved gases released inside the dome. This dome therefore has connections for feed water inlet (at one side of the dome near the top end) from HP feed heater and also for the deaerating steam from bottom of dome,(which also incidentally heats the feed water).This steam is generally from an extraction point of the Turbine to improve the cycle efficency. The deaerator therefore is also termed as one of the feed heaters.[[6]]in the turbine cycle.
During cold start of the unit, it is possible the water in the Feeds tank may be cold. At that time to bring up the water to normal operating temperature to expel the dissolved gases this water has to be heated. For this, a provision of a heater pipe inside the tank longigutudinally and at the bottom level is provided. Few vertical pipes on this line is provided with holes to distribute the heating steam uniformly to avoid water hammer in the initial stages of heating. For this normally auxiliary steam conncetion is provided, since the auxiliary steam is available first after statrup of boiler.
A small bore connection with a pipe line to the full length of the feed tank at the bottom, is also provided for injection of chemical liquid.
Generally a direct reading guage glass is provided on each end for positive level indication.
Since the Feed tank and deaerator are always hot, sufficient insulation covering is provided to minimize the heat loss.
Mounting arrangement
The deaerator is mounted horizontally at a sufficient height above Boiler feed pumps level to give the necessary positive head (known as NPSH)to the Boiler feed pumps under all conditions of the system operation. The mounting arrangement is such that one end of the dished end is able to move or expand due to hot boiler feed water storage where as the other end is fixed.
Controls and monitoring
Normally all the control and monitoring equipment for startups, normal operation and alarms for out of parameter operations are provided at the operators' comsole.
References
KERNT’S MECHANICAL HANDBOOK, Design, Shop Practice Eleventh edition, Rewritten by Robert Thurston Kent. M.E., Editor in Chief, WILEY ENGINEERING HANDBOOPK SERIES. NEW YORKL ;JOHN WILEY & SONS, INC, LONDON:CHAPMAN & HALL LIMITED