BOILER’S DEAERATOR WORKING / OPERATION
Boiler Deaerators is very important equipment of any power plant industry. In boiler d.m water is used for the steam generation because it is free from the TDS ( total dissolved solids ) , minerals, and dissolved gases. The steam is used to drive turbine is condensed in a condenser and then this condensate is used again as feed water. In steam turbine power plant water is traveled in closed loop like in the form of steam and condensate through condenser some water is makeup in the Deaerators in the manner of blow down leakages and losses.
Degasification (remove dissolved gases from feed water) is the main function of a Deaerators . it also a storage tank for the boiler feed water. Deaerator may be horizontal or vertical according to the space available at room head tank. Deaerator preheats the feed water before interning the boiler low pressure steam comes from the bleed line from the steam turbine. And preheat the boiler feed water and raise the temperature upto 120-150 degree Celsius . It also play a very important role for increase the efficiency of boiler. A l.p dosing pump is also use for dosing the hydrazine into the deaerator tank for removing the oxygen from feed water. Deaerator is also a backup for feed water 20-30 minutes boiler when any emergency take place .
In steaming deaerator, water entered from the top. Then this water spray on the perforated try and divided into small droplets and this water droplets comes with the contact of steam .Low pressure steam is supplied to the steam distributor which comes from the bleed line from the steam turbine. This steam is move up in the deaerator column and come in contact with droplets of feed .Water falls down into the water column into the deaerator and get heated up to the boiling point. Due to formation of small water droplets, the contact surface exposed to steam increase, which result complete removal of dissolved gases.
WORKING PRINCIPAL OF DEAERATOR
When the water is heated dissolved properties of gases decrease. After heating the water dissolved gases removed easily. When the hot gases remove with some non condensable gases comes out from the deaerator column vent. After that some non condensable gases remains into the water these gases removed here because large heating surface area. These deaerator working of the principal Of Henry’s law of partial pressure it stat that The solubility of the gas in a liquid is directly proportional to the partial pressure. When a liqud is heated up to saturation limit under the pressure then the solubility of liquid decreases
CONSTRUCTION AND FEATURES OF DEAERATOR:-
The deaerator shell is made of carbon steel and the deaearator internal which come into the contact of the steam with made of stainless steel for protect from the oxygen reaction. A spring loaded nozzle is the heart of the system these nozzles is spray the feed water in finesse particles. Two type of Deaerators is employed in the power plant one of is horizontal and other is vertical both of use dby low stem consumption and get maximum efficiency. Feed water is heated into the Deaerators tank. a level control valve is installed for controlling the Deaerators level , and level gauge is fitted to show the actual level of the Deaerators manually. A PRV (pressure reducing valve) also installed for regulating the stem pressure. A safety valve is also installed at the top of Deaerators for relief the pressure when the pressure riche the above the safe working condition. A blow down valve is also installed at the bottom of the Deaerators tank for blow down the water when the level increase above the safe working limit.
MAINTAINING NPSH ( NET POSITIVE SUCTION HEAD ) FOR BOILER FEED PUMP :’-
When we used steaming deaerator into the power plant a generally condition face with the suction of the feed pump of the boiler. It left the suction because when the dearator water heating under the pressure , it’s a highly chance of steaming of water at suction side of the boiler feed pupm. This condition is called cavitation. In this condition pump falls below saturated pressure, for avoiding this situation Deaerators are normally placed at high elevation in order to provide enough NPSH for the boiler feed pump in the event of failure in steam pressure pressure control also. We generally take the idea of boiler feed suction calculation If the deaerator pressure 3 kg and the deaerator is placed at an elevation of 20 meter, then the feed pump suction pressure will be appropriately 5 kg/cm
Two limitations of deaerator:-
1. They can remove many dissolved gases of the condensate but not the large amount of dissolved gases found in the waste streams of many power plants industries.
2. In steaming deaertor free CO2 is reoved completely ,But only a small part of the combined CO2 is released in the deaerator and the bulk is released with the steam in the boiler.so that it is dissolved in the condensate, causing corrosion. This can be controlled by using neutralizing or filming amines.
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