Procedure of Deaerator Charging in Power Plant :-
Today we are discussed about very important topic which is (Procedure of deaerator charging in power plant ) . In modern steam power plant deaerator is very important equipment’s. Deaerators work as a feed water heater, these feed water heaters are also called Deaerators, and they serve the dual purpose of heating the feed water to improve plant efficiency and deaerating the feed water to remove gases that could cause corrosion of equipment and piping systems. Deaerators also provide the storage of high-quality feed water for the boiler feed pump. In Deaerators heat transfer take place by direct contact between the feed water and the turbine extraction steam, and various design techniques are used such as bubbling, tray, spray, or various combinations of these.
The drains from the high-pressure heaters usually flow into the deaerator, and non-condensable gases are vented to the atmosphere. Deaerator’s main function is to deaerate or remove dissolved gasses from feed water. Also it serves the purpose of storage tank from where feed water feed water is pumped in to the boiler. It is the place where feed water is preheated before entering into boiler. The preheated feed water; low pressure steam from process is utilized. L.p dosing also done here for removing dissolved oxygen from the water.
Charging of Deaerator :
It removes the dissolved gases from the condensate mechanically by following two laws
1. Henry’s Law
2. Dalton’s Law of Partial Pressure.
According to Henry’s Law, Solubility of dissolved gases decreases by increasing water temperature. So by charging steam in Deaerator water temperature increases and soluble gases in condensate departs.
According to Dalton’s Law of Partial Pressure Pm= Ps+Pa
Where Pm= Partial pressure of Mixture
Ps= Partial pressure of Steam
Pa= Partial pressure of Air
• The partial pressure of air present inside the Deaerator comes out
• through Deaerator vent for equilibrium state.
How to charge deaerator during startup of plant ?
1. In starting of deaerator charging ensure that the DM Storage Tank level is more than 60%.
2. Start DM Transfer Pump by opening Recirculation valve.
3. Ensure Deaerator level is 60%. If the level is less then take the makeup water.
4. Open all drain lines of Pegging PRDS line and observe that condensate is completely drained out.
5. Slowly open Pegging PRDS (pressure reducing desuperheating system) pressure Control Valve and ensure that condensate is drained out completely. Then close the drains.
6. Slowly -2 increase the pressure to 2.8 Kg/cm2 by increasing pegging PRDS pressure control valve.
7. Slowly heat the Deaerator by opening the heating line isolation valve and raise the Deaerator temperature to 90 deg C.
8. Open the before and after isolation valve of Deaerator Pressure Control valve. Then open the pressure control valve gradually. Slowly increase the Deaerator pressure up to 2 kg/cm2 .After that put the Deaerator Pressure control valve in Auto mode.
9. Start LP Dosing pump.
10. In LP Dosing Hydrazine is used. Hydrazine removes oxygen by chemical reaction.
11. EQUATION- N2H4+O2=2H2O+N2
12. By adding Hydrazine dissolved oxygen becomes water and Nitrogen gas releases.
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