Feed water to Boiler or Steam Generator
The main function of feed water system is to maintain the quantity and quality of water supplied to steam generators as required. Water is normally extracted from condensate system (Condensed steam) to treat it chemically and store in a reservoir for feed water pumps to deliver it to Boiler.
There are two main purposed of feed system other than supplying in required quantity as
- Heating up the feed water from turbine extraction heaters
- Chemically treating for pH and Gases contents control.
Feed pumps are designed to deliver the water at certain pressure and temperature so that the cycle efficiency cannot be compromised.
Startup of the system
Confirm and fulfill the system prerequisites:
- Electrical and control power available
- No Deficiency in system equipment all maintenance work completed
- Lube oil system for main pump is available and working
- Cooling system for lube oil and main motor working normal
- All the instrumentation like PI ,FT and TEs are in working condition
- Sealing water of main pump is working
- Level of water reservoir is normal
- makeup system for reservoir is available
Cycle steam is used to heat up the water in heat exchangers (Heaters), in which cycle steam is extracted from high pressure turbine extraction. Extraction steam is supplied of shell side of heater and transfer heat to feed water at tube side, usually multistage heating system is used taking extraction steam from different points.
What if Heaters are out of service
If any of the heaters is out of service then it affects the cycle efficiency and power needs to be reduced because the feed water temperature will be lower than required for full power operation.
Possible causes for heater outage are High level at shell side due to no proper drain of condensed steam or tube rupture of water side. Heater must be taken out of service by bypassing it so that water may not enter turbine.
Amonia is added before pumping the water to control the pH of the water, it should be near 9 for better quality otherwise it may add to the corrosion process of system piping and steam generator tubing as well. Hydrazine (H2N2) is added to control the Oxygen contents in feed water