ED- Extraction Steam and Drains Flashcards
What is the purpose of the ED system?
Preheats condensate and feedwater prior to feedwater entering the Steam Generators to increase overall plant efficiency
What system has the ability to provide steam to the #4 LP feedwater heaters during startup?
Auxiliary Steam
What system is used to add cool water to the water volume that is maintained in the bottom of the ED blowdown stack?
Domestic Water (DS)
What is the purpose of the ED blowdown stack?
Provides a collection point for various steam traps, HP heater relief valves and miscellaneous aux steam header drains
When is DS added to the ED blowdown stack? What if DS is not available?
When temperature of blowdown stack water volume exceeds 150F
If not available, there will be steam coming out of the blowdown stack and the north condenser area sump
How does GA interact with ED?
During long term shutdown conditions, the GA system supplies nitrogen for blanketing of the feedwater heater shells and heater drain tanks to protect against rust and prevent oxygen from dissolving in the water
How does IA interact with ED?
MT control system admits IA through Turbine Critical and Non-Critical Relay Dump Valves which provide a signal to control Bleeder Trip Valves
Provides motive force for all air operated valves in ED system
How are BTV’s affected by a loss of IA?
BTVs will lose their open permissives and go partially closed
They will remain open due to the extraction steam flow
Where are the Heater Drain Pumps powered from?
‘A’ from NBN-S02
‘B’ from NBN-S01
Where does the seal water for each Heater Drain Pump come from?
Directly from the Condensate Header at 375-500 psig
What positions the Heater Drain Pump mini-flow valves? When will it close? What controls the position of the heater drain pump discharge valve?
Heater Drain Pumps flow transmitter
as the unit comes up in power and more extraction drain flow is available
heater drain tank normal level control valve
What three signals would stop the Heater Drain Pumps?
A Heater Drain Tank lo-lo level alarm
Heater Drain Pump low flow after a time delay
Electrical protection signal
Where are the Heater Drain Pumps located? What allows one heater drain pump operation?
100’ Turbine Building west of the Main Feed Pumps
opening a suction and vent cross-tie between the heater drain tanks
Why does #5 feedwater Heater not have a level control system?
Does not contain a drain cooler region and drains directly to the Heater Drain Tank
Which Low pressure Feedwater heaters have four inlets on the top? How many do the others have?
1 and #2
Which feedwater heater has an input from S/G blowdown system?
3
What is the purpose of the Bleeder Trip Valves in the ED system? Which feedwater heaters have BTVs?
3, 4, 5, 6, 7
To prevent reversed steam flow when the Turbine is tripped
(Closure of these valves will ensure the Turbine does not overspeed)
What is installed on the BTVs that assists in opening the disc with a minimum differential steam pressure in the ED system?
Balance Arm device
What happens upon activation of the Bleeder Trip Valve test valve?
Valve equalizes the air pressure across the operator piston to allow partial closing of the valve disc by spring force
Why is there two BTVs installed on #4 feedwater heater extraction line?
4 heater, by itself, has enough energy to cause an overspeed trip
Which level control valves are reverse acting in the ED system?
All of the high level control valves and #1 LP heater normal level control valves
At what air signals are the reverse acting valves full open and full closed in the ED system?
Full open with 3#
Full closed with 15#
(Direct acting is the complete opposite)
What happens upon a hi-hi signal in a HP feedwater heaters?
Isolates extraction steam
Closes the normal level control valve of the preceding heater
Opens the affected heater’s motor operated extraction steam line drain valve
In addition, for the HP heaters, the 1st and 2nd stage reheater drain tank vents isolate from the affected heater and vent to the main condenser
What happens upon a hi-hi signal in a LP feedwater heaters?
Isolated entire LP heater train by closing the heater train isolation valves
Isolated extraction steam to #3 and #4 heaters
Opens the extraction line solenoid operated drain valves for #3 and #4 heaters
Below what power level may there be insufficient D/P between the heater shells to allow for proper operation of the normal level control valves in the ED system?
20%
high level control valves operate to keep alarms clear until power level is sufficiently raised
When is the first heater drain pump started?
25% power
When is the second heater drain pump started?
Between 30 and 40%
During a plant shutdown, when are the Heater Drain Pumps secured?
First one at 40%, second one at 25%
How is the ED system affected by a loss of IA?
Heater Drain Pump discharge valve fails closed, recirc valve fails open, putting the pump on recirc
Heater Drain Tank, MSR Drain Tank, 1st and 2nd Stage Reheater Drain tank, and Feedwater heater High Level Dump valves will all fail open and the Normal Level Control Valves fail closed (Except #1 heater)
Heater Drain pump will eventually trip on low flow or Heater Drain tank lo lo level signals
The main steam supply to the 2nd stage reheater will isolate and the 1st and 2nd stage Reheater Drain Tanks and Tube Bundles will vent to the condenser instead of their associated Feedwater heaters
What is the purpose of the HDTs (heater drain tanks)?
ultimate collection point for most of the normal drains within the ED system
provides suction for the heater drain pumps
tank level regulated flow to the Main feed pumps
receives mini flow line from heater drain pump
Where are the heater drain tanks located?
120’ turbine building, above the heater drain pumps
Concerning the ED system, where do the MSR 1st stage reheater drain tanks flow to? 2nd stage reheater drain tanks?
6 FW heaters, then to the heater drain tank
How many stages are the heater drain pumps?
5
What is the purpose of the Feedwater heaters?
aid in improving the secondary system efficiency
Concerning the High pressure feedwater heaters, what are the flow paths for the extraction steam and feedwater flow?
extraction steam from HP turbine comes in through the top, condenses and is drained from the bottom
feedwater flows in through the bottom, passes through the U-tubes and exits through the top
Concerning the HP feedwater heaters, what are the differences between the #6/7 heaters and the #5 heaters?
6/7 have condensing and subcooling zones, has level control system, #7 drains to the #6 heater, #6 drains to the HDT
What is the purpose of the vents on the various tanks, heat exchangers and pumps in the ED system?
to remove non-condensable gases and direct them to the condenser for removal
What is the motive force of extraction steam while traveling from the turbine to the feedwater heaters?
the differential pressure between the turbine stages and the feedwater heater shells
Which feedwater heaters have the supplying extraction lines cross-connected and what does the cross connect allow for?
3a, b, c
4a, b, c
6a, b
7a, b
allows unit operation without all high and low pressure feedwater heaters in service
What does the High Pressure turbine provide extraction steam to?
3rd stage- 7A/B heaters and first stage reheating steam in the MSRs
5th stage- 6A/B heaters
cold reheat- 5A/B heaters
Where do the heater drain pumps send their effluent?
to the suction of the main feedwater pumps
combines with the condensate just downstream of the feedwater heaters
What is the difference in operation between direct acting and reverse acting level control valves in the feedwater heater level control system?
direct acting- higher air pressure opens the valve
reverse acting- higher air pressure closes the valve
Where do the MSR drain tanks vent to? Where does the heater drain pump vent its suction line to?
their respective MSR/Hot reheat line
respective heater drain tank
Where do the first stage reheater drain tanks normally vent to?
A and C vent to #6A heater extraction line
B and D vent to #6B heater extraction line
all four vent back to their respective 1st stage reheater tube bundle outlet for steam scavenging
(on high level, vent to the condenser)
Where do the 2nd stage reheater drain tanks normally vent to?
A and C vent to #7A heater extraction line
B and D vent to #7B heater extraction line
all four vent back to their respective 2nd stage reheater tube bundle outlet for steam scavenging
(on high level, vent to the condenser)
Where do the heater drain tanks vent to?
to their respective #5 FW heater
both tanks also have a vapor cross-connect line to each other
Where do the #5, 6 and 7 feedwater heaters vent to?
both trains all tie in together to a common header and vent to the condenser
How does the ED system interface with the SC (secondary chemical control) system?
Blowdown Flash Tank (BFT) vents to both of the Heater Drain Tanks by way of the vapor cross tie line between the HDT’s.
The blowdown flow from the Blowdown Flash Tank can be directed to the shell side of the #3 LP Heaters.
Cooling water from the blowdown heat exchanger is returned to the discharge of the heater drain pumps, which is then directed to the main feedwater pump suction.
How does ED interface with GS?
LP turbine 9th stage extraction supplies sealing steam to GS on power ascension
In the ED system, what is powered by NH?
MOVs, HP heater extraction steam block and drain valves, heater drain pump motor space heaters
In the ED system, what is powered by NK?
solenoids, controls, indication and alarms for various valves
In the ED system, What is powered by NN?
LP FW heater steam pressure instrumentation
HTR DRN pump discharge/suction D/P, tank level and pump flow instrumentation
What cools the HTR DRN pump lube oil coolers?
turbine cooling water
What maintains water level in the LP feedwater heater drain cooler, or subcooling zone?
normal level control valve
What is the purpose of having reverse acting normal and high level control valves in the ED system?
to ensure that on a loss of IA, the ED system will drain its contents to the main condenser
Describe the new level control valves for the LP feedwater heaters.
Vee style ball valve, provides beter throttling and seal off flow
can be positioned in either fail open or fail closed designation with the same valve mounting configuration, causing less installation errors
rotory positioners with rotary actuators with a lever
4 gauges instead of three
smaller in size
What is the sequence for putting the MSR and 1st/2nd stage drain tanks in service to their normal level control valves?
At 10% turbine power, 1st stage and MSR drain tanks go to normal level control valves, leading to the #6 FW heaters (1st stage) and the HTR DRN tank (MSR drain tank)
At 20% turbine power, 2nd stage drain tank goes to normal level control valve, leading to #7 FW heaters
