Extraction Steam Drains

Question 0

Which side of the feedwater heaters is the extraction steam piped to?

Answer 0

The shell side

Question 1

What is the ED system used for?

Answer 1

Preheat CD & FW entering S/Gs to increase efficiency

Question 2

What is the motive force for the extraction steam subsystem?

Answer 2

D/P between turbine stages and heater shells

Question 3

Which heaters are supplied ED from the high pressure turbine?

Answer 3

7A, 7B, 6A, and 6B and first stage reheating steam for MSRs.

Question 4

Which drain heater gets cold reheat?

Answer 4

5A & 5B

Question 5

Which heaters’ extraction lines are cross connected and why?

Answer 5

3A, B, C with 4A, B, C and 6A, B and 7A, B to allow unit operation without all high and low pressure heaters in operation.

Question 6

What drains make up the heater drain subsystem?

Answer 6

Drains from:
 HP heaters
 MSRs
 1st and 2nd stage reheater drain tanks
 MSR drain tanks

Question 7

Describe the flow path of extraction drains from the HP turbine.

Answer 7

Drainage from 1st stage reheater drains and 5th turbine stage extraction drains goes to #6 htrs then to the Htr drain tank
Drainage from 2nd stage reheater drains and 3rd hp turbine stage extraction drains goes to #7 htrs then to #6 heaters, then to htr drain tank
Drainage from MSRs (7th stage cold reheat extraction drains) go to #5 htr and then to heater drain tank.

Question 8

How do the LP heaters cascade?

Answer 8

4=> 3=>2=>1 then to the condenser.

Question 9

Where does the MSR vent to?

Answer 9

Its associated MSR hot reheat line.

Question 10

Where does the heater drain pump vent to?

Answer 10

It vents it’s suction line back to the associated train heater drain tank.

Question 11

What does the blowdown stack do in regards to the ED system?

Answer 11

Provides a collection point for steam traps, HP heater relief valves, and misc aux steam header drains.

Question 12

What happens to the bleeder trip valves on a loss of IA?

Answer 12

BTV loses it’s open per missives and go partially closed. Extraction steam flow keeps it hanging open.

Question 13

What powers the heater drain pump?

Answer 13

NB

Question 14

What provides cooling for the heater drain pump lube oil coolers?

Answer 14

TC

Question 15

Where do the drains from the heater drain tank go?

Answer 15

To the suction of the heater drain pump which sends them to the suction of the main feed pumps.

Question 16

Where does seal water for the heater drain pump come from?

Answer 16

It comes directly from the condensate header at 375-500psig.

Question 17

What controls the heater drain pump mini flow valve position?

Answer 17

The heater drain pumps flow transmitter. The more flow through the pump, the more closed the mini flow valve is.

Question 18

What controls the heater drain pumps discharge valve?

Answer 18

The heater drain tank normal level controller.

Question 19

What will stop a feed heater drain pump?

Answer 19

Heater drain tank Lo-Lo level alarm
Heater drain pump low flow after a time delay
Electrical protection signal

Question 20

Can one heater drain pump take a suction on both heater drain tanks?

Answer 20

Yes through a suction and vent cross tie valve between the heater drain tanks.

Question 21

Which HP feed heater does not have a level control valve?

Answer 21

5 does not

Question 22

How many trains of low pressure feed heaters are there?

Answer 22

3 parallel trains each having 4 HX within the condenser neck.

Question 23

How many inlets for LP turbine steam does each LPFH have?

Answer 23

#1 and 2 each have 4
#3 and 4 each have 1

Question 24

What does the bleeder trip valve do?

Answer 24

Prevents the back flow of steam when the turbine trips. This helps prevent an over speed condition.

Question 25

How is the bleeder trip valve tested?

Answer 25

Using the manual 3 way test valve. The test valve equalizes the pressure across the operator piston to allow a partial closing by spring force

Question 26

Which level control valves are reverse acting?

Answer 26

All of the high level control valves and the #1 LP heater normal level controller are reverse acting.
This means that the smaller the air signal, the more open the valve is. (Open with 3, closed with 15#)

Question 27

What happens on a Hi-Hi level in the HP feed heater?

Answer 27

Extraction steam isolates, the normal level control valve of the preceding heater closes, and the affected heater’s extraction drain valve opens (motor operated). Also, the 1st & 2nd stage reheater drain tank vents isolate from the heater and vent to the main condenser.

Question 28

What happens to the LP feed heater on a Hi-Hi level?

Answer 28

The entire LP heater train isolates by closing the condensate isolation valves
Extraction steam to #3 & #4 heaters isolates
The extraction line solenoid operated drain valves open for #3&#4 heaters.

Question 29

Why does the high level alarm have a difficult time clearing on #3 LPFH when less than 20% power?

Answer 29

Because the normal level control valve drains “uphill” to #2 LPFH which is physically located above #3.

Question 30

When are the feed heater drain pumps placed in operation?

Answer 30

The first one is placed in service at 25% power and the second one is started between 30-40% power.

Question 31

What is the major concern when operating with only one feed heater drain pump?

Answer 31

Precautions must be taken to limit the vibration and erosion in the condenser tube bundle due to the heater drain tanks high level control valves directing high energy fluid to the condenser.

Question 32

What happens to the heater drain pump on a loss of IA?

Answer 32

The discharge valve closes and the recirc opens all the way to put the pump in full recirc

The pump will eventually trip on low flow or heater drn tank Lo-Lo level.