FeedWater Heaters

Question 1

What is the purpose of Feedwater Heating?

Answer 1

Improve overall plant efficiency and provide path for moisture removal from Turbine stages

Provides a path for moisture removal pathway from low pressure turbine stages

Question 2

What provides power to all solenoids for AOVs and unlatching solenoids?

Answer 2

Instrument Bus

Question 3

How do the AOV’s that drain to condenser fail? How do drains between heaters fail?

Answer 3

All to condenser fail open. All that fail to other components fail closed.

Question 4

What is the Drain flowpath for feedwater heating?

Answer 4

HP Turb - Moist Sep - MSDT - D FWH - C - B - Flash Tank - Flashed steam to A Heater & Drained water to A Drain Cooler - Condenser

Question 5

What is on the shell side fo FWH? Tube Side?

Answer 5

Heater Drains and Extract Steam; Condensate

Question 6

What turbines does extraction steam come off?

Answer 6

Low Pressure turbines,

There is some discrepancy on the stages that it comes off. LP says 7, 9, 11, 12

Question 7

What is the purposed of the Extraction Steam Non-Return Check Valves and which lines have them?

Answer 7

D, C, & B have them.

Designed to protect backflow from heater creted by flashing, would cause turbine overspeed

Question 8

What is the purpose of extraction steam?

Answer 8

Pressure provides the motive force for moving drain fluid to next downstream heater - also provides heating

Question 9

What is the purpose of the Extraction Steam Bypass Valve?

Answer 9

Sends Extraction Steam direct to condenser - opens on FWH High Level

Question 10

What provides the control for Non-Return Check Valves?

Answer 10

Air assisted from IA - closes on loss of Trb

Question 11

What is the function of the Heater Inlet and Outlet MOV protection?

Answer 11

High level will cause the inlet valves to close and the drain valves to open.

High level in A Heater will cause MOVs to close and bypass valves to open since A does not have isolation - this provents flooding turbine in event of tube rupture

Question 12

What will cause the Extraction Steam MOVs to auto close?

Answer 12

High Level for >2 sec

Question 13

How do Extration Bypass AOV’s function?

Answer 13

Air to close, spring to open - drain to condenser

Auto open on :
Extraction MOV full open
High Level >2 sec in assocaited heater
Condensate inlet or Outlet MOV closed
Turb Trip/loss of IA/ loss of IB

Question 14

How do the FWH Normal Drain Valves function?

Answer 14

Air to open, spring to close;
3-15psig range for accumulation
Normal Drain valve drain to next heater downstream and typically veryclose to downstream heater.

Question 15

How does A Drain Cooler Normal Drain Valve differ from others FWH normal drain valves?

Answer 15

Fails open instead of closed, and drains directly to condenser

Question 16

How do FWH Emergency Drain Falves Function?

Answer 16

Air to close, spring to open (fail open) and drain to condenser.
3-15 psig

Question 17

How do MSDT Drain Valves function?

Answer 17

Each tank as 3 normal drains to D heaters - fail closed (6-30psig)
Each tank has 2 emergency drain valves - fail open
A opens first at 30psi, B fails next at 18psi - full open at 6psi

Question 18

What is the latching order for Heater latching?

Answer 18

B, C, D, MSDT

Question 19

How do the Heater Latching valves function?

Answer 19

When de-latched, drain valve will still have an output as it tries to control
Normal drain de-latches on high level of downstream heater;
Solenoids powered by IB- energize to de-latch
Air is ported away from controller, so the air never reaches actuator

Question 20

How does Heater Level Control system react on high level in MSDT?

Answer 20

Normal drain goes full open, and emergency also opens to try to maintain lvl
if level backs up to Moist Sep, Hi Alarm
If level continues to rise, High High Alarm at 24” from bottom and turb. trips after 15 sec. BOTH HI & HI HI NEEDED FOR TRIP

Question 21

How does HEater Level Control react to D, C, or B Level increase?

Answer 21

Normal drain goes full open and emergency opens to try to maintain lvl
High level alarm at setpoint
Normal drain valve for upstream heater unlatches
Extraction Steam MOV closes
Extraction Bypass Opens
Emergency valve for upstream heater will likely open to control

Question 22

How does Heater Level Control function for flash tank?

Answer 22

Normal Drain from drain cooler continues to try to maintain lvl
High alarm at setpoint (15”)
Normal drain for B unlatches
A heater emergency drain de-energizes to opn A heater emerg. drain

Question 23

How does Heater Level Control respond to A Heater Level Rise?

Answer 23

No isolation valves on extration steam side:
Close condensate side string isolation valves.
When either valves fully close, B & C extration steam bypass valves open and the A heater emerg. drain opens.
Operator must close extration steam MOVs for B & C heaters
Open condensate bypass MOV to allow 33% condensate bypass flow

Question 24

What is the purpose of the FWH bias panel?

Answer 24

Equalizes drain flows down all 3 heater strings - adjusts air signal to MSDT drain valves to D Heaters to make-up different size piping and different valve characteristics

Question 25

What happens with a Heater Tube Leak?

Answer 25

Can cause loss of suction pressure to RFPs and they may not trip.
Can also cause high level in Flash tank and A heater

Question 26

What happens to cycle efficiency on loss of FWH?

Answer 26

Colder water adds positive reactivity.

Initially Power goes up, then will go down when operator stabilizes due to loss of cycle efficiency.