Extraction Steam and Heater Drains Flashcards
Where does the shell side and tube side of the MSR’s drain?
Shell Side
- This is the exhause of the HP Turbine. It is dried and re-heated in the MSR before entering the LP turbines.
- Condensate from the shell side drians to T-5, MSR Drain Tank.
Tube Side
- This is HP steam off the the main steam line. It used to heat the shell side steam. Makes 4 passes then flows to T-4A/B, Reheater Drain Tanks.
Where do the high pressure feedwater heaters get heating from?
E-6A/B
- Third stage HP turbine exhaust
- T-4A/B Reheater Drain Tanks
E-5A/B
- E-6A/B Drains
- HP Turbine Exhaust Cross Under Drains (East Side Cross Under Only)
What is the purpose of a Bleeder Trip Valve?
On turbine trip, it closes to prevent the steam in the feedwater heaters from rushing backing into the turbine and causing an overspeed.
Closes on high level in feedwater heater
BTVs are on lines feeding:
- E-6A/B
- E-4A/B
- E-3A/B
How are the drains “cascade” in the High Pressure Feedwater Heater System?
Condensed extraction steam and drains from tanks T-4A/B are drained from the 6A/B heaters to the 5A/B heaters respectively.
5A/B also receive east side cross-under drains.
How is level controlled in E-5A/B?
Controlled by the valve “disc operating position”, which is influenced by the sum of the torques around the disc hinge pin (i.e., flow momentum, disc weight, bushing friction forces, etc.
Essentially weighted check valves in the drain lines to T-5, MSR Drain Tank.
High level in E-5A/B causes, E-6A/B Level control valve to close (on drain line)
High level in E-6A/B, High Level Dump opens to main condenser.
What is the high pressure portion of the extraction and heater drain system?
High pressure components.
- High Pressure Turbine
- Feedwater Heaters, 6A/B and 5A/B.
- Moisture Separator Drain Tank, T-5
- Heater Drain Pumps, P-10A/B
What are the low pressure components of the extraction steam and heater drain system?
Low pressure components.
- Low Pressure Turbine
- Feedwater heaters 4A/B, 3A/B, 2A/B, 1A/B.
- Drain Coolers 7A/B
What happens if feedwater heater level is maintained too high?
Result in tubes covered with liquid phase and not receiving heat transfer though latent heat of vaporization as steam condenses.
- Heater drain temperatures rise
- Feedwater out temperature lowers
What happens if a feewater heater level is maintained too low?
Results in steam blowing through heater. Reduction in heat transfer as steam is not kept in heater to condense (latent heat of vaporization).
- Heater drain temperatures rise.
- Feedwater out temperature lowers.
How does the MSR control system ramp function work?
Ramp
Normally used at 30% load after the shutoff valves are opened. This button energizes the circuit that regulates the opening of the 6” Reheater steam control valves CV-0594, 0595, 0597 and 0598 to MSRs E-9A, B, C and D respectively over a period of two hours.
The ramp feature assures an acceptable rate of differential expansion between the LP turbine casing and rotor.
Why do have the MSR control system?
Used to insure proper heating of the LP turbine during cold startups,
Minimum differential steam - Protects against thermal stress and possible distortions of the L.P. turbine stationary parts.
What steam load does the MSR represent when placed in service?
3 to 5%
What does the reset push button do on the MSR control panel?
resets the controller and shuts the reheat control valves.
How does MSR manual control function?
Manual Set Point Knob
Positioned at the procedurally prescribed rate/position. Opens Reheater steam control valves to some position immediately.
SOP-8 table must be adhered to for the same reasoning as the RAMP feature or possible LP Turbine damage could occur do to differential expansion of the turbine casing and rotor.
What are the MSR control interlocks?
Turbine trip
Control valves are automatically closed
Prevents flooding the reheater drain tanks and feedwater heaters E‑6A/B. This reduces the possibility of a water hammer.
The trip relay (386/AST) must be reset to enable control of the reheat control valve.
What supplies control power to the MSR panel and what happens on loss of power?
MCC-1 via L-25A, Breaker #5
Upon loss of power to the control panel, all CVs close. They do not auto re-open when power is restored
Tank 4A/B receives what and drains to where?
T-4A Reheater Drain Tank
- MSRs E-9B&D coils
T-4B Reheater Drain Tank
- MSRs E-9A&C coils
T-4A/B normally drains to heaters E-6A/B respectively via air operated level control valves CV-0538/CV-0554. Level controller LC-0538/LC-0554 is the normal level controller for T-4A
What is the function of DPIC-0609?
Monitors the differential pressure between T-5 and the E-5s.
With a drop in E-5s pressure DPIC-0609 closes down on CV-0610 to maintain pressure in T-5
Avoics flashing in the P-10 pumps,
- At 75% closed on CV-0610
- DPIC-0609 opens CV-0716 and CV‑0717
- Provides subcooling condensate to the suction of the P-10 pumps.
How does the controller for CV-0610 function?
CASCADE (C) - This is the normal mode of operation.
- Blue indicates T-5 pressure.
- Red pen indicates E-5 Feedwater Heaters pressure.
- Output signal to CV-0610 is indicated on the horizontal meter.
AUTO (A) -
- Red pen indicates E-5 Feedwater Heaters pressure.
- Blue pen is controller setting indicator.
- Adjusted using the ‘SET’ arrow pushbuttons
- Adjust the Blue pen to T-5 pressure. The controller program will adjust CV-0610 opening to maintain E‑5 pressure (Red pen) greater than the Blue pen setting.
- Output signal to CV-0610 is indicated on the horizontal meter.
MANUAL (M) -
- Red pen indicates E-5 Feedwater Heaters pressure.
- Blue pen indicates T-5 pressure.
- Using the lever at the bottom of the controller controls CV‑0610.
- Maintain CV-0610 open as long as E-5 heater pressure is greater than T-5 pressure.
- Signal to CV-0610 is indicated on the horizontal meter.
How are mode changes handles for CV-0610’s controller?
Mode shifts between “C”, “A”, and “M”, are allowed in all but one direction. The one exception is Manual to Cascade. To go to Cascade (C) from Manual (M), the “A” button must first be pushed.
How is level in T-5, MSR Drain Tank handled?
CV-0608 P-10A/B Discharge modulates
T-5 level based on input from normal level controller LC- 0608
Normal level: 60% to 65 %. 66% should be full open
How does main feed pump suction pressure interact to T-5 level control?
Low suction pressure of 270 psig sensed by PS‑0786
- Overrides the normal level control signal by deenergizing SV‑0786 bleeding air off of CV-0608
- Causes CV‑0608 to fail open.
- Increases Main Feedwater pump suction pressure to help prevent a low suction pressure trip at 250 psig
How is high level in T-5 sensed and controlled?
80% sensed by level controller LC-0609
Opens control valve CV-0609 directing water to the condenser directly from T-5.
Discuss P-10A/B function, design and power supplies.
- Power Supplies: Both pumps - Bus 1E
- Provide roughly 6100 gpm flow to Main Feed Pumps at 350 psig.
- Mini-flow lines are provided for each pump around the CV-0608. Normal flow is approximately 250 gpm per pump.
What trips P-10A/B Heater Drain Pumps?
T‑5 low level 2/2 on LS-0608 and LS-0629
- P-10B at 22.5%
- P-10A at 12.5%
Overcurrent
Indirectly from SIAS since Bus 1E is Loadshed
What controls are in the control room for feedwater heater level control?
Handswitches for High Level Dump valves only.
Note E-5s are controlled via E-6s normal level control valve and/or T-5 Check valve/pressure difference.
How is high level in E-5A/B Feedwater Heaters Controlled?
High level sensed level switches 0603/0604
E-6A/B level control valves close( SV deenergize)
Loss of DC defeats this feature.
How does a loss of instrument air impact feedwater level control?
All NORMAL level control valves fail CLOSED
All high level DUMP valves fail OPEN.
How does the Extraction Steam and Heater Drain System interface with the feedwater system?
The Heater Drain pumps discharge into the suction of the MFW pumps.
Feedwater flows through the tubes of the E-6 heaters.
How does the Extraction Steam and Heater Drain System interface with the condensate system?
- Condensate pumps supply seal cooling to the heater drain pumps as well as supplying subcooled water to the suction of the heater drain pumps (CV-0716, CV‑0717) as called for by the T-5 pressure controller.
- Hotwell is a collection reservoir for the drains leaving the E-7A/B drain coolers, to be pumped back into the condensate system.
- Heater shell vents and MSR vents are directed back to the condensers.
- Condensate flows through the tubes of the E-5 , 4, 3, 2, 1 heaters and the E-7 drain coolers..
- Seal Water supply to the Heater Drain pumps.
How does the Extraction Steam and Heater Drain System interface with the main turbine system?
- Extraction steam is taken from the HP and LP Turbines as well as the HP Turbine exhaust.
- Turbine trip circuit trips closed the MSR steam supply valves and isolates air to the BTVs allowing them to close
How does the Extraction Steam and Heater Drain System interface with the main steam system?
Provides heating steam to the MSR heating coils to heat the HP Turbine exhaust prior to entering the LP Turbine.
How does the Extraction Steam and Heater Drain System interface with the instrument air system?
Provides motive force for operation of BTVs, heater level control valves T-5 and T-4 level control valves and MSR steam control valves.
How does the Extraction Steam and Heater Drain System interface with the plant heating system?
Extraction steam supplies heating steam when >35% power.
Plant heating supplies vent path for Flash Tank
What are the effects on the HED system of bypassing heaters?
Colder feedwater from bypass of lower pressure heaters can result in lower shell pressures in up-stream feedwater heaters, causing excess extraction flow into those heaters. This can result in a high level condition, as normal drain cannot handle volume.
Reduction in shell pressure can result in flashing in shell which can cause false level in hot sensing lines, leading to further transients and system upsets.
Reduction in shell pressure can also lead to condensate induced water hammer from up stream drains.
Excessive extraction flow can worsen Flow Accelerated Corrosion (FAC) in extraction lines and Heater shells.
What is a heater stage?
A Heater Stage may be an individual Feedwater Heater or, when considering
both Feedwater Trains, a stage may consist of two heaters.
Example: E-3A is one heater stage (a third stage) while E-3A and E-3B are considered one stage of Feedwater Heating (also, a third stage).
Feedwater Heaters E-3A and E-4A are considered two stages of Feedwater Heating (a third and fourth stage).
E-7A and E-7B, Drain Coolers, are NOT considered to be a heater stage.
What heaters can be completly isolated during plant operations?
The only Feedwater Heaters that can be completely isolated during Plant
operation are E-3A, E-3B, E-4A, E-4B, E-6A, and E-6B.
What must be done if two stages of feedwater heating are bypassed?
Turbine load is restricted to less than 600 MWe to prevent excessive extraction steam velocity in the next higher pressure heater.
Heaters are to be bypassed before the load is lowered unless E-5A/B, which requires E-6A/B bypassed, which requires load reduction to 97% prior to isolating an E-6.
