Systems Exam 4 - Extraction Steam & Heater Drains Flashcards
(17 cards)
What is the function of the Heater Drains System?
The Heater Drains System functions to aid in regeneratively heating feedwater by cascading the higher energy drains through successively lower energy stages of feedwater heaters.
How do Normal and Alternate drain valves fail?
→normal - fail closed
→alternate - fail open
Why don’t Feedwater Heaters 5 & 6 have MOVs or check valves?
→not enough stored energy
→located inside main condenser, so have limited accessibility for operation/maintenance
→feedwater heaters have anti-flash baffles
→condensate side of feedwater heaters provided with auto isolation on Hi-Hi Level
Drain paths for Heater Drain Tanks and Feedwater Heaters 1, 2, & 3
Heater Drain Tank 01:
→MSR Separator Drains
→MSR Shell Drains
→SGBD Drain
→HDT-01 drains to HDT-02
Heater Drain Tank 02:
→Feedwater Heaters 1, 2, & 3
→FWH 1A/B drains to FWH 2A/B
→FWH 3A/B have no alternate drains (dry heater)
→U2 only: FWH 3A/B have vent isolations
→HDT-02 provides suction to Heater Drain Pumps
What is the purpose and source of HDP Seal Injection?
→Seal Water and Cold Water Injection both supplied from Condensate
→Cold Water Injection provided to prevent cavitation through HDPs & TV-2598
Heater Drain Pumps
→powered from uA1 and uA2
→oil coolers supplied by TPCW
→minimum flow 1400 gpm
→if one HDP trips, turbine will runback to <812 MWe (≈70%) at 35% per min
Pumps Trip On:
→Lo-Lo Level HDT-02 5%, ≤806’6” (2/2)
→overcurrent, phase-to-ground
→locked rotor
→thermal overload (26 relay)
→motor DOES NOT trip on motor overload; 74 relay is alarm only
Heater Drain Pump Recirc Valves FV-2589A/B
→fail open AOVs
→minimum HDP flow is 1400 gpm.
→auto open when HDP flow <1470 gpm (both valves open on low flow from either pump)
→auto close when HDP flows >1520 gpm (both valves close when both HDP flows above setpoint)
→auto close 10 sec after associated pump trip
Extraction Steam MOVs - Motor Operated Stop Valves
→close slower than check valves
→protect turbine from water induction and high level
Auto Close On:
1. Hi-Hi FWH Level
2. Turbine Trip
Interlocked With:
→associated power assisted check valve
→upstream drip pot drain isolation valve
→normal drain valve from its associated drains source
Extraction Steam Power Assisted Check Valves
→close fast
→protect turbine from overspeed due to reverse flow
Auto Close On:
1. Hi-Hi FWH Level
2. Turbine Trip
Hi-Hi Level in an MSR will…
…trip the Main Turbine.
Heater Drain Pump Temperature Limits
Shut down immediately if:
→bearing temp >200°F
→lube oil temp >160°F or it doesn’t build lube oil pressure
Feedwater Heater Hi Level Limits
→Hi Level produces Control Room alarm
→Hi-Hi Level FWH 1:
→closes normal drains from RHDT to FWH 1
→closes Extraction Steam valve to FWH 1
→opens alternate drain valves to Main Condenser
→Hi-Hi Level FWH 2:
→closes normal drains from FWH 1 to FWH 2
→closes Extraction Steam valve to FWH 2
→opens alternate drain valves to Main Condenser
Heater Drank Tank Level Control Valves u-LV-2592 & 2594
The goal is to maintain HDT-02 Level at 50%.
u-LV-2592:
→comes off HDP discharge header; supplies MFP suction
→PI Controller, uses auctioneered high level
→HDT-02 Level >50% - valve opens further
→HDT-02 Level <50% - valve closes further
→if level goes too low, valve could close enough that forward flow is lost
u-LV-2594:
→comes off HDP-02; discharges to Main Condenser Shell B
→Proportional Controller; uses auctioneered low level
→HDT-02 Level >65% (approx.), valve modulates open
→HDT-02 Level >70% (approx.), valve fully open
Heater Drank Tank Level Control Failures / Malfunction
HDP Common Discharge LV-2592 controlled by auctioneered HI signal from LT-2592A/B:
→failing low has minimal impact
→failing high will cause 2592 will go full open
→could result in HDT level lowering to 2/2 level HDP trip (5%)
HDT-02 Alt. Drain Valve LV-2594 controlled by auctioneered LOW signal from LT-2594B/C:
→failing high will have minimal effect
→failing low will cause 2594 to close if open
Note: the Lo-Lo Level HDT-02 5% trip of the HDPs comes off of different level transmitters than the ones that control LV-2592 & 2594.
Feedwater Heaters Normal and Alternate Drains
Drain Tanks Normal and Alternate Drains
Extraction Steam Source and Application Points
