Moisture Separators Reheaters (MT) Flashcards
What is the purpose of the MSRs ?
-Used to improve quality of HP turbine exhaust before going into LP Turbine
-Improves plant efficiency & longer LP turbine life
How do the MSRs work ?
-Mechanically remove moisture & reheats dry steam passing across 1st & 2nd stage reheater tubes
-This minimizes erosion in LP turbine bucket & momentum losses
What steam is used for the MSR 2nd stage reheating ?
Main steam provides heating for second stage
What is aux steam used for on the MSRs ?
It’s used for steam blanketing of the MSRs
How does the Moisture Separator Section work of the MSR ?
Goes through chevron canes that puts wet steam through changes in direction, which causes heavy droplets from steam flow
What happens once dry steam flow exits moisture separator panels ?
Steam flow is reheated by tube bucndle s
Where does MSR Drain Tank drain to ?
Has level controller that directs tank discharge to either HTR Drain Tank or to Main Condenser on HI-HI Level
What happens if MSR vessel water backs up to within 3 inches ?
-Turbine trip initiates to prevent water induction in the turbine
-3level switches for 2/3logic
What does the Reheater Section do inside the MSR ?
-Supplied with heating steam that heats dried steam to superheater conditions
-Superheater steam is then directed to LP Turbine
Where is the 1st stage reheater receive its steam from ?
Receives steam from 3rd stage extraction line
What does the 2nd stage reheat require ?
Requires control system because it taps off upstream of turbine throttle valve & is therefore at main steam temp & pressure
Where does the 1st stage heater condensate drain to ?
Drains to 1st stage drain tank that drains to:
- #6 HPFWH
-Main Condenser on HI-HI lvl in tank
Where does the 2nd stage heater condensate drain to ?
It drains to the 2nd Stage Drain Tank which then drains to:
-#7HPFWH
-Main Condenser on HI-HI lvl in tank
What is the purpose for the MSR Drain Tank ?
-Collection point for moisture that was removed from HP Turbine exhaust
-Each MSR has one MSR Drain Tank
Where do the two MSR Drain Tank level control valves drain to ?
-Normal level control valve drains to to HTR Drain Tank
-High level control valve drains to Main condenser
What is the position of the MSR Drain Tank level control valves during start up ?
Startup will have Normal level control valve closed, & High level control valve will be opened
When less than 10% power what is the status of the MSR Drain Tank level control valves ? What happens when turbine power is greater than 10%?
-High level dump valve is failed open
-High level dump valve will go close & Normal level control valve will maintain level
What happens if MSR Drain Tank level has a continuous rise in level ?
-High level dump valve will modulate open to condenser
-If level continues to rise to MSR 3in setpoint, a main turbine trip initiates
What happens to the MSR Drain Tank level control valves on loss of instrument air ?
-Normal level control valve will fail closed
-High level dump valve will open
What happens to the MSR Drain Tank level control valves on a HI-HI lvl?
Normal level control valve will fail closed
Why does 3rd stage extraction used for 1st stage steam supply have acceptable rates of temperate changes ?
3rd stage extraction, temperature, and pressure of steam supplied 1st stage reheaters varies in turbine load
How is the steam supply to 1st stage bundle of the MSR isolated ?
Isolated by Motor Operated Reheat Stop Check Valve, operated from Control Room
What is the difference between the 1st & 2nd stage reheat steam supplied ?
-HP 3rd stage extraction is self regulating for the 1st stage reheat
-Main Steam needs a regulation when being supplied to 2nd stage of MSR
How is the steam supply to the 2nd stage bundle isolated ?
Isolated by Reheating Steam Source Valves(RSSV)
What valves are used to regulate the main steam pressure supplying the 2nd stage reheat steam for MSR ?
-Reheat Steam Low Load Valve(RSLLV)
-Motor Operated Reheat Steam High Load Valve (RSHLV)
What do the low load valve & high load valves do for the main steam supply to the 2nd stage reheat ?
Work together to regulate steam pressure with MSR & LP Turbine operational limits
What is the 2nd stage reheater supply pressure adjustments based on ?
-Control system adjusted 2nd stage pressure based on Turbine cross around piping
-Varies over desired load range & ensure temperature rate of change limitation are maintained
During startup when is the 1st stage reheater bundle placed in service ?
When turbine is at rated speed & minimum load 1st stage reheater bundle is placed in service
What’s the status of the 1st stage Drain Tank level control valves when there is low steam flow ?
-Normal control valve is closed
-High level control valve opened to ensure proper draining & no moisture buildup in reheater tube bundle
What happens to the 1st stage drain tank level control valves when turbine load is raised above 10% load ?
-High level dumb valve will auto close
-Normal control valve will begin to open
Where is turbine load sensed ?
Sensed at inlet to the LP ‘A’ Turbine
What happens to 2nd stage drain tank high level dump valves when turbine load is less than 20% ?
2nd stage drain tank high level dump valve will fail open
What happens to 2nd stage drain tank high level dump valve when turbine load rises above 20% ?
-High level dump valve will close
-Normal control valve will open to maintain level
How does the MSR Steam Scavenging work ?
Prevents condensate buildup in the the piping, which could cause thermal expansion in reheater stages
How does Steam Scavenging work on the MSR system ?
-Orifice lined on vent line is connect to same HPFWH as the associated Drain Tank
-HPFWH is lower pressure than reheater which causes excess steam flow that sweeps condensate from tubes
How much additional steam flow does the Steam Scavenging provide ?
Provides additional 10% of steam flow on top of flow that performs actual stage heating
Why is air purging important for the reheater tube bundles ?
-Important to evacuate air from bundles prior to admission of steam
-This ensures uniform heating as bundles pressurize
How does the air purging of the reheater bundles work ?
Removes air from bundles & places to condenser vacuum
Why is it important to prevent sustained steam flows to condenser?
Impinges condenser tubes & can cause damage
What would happen if steam were admitted to an unpurged reheater bundle ?
Top half of bundle would heat up first & then bottom half, which could cause differential expansion causing tube failure
When is air purging performed?
Performed prior to admitting reheat steam or steam blanketing
How does the Drain Tank high level control valve help during the purging process ?
High level dump valve will be open draining tank exposing bundles to condenser vacuum
Where is MSR Steam Blanketing supplied from ? What is it used for ?
Supplied from Aux Steam & used to prevent corrosion of tubes by keeping air out
What must be done to MSR drain flow paths during steam blanketing ?
-Vent steam scavenging valves are BOTH closed
-Drain Tank Drain Valves are closed
What is the blanketing steam temperature maintained at? Where is small amount of condensate directed to during steam blanketing process?
Maintained 300F & any condensate during process drain to reheater drain tank
