automatic boiler controls
TRANSCRIPT
62B-208-411 AUG 00
Automatic Boiler Controls
• Consist of three sub-systems
• Automatic combustion control• Automatic FEEDWATER control• Main feed pump constant pressure
62B-208-511 AUG 00
Combustion Control
• Maintains steam drum or SUPERHEATER outlet pressure
• Within 5 PSI of SETPOINT during steady state conditions
62B-208-611 AUG 00
Combustion Control
ACC MEASURES
STEAM PRESSURE
GENERATES A MASTER DEMAND FOR FUEL AND AIR
MANIPULATES THEFORCED DRAFT BLOWERS &FUEL OIL CONTROL VALVE
STEAMDRUM
62B-208-711 AUG 00
Combustion Control
MEASURES STEAM
PRESSURE
ACC
FORCED DRAFT BLOWER
MANIPULATES AIR FLOW TO THE BOILER BY INCREASING/DECREASING THE SPEED
OF THE FORCED DRAFT BLOWER
62B-208-811 AUG 00
Combustion Control
ACC
FUEL OIL CONTROL VALVE
MEASURES STEAM
PRESSURE
MANIPULATES FUEL FLOWTO THE BOILER BY
INCREASING/DECREASINGFUEL FLOW TO THE BURNERS
62B-208-911 AUG 00
Combustion Control
MEASURES STEAM
PRESSURE
FORCED DRAFT BLOWER
ACC
FUEL OIL CONTROL VALVE
62B-208-1011 AUG 00
Automatic/manual Control Stations
PRIOR TO THE FINAL CONTROL
ELEMENT TO ALLOW
FOR HUMAN INTERVENTION
FINAL CONTROLELEMENT
AUTOMATIC SYSTEM
62B-208-1111 AUG 00
Automatic FEEDWATER Control
• Maintains water level in boiler steam drum
• Plus or minus one inch from normal
• All steady state load conditions
62B-208-1211 AUG 00
Automatic FEEDWATER Control
3 Element Feed
Water Level
+/-1 inch of Normal
MANIPULATES THE FEEDWATER
CONTROL VALVE TO REGULATE FEED FLOW
TO THE BOILER
62B-208-1511 AUG 00
Compensates For Shrink And Swell
• Steam flow and drum level will respond in the same direction upon a boiler load change
• Increase to increase
62B-208-1611 AUG 00
Shrink & Swell
• During up PWR MANUEVERS, a temporary rise in BLR WTR LVL occurs -- called swell
• During DWN PWR MANUEVERS, a temporary drop in BLR WTR LVL occurs -- called shrink
Swell
• Increase in STM demand:– More STM leaves BLR.– Drum press starts decreasing.– STM bubbles in GEN tubes expand.– WTR level appears to “swell”.
62B-208-1811 AUG 00
Swell• Automatic combustion CONTRL system (acc
sys) senses decrease in drum press and increases firing rate
• Drum press increases and regains SETPOINT• WTR LVL decreases as bubble size decreases
62B-208-1911 AUG 00
Swell
• WTR reaches normal and get slightly below normal
• Automatic boiler control system (ABC sys) will increase feed flow to match STM flow
• WTR LVL achieves normal
62B-208-2011 AUG 00
Shrink
• During a DWN PWR MANUEVER shrink has the opposite effect :– Co wants all stop -- man overboard!– Throttle closes– STM drum press rises– WTR level lowers or “shrinks”
62B-208-2111 AUG 00
Shrink
• Acc sys decreases firing rate • Drum press regains SETPOINT• WTR LVL increases• WTR LVL reaches normal, and slightly
above normal• ABC sys decreases feed flow
62B-208-2211 AUG 00
Main Feed Pump Controls
• Maintain a constant pressure FEEDWATER supply to the boiler while on line
• Designed to supplement the FEEDWATER control valve
• 150 -200 PSI above steam drum pressure
62B-208-2311 AUG 00
Main Feed Pump Controls
• The output of the header pressure controller will be directly proportional to the actual header pressure
• Increase - increase
62B-208-2411 AUG 00
Feed Pump Controls
MAIN FDPUMP CONT.
MEASURES FEEDPRESSURE FROM A COMMON HEADERTO ONE OR MORE
BOILERS
62B-208-2511 AUG 00
Feed Pump Controls
MAIN FDPUMP CONT.
GENERATESA DEMAND
SIGNAL TO THEFEED PUMP STEAMADMISSION VALVE
62B-208-2811 AUG 00
Constant Pressure Regulator
• Feed pressure directly opposes spring compression
From common
Header
62B-208-2911 AUG 00
Boiler Control Test
• On-line alignment and verification• Boiler flexibility test
• Overall system reliability
62B-208-3011 AUG 00
Final Control Elements
• Fail safe positions
• Combustion to minimum• Water level to maximum• FEEDWATER control valve open• Feed pump steam admission valve fully
open
62B-208-3211 AUG 00
Air Pressure Failure
• Air lock system
• Holds final control elements
• Allows WATCHSTANDERS to take control of the plant
62B-208-3311 AUG 00
ALARM PRESSURE SWITCH
RESET
MASTERTRIP
NEEDLE VALVE
REDUCER THREE WAYVENT
INDIVIDUALTRIP VALVE
FROMA/M STATION
TOFINAL CONTROLELEMNT
40 PSI
65 PSI
80 PSI
125 PSI75 PSI