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Control & Automation For

Super Critical Units

K.S. SundaramNTPC, SIPAT

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Introduction

• Requirements

• Comparison of Auto loops -Sub Critical Vs Super Critical

• Feed Water Control

• Steam Temperature Control

• Unit Control

• Turbine Control

• Discussions

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Super Critical Units

• Increased requirement of accuracy and resolution of DDCMIS

systems.

• No drum, hence no energy reserve.

• Need to match fuel ,air and feed water accurately.

• Stringent requirement of temperature controls as unbalance in

fuel and feed water has significant change in temperatures.

• Smooth changeovers between wet to dry operation and vice versa

• Control system should ensure smooth steady state operation.

• Little need for operator intervention.

4Source :KEPRI

5Source :KEPRI

6Source :KEPRI

7

Comparsion Of Major Loops

Name of the loop Remarks SIPAT 660 MW

Furnace Draft No major difference Blade pitch control, Hydraulic

Air flow control No major difference Blade pitch control, Hydraulic

PA Hdr. control No major difference Blade pitch control, Hydraulic

Fuel master Cross limiting from FW VFD in feeders

FW control Saturation Temp Controller TDBFP 2 X 65%,

MDBFP 2X30%

SH temp control FW plays a major role FW plays a major role (Trip at Temp >565 Deg)

RH temp control No major difference .

Spray Should be Zero

Two tilts per corner (Trip at Temp>580 Deg)

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List Of Loops For DiscussionS.N. Name of the loop Sub loops

01 Feed Water control Feed Water Master

BCP / UG valve

FWPCV control

Separator Drains control

02 Super heater temp control

Platen SH temp control

SH steam temp control

03 RH steam temp control

Burner tilt control

Spray valves control

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Feed Water Control Requirements• Ensure feed water flow in relation to unit demand.

• Adjust feed water flow to get the desired separator outlet temperature and degree of super heat.

• Ensure the rangeability of platen SH spray valves

• Incorporate the start up level demand.

• Ensure minimum required feed water flow.

• Convert the flow requirement into pump demand with compensation for pump capacities.

• Ensure protection for Fuel /FW ratio.

• Ensure the pumps are within the operating range.

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Final Control Elements In FW Loop

Control Element Initial Condition Till Chemical Parameter Is Achieved Before

BC Pump Start

Condition From BC Pump Start / BLU Up To Load < 30 %

WET MODE

Load > 30 %

DRY MODE

MDBFP SCOOP/TDBFP Speed

FW master in manual control. Initial FW flow at 200 T/Hr and

Later 600T/Hr when

WR opens to 30%

Separator

Level control

Feed water flow control

BC Pump Discharge Valve -- Feed water flow

control --

Feed water

Valve ( Eq. to

30% Valve )

FW pressure control at upstream of valve

FW pressure control at

upstream of valve

Full open and bypass valve opens

Separator Drain Valves WR/ZR

Separator

Level control

Separator Hi

Level--

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SUB

PID

SEPARATOR SEPARATOR LEVEL SET LEVEL SET POINT FROM POINT FROM ULDULD

ACTUAL LEVELACTUAL LEVEL

TO BFPS

SEPARATOR LEVEL SETPOINT

0

2

4

6

8

10

0 100 200 300 400

ULD

LEVE

L SE

TPO

INT

Series1

ULD 0 300

SP 9 3

Feed Water Master In Wet Mode

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SUB

PID

<

SUB

PID

MIN. FW FLOW MIN. FW FLOW SET POINTSET POINT

FW FLOW TO FW FLOW TO ECONOMISERECONOMISER

DP ACROSS BC DP ACROSS BC PUMPPUMP

DP SET POINT DP SET POINT ACROSS BC ACROSS BC PUMPPUMP

UG VALVE

BC PUMP WILL TRIP IF DP

IS < 4.5 Kg/Sqcm

Min FW Flow Control In Wet Mode

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SEL

FGSUB

PID >

BFP HEADER BFP HEADER PRESSURE PRESSURE TRANSMITTERSTRANSMITTERS

FWPCV

FG

HIGHEST OF TDBFP HIGHEST OF TDBFP SUCTION SUCTION FLOWSFLOWS

HIGHEST OF MDBFP HIGHEST OF MDBFP SUCTION FLOWS SUCTION FLOWS

FWPCV Valve Control In Wet Mode

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F(X)F(X)F(X)F(X)

WR

ZR

MEASURED SEPERATOR LEVELMEASURED SEPERATOR LEVEL

Separator Drains Control

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• Separator level control by BFPs and FW flow control by UG .Min FW

flow set point from boiler desk. Initial level set point is 9 Mtr. WR and

ZR will act as emergency control for separator level

• If water disappears in separator during wet mode then boiler will trip

on separator level low low – 1.1 Mtr (3 Sec delay)

• Boiler will trip if separator outlet level goes high high in wet mode –

17.7 Mtr

• WR opens at 14.2 Mtr in auto

• ZR opens at 16.2 Mtr in auto

•

Wet Mode Operation

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Wet Mode & Dry Mode Of Operation

Source: Doosan

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• First controller acts on load dependant average DT across PDSH.

Its output represents the required adjustment to maintain the

steam conditions, flue gas temperatures entering Platen SH so

as to ensure adequate spray platen range.

• Second controller acts on load dependant separator temperature

set point corrected by first controller. The output adjusts feed water

in response to firing system disturbances.

• Minimum set point of 30% for safety is additionally provided.

Feed Water Control In Dry Mode

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SEPDSH

F2(x)

PI

∑

PI

∑

F1(x)

PI

>

BMD

A

AT2

BOILER MASTER DEMAND

PLATEN SH DTSEPERATOR OUT STM TEMP

SEPERATOR OUTLET TEMP SET POINT

SET TO ZERONOT DRY MODE

ANY SCANNER FLAME (AND) BCP OFF

a b

0 %

30 %

FWF F(x)FB SIGNAL

TOTAL FW FLOW

FF SIGNAL

TO BFPs

FG

FW Master In DRY Mode

Source : KEPRI

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DT SETPOINT IN FW LOOP

0

5

10

15

20

25

30

0 50 100

BOILER MASTER

DT S

ETPO

INT

Series1

BM(%) DT

0 0

28.8 11

43.3 28

52.1 22

70.7 9

91 9

100 11

Platen DSH DT Set Point

Source : EMERSON

Source : EMERSON

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Source : EMERSON

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Runbacks /Rundowns

• Two TDBFPs – 120%• One TDBFP + One MDBFP – 95%• One TDBFP – 65%• One MDBFP – 30%• Rundown if FW deviation is high • BFPS will go for pressure control when FW deviation is very high• ID / FD / PA runback demand is 396 MW and turbine trip is 330 MW

Protections

• Feed water flow low low for 10 sec ( 440 T/Hr)• Vertical wall tube metal temperature Hi Hi (4/48) (479 Deg)• MS / RH STEAM temperature Hi Hi 565/580 Deg• All BFP off for 20 Sec

Runbacks /Rundowns/Protections

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• DT across PDSH is taken care by Feed water control.

• DT across FDSH and Load dependant DT SP acts on master

with over/ under firing FF which is derived from comparing rate of

change of fuel flow to rate of change of steam flow.

• Master output goes to slave via SP correction from steam flow

where input is PDSH outlet with saturation temp limitation.

• Incase of start up only master controller will be in service.

Platen SH Temperature Control

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BM(%) DT

0 0

28.8 27

43.3 21

52.1 18

70.7 7

91 7

100 7

DT SETPOINT FOR FDSH

0

5

10

15

20

25

30

0 50 100

BOILER MASTER

DT S

ETPO

INT

Series1

Final DSH DT Set Point

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406 451 440 486 480 540

DSH1 DSH2

15% 3%

PLATEN SH FINAL SH DIV SH

SH Temperature Profile

27Source : KEPRI

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• DT across FDSH is taken care by Platen SH temperature control.

• Final SH O/L temp and Load dependant temp SP acts on master with over/under firing FF which is derived from comparing rate of change of fuel flow to rate of change of steam flow.

• Master output goes to slave via SP correction from steam flow where input is FDSH outlet with saturation temp limitation.

• Incase of start up only master controller will be in service.

Final SH Temperature Control

29Source : KEPRI

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RH Temperature Control (Tilt)RH O/L AVG temp and temp SP (568 DEG) with

RHDSH DT correction (Max 5 DEG) correction fed to

PID, PID output with airflow FF goes to 2 sets of tilt - one

for wind box and other for SOFA

31Source : KEPRI

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• RH O/L temp and load dependant temp. SP acts on master controller.

• Master controller output is corrected with over/ under firing FF which is derived from comparing rate of change of fuel flow to rate of change of steam flow.

• Master O/P goes to slave via SP correction from steam flow where input is RHDSH outlet with saturation temp. limitation.

RH Temperature Control By Spray

33Source : KEPRI

34Source :KEPRI

Source : EMERSON

Source : EMERSON

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Turbine Control

• Speed Loop- Till synchronization (IP Rolling)

• IP is Throttle governing & HP is Nozzle governing

• Open load loop till HP is charged

• Pressure Control when HP is charged

• Sliding Pressure Operation from 90 to 247 Kg/sqcm

• Achieve full load & put on CMC

Salient Features:

• Individual EHC for individual valves

• No Hydraulic back up operation

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HP BP Control

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LPBP Control

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• KEPRI logics

• EMERSON Logics

References

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THANK YOU

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HPHECO I/L

ECONOMISER

Spiral w

ater

walls

VERTICAL WW

F L ASH

T ANK

WR

ZR

SEPARATORS

STORAGE TANK

CONDENSER CEP LPH DA

FWRS

Back

FEED WATER PATH INITIAL STAGE

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HPH

ECO I/L

ECONOMISER

Spiral w

ater

walls

VERTICAL WW

STORAGE TANK

SEPARATORS

MIXING PIECE

BCP UG

BackFEED WATER PATH - LOAD < 30%

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HPH

ECO I/L

ECONOMISER

Spiral w

ater walls

VERTICAL WW

TO BACKPASS CONNECTING PIPES

SEPARATOR

SEPARATOR

FEED WATER PATH – LOAD > 30% Back

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CCP Auto Start And Auto Stop Conditions

Source :Doosan