CMC

WHAT IS A CONTROL SYSTEM ?

• A SYSTEM WHICH AUTOMATICALLY TAKES CORRECTIVE ACTION TO ELIMINATE ANY ERROR IN THE PROCESS AND KEEPS THE DESIRED OUTPUT WITHIN PERMISSIBLE LIMITS. • A CONTROL SYSTEM CAN BE AN OPEN LOOP OR CLOSED LOOP, DEPENDING UPON THE ERROR DETECTION MECHANISM.

TYPES OF CONTROL SYSTEM

• AN AUTOMATIC CONTROL SYSTEM IS USED TO MAINTAIN ITS OUTPUT WITHIN DESIRABLE LIMITS BY MEANS OF A CONTROL ACTION.THE ERROR  SIGNAL IS USED TO ACTUATE CONTROL ACTION THROUGH CONTROLLER. THESE CONTROL ACTIONS ARE : •

PROPORTIONAL

•

DERIVATIVE

•

INTEGRAL

•

COMBINATON OF ABOVE

CONTROL LOOPS IN SERVICE AT UNCHAHAR 

• PI CONTROLLER:1.DRUM LEVEL 2.FUEL MASTER  3.AIR MASTER  4.MILL AIR FLOW 5.PA HEADER PRESSURE 6.FEEDER SPEED OR COAL FLOW • PI-PI CONTROLLER  1.FURNACE DRAFT 2.FRS DP 3.SH/RH CONTROL • PID CONTROLLER:1.MILL O/L TEMP. CONTROL 2.COMBUSTION CONTROL

COMBUSTION CONTROL

THE OBJECTIVE OF ANY CONTROL SYSTEM IS TO MONITOR AND CONTROL VARIOUS PARAMETERS AND INTER LINKED SYSTEMS WITHIN THE DESIRED LIMITS.IT WOULD OTHERWISE BE VERY DIFFICULT OR  VIRTUALLY IMPOSSIBLE TO MONITOR  & CONTROL SO MANY DIFFERENT PARAMETERS AND SYSTEMS SIMULTANEUOSLY.

COMBUSTION CONTROL

IT IS A CONTROL LOOP SYSTEM WHICH CONTROLS AND CREATES AN ENVIRONMENT INSIDE FURNACE TO ENSURE CORRECT AMOUNT OF AIR  WITH RESPECT TO THE ADMITED COAL SO AS TO COMPLETELY BURN ALL THE FUEL. INSUFFICIENT AIR RESULTS IN UNBURNT FUEL WHILE EXCESS AIR INCREASES THE QUANTITY OF WASTE HEAT.

ADVANTAGE

WITH A SINGLE COMMAND i.e.VARIATION OF THROTTLE PRESSURE FROM TURBINE DESK ONE CAN CONTROL TOTAL AIR FLOW IN THE FURNACE ,TOTAL FUEL IN THE FURNACE AND THEIR COORDINATED CONTROL TO MAINTAIN AIR FUEL MIXTURE AND THROTTLE PRESSURE. DISADVANTAGE

RATIO OF FUEL TO AIR / FEEDER SPEED IS IN ITSELF VARIABLE AND DEPENDS ON MANY FACTORS SUCH AS EFFICIENCY OF MILL CONTROL SCHEME ,PERCENTAGE OF ASH IN FUEL AND EFFIENCY OF THE MILL CONTROL SYSTEM.

COMPONENTS OF COMBUSTION CONTROL

THIS LOOP CONTAINS TWO MAJOR SECONDARY LOOPS:

AIR MASTER AND FUEL MASTER 

MASTER CONTROL OF THESE TWO CONTROLLERS IS COMBUSTION CONTROL.

MASTER PRESSURE CONTROLLER  THROTTLE THROTTLE PR. PRESSURE SP ACTUAL

PID CONTROLLER 

ACTUAL TOTAL FUEL

MIN

75 %

MAX

40 %

ACTUAL TOTAL AIR 

F(X) MAX

MIN

A

B

TO AIR MASTER 

TO FUEL MASTER 

BTU

AIR FLOW MASTER  FROM MASTER  CONTROLLER 

A

O2 TRIM

F(x)

70 % TO 110%

ACTUAL AIR FLOW PI

TO FD FAN VANES

FUEL MASTER 

FROM MASTER 

ACTUAL FUEL

CONTROL

FLOW

B

PI

BTU CURVE

RELATION BETWEEN BTU AND FUEL/ AIR  RATIO

180

140

0 % = 0.5 50 % = 0.7

        100  C          O 0 50          A          L BTU IN %          F          L          O          W TOTAL AIR AT 800 T/HR 

100 % = 0.9 100

CCS-

CO-ORDINATE CONTROLS

AN INTEGRATED APPROACH TO CONTROL FINAL OUTPUT OF THE TURBO-GENERATOR  i.e. LOAD, KEEPING ALL OTHER IMPORTANT PARAMETERS LIKE THROTTLE PRESSURE , TOTAL FUEL FLOW , TOTAL AIR FLOW i.e. COMBUSTION INSIDE FURNACE ,OXYGEN AND FURNACE PRESSURE WITHIN LIMITS.

CCS-

CO-ORDINATE CONTROLS

THE OBJECTIVE OF THIS CONTROL SYSTEM IS TO OPERATE THE TURBINE ,GENERATOR AND BOILER  AS AN INTEGRATED UNIT.BY THE COORDINATED ACTON IS MINIMUN INTERACTION BETWEEN CONTROL VARIABLES OF UNIT GENERATION , STEAM PRESSURE ,FLUE GAS OXYGEN,FURNACE DRAFT AND STEAM TEMPERATURE BY APPROPRIATE SIMULTANEOUS OPERATION . MANIPULATED VARIABLES OF FUEL,FEEDWATER , AIR AND TURBINE GOVERNER  THE CCS PROVIDES FOUR DIFFERENT OPERATING MODES

CCS

CCS IS DESIGNED FOR FOUR DIFFFERENT MODE OF OPERATIONS DEPENDING UPON THE STATUS OF THE TWO MAIN UNITS i.e. TURBINE AND BOILER. AT ANY ONE POINT OF TIME ONLY ONE MODE CAN BE SELECTED.

MANUAL MODE

TURBINE

BOILER  

MANUAL

MANUAL

TURBINE FOLLOW MODE

AUTO(REMOTE)

BOILER FOLLOW MODE

MANUAL AUTO(REMOTE)

CO-ORDINATE MODE

MANUAL AUTO AUTO

CCS

MODE SELECTION LOGIC: CO-ORDINATE MODE PR. CONTROL BY BOILER  MW CONTROL BY TURBINE BASED ON SP FROM CMC .

BOILER FOLLOW MODE PR. CONTROL BY BOILER  MW CONTROL BY TURBINE BASED ON LOCAL SP(EHTC)

TURBINE FOLLOW MODE PR. CONTROL BY TURBINE MW CONTROL BY BOILER 

MANUAL MODE MW CONTROL BY TURBINE PR. CONTROL BY BOILER 

CCS COORDINATE MASTER CONTROL: IN THIS MODE OF OPERATION BOTH TURBINE AND BOILER  REMAINS IN AUTO . M W IS CONTROLLED BY EHTC AND THE STEAM PRESSURE i.e. MS THROTTLE PRESSURE IS CONTROLLED BY BOILER FIRING RATE CONTROL. THE SET POINT FOR EHTC IS GENERATED FROM CMC CONSOLE. BOILER FOLLOW MODE: IN THIS MODE OF OPERATION TURBINE REMAINS IN LOCAL i.e. LOAD IS CONTROLLED BY EHTC SET POINT FROM TURBINE CONSOLE.WHEREAS BOILER FUNCTIONS TO MAINTAIN THE THROTTLE PRESSURE.EHTC LOAD SET POINT IS USED FOR FEEDFORWARD TO BOILER MASTER. BOTH CMC AND BFM HAVE THE ADVANTAGE OF QUICK  RESPONSE TO LOAD CHANGES AND BETTER CONTROL

CCS TURBINE FOLLOW MODE: IN THIS MODE OF COTROL STEAM PRESSURE IS CONTROLLED BY TURBINE AND LOAD IS CONTROLLED BY BOILER  TFM WILL AUTOMATICALLY SELECTED WHEN RUNBACK  OCCURS AND SYSTEM IS NOT IN MANUAL MODE.

BOILER MASTER : THIS CONTROLLER CONTROLS COMBUSTION IN THE FURNACE AND MAINTAINS THROTTLE PRESSURE BY VARYING FIRING RATE. SLIDING PRESSURE MODE CHECKES BOILER LOAD INDEX FOR THE CALCULATION OF THROTTLE PRESSURE SET POINT.

MANUAL MODE SELECTION

MANUAL MODE SELECTED

THROTTLE PRESS TX OK 

AND

AIR MASTER AND FUEL MASTER AUTO. TURBINE IN LOCAL

OR 

OR 

2 3

1

4 S

R 

MA

MANUAL MODE

TFM MODE SELECTION

CMC

TFM

RELEASE

BFM

PR DEV >< +-1.5%

AND

AIR MASTER AND FUEL MASTER AUTO.

TUR.IN LOCAL AND THROTTLE PRESS TX OK 

AND OR 

OR 

RUNBACK IN ACTION 1 3

2

4 S

R 

TF

BFM MODE SELECTION CMC TFM

RELEASE

BFM

EHC LOAD >< +-2.4%

AND

AIR MASTER AND FUEL MASTER AUTO.

TUR.IN LOCAL AND

4 OR 

1 2 3

S

R 

BF

BFM

CO-ORDINATE CO-ORDINATE MODE SELECTION

CMC TFM

RELEASE

BFM

EHC LOAD >< +-2.4%

AND

TUR.IN LOCAL

AIR MASTER AND FUEL MASTER AUTO.

AND

3 OR 

1 2 4

S

R 

C O

CMC BLOCK 

UNIT LOAD SP CMC CONSOLE

DIAGRAM

MINIMUM LOAD SP

MAX

MAXIMUM LOAD SP

EHTC LOAD SP

MAXIMUM TURBINE LOAD (FROM TG)

MIN

ACTUAL TURBINE LOAD

2

1 SELECTOR 

SEL. 2

1 ACTUAL TURBINE LOAD 2 1 SEL. 2 2 SELECTOR  SELECTOR  TFM SEL. 2 AND OR  RUNBACK IN ACTION LOAD

MANUAL MODE SELECTED

INTEGRATOR  (SWI)

BFM

EHTC LOAD SP

2 SELECTOR 

II ND ORDER  DELAY

LOAD SET POINT TO TURBINE CONTROL EHTC

1

SEL. 2

SELECTOR 

FEEDFORWARD TO BOILER MASTER 

CMC SELECTED

CMC BLOCK  DIAGRAM

THROTTLE PRESSURE SP CMC CONSOLE 1 FKG

BLI

INT (SWI)

2

SEL. 2

SELECTOR 

ACTUAL THROTTLE PRESSURE

ADDER 

EHTC LOAD SP

SLPR. MODE SELECTED

1 CMC SEL

SEL. 2

FKG

SELECTOR 

MUL

2 LOAD SP

PID CONTROLLER  BFM CMC

OR 

RA

ADDER 

FEEDFORWARD TO BOILER MASTER  SEL. 2 RUNBACK IN ACTION

1 SELECTOR 

A

2

UNIT CAPABILITY

AIR MASTER  DIAGRAM

A FKG

O2 TRIM

TOTAL FUEL ACTUAL

FKG

MAX

INT (SWI)

BLI

FKG BLI

FKG

MAX

PIR

MAX

ADS

MUL

TOTAL AIR FLOW ACTUAL

PIR 

AIR FLOW

SAD 1A/1B

MASTER SP

O2 TRIM RAISE LOWER 

FUEL MASTER  A

DIAGRAM DIAGRAM TOTAL SA FLOW

ADDER

FKG

MIN

TOTAL PA FLOW

PIR 

TOTAL FUEL ACTUAL

MILL BIASING MAB END BIASING PIR 

MAIN AIR DAMPER 

MCD

MEF

THROTTLE PRESSURE VARIATION VS LOAD CHANGE

100% = 250 MW 3..2%

-1..5%

1%

-1%

L O A 1..5% D IN %

-3..2% THRT. PR.VARIATION IN % (100% =200KG/CM3)

THROTTLE PRESSURE VARIATION VS LOAD CHANGE

0 – 2.0

KG/CM3

 NO VARIATION IN LOAD

2.0 – 2.6 KG/CM 3

0-3.675 MW / KG/CM 3

2.6 – 3.0 KG/CM3

3.675-6.72 MW / KG/CM 3

RUNBACK SYSTEM:

TO MAINTAIN LOAD AS PER THE AVAILABLE CAPACITY OF THE UNIT AND TO SAVE UNIT FROM TRIPPING RUNBACK  SYSTEM IS INITIATED.EACH AUXILLIARY WHICH IS USED FOR  KEEPING THE RESPECTIVE PARAMETERS WITHIN RANGE HAS CERTAIN CAPACITY UPTO WHICH IT CAN BEAR LOAD.THIS LIMIT IN TURN DEFINES THE BOILER LOADING CAPACITY i.e. HOW MUCH LOAD CAN BE GENERATED WITH THAT AVAILABILITY. ALL THESE LIMITS ALONG WITH THE MAXIMUM LOAD i.e. 100% ARE THEN COMPAIRED BY A MINIMUM BLOCK ,THE OUTPUT OF WHICH THEN DEFINES THE UNIT CAPABILITY.

RUNBACK SYSTEM: THESE LIMITS ARE AS FOLLOWS FOR THE RESPECTIVE AUXILLIARIES:1. ID FAN

65% EACH

130 % FOR TWO FANS

2. FD FAN

65% EACH

130 % FOR TWO FANS

3. PA FAN

65% EACH

130 % FOR TWO FANS4.

4. MILL

65% EACH

130 % FOR TWO MILLS

5. TURBINE TRIP/LSR OPER.

60%

100% FOR NORMAL RUNNING

6. BFP

50% EACH

100 % FOR TWO BFPS

ID FAN LIMIT(130 %) FD FAN LIMIT(130%) PA FAN LIMIT(130%) FUEL LIMIT(130%) BFP LIMIT(100%) (DELAY 3SEC) TURBINE / LSR LIMIT(60%) MAX LOAD (100 %)

M I    N I   M  U  N

UNIT CAPABILITY

RUNBACK SYSTEM:

FINAL CMC DEMAND i.e. BOILER MASTER DEMAND CONTINUOUSLY CHECKS UNIT CAPABILITY AND DEPENDING UPON THE UNIT CAPABILITY THE FINAL OUTPUT IS GOVERNED. FOR EX. IF 80 % IS THE NORMAL BOILER O/P DEMAND AND UNIT CAPABILITY IS 100% AND SUPPOSE ANY AUX. SAY ID FAN TRIPS THEN BOILER MASTER O/P WILL BECOME (80 X 65 =52).

BOILER MASTER DMD UNIT CAPABILITY

1 FINAL BOILER 

2

SELECTOR 

MASTER OUTPUT TO AIR AND FUEL MASTER 

RUNBACK IN ACTION

SEL 2

RUNBACK SYSTEM:

RUNBACK SEL RUNBACK IN SERVICE

AND

S

MANUAL MODE

R  MANUAL MODE SEL

RUNBACK IN ACTION

WHENEVER THESE CONDITIONS FULFILL “RUNBACK IN ACTION” ALARM WILL APPEAR AND TURBINE CONTROL WILL TRANSFER INTO PRESSURE CONTROLLERFROM LOAD CONTROLLER AND TFM OF CMC WILL ACTIVATE.