CMC

(COORDINATED MASTER CONTROL)

Atul Anand SoniSuperintendent (C&I)

CMC ensure proper coordination between Auxiliaries, boiler and turbine to attain efficient and safe running of the plant.

(1)CMC – coordinated mode (2)BOILER follow mode- Boiler follow turbine(3)Turbine follow mode- Turbine follow Boiler

(critical Pr. Mode)

CMC coordinate sensitive turbine & slow response boiler & Auxiliaries. Limited with help of turbine control (EHC) and TSE.

CMC Boiler master on Auto Turbine master on Auto Unit master - Receiving load demand

from ALDC or Manually from desk.

1) CMC:

Basically to control internal parameter’s of unit like (1) M S Pressure, (2) Load. Also to coordinate sensitive turbine and slow response of boiler auxiliaries, Good for network and Unit stability. Both Boiler and Turbine control ON Auto.

 2) BFM:

Boiler follow turbine. Turbine on Load control- Boiler ON Auto-control pressure with BLI as feed forward. MW demands are met by Turbine firstly and lesser importance to unit stability.

 3) TFM:

Turbine follow Boiler. Boiler Master on manual control. Pressure control. Turbine maintains pressure by varying MSCV ,Unit load depends on steam output from boiler Best for unit stability

RUNBACK MODE.RUNBACK MODE.

under runback conditions the firing for the boiler must be reduced to preset values, as close as possible to the tolerable limits. Therefore the swings of firing rate caused by the action of the PID controller must be avoided. As consequence of this condition the system has to switched to pure feed forward to control where the firing rate set point is directly proportional to load capability signal. To avoid any mismatch between steam production of the boiler and the turbine load turbine has to be switched to initial pressure control.

04) RUNBACK:

In R/B mode boiler controls give command in proportion to unit capability. Turbine – Pre. Control. R/B mode sets in automatically.

 

05) BOILER MASTER:

Basically a pressure controller

FEED FORWARD SIGNAL

 GNI OUTPUT - CMC

BLI - B.F.M

PRTD - T.F.M

GET BYPASSED - R/B

F/F Pre. Set point Actual pressure +

BM

06) G N I :

Control tracking generator or set point control module. Generates increase/decrease rate.

 Target to GNI:

CMC : Load dispatch center or unit- master [frequency

corrected]

BFM : Boiler demand (BM O/P)

TFM : Actual Load.

R/B : Unit capability. 

07) UNIT CAPABILITY:

Capability to produce MW at that instant, W.C signal depends on the number of auxiliaries in service and their contribution is expressed as MW signal, which they can support.

08) FGMO:

Free Governing mode of operation Intro duce critical external parameter i.e. freq. of network to our control system. To ensure stability of network or grid it is necessary to have frequency regulation in CMC/EHC. But frequency is network parameter, which cannot be controlled by few units in the network. Total disturbance in network will be passed on to the units having regulation by the many units do not have regulation.

09) CMC TABLE ModeBoiler

controlsTurbine controls

InputTo BoilerControls

Feed Forward

InputTo turbine

control

BFMThrottle

PressureMW

Pressure error

Steam Flow[BLI]

MW error(Load controller

active)

CMC Pressure MWPressure

errorMW errorGNI O/P

MW error(Load controller

active)

TFM

MW & Pressure

[Manual at KORBA]

Throttle- pressure(Pressure

controller active)

Pressure error

PRTD Turbine load set

point

Pressure error

RUNBACK

Produces steam as per unit

capability

Throttle- pressure(Pressure

controller active)

UNIT Capability

Signal

BMBypassed

Pressure error

BOILER FOLLOW BOILER FOLLOW MODEMODE

1. Turbine on load control2. Boiler master on Auto-controls throttle steam Pressure with steam flow as feed forward. Varying fuel I/P (firing rate) in the furnace.

In this mode boiler has to supply the steam for whatever load has been set from Turbine desk. In this way if the throttle steam reaches a limit (10 kg below the set throttle steam Pr.) “limit Pr. Engaged” condition comes and load would be scarified to maintain/restore the throttle steam Pr.

SELECTION OF BOILER FOLLOW MODE ( BFM)SELECTION OF BOILER FOLLOW MODE ( BFM)

1. Put air control on auto (at least one FD fan)

2. Put feeders speed control on auto after varying fuel master(FM) output and making feeder speed controller error zero.

3. Vary Blr. Master O/P so that FM error becomes zero. Then put FM on auto.

4. Make throttle pr. Set point and actual pr. Difference zero.

5. Put BM on auto.

If unit in turbine follow or coordinated mode change over to boiler follow occurs under following condition :-

turbine goes to manual because of any reason or operator action

Pr CMC - Pr Lim > 60MW

TURBINE FOLLOW TURBINE FOLLOW MODEMODE: - : -

1. Boiler manually controlled2. Turbine master On Auto -controls throttle

steam Pre. (With steam flow as feed forward) by varying load.

In T.F.M Pr. Controller comes into picture and the throttle Steam Pre. Varies the opening of MSCV to maintain the set throttle steam Pre.

MW SET PT.

PI

G

NF

T

+PR. SET PT.

B

PI

FUEL FIRING DEVICE +

-

-

-P

TURBINE FOLLOW MODE 

                 

 

MW SET PT.

G

MW

F

T

+ -

PR. B

FUEL FIRING DEVICE

+ -U

PID PI

F

P-

BOILER FOLLOW MODE                

 

 

SELECTION OF TURBINE FOLLOW MODE ( TFM)SELECTION OF TURBINE FOLLOW MODE ( TFM)

1. Boiler master on manual.

2. Throttle pressure deviation zero.

3. Turbine in auto.

4. Press. Turbine flow push button along with manual release on CMC desk and turbine goes to initial pressure mode from LMT mode by itself.

5. Now load set point can be changed by varying the boiler master manually.

O2 TRIMO2 TRIM - -

A section station and a setter for oxygen set point are provided to achieve the desired excess air. If variable O2 set point (SP) is selected, set point is generated by a function generator which is a function of max ( air flow SP and total air flow). In other mode SP is set from UCB. O2 in flue gas is compared with this SP and error is fed to PI controller, output of which is limited between 0.8 and 1.2% of total air flow.

Pressure Correction in CMCUnder normal operating conditions including small load

(pressure) variation boiler and turbine are controlled independently as per set point from GNI. Any unbalance in power generation and power consumption due to frequency variation in FGMO , throttle pressure may increase or decrease which may cause dangerous condition in the boiler.

If DP (Set throttle pre.- Actual throttle pre.) variation goes below set point ( - ve pressure deviation) , boiler storage capacity is used. However, any large variation in throttle pressure shall restrict the Turbine output till the Boiler has produced the additional output to match the increased demand. Similarly in case of +ve pressure deviation turbine output will increase.

MW

2 Kg - DP

15MW

1 Kg 15MW

1 Kg 2 Kg + DP

Note:- Note:- THROTTLE PRESSURE (DP) correction starts at +/- 1Kg and acts upto +/- 2Kg. It will add or subtract +/- 15 MW to the GNI output, thereby generating pressure corrected GNI output to EHC.(# unit 5)

+

+-

MaxnMin

P

Th.Pre. Set.Pre

F/F

Pre. Correction

Adder

Adder

O/p

K F

Min

UnitMaster

GNI

MAX

MIN

Boiler master PI+D

Delay

Frequency connected GNI O/P

Frequency & Pr.Connected GNI O/P to EHC

P

+---

+ +

Air master Fuel master

FREQUENCY INFULENCE ON CMC

1.5 %

MW

39923012

10MW

20MW

TSE upper margin

TFM

MIN

P

P

MAX

MIN

CMC

F/D

TFM

PRTD

UnitMaster

MAX

MIN

MAX

MIN

LOADUNIT

+

+-

MIN

MAX

MIN

Delay

Boiler master PI+D

Air master Fuel master

BFM

Set.Pre Th.Pre

TFM

BFM

P

MIN

UNIT load rate

Runback limit

TSE lower margin

PR (CMC set

Pt to turbine)BLI P

F(x)

UNITCOORDINATER

GNI

Runback in action

Capability

LDC

PULV A -J

Frequency influence

PA FAN A

CMC

BFM

PA FAN B

UNIT Capability

LIMITING BLOCK

Turbine load limiter

Actual MW

Boiler demand

Target of unit

D action

load

+ + -

+

+ +

+

-

Load Reference

FrequencyInfluenceON

Pressure Correction

Load Limiter

FrequencyUnloadingCharacteristic

Load controller

TSE Influence

+

+

+ MIN

+

-

Max / Min.Limiter

Max Min

Load Setter

GNI

Delay

Boiler Master

( f ) Load

Actual Pressure

Throttle Pressure Set.

+

+

+ +

++

++

+

-

EHC

Load

25MW

40MW

0. 2HZ

0. 125 HZ

Freq

X Y P AB

P

P

Y1Y2

Y2Y1

28.6%85.7%

3X1.01

X001 XM03 XP01 PT3 X001

CVCORRECTED COAL FLOW

A

B

TOTAL OIL FLOW

MW GENERATED

XP01

TOTAL COAL FLOW

-+

+-

+ +

B/M O/P AIR

MIN

FUEL MASTER

A B J

CV Correction loop manipulates the coal flow measurement signal by increasing or decreasing it, to show less coal is going when coal quality is bad and more when coal is good the effect is limited to 85% to 100% of actual coal flow

Max

Max

XN01

XN01

P XP01

Max XN01MIN

AIR FLOWTOTAL

AIR FLOW

XN01

AIR FLOW DEMAND

PIR L

RS04OXYGEN MASTER

80%

+ +

HK7715D WY

Ua = Ui

20%

TOTAL FUEL FLOW BOILER DEMAND

( = 0..1)XM02

Ui

FDA FDB

AIR MASTER

TOTAL AIR FLOW

- +

O2 Correction loop manipulates the total airflow

measurement by increasing or decreasing O2 master to show

less air/more air is flowing. This influence is limited to 30% of the total air flow [Presently]

SEC.AIR FLOW (L)

MAX

O O O 

MAX

P

PI

RL

Y

+

PI

RL

Y

- <

F(X)

P

BIAS

O O O 

+

PI

RL

Y

F(X) <

-

PIRL

OOO

+

Σ

Σ/n +

AW02 AW02

O2

-

O2

-

O2 PROBE (L)

O2 PROBE (R)

FLUEGAS O2

A/M

MAX

~

Σ

ΣSEC.AIR FLOW (R)

PA FLOW FROM MILLS

ANY 6 MILLS

TOTAL FUEL FLOW BOILER DEMAND

TOTAL AIR

GAIN CHANGE

MW AIR FLOW

A B C D E J

+ + - -P

20%+ +

80%

Ua= Ui X∞

( = 0.1)

RS04

AW02 AW02- -+ - + -

FD FAN B BLADE PITCH

FD FAN A BLADE PITCH

Y ActY Act

+- + -- +

AIR FLOW CONTROL SCHEME ( EXCESS AIR)

                              

A/MA/M 

SELECTION OF CMCSELECTION OF CMC

1. Put air control on auto (at least one FD fan)

2. Put feeders speed control on auto after varying fuel master(FM) output and making feeder speed controller error zero.

3. Vary Blr. Master O/P so that FM error becomes zero. Then put FM on auto.

4. Make throttle pr. Set point and actual pr. Difference zero.

5. Put BM on auto.

6. Increase /decrease unit master output so that it becomes equal to actual load. (wait unit load set value and load value matches as shown in the CMC panel digital indicator).

7. Form TG desk put turbine control on auto.

8. Press coordinated push button along with manual release on CMC desk.

Controller

Mill PA Flow

+ -

FEED RATE

UCB Set Point

Max

HAD

CURVE GENERATOR Generator

MILL PA FLOW AUTO SETTING

                     

  CURVE GENERATOR SETTINGS  XU01 CARD

HAD SET POINT FOR PA FLOW AS PER FEED RATE

  

FEED RATE (T/H) MILL PA FLOW SETPOINT (T/H)

0 70

17.5 75

20 77

30 92.5

40 96.5

50 100

60 105

70 108

CURVE GENERATOR SETTING

7075

77

92.596.5

100

105108

0

20

40

60

80

100

120

140

0 17.5 20 30 40 50 60 70

FEED RATE(T/H)

MIL

L P

A F

LO

W S

ET

PO

INT

(T/H

)

THANK YOU THANK YOU