1. Control & Automation For Super Critical Units
K.S. Sundaram
NTPC, SIPAT

2. Introduction Requirements
Comparison of Auto loops -Sub Critical Vs Super Critical
Feed Water Control
Steam Temperature Control
Unit Control
Turbine Control
Discussions

3. 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.

4. Source :KEPRI

5. Source :KEPRI

6. Source :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
PA Hdr. control
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)

8. List Of Loops For Discussion
S.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

9. 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.

10. Final Control Elements In FW Loop
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
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 Hi
Level

11. Feed Water Master In Wet Mode
SEPARATOR LEVEL SET POINT FROM ULD
ACTUAL LEVEL
SUB
PID
ULD
300 SP 9 3
TO BFPS

12. Min FW Flow Control In Wet Mode
MIN. FW FLOW SET POINT
FW FLOW TO ECONOMISER
SUB
DP ACROSS BC PUMP
DP SET POINT ACROSS BC PUMP
PID
SUB
<
PID
BC PUMP WILL TRIP IF DP
IS < 4.5 Kg/Sqcm
UG VALVE

13. FWPCV Valve Control In Wet Mode
BFP HEADER PRESSURE TRANSMITTERS
SEL
HIGHEST OF TDBFP SUCTION FLOWS
HIGHEST OF MDBFP SUCTION FLOWS
SUB FG FG
>
PID
FWPCV

14. Separator Drains Control
MEASURED SEPERATOR LEVEL
F(X)
F(X) WR ZR

15. Wet Mode Operation
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

16. Wet Mode & Dry Mode Of Operation
Source: Doosan

17. Feed Water Control In Dry Mode
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.

18. FW Master In DRY Mode FG > TO BFPs ∑ ∑ BMD DSH SEP F2(x) F1(x) PI
SEPERATOR OUT STM TEMP
FW Master In DRY Mode
PLATEN SH DT
BMD
BOILER MASTER DEMAND
DSH
SEP
SEPERATOR OUTLET TEMP SET POINT
F2(x)
F1(x)
NOT DRY MODE
SET TO ZERO PI FG ∑ PI
FF SIGNAL ∑
ANY SCANNER FLAME (AND) BCP OFF
0 % A a
30 % b
> T2 A
TOTAL FW FLOW
FWF
FB SIGNAL
F(x) PI
Source : KEPRI
TO BFPs

19. Platen DSH DT Set Point
BM(%) DT
28.8 11
43.3 28
52.1 22
70.7 9 91
100

20. Source : EMERSON

21. Source : EMERSON

22. Source : EMERSON

23. Runbacks /Rundowns/Protections
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

24. Platen SH Temperature Control
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.

25. Final DSH DT Set Point
BM(%) DT
28.8 27
43.3 21
52.1 18
70.7 7 91
100

26. SH Temperature Profile
DIV SH
PLATEN SH
FINAL SH
451
440
486
480
406
540
DSH1
DSH2
15% 3%

27. Source : KEPRI

28. Final SH Temperature Control
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.

29. Source : KEPRI

30. 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

31. Source : KEPRI

32. RH Temperature Control By Spray
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.

33. Source : KEPRI

34. Source :KEPRI

35. Source : EMERSON

36. Source : EMERSON

37. 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

38. HP BP Control

39. LPBP Control

40. References
KEPRI logics
EMERSON Logics

41. THANK YOU

42. FEED WATER PATH INITIAL STAGE
Back
VERTICAL WW
SEPARATORS
FWRS
STORAGE TANK
ECONOMISER
Spiral water walls
ECO I/L
HPH
F L ASH
T ANK WR ZR
CONDENSER
CEP
LPH DA 42

43. FEED WATER PATH - LOAD < 30%
Back
VERTICAL WW
SEPARATORS
STORAGE TANK
HPH
ECONOMISER
Spiral water walls
ECO I/L
MIXING PIECE
BCP UG

44. FEED WATER PATH – LOAD > 30%
Back
FEED WATER PATH – LOAD > 30% S E P A R T O S E P A R T O
VERTICAL WW
HPH
ECONOMISER
Spiral water walls
ECO I/L
TO BACKPASS CONNECTING PIPES

46. CCP Auto Start And Auto Stop Conditions
Source :Doosan