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Control & Automation For Super Critical Units

Control & Automation For Super Critical Units. K.S. Sundaram NTPC, SIPAT. Introduction. Requirements Comparison of Auto loops -Sub Critical Vs Super Critical Feed Water Control Steam Temperature Control Unit Control Turbine Control Discussions. Super Critical Units.

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Control & Automation For Super Critical Units

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  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

  8. List Of Loops For Discussion

  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

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

  19. Platen DSH DT Set Point

  20. Source : EMERSON

  21. Source : EMERSON

  22. Source : EMERSON

  23. Runbacks /Rundowns/Protections 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

  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

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

  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 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 RH Temperature Control (Tilt)

  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

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

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

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

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