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Control valves for thermal power plants
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Control valves for thermal power plants

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  • 1. CONTROL VALVES FOR THERMAL POWER PLANTS SHIVAJI CHOUDHURY
  • 2. IN THIS PRESENTATION  CONTROL VALVES  CONTROL VALVE SIZING  VALVE CONSTRUCTION  TOP GUIDED CONTROL VALVE  CAGE GUIDED VALVES DOUBLE  DOUBLE SEATED CONTROL VALVE  CAGES/TRIM  GLAND PACKING  TURNDOWN RATIO  CAVITATION  BODY/TRIM MATERIAL  SEAT LEAKAGE CLASSIFICATION  FAIL SAFE DESIGN  NOISE  END PREPARATION  VALVE ACTUATORS  CONTROL VALVE ACCESSORIES  TESTS  STANDARDS
  • 3. CONTROL VALVES  Control valves are valves used to control conditions such as flow, pressure, temperature, and liquid level by fully or partially opening or closing in response to signals received from controllers that compare a "setpoint" to a "process variable" whose value is provided by sensors that monitor changes in such conditions.
  • 4. CONTROL VALVE SIZING  The control valve shall be of globe body design with single port. The valve trim, shall be suitable for quick removal without any cutting or welding.  Sizing shall be accordance with ANSI/ISA 75.01,01.  Valve outlet velocity does not excesed 8 m/sec for liquid service and 150 m/sec for steam services.
  • 5. CONTROL VALVE SIZING  The valve sizing shall be suitable for obtaining maximum flow conditions with valve opening at approx 80% of total valve stem travel and minimum flow conditions with valve stem travel not less than 10% of total valve stem travel.  All valves shall capable of handling at least 120% of required maximum flow.  Valve body rating shall meet the pressure and temperature requirement as per ANSI B 16.34.
  • 6. VALVE CONSTRUCTION  Conform to requirement of ANSI for dimensions, material thickness and material specification for their respective pressure class.  All valves shall be globe body design and straightway pattern with single or double port or angle body design.  All valves connected to vacuum on down stream side shall be provided with packing suitable for vacuum application (e.g double vee type chevon packing).  Extension bonnets shall be provided when the maximum temperature of flowing fluid is greater than 275 deg c.  If the downstream is subjected to vacuum, flow direction of the fluid shall be to close.
  • 7. TOP GUIDED CONTROL VALVE Top-guided, single-ported valves may be used for tight shutoff applications; however, because these valves are unbalanced, they can require more force from the actuator to achieve shutoff if the flow is under the plug.
  • 8. CAGE GUIDED VALVES  Cage-guided valves have a cylindrical plug guided through a guide.  The increased guiding area is desirable for high pressure drop, high noise, and anticavitation applications  Unbalanced types can provide a tight shutoff if sufficient  For balanced styles, the plug is vented and the process pressure interacts with the top and bottom side of the plug.
  • 9. DOUBLE SEATED CONTROL VALVE  Double-seated control valves are used to a lot of industrial applications due to advantages of reduction in actuator force, a great flow capacity and a deal of slurry fluids.  Double-seated valves cannot provide the same shutoff capability as the single-ported types.
  • 10. Characterized Cages/Trim for Globe valve QUICK OPENING EQUAL PERCENTAGE LINEAR
  • 11. GLAND PACKING  PTFE if fluid temperature is less than 180 deg C.  Graphite if fluid temperature is more than 180 deg C.  All valves connected to vacuum on down stream side shall be provided with packing suitable for vacuum application (e.g double vee type chevon packing). GLAND PACKING
  • 12. TURNDOWN RATIO  The valve-sizing coefficient for globe valves should be selected to limit turndown to a ratio of about 30:1.  This limits the valve opening to approximately 10% of maximum for globe valves with equal percentage trim.
  • 13. CAVITATION  Cavitation is a two stage phenomena with liquid flow.  The first stage is the formation of vapor bubbles in the liquid as the fluid passes through the trim and the pressure is reduced below the fluid's vapor pressure.  The second stage is the collapse of the vapor bubbles as the fluid passes the vena contracta and the pressure recovers and increases above the vapor pressure.  The collapsing bubbles are very destructive when they contact metal parts and the bubble collapse may produce high noise levels.
  • 14. Cavitation  Cavitation in control valves can have four negative effects; • Restricts fluid flow • Causes severe vibrations • Erodes metal surfaces • Generates high noise levels.
  • 15. ANTI CAVITY TRIM  The anti cavity trim of control valve shall be multi stage ,multi path type.  ISA- RP75.23 – 1995, “Considerations for Evaluating Control Valve Cavitation”, Recommended Practice, June 1995  The High FL Factor ( pressure recovery factor) shall be 0.98 or better.
  • 16. Cavitation is alleviated by anti-cavitation valve trim
  • 17. Anti cavitation Trim
  • 18. CONTROL VALVES WITH ANTI CAVITY TRIM IN THERMAL POWER PLANTS 500 MW  CEP /BFP Min recirculation valve  Excess dump control  Condenser for SD flash tank  HP/LP heater alternate drain to drain flash tank.  D M normal/emergency makeup to hotwell.  Low load feed water control valve.  S H/ R H/PRDS/HPBP temperature (spray) control valve
  • 19. BODY/TRIM MATERIAL  SEVERE FLASHING/CAVITATION SERVICES BODY MATERIALS- Alloy steel as per ASTM – A217 GR WC 9 TRIM MATERIAL-- 440 C series SS  LOW FLASHING/CAVITATION SERVICES BODY MATERIALS--Alloy steel as per ASTM A – 217 GR WC 6 TRIM MATERIAL- 17-4 PH SS  CONDENSATE & DM SERVICES BODY MATERIALS--316SS for condensate service below 275 deg C and above 275 deg C – ALLOY STEEL A217 GR WC 6 and 316 SS for DM WATER makeup etc TRIM MATERIAL -316SS stellited with stellited facedguide posts and bushings.
  • 20. Boiler startup valve for supercritical boiler  Once through boilers require a minimum evaporator flow for cooling of boiler tubes during startup .  Recirculation of the water from the separator back to the feedwater tank  the start up is operating continuously at high differential pressure while boiler load is below 30%.
  • 21. Severe services control Valves  SEVERE FLASHING/CAVITATION SERVICES low load and full load feed water control, HP and LP heaters emergency drains, Deaerator overflow drain to Hotwell, CRH flow to Deaerator, Spray control valve (SH, RH, HPBP), RH block valve etc.  LOW FLASHING/CAVITATION SERVICES HP heaters & LP heaters normal drain control, drain cooler normal level control, gland steam cooler minimum flow etc.
  • 22. CONTROL VALVE SEAT LEAKAGE CLASSIFICATION (ANSI/FCI 70-2-1991) S.N LEAKAGE CLASS MAX LEAKAGE ALLOWABLE 1 I --- 2 II 0.5 % of rated capacity 3 III 0.1 % of rated capacity 4 IV 0.01 % OF RATED CAPACITY 5 V 0.0005 ml per minute of water per inch of orifice per psi differential
  • 23. LEAKAGE CLASS OF VALVES  Control Valves with leakage rate as per leakage Class-V to increase cycle efficiency of plant and safety of equipments  Control Valves with leakage Class-V 1. .SH/RH spray control, 2. . Heavy oil pressuring & control system, 3. . HP/LP heater emergency level control, 4. .CEPs/BFP minimum flow 5. .Emergency make up to condensate, 6. . GSC minimum flow, 7. .Dearator drain to condenser hotwell, 8. .condensate spill to condensate reserve tank control 9. . heavy oil heating, 10. . condenser normal make-up 11. . valve gland sealing supplying pressure control 12. . HFO, LDO shut-off valve, 13. PRDS spray valve
  • 24. FAIL TO SAFE DESIGN  Valve shall close if signal fails :  SH/RH spray valve  HP/LP HEATERS normal drains  Valve shall open if signal fails  CEP/BFP recirculation valve.  HP/LP HEATERS emergency drain to flash tank .
  • 25. NOISE  Control valve induced noise shall be limited to 85 db at 1 mtr from valve surface under actual operating condition .  The noise abetment shall be achieved by valve body and trim design or by use of silencers.  Noise calculation shall be as per ISA-75-17-1989.  VALVE with Cage-Style Noise Abatement
  • 26. HP LP BYPASS VALVE
  • 27. END PREPARATION  Valve body ends shall be either butt welded/socket welded, flanged .  The welded ends wherever required shall be butt welded type as per ANSI B 16.25 for control valves of sizes 65 mm and above.  For valves size 50 mm and below welded ends shall be socket welded as per ANSI B 16.11  Flanged ends wherever required shall be of ANSI pressure-temperature class equal to or greater than that of control valve body.
  • 28. VALVE ACTUATORS  The HP and LP Bypass, turbine inlet control valves shall be with electro-hydraulic actuators and all other control valves shall be furnished with pneumatic actuators.  proper selection and sizing of valve actuators in accordance with the pressure drop and maximum shut off pressure and leakage class requirements.  The valve actuators shall be capable of operating at 60 deg. C continuously.
  • 29. ACTUATERS
  • 30. PERFORMANCE OF VALVE  i) linearity :1% of FS .  ii)Hysterisis :1% of FS.  iii)Sensitivity :0.5% of span.  iv)Accuracy : 2% of span.
  • 31. CONTROL VALVE ACCESSORIES  Positioner,  Air filter regulator,  Air lock relay,  Position limit switch,  Position transmitter,  Solenoid valve,  E/P converter,  Junction box,  Hand wheel,  Local position indicator,  Electro pneumatic positioner ,  Volume booster,  Fail freeze type IP Converter etc. as per the requirements.
  • 32. SMART POSITIONER  smart digital microprocessor based valve positioners and compatibility for remote calibration & superimposed HART signal on input signal 4-20 m Amp & connected with hart management system.
  • 33. Control valve hookup diagram with smart positioner
  • 34. TESTS  i) Non destructive test - ANSI B-16.34  ii) Hydrostatic shell test - ANSI B 16.34  iii) Valve seat leakage- ANSI- B 16.34.  iv) Functional test: The fully assembled valves including actuators control devices and accessories shall be functionally tested .  v) CV test: CV test - ISA 75.02
  • 35. LIST OF CONTROL VALVES IN 500 MW THERMAL POWER PLANT  1. D/A Pegging from Aux. Steam Header  2. D/A Pegging from CRH Line  3. Main Condensate Control  4. CEP A/B/C Minimum Recirculation  5. GSC min. flow recirculation  6. Excess Dump Control  7. Condensate for SD F/T  8. Condensate for Valve Gland Sealing  9. HPH ‐7A/7B Normal Drain to HPH  10. HPH-7A/7B Alt.Drain to HP Drain F/T  11. HPH‐6A/6B Normal Drain to Deaerator  12. HPH‐6A/6B Alt. Drain to HP Drain F/T  13. LPH‐3 Normal Drain to LPH‐2  14. LPH‐3 Alt. Drain to LP Drain F/T  15. LPH‐2 Normal Drain to LPH‐1  16. LPH‐2 Alt. Drain to LP Drain F/T  17. Deaerator Overflow  18. HPH‐8A/8B Normal Drain to HPH‐7A/7B  19. HPH‐8A/8B Alt. Drain to HP Drain F/T  20. LPH‐4 Normal Drain to LPH‐3  21. LPH‐4 Alt. Drain to LP Drain F/T  22. DM Normal Makeup to Hotwell  23. Emergency MU to Hotwell  24. Low Load Feed Control  25 SUPER HEATER SPRAY  26 REHEATER SPRAY  27. PRDS SPRAY
  • 36. PUMP PERFORMANCE CURVE
  • 37. STANDARDS  ANSI/ISA-75.01.01 (IEC 60534-2-1 Mod) - 2007 - Flow Equations for Sizing Control Valves  ANSI/ISA – SP75.02, 1996, “Control Valve Capacity Test Procedure”, October 1996  ISA- RP75.23 – 1995, “Considerations for Evaluating Control Valve Cavitation”, Recommended Practice, June 1995  ANSI/ISA-75.19.01-2001 (R2007) - Hydrostatic Testing of Control Valves  ISA-75.17-1989 - Control Valve Aerodynamic Noise Prediction  IBR
  • 38. THANKING YOU