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Energy Seminar

Energy Seminar. Emerson Process Management June 22/23, 2010. Final Control Element Best Practices for Efficient Energy Use. Mike Lewis Novaspect, Inc. Emerson Process Management Energy Management Seminar. Agenda. Process variability defined and its effect on energy waste

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Energy Seminar

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  1. Energy Seminar Emerson Process Management June 22/23, 2010

  2. Final Control Element Best Practices for Efficient Energy Use Mike Lewis Novaspect, Inc. Emerson Process Management Energy Management Seminar

  3. Agenda • Process variability defined and its effect on energy waste • Control valve shut-off defined and its effect on energy waste • How to engineer improvement

  4. Probability of Occurrence Mean Value =  Shower Temperature Variability, defined by a Real Life Example Acceptable shower temperature Perfectshower temperature Cardiac arrest 2nd degree burns Hot Cold

  5. Causes of Variability Loops The Cause Design 20% Tuning 30% Increases Variability Control Valve Performance 30% As Many As 80% of Loops Actually Increase Variability 20% Source: Entech---Results from audits of over 5000 loops in Pulp & Paper Mills

  6. A Typical Control Valve Specification • You specify … • Fluid properties • Sizing requirements • Design pressure and temperature • Allowable leakage when closed • Failure mode • Connecting pipe size • End connections • We engineer … • Valve size • Valve trim Cv versus % open characteristic • Valve type • ANSI P/T rating • ANSI leak class • Actuation system • Materials of construction • Special characteristics for noise, cavitation, flashing, corrosion

  7. Setpoint = 955 F PV Distribution +/-1-Sigma +/-2-Sigma +/-3-Sigma An Industrial Example Main Steam Temperature Control ΔT = 50 F 1005 F 0.75% NPHR 0.30% load !! MS design temp

  8. Upper Specification Limit Set Point PV Distribution 2-Sigma 2-Sigma Set Point Reduced PV Distribution 2-Sigma 2-Sigma Control Loop Objective …Reduce Process Variability

  9. Main Steam Temperature Control Decreased Variability = Increased Profit Upper Limit • NPHR • = 0.75% • Reduction Set Point SUPERHEAT TEMP. Increased Temp. Set Point Reduced Process Variability Provides the Opportunity for Setpoint Change = ( NPHR) X Fuel cost X KW-HR generated/year = Savings = .75% x 11,000 BTU/KW-HR X $2.22/MM BTU X 320,000 KW X 8760 hours / year = $516,517 per operating year !!

  10. Dynamic Valve Performance • We’ve demonstrated value in reducing variability in critical control loops • Poor control valve dynamic performance contributes to variability • Let’s discuss … • A specification for performance • Designing for performance • Testing for performance • Maintaining performance

  11. A Dynamic Control Valve Specification • Combined backlash and stiction should not exceed 1% of input signal span • Speed of valve position response to input signal changes from 1% to 10% shall meet specific Td, T63 and T98 times • Overshoot to step input changes of 1% to 10% shall not exceed 20% • Loop process gain should fall between 0.5 and 2.0 … Entech “Control Valve Dynamic Specification” March 1994

  12. Achieving Dynamic Performance by Design • Friction • Machining accuracy • Clearances • Flow geometry designed for stability • Plug/stem connection • Lost motion linkages • Actuator spring flatness and stiffness • Positioner design • Positioner gain adjustability • Positioner tuning matched to the valve assembly • Air delivery system • Transducer design • Soft part flexibility

  13. Testing for PerformanceOpen-Loop Fixed position – constant load Signal generator flow Control valve FT Transmitter Pump

  14. Open Loop Valve Performance

  15. Testing for PerformanceClosed Loop Load disturbance z flow Control Valve FT Transmitter Controller Pump

  16. Closed-Loop Valve Performance

  17. Sustaining Performance Through On-Line Diagnostics Plugging of I/P transducer Travel Deviation Insufficient Air Supply Calibration Changes Diaphragm Leaks Piston Leaks O-ring Failures in Actuators Packing condition Friction and Deadband External Leaks Insufficient Seat Load for Shut-off Many others G H D A E F B C

  18. Control Valve Shut-off Decreasing leakage Increasing first cost Increasing maintenance cost

  19. An Industrial Example – a Feedwater Heater Emergency Level Valve • Shell & tube heat exchanger …. • In heater: 31 psia, 215 F., 183.1 BTU/# • In the condenser: 1” Hg abs., 79 F., 47.1 BTU/# • Leakage worth 136 BTU/# • Difference in leakage between an ANSI Class II and Class IV is 1653-33=1620 #/hr • Result: 220,320 BTU/hr • At 3415 BTU/hr/KW: 64 KW! • At $1.58/MBTU coal cost: $4,284 / op. year!

  20. Typical Power/Boiler Plant Energy Efficiency Opportunities • Aux boiler mode steam • Air preheating • Aux steam header pressure balancing • Blowdown and sampling • Condenser performance • Feedwater heater efficiency • Superheat attemperation • Reheat attemperation • Emergency heater drain valve leakage • Sootblowing steam system • Station heating • Steam and water loss • Turbine cycle condition • Throttle pressure • Throttle temperature

  21. Other Energy-related Variability Examples • Fuel/air ratio control • Load change responsiveness • Steam header pressure balancing • Ramp rate improvement • Burner light-off • Drum level stability • Conditioned steam temperature stability and turndown

  22. The Takeaway The undesirable behavior of control valves is the biggest single contributor to poor control loop performance and energy waste … spend your money in the basement!

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