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

AgendaAgenda Process variability defined and its effect on energy waste Control valve shut-off defined and its effect on energy waste How to engineer improvement

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

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

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

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

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

SUPERHEAT TEMP. Upper Limit Set Point  NPHR = 0.75% Reduction Increased Temp. Set Point = (  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 !! = (  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 !! Reduced Process Variability Provides the Opportunity for Setpoint Change Main Steam Temperature Control Decreased Variability = Increased Profit

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

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 T d, T 63 and T 98 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

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

Testing for Performance Open-Loop Fixed position – constant load flow Signal generator Control valve FT Transmitter Pump

Open Loop Valve Performance

Testing for Performance Closed Loop Control Valve Controller FT Transmitter flow z Pump Load disturbance

Closed-Loop Valve Performance

Sustaining Performance Through On-Line Diagnostics B G D A H C E F 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

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

An Industrial Example – a Feedwater Heater Emergency Level Valve Shell & tube heat exchanger …. In heater: 31 psia, 215 F., 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 =1620 #/hr Result: 220,320 BTU/hr At 3415 BTU/hr/KW: 64 KW! At $1.58/MBTU coal cost: $4,284 / op. year!

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

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

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!