Energy SeminarEnergy SeminarEnergy SeminarEnergy Seminar

Emerson Process ManagementJune 22/23, 2010

Final Control Element Best Final Control Element Best Practices for Efficient Practices for Efficient Energy UseEnergy Use

Final Control Element Best Final Control Element Best Practices for Efficient Practices for Efficient Energy UseEnergy UseMike Lewis

Novaspect, Inc.

Emerson Process Management

Energy Management Seminar

AgendaAgendaAgendaAgenda

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 Variability, defined by a Real Life ExampleExampleVariability, defined by a Real Life Variability, defined by a Real Life ExampleExample

Perfect shower temperature

2nd degree burns

Acceptable shower temperature

Cardiac arrest

Control ValvePerformance

Tuning

Design

Loops

IncreasesVariability

The Cause

20%

30%

30%

20%

Source: Entech---Results from audits of over 5000

loops in Pulp & Paper Mills

Causes of VariabilityCauses of VariabilityCauses of VariabilityCauses of Variability

As Many As 80% of Loops Actually

Increase Variability

A Typical Control Valve SpecificationA Typical Control Valve SpecificationA Typical Control Valve SpecificationA 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 An Industrial Example Main Steam Temperature ControlMain Steam Temperature ControlAn Industrial Example An Industrial Example Main Steam Temperature ControlMain 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 …Control Loop Objective …Reduce Process VariabilityReduce Process VariabilityControl Loop Objective …Control Loop Objective …Reduce Process VariabilityReduce Process Variability

2-Sigma 2-Sigma

Set Point

Set Point

2-Sigma2-Sigma

Upper Specification

Limit

PV Distribution

Reduced PV Distribution

SU

PE

RH

EA

T T

EM

P.

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 VariabilityProvides the Opportunity

forSetpoint Change

Main Steam Temperature Control Main Steam Temperature Control Decreased Variability = Increased ProfitDecreased Variability = Increased Profit

Dynamic Valve PerformanceDynamic Valve PerformanceDynamic Valve PerformanceDynamic 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 A Dynamic Control Valve SpecificationSpecificationA Dynamic Control Valve A Dynamic Control Valve SpecificationSpecification 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

AchievingAchieving Dynamic Performance by Dynamic Performance by DesignDesignAchievingAchieving Dynamic Performance by Dynamic Performance by DesignDesign

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

TestingTesting for Performance for PerformanceOpen-Loop Open-Loop TestingTesting for Performance for PerformanceOpen-Loop Open-Loop

Fixed position – constant load

flow

Signal generator

Control valveFT

Transmitter

Pump

Open Loop Valve PerformanceOpen Loop Valve PerformanceOpen Loop Valve PerformanceOpen Loop Valve Performance

TestingTesting for Performance for PerformanceClosed LoopClosed LoopTestingTesting for Performance for PerformanceClosed LoopClosed Loop

Control Valve

Controller

FT

Transmitter

flow

z

Pump

Load disturbance

Closed-Loop Valve PerformanceClosed-Loop Valve PerformanceClosed-Loop Valve PerformanceClosed-Loop Valve Performance

SustainingSustaining Performance Through On-Line Performance Through On-Line DiagnosticsDiagnosticsSustainingSustaining Performance Through On-Line Performance Through On-Line DiagnosticsDiagnostics

B

G

D A

H

C

E

F

Plugging of I/P transducerTravel Deviation

Insufficient Air SupplyCalibration Changes

Diaphragm LeaksPiston Leaks

O-ring Failures in ActuatorsPacking condition

Friction and DeadbandExternal Leaks

Insufficient Seat Load for Shut-offMany others

Control Valve Shut-offControl Valve Shut-offControl Valve Shut-offControl Valve Shut-off

Increasing first cost

Increasing maintenance cost

Decreasing leakage

An Industrial Example – a Feedwater An Industrial Example – a Feedwater Heater Emergency Level ValveHeater Emergency Level ValveAn Industrial Example – a Feedwater An Industrial Example – a Feedwater Heater Emergency Level ValveHeater 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!

Typical Power/Boiler Plant Energy Typical Power/Boiler Plant Energy Efficiency OpportunitiesEfficiency OpportunitiesTypical Power/Boiler Plant Energy Typical Power/Boiler Plant Energy Efficiency OpportunitiesEfficiency 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 Other Energy-related Variability ExamplesExamplesOther Energy-related Variability Other Energy-related Variability ExamplesExamples

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 TakeawayThe TakeawayThe TakeawayThe 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!