Energy Seminar Emerson Process Management June 22/23, 2010.
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Transcript of Energy Seminar Emerson Process Management June 22/23, 2010.
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!