Theoretical Overview of Surge Analyses
Transcript of Theoretical Overview of Surge Analyses
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THEORETICAL OVERVIEWTHEORETICAL OVERVIEW
OF SURGE ANALYSESOF SURGE ANALYSES
3 December 2001
University of Pretoria
Prof SJ van Vuuren
Tel: +27 012 420 2438Website:
http://www.up.ac.za/academic/civil/divisions/water.html
Layout of PresentationLayout of Presentation
Introduction
Basic theory of transient flows Rigid Column Theory
Elastic Theory
Influence of pipeline support on wave celerity
Propagation of transient waves
Theory for non-instantaneous disturbances
Calculation of transient pressures
Causes of transient flows
Fluid transient risk assessment procedure(TRAP)
Surge protection options
Computer-aided transient analysis
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IntroductionIntroduction
What is surge?Variation in pressures that are generated
by a change in the operational status
How are surge waves
created?Foreseen operational changesUnforeseen operational changes
Layout changes
Basic theory of transient flowBasic theory of transient flow
RIGID COLUMN THEORY
dt
dv
g
LH =
ELASTIC THEORY (RIGID PI PE)
0cVP =
)/(
)/(
)/(
)/(
0
3
2
smvelocityflowV
mkgwaterofmassunit
smpiperigidaforceleritywaveC
mNnfluctuatiopressureP
=
=
==
Where:
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Basic theory of transient flowBasic theory of transient flow
ELASTIC THEORY (RIGID PIPE)(Continued)
+
=
t
D
D
Kcc
1
1'
Where:
)(
)(
)/(
)/(mod
)/('
*2
*2
mpipeofthicknesswallt
mpipeofdiameterD
mmNmaterialpipeofelasticityE
mmNwaterofulusbulkK
smpipeelasticanforceleritywavec
===
=
=
*Values of K and E are shown in Annexure 1
Basic theory of transient flowBasic theory of transient flow
SUPPORT OF THE PIPEL INE
PROPAGATION OF TRANSIENT WAVES
Case 1: Anchored at upstream end
21
=C
Case 2: Anchored throughout against longitudinal movement
2
11 =C
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Transient flow theory for nonTransient flow theory for non--
REQUIREMENTS
elasticity
effect of losses
non-instantaneous valve movement
PARTIAL DIFFERENTIAL FORMULAE
instantaneous disturbancesinstantaneous disturbances
0sin2
=+
++
x
u
g
c
t
Hu
x
Hu
02
=++
dt
du
D
uu
x
Hg
Visualizing the movementVisualizing the movement
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Visualizing the movementVisualizing the movement
Visualizing the movementVisualizing the movement
Surgemov1.mov
Surgemov2.mov
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Calculation of transientCalculation of transient
arithmetic
graphic
characteristics
algebraic
implicit
linear
wave-plan
other
pressurespressures
Causes of transient flowsCauses of transient flows
Pump start-up
Pump trip
Variation in demand
Unintentional changes in operationalposition of control valves
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Fluid Transient RiskFluid Transient Risk
Checklist of fault conditions
TRAP
Assessment Procedure (TRAP)Assessment Procedure (TRAP)
Fluid Transient RiskFluid Transient Risk
The route of the pipeline is changed?
The demand on the system is increased?
The basic design data is unreliable by x % (e.g. heads,
flows, component operating characteristics, materials
specifications, fluid properties and quality, etc.)?
Changes are made to the system design?
Assessment Procedure (TRAP)Assessment Procedure (TRAP)Checklist of fault conditions
Design/Installation
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Fluid Transient RiskFluid Transient Risk
The power fails to the motors driving the pumps?
The pump delivery valve is closed in t seconds?
One pump trips but others keep running?
An operator opens/shuts valve y too quickly?
The demand on the system is increased?
Assessment Procedure (TRAP)Assessment Procedure (TRAP)Checklist of fault conditions
Normal operation
Fluid Transient RiskFluid Transient Risk
A pump is re-started within t seconds of being tripped?
A control or emergency shut-down valve is shut rapidly?
An operator opens/shuts valve y too quickly?
Assessment Procedure (TRAP)Assessment Procedure (TRAP)Checklist of fault conditions
Hazardous operation
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Fluid Transient RiskFluid Transient Risk
Component x malfunctions (e.g. an automatic control
valve, pressure relief valve, vacuum breaker, etc.)?
The surge suppression strategy/control devices
malfunction?
Assessment Procedure (TRAP)Assessment Procedure (TRAP)Checklist of fault conditions
System malfunction
Fluid Transient RiskFluid Transient RiskAssessment Procedure (TRAP)Assessment Procedure (TRAP)
All the operational
variances should be
identified
List all the possible causes that can change
the steady state situation and distinguish
between: internal and external factors that
can result in transients (Use Annexure 2).
The bottom line: What can go wrong,
where, how, and why? How will the flowbe influenced?
3
Quantify the operational
scenarios
Define the operating regimes and the
operational limits of the system.
2
Obtain the characteristics
of the system
Describe the system which normally
consists of pumping stations, pipelines,
control equipment, demand centres, etc.Define the operating regimes and the
operational limits of the system.
1
ObjectiveDescriptionAction
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Fluid Transient RiskFluid Transient RiskAssessment Procedure (TRAP)Assessment Procedure (TRAP)
Cost effective controlReview options for a control and
transient suppressions strategy
6
Ultimate solution for possible
future system application
Consider the influence of future
extensions or alterations to the system
7
First indication of the
magnitude of the transient
pressures
Determine the celerity, pipeline period,
pump rundown time, valve operation
and the Joukowskys head for all the
situations listed in 3
5
The difference between the
residual pressures and
permissible internal pressures
will indicate the ability of the
system to handle higher
pressures.
Draw a longitudinal section and
determine the hydraulic grade lines
(both for static and dynamic conditions).
4
ObjectiveDescriptionAction
Fluid Transient RiskFluid Transient RiskAssessment Procedure (TRAP)Assessment Procedure (TRAP)
Successful
implementation
Devise test programme for commissioning
procedures
10
Ensure long term
efficiency
Finalize the design, and prepare operational
constraints and guidelines in accordance
with the validated control and suppression
strategy
9
Optimal surge analysisPrepare specifications for detailed computer
analysisRefine the control measures
8
ObjectiveDescriptionAction
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Surge protection optionsSurge protection options
Pump start-up
Pump trip
Surge protection optionsSurge protection options
Surge tank Air valve Reflux valve
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Surge protection optionsSurge protection optionsWhere is the transient
event initiated?
Upstream end An intermediate point Downstream end
Pressure
rises first
Pressure
drops first
Pressure
rises first
Pressure
drops first
Air vessel /accumulator
Check valve
Relief
system
Surge shaft
Could secondary devices elsewhere in the system be of benefit ?
e.g. Air valves, Feed tanks, surge shafts, etc.
Air vessel /accumulator
By-pass
Check valve
Vacuum
breaker
Air vessel /accumulator
Reliefsystem
Surge shaft
Air vessel /accumulator
Feed tank
Surge shaft
Vacuum
breaker
Can a By-
pass device
help ?
No No
Select and/or Design
Yes
Select and/or Design
Surge protection optionsSurge protection options
Summary of Water Hammer Protection
Normally used in conjunction
with some other method of
protection. Water column
separation possible
In-line reflux valve
Pipeline profile should be
convex downwards. Water
column separation likely
Automatic release valve
Some water may also be
drawn through the pump
Pump bypass reflux valve
Approximate onlyInertia of pump
RemarksRequired range of
variables
Method of protection (in
approximate order of
increasing cost)
01.02
0
2
>wALH
MN
10
0 >>gH
cV
10 >gh
cV
10
0
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Surge protection optionsSurge protection options
Summary of Water Hammer Protection
Pipeline profile should be
near hydraulic grade line tolimit the height of tank
(practical)
Limited heightSurge tanks
H = pressure head at tank,
Pipeline profile should be
convex upwardsDischarge tanks
Pipeline profile preferably
convex downwards
Air vessel
RemarksRequired range of
variables
Method of protection (in
approximate order of
increasing cost)
10 >gh
cV
10
0