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NEL Slide 1ISO Flow Measurement Standards18-10-11
Flow measurement: some problems to solve
and some surprises
Dr Michael Reader-Harris, NEL
• 1 Difficult Reynolds numbers– 1.1 Heavy oil– 1.2 LNG
• 2 Difficult installations– 2.1 Emissions– 2.2 Flare gas
• 3 Difficult fluids– 3.1 Carbon dioxide– 3.2 Wet gas flow Venturi tubes Orifice plates
Scope
• Worldwide reserves of heavy hydrocarbons now significantly outweigh conventional light crudes.
Difficult Reynolds numbers: 1.1 Heavy oil
Ultrasonic 4” Multipath
Meter D (Ultrasonic)Volume Flow
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
100 1000 10000 100000 1000000Reynolds Number
Volu
met
ric F
low
Err
or (%
)
Kerosene 10°C Gasoil 10°C Velocite 10°C Primol 10°CKerosene 20°C Gasoil 20°C Velocite 20°C Primol 20°CKerosene 30°C Gasoil 30°C Velocite 30°C Primol 30°CKerosene 40°C Gasoil 40°C Velocite 40°C Primol 40°C
•
Ultrasonic 4” Multipath
Meter D (Ultrasonic)Volume Flow
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
100 1000 10000 100000 1000000Reynolds Number
Res
idua
l Flo
w E
rror
(%)
'Laminar' Region'Turbulent' Region
Coriolis – uncorrected data
-1.5
-1.0
-0.5
0.0
0.5
0 10 20 30 40 50 60 70 80
Mas
s Fl
owra
te E
rror
(%)
Reference Flowrate (kg/s)
Kerosene 10°C (3 cSt)Kerosene 20°C (2 cSt)Kerosene 30°C (2 cSt)Kerosene 40°C (2 cSt)
-1.5
-1.0
-0.5
0.0
0.5
0 10 20 30 40 50 60 70 80
Mas
s Fl
owra
te E
rror
(%)
Reference Flowrate (kg/s)
Primol 10°C (300 cSt)Primol 20°C (175 cSt)Primol 30°C (80 cSt)Primol 40°C (50 cSt)
Coriolis – uncorrected data
Coriolis– uncorrected data
-1.50
-1.00
-0.50
0.00
0.50
100 1000 10000 100000 1000000
Mas
s Fl
owra
te E
rror
(%)
Pipe Reynolds Number
Kerosene 10°C (3 cSt)Kerosene 20°C (2 cSt)Kerosene 30°C (2 cSt)Kerosene 40°C (2 cSt)Primol 10°C (300 cSt)Primol 20°C (175 cSt)Primol 30°C (80 cSt)Primol 40°C (50 cSt)
Compensation possible versus Reynolds Number
1 Reynolds number issues
• 1.1 Heavy oil– Performance may be difficult through
transition (ultrasonic)– Performance may be different below
transition (Coriolis)– Air entrainment– Extension to 1500 cSt
• 1.2 LNG– The Reynolds number in LNG (or in
pressurized hot water) is much higher than in cold water
Difficult Reynolds numbers: 1.2 LNG
Most measurement is on board ship, but it would be good to use a flowmeter
Test Programme
• Flow meters:– Coriolis– (Ultrasonic)
• Test plan - performance evaluation:– Water (20 oC) at NEL– Liquid N2 (-193 oC) at NIST– Retest with Water
Coriolis – Water - Mass
Test 1
-0.50
-0.40
-0.30
-0.20
-0.10
0.00
0.10
0.20
0.30
0.40
0.50
0 2 4 6 8 10
Ref. Mass Flow, kg/s
%Er
ror (
mas
s)
Meter deviationMeter claimed accuracy
100M
M - MError%r
rmMeasurements:-• 5 points over test range
• Each point repeated 4 times
• Tests repeated 4 times
Results:• Good repeatability
• Good reproducibility
• All measurements are within claimed accuracy
One test was taken with no insulation jacket
4 tests were taken with insulation jacket
Liquid N2 Calibration Results- Mass
-0.50
-0.40
-0.30
-0.20
-0.10
0.00
0.10
0.20
0.30
0.40
0.50
0 2 4 6 8 10
Ref. Mass Flow, kg/s
%Er
ror (
Mas
s)
Meter deviation (LN2)Meter claimed accuracy
Test 2
Results
Coriolis: – Good results: within 0.2%– Water calibration can be successfully transferred to cryogenic
conditions if allowance is made for the non-linear temperature dependence of the Young’s Modulus of elasticity of stainless steel.
Next stage
Coriolis: – Compare water results with LNG results
Difficult Installations: 2.1 Stack emissions
• Significant work was undertaken in the 1960s and 1970s to establish the uncertainty of flowrates measured with pitot tubes.
• Errors of less than 1% were regularly obtained if the utmost care was taken in good flow conditions.
• An uncertainty of not greater than 2% can be achieved by following ISO 3966 (: 4.1). To do this corrections are required and were determined together with the uncertainty.
.
Stack emissions: are Pitot tubes a good method of flow measurement?
The problem: errors using Pitots
• Compressibility correction factor• Head loss• Transverse velocity gradient• Reynolds number• Turbulence• Static hole error• Wall proximity• Blockage• Misalignment• Swirl• Integration scheme
• Asymmetry• Leakage• Positioning• Diameter• Unsteadiness• Vibration• Differential pressure• Density
Systematic, correctable over-reading
Transverse velocity gradient 0.4% 0.4%Turbulence 1.25% 0.75%Swirl 1.5% 1.5%Blockage 0.4% 0.4%Integration scheme (ISO 10780) 1%TOTAL 4.5%
Problem
• Discarding good flow measurement in the quest for simplicity• The stack emissions standards (e.g. ISO 10780) need to be changed.
Difficult Installations: 2.2 Flare gas
EU Emissions Trading Scheme • Phase I (2005 – 2008) – Trial period• Phase II (2008 – 2012) – Mandatory
• Sets maximum uncertainty level on activity data (flowrate)• UK Offshore = Tier 2 (12.5% on m3/yr)• Highest tier = Tier 1 (7.5% on m3/yr)
• Phase III (2013 - 2020) Free allocations will reduce to 80%, reducing annually to 0% in
2020 No free allowances for electrical power generation Offshore electricity production will be hit hard Direct-drive equipment will get allowances
Functions of a flare system
• Ultimately a safety relief system− Emergency Blow-Downs− Pressure relief− Venting of vessels etc. for maintenance
• c 30% of UK offshore CO2 emissions
Flare metering - issues
• Typically no calibration = no traceability to Standards
• Very wide velocity range (> 1 000:1)
• Minimal pressure drop required
• Large line sizes
• Liquids, solids, low temperatures
• Winds causing pulsations, noise
• Installation errors can be large
Ultrasonic Flare Gas Meters
• Most widely adopted technology for flare
• Very wide range (> 2 000:1 is quoted)
• Wide turndown, negligible pressure loss
• Can calculate Density = f(SOS, T, p) using proprietary correlations
Difficult Fluids: 3.1 Carbon Capture & Storage
NEL Slide 26 ISO Flow Measurement Standards18-10-11
The issue
• Kyoto Protocol
• CO2 could be captured and stored
• It will need to be measured
• Total UK emissions = 548 million tonnes
• Suppose mass flow uncertainty is 1.5%
• If CO2 price = $45 per tonne uncertainty ≈ $375 million
• But at 5c per tonne uncertainty ≈ $0.4 million
Pure CO2 Phase Diagram
0
20
40
60
80
100
120
140
‐60 ‐50 ‐40 ‐30 ‐20 ‐10 0 10 20 30 40 50 60
Pressure (b
ar)
Temperature (oC)
Gas
Supercritical
Critical point: 31.1OC, 73.8bar
Liquid
Liquid and vapour phases in co-existence – distinct meniscus
Liquid and vapour phases in co-existence – visible meniscus
Liquid and vapour densities converging – barely visible meniscus
Single phase supercritical fluid – no meniscus
CO2 going supercritical
Operating regions
0102030405060708090
100110120130140150
0 5 10 15 20 25 30 35 40
Pressure (b
ar)
Temperature (oC)
CO2 Saturated vapour pressure95.8% CO2 2% H2 2% N2 0.2% CO95.5% CO2 (balance N2, O2, Ar, CO, CH4 etc)
Operating region for liquid pipeline
Operating region for gas pipeline
Two-phase regions
Potential CCS Metering Technologies
• CO2 has been metered for 30 years in EOR applications– no legislation on accuracy (sacrificed for cost)– not as stringent on impurities– shorter pipe distances
• However, a number of metering technologies could be suitable– DP metering– volumetric metering– mass metering (Coriolis)– non-invasive metering
Difficult Fluids: 3.2 Wet gas
• Increasing need to measure wet gas or multiphase• Separators are very large and expensive
Two possible ways of measuring wet gas
• Venturi tubes• Orifice plates
Look at Venturi tubes in dry gas first
• In incompressible flow Bernoulli gives
• In practical application
pdqm
241
1 2
4
pdCqm
1
2
42
41
Overall Length
D
d
High pressure connectionLow Pressure Connection
Flow
7 to 15°entrancecylinder convergent throat divergent
Discharge coefficients
• Should the discharge coefficient, C, always be less than 1?
𝑚,𝑔𝑎𝑠 42
1,𝑔𝑎𝑠
4” (100 mm) Venturi tubes in gas: Surprise 1
1.005
1.010
1.015
1.020
1.025
0.0E+00 2.0E+06 4.0E+06 6.0E+06 8.0E+06 1.0E+07
C
ReD
4 inch (beta 0.5) (20 bar)4 inch (beta 0.5) (60 bar)4 inch (beta 0.65) (20 bar)4 inch (beta 0.65) (70 bar)4 inch (beta 0.7) (20 bar)4 inch (beta 0.7) (70 bar)
C v throat velocity: 4” = 0.65 Venturi
1.005
1.010
1.015
1.020
1.025
0 10 20 30 40 50 60 70 80 90
C
Throat velocity (m/s)
4 inch (20 bar)
4 inch (70 bar)
Static Hole Error
• The difference between the pressure measured with a tapping hole of finite size and that which would have been measured using an infinitely small hole:
• dp shift in pressure, wall shear stress, density, kinematic viscosity, dtap tapping diameter.
dpf Retap
( )
Red
taptap
( / )
Streamline contours in pressure slot
RSM+wr model with ReD at: a) 2.0106, b) 5.3106, c) 2.0107.
a) b) c)
Static hole error: low Reynolds number (Red < 2 x 106)
Leads to increase of 0.6% in measured C
8”, β = 0.5, 4 mm taps, Red= 106
Static hole error: high Reynolds number (up to Red > 107)
Same points from McKeon & Smits as on previous slide
Static hole error: low Reynolds number (Red < 2 x 106)
Leads to increase of 0.6% in measured C
8”, β = 0.5, 4 mm taps, Red= 106
Static hole error: high Reynolds number (up to Red > 107)
Same points from McKeon & Smits as on previous slide
Venturi discharge coefficient: why the surprise in the 1990s?
• Simple physical explanation of C was inadequate• Literature (mostly c 1960 – 75) was not well known• The extrapolation was wrong
Wet Gas Facility
NEL Slide 45 High Pressure Wet Gas Facility Upgrade18-10-11
4” & 6” Ultrasonics in parallel Test Section
Pre-Separator
8” Pipework
Wet-gas correlations ( is the overreading)
1,gas2,gas 4
2
41m
pCq d
2Ch1 C X X
liquid 1,gasCh
1,gas liquid
n n
C
gas0.5 1.5Fr
gas0.7460.606 1 Frn e gas 1.5Fr
Chisholm de Leeuw
0.41n n=0.25
for
for
liquid
gas,1
gas,
liquid,
m
m
X
gas,1liquid
gas,12
gas,1
gas,gas
4
gDD
qFr m
1
1.1
1.2
1.3
1.4
1.5
1.6
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
Vent
uri M
eter
Ove
rrea
ding
,
Lockhart-Martinelli Parameter, X
Nitrogen-Exxsol D80
Argon-Exxsol D80
Nitrogen-Water
4” Venturi = 0.6, 1,gas/liquid = 0.024, Frgas = 1.5
4” Venturi = 0.6, 1,gas/liquid = 0.024, Frgas = 1.5
1
1.1
1.2
1.3
1.4
1.5
1.6
0 0.025 0.05 0.075 0.1 0.125 0.15 0.175 0.2 0.225 0.25 0.275 0.3 0.325
Lockhart-Martinelli Parameter, X
Vent
uri M
eter
Ove
rrea
ding
,
Nitrogen-Exxsol D80Argon-Exxsol D80Nitrogen-WaterEquation (6)
2Ch1.0532 1 C X X
0.3162 0.3162liquid 1,gas
Ch1,gas liquid
C
Effective Cwet gas ≠ Cdry gas
not through origin
Nitrogen-Exxsol D80Argon-Exxsol D80Nitrogen-WaterModified Chisholm eqn
Wet-gas C based on 0.02 < X < 0.065
gasgas,th 2,5
FrFr
0.93
0.94
0.95
0.96
0.97
0.98
0.99
1
1.01
0 5 10 15 20 25 30 35 40Fr gas,th
C
Beta = 0.4Beta = 0.4 CEESI Natural gas/decaneBeta = 0.6Beta = 0.6 Argon/Exxsol D80Beta = 0.6 Nitrogen/waterBeta = 0.6 Intercomparison NELBeta = 0.6 Intercomparison CEESIBeta = 0.75Beta = 0.75 Argon/Exxsol D80Beta = 0.75 Nitrogen/water2-inch CEESI Natural gas/water2-inch CEESI Natural gas/Stoddard6-inch Beta = 0.55Fit
Determine new value for n and C using extended data set
H = 1 for hydrocarbon1.35 for water, 0.79 for very hot water
Limits of use• 0.4 0.75• 0 < X 0.3• 3 < Frgas,th
• 0.02 < gas/liquid
• D ≥ 50 mm
gas,th-0.05 = 1-0.0463e min 1,0.016
Fr XC
0.8 /2 2max(0.583 0.18 0.578 ,0.392 0.18 )gasFr Hn e
Use of wet-gas correlations for Venturi tubes
1,gas2,gas 4
2
41m
pCq d
2Ch1 C X X
liquid 1,gasCh
1,gas liquid
n n
C
If C is the dry-gas value this pattern is inadequate; there is an effective wet-gas discharge coefficient: Surprise 2
Wet-gas flow through Venturi tubes: ISO/TR 11583 (NEL) equation: NEL database
-4
-3
-2
-1
0
1
2
3
4
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
% E
rror
in g
as m
ass
flow
rate
X
All regression and validation data
Wet-gas flow through Venturi tubes: de Leeuw Equation: NEL database
-14
-12
-10
-8
-6
-4
-2
0
2
4
6
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
% e
rror
in g
as m
ass
flow
rate
X
beta = 0.4beta = 0.43 - 0.47beta = 0.55 - 0.61beta = 0.7 - 0.75
My theory
• In wet-gas flow there is a thin film of liquid on the wall.• The dry-gas discharge coefficient no longer matters• There is no resonance.
NEL Slide 54 ISO Flow Measurement Standards18-10-11
My theory
• In wet-gas flow there is a thin film of liquid on the wall.• The dry-gas discharge coefficient no longer matters (there is no resonance).• Errors for two Venturi tubes from the ISO/TR 11583 (NEL) Equation:
NEL Slide 55 ISO Flow Measurement Standards18-10-11
-4
-3
-2
-1
0
1
2
3
4
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45
% e
rror
in g
as m
ass
flow
rate
X
C(dry) = 0.9694C(dry) = 1.0331Mean dry-gas point: C(dry) = 0.9694Mean dry-gas point: C(dry) = 1.0331
Surprise 3
• Uncalibrated Venturi tube uncertainty– Dry gas 3%– Wet gas 2.5 to 3%
NEL Slide 56 ISO Flow Measurement Standards18-10-11
Wet gas
• Given an uncalibrated Venturi tube and an uncalibrated orifice plate, which has the lower uncertainty?
Wet-gas flow through Venturi tubes: ISO/TR 11583 (NEL) equation: NEL database
-4
-3
-2
-1
0
1
2
3
4
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
% E
rror
in g
as m
ass
flow
rate
X
All regression and validation data
Wet-gas flow through orifice plates: ISO/TR 11583 (Steven)equation: NEL database
-4
-3
-2
-1
0
1
2
3
4
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
% e
rror
in g
as m
ass
flow
rate
X
Wet gas: Surprise 4
• For an uncalibrated Venturi tube and an uncalibrated orifice plate which has the lower uncertainty?
The orifice plate
Measurement over a range of 10000:1
• How can I measure natural gas in a 4” pipe as the flow declines over years over a flowrate range of 10000:1?
ConocoPhillips: 4” orifice run: spark-eroded plates
0.590
0.595
0.600
0.605
0.610
0.615
0.620
0.625
0.630
0.635
0 5 10 15 20 25 30 35
Disc
harg
e co
effic
ient
(106/Red)0.7
d = 1.577 mm (1/16")
d = 3.157 mm (1/8")
d = 3.169 mm (1/8")
d = 6.32 mm (1/4")
ConocoPhillips: 4” orifice run: spark-eroded plates
0.590
0.595
0.600
0.605
0.610
0.615
0.620
0.625
0.630
0.635
0 5 10 15 20 25 30 35
Disc
harg
e co
effic
ient
(106/Red)0.7
d = 1.577 mm (1/16")
d = 3.157 mm (1/8")
d = 3.169 mm (1/8")
d = 6.32 mm (1/4")
RG (1998) Equation
Stolz Equation
4” orifice run
0.590
0.595
0.600
0.605
0.610
0.615
0.620
0.625
0.630
0.635
0 5 10 15 20 25 30 35
Disc
harg
e co
effic
ient
(106/Red)0.7
d = 1.577 mm (1/16")d = 3.157 mm (1/8")d = 3.169 mm (1/8")d = 6.32 mm (1/4")RG (1998) EquationRG (1998) Equation: 8.9 micron edge, d = 1.577 mmRG (1998) Equation: 8.9 micron edge, d = 3.157 mmRG (1998) Equation: 8.9 micron edge, d = 6.32 mmStolz Equation
10,000:1 is available: Surprise 5(about 8 plates and remember e/d 0.1)
The discharge coefficient, C, is given by the Reader-Harris/ Gallagher (1998) equation:
A = (19000/ReD)0.8
upstream and downstream tapping terms
C 0,5961 + 0,0261 - 0,216 + 0,000521 10
(0,0188 + 0,0063A) 10Re
(0,043 + 0,080e - 0,123e (1- 0,11A) 1-
0,031 (M M
2 86
D
3,56
D
-10L -7L4
4
' ' 1,3
1 1
Re
)
, )
,
,
,
0 7
0 3
2 2110 8
Discharge Coefficient, C
It is 1988: will differential-pressure meters last another 30 years?
They have improved!• Diagnostics• Better dp transmitters• Better standards
Diagnostics
• Use PL/P to show that a meter is out of specification, even to correct a measurement
• ‘Prognosis’ (DP Diagnostics)
Flow
P PR
PL
25.4 mm 25.4 mm
6D
Differential-pressure transmitters (Yokogawa EJX110A)
-0.10
-0.05
0.00
0.05
0.10
0.15
10 100 1000 10000
Drif
t fro
m p
revi
ous
calib
ratio
n (%
of r
eadi
ng)
Differential pressure (mbar)
Transmitter A: 10 weeks Transmitter A: 11 months
Transmitter B: 10 weeks Transmitter B: 12 months
Transmitter C: 10 weeks Transmitter C: 9 months
Transmitter D: 7 months Transmitter D: 11 months
Transmitter E: 7 months Transmitter E: 11 months
Better standards: 24” gas data: flange tappings
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Disc
harg
e co
effic
ient
dev
iatio
n fr
om e
quat
ion
(%)
British Gas: Reader-Harris/Gallagher (1998)British Gas: StolzBritish Gas: RG (API)Gasunie: Reader-Harris/Gallagher (1998)Gasunie: StolzGasunie: RG (API)
The real surprise is not using the new standards
Scope of this talk
• 1 Difficult Reynolds numbers• 1.1 Heavy oil• 1.2 LNG
• 2 Difficult installations• 2.1 Emissions• 2.2 Flare gas
• 3 Difficult fluids• 3.1 Carbon dioxide• 3.2 Wet gas flow
• Venturi tubes• Orifice plates• There are surprises
Even for flow metrologists…
• There are surprises– Discharge coefficients – greater than 1– Wet gas – orifice plates can perform very well
- wet-gas Venturi tubes have a different effective discharge coefficient
– 10000:1 – use a set of orifice plates– Pitot tube standards
Written by a metrologist?
What do others think when at a party you say ‘I’m a metrologist?’
• Someone who makes minor and dull improvements on something that is well known?
Why are we surprised?
Why are we surprised?
• Too simple a physical model– ‘The Venturi-tube discharge coefficient just describes the
friction loss’– ‘A single power of Reynolds number will be sufficient for an
orifice plate’
Why are we surprised?
• Too simple a physical model• Ignorance of other work
– Static hole error– Better differential-pressure transmitters
Why are we surprised?
• Too simple a physical model• Ignorance of other work• False assumptions
– Extrapolation will be OK – The discharge coefficient is the discharge coefficient– Damming up must be bad for wet-gas flow through orifice plates– Diagnostics cannot be used for differential-pressure meters– New meters must be better
Why are we surprised?
• Too simple a physical model• Ignorance of other work• False assumptions• Standards that need to be improved
– Pitot tubes for emissions
• The Flow Programme of UK BEIS
• NMIJ and the Metrology Club
NEL Slide 80ISO Flow Measurement Standards18-10-11
Acknowledgments
Scope of this talk
• 1 Difficult Reynolds numbers• 1.1 Heavy oil• 1.2 LNG
• 2 Difficult installations• 2.1 Emissions• 2.2 Flare gas
• 3 Difficult fluids• 3.1 Carbon dioxide• 3.2 Wet gas flow
• Venturi tubes• Orifice plates• There are surprises