Flow measurement: some problems to solve and some surprises · NEL Slide 26 ISO Flow Measurement Standards18-10-11. The issue • Kyoto Protocol • CO 2 could be captured and stored

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

qq

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.


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:


-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%


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?


• 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’


• Too simple a physical model• Ignorance of other work

– Static hole error– Better differential-pressure transmitters


• 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


• 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

Documents

Flow measurement: some problems to solve and some surprises · NEL Slide 26 ISO Flow Measurement Standards18-10-11. The issue • Kyoto Protocol • CO 2 could be captured and stored