turbine meters in carbon dioxide - fortisbc · pdf filehigh pressure calibration of gas ......

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October 9, 2008Paul W. Tang, B.A.Sc., M.Sc., P.Eng.

High Pressure Calibration of Gas Turbine Meters in Carbon Dioxide

pwt 2008.10.10

Topics

High Pressure Calibration of Turbine Meters in CO2

A brief history of Triple PointReynolds number and flowMeter calibration requirements in different jurisdictionsProver technologies

High pressure meter test facilities around the world

TRIPLE POINT facility

Measurement uncertainty and Quality Control

Questions?

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A Brief History of Triple Point

For over 15 years, Terasen Gas has been searching for a high pressure turbine meter calibration solution.

The original concept was centered around building a meter testing facility adjacent to a high pressure natural gas transmission line , and preferably also close to a gate station with high flow rate throughout the entire year.

A suitable location for such project was very difficult to find.

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The original “Alternate Fluid Turbine Meter


The original Alternate Fluid Turbine Meter Calibration” concept was first proposed in November 2002 in an internal discussion paper.

The paper discussed the operational advantages of using a “heavy gas”, such as carbon dioxide, to perform high Reynolds number turbine meter testing.

Th l l t d h th fThe paper also speculated on how the performance of such a “heavy gas” turbine meter calibration facility would compare with that of a conventional facility.

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The concept paper was reviewed by an international panel of turbine meter experts.

The experts could not find any fault in the proposed “heavy gas” turbine meter prover concept.

The experts also agreed with the paper’s author about the advantages of “heavy gas” turbine meterabout the advantages of heavy gas turbine meter calibration, and that an advance turbine meter testing facility may be built based on such principle.

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Funding was made available for a “proof of concept” test at the Southwest Research Institute, San Antonio, Texas in October of 2003.

A total of six turbine meters of different manufacturers and sizes were tested in both natural gas and carbon dioxide at various pressures.

Test results confirmed that turbine meters do display the same characteristics at the same Reynolds number, regardless of the test medium used.

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Project approved in July 2004.

“Fast-track” schedule – design and construction to be completed within one year.

Most of the engineering and fabricating were done in-house.

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Construction completed in April 2005

Facility commissioned in September 2005

Obtained Measurement Canada recognition as a high pressure turbine gas meter calibration facility in August 2006

US patent was granted in January 2007, international patent pending.

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Concept Test

Project team at SwRI to witness the “proof-of-concept “ tests

System Fabrication

Reference meter header being fabricated in Terasen’s Burnaby shop

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Hydrostatic Testing of Pipes

Main loop assembled for pressure test

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Lifting the Tank

Construction crew installing the liquid CO2 storage tank

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Reynolds Number

ρνDρνD

ηReynolds Number =

ρ = fluid density

ν = flow velocity

D = pipe diameterη = fluid viscosity

Recent research conducted at CEESI and SwRI on behalf of AGA has demonstrated that commercially available gas turbine meters have markedly different responses to given volumes of natural gas at different Reynolds number.

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Visible Reynolds Number?

Reynolds Number can be observed in everyday life….

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Effective Test Pressure - Air

Comparing Air to Natural Gas:

Effective Test Pressure (Air) =

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Effective Test Pressure – CO2

Comparing CO2 to Natural Gas:

Effective Test Pressure (CO2) =

2.1

2.1

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Turbine Meter Operating at Various Pressure Ranges

50 psig

175 psig

720 psig

1440 psig

Turbine meter operating close to atmospheric pressure shows a very non‐linear performance curve

T bi t ti i hi h li di l

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Turbine meter operating in a high pressure line displays a much more linear and predictable characteristic

Pressure and Density Effects on Turbine Meters

Turbine meters need to be calibrated under operational conditionsTurbine meters need to be calibrated under operational conditions. This is confirmed by research for AGA and GRI:

(1) Effects of Line Pressure and Density of Turbine Meter Measurement Accuracy Between 30 and 700 psig in Natural Gas, GRI-03/0050, July 2003;

(2) Effects of Line Pressure and Density of Turbine Meter Measurement Accuracy at Conditions from Atmospheric Air to 700 psig NaturalAccuracy at Conditions from Atmospheric Air to 700 psig Natural Gas, GRI-03/00172, August 2004;

(3) Measurement of Natural Gas by Turbine Meters, 3rd revision published by AGA, February 2006.

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Pressure and Density Effects on Turbine Meters

Some highlights reported by the AGA and GRI research:

Worst calibration shift observed was 12.5 per cent.

Each of the meters tested was affected by the pressure and density effects.

Calibration shift up to 1% is not uncommon.

Most serious effects at low flow and pressure.

Some highlights reported by the AGA and GRI research:

Atmospheric calibrations are not accurate for pipeline pressure applications.

K-factor vs Reyolds number is superior to K-factor vs flow rate

1Maximum Reynolds N b i

Maximum Reynolds N b i 120 i

Maximum Reynolds N b i 750 i

Turbine Meter Performance vs Reynolds Number

0

120 psig Natural Gas

rror

of i

ndic

atio

n (%

)

Number in atmospheric air test

Number in 120 psig natural gas test

Number in 750 psig natural gas test

Reynolds Number (x 1,000)

-1

750 psig Natural Gas

atm. Air

Er

10,0001,00010010

Typical Turbine Meter Performance vs Reynolds Number

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Pressure Effect on a Turbine Meter

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Each one of these three curves has very distinct

Pressure Effect on a Turbine Meter

curves has very distinct and different attributes.

Any one of these three calibration curves does not represent the behavior of the meter operating under the other two sets of conditions.

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Performance Curve Expressed in Reynolds number

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Cost of Flow Measurement Error

Turbine Meter Operating at 50 psig Turbine Meter Operating at 500 psigTurbine Meter Operating at 50 psig

Meter Size

Energy Delivered in a 6 year Calibration

Cycle *

Cost of Energy Delivered *

Cost of 0.5% Measurement

Error

Inches MMBtu US$ US$

4 1,271,208 8,898,458 44,492

6 2,478,052 17,346,361 86,732

8 4,264,180 29,849,258 149,246

Turbine Meter Operating at 500 psig

Meter Size

Energy Delivered in a 6 year

Calibration Cycle *

Cost of Energy

Delivered *

Cost of 0.5% Measurement

Error

Inches MMBtu US$ US$

4 10,990,320 76,932,238 384,661

6 21,369,172 149,584,204 747,921

8 36,623,671 256,365,699 1,281,828

8 HC 6,388,224 44,717,567 223,588

12 9,944,389 69,610,722 348,054

12 HC 16,332,613 114,328,289 571,641

8 HC 54,951,598 384,661,188 1,923,306

12 85,476,688 598,336,817 2,991,684

12 HC 140,428,286 982,998,005 4,914,990

Note 1: Turbine meters operating at 30% of Qmax average 2. Energy content of natural gas based on 1.0205 MBtu/cu.ft.3. Cost of energy calculated based on $7.00 USD per MMBtu (2008.09)

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Natural Gas Pricing

The cost of natural gas has increasedThe cost of natural gas has increased many times since the mid 90’s

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NYMEX Previous 12 Month Natural Gas Pricing

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5Sep (07) Oct Nov Dec Jan (08) Feb Mar Apr May Jun Jul Aug Sep

Prepared 2008.09.1325

International Recommendation – OIML R 137-1 Edition 2006

The OIML R 137‐1 (2006) document Section 7.5.5 recommends

The accuracy requirements of 5.3 and 5.4 shall be verified while using the conditions of the gas which are as close as possible to the operating conditions (pressure, temperature, gas type) under which the meter will be put into service.

that all gas meters, without exception, to be tested at or close to operating conditions:

International Organization of Legal Metrology

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Recommendations in EN 12261

In Europe, the CEN document EN 12260‐2002 (Turbine Meter) section 5 2 1 2 specifies that:Meter) section 5.2.1.2 specifies that:

For a meter type specified for measurement in a pressure range below or equal to 4 barthe error of indication test shall be carried out with a gas at atmospheric conditions (±100 mbar).

For a meter type specified for measurement in a pressure range extended above 4 barthe error of indication test shall be carried out with a gas in the range of the specified metering conditions. The tests shall be carried out at least at the lowest and the highest working pressure specified by the manufacturer However for specified maximumworking pressure specified by the manufacturer. However, for specified maximum pressures above 50 bar a test at 50 bar is deemed acceptable.

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Recommendations in AGA-7 Report

AGA R t N 7 3 d R F b 2006 ti 6 3 2

…….….a meter calibration carried out in a test facility over a particular range of Reynolds numbers characterize the meter’s performance when used to measure gas over the same range of Reynolds number when the meter is in service

……… the expected operating Reynolds number range and/or density for a meter needs to be taken into account when designing a calibration

AGA Report No. 7 3rd Rev. February 2006, section 6.3.2 “Calibration Guidelines”

meter needs to be taken into account when designing a calibration program ……

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The ERCB Directive 017

Revised edition – approved May 7, 2007Section 2.5.2.1.4

………….The (gas meter) proving may be done with the meter in service, or the meter may be removed from service and proved in a shop at a pressure that is within the normal operating condition for that meter location………

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Triple Point Turbine Meter Proving Facility

Excerpt from public correspondence from Measurement Canada dated April 10, 2000

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Regulatory Agencies and Industry Associations

All of these organizations are either specifying, recommending, or considering d bmandatory turbine meter proving at operating pressure.

International Organization of Legal Metrology

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Principle of a Transfer Meter Prover

Reference Meter Meter Under TestTest flow Reference Meter(Master)

Meter Under Test(MUT)

Comparing the volume throughput with a well known reference under the same conditions

Test flow

i.e. Testing or converting to the same pressure and temperature

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Open-loop Prover

REFTest flow

Transmission pipeline

REF

Bypass flow

MUT

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Turbine Meter - Pressure Loss vs Flow1.0

Working with Pressure Loss

0 3

0.4

0.5

0.6

0.7

0.8

0.9

e Lo

ss (N

orm

aliz

ed to

ΔP

at Q

max

)

pressure loss

f

bw PK

GQhP

1

2

≅=Δ

0.0

0.1

0.2

0.3

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Flow ( % of Qmax)

Pre

ssur

e

Constant Pressure and Specific Gravity

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Conventional Closed-loop Prover

Compressor

REF

Cooler

MUT

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Loop Cooling Requirements

Much of the energy consumption of a high pressure meter prover station is due to compression and loop cooling. An efficient cooling system is therefore crucial to thetherefore crucial to the overall operating efficiency of a prover station.

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Prover Station Flow Capacity Requirements

A prover station needs a wide range of flow rates to be available at any given time.

Suitable pipeline locations for such operation are rare.

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High Pressure Meter Calibration

High Pressure Turbine Gas Meter Calibration:

There are limited high pressure meter testing capacity available for industrial turbine meter testing worldwide.

NMI – Westerbork Facility, Netherlands

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While high quality calibration laboratories exists, the meter testing capacity traditionally falls far short of being able to

Pigsar Flow Test Facility, Germany

handle demands.

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The shortage of high pressure meter test capacity worldwide results in long waiting list for calibration services.


NMI Bergum High Pressure Meter Test Facility - Netherlands

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The magnitude of pressure related turbine metering errors was demonstrated by recently published research. As a result, more gas companies are

Southwest Research Institute, San Antonio, Texas

g pdemanding high pressure meter calibration.

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Here in Canada, TransCanada Calibration at Ile des Chenes, Manitoba is a pioneer in offering high pressure meter calibration services


services.

TCC – TransCanada Calibration, Ile des Chenes, Manitoba, Canada

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The Terasen Triple Point High Pressure Meter Calibration Facility was designed to provide a solution to the meter test capacity problem


by using a novel approach to flow calibration.

TRIPLE POINT Turbine Meter Calibration Facility, Penticton, BC

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Triple Point Project – Why Carbon Dioxide?

Reasons for using CO2 as a

Higher Reynolds number and density at lower pressure ‐reduced capital and operating costs

Direct injection temperature control

Minimal safety concerns

Reasons for using CO2 as a test medium:

Minimal safety concerns

Inexpensive

Easy to handle

Carbon dioxide gas used during the SwRI proof-of-concept test in October 2003

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The Triple Point Advantages

TRIPLE POINT solves the test capacity problem by :TRIPLE POINT solves the test capacity problem by :

1. Using carbon dioxide gas as a test medium in a close‐loop meter prover system, making it feasible to reach very high Reynolds number in a compact system;

2. Concurrently using the test medium as a refrigerant to cool the test system, thus further reducing the physical size and the capital cost of the test loop;

3 Si th TRIPLE POINT t h l d t t l3. Since the TRIPLE POINT technology does not use natural gas as a test medium, there is no restriction on where and how many test facility can be built.

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The Triple Point Proving Loop

LCO2

REF

MUT

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LCO2

ΔPcomp= 12.5 psig

REFΔPV(m+1)ΔPV(m

)

ΔPfilter

ΔPS(m)

ΔPRef

ΔPinject

ΔPpipe(distributed)

MUTΔPV(n)ΔPV(n+1) ΔPS(n)

ΔPMUT

injectionfilterMUTrefpipeSVcomp PPPPPPPP Δ−Δ+Δ+Δ+Δ+Δ+Δ=Δ ∑ ∑ ∑

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Performance Curve of High Pressure Blower in the Test Loop

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Phase Diagram of Carbon Dioxide

Approx.area of

3P operationp

Triple point of CO2 is ‐56.7°C, 5.1 atm (or ‐69.9°F, 75.1 psia)

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Unconventional Cooling System

The Triple Point cryogenic cooling system is i l t t d h ti ll

Array of motorizedcryogenic needlevalves and nozzles

Liquid CO2 Injection Nozzle

very simple to operate and has exceptionally fast response time.

Nozzle CO2 Gas120 psig70°FFlow rate 1,200 - 230,000ACFH

Bulk CO2storage tank

The Triple Point Cryogenic Cooling System

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Triple Point Control Panel

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Triple Point Differential Pressure Sensing

Triple Point Differential Pressure Sensing Schematic

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Efficiency of the MUT Test Stand

• Mounting meter‐under‐test (MUT) on a prover stand is a time consuming process.

• Many bolts have to be installed and removed for each test.

• Preparing a meter for calibrationPreparing a meter for calibration sometimes may take several hours.

Mounting and preparing a MUT at the SwRI test loop

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Efficiency of the MUT Test Stand

The focus of the Terasen Triple Point facility is production efficiency for commercial and industrial meter testing.

Hydraulic slip-joint system enable rapid installation and removal of meter under test (MUT)

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Triple Point Control and Data Acquisition System

Control and Data Acquisition Package

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Triple Point Test Data Presentation Panel

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Triple Point Test Data Analysis

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Triple Point Calibration Certificate

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The Triple Point Loop

Meter Under Test (MUT) Section Cooling Section

Reference Meter Section

Piping Layout of the Triple Point Turbine Meter Proving System

Blower Section

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The Triple Point Calibration Facility

The Triple Point Loop consists of five master meter runs and three meter‐under‐test (MUT) runs.

The MUT runs can accommodate meters from 2‐inch to 12‐inch diameter as well as complete meter run

Meter test loop at the TRIPLE POINT test facility

passembly.

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Triple Point Turbine Meter Proving Facility Specifications

Specifications

1. Type of Meter Gas Turbine Meter

2. Meter Size 2” to 12”

3. Flange Rating ANSI 150, 300, 600

4. Test Medium Carbon Dioxide

5. Flow Range4”,8”, and 12” meter 2,700 to 230,000 ACFH2” and 3” meter 700 to 10,000 ACFH

6. Operating Pressure Atmospheric to 240 psig CO2Equivalent to approx. 600 psigNatural gas

7. Pressure Stability ± 1.0 psig

8. Operating Temperature 40 to 104 ºF (±2ºF)

Triple Point master meter

8. Operating Temperature 40 to 104 F (±2 F)

± .5°F stability during test

9. Reynolds Number 100,000 to 9,200,00010. Measurement Uncertainty ±0.27 of deviation (GUM method)

Confident level 95% (k = 2)11. Traceability NMI (Netherlands)

12. Government Recognition Measurement Canada underBulletin G-16

2008.01.08 61

What is Measurement Uncertainty?

Measured value = Best estimate of the value ± Uncertainty

Measurement uncertainty is an expression of the quality of the measurement in question.

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What is Measurement Uncertainty?

Measurement uncertainty Quality of a measurement result

Measurement uncertainty must always be expressed with an indication of the level of confidence

Example

The uncertainty of a temperature measurement is ±0.10°Cwith a confidence level of 95% (coverage factor k=2)

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Level of Confidence

Coverage Level ofCoveragefactor, k

Level ofConfidence

0.676 50%

1 68.27%

1.645 90%

1.960 95%

2 95 45%

The expanded uncertainty is calculated by multiplying the standard uncertainty by the coverage factor

Most calibration institutions report uncertainty at 95% confidence level or k=2

2 95.45%

2.576 99%

3 99.73%

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Modeling Equations

Metering Error Equation:

eMUT Meter under test calibration errorN Pulse count meter under test

%1001 ×

⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜

⎝

⎛

−××××

=ZTPRE

REF

REF

MUT

MUT

MUT

CCCCKN

KN

e

NMUT Pulse count – meter under testNREF Pulse count – reference meterKREF K-factor – reference meterKMUT K-factor – meter under testCRE Reynolds number correction factorCP Pressure correction factorCT Temperature correction factorCZ Compressibility correction factor

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Guide to Expression of uncertainty in Measurement (GUM)

The GUM (Guide to the Expression of Uncertainty in Measurement) report classifies the evaluation of measurement uncertainty into Type A and Type B

Type A evaluation is built on and calculated from a series of repeated observations of a measurement process

Type B evaluation is based on using available knowledge of the process and process elements. The Type B contributors are those that must be determined by non-statistical methods

For a new facility such as Triple Point for which repeated observations and long term measurement data are not yet available, we have to rely on the Type B evaluation approach.

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Type A and Type B Measurement Uncertainty

The GUM (Guide to the Expression of Uncertainty in Measurement) report classifies the evaluation of measurement uncertainty into Type A and Type B

Type A evaluation is built on and calculated from a series of repeated observations of a measurement process

Type B evaluation is based on using available knowledge of the process and process elements. The Type B contributors are those that must be determined by non-statistical methods

For a new facility such as Triple Point for which repeated observations and long term measurement data are not yet available, we have to rely on the Type B evaluation approach.

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Sources of Measurement Uncertainty in Triple Point

Contributing factors to Triple Point’s Measurement Uncertainty

Uncertainty in the calibration of reference metersUncertainty of the equivalency of CO2 Temperature sensitivity of reference meters Pressure sensitivity of reference metersEquations of state and transport properties variable Calibration of temperature and pressure sensorsPulse counting uncertainty Connecting volume considerationgUncertainty caused by contaminant in the test streamSampling errorsResolution ErrorsLong-term Stability and Repeatability Other additional assumptions

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Uncertainty in the calibration of reference meters

Each of the Triple Point reference meters was calibrated at NMI and has a current NMI calibration certificate specifying the measurement uncertainty figure with a coverage factor of k = 1.96.

A worse case metering deviation uncertainty figure of ±0.21% (coverage factor 1.96) from the NMI calibration

tifi t d t t bli h th b dcertificates was used to establish the upper bound measurement uncertainty of Triple Point.

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Uncertainty of the equivalency of CO2

Not very much turbine meter test data for carbon dioxide gas was available for consideration.

The results of the “Dual Fluid Turbine Meter Test” program at SwRI was used as a basis for estimating the calibration performance of carbon dioxide.

Due to the absence of further experimental data on CO2 tests, a worse case assumption that the 0.15% uncertainty observed at SwRI was entirely caused byuncertainty observed at SwRI was entirely caused by the difference in the fluid properties of carbon dioxide and natural gas.

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Pressure sensitivity of reference meters

Triple Point is a meter testing facility designspecifically to address the K-factor versusReynold’s number interdependency. Inorder to evaluate the Reynold’s numbersensitivity of the reference meters, all of thereference meters were calibrated at threedifferent NMI facilities in order tocharacterize them over a wide operatingpressure range. The measurement errors ofthese reference meters obtained from theNMI calibration charts were converted into aset of nth order polynomial functions ofReynold’s number, thus fully accounting forthe pressure effect on them.

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Equations of state and transport properties variable

The Benedict-Webb-Rubin (BWR) equation of state is applicable fortemperature range from -30 to 150°C for densities up to 900kg/m3 andtemperature range from 30 to 150 C, for densities up to 900kg/m , and maximum pressure of 200 bar:

where A0, B0, C0, a, b, c, α, γ — gas constants for the equation A = 0 313 kg m5 s-2 mol-2A0 = 0.313 kg m5 s-2 mol-2B0 = 5.1953×10-5 m3 mol-1C0 = 1.289×104 kg m5 K2 s-2 mol-2a = 1.109 ×10-5 kg m8 s-2 mol-3b = 3.775×10-9 m6 mol-2c = 1.398 kg m8 K2 s-2 mol-3α = 9.377×10-14 m9 mol-3γ = 5.301×10-9 m6 mol-2

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Equations of state and transport properties variable

Triple Point makes use of the REFPROP database DDL module developed by NIST to generate figures for the thermodynamic and transport properties of the test mediumof the test medium.

At pressures up to 30 MPa (4,350 psia) and temperatures up to 523 K (250 ºC), the estimated uncertainty in REFPROP’s carbon dioxide density (ρ) ranges from 0.03% to 0.05%.

The estimated uncertainty in viscosity (η) of carbon dioxide is 0.3% for the same operating range.

Due to the favorable interdependency of the density variables in the p y yderiving formula, the uncertainty of CZ is considered negligible

Since the estimated uncertainty of viscosity is an order of magnitude larger than that of density, it is assumed that the contribution of viscosity dominates the Reynold’s number calculation, and the effect of density is negligible.

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Calibration of temperature and pressure sensors

The measurement uncertainty specificationof the Rosemount differential pressuretransducers used at Triple Point was givenby the manufacturer as ±0.025% of span(250”w.c.) with k=3. Assuming normaldistribution, this would translate into astandard uncertainty figure of ±0.021”w.c..Similarly, the standard measurementuncertainties of the static pressureptransducer and the RTDs would beexpressed as ±0.021 psia and ±0.09 ºFrespectively.

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Pulse counting uncertainty

The worst case maximum timing discrepancy between the reference metercounts and the meter-under-test counts is expected to be less than ± 5msec according to the specification of the data acquisition system. Over aminimum meter test time of 60 seconds, the timing error is estimated to beless than ± 0.008%.

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Connecting volume consideration

Since both the reference meters and the meter-under-test are in closei it d d t th i t it i d th t thproximity and exposed to the same environment, it is assumed that the

contribution of dimensional changes in the meter runs due to temperatureor pressure differences is very small and may be considered negligible.

Leakage through the isolation ball valves at the meter runs may alsointroduce metering error. Since this type of leakage is driven entirely by thedifferential pressure across the isolation valves, it can be eliminated byequalizing the pressure around the entire loop during a test.

Small leaks can be detected by the ambient CO2 detectors in the test areaSmall leaks can be detected by the ambient CO2 detectors in the test areaas well as by a portable CO2 detector used by the operator to check theflange couplings after a new meter-under-test is mounted. Metering errorcaused by external leak is negligible when the proper operating procedureis observed.

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Uncertainty caused by contaminant in the test stream

The presence of air contaminant affects the physical properties of thecarbon dioxide test stream.

Low level (less than 1,000 ppm) air contaminant causes insignificant error(less than 0.01%) in the compressibility ratio and density ratio used in thederivation of eMUT.

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Sampling errors

Due to the use of an active temperature and pressure control system inTriple Point, the test loop operates in a steady state condition throughoutthe entire calibration cycle.

Sampling error is considered to be negligible when a steady state operatingcondition is maintained.

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Resolution Errors

Measurement uncertainty contribution by Triple Point Instruments:

Instrument Minimum Digital Increment

ResolutionUncertainty

Calibration Uncertainty

Total Uncertainty

RTD (Temperature) ±0.01ºF ±0.0029ºF ±0.09ºF ±0.09ºF

2)(

2)(

2 )( CresolutionCncalibratioc uuCu +=

Differential Pressure Transducer ±0.1”w.c. ±0.029”w.c. ±0.021”w.c. ±0.036”w.c.

Static Pressure Transducer ±0.1 psia ±0.029 psia ±0.021 psia ±0.036 psia

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Long-term Stability and Repeatability

Due to the newness of the Triple Point Facility and process, no long-termstability and repeatability data is available for analysis at the time of writingof this report. In order to maintain a high level of long term systemperformance, a strict quality control program is planned for the start up andon-going operation of the facility. This control program will be implementedin accordance with the ISO 17025 standard.

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Temperature sensitivity of reference meters

Array of motorized

• Although the effect of temperature on the gas test medium is well known and

Nozzle CO2 Gas120 psig70°FFlow rate 1,200 - 230,000ACFH

Array of motorizedcryogenic needlevalves and nozzles

Bulk CO2storage tank

• Although the effect of temperature on the gas test medium is well known and understood, there is little data available concerning how the calibration of a turbine meter may be affected by changes in its body temperature.

• The Triple Point test facility has complete control on the operating temperature of the test loop. For the narrow test temperature range the Triple Point reference meters are exposed to, the calibrations of these meters are assumed to be unaffected.

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Other additional assumptions

The minimum volume counts registered by the reference meters are kept above 10,000 so that the ± 1 count error represents less than ±0.01% of the fractional error.

Th i i ti i d f l ti t lib ti l i k tThe minimum time period for completing a meter calibration cycle is kept above 60 seconds in order to keep the timing error to less than 0.008%.

The conductive and radiative heat exchange between the RTD probes and the meter run piping is assumed to be insignificant due to the small temperature gradient from the pipe to the temperature sensing elements.

The RDT self-heating effect is considered negligible in comparison to the overall heat balance of the temperature probes.

The reference meters and the MUT are assumed to produce smooth and pcontinuous pulse signals.

The meter “put-in” and “take-out” effect on measurement uncertainty uRio is kept small enough to be negligible by using special flange alignment tools and by following the meter mounting method specified in Triple Point Test Procedures Manual (OPM-01 Manual).

No uncertainty figure has been assigned for all of the above items.

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GUM General Formula for Error Propagation

The general propagation of errors equation from the GUM

)( PPTTPPTKNNf ΔΔΔΔΔ

u ydfdx

u xci

N

ii

2

1

22( ) ( )=

⎡⎣⎢

⎤⎦⎥=

∑

Expressing metering error as a function of meter parameters and correction factors in a multiple reference meter system:

)..,..,,,,,,( )()1()()1( NREFREFNREFREFsMUTMUTREFREFMUTMUT PPTTPPTKNNfe ΔΔΔΔΔ=

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)(2MUTc eu )()()( 2

22

22

2

REFcREF

REFcREF

MUTcMUT

KuKfNu

NfNu

Nf

⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

+⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

+⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

=

)()..(

)()..(

)()()(

)(2

2

)()1(

2

2

)1(

)(2

2

)()1(

2

2

)1(

22

22

22

NREFcNREF

REFcREF

NREFcNREF

REFcREF

scS

MUTcMUT

MUTcMUT

PuPfPu

Pf

TuTfTu

Tf

PuPfPu

PfTu

Tf

Δ⎟⎟⎠

⎞⎜⎜⎝

⎛

Δ∂∂

Δ⎟⎟⎠

⎞⎜⎜⎝

⎛

Δ∂∂

+

⎟⎟⎠

⎞⎜⎜⎝

⎛

∂∂

⎟⎟⎠

⎞⎜⎜⎝

⎛

∂∂

+

⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

+Δ⎟⎟⎠

⎞⎜⎜⎝

⎛Δ∂∂

+⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

+

where MUTNf ∂∂ / , REFNf ∂∂ / ,……, )()1( /../ NREFREF PfPf Δ∂∂Δ∂∂

of the partial differential equation are the sensitivity coefficients of the independent variables, and the uc value of each variable is the standard uncertainty associated with that variable.

etc.

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43

The combined standard uncertainty uc(eMUT) of the Triple Point meteringerror measurement is derived:


1324.0)( 22

=⎥⎥⎦

⎤

⎢⎢⎣

⎡×⎟⎟

⎠

⎞⎜⎜⎝

⎛∂∂

= ∑ Ci

MUTC uxfeu

The standard uncertainty uC(eMUT) is then converted into anexpanded uncertainty U(eMUT) with a coverage factor k = 2:

(unit in %)

27.2(%)1324.0)( =×=MUTeU

expanded uncertainty U(eMUT) with a coverage factor k 2:

(unit in %)

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Measurement Uncertainty of Triple Point

The expanded measurement uncertainty of the Triple Point turbine meter calibration facility is ±0.27% of deviation with a confidence level of approximately 95% assuming a normal distribution. This uncertainty figure was developed in accordance with the GUM 1995 d t

General conclusion about the Measurement Uncertainty of Triple Point:

1995 document.

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Triple Point Uncertainty Budget

By understanding the measurement uncertainty budget of a measurement system, one can make rational decision on how to optimize its operation.

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1995 document.

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45




1995 document.

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Quality Assurance Program

Routine check meter comparison program ensures that a minimum level of master meter calibration drift is maintained

90

46

Quality Assurance Program

Drawing of the BIPM/CIPM KC5a package consisting of two G650 turbine meters

BIPM – Bureau International des Poid et MesuresCIPM - International Committee for Weights and Measures

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Comparing the Performance of Two Facilities

Red error bars represent ± 0.21% measurement uncertainty reported by NMI’s

Data based on 3P test certificates on 2006.10.12

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47

Quality Assurance Programs

Terasen Measurement is one of the founders and a participant in the TeST program, which is a flow lab quality assurance program jointly supported by Terasen Measurement, Southwest Research

TeST artifact for inter-facility comparison being prepared for shipping

Institute, and TransCanada Calibration.

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Turbine Meter Training Course

THANK YOU VERY MUCH

Questions???

Contact:

Paul W. Tang, B.A.Sc.,M.Sc., P.Eng.Engineering ServicesTerasen GasPhone 604.592.7783Email [email protected]

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turbine meters in carbon dioxide - fortisbc · pdf filehigh pressure calibration of gas ......

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