introduction to gas metering - barchard engineering...

Introduction to Gas Metering

Presented for informational purposes only, Barchard Engineering does not assume any liability for use of information, consult appropriate sources where required


Topics Covered:

- Gas Metering Principles

- Gas Meter Types and Installation Considerations

- Measurement Canada and other Regulations

- Design Considerations

- Summary

Gas Metering Principles

- Natural Gas, like all other gasses, is a compressible substance and has a density determined by its pressure, temperature and composition

- When buying and selling gas, people want to know the quantity of ( or amount of energy provided by) the gas they are purchasing, not the volume

- Gas meters of all types are capable of measuring the actual volume of gas that flows through them, and then various correction factors need to be applied to account for the effects of pressure, temperature, and gas composition

- Gas quantities are expressed in standard volumes. In Canada, the two most common standard volumes used (and recognized by Measurement Canada ) are the Standard Cubic Foot and the Standard Cubic Metre

One Standard Cubic Foot is the Quantity of Gas contained by a 1 cubic foot container at 60 F and 14.73 psi

One Standard Cubic Metre is the Quantity of Gas contained by a 1 cubic metre container at 15C and 101.325 kPa = 59F and 14.696 psi


One Standard Cubic Foot is the Quantity of Gas contained by a 1 cubic foot container at 60 F and 14.73 psi

A Standard Cubic Foot is a QUANTITY of gas, not a VOLUME, as it can occupy any VOLUME


𝑉𝑠 = 𝑉𝐴 × 𝐹𝑃 × 𝐹𝑇 × 𝐹𝐹𝑃𝑉2 × 𝐹𝑀

Standard Volume

Actual Volume

Pressure Factor

Temperature Factor

Super Compressibility Factory

Meter Factor


𝑉𝑠 = 𝑉𝐴 × 𝐹𝑃 × 𝐹𝑇 × 𝐹𝐹𝑃𝑉2 × 𝐹𝑀

Ideal Gas LawPV=nRT

Pressure Factor is big: 2 psi : 1.14, 14%

10 psi : 2.36, 136% 80 psi : 6.43, 543%

Temperature Factor is smaller:32 F: 1.06, 6%60 F: 1.00, 0%

90 F : 0.945, -5.5%

Super Compressibility-Corrects for the difference

between a real gas and an ideal gas-M.C. Requires correction

for over 100 psi- Need to know Pressure, Temperature,

S.G., %N2, %C02-Approximately 1%, F=1.01 at 100 psi

-Generally ignored below 100 psi

Meter Factor-Account for the meter test results

(difference between actual and meter)Generally less than 1%

-Not used in M.C. Applications


𝑉𝑠 = 𝑉𝐴 × 𝐹𝑃 × 𝐹𝑇

Standard Volume in Standard Cubic Feet ( scf ) used for billing, frequently corrected for heat value when gas is sold by energy content ( approximately 1000 BTU/scf, or 1000scf/GJ )

Actual Volume is read of the meter, typically stop read minus start read over a billing period. Many metershave built in temperature compensation which is then called a temperature compensated volume

Pressure Factor 𝐹𝑃 =𝑃𝐴𝑏𝑠

𝑃𝐵𝑎𝑠𝑒=

𝑃𝐴𝑡𝑚+𝑃𝐿𝑖𝑛𝑒

𝑃𝐵𝑎𝑠𝑒=

𝑃𝐴𝑡𝑚+𝑃𝐿𝑖𝑛𝑒

14.73 𝑝𝑠𝑖

Temperature Factor 𝐹𝑇 =𝑇𝐵𝑎𝑠𝑒

𝑇𝐿𝑖𝑛𝑒=

459.67 𝐹+60 𝐹

459.67 𝐹 +𝑇𝐿𝑖𝑛𝑒𝑂𝑅 1.00 𝑜𝑛 𝑎 𝑇. 𝐶.𝑀𝑒𝑡𝑒𝑟

Presented for informational purposes only, Barchard Engineering does not assume any liability for use of

information, consult aproriate sources where required

Meter Range Turndown


Rotaries: Medium PressureMedium to High Flow RatesGood Turndown ~50:1

Diaphragm: Lowest PressureLowest Flow RatesExcellent Turndown ~100:1

Turbines: Highest PressureHighest Flow RatesPoor Turndown ~20:1

HP Rotaries: High PressureHigh Flow RatesGood Turndown ~50:1


0

5000

10000

15000

20000

25000

0 20 40 60 80 100

Cap

acit

y (s

cf/h

r)

Pressure (psi)

Capacities of Meters

3M

AL 1000

AC 630

AL 425

AC250


Capacities of Diaphragm Meters at Pressure

(in scf/h of 0.6 SG Natural Gas)

Gauge Pressure

(psi)

Differential Pressure

("WC)

New Meters Discontinued: Rebuilds may be available

Elster Sensus Elster Sensus Elster Sensus Elster Sensus Sensus Elster Elster

AC250R-275 MR-8

AL 425415

MR12AC 630 AL 1000 RC 750 AL 800 RC 1600 RC1000 AL 1400 AL 2300

0.25 0.5 250 275 425 415 630 1000 750 800 800 1000 1400 2300

0.25 1 355** 383** 583** 577** 860** 1400** 1033** 1100** 1067** 1400** 1933** 3200**

0.25 2 565 600 898 900 1320 2200 1600 1700 1600 2200 3000 5000

2 2 600 635 955 952 1390 2400 1688** 1850 1688** 2321** 3265 5440

5 2 656 690 1038 1035 1515 2700 1840 2100 1840 2530 3700 6200

10 2 - - 1154 1160 1710 3400 2080 2600 2080 2860 4600 7700

20 2 - - 1367* 1377* 2010 4100 2480 3200 2480 3410 5600 9400

25 2 - - 1462* 1473* 2160 4600 - 3500* 2640 3630 6200 10400

50 2 - - - - - 6600* - 5100* 3360 - 9000 15000

75 2 - - - - - 8540* - 6600* 3920** - 11650 19400

100 2 - - - - - 10100* - 7800* 4480 - 13800 23000

Notes:

* Multiple options exist for MAOP, insure meter is rated for pressure

** These values have been interpolated and are estimates

For Propane capacities multiply Gas capacities by 0.63

For BTU flow rates assume 1000 BTU/scf Gas or 2500 BTU/scf Propane

For 200 series, we recommend using 0.5" differenetial capacities to ensure long-life performance

Diaphragm Meters:- 0-100 psi - 1-10,000 scf/hr- Diaphragm meter sizing is done

empirically. The parts have been proven to last with a 2” W.C. differential, and the factory will run a test increasing the flowrate until that differential pressure is achieved. The flow rate is recorded to that product spec’ sheet.

- Diaphragm meters use a spud and nut connection allowing removal without piping modifications and are typically sold with connections to pipe to NPT.

1” MNPT

20 LT(light) connectionHand Hole Cover

Index

Top Cover

Meter Body

Plug Seal

Front Cover

Meter Spud

Nut

Gasket

X 2 = Meter Connection Set

Dust Cap(for shipping)

Diaphragm Meters:-Typically Temperature-Compensated-Options include low frequency pulsers for remote reading, high frequency pulsers for laboratory applications, high res. indexes, pressure taps and AMR-Meters with 5-25 psi MAOP are hung from the piping ( leave room to disconnect below)-Meters with 100 psi rating come with FNPT threads and are set on the ground or a stand. Use a nipple and union to disconnect-Must be installed and transported upright. Rough handling or dropping will affect meter accuracy


Rotary Meters:- 0-175 psi - 30-300,000 scf/hr

High Pressure Rotary Meters:- 0-300/740/1480 psi- 30-16,000,000 scf/hr- Rotary meters are sized by their actual flow rate and indicated in the model name. Ex. 3M is for 3000 acf/hr- Letters come from Roman Numerals C=100, M=1,000- Sizing meters is done mathematically, converting the standard flowrate requirement ( in scf/hr, BTU/hr, GJ/day etc. ) to an actual volume flow rate

Rotary Meters:-Rotary Meters have a variety of index configurations which are interchangeable on each meter body: They can be fitted with metric or imperial, temperature-compensated or not (standard counter), or with an instrument drive, as well as electronic indexes that can correct for temperature only, or pressure temperature and super-compressibility-Mechanical indexes can be fitted with low frequency pulsers from remote read (non M.C. applications), high frequency pulsers, or instruments capable of a variety of output formats

Meter BodyIndexT.C. Module

Sight Glass Sight Glass

Meter Instruments:-Can be placed on diaphragm, rotary, or turbine meters (with instrument drive)-Correct for temperature only, pressure and temperature, or pressure temperature and super-compressibility-Feature rich: many configurable parameters, pulse output, optional 4-20 mA, MODBUS, modems, etc.

Display:-Corrected Volume-Uncorrected Volume-Pressure-Temperature-Factors-Programmable

Mechanical Index

Regulations:

- Depending on application and location, many different regulations can come into place. The Electricity and Gas Inspection Act, Measurement Canada, Boilers Branches (ABSA), Local Building Codes, ASTM, ASME, and others can have a say in what is required

- -Many, but not all, meters do have CRN numbers, MTRs and other certificates. If there are any specific documentation or certification requirements, it is important to collect that information upfront because it will limit the applicable options. If certifications are not available for a product, generally speaking manufacturers will not pursue additional certifications for sales less than a million dollars

- Measurement Canada has a large impact on metering Canada. They are responsible for insuring all devices used to sell goods based on a measurement are accurate

Measurement Canada:

- Measurement Canada enforces many laws, acts, requirements, and bulletins. It is the responsibility of the contractor to know and meet all requirements. General Concepts to keep in mind are:

- Any time gas is sold off a meter, or a bill is divided using meters, that meter must be sealed under Measurement Canada

- To sell gas using a meter, the meter owner must be registered with Measurement Canada and obtain a contractor registration number. When meters are sealed they are issued a certificate which detail meter information, test results, and seal period. The meter owner ( contractor ) is responsible for insuring all the criteria within the Electricity and Gas Inspection Act are met, including that meters are re-verified after their seal period has expired

Measurement Canada:

- General Concepts to keep in mind :

- Meter readings must account for:- Pressure

-Fixed Factors are allowed for low pressure (.25 psi) sets-Fixed Factors are allowed at higher pressure with use of a PFM ( Pressure Factor Metering)

approved regulator. These regulators are subject to scheduled testing-Approved Instruments can measure and correct for live pressure conditions

-Temperature:-Mechanical T.C. tangents, or T.C. Indexes on meters may correct for temperature-Approved Instruments can measure and correct for live temperature conditions

Super Compressibility: -Approved Instruments can measure and correct for live pressure, temperature, and super

compressibility conditions if provided information on gas composition

Design Considerations:

- As Gas flows down pipe pressure decreases. Increasing pressure or pipe diameter can insure that adequate supply reaches equipment. Typically residential gas will be at .25 psi, and commercial gas at higher pressures such as 2, 5, or 10 psi is more common

-Meters and regulators may be installed indoors or outside. Installing equipment outside facilitates meter change outs much easier and allows regulator vents to perform unrestricted. If regulators are placed inside, the relief must be vented outside – keep the pipe for this system as large and as short as practical – keeping regulators near the building exterior will help with this. Using unions on the relief line at the regulator end will facilitate servicing and trouble shooting the regulator

-Certain equipment such as large boilers has large and instantaneous demand. It can be challenging for regulators to keep up with certain equipment demands. Adding volume between the regulator and the equipment through oversized pipes or dead end tees, external sense, or upgrading regulators can help with this

Design Considerations:

-Design must be compliant with local codes, but there are many excellent resources online such as www.EngineeringToolbox.com which has a variety of material such as capacities of pipe on low pressure gas lines.

Assumptions:

-pressure less than 1.5 psi

-common to use fittings factor 1.5 -

equivalent pipe length in table above =

pipe length + 50%

-pressure drop 0.5 inches water column

-specific gravity of natural gas 0.6

-energy content in natural gas 1000

Btu/ft3 (37.26 MJ/m3)

http://www.engineeringtoolbox.com/


Presented for informational purposes only, Barchard Engineering does not assume any liability for use of information, consult appropriate sources where required

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