Gas Technology Institute Presentation

8/12/2019 Gas Technology Institute Presentation

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Natural Gas Compositionand Quality

William E. LissDavid M. Rue

Gas Technology Institute


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Panel 1: Current Gas QualityHighlights

> What is natural gas Its chemical composition and properties

What are the variations that occur

> How does California compare withelsewhere

> Key points Wobbe Number is key metric

> Methane Number rarely used in industry

Variations are common

Rule 30 plus NGC + Work Group

> Good foundation for natural gas qualitystandards


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Natural Gas Industry

> Natural gas has anintegrated & highly

efficient energy

delivery system

> Natural gas industry

is interconnected to

crude oil and

natural gas liquids(NGL) marketplace


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Natural Gas Measurement

> Chemical Composition

Hydrocarbonsmainly straight-chain alkanes

> Methane, ethane, propane, butanes+, etc

Inert gasesnitrogen and carbon dioxide

> Physical Properties

Heating Value: Higher (Gross), Lower (Net)

Specific Gravity: Relative density to air

> Natural gas lighter than air Wobbe Number(or Wobbe Index)

Combustion interchangeability

Others...Methane Number, dewpoint


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Wobbe Number

> Wobbe Number (or Wobbe Index) is a keymetric for combustion performance

More meaningful than heating value

WN = Heating Value(Specific Gravity)0.5

Accounts for flow

and heat input

of gas through

an orifice


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What Is Natural Gas?

> Naturally occurringgaseous resource Can also be made

> Natural gas is

mainly methane Typically about 90-95%

by volume

> Balance: Non-methane

hydrocarbons (e.g.,ethane, propane)

Other gases (e.g.,carbon dioxide,nitrogen)

Ethane

3.6%

Propane

0.8%

Butanes+

0.5%

CO2

1.0%

Nitrogen

1.8%

Methane

92.3%

Non-

Methane

7.7%

Non-

Methane

Fraction

Average U.S. Natural Gas

Composition

Source: Gas Technology Institute

Based on survey data

containing 7000 natural gas

samples across 26 US cities


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Regional Natural Gas Composition

Difference Common

AverageNatural Gas Composition -- Twenty Six US Cities(19891992 time period)


Non-Methane Natural Gas Constituents

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

Survey City Number

0

5

10

15

20Non-Methane Constituents (Mole%)

Ethane Propane Butanes+ Inerts

Lean

Gases

Rich

Gases

Rich

gases

often exist

near

producing

areas


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Average US and CA Natural Gas

Composition Similar

Minimum

National

Average

California

Average Maximum

Methane 74.5 93.9 93.1 98.1

Ethane 0.5 3.2 3.4 13.3

Propane 0.0 0.7 0.7 2.6

C4and higher 0.0 0.4 0.3 2.1

N2+ CO2 0.0 2.6 2.5 10.0

Data exclude effect of propane-air peakshaving Source: Gas Technology Institute

National: 26 cities, about 7000 samples

California: 12 locations, about 1200 samples


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Average US & CA Natural Gas

Physical Property Statistics

MinimumNationalAverage

CaliforniaAverage

Maximum

Heating

Value(BTU/scf) 970 1033 1035 1127

SpecificGravity

0.563 0.598 0.599 0.698

WobbeNumber

(BTU/scf)1201 1336 1337 1418

Data exclude effect of propane-air peakshaving Source: Gas Technology Institute


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California Statistics12 Sites, 1226 samples

SITEMETHANE

(Vol.%)

HEATINGVALUE(Btu/scf)

WOBBENUMBER(Btu/scf)

NorthernCaliforniaRegion

1 93.92 1033 1340

2 94.33 995 1301

3 95.53 1017 1326

4 96.64 1011 1336

5 94.94 1026 1340

SouthernCalifornia/SanDiego Region

6 93.10 1039 1341

7 93.73 1028 1335

SouthernCalifornia/LA Region

8 93.60 1030 1335

9 92.25 1040 1335

10 91.19 1048 1337

11 93.48 1029 1333

12 92.34 1042 1340Summary

Average 93.09 1035 1337

Minimum 90.31 986 1290

Maximum 96.88 1060 1358

Lean

Gases

Rich

Gases


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CA In-State ProductionRich Natural Gas

> Select regions in state can have wider gascomposition & properties range

Proximity to associated gas wellsresult in

higher ethane levels

Lack of regional market limits ability to

economically lower ethane

> Ethane removal expensive, energy losses

2001 - 2004 Data #1 #2 #3

Methane 86.9 85.6 84.1

Ethane 9.0 9.55 10.3

Heating Value 1103 1107 1117

Specific Gravity 0.638 0.647 0.661

Wobbe Number 1381 1376 1374


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Methane Number measures Natural Gas

engine knock resistance

- Like Octane Number, but higher than gasoline- Not commonly used in natural gas industry

80

90

100

110

120

130

140

40 50 60 70 80 90 100

Methane Number

MotorOctaneNum

ber


Gasoline

Natural Gas


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Panel 1 SummaryCurrent Gas Quality

> Natural gas composition variations are common inCalifornia, US, and World

Support ample supplies from various sources

In-state producersethane issue

Future sources likely need composition limitleewayLNG, bio-energy, hydrogen

> Wobbe Number best single measure of fuel gas

interchangeability

Other indices can account for secondary combustion

interchangeability considerations

Methane Number not commonly used

Compositional specs should be used with carecan be

overly restrictive


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Panel 1 SummaryCurrent Gas Quality

> Current utility requirements (e.g., Rule 30)provides a very good framework

Already includes main interchangeability

indices

Also speak to pipeline-specific issues

> Ongoing NGC + Work Group developing

consensus industry position on specific

values and ranges Draft recommendations in process

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