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LPG Data

Definitions and Technical Data
for LPG, Natural Gas and LPG/Air Mixtures


The following definitions, conversion factors, tables, and other information for and about propane, butane and propane/butane mixtures are compiled from commonly available sources and are reproduced for convenience only. While we exercised great caution during the compilation, we can not guarantee accuracy and urge everybody to verify the correctness of the data before using them. Also, we appreciate if you alert us of any errors you find.

   
Page Index
  
 
Definitions  
   
Miscellaneous Tables  
Standby Plant Sizing Chart

Cost Savings through Standby Plants

Download these tables as PDF File

   
 

THEORETICAL COMPATIBLE PROPANE/AIR MIXTURES

The table below shows Propane/Air mixtures, compatible with natural gas with several different specific gravities and calorific values.
All figures are approximate and are given for Propane with specific gravity of 1.53 and calorific value of 2516 BTU/cuft.
  

Natural Gas

Propane / Air Mixture

SGU

BTU/cuft

% LPG

% Air

SGU

BTU/cuft

0.56

800

47.54

52.46

1.252

1196

850

50.87

49.13

1.270

1280

900

54.24

45.76

1.287

1365

950

57.65

42.35

1.306

1450

1000

61.11

38.89

1.324

1538

1050

64.62

35.38

1.342

1626

1100

68.16

31.84

1.361

1715

1150

71.76

28.24

1.380

1805

1200

75.40

24.60

1.400

1897

0.58

800

46.62

53.38

1.247

1173

850

49.88

50.12

1.264

1254

900

53.18

46.82

1.282

1338

950

56.52

43.48

1.300

1422

1000

59.90

40.10

1.317

1507

1050

63.33

36.67

1.336

1593

1100

66.80

33.20

1.354

1681

1150

70.32

29.68

1.373

1769

1200

73.88

26.12

1.392

1859

0.60

800

45.76

54.24

1.243

1151

850

48.95

51.05

1.259

1232

900

52.18

47.82

1.276

1313

950

55.45

44.55

1.294

1395

1000

58.76

41.24

1.311

1478

1050

62.12

37.88

1.329

1563

1100

65.51

34.49

1.347

1648

1150

68.95

31.05

1.365

1735

1200

72.43

27.57

1.384

1822

 

Natural Gas

Propane / Air Mixture

SGU

BTU/cuft

% LPG

% Air

SGU

BTU/cuft

0.62

800

44.93

55.07

1.238

1130

850

48.06

51.94

1.255

1209

900

51.23

48.77

1.272

1289

950

54.43

45.57

1.288

1369

1000

57.68

42.32

1.306

1451

1050

60.97

39.03

1.323

1534

1100

64.29

35.71

1.341

1618

1150

67.66

32.34

1.359

1702

1200

71.07

28.93

1.377

1788

0.64

800

44.15

55.85

1.234

1111

850

47.22

52.78

1.250

1188

900

50.32

49.68

1.267

1266

950

53.47

46.53

1.283

1345

1000

56.65

43.35

1.300

1425

1050

59.87

40.13

1.317

1506

1100

63.13

36.87

1.335

1588

1150

66.44

33.56

1.352

1672

1200

69.78

30.22

1.370

1756

0.66

800

43.41

56.59

1.230

1092

850

46.42

53.58

1.246

1168

900

49.47

50.53

1.262

1245

950

52.55

47.45

1.262

1322

1000

55.68

44.32

1.295

1401

1050

58.84

41.16

1.312

1480

1100

62.04

37.96

1.329

1561

1150

65.27

34.73

1.346

1642

1200

68.55

31.45

1.363

1725

   
Properties of

Natural Gas

Propane

Butane

Chemical formula   

CH4

C3H8

C4H10

Boiling point of liquid at atmospheric pressure

F
C

-259
-162

-44
-42

32
0

Specific Gravity of vapor (Air = 1)   

0.6

1.53

2.00

Specific Gravity of liquid (Water = 1)   

0.6

0.51

0.58

Calorific value @ 60F (15C)

BTU/cuft
kcal/m
MJ/m

1012
9005
37.71

2516
22,390
93.74

3280
29,189
122.21

BTU/gal
kcal/liter
MJ/liter

  

91,690
6,103
25.56

102,032
6,792
28.44

BTU/lb
kcal/kg
MJ/kg

  

21,591
11,995
50.22

21,221
11,789
49.36

Latent heat of vaporization

BTU/gal
kcal/kg
MJ/kg
kW/kg

   

785
102.9
0.431
0.1196

808
105.9
0.444
0.1231

Liquid weight

lbs/gal
kg/liter

 

4.24
0.508

4.81
0.576

Vapor volume from 1 gallon of liquid at 60F
Vapor volume from 1 liter of liquid at 15C

cuft
m

  

36.39
0.272

31.26
0.234

Vapor volume from 1 lb. of liquid at 60F
Vapor volume from 1 kg of liquid at 15C

cuft
m

  

8.547
0.534

6.506
0.406

Combustible limits

% of gas in air

5 - 15

2.4 - 9.6

1.9 - 8.6

Amount of air required to burn 1 cuft. of gas
Amount of air required to burn 1 m3 of gas

cuft
m

9.53

23.86

31.02

Ignition temperature in air

F
C

1200
650

920 - 1020
490 -   550

900 - 1000
480 -   540

Maximum flame temperature in air

F
C

3568
1964

3595
1980

3615
1991

Octane Number   

100

Over 100

92

All data is approximate. For actual properties of any particular batch, contact your fuel supplier.

   

Approximate Vapor Pressure in psig

Temperature

Propane    ---->    To    ---->    Butane

F

C

100%

95/
5*

80/
20

70/
30

60/
40

50/
50

40/
60

30/
70

20/
80

100%

-40

-40.0

1.5 1.4 1.2 1.1 0.9 0.8 0.6 0.5 0.3  

-30

-34.4

5.6 5.3 4.5 3.9 3.4 2.2\8 2.2 1.7 1.1  

-20

-28.9

10.7 10.2 8.6 7.5 6.4 5.4 4.3 3.2 2.1  

-10

-23.3

16.7 15.9 13.4 11.7 10.0 8.4 6.7 5.0 3.3  

0

-17.8

23.5 22.3 18.8 16.5 14.1 11.8 9.4 7.1 4.7  

10

-12.2

31.3 29.7 25.0 21.9 18.8 15.7 12.5 9.4 6.3  

20

-6.7

40.8 38.8 32.6 28.6 24.5 20.4 16.3 12.2 8.2  

30

-1.1

51.6 49.0 41.3 36.1 31.0 25.8 20.6 15.5 10.3  

40

4.4

63.3 60.3 51.2 45.2 39.2 33.2 27.1 21.1 15.1 3.0

50

10.0

77.1 73.6 63.1 56.0 49.0 42.0 35.0 28.0 20.9 6.9

60

15.6

92.4 88.4 76.2 68.2 60.1 52.0 43.9 35.8 27.8 11.6

70

21.1

109 105 90.8 81.6 72.3 63.1 53.9 44.6 35.4 16.9

80

26.7

128 123 107 96.5 86.0 75.5 65.0 45.5 43.9 22.9

90

32.2

149 143 125 113 101 89.4 77.5 65.6 53.6 29.8

100

37.8

172 165 145 132 118 105 91.3 77.9 64.4 37.5

110

43.3

197 189 167 152 137 122 106 91.4 76.3 46.1

* HD5, Commercial Grade Propane

  

Temperature Conversion Table

F

C

 

C

F

- 50

- 45.6

- 50

- 58

- 40

- 40.0

- 40

- 40

- 30

- 34.1

- 30

- 22

- 20

- 28.9

- 20

- 4

- 10

- 23.3

- 10

14

0

- 17.8

0

32

+ 10

- 12.2

+ 10

50

20

- 6.7

20

68

30

- 1.1

30

86

32

0

35

95

40

+ 4.4

40

104

50

10.0

50

122

60

15.6

60

140

70

21.1

70

158

80

26.7

80

176

90

32.2

90

194

100

37.8

100

212

110

43.3

110

230

120

48.9

120

248

130

54.4

130

266

140

60.0

140

284

150

65.6

150

302

160

71.1

160

320

170

76.7

170

338

180

82.2

180

356

190

87.8

190

374

200

93.3

200

392

212

100

210

410
Formula:

Degrees C = (F - 32) x 5/9
Degrees F = 1.8 x C + 32
  

BTU content of common fuels

   

Per Pound

Per Gallon

Propane

21,591

91,690

Butane

21,221

102,032

Gasoline

20,930

110,250

Fuel Oil #1

16,960

135,425

Diesel

18,500

142,800

Butane Equivalents

Unit 

BTU

Pound

Therm

Dekatherm

Cuft.

Gallon

1 Pound =

21,221

1

0.212

0.0212

6.50

0.208

1 Therm =

100,000

4.714

1

0.1

30.64

0.98

1 Dekatherm =

1,000,000

47.14

10

1

306.4

9.8

1 Cuft. =

3,280

0.1537

0.032

0.0032

1

0.03199

1 Gallon =

102,032

4.81

1.02

0.1020

31.26

1

          

General Information

1 Lb. Steam

970 BTU

1 Boiler HP (per hr)

33,475 BTU

1 Kilowatt Hour

3,412 BTU

1 Gallon, Water

8.337 lbs

1 Cubic Foot, Water

7.481 gallons

1 Cubic Foot

1,728 cubic inches

1 Gallon

231 cubic inches

Propane Equivalents

Unit

BTU

Pound

Therm

Dekatherm

Cuft.

Gallon

1 Pound =

21,591

1

0.216

0.0216

8.58

0.239

1 Therm =

100,000

4.622

1

0.1

39.7

1.10

1 Dekatherm =

1,000,000

46.22

10

1

397

11.0

1 Cuft. =

2,516

0.1164

0.025

0.0025

1

0.027

1 Gallon =

91,690

4.24

0.917

0.0917

36.39

1

   

Specific Gravity and Heat Content by Volume of LP Gas-Air Mixtures

Propane - Air Mixtures

% Propane

%
Air

Specific
Gravity

Gross BTU/cuft

100

0

1.530

2516

95

5

1.504

2390

90

10

1.477

2264

85

15

1.451

2139

80

20

1.424

2013

75

25

1.398

1887

70

30

1.371

1761

65

35

1.345

1635

60

40

1.318

1510

59

41

1.313

1484

58

42

1.307

1459

57

43

1.302

1434

56

44

1.297

1409

55

45

1.292

1384

54

46

1.286

1359

53

47

1.281

1333

52

48

1.276

1308

51

49

1.270

1283

50

50

1.265

1258

49

51

1.260

1233

48

52

1.254

1208

47

53

1.249

1183

46

54

1.244

1157

45

55

1.239

1132

40

60

1.212

1006

35

65

1.186

881

30

70

1.159

755

25

75

1.133

629

20

80

1.106

503

15

85

1.080

377

10

90

1.053

252

5

95

1.027

126

0

100

1.000

0

 

Butane - Air Mixtures

% Butane

%
Air

Specific
Gravity

Gross BTU/cuft

100

0

2.000

3280

95

5

1.950

3116

90

10

1.900

2952

85

15

1.850

2788

80

20

1.800

2624

75

25

1.750

2460

70

30

1.700

2296

65

35

1.650

2132

60

40

1.600

1968

59

41

1.590

1935

58

42

1.580

1902

57

43

1.570

1870

56

44

1.560

1837

55

45

1.550

1804

54

46

1.540

1770

53

47

1.530

1738

52

48

1.520

1706

51

49

1.510

1672

50

50

1.500

1640

49

51

1.490

1607

48

52

1.480

1574

47

53

1.470

1542

46

54

1.460

1509

45

55

1.450

1476

40

60

1.400

1312

35

65

1.350

1148

30

70

1.300

984

25

75

1.250

820

20

80

1.200

656

15

85

1.150

492

10

90

1.100

328

5

95

1.050

164

0

100

1.000

0

 

Propane (30%) Butane (70%)

%
LPG

%
Air

Specific
Gravity

Gross BTU/cuft

100

0

1.859

3051

95

5

1.816

2898

90

10

1.773

2746

85

15

1.730

2593

80

20

1.687

2441

75

25

1.644

2288

70

30

1.601

2136

65

35

1.559

1983

60

40

1.515

1831

59

41

1.507

1800

58

42

1.498

1769

57

43

1.490

1739

56

44

1.481

1709

55

45

1.473

1678

54

46

1.464

1647

53

47

1.455

1617

52

48

1.447

1587

51

49

1.438

1555

50

50

1.430

1525

49

51

1.421

1495

48

52

1.412

1464

47

53

1.404

1434

46

54

1.395

1404

45

55

1.387

1373

40

60

1.344

1220

35

65

1.301

1068

30

70

1.258

915

25

75

1.215

763

20

80

1.172

610

15

85

1.129

458

10

90

1.086

305

5

95

1.043

153

0

100

1.000

0

All data is based on the 
following assumptions:
  Propane Vapor SGU = 1.53
2516 BTU/cuft
 

Butane 
Vapor

SGU = 2.00
3280 BTU/cuft
   

Engineering Units Conversion Factors

Multiply

By

To Obtain
  
Pressure
Atmospheres

atm

1.0332 Kilogram per cm2 [kg/cm2]

atm

14.70 Pounds per squ. inch [psi]

atm

404.189 Inches of Water [inWC]
Inches
of Mercury

inHg

0.4912 Pounds per squ. inch [psi]

inHg

1.134 Feet of Water [ftWC]
Inches
of Water

inWC

0.0361 Pounds per squ. inch [psi]

inWC

0.0735 Inches of Mercury [inHg]

inWC

0.5776 Ounces per square inch
Kilo Pascals

kPa

0.01 bar
kg per cm2

kg/cm2

14.22 Pounds per squ. inch [psi]
Pounds per square inch

psi

0.06805 Atmospheres [atm]

psi

0.07031 Kilogram per cm2 [kg/cm2]

psi

6.8948 kPa

psi

0.06895 bar

psi

2.036 Inches of Mercury [inHg]

psi

27.68 Inches of Water [inWC]

Length
Centimeters

cm

0.3937 Inches [in]
Feet

ft

0.3048 Meters [m]
Feet

ft

30.48 Centimeters [cm]
Feet

ft

304.8 Millimeters [mm]
Inches

in

2.54 Centimeters [cm]
Inches

in

25.4 Millimeters [mm]
Kilometers

km

0.6214 Miles [mi]
Meters

m

1.094 Yards [yd]
Meters

m

3.281 Feet [ft]
Meters

m

39.37 Inches [in]
Miles, nautical

NM

1853.0 Meters [m]
Miles, statute

SM

1609.0 Meters [m]
Miles, statute

SM

5280 Feet [ft]
Miles, statute

SM

63360 Inches [in]
Multiply

By

To Obtain

Length (continued)
Yards

yd

0.9144 Meters
Yards

yd

91.44 Centimeters
  
Volume
Cubic centimeter

cm3

0.061023 Cubic inches [in]
Cubic feet

cuft

7.48 Gallons (US) [gal]
Cubic feet

cuft

28.316 Liters [l]
Cubic feet

cuft

1728 Cubic inches [in]
Cubic feet

cuft

0.037037 Cubic yards [yd]
Cubic feet

cuft

0.028316 Cubic meters [m]
Gallons (UK)

gal

1.20095 Gallons (US) [gal]
Gallons (US)

gal

0.13368 Cubic feet [ft]
Gallons (US)

gal

0.83267 Gallons (Imperial)
Gallons (US)

gal

3.785 Liters [l]
Gallons (US)

gal

231 Cubic inches [in]
Liters

l

0.03531 Cubic feet [ft]
Liters

l

0.2642 Gallons (US)
Liters

l

1.057 Quarts (US)
Liters

l

2.113 Pints (US)
Pints (US)

pnt

0.4732 Liters

Miscellaneous
BTU

BTU

252.0 Calories [cal]
Calories

kcal

3.968 BTU
Kilogram

kg

2.205 Pounds [lbs]
Kilowatt Hour

kWh

3412 BTU
Ounces

oz

28.35 Grams [g]
Pounds

lb

0.4536 Kilograms [kg]
Pounds

lb

453.5924 Grams (metric) [g]
Pounds

lb

21600 Propane BTU
 
   

Definitions

Several characteristics affect Liquefied Petroleum Gas (LPG) as a replacement fuel. These include:
  1. Flame Velocity and Color
  2. Specific Gravity
  3. Calorific Value
  4. BTU Measurement (Wobbe Index)

1. Flame Velocity and Color

Because of the different number of carbon atoms in propane, propane-air mixtures produce a flame that is more yellow in color than that of natural gas. However, the yellow tips are not of any consequence and do not affect burner operation or efficiency. Flame velocities of LPG are near equal to that of natural gas. Therefore, there is no significant flame lift difference between natural gas and propane-air mixtures.

2. Specific Gravity

The density of gas, relative to air, is called specific gravity. The specific gravity of air is defined as 1. Since propane gas has a specific gravity of 1.5, propane-air mixtures have a specific gravity of greater than 1. The chart on the right indicates heat value in BTU per cubic foot, kcal per cubic meter, and the specific gravities of various propane-air mixtures.

Propane - Air Mixtures

BTU/cuft
Kcal/Nm3

% Propane
by Volume

% Air
by Volume

% Oxygen
by Volume

Specific Gravity
of Mixture

Wobbe Index
US Units
SI Units

1700
15,130

66.67

33.33

6.694

1.349

1464
13,027

1650
14,685

64.70

35.30

7.378

1.338

1426
12,695

1600
14,220

62.74

37.26

7.787

1.328

1388
12,340

1550
13,795

60.78

39.22

8.197

1.318

1350
12,016

1500
13,350

58.82

41.18

8.606

1.308

1312
11,673

1450
12,950

56.86

43.14

9.016

1.297

1275
11,384

1400
12,450

54.90

45.10

9.246

1.287

1234
10,974

1350
12,015

52.94

47.06

9.835

1.277

1195
10,632

1300
11,580

50.98

49.02

10.245

1.267

1155
10,288

1250
11,135

49.02

50.98

10.654

1.257

994
9,932
 

LP - Air Mixtures (LP with 30% Propane / 70% Butane)

BTU/cuft
Kcal/Nm3

% LP Vapor
by Volume

% Air
by Volume

% Oxygen
by Volume

Specific Gravity
of Mixture

Wobbe Index
US Units
SI Units
1800
16018
59.00 41.00 8.588 1.507 1466
13049
1750
15574
57.36 42.64 8.931 1.493 1432
12747
1700
15129
55.72 44.28 9.275 1.479 1398
12441
1650
14684
54.08 45.92 9.618 1.465 1363
12133
1600
14239
52.45 47.55 9.962 1.451 1328
11822
1550
13794
50.81 49.19 10.305 1.436 1293
11509
1500
13349
49.17 50.83 10.648 1.422 1258
11193
1450
12904
47.53 52.47 10.992 1.408 1222
10874
1400
12459
45.88 54.12 11.335 1.394 1186
10552
1350
12014
44.25 55.75 11.678 1.380 1149
10226

Different heat values result primarily from differences in specific gravity. The higher the specific gravity, the heavier the gas. Since burner orifices, flow meters, regulators, etc. have fixed openings, they allow less flow of heavier gas and therefore must have a higher heat value to provide the same energy input as a lighter gas.

Most natural gas has an average heat value of approximately 1050 BTU/cuft (9350 kcal/m) and a specific gravity of 0.6 (nominal). Compatible propane-air replacement should have a heat value of approximately 1450 BTU/cuft (12,467 kcal/m) and a specific gravity of 1.297.


3. CALORIFIC VALUE

The calorific value is the measurement of the amount of heat or energy produced, and is measured either as gross calorific value or net calorific value. The difference being the latent heat of condensation of the water vapor produced during the combustion process. Gross calorific value assumes all water produced during the combustion process is fully condensed. Net calorific value assumes the water leaves with the combustion products without being fully condensed.

Since most gas burning appliances cannot utilize the heat content of the water vapor, gross calorific value is of little interest. Fuel should be compared based on the net calorific value. This is especially true for natural gas, since increased hydrogen content results in high water formation during combustion.


4. WOBBE INDEX

The Wobbe Index, a critical factor when analyzing Propane-Air plant requirements, is a function of gas quality and allows matching one gas (in this case, natural gas) to a replacement gas (in this case, Propane-Air). If the two different gases have an identical Wobbe Index, they will produce an equal amount of heat and combustion products and will require the same amount of combustion air. Burners, adjusted for a specific calorific value and fitted with a replacement orifice to match a lower Wobbe Index, result in minor combustion changes. Substituting a gas for one with a higher Wobbe Index, generally allows a narrow acceptance range. Flame characteristics determine the acceptance range for the replacement gas.

The Wobbe index is defined as:
 
and is used to compare the energy input into an appliance with different composition fuel gases. If two fuels have identical Wobbe indices, then for a given burner pressure, the energy input will also be identical.
   


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