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

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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.

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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
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 @ 60°F (15°C) BTU/cuft
kcal/m³
MJ/m³
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 60°F
Vapor volume from 1 liter of liquid at 15°C
cuft
  36.39
0.272
31.26
0.234
Vapor volume from 1 lb. of liquid at 60°F
Vapor volume from 1 kg of liquid at 15°C
cuft
  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 m3of gas
cuft
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 and bar
Temperature Propane    ---->   To   ---->    Butane
upper row is pressure in psig
bottom row is pressure in bar
°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
0.10
1.4
0.10
1.2
0.08
1.1
0.08
0.9
0.06
0.8
0.06
0.6
0.06
0.5
0.03
0.3
0.02
 
-30 -34.4 5.6
0.39
5.3
0.37
4.5
0.31
3.9
0.27
3.4
0.23
2.8
0.19
2.2
0.15
1.7
0.12
1.1
0.08
 
-20 -28.9 10.7
0.74
10.2
0.70
8.6
0.59
7.5
0.52
6.4
0.44
5.4
0.37
4.3
0.30
3.2
0.22
2.1
0.14
 
-10 -23.3 16.7
1.15
15.9
1.10
13.4
0.92
11.7
0.81
10.0
0.69
8.4
0.58
6.7
0.46
5.0
0.34
3.3
0.23
 
0 -17.8 23.5
1.62
22.3
1.54
18.8
1.30
16.5
1.14
14.1
0.97
11.8
0.81
9.4
0.65
7.1
0.49
4.7
0.23
 
10 -12.2 31.3
2.16
29.7
2.05
25.0
1.72
21.9
1.51
18.8
1.30
15.7
1.08
12.5
0.86
9.4
0.65
6.3
0.43
 
20 -6.7 40.8
2.81
38.8
2.68
32.6
2.25
28.6
1.97
24.5
1.69
20.4
1.41
16.3
1.12
12.2
0.84
8.2
0.57
 
30 -1.1 51.6
3.56
49.0
3.38
41.3
2.85
36.1
2.49
31.0
2.14
25.8
1.78
20.6
1.42
15.5
1.07
10.3
0.71
 
40 4.4 63.3
4.36
60.3
4.16
51.2
3.53
45.2
3.12
39.2
2.70
33.2
2.29
27.1
1.87
21.1
1.45
15.1
1.04
3.0
0.21
50 10.0 77.1
5.32
73.6
5.07
63.1
4.35
56.0
3.56
49.0
3.38
42.0
2.90
35.0
2.41
28.0
1.92
20.9
1.44
6.9
0.48
60 15.6 92.4
6.37
88.4
6.09
76.2
5.25
68.2
4.70
60.1
4.14
52.0
3.59
43.9
3.03
35.8
2.47
27.8
1.92
11.6
0.80
70 21.1 109
7.52
105
7.24
90.8
6.26
81.6
5.63
72.3
4.98
63.1
4.35
53.9
3.72
44.6
3.08
35.4
2.44
16.9
1.17
80 26.7 128
8.83
123
8.48
107
7.38
96.5
6.65
86.0
5.93
75.5
5.21
65.0
4.48
45.5
3.14
43.9
3.03
22.9
1.58
90 32.2 149
10.3
143
9.86
125
8.62
113
7.79
101
6.96
89.4
6.16
77.5
5.34
65.6
4.52
53.6
3.70
29.8
2.05
100 37.8 172
11.9
165
11.4
145
10.0
132
9.10
118
8.14
105
7.24
91.3
6.29
77.9
5.37
64.4
4.44
37.5
2.59
110 43.3 197
13.6
189
13.0
167
11.5
152
10.5
137
9.45
122
8.41
106
7.31
91.4
6.30
76.3
5.26
46.1
3.18
*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 SpecificGravity 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 SpecificGravity 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    SGU = 1.53
Vapor      2516 BTU/cuft
  Butane    SGU = 2.00
Vapor     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
Kilopascals 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 [in³]
Cubic feet cuft 7.48 Gallons (US) [gal]
Cubic feet cuft 28.316 Liters [l]
Cubic feet cuft 1728 Cubic inches [in³]
Cubic feet cuft 0.037037 Cubic yards [yd³]
Cubic feet cuft 0.028316 Cubic meters [m³]
Gallons (UK) gal 1.20095 Gallons (US) [gal]
Gallons (US) gal 0.13368 Cubic feet [ft³]
Gallons (US) gal 0.83267 Gallons (Imperial)
Gallons (US) gal 3.785 Liters [l]
Gallons (US) gal 231 Cubic inches [in³]
Liters l 0.03531 Cubic feet [ft³]
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 Liquified Petroleum Gas (LPG) as a   replacement fuel. These include:    
  1. Flame Velocity and Color
  2.      
  3. Specific Gravity
  4.      
  5. Calorific Value
  6.      
  7. BTU Measurement (Wobbe Index)
  8.    
   
  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
    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/m³) 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/m³) 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 eitheras 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:
    Wobbe Formula
    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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