WEIGHT AND CALORIFIC VALUE OF VARIOUS GASES
AT 32 DEGREES FAHRENHEIT AND ATMOSPHERIC PRESSURE
WITH THEORETICAL AMOUNT OF AIR REQUIRED FOR COMBUSTION
+---------------+----------+------+-----+------+----------+-----------+
| Gas | Symbol |Cubic |B.t.u|B.t.u.|Cubic Feet|Cubic Feet |
| | | Feet | per | per | of Air | of Air |
| | |of Gas|Pound|Cubic | Required | Required |
| | | per | | Foot |per Pound | Per Cubic |
| | |Pound | | | of Gas |Foot of Gas|
+---------------+----------+------+-----+------+----------+-----------+
|Hydrogen | H |177.90|62000| 349 | 428.25 | 2.41 |
|Carbon Monoxide| CO | 12.81| 4450| 347 | 30.60 | 2.39 |
|Methane |CH_{4} | 22.37|23550| 1053 | 214.00 | 9.57 |
|Acetylene |C_{2}H_{2}| 13.79|21465| 1556 | 164.87 | 11.93 |
|Olefiant Gas |C_{2}H_{4}| 12.80|21440| 1675 | 183.60 | 14.33 |
|Ethane |C_{2}H_{6}| 11.94|22230| 1862 | 199.88 | 16.74 |
+---------------+----------+------+-----+------+----------+-----------+
In applying this table, as gas analyses may be reported either by weight
or volume, there is given in Table 33[36] a method of changing from
volumetric analysis to analysis by weight.
Examples:
1st. Assume a blast furnace gas, the analysis of which in percentages by
weight is, oxygen = 2.7, carbon monoxide = 19.5, carbon dioxide = 18.7,
nitrogen = 59.1. Here the only combustible gas is the carbon monoxide,
and the heat value will be,
0.195 × 4450 = 867.75 B. t. u. per pound.
The _net_ volume of air required to burn one pound of this gas will be,
0.195 × 30.6 = 5.967 cubic feet.
2nd. Assume a natural gas, the analysis of which in percentages by
volume is oxygen = 0.40, carbon monoxide = 0.95, carbon dioxide = 0.34,
olefiant gas (C_{2}H_{4}) = 0.66, ethane (C_{2}H_{6}) = 3.55, marsh gas
(CH_{4}) = 72.15 and hydrogen = 21.95. All but the oxygen and the carbon
dioxide are combustibles, and the heat per cubic foot will be,
From CO = 0.0095 × 347 = 3.30
C_{2}H_{4} = 0.0066 × 1675 = 11.05
C_{2}H_{6} = 0.0355 × 1862 = 66.10
CH_{4} = 0.7215 × 1050 = 757.58
H = 0.2195 × 349 = 76.61
------
B. t. u. per cubic foot 914.64
The _net_ air required for combustion of one cubic foot of the gas will
be,
CO = 0.0095 × 2.39 = 0.02
C_{2}H_{4} = 0.0066 × 14.33 = 0.09
C_{2}H_{6} = 0.0355 × 16.74 = 0.59
CH_{4} = 0.7215 × 9.57 = 6.90
H = 0.2195 × 2.41 = 0.53
----
Total net air per cubic foot 8.13
Proximate Analysis--The proximate analysis of a fuel gives its
proportions by weight of fixed carbon, volatile combustible matter,
moisture and ash. A method of making such an analysis which has been
found to give eminently satisfactory results is described below.
From the coal sample obtained on the boiler trial, an average sample of
approximately 40 grams is broken up and weighed. A good means of
reducing such a sample is passing it through an ordinary coffee mill.
This sample should be placed in a double-walled air bath, which should
be kept at an approximately constant temperature of 105 degrees
centigrade, the sample being weighed at intervals until a minimum is
reached. The percentage of moisture can be calculated from the loss in
such a drying.
For the determination of the remainder of the analysis, and the heating
value of the fuel, a portion of this dried sample should be thoroughly
pulverized, and if it is to be kept, should be placed in an air-tight
receptacle. One gram of the pulverized sample should be weighed into a
porcelain crucible equipped with a well fitting lid. This crucible
should be supported on a platinum triangle and heated for seven minutes
over the full flame of a Bunsen burner. At the end of such time the
sample should be placed in a desiccator containing calcium chloride, and
when cooled should be weighed. From the loss the percentage of volatile
combustible matter may be readily calculated.
The same sample from which the volatile matter has been driven should be
used in the determination of the percentage of ash. This percentage is
obtained by burning the fixed carbon over a Bunsen burner or in a muffle
furnace. The burning should be kept up until a constant weight is
secured, and it may be assisted by stirring with a platinum rod. The
weight of the residue determines the percentage of ash, and the
percentage of fixed carbon is easily calculated from the loss during the
determination of ash after the volatile matter has been driven off.
Proximate analyses may be made and reported on a moist or dry basis. The
dry basis is that ordinarily accepted, and this is the basis adopted
throughout this book. The method of converting from a moist to a dry
basis is the same as described in the case of an ultimate analysis. A
proximate analysis is easily made, gives information as to the general
characteristics of a fuel and of its _relative_ heating value.
Table 38 gives the proximate analysis and calorific value of a number of
representative coals found in the United States.