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| | | | Common in |
| | | |Proximate &|
| | Proximate | | Ultimate |
| | Analysis | Ultimate Analysis | Analysis |
|--------------------|-----------|--------------------------|-----------|
| | | | V | | | H | | N | | | M |
| | | | o | | | y | | i | S | | o |
| | | | l M | C | C | d | O | t | u | | i |
| S | | | a a | F a | a | r | x | r | l | | s |
| t | | | t t | i r | r | o | y | o | p | | t |
| a | Field | | i t | x b | b | g | g | g | h | A | u |
| t | or | | l e | e o | o | e | e | e | e | s | r |
| e | Bed | Mine | e r | d n | n | n | n | n | r | h | e |
|---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----|
| | |Icy Coal| | | | | | | | | |
| | | & Iron | | | | | | | | | |
| | Horse | Co. | | | | | | | | | |
|Ala| Creek | No. 8 |31.81|53.90|72.02|4.78| 6.45|1.66| .80|14.29| 2.56|
|---|----------------|-----|-----|-----|----|-----|----|----|-----|-----|
| | |Central | | | | | | | | | |
| | |C. & C. | | | | | | | | | |
| | Hunt- | Co. | | | | | | | | | |
|Ark|ington | No. 3 |18.99|67.71|76.37|3.90| 3.71|1.49|1.23|13.30| 1.99|
|---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----|
| | Pana | Clover | | | | | | | | | |
| | or | Leaf, | | | | | | | | | |
|Ill| No. 5 | No. 1 |37.22|45.64|63.04|4.49|10.04|1.28|4.01|17.14|13.19|
|---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----|
| |No. 5, | | | | | | | | | | |
| |Warrick| | | | | | | | | | |
|Ind| Co. |Electric|41.85|44.45|68.08|4.78| 7.56|1.35|4.53|13.70| 9.11|
|---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----|
| |No. 11,| St. | | | | | | | | | |
| |Hopkins|Bernard,| | | | | | | | | |
|Ky | Co. | No. 11 |41.10|49.60|72.22|5.06| 8.44|1.33|3.65| 9.30| 7.76|
|---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----|
| |"B" or | | | | | | | | | | |
| |Lower | | | | | | | | | | |
| |Kittan-| Eureka,| | | | | | | | | |
|Pa | ning | No. 31 |16.71|77.22|84.45|4.25| 3.04|1.28| .91| 6.07| .56|
|---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----|
| |Indiana| | | | | | | | | | |
|Pa | Co. | |29.55|62.64|79.86|5.02| 4.27|1.86|1.18| 7.81| 2.90|
|---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----|
|W. | Fire | Rush | | | | | | | | | |
|Va | Creek | Run |22.87|71.56|83.71|4.64| 3.67|1.70| .71| 5.57| 2.14|
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Table 39 gives for comparison the ultimate and proximate analyses of
certain of the coals with which tests were made in the coal testing
plant of the United States Geological Survey at the Louisiana Purchase
Exposition at St. Louis.
The heating value of a fuel cannot be directly computed from a proximate
analysis, due to the fact that the volatile content varies widely in
different fuels in composition and in heating value.
Some methods have been advanced for estimating the calorific value of
coals from the proximate analysis. William Kent[38] deducted from
Mahler's tests of European coals the approximate heating value dependent
upon the content of fixed carbon in the combustible. The relation as
deduced by Kent between the heat and value per pound of combustible and
the per cent of fixed carbon referred to combustible is represented
graphically by Fig. 23.
Goutal gives another method of determining the heat value from a
proximate analysis, in which the carbon is given a fixed value and the
heating value of the volatile matter is considered as a function of its
percentage referred to combustible. Goutal's method checks closely with
Kent's determinations.
All the formulae, however, for computing the calorific value of coals
from a proximate analysis are ordinarily limited to certain classes of
fuels. Mr. Kent, for instance, states that his deductions are correct
within a close limit for fuels containing more than 60 per cent of fixed
carbon in the combustible, while for those containing a lower
percentage, the error may be as great as 4 per cent, either high or low.
While the use of such computations will serve where approximate results
only are required, that they are approximate should be thoroughly
understood.
Calorimetry--An ultimate or a proximate analysis of a fuel is useful in
determining its general characteristics, and as described on page 183,
may be used in the calculation of the approximate heating value. Where
the efficiency of a boiler is to be computed, however, this heating
value should in all instances be determined accurately by means of a
fuel calorimeter.
[Graph: B.T.U. per Pound of Combustible
against Per Cent of Fixed Carbon in Combustible
Fig. 23. Graphic Representation of Relation between Heat Value Per Pound
of Combustible and Fixed Carbon in Combustible as Deduced by Wm. Kent.]
In such an apparatus the fuel is completely burned and the heat
generated by such combustion is absorbed by water, the amount of heat
being calculated from the elevation in the temperature of the water. A
calorimeter which has been accepted as the best for such work is one in
which the fuel is burned in a steel bomb filled with compressed oxygen.
The function of the oxygen, which is ordinarily under a pressure of
about 25 atmospheres, is to cause the rapid and complete combustion of
the fuel sample. The fuel is ignited by means of an electric current,
allowance being made for the heat produced by such current, and by the
burning of the fuse wire.
A calorimeter of this type which will be found to give satisfactory
results is that of M. Pierre Mahler, illustrated in Fig. 24 and
consisting of the following parts:
A water jacket A, which maintains constant conditions outside of the
calorimeter proper, and thus makes possible a more accurate computation
of radiation losses.
The porcelain lined steel bomb B, in which the combustion of the fuel
takes place in compressed oxygen.
[Illustration: Fig. 24. Mahler Bomb Calorimeter]
The platinum pan C, for holding the fuel.
The calorimeter proper D, surrounding the bomb and containing a definite
weighed amount of water.
An electrode E, connecting with the fuse wire F, for igniting the fuel
placed in the pan C.
A support G, for a water agitator.
A thermometer I, for temperature determination of the water in the
calorimeter. The thermometer is best supported by a stand independent of
the calorimeter, so that it may not be moved by tremors in the parts of
the calorimeter, which would render the making of readings difficult. To
obtain accuracy of readings, they should be made through a telescope or
eyeglass.
A spring and screw device for revolving the agitator.
A lever L, by the movement of which the agitator is revolved.
A pressure gauge M, for noting the amount of oxygen admitted to the
bomb. Between 20 and 25 atmospheres are ordinarily employed.
An oxygen tank O.
A battery or batteries P, the current from which heats the fuse wire
used to ignite the fuel.
This or a similar calorimeter is used in the determination of the heat
of combustion of solid or liquid fuels. Whatever the fuel to be tested,
too much importance cannot be given to the securing of an average
sample. Where coal is to be tested, tests should be made from a portion
of the dried and pulverized laboratory sample, the methods of obtaining
which have been described. In considering the methods of calorimeter
determination, the remarks applied to coal are equally applicable to any
solid fuel, and such changes in methods as are necessary for liquid
fuels will be self-evident from the same description.
Approximately one gram of the pulverized dried coal sample should be
placed directly in the pan of the calorimeter. There is some danger in
the using of a pulverized sample from the fact that some of it may be
blown out of the pan when oxygen is admitted. This may be at least
partially overcome by forming about two grams into a briquette by the
use of a cylinder equipped with a plunger and a screw press. Such a
briquette should be broken and approximately one gram used. If a
pulverized sample is used, care should be taken to admit oxygen slowly
to prevent blowing the coal out of the pan. The weight of the sample is
limited to approximately one gram since the calorimeter is proportioned
for the combustion of about this weight when under an oxygen pressure of
about 25 atmospheres.
A piece of fine iron wire is connected to the lower end of the plunger
to form a fuse for igniting the sample. The weight of iron wire used is
determined, and if after combustion a portion has not been burned, the
weight of such portion is determined. In placing the sample in the pan,
and in adjusting the fuse, the top of the calorimeter is removed. It is
then replaced and carefully screwed into place on the bomb by means of a
long handled wrench furnished for the purpose.
The bomb is then placed in the calorimeter, which has been filled with a
definite amount of water. This weight is the "water equivalent" of the
apparatus, _i. e._, the weight of water, the temperature of which would
be increased one degree for an equivalent increase in the temperature of
the combined apparatus. It may be determined by calculation from the
weights and specific heats of the various parts of the apparatus. Such a
determination is liable to error, however, as the weight of the bomb
lining can only be approximated, and a considerable portion of the
apparatus is not submerged. Another method of making such a
determination is by the adding of definite weights of warm water to
definite amounts of cooler water in the calorimeter and taking an
average of a number of experiments. The best method for the making of
such a determination is probably the burning of a definite amount of
resublimed naphthaline whose heat of combustion is known.
The temperature of the water in the water jacket of the calorimeter
should be approximately that of the surrounding atmosphere. The
temperature of the weighed amount of water in the calorimeter is made by
some experimenters slightly greater than that of the surrounding air in
order that the initial correction for radiation will be in the same
direction as the final correction. Other experimenters start from a
temperature the same or slightly lower than the temperature of the room,
on the basis that the temperature after combustion will be slightly
higher than the room temperature and the radiation correction be either
a minimum or entirely eliminated.
While no experiments have been made to show conclusively which of these
methods is the better, the latter is generally used.
After the bomb has been placed in the calorimeter, it is filled with
oxygen from a tank until the pressure reaches from 20 to 25 atmospheres.
The lower pressure will be sufficient in all but exceptional cases.
Connection is then made to a current from the dry batteries in series so
arranged as to allow completion of the circuit with a switch. The
current from a lighting system should not be used for ignition, as there
is danger from sparking in burning the fuse, which may effect the
results. The apparatus is then ready for the test.
Unquestionably the best method of taking data is by the use of
co-ordinate paper and a plotting of the data with temperatures and time
intervals as ordinates and abscissae. Such a graphic representation is
shown in Fig. 25.
[Graph: Temperature--° C. against Time--Hours and Minutes