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Page 9
The fuel used was a smokeless Welsh coal, from the Llangennech
colleries. It was analyzed by Mr. Snelus, of the Dowlais Ironworks,
and in Table II. are exhibited the details of its composition, and the
weight and volume of air required for its combustion. The total heat
of combustion in 1 lb of water evaporated:
= 15.06 � (0.8497 + 4.265 � (0.426 - 0.035/8))
= 15.24 lb. of water from and at 212�
= 14,727 units of heat.
TABLE II.--PROPERTIES OF LLANGENNECH COAL.
---------------------+----------+------------+---------------------+
| | | |
| | | Products of |
| | Oxygen | Combustion at 32� F.|
| Analyses | required +--------+------------+
| of 1 lb. | for | | |
| of Coal. | Combustion.| Cubic | Volume |
| | Pounds. | feet. | per cent. |
---------------------+----------+------------+--------+------------+
Carbon........... | 0.8497 | 2.266 | 25.3 | 11.1 |
Hydrogen......... | 0.0426 | 0.309 | 7.6 | 3.4 |
Oxygen........... | 0.0350 | --- | --- | --- |
Sulphur.......... | 0.0042 | --- | --- | _ --- |
Nitrogen......... | 0.1045 | --- | 0.18 | | |
Ash.............. | 0.0540 | --- | --- | | |
+----------+------------+ | | 85.5 |
| | | | | |
Total........... | 1.0000 | 2.572 | --- | | |
9-1/3.lb nitrogen | --- | --- | 118.9 | | |
6 lb. excess of air. | --- | --- | 71.4 | _| |
+----------+------------+--------+------------+
Total cubic feet of | | | | |
products per 1 lb. | | | | |
of coal........... | -- | -- | 226.4 | 100.0 |
---------------------+----------+------------+--------+------------+
The temperature of the furnace not having been determined, we must
calculate it on the supposition, which will be justified later on,
that 50 per cent more air was admitted than was theoretically
necessary to supply the oxygen required for perfect combustion. This
would make 18 lb. of air per 1 lb. of coal; consequently 19 lb. of
gases would be heated by 14,727 units of heat. Hence:
14,727 u.
T = ---------------- = 3,257�
19 lb. � 0.238
above the temperatures of the air, or 3,777� absolute. The temperature
of the smoke, _t_, was 849� absolute; hence the maximum duty would be
3,777� - 849�
--------------- = 0.7752.
3,777�
The specific heat of coal is very nearly that of gases at constant
pressure, and may, without sensible error, be taken as such. The
potential energy of 1 lb. of coal, therefore, with reference to the
oxygen with which it will combine, and calculated from absolute zero,
is:
Units.
19 lb. of coal and air at the temperature
of the air contained 19 lb. � 520� � 0.238 2,350
Heat of combustion 14,727
-------
17,078
Deduct heat expended in displacing atmosphere 151 cubic feet - 422
------
Total potential energy 16,656
Hence work to be expected from the boiler:
/ 3,777� - 849� \
= 17,078 units X ( --------------- ) - 422 units
\ 3,777� /
---------------------------------------------- = 13.27 lb.
966 units
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