The other losses, namely, items 2, 5 and 8 of the first classification, are ordinarily grouped under one item, as unaccounted for losses, and are obviously the difference between 100 per cent and the sum of the heat utilized and the losses accounted for as given above. Item 5, or the loss due to the moisture in the air, may be readily computed, the moisture being determined from wet and dry bulb thermometer readings, but it is usually disregarded as it is relatively small, averaging, [Pg 262] say, one-fifth to one-half of one per cent. Lack of data may, of course, make it necessary to include certain items of the second and ordinary classification in this unaccounted for group.
A schedule of the losses as outlined, requires an evaporative test of the boiler, an analysis of the flue gases, an ultimate analysis of the fuel, and either an ultimate or proximate analysis of the ash. As the amount of unaccounted for losses forms a basis on which to judge the accuracy of a test, such a schedule is called a “heat balance”.
A heat balance is best illustrated by an example: Assume the data as given in [Table 57] to be secured in an actual boiler test.
From this data the factor of evaporation is 1.1514 and the evaporation per hour from and at 212 degrees is 65,671 pounds. Hence the evaporation from and at 212 degrees per pound of dry coal is 65,671 ÷ 5609 = 11.71 pounds. The efficiency of boiler, furnace and grate is:
| ( | 11.71 | × | 970.4 | ) | ÷ | 14,225 | = | 79.88 per cent. |
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The heat losses are:
(A) Loss due to moisture in coal,
| = | .01831 | ( | (212 - 81) | + | 970.4 | + | .47 (480 - 212) | ) |
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(B) The loss due to the burning of hydrogen:
| = | 9 | × | .0560 | ( | (212 - 81) | + | 970.4 | + | .47 (480 - 212) | ) |
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