DATA FROM WHICH HEAT BALANCE
(TABLE 58) IS COMPUTED
+------------------------------------------------------+
|+----------------------------------------------------+|
||Steam Pressure by Gauge, Pounds | 192 ||
||Temperature of Feed, Degrees Fahrenheit | 180 ||
||Degrees of Superheat, Degrees Fahrenheit |115.2||
||Temperature of Boiler Room, Degrees Fahrenheit| 81 ||
||Temperature of Exit Gases, Degrees Fahrenheit | 480 ||
||Weight of Coal Used per Hour, Pounds | 5714||
||Moisture, Per Cent | 1.83||
||Dry Coal Per Hour, Pounds | 5609||
||Ash and Refuse per Hour, Pounds | 561||
||Ash and Refuse (of Dry Coal), Per Cent |10.00||
||Actual Evaporation per Hour, Pounds |57036||
|| .- C, Per Cent |78.57||
|| | H, Per Cent | 5.60||
||Ultimate | O, Per Cent | 7.02||
||Analysis -+ N, Per Cent | 1.11||
||Dry Coal | Ash, Per Cent | 6.52||
|| '- Sulphur, Per Cent | 1.18||
||Heat Value per Pound Dry Coal, B. t. u. |14225||
||Heat Value per Pound Combustible, B. t. u. |15217||
||Combustible in Ash by Analysis, Per Cent | 17.9||
|| .- CO_{2}, Per Cent |14.33||
||Flue Gas -+ O, Per Cent | 4.54||
||Analysis | CO, Per Cent | 0.11||
|| '- N, Per Cent |81.02||
|+----------------------------------------------+-----+|
+------------------------------------------------------+
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.
The heat losses are:
(A) Loss due to moisture in coal,
= .01831 ((212-81)+970.4+.47(480-212))
= 22. B. t. u.,
= 0.15 per cent.
(B) The loss due to the burning of hydrogen:
= 9×.0560((212-81)+970.4+.47(480-212))
= 618 B. t. u.,
= 4.34 per cent.
(C) To compute the loss in the heat carried away by dry chimney gases
per pound of coal the weight of such gases must be first determined.
This weight per pound of coal is:
(11CO_{2}+8O+7(CO+N))
(-------------------)C
( 3(CO_{2}+CO) )
where CO_{2}, O, CO and H are the percentage by volume as determined by
the flue gas analysis and C is the percentage by weight of carbon in the
dry fuel. Hence the weight of gas per pound of coal will be,
(11×14.33+8×4.54+7(0.11+81.02))
(-----------------------------)×78.57 = 13.7 pounds.
( 3(14.33+0.11) )