in which the letters have the same significance as in formulae ( [11] ) and ( [12] ).
The ratio of the air supplied per pound of combustible to the amount theoretically required is:
| ( 14 ) |
which is derived as follows:
The N in the flue gas is the content of nitrogen in the whole amount of air supplied. The oxygen in the flue gas is that contained in the air supplied and which was not utilized in combustion. This oxygen was accompanied by 3.782 times its volume of nitrogen. The total amount of excess oxygen in the flue gases is (O - ½CO); hence N - 3.782(O - ½CO) represents the nitrogen content in the air actually required for combustion and N ÷ (N - 3.782[O - ½CO]) is the [Pg 158] ratio of the air supplied to that required. This ratio minus one will be the proportion of excess air.
| The heat lost in the flue gases is L = 0.24 W (T - t ) ( 15 ) | |||
| Where | L | = | B. t. u. lost per pound of fuel, |
| W | = | weight of flue gases in pounds per pound of dry coal, | |
| T | = | temperature of flue gases, | |
| t | = | temperature of atmosphere, | |
| 0.24 | = | specific heat of the flue gases. | |
The weight of flue gases, W, per pound of carbon can be computed directly from the flue gas analysis from the formula: