al amount of
excess oxygen in the flue gases is (O - CO/2); hence N - 3.782(O - CO/2)
represents the nitrogen content in the air actually required for
combustion and N / (N - 3.782[O - CO/2]) is the 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:

11 CO_{2} + 8 O + 7 (CO + N)
---------------------------- (16)
3 (CO_{2} + CO)

where CO_{2}, O, CO, and N are the percentages by volume as determined
by the flue gas analysis of carbon dioxide, oxygen, carbon monoxide and
nitrogen.

The weight of flue gas per pound of dry coal will be the weight
determined by this formula multiplied by the percentage of carbon in the
coal from an ultimate analysis.

[Graph: Temperature of Escaping Gases--Deg. Fahr.
against Heat carried away by Chimney Gases--In B.t.u.
per pound of Carbon burned.[31]

Fig. 20. Loss Due to Heat Carried Away by Chimney Gases for Varying
Percentages of Carbon Dioxide. Based on Boiler Room Temperature = 80
Degrees Fahrenheit. Nitrogen in Flue Gas = 80.5 Per Cent. Carbon
Monoxide in Flue Gas = 0. Per Cent]

Fig. 20 represents graphically the loss due to heat carried away by dry
chimney gases for varying percentages of CO_{2}, and different
temperatures of exit gases.

The heat lost, due to the fact that the carbon in the fuel is not
completely burned and carbon monoxide is present in the flue gases, in
B. t. u. per pound of fuel burned is:

( CO )
L' = 10,150 x (-----------) (17)
(CO + CO_{2})

where, as before, CO and CO_{2} are the percentages by volume in the
flue gases and C is the proportion by weight of carbon which is burned
and passes up the stack.

Fig. 21 represents graphically the loss due to such carbon in the fuel
as is not completely burned but escapes up the stack in the form of
carbon monoxide.

[Graph: Loss in B.T.U. per Pound of Carbon Burned[32]
against Per Cent CO_{2} in Flue Gas

Fig. 21. Loss Due to Unconsumed Carbon Contained in the
CO in the Flue Gases]

App