Part 19 (1/2)

153 2 = 306 cubic feet of air per pound of carbon

_Actual Volume_ _for One Pound Carbon_ _Per Cent_ _Cubic Feet_ _by Voluen 32 = 1045 } = 2091 per cent Nitrogen 242 = 7909 --- ------ 306 = 10000

In each case the voluen which combines with the carbon is equal to (cubic feet of air 2091 per cent)--32 cubic feet

It will be seen that no matter what the excess of air supplied, the actual amount of carbon dioxide per pound of carbon ree by volume decreases as the excess of air increases

The actual volue by volue of oxygen is, therefore, an indication of the aes of CO_{2} and O is the saen increases with the excess of air, its percentage by volue while coe for any amount of air excess, therefore, will be the same after combustion as before, if cooled to the same temperature It must be borne in mind that the above conditions hold only for the perfect combustion of a pound of pure carbon

Carbon monoxide (CO) produced by the imperfect coen entering into its coases over that of the air supplied for combustion in the proportion of

100 + the per cent CO 1 to ----------------------- 100

When pure carbon is the fuel, the suen and one-half of the carbon en in the flue gases as is the oxygen to the nitrogen in the air supplied, that is, 2091 to 7909 When burning coal, however, the percentage of nitrogen is obtained by subtracting the suases from 100 Thus if an analysis shows 125 per cent CO_{2}, 65 per cent O, and 06 per cent CO, the percentage of nitrogen which ordinarily is the only other constituent of the gas which need be considered, is found as follows:

100 - (125 + 65 + 06) = 804 per cent

The action of the hydrogen in the volatile constituents of the fuel is to increase the apparent percentage of the nitrogen in the flue gases

This is due to the fact that the water vapor foren will condense at a teen which accoinally coaseous forases For this reason coals containing high percentages of volatile er quantity of water vapor, and thus increase the apparent percentage of nitrogen

Air Required and Supplied--When the ultimate analysis of a fuel is known, the air required for complete combustion with no excess can be found as shown in the chapter on co approximate formula:

Pounds of air required per pound of fuel =

(C O S) 3456 (- + (H - -) + -)[29] (11) (3 8 8)

where C, H and O equal the percentage by weight of carbon, hydrogen and oxygen in the fuel divided by 100

When the flue gas analysis is known, the total, amount of air supplied is:

Pounds of air supplied per pound of fuel =

N 3036 (-----------) C[30] (12) CO_{2} + CO

where N, CO_{2} and CO are the percentages by voluen, carbon dioxide and carbon ht of carbon which is burned froas This percentage of C which is burned e of C as found by an ultie of C which is burned, deduct froe of carbon as found in the ultie of unconsumed carbon found in the ash This latter quantity is the difference between the percentage of ash found by an analysis and that as determined by a boiler test It is usually assumed that the entire combustible element in the ash is carbon, which assumption is practically correct Thus if the ash in a boiler test were 16 per cent and by an analysis contained 25 per cent of carbon, the percentage of unconsumed carbon would be 16 25 = 4 per cent of the total coal burned If the coal contained by ultie burned, and of which the products of combustion pass up the chiure to use in calculating the total aht of flue gases resulting from the cohts of the air per pound of coal and the co equal to one e of ash as found in the boiler test The weight of flue gases per pound of dry fuel may, however, be computed directly from the analyses, as shown later, and the direct computation is that ordinarily used

The ratio of the air actually supplied per pound of fuel to that theoretically required to burn it is:

N 3036(---------)C CO_{2}+CO ------------------ (13) C O 3456(- + H - -) 3 8

in which the letters have the sanificance as in formulae (11) and (12)

The ratio of the air supplied per pound of combustible to the amount theoretically required is:

N ------------------ (14) N - 3782(O - CO)