ANALYSIS OF FLUE GASES
The object of a flue gas analysis is the determination of the completeness of the combustion of the carbon in the fuel, and the amount and distribution of the heat losses due to incomplete combustion. The quantities actually determined by an analysis are the relative proportions by volume, of carbon dioxide (CO 2 ), oxygen (O), and carbon monoxide (CO), the determinations being made in this order.
The variations of the percentages of these gases in an analysis is best illustrated in the consideration of the complete combustion of pure carbon, a pound of which requires 2.67 pounds of oxygen, [28] or 32 cubic feet at 60 degrees Fahrenheit. The gaseous product of such combustion will occupy, when cooled, the same volume as the oxygen, namely, 32 cubic feet. The air supplied for the combustion is made up of 20.91 per cent oxygen and 79.09 per cent nitrogen by volume. The carbon united with the oxygen in the form of carbon dioxide will have the same volume as the oxygen in the air originally supplied. The volume of the nitrogen when cooled will be the same as in the air supplied, as it undergoes no change. Hence for complete combustion of one pound of carbon, where no excess of air is supplied, an analysis of the products of combustion will show the following percentages by volume:
|
Actual Volume for One Pound Carbon Cubic Feet |
Per Cent by Volume | ||
|---|---|---|---|
| Carbon Dioxide | 32 | = | 20.91 |
| Oxygen | 0 | = | 0.00 |
| Nitrogen | 121 | = | 79.09 |
| –––––– | ––––––––––– | ||
| Air required for one pound Carbon | 153 | = | 100.00 |
For 50 per cent excess air the volume will be as follows:
| 153 × 1½ = 229.5 cubic feet of air per pound of carbon. |
| Actual Volume for One Pound Carbon Cubic Feet | Per Cent by Volume | |||||
|---|---|---|---|---|---|---|
| Carbon Dioxide | 32 | = | 13.91 | } | = | 20.91 per cent |
| Oxygen | 16 | = | 7.00 | |||
| Nitrogen | 181.5 | = | 79.09 | |||
| –––––––––– | ––––––––––– | |||||
| Air required for one pound Carbon | 229.5 | = | 100.00 | |||
For 100 per cent excess air the volume will be as follows:
| 153 × 2 = 306 cubic feet of air per pound of carbon. |
| Actual Volume for One Pound Carbon Cubic Feet | Per Cent by Volume | |||||
|---|---|---|---|---|---|---|
| Carbon Dioxide | 32 | = | 10.45 | } | = | 20.91 per cent |
| Oxygen | 32 | = | 10.45 | |||
| Nitrogen | 242 | = | 79.09 | |||
| –––––– | ––––––––––– | |||||
| Air required for one pound Carbon | 306 | = | 100.00 | |||