| Figure 9.1: |
Plot of variation of CO and heat losses with excess oxygen in POC. Note zero value of oxygen in POC denotes stoichiometric oxygen. |
X- axis on the figure is  in POC. Theoretically percent oxygen in POC is zero at theoretically amount of air. Increase in excess air increases percent oxygen in POC (see black line in the figure). It can be seen in the figure that amount of CO (see green line) decreases drastically by using slight amount of excess air. Beyond around 1 to 2% O2, CO in POC disappears completely. But increase in excess air at the same time increases  in POC as shown by (blue line).
Heat losses are shown by the blue line. Heat losses decrease drastically with the excess air and become minimal at around  which is due to decrease in CO. Beyond  heat losses increases further because now nitrogen and oxygen in POC increases.
Ref : O.P. Gupta: elements of fuels. furnaces and refractories.
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