3 replies to this topic

[rajeshtiwari]

As there is 21% oxygen(v/v) in air why I get 16-17% summation of Oxygen,Carbondioxide,SOx, CO and NOx in flue gas analysis of pulverised coal fired boilers of a thermal power plant.Coal contains about 43% ash and 14% total moisture.

[mbeychok]

The moisture in the coal (which you said was 14 percent of the coal) and the moisture in the combustion air appear in the wet flue gas as water vapor, which dilutes the percent carbon dioxide, carbon monoxide, sulfur dioxide, NOx, oxygen, and nitrogen in the wet flue gas.

Also, any hydrogen in the coal combines with air to yield water vapor and nitrogen, both of which further dilute the oxygen and the carbon, sulfur and nitrogen oxides in the wet flue gas.

To give you a more definitive answer, you would need to provide us with more information such as:

(1) What is the complete analysis of your coal ... that is, what is the weight percent of carbon, hydrogen, oxygen, sulfur, nitrogen. water and ash in the coal? And those percentages should add up to 100 percent.

(2) What is the complete analysis of your wet flue gas ... that is, what is the volume percent of carbon dioxide, carbon monoxide, sulfur dioxide, NOx, oxygen, water vapor, and nitrogen? And those percentages should add up to 100 percent.

(3) What is the percent excess combustion air being fed into the steam-generating boiler? And what is the percent relative humidity of your typical combustion air?

I am also curious as to the source of your coal ... 43 weight percent ash is much higher than any coal with which I am familiar.

[siretb]

As Milton states, you probably have a wet basis for the analysis of gas.
This matches the composition you give (14%wt water) that would yield about 4% in the gases after combustion.
Exact calculation requires more detailed analysis of your coal and also the O2 excess you end up with.

[rajeshtiwari]

Thanks Milton and Siretb for the reply.Soon I will post the desired details.