# Combustion of Coal in a boiler

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1. Nov 3, 2015

### raniero

A quantity of coal used in a boiler had the following analysis: 82% C; 5% H; 6% O; 2% N; 5% ash. The dry flue gas analysis showed 14% CO2 and some oxygen. Calculate the oxygen content of the dry flue gas.

I have first written the formula for combustion including the variables for balancing the equation:

Considering 1kg of coal:

0.82/12 C + 0.05 H + 0.06/1 O + 0.02/14 N + x(0.233/32 O2 + 0.767/28N2) → B(0.14 CO2 + a O2 + (0.86-a) N2)+ b H2O

When balancing the equation this yields:

Carbon Balance: B = 0.4881

Hydrogen Balance: 0.05 = 2b → b =0.025

The problem I am encountering arises in the oxygen balancing:

Oxygen balance: 0.06/16 + x(0.233/32)2 = (0.14)2B + 2aB + b

The book's answer states: 0.06/16 + x(0.233/32) = (0.14)B + aB + b/2

How come the book's answer doesn't add double the amount of substance (kmol) as I did for Oxygen molecules?
Other answers from the book compensate by multiplying by two when molecules such as O2 are present. Another disagreement I have with the solution is the 'b' divided by 2.

Thanks in advance

2. Nov 8, 2015

### Staff: Admin

Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?

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