Products of Combustion:

Hydrocarbon combustion produces CO2, and water vapor and possibly some CO.  The combustion of wastes containing sulfur produces SO2 and possibly SO3.  Halogen containing wastes produce acid halogen gas of each in a combustion reaction -HCl, HF, and HBr.

 

Example 3.5: A gas having the following composition:

CH4 = 94.44%, C2H6 = 4.56%, CO = 0.1%, CO2 = 0.2%, N2 = 0.4%, O2 = 0.3%

leaves a furnace after complete combustion when 125 % excess air is used.  Determine the composition of the product.

 

Solution Basis: 1 mole of gas

 

C                  Moles of O2 required, and CO2 and H2O:

 

 

 

 

y

 

O2

 

CO2

 

H2O

 

CH4

 

0.9444

 

2

 

1

 

2

 

C2H6

 

0.0456

 

3.5

 

2

 

3

 

CO

 

0.001

 

0.5

 

1

 

0

 

C                  Stoichiometric O2 requirement = 0.9444(2) + 0.0456(3.5) + 0.001(0.5) = 2.0489 mole

Available oxygen in the feed = 0.003 mole

C                  Net oxygen required = 2.0489 - 0.003 = 2.0459 mole

C                  Oxygen to be supplied from the air = (1 + 1.25)(2.0459) = 4.603

C                  Nitrogen associated with air = 4.603(3.764) = 17.326

 

Combustion Products:

C                  CO2 = 0.9444(1) + 0.0456(2) + 0.001(0.5) + 0.002 = 1.0386 mole

C                  N2 = 17.326 + 0.004 = 17.33 mole

C                  H2O = 0.9444(2) + 0.0456(3) = 2.0256 mole

C                  O2 = 1.25(2.0459) = 2.557 mole

C                  Total number of moles = 22.452

C                  Composition of products:

CO2 = 1.0386/22.452 = 4.5%; N2 = 17.33/22.452 = 75.6%

H2O = 2.0256/22.452 = 8.8%; O2 = 2.557/22.452 = 11.1%