Sample Combustion Calculations by weight method

Sample Combustion Calculations by weight method

Combustion calculations are starting point for Boiler or any Thermal equipment design. Here is a sample calcualtion done for Coal with a calorific value of approximately 7200 Kcal/kg (12960 BTU/Lb).

Coal composition in % is as follows :

Carbon , C - 76.0 ; Hydrogen, H2 - 4.1 ; Nitrogen , N2 - 1.0  ;   Oxygen, O2 - 7.6 ;   Suphur, S - 1.3 ;   Moisture, H2O - 3.0 ;   Ash - 7.0 ;   

Excess Air : 30 %

Molecular Wt of C - 12 ,  O2 -32 , H2 - 2, S - 32

The Chemicl equations are as follows: C + O2 --> CO2 ; S + O2 --> SO2 ; H2 + O --> H2O

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Comp    Wt.   O2 reqd     CO2    H2O    N2    SO2      

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C        0.76                  2.0267      2.7867      -         -         -         

H2      0.041                  0.328         -         0.369      -         -         

O2       0.076                 (-0.076)

N2       0.01                     -               -            -      0.01      -

S       0.013                  0.013            -            -      -        0.026      

H2O    0.03                    -               -         0.03         -       -       

ASH    0.07

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      100.0           2.2917          2.7867     0.399   0.01    0.026







From the above table, Theoritical O2 required  = 2.2917 kg/kg of coal

There fore, Theoritical dry Air required = 2.2917/0.23 = 9.964 kg of dry air/ kg of fuel

considering 30% Excess Air , Th air reqd = 9.964 x 1.3 = 12.9532 kg/kg

Wet air required (assuming 60% RH)     = 12.9532 x 1.013 = 13.12 kg/kg of fuel

Gas composition :

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Gas     Weight               %Wt                  %WT/MW           %Volume

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CO2    2.7867                  19.832               0.4507               13.381

H2O    0.567                    4.035                 0.2242               6.655

SO2    0.026                    0.185                 0.0029               0.086

N2     9.9837                  71.055                2.5376               75.339

O2    0.6875                  4.893                 0.1529              4.539

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      14.0509                  100.0                  3.3654                  100

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