[arnab]

Hi all....

Could anyone please tell me how FLUENT calculates the volatile composition from proximate and ultimate analysis??.....
e.g. my coal analysis are:

Proximate(FLUENT input)[/B] (%)
FC-43.7
VM-45.6
Moisture-2.2
Ash-8.5

Ultimate(dry ash free basis)(FLUENT input)[/B] (%)
C-77.6
H-6
O-12.7
N-1.3
S-0.5
Ash-8.5

Proximate (Dry basis) (%)
FC-44.8
VM-46.7
Ash-8.5

Ultimate(Dry basis) [B] (%)
C-71
H-6
O-12.7
N-1.3
S-0.5
Ash-8.5


The volatile composition it shows in the coal calculator when I input these values is completely different what it comes out from hand calculation...

Hand calculation: (From dry basis of both)
wt%C in volatile = (71-44.8)/46.7 = 0.561 => moles = 0.561/12 = 0.04675
wt%H in volatile = (6.5)/46.7 = 0.128 => moles = 0.128/1 = 0.128
wt%O in volatile = (12.7)/46.7 = 0.272 => moles = 0.272/16 = 0.017
wt%N in volatile = (1.3)/46.7 = 0.028 => moles = 0.028/14 = 0.002
wt%S in volatile = (0.5)/46.7 = 0.011 => moles = 0.011/32 = 0.00034

So, Volatile = C0.04675 H0.128 O0.017 N 0.002 S0.00034

But FLUENT calculates (based on FLUENT input) :
C1.4 H3.78 O0.51 N0.0587 S0.0109

The FLUENT calculation is also not an exact multiple of hand calculation...could anyone please explain why is the discrepancy and how FLUENT calculates the volatile matter composition...

Thanks....

[HKhalish]

Hand Calculation
C0.04675 H0.128 O0.017 N 0.002 S0.00034

But FLUENT calculates (based on FLUENT input) :
C1.4 H3.78 O0.51 N0.0587 S0.0109

If you change the C ratio into 1, you will find the result quite similar

Hand Calculation
CH2.738 O0.364 N0.043 S0.007

But FLUENT calculates (based on FLUENT input) :
CH2.7 O0.364 N0.042 S0.008

[mj2malik]

Include the molecular weight. It seems like for Fluent your MW for the volatile is around 30 kg/kmol.

Therefore, you should multiply the volatile MW value (kg/kgmol) to the mass fraction, before converting into mols.

So, for instance, if we take C for now

wt%C in volatile = (71-44.8)/46.7 = 0.561 * 30=16.83=> moles = 16.83/12 = 1.4025

This is applicable to the other elements in the volatile, which will give
C1.4 H3.78 O0.51 N0.0587 S0.0109