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Topic: Urgent Chemical Engineering Problem.  (Read 4140 times)

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Offline ian123

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Urgent Chemical Engineering Problem.
« on: April 15, 2015, 04:29:51 PM »

I just want to ask question about this as I'm not sure what I to do next:
The product gas from a combustion reaction has the following dry basis molar composition:
CO2 80.35%
CO 4.73%
SO2 0.03%
O2 14.89%
Pure oxygen is fed to the furnace in 10% excess of that required for complete combustion. There is no oxygen in the fuel (fixed or gaseous). Calculate the elemental composition of the fuel (mole % of elements C,H & S).Base calculations on 100 moles of dry outlet gas.
 
Take SO2 to be the fully combusted form of S.

Here is my working so far:
'O'in='O'out
2*'O2'in=2*'CO2'out+1*'CO'out+2*'SO2'out+2*'O2'out+1*'H2O'out
 
2*'O2'in=2*80.35+1*4.73+2*0.03+2*14.89+1*'H2O'out

'C'in='C'out
'C'in='CO2'out+'CO'out=80.35+4.73=85.08mols

'S'in='S'out
'S'in=1*'SO2'out=1*0.03=0.03mols

0.1=(O2feed-O2theoretical)/(O2theoretical)

Complete combustion
S+O2->SO2              0.03mols O2
C+O2->CO2             85.08mols O2
H2+1/2O2->H2O     x mols       O2

Incomplete Combustion
C+1/2O2->CO

Thanks
« Last Edit: April 15, 2015, 06:28:07 PM by ian123 »

Offline mjc123

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Re: Urgent Chemical Engineering Problem.
« Reply #1 on: April 16, 2015, 06:38:57 AM »
Hello again.

Can I suggest again that you start by writing a balanced equation for the combustion (the one you suggested was not balanced). If you have x moles of C, how many moles of CO2 do you get? How many moles of O2 does this consume? Likewise with H2O and SO2.

Please do not use the personal message function unless you actually have a personal message for me. (See rule 3.9 in the Forum Rules.) The point of the forum is that others can see the discussion and (hopefully) learn from it; it is not a private conversation. And it won't get you a quicker response - it may even be slower, if I don't notice that there's a message for me.

Offline ian123

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Re: Urgent Chemical Engineering Problem.
« Reply #2 on: April 16, 2015, 06:49:12 AM »
2CxHySz+(2x+(1/2)y+2z)O2->2xCO2+yH2O+2zSO2

Or this
C+O2->CO2
C+1/2O2->CO
H2+1/2O2->H2O
S+O2->SO2

Offline Arkcon

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Re: Urgent Chemical Engineering Problem.
« Reply #3 on: April 16, 2015, 09:11:59 AM »
So, we know complete combustion happens, even though there is some CO product.  You have 100 moles of product, and it is CO2 80.35% and CO 4.73%, so how much carbon is that?  Likewise for sulfur.  The balance is hydrogen.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline mjc123

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Re: Urgent Chemical Engineering Problem.
« Reply #4 on: April 16, 2015, 09:39:45 AM »
OK; it will probably be easier if you divide through by 2, so
CxHySz + (x + y/4 +z)O2  :rarrow: xCO2 + y/2H2O + zSO2
Let us write A = x + y/4 + z. Now if we have 10% excess of oxygen, it becomes
CxHySz + 1.1A O2  :rarrow: xCO2 + y/2H2O + zSO2 + 0.1A O2
Can you write the equation for the incomplete combustion case where each mole of C generates β mol CO and (1-β) mol CO2?

Offline Enthalpy

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Re: Urgent Chemical Engineering Problem.
« Reply #5 on: April 16, 2015, 10:04:12 AM »
Not knowing the amount of water produced, I believe the proportion of hydrogen in the fuel is impossible to determine.

Offline mjc123

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Re: Urgent Chemical Engineering Problem.
« Reply #6 on: April 16, 2015, 12:46:24 PM »
No it isn't. You can get an expression for the amount of oxygen left over, from which (knowing x, z and β) you can find y.

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