4 replies to this topic

[wachawacha]

I'm trying to model a Fischer-Tropsch process using a PFR in HYSYS.  The probability of getting a certain hydrocarbon follow the ASF distribution (W=[(1-a)^2]a^(n-1)) where n is the number of carbons.  I also have the reaction rate expression which follows a langmuir hinshelwood form which I figure out how to put into HYSYS using the heterogeneous catalytic reaction.  The problem  I have is what do I put down as the hydrocarbon product since the probabilty of getting ethane, pentane, butane etc changes with the ASF distribution.  

 

Is there a way in HYSYS to use the probability distribution while still using the reaction rates in a PFR? 

[curious_cat]

You multiply your overall rate by the probability of a particular HC. 

 

The first term comes from LHHW in terms of T, P etc. and the second term is a constant once you fix your n. 

[wachawacha]

So my reaction rate is r=(k₁P_COP_H)/(1+k₂P_COP_H)^2  where the k's are temp dependent, and I just multiply that by the probability of getting methane, ethane, octane etc? Which would change my "A" term in HYSYS

 

I guess that makes sense since it then just weights the rxn rate.  This is going to be a pain to put into HYSYS for all HC up to C30 

 

Thanks!

Edited by wachawacha, 01 October 2013 - 10:36 AM.

[curious_cat]

So my reaction rate is r=(k₁P_COP_H)/(1+k₂P_COP_H)^2  where the k's are temp dependent, and I just multiply that by the probability of getting methane, ethane, octane etc? Which would change my "A" term in HYSYS

 

I guess that makes sense since it then just weights the rxn rate.  This is going to be a pain to put into HYSYS for all HC up to C30 

 

Thanks!

 

I'm not a Hysys expert but I think you get the right idea. 

 

If it's a pain to put them all individually often people combine several C's together in a model. Say C23 - C26 or something like that.

 

Bigger question is how will you model the oxygenates or unsaturated compounds or branching. ASF isn't very useful at that although those selectivities are more important. 

[curious_cat]

PS. For your mass balance to work make sure your probabilities add to one.