Re: [dwsim-users] reactor application - ethyl acetate

[Daniel W. <dan...@gm...>]

Hi Hector,

I don't know how the volume calculation works on Aspen but, in DWSIM, I do
the following:

PFR code (use this for line number references in the text below):
https://github.com/DanWBR/dwsim3/blob/master/DWSIM/Objects/Reactors/PFR.vb

- For the PFR, if you have a reactor of volume X, and the volume delta is
0.05, then the ODE (ordinal differential equation system) mass balance
calculation will be done in 0.05*X volume steps until the entire volume is
calculated (line 832). If you don't care about the actual pressure drop
calculation, you can enter any value for the reactor length. Just be sure
to input a length that doesn't result in a high pressure drop across the
reactor. DWSIM calculates the pressure drop using the reactor volume and
length to estimate the internal diameter, then uses the Darcy formula to
calculate pressure drop. If the reactor has a catalyst bed, then the Ergun
formula is used (line 797).

CSTR code (use this for line number references in the text below):
https://github.com/DanWBR/dwsim3/blob/master/DWSIM/Objects/Reactors/CSTR.vb

- For the CSTR, the entire reactor volume is used at once and the ODE
system is solved one time only (lines 559/111). There is no pressure drop
calculation because this is supposed to be a batch (tank) reactor. :-)

Regards
Daniel


2016-04-27 0:06 GMT-04:00 Hector Perez <hpe...@gm...>:

> Hi Daniel,
>
> Thanks for sending the file along with the updated build! I actually went
> through the file and included the reverse reaction by adjusting the Reverse
> Order exponents (the Aspen Plus video has both forward and reverse
> reactions). I also dropped the conversion on the Conversion reactor
> (to~70%) and set the equilibrium constant (for the Equilibrium Reactor) to
> be k_forward/k_reverse (ratio of rate constants). My numbers are now very
> close, if not the same as the ASPEN simulation video.
>
> One thing I did run into is that the reactor dimensions for the PFR and
> CSTR in the aspen video create errors in DWSIM. I had to decrease the PFR
> length because it gave me a warning about the pressure drop being too high.
> The CSTR volume also had to be decreased because it gave me a mass balance
> error. Do you know why the aspen dimensions don't work? This could perhaps
> be a lack of feasibility check on the ASPEN side.
>
> Also, what is "Volume Delta (Relative)" on the PFR specs?
>
> One other thing I checked was the CSTR duty (compared to the ASPEN video)
> and found the DWSIM value to be about 6 times lower than the ASPEN value
> (perhaps something having to do with the smaller volume used in DWSIM?).
>
> Thanks once again. I am really liking this simulator. It seems easier to
> use than aspen.
>
> Hector D. Perez
>
>
> On Tue, Apr 26, 2016 at 7:11 PM, Daniel Wagner <dan...@gm...>
> wrote:
>
>> Hi Hector,
>>
>> By following the Aspen Plus video I was able to make it work, there is no
>> reverse reaction. Also, there was a bug in the PFR pressure drop
>> calculation, you'll have to use an updated build. Download it from this
>> link and unpack the files in DWSIM's installation directory:
>> https://sourceforge.net/projects/dwsim/files/DWSIM/DWSIM%203.7/Build5960.rar/download
>>
>> Also, I forgot to tell you that, for kinetic reactions, every compound in
>> the reaction must be present even if in a small amount, i.e. 0.000001. 0
>> will give you an error.
>>
>> You can also try the updated simulation file, I've added the equilibrium
>> reactor as well.
>>
>> Regards
>> Daniel
>>
>>
>> 2016-04-26 18:17 GMT-04:00 Hector Perez <hpe...@gm...>:
>>
>>> Hi Daniel,
>>>
>>>
>>>
>>> For kinetic reactions, what are the units on the activation energy?
>>> (same units as those specified for the molar entropy?). I included the DO
>>> and RO exponents as well as the base compound and now get a new error on
>>> the CSTR: “An error occurred during the mass balance calculation. Check
>>> reaction kinetics data and reactor sizing information as well.”
>>>
>>>
>>>
>>> The PFR gives me the error: “One or more flash specification values are
>>> invalid. Please check the associated UO or Material Stream for incorrect
>>> specifications or miscalculated values.
>>>
>>>
>>>
>>> Thank you, I really appreciate your assistance.
>>>
>>>
>>>
>>> Hector D. Perez
>>>
>>>
>>>
>>> *From: *Daniel Wagner <dan...@gm...>
>>> *Sent: *Tuesday, April 26, 2016 3:59 PM
>>> *To: *Hector Perez <hpe...@gm...>
>>> *Cc: *dws...@li...
>>> *Subject: *Re: [dwsim-users] reactor application - ethyl acetate
>>>
>>>
>>>
>>> For the existing reactions, you've missed the compound concentrations'
>>> direct and reverse order exponents. You also didn't define the base
>>> compound, which should be the main reactant.
>>>
>>>
>>>
>>> For the conversion and equilibrium reactors, you must define the
>>> corresponding reactions. Kinetic reactions only work with the PFR and the
>>> CSTR.
>>>
>>>
>>>
>>> 2016-04-26 16:43 GMT-04:00 Hector Perez <hpe...@gm...>:
>>>
>>> Hi,
>>>
>>>
>>>
>>> I am trying to replicate the following ASPEN tutorial to set up the
>>> liquid reaction for ethyl acetate formation from ethanol and acetic acid
>>> using different types of reactors:
>>>
>>>
>>>
>>> https://www.youtube.com/watch?v=_DOdlUDI-kI
>>>
>>>
>>>
>>> Unfortunately, only the Gibbs reactor yielded any result with a ethyl
>>> acetate flow that was 12 kmol/hr lower than the ASPEN simulation. The only
>>> differences I can see is that the ASPEN simulation uses the NRTL-hoc,
>>> whereas my simulation uses NRTL.
>>>
>>>
>>>
>>> The conversion reactor had zero conversion and both the PFR and CSTR
>>> reactors gave the error: "The given key was not present in the dictionary."
>>> I'm not sure what this means. I tried different thermodynamic models
>>> besides NRTL with no avail.
>>>
>>>
>>>
>>> I will send my simulation file attached.
>>>
>>>
>>>
>>> I would really appreciate any light on the matter.
>>>
>>>
>>>
>>> Obrigado!
>>>
>>>
>>>
>>>
>>> Hector D. Perez
>>>
>>> Chemical Engineering Consultant
>>>
>>>
>>>
>>>
>>>
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>>
>>
>