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

[Hector P. <hpe...@gm...>]

Hi Daniel,

Thank you for the clarification. What is the criteria for "high pressure
drop" in a PFR? I'm seeing that in the acetate problem, DWSIM won't let me
go beyond a pressure drop of 0.23 atm.

Thanks,

Hector D. Perez


On Wed, Apr 27, 2016 at 8:09 AM, Daniel Wagner <dan...@gm...> wrote:

> 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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>>>>
>>>>
>>>
>>>
>>
>