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

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

Hi Hector,

For liquids, a high pressure drop would be one that vaporizes part of it...
for gases, I guess that it would be worse because gas properties are
heavily dependent on pressure, and that can cause changes in concentrations
and/or fugacities, impacting the final conversion.

Regards
Daniel


2016-04-27 9:22 GMT-04:00 Hector Perez <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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>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>
>>
>