3 replies to this topic

[Pingue2008]

All,

 

My questions may be very basic for some but need to ask.

I have asked similar question in the past (see link below).

Background: The company i work for produces PET resin. Acetaldehyde (AA/Ethanal) is a byproduct of the esterification reaction of ethylene glycol and TPA (Pure terephthalic acid). the AA needs to be stripped downstream. The stripper column has not be performing well and my superior wants to recirculate bleach through the column to try to clean the column. the stripper column is a packed column and the temperatures set points are kinda questionable in my opinion ("we have always run it this way" is what i hear). the AA+water is fed to the top and Air + Steam is fed from the bottom. I thought it be a good idea to run a simulation to do some case analysis. questions:

 

1- Did any of you design and operate such column if so how do you operate the column?

2- Have you ever clean the column with bleach? if so how effective was it?

3- While setting up my simulation, i realized i have to enter the # of tray in the Redfrac even though reboiler     and condenser option was selected to none. In Aspen Plus how does one convert HETP to # of tray? in the rating option I entered the known HETP of column but the number of trays i don't what to enter.

 

Any help will greatly be appreciated

 

http://www.cheresour...-packed-column/

 

[Bobby Strain]

I would think that your process licensor will have an answer for you.

 

Bobby

[Lucian Gomoescu]

Hello,

Regarding point 3, i have the following observations:

1. If you want to mention the geometry of column and sections' packing characteristics and get the outlet streams properties without mentioning any number of stages, then you can use  RateFrac (it requires Aspen RateFrac license ! ).

 

2. If you want a model which includes mass rate transfer limitations then, again, you need RateFrac license.

3.1. If you want to find the number of theoretical plates (NTP) of a packed column section which has a total pack height H, an internal diameter D and a given packing material etc by using RadFrac without RateFrac license (i.e., Calculation type: equilibrium vs RateBased) then you can follow this procedure:

 

i. Create a RadFrac with a number of trays (whatever valid value you want).
ii. Create a Pack Sizing.
iii. Specify packing type , material, size etc
iv. Adjust HETP until at results the packing diameter is equal to D. When this happens, you found the HETP.
v. Divide H to HETP to find NTP (which is not an integer number).

 

3.2. In addition to point (3.1) you want to know the outlet streams properties of this column section.
 

Solution a: Round down NTP obtained at 3.1 and use it instead of the one specified at 3.1.i.

Solution b: Round up NTP obtained at 3.1.v. and use it at 3.1.i. Then specify stages Murphree efficiency equal to NTP/RoundUp(NTP)

 

BR,
Lucian

P.S.: It is ok that RadFrac asked for number of stages, despite it has only packed sections.

[Pingue2008]

Thank you Lucian.