Troubleshooting of WFE - (Wiped Film Evaporator)

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Discussion Overview

The discussion revolves around troubleshooting the performance of a Wiped Film Evaporator (WFE) used to separate two components, X and Y, from a feed mixture. Participants explore the operational challenges faced in achieving the desired separation efficiency, specifically the removal of 99% of component X from component Y, and the discrepancies between model predictions and actual observations.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant describes the feed details, including the composition and boiling points of components X and Y, and the operational conditions of the WFE.
  • Another participant questions whether the operation has been modeled and if Raoult's Law is applicable, suggesting that the solution may not be ideal.
  • A later reply confirms that the solution is not ideal but provides a modeled result from Aspen Plus, indicating a much lower concentration of component Y in the top distillate than observed.
  • One participant emphasizes the importance of determining why the model does not match observed results and asks about the confidence in the vapor-liquid equilibrium (VLE) part of the model.
  • Another participant suggests using Aspen Plus properties packages and emphasizes the need for trained process engineers to analyze field process data for optimization.

Areas of Agreement / Disagreement

Participants express differing views on the modeling accuracy and the applicability of Raoult's Law. There is no consensus on the reasons for the discrepancies between model predictions and actual observations, indicating ongoing debate and exploration of the topic.

Contextual Notes

Participants note that the solution is not ideal, which may affect the applicability of certain modeling approaches. There are unresolved questions regarding the accuracy of the VLE model and the selection of appropriate properties packages in Aspen Plus.

Who May Find This Useful

Individuals interested in process engineering, particularly those working with evaporative separation techniques and simulation software like Aspen Plus, may find this discussion relevant.

Rachit
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TL;DR
Continuous boiloff operation in WFE.
Feed Details :
Component X : 80% ( Boiling point : 105 deg.C)
Component Y : 20% ( Boiling point : 256 deg.C)
Feed Rate : 600 kg/hr
Heating medium : Steam @ 145 deg.C
operating condition : 50 Torr, 90 deg.C ( Based on Aspen Flash Simulation).

Desired Outcome :
TO remove 99% of component X from Component Y.

History :
Earlier this operation was performed in batch mode. Where all of component X was boiled off.
During this, Bottom mass temperature was observed to go upto 120 deg.C uder 50 torr of vacuum.
No component Y was observed in the top distillate - throughout the operation.

Current Scenario :
Observations in WFE :
  1. In top distillate component Y is found ~10%.
  2. In bottom residue component Y is found ~80%.
  3. At 50 torr vacuum, operating temperature is only 40 deg.C.
  4. Upon increasing flowrate, component Y is found less in top distillate.

What should be done to minimize loss of component Y in top distillate ?
 
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Have you tried to model this operation? Is the solution ideal so that Raoult's Law can be applied.
 
Chestermiller said:
Have you tried to model this operation? Is the solution ideal so that Raoult's Law can be applied.
The solution is not ideal, but I have modeled the operation in Aspen plus and component Y in top distillate is ~0.5% w/w.
 
The first step is to determine why your model is not matching the observed split. What are your thoughts on this? How do other observational measurements compare with model predictions? How confident are you in the VLE part of the model?
 
My friend

Aspen Plus has a set of properties packages that will approach the simulation to the real process. It has a tutorial to select the best ones. However, you have to select PR if your components do not have a polar behavior.

To optimize the process, it could be done with the process data. Of course, anyone needs to know X and Y, to have a view of the distillation equilibrium of the mix. Simulation is a tool, just that; but trained process engineers should do it by analyzing the field process data.

Horacio
 

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