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Optimization and Control Properties for a Dividing Wall Distillation Column

Wallin, Richard LU (2016) KET920 20152
Chemical Engineering (M.Sc.Eng.)
Abstract
Dividing wall columns are single shell distillation columns which are thermally fully coupled. DWC has the ability to create three product streams from one feed stream. A simulation of DWCs is hard due to the complexity of the system. Unfortunately, there is no good software package that can be used for simulations. Instead a detailed flowsheet with the right components and good arrangement over the system must be used. In this respect, simulations of DWCs are much harder than simulations of conventional columns.
The main purpose with this project was to design a model, i.e., implement a setup in Aspen PlusTM and analyse how it behaves when it is subjected for various impacts. Dynamic simulations of the system were done to investigate... (More)
Dividing wall columns are single shell distillation columns which are thermally fully coupled. DWC has the ability to create three product streams from one feed stream. A simulation of DWCs is hard due to the complexity of the system. Unfortunately, there is no good software package that can be used for simulations. Instead a detailed flowsheet with the right components and good arrangement over the system must be used. In this respect, simulations of DWCs are much harder than simulations of conventional columns.
The main purpose with this project was to design a model, i.e., implement a setup in Aspen PlusTM and analyse how it behaves when it is subjected for various impacts. Dynamic simulations of the system were done to investigate design and operation parameter sensitivity e.g. effect of feed specification variation (and other parameters) on the compositions of the product streams. The aim was to create a model that was robust and could withstand fluctuations.
The simulation of the system can be carried out in many ways. For instance, the model can be created directly in the dynamic environment or it can first be created in steady state and then converted for dynamic purposes (the latter is applied in this master thesis). It turned out that it was easier to achieve the desired values in the dynamic environment. However, the steady-state model in Aspen Plus was much more robust and easier to do modifications in. Minor adjustments such as changes in the internal specifications were easy to implement in both Aspen Plus and Aspen dynamics. (Less)
Popular Abstract
Optimization and Control Properties for a Dividing Wall Distillation Column

DWC is a new promising technology in the chemical industry. With DWC it is possible to obtain almost pure components from a multicomponent feed. However, a simulation of DWCs is hard due to the complexity of the system.
Conventional distillation is an energy consuming unit operation. Since the energy demand is in focus worldwide many attempts for development of energy efficient distillation has been done through the years. DWC (Dividing Wall Distillation) is one result of all the attempts that have been made.
Dividing wall columns are single shell distillation columns which are thermally fully coupled. There are a number of advantageous with DWC compared... (More)
Optimization and Control Properties for a Dividing Wall Distillation Column

DWC is a new promising technology in the chemical industry. With DWC it is possible to obtain almost pure components from a multicomponent feed. However, a simulation of DWCs is hard due to the complexity of the system.
Conventional distillation is an energy consuming unit operation. Since the energy demand is in focus worldwide many attempts for development of energy efficient distillation has been done through the years. DWC (Dividing Wall Distillation) is one result of all the attempts that have been made.
Dividing wall columns are single shell distillation columns which are thermally fully coupled. There are a number of advantageous with DWC compared with conventional distillation columns. First of all, the energy demand can be reduced up to 30 %. Beyond this, investment costs will also be reduced since there is no need for one extra reboiler. However, there are still some disadvantages with DWC as well. The pressure drop will always be bigger in DWC since the column is taller.
The partitioning wall consists of thin, flat metal sheets and is welded to the column shell and thereby splits the column into two semicylindrical sections. However, it is not necessary for the wall to be applied in the middle, instead off-center positioning is also common.
The purpose with this work was to create a DWC arrangement that could produce three product streams with purity of 98% in the middle stream. To achieve this Aspen Plus and Aspen Dynamics were used. The results shown that to achieve the desired values a four column arrangement was needed.
When the amount of columns increases the system was hard to simulate, due to the degree of freedom. Different techniques such as splitting streams and change tolerance for solver were used.
There are several methods to create the dynamic model. One method is to build the whole model in the dynamic environment. This is not recommended due to the complexity of the system. Another method is to first create a state model in Aspen Plus and then convert the model to Aspen Dynamics. In this thesis the second method was used.
In the future this project will properly be tested in a pilot scale. In a pilot it is possible to investigate how the system will react when it starts up, how different control structures will collaborates with each other and so on. If this turns out well there will be a huge difference in the chemical business. (Less)
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author
Wallin, Richard LU
supervisor
organization
course
KET920 20152
year
type
H2 - Master's Degree (Two Years)
subject
keywords
chemical engineering, kemiteknik
language
English
id
8891922
date added to LUP
2016-09-30 08:42:16
date last changed
2016-09-30 08:42:16
@misc{8891922,
  abstract     = {Dividing wall columns are single shell distillation columns which are thermally fully coupled. DWC has the ability to create three product streams from one feed stream. A simulation of DWCs is hard due to the complexity of the system. Unfortunately, there is no good software package that can be used for simulations. Instead a detailed flowsheet with the right components and good arrangement over the system must be used. In this respect, simulations of DWCs are much harder than simulations of conventional columns. 
The main purpose with this project was to design a model, i.e., implement a setup in Aspen PlusTM and analyse how it behaves when it is subjected for various impacts. Dynamic simulations of the system were done to investigate design and operation parameter sensitivity e.g. effect of feed specification variation (and other parameters) on the compositions of the product streams. The aim was to create a model that was robust and could withstand fluctuations.
The simulation of the system can be carried out in many ways. For instance, the model can be created directly in the dynamic environment or it can first be created in steady state and then converted for dynamic purposes (the latter is applied in this master thesis). It turned out that it was easier to achieve the desired values in the dynamic environment. However, the steady-state model in Aspen Plus was much more robust and easier to do modifications in. Minor adjustments such as changes in the internal specifications were easy to implement in both Aspen Plus and Aspen dynamics.},
  author       = {Wallin, Richard},
  keyword      = {chemical engineering,kemiteknik},
  language     = {eng},
  note         = {Student Paper},
  title        = {Optimization and Control Properties for a Dividing Wall Distillation Column},
  year         = {2016},
}