Distillation

1. Basic understanding of process engineering
2. Aspen Plus Software installed on your computer
3. Have a Computer
4. Have a Desire

In this part you are taught the procedure to design a distillation column for specific mixture. In order to do so the trainer at first uses a DSTWU model in Aspen Plus to model a column for the mixture in shortcut form. By doing so, he gains estimated value by Aspen Plus and later uses these estimated values to be used in rigorous model in Aspen Plus which is RadFrac.Before switching to rigorous model he shows how the plot (Stage numbers versus reflux ratio) could be interpreted in order to select tray number and reflux ratio. After providing the software with the required information for running the column, the column converges.

Overview

DSTWU performs a Winn Underwood Gilliland shortcut design calculation for a single feed, two product distillation column, with a partial or total condenser. For the specified recovery of the light and heavy key components, DSTWU estimates the minimum for either:
•Reflux ratio
•Number of theoretical stages

DSTWU estimates one of the following requirements:
•Reflux ratio given the number of theoretical stages
•Number of theoretical stages given the reflux ratio
DSTWU also estimates:
•Optimum feed stage location
•Condenser and reboiler duties

DSTWU can produce tables and plots of reflux ratio versus number of stages.
Distl is a shortcut multicomponent distillation rating model. This model uses the Edmister approach to separate an inlet stream into two products. You must specify:
•Number of theoretical stages
•Reflux ratio
•Overhead product rate

Distl estimates the condenser and reboiler duties. You can specify a partial or a total condenser.
RadFrac is a rigorous model for simulating all types of multistage vapor liquid fractionation operations. In addition to ordinary distillation, it can simulate:
•Absorption
•Reboiled absorption
•Stripping
•Reboiled stripping
•Extractive and azeotropic distillation
RadFrac is suitable for:
•Three phase systems
•Narrow boiling and wide boiling systems
•Systems exhibiting strong liquid phase nonideality

RadFrac can detect and handle a free water phase or other second liquid phase anywhere in the column. You can decant free water from the condenser.
RadFrac can handle solids on every stage.
RadFrac can model columns where chemical reactions are occurring. Reactions can have fixed conversions, or they can be:
•Equilibrium
•Rate controlled
•Electrolytic

RadFrac can model columns where two liquid phases exist and different chemical reactions occur in the two liquid phases. RadFrac can also model salt precipitation.
RadFrac can operate in rating mode or design mode.

In this part the trainer performs the same procedure for a new mixture. After convergence of the RadFrac, he defines column internals and shows how the sizing of trays, column diameter, and other characteristics of the column are performed. Finally, he switches to Rate-Based Modeling of RadFrac and explains the procedure it is done in rating mode. During running the column, process engineers learn how he deals with the problems of convergence of the column.

Overview

RadFrac is a rigorous model for simulating all types of multistage vapor liquid fractionation operations. In addition to ordinary distillation, it can simulate:
•Absorption
•Reboiled absorption
•Stripping
•Reboiled stripping
•Extractive and azeotropic distillation

RadFrac is suitable for:
•Three phase systems
•Narrow boiling and wide boiling systems
•Systems exhibiting strong liquid phase nonideality

RadFrac can detect and handle a free water phase or other second liquid phase anywhere in the column. You can decant free water from the condenser.
RadFrac can handle solids on every stage.
RadFrac can model columns where chemical reactions are occurring. Reactions can have fixed conversions, or they can be:
•Equilibrium
•Rate controlled
•Electrolytic

RadFrac can model columns where two liquid phases exist and different chemical reactions occur in the two liquid phases. RadFrac can also model salt precipitation.
RadFrac can operate in rating mode or design mode.
In design mode, you can specify temperatures, flow rates, purities, recoveries, or stream properties anywhere in the column. Examples of stream properties are volume flow and viscosity. You can specify all flow, flow ratio, composition, and recovery specifications in mole, mass, or standard liquid volume units.
RadFrac has extensive capabilities for sizing and rating trays and packings. You can choose from several common tray types, and random and structured packings.
In rating mode RadFrac calculates:
•Temperature
•Flow rate
•Mole fraction profiles

These profiles are based on specified column parameters, such as reflux ratio, product rates, and heat duties.
All rating mode flow specifications can be in mole, mass, or standard liquid volume units.
You can specify component or stage efficiencies.
RadFrac accepts both Murphree and vaporization efficiencies. You can manipulate Murphree efficiencies to match plant performance.