Distillation of C2H5OH-H2O Mixture 

This example shows the instruction for a distillation process of ethanol-water mixtures in 7 steps.
This calculations enable to determine
- Mass balance for C2H5OH

- The influence of  the location of the feed tray  location (Tray 6 and Tray 7) on the products and C2H5OH lost

- Tray efficiency of the real system and process analogy
Further, the results of the calculations are compared  with the  multistage tray towers-method of the McGabe and Thiele.
Concept:



We will define a fluid mixture named Mix consisting of 10 mol % C2H5OH and 90 mol % H2O.
The mixture is to feed in the distillation column, as the picture above shows. You can see also other conditions from picture.
Configuration of the application
Execute the application ProCalc.exe

1. Make a new Project

 In the dialogbox for System Settings on the page Dimensions, set dimensions as mol all phases 
and Save Settings

2. Define thermodynamic System
Main Menu: Project -> Thermodynamic System
In the following window:

2.1. Select Elements
In the window for Thermodynamic System: Menü System -> Elements
Select H, O, C
Close the dialog box with Button OK.
2.2. Select Compunds
In the window for Thermodynamic System: Menu System -> Compounds -> Gases
Select the compounds C2H5OH (g) and H2O (g)
In the window for Thermodynamic System: Menu System -> Compounds -> Liquids
Select the compounds  C2H5OH (l) and H2O (l)
2.3. Activity Coefficients
In the window for Thermodynamic System: Menü System ->Activity Coefficients
Add
two equations with the constants as in the follwing picture shown

2.4. Save thermodynamic System

 3. Define the mixture for feed 

Main Menu: Project -> Substances
Enter name: Mix:
Check the radio button Liquid
Press Button Select
in the following dialogbox add the substances C2H5OH (l) and H2O (l) with the button -> 
Press Button OK and close the dilogbox for Compunds
Set the combo-Box to mol %
Set for ratios 10 for C2H5OH and 90 for H2O
Save Settings
Close the dialog box 

4. Define Input
In the main window, select menu Process ->Inputs
4.1. Set the Position for Input ID: 1
Enter Name: Feed (or other)
In Combo Box Subst.  Select item Mix
Press Button Add
 Save Settings
Close the dialog box 


5. Define Processes
In the main window, Menu Project -> Processes
In the Following dialog box

5.1. Set the position for Process ID 1
5.1.1. Enter name: T1
5.1.2. Set the temperature 78 °C
5.1.3. Set Pressure 1 bar
5.1.4. Check the check box T Const, if not checked (default checked)
5.1.5. Check the check box Phase definition given by thermodynamic system, if not checked (default checked)
5.1.6. Save settings

5.2. Set the position for Process ID 2 to 7
5.2.1. Enter name: T2 .... T7
5.2.2. Make same setting as P1 (5.1)
5.2.3. Save settings for each definition.

5.3. Set the position for Process ID 8
5.3.1. Enter name: Cond.
5.3.2. Make same setting as P1 (5.1)
5.3.3. Save settings.

5.3. Set the position for Process ID 9
5.3.1. Enter name: Boiler
5.3.2. Make same setting as P1 (5.1)
5.3.3. Save settings.


6. Assignment of the mass flow

In the main window menu item Process ->Mass Flow

6.1. Set the position for process ID 1
6.1.1. Check item P.2: T2 in the check box for Gases for 100%
6.1.2. Check item P.8: Cond in the check box for Liquids for  75%
6.1.3. Save settings

6.2. Set the position for process ID 2
6.2.1. Check item P.3: T3 in the check box for Gases for  100%
6.2.2. Check item P.1: T1 in the check box for Liquids for  100%
6.2.3. Save settings

6.3. Set mass flow for ID 3 to ID 5  like ID 2
6.3.1. Check item P.N+1: TN+1 in the check box for Gases  for  100%
6.3.2. Check item P.N-1: TN-1 in the check box for  Liquids  for  100%
6.3.3. Save settings

6.3. Set the position for process ID 6
6.3.1. Check item P.7: T7 in the check box for Gases for  100%
6.3.2. Check item P.5: T5 in the check box for Liquids for  100%
6.3.3. Check item I.1: Feed in the check box for Inputs for  100%
6.3.4. Save settings

6.4. Set the position for process ID 7
6.4.1. Check item P.1: T1 in the check box for Gases for 100%
6.4.2. Check item P.7: Cond. in the check box for Gases for 100%  (Gases don't leave condenser)
6.4.3. Save settings

6.5. Set the position for process ID 8 for 100%
6.5.1. Check item P.7: T7 in the check box for Liquids  100%
6.5.3. Save settings

Now, the configuration is complete.


7. Calculation
Change to main window
Enter the values for Input Window (I.1. Mix Feed). Enter a value, press button Calculation 
In each windows for processes, the current values from the result will be shown.


Enter for input value for example 10, as in the picture above shown


Enter in each process windows in colums for activity coefficients
for C2H5OH(l) [1]; for H2O(l) [2]
I.e.:the activity coefficients of C2H5OH(l) is to calculate with the equation [1], and the activity coefficients of H2O(l) is to calculate with the equation [2] defined in Chapter  2.3. Activity Coefficients system

Check the check box for recalculation Recalc

Press for recalculation count, for example 40

Press button calculation (with arrow right). 

8. Monitoring 

8.2 Definition of the record variables
The menu Monitoring -> Record Variables  shows the dialog box for data record.
Set position for process to 6 (Cond.)  
Set in the combination box  Liquids , C2H5OH(s) und X and press button Add  
Set in the combination box  Liquids , C2H5OH(s) und Out and press button Add  

Include also other variables, wich are relevant for decision.
 Close the dialog box with OK

8.3. Definition of the  Graphic Variables 
The menu Monitoring -> Graphic Variable shows the dialog box for graphic variables 

Add from Record Variables X C2H5OH (l) - Liquids (P6) to the first page of Y-Coordinates
Include also other variables, wich are relevant for decision.

Close the dialog box with OK

Restart the calculation, as above (7. Calculation) again

9. Steady State
When calculation carried out 200 times, the system becomes steady.  200 calculation cycles take less than 1 minute in a computer with an processor of 233 MHz.  The following picture shows the course of the concentration in the trays.

10. Infulence of the Feed Tray Location on the Products and C2H5OH Lost

Menu: Monitoring -> System Balance. In the following dialog box, select balance for C2H5OH in Entire System and press button Update.
In following, The C2H5OH balance is shown, when feed point is tray 6

When the feed tray is 7 , the calculations yield following result


The follwing picture shows the course of the ethanol-concentration in the trays, when feed tray location is changed from 6 to 7



Comparison of the results with the  multistage tray towers-method of the McGabe and Thiele.


The numbers shows calculated values of the concentrations with the Process Calculator for liquid and gas phases of the trays . Blue lines are operating lines, and they correspond to the operation line multistage tray towers-method of the McGabe and Thiele

Efficiency
Tray efficiency is depends from geometry and turbulence in trays. Using this efficiency parameters as Rel.-Value for each compound, you can determine the influence of the another parameters on the distillation processes. In following, the mass balance of the system is shown for tray efficiency 0.7