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.
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 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
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