TUTORIAL: Flash tank design in CHEMSEP
Download and install CHEMSEP from chemsep.org
Open CHEMSEP
and select
components:
Acetone and
Water.
Select
operation:
Flash
Select
properties
(thermodynami
c model):
Raoult’s law
Specify feed
conditions:
Sate: T & p
Pressure:
100000 N/m2
Temperature:
320 K
Flowrates
(kmol/s):
Acetone: 5
Water 5
Define flash
specifications:
Pressure
100000 N/m2
Temperature
354 K
Solve and see
results:
Molar flow
rates:
V = 5.838
kmol/s
L = 4.161
kmol/s
Mole fractions:
Y_acet = 0.647
Y_wat = 0.352
X_acet = 0.292
X_wat = 0.707
The results of simulation depend on selection of a thermodynamic model!
Selecting thermodynamic model for the mixture acetone-water.
Experimental VLE data: (from http://www.ddbst.com/en/EED/VLE/VLE%20Acetone%3BWater.php)
Plot Txy diagram and compare thermodynamic model prediction with experimental data.
1. Select Raoult’s law to calculate K-value
2. Check if this thermodynamic model predicts correct VLE: compare experimental Txy data
and calculated Txy diagram.
NO
MATCHING: dew curve and bubble point curve are far from experimental points!
3.
Next, Select UNIQUAC
thermodynamic model.
4. Compare experimental Txy data and calculated Txy diagram.
Much better matching between experimental data and calculated dew point and bubble
point curves!
You can compare results of flash tank calculations for 2 thermodynamics models (Raoult’s
law and UNIQUAC models). See the difference in vapor phase and liquid phase
compositions!