Date:
September 22, 2010
To:
Dr. Kline
From:
Ken McFarland
Subject:
CHEG 3810 Lab 2
Lab Overview
This lab consisted of two parts. The first involved analyzing 4 different vapor liquid
equilibriums using the IDEAL, NRTL, and UNIFAC property packages. This showed the
differences that can result from changing the property package on a system. The second part
involved creating a more complicated system that performed a number of unit operations on the
product stream.
Problem 1
For problem 1, a mixing point was created that created equal molar systems that were used to
create T-x-y diagrams. There were four different systems to be created:
 Methanol – Water
 Ethanol – Water
 Chloroform – Tetrahydrofuran
 Ethanol – Toluene
Three T-x-y diagrams had to be created for each of these 2 component systems, one using each
of the three property packages listed above. These diagrams plot the liquid / vapor fractions by
mole of a species in the system with respect to temperature. These can then be used to find the
needed temperature for a desired phase fraction, or phase fraction for a given temperature. The 3
diagrams that were generated for the Methanol – Water system are included. Figure 1 shows the
Vapor / Liquid equilibrium diagram generated using the IDEAL package. This uses the ideal gas
law as the equation of state generating the data, which assumes no interaction between molecules
of the gas. The next two figures, 2 and 3, show the same diagram generated using the NRTL and
UNIFAC packages, respectively. These both use different equations of state or systems of
equations to attempt to model the interactions between molecules as accurately as possible.
Problem 2
The second problem required the addition of several more unit operations to the system that was
created in problem 1. As in that problem, the Methanol – Water system was used. In order to set
up the additional unit operations, a fourth T-x-y diagram had to be created, that was at 10 atm.
This is attached as Figure 4. Due to the fact that gasses at 10 atm are not ideal, the UNIFAC
package was used. This diagram was used to find the temperature 5 degrees below the saturation
temperature for the .6 mol ratio methanol system, which was found to be 289°F. The mixture
was compressed to 10 atm, with a power requirement of 1.24 kW. It was then heated to 289°F,
bya heater with a heat duty of 500000 BTU/hr. This heated stream was then flashed back to 1
atm adiabatically. This resulted in two streams, T-Out, a vapor stream, and B-Out a liquid
stream. The flow rates and composition of both of these streams are included in Table 1. As can
be seen, the majority of the materials remain in the liquid stream with approximately 1/5 moles
vaporizing in the flash. The final compositions of the flashed streams can be seen to correspond
to Figure 3, the T-x-y diagram for 1 atm of pressure using the UNIFAC package, which was
previously referenced.
Lab Overview
This lab allowed us to see the difference that can result from using just 2 of the many different
properties packages that are available to use in Aspen. In problem 1 there are noticeable
differences between the T-x-y charts made using the IDEAL equation of state, and the NRTL
and UNIFAC equations of state. Problem 2 shows that at extreme temperatures and pressures,
gasses behave in a very non-ideal manner, at which one of the packages that account for
interactions between molecules of gasses must be used.
Figure 1: T-x-y IDEAL for Methanol / Water system
Figure 2: T-x-y NRTL for Methanol / Water system
Figure 3: T-x-y UNIFAC for Methanol / Water system
Figure 4: T-x-y UNIFAC for Methanol / Water system at 10 atm
Table 1: Flow rates and Temperatures of T-Out and B-Out
Mole Flow (lbmol/hr) B-OUT
T-OUT
METHANOL
43.36383 16.63617
WATER
36.01197 3.988032
Total Flow (lbmol/hr)
79.3758 20.6242
Temperature (F)
162.2001 162.2001