Page 118 - Process simulation and control using Aspen

108 PROCESS SIMUKATION AND CONTROL USING ASPEN

strippers, pumparrounds, etc. This rigorous column mo del can be used as an alternativ e
of PetroFrac, especially when the configuration is beyond the capabilities of PetroFrac
.
As mentioned earlier, SCFrac is a shortcut column model. It simulates a distillation
unit connected with a single feed, multiple products and one optional stripping steam
.
It is used to model refinery columns, such as atmospheric distillation unit (ADU) and
vacuum distillation unit (VDU).
PetroFrac is commonly employed to fractionate a petroleum feed. This rigorous model
simulates the refinery columns, such as ADU, VDU, fluidized-bed catalytic cracking (FCC)
fractionator, etc., equipped with a feed furnace, side strippers, pumparounds and so on.
RateFrac is a rate-based nonequilibrium column model employed to simulate all
types of vapour-liquid separation operations, such as absorption, desorption and
distillation. It simulates single and interlinked columns with tray type as well as packed
type arrangement.
BatchFrac is a rigorous model used for simulating the batch distillation columns. It
also includes the reactions occurred in any stage of the separator. BatchFrac model
does not consider column hydraulics, and there is negligible vapour holdup and constant
liquid holdup.
It is worthy to mention that for detailed information regarding any built-in Aspen
Plus model, select that model icon in the Model Library toolbar and press Fl.
In this chapter, we will simulate different distillation models, including a petroleum
refining column, using the Aspen Plus software. Moreover, an absorption column will
be analyzed. In addition to the steady state simulation , the process optimization will
also be covered in the present study.

3 .2 ASPEN PLUS SIMULATION OF THE BINARY DISTILLATION
COLUMNS

3 .2 .1 Simulation of a DSTWU Model

Problem statement
enters a DSTWU
A feed stream, consisting of 60 mole% ethane and 40 mole% ethylene ,
column having a flow rate of 200 Ibmol/hr at 750F and 15 psia. This feed is required to
fractionate in a distillation column capable of recovering at least 99 .6% of the light key
component in the distillate and 99 . 9% of the heavy key component in the bottoms. The
sample process operates at 300 psia with zero tray-to-tray pressure dro p . The pressure
in the reboiler as well as condenser is also 300 psia . In the simulation, use total
30 theoretical stages (including condenser and reboiler) and a total condenser . Applying
the RK-Soave property method , simulate the column and calculate the minimum reflux
ratio, actual reflux ratio , minimum number of stages , actual number of stages, and
feed location.

Simulation approach
From the desktop , select Start button , and then click on Programs, AspenTech, Aspen
Engineering Suite , Aspen Plus Version and Aspen Plus User Interface. Then choose
Template option in the Aspen Plus Startup dialog and hit OK (see Figure 3 .1).