Chemical Engineering April 2012 - 60

Feature Report
Engineering Practice
Better
Chemistry
By Design
Simulation software helps
to create higher-performance,
safer and more-economical
CPI plants
David Jechura
SSOE Group
A
t one time, the design of distillation
columns and other major
components for the chemical process
industries (CPI) required
engineers to make one-at-a-time calculations
in order to project whatif
scenarios covering the processes,
equipment, raw materials and capital
necessary for renovation or construction.
If an engineer was fortunate, he
or she might have had access to central
computer facilities that would shorten
the time to make these calculations to
provide decision-making support. Otherwise,
it was a slow, manual process
that made it difficult to cover all bases.
In fact, some bases were never touched.
Today, modern simulation software
running on a desktop computer makes
it possible to automate these scenarios'
creation. Simulation software works
well with straightforward chemical
processes, as well as processes that
require intermediate feedstock mixes,
equipment and piping sizing, optimum
inventories, raw materials costs and
applications analysis, and even comprehensive
safety designs.
Process equipment sizing
With distillation column design, simulation
software can help maintain exSIMULATION
SOFTWARE
IN THE CPI
Simulation software works well in the CPI for the following activities:
* Test the ranges of distillation and calculate values to maximize
production
* Repurpose equipment as processing goals change
* Establish optimum order and efficiency of raw material processing
* Set up a work and material flow that makes sense
pensive components within the overall
project's budget limits. The software
enables the engineer to work with the
program features to ensure that a distillation
column will be no taller than
the process requires. The simulation
itself tests the ranges of distillate that
different feedstocks will produce, and
calculates values that will enable the
plant to maximize production.
In a real world example, simulation
helped design a distillation column
that maximized the value of various
products being distilled out of a stream
of liquid natural gas. By adjusting the
software program to simulate the culling
of propane, butane and ethane
more efficiently, the resulting design
cut the column's cost by $2 million.
This brought an over-budget project
back in line.
A simulation program can also help
to repurpose equipment as processing
goals change. For instance, in one project
a distillation unit that originated
from a canceled project was located at
a used equipment vendor. Although
not an optimal solution to the process'
needs, performance simulation showed
that with modification, the unit could
produce the required fractionation.
The combined purchase and modifi60
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cation costs came in under what was
budgeted for a new unit. Additionally,
starting with the base unit as already
constructed shortened the construction
schedule, which improved cash
flow for the project.
Inventory and material flows
Simulation software can also help to
develop production routines, such as
establishing the optimum order in
which each raw material should be
processed to produce the timeliest
result. An efficient routine, in turn,
influences raw material purchases so
that they will be efficiently incorporated
into the process, while keeping
inventory costs low.
An even more complex task for
simulation software sets the routine
for producing and then using intermediate
raw materials. Software can
incorporate details, such as the length
of time that various materials must
age before they reach a specification
acceptable to the process.
For example, water-based paint is
an emulsion normally produced in
batches due to the ever-changing formula
differences between batches.
Each batch might require as many as
ten raw materials, plus half a dozen
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Chemical Engineering April 2012

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