Chemical Engineering December 2017 - 21

Better control
Another trend in simulation, says
Steve Brown, president of Chemstations
(Houston; www.chemstations.
com), is the demand for a simulator
arrangement where there is a " virtual
plant " running alongside the actual
plant, calculating optimal conditions,
allowing users to compare optimal
versus actual and displaying it to the
operator who may not have experience
with simulation tools. " In these
cases, the operator doesn't need
to understand thermodynamics or
the calculations or functions that are
core to simulation, but he needs to
understand what changing values in
the actual production facility mean, "
says Brown, who's company is currently
working with partners to deliver
solutions that will work in this manner.
" The partner builds a very complex
model of the virtual plant that
operates exactly like the facility does,
then embeds that technology inside
their deliverable, which may include
an interface like a SCADA [supervisory
control and data acquisition] or
Excel that is accessible to teams that
don't need to know anything about
simulation to use it. "
He says this provides a true production
environment, which can be
employed to build a " decision thinking
environment " that not only measures
what is happening in the actual
plant, but also what the virtual simulation
engine is calculating, and deliver
a dashboard to the management of
the company so they can make decisions
about how to best operate. " I
would call it advanced process control
using a virtual plant that is based
on first-principle simulation. "
While this has been attempted before,
Brown says calculation speeds
have caught up, allowing simulators
to calculate fast enough to keep up
with the distributed control system
(DCS). " The DCS is constantly polling
all of the data sources and if the
simulator can't keep up, there's a
hole in the system and lagging, so
users can't make decisions based
on that. But with increases in speed,
our simulation can deliver results as
fast as needed to make realtime decisions
and do advanced process
control, " he says.
Every plant, he says, is subject to
variability in terms of raw material
quality, ambient temperatures, humidity
and so on, and typical control
systems are one way to address
these variables. " However, advanced
process control that has access to
rigorous first-principle simulation allows
management to find alternative
operating conditions that are global
optimum conditions, opening the
door to massive savings in energy
and other efficiencies over a wide
range of variable operating conditions, "
explains Brown.
This type of simulation can also
be used for complex functions such
as calculating the composition of
stream, says Brown. " Typically to
measure the composition of
the
stream requires an online analyzer,
which is very difficult and expensive
WHERE THE INDUSTRY TURNS
FOR PRECISE CONTROL
Achieve precise control over every aspect of your chemical operation.
MODEL 521
MODEL 1078
The Model 1078
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MODEL 987
The Model 987 is a pneumatic control
valve designed to control moderate
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The Model 521 is a sliding
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sealed, pneumatically
actuated control valve
designed for maximum
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chemical service.
MODEL 1049
The Model 1049 Secure-Gard
is a pilot-operated vent valve
intended for installation
on atmospheric and lowpressure
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MODEL 3100
The Model 3100 is a
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designed to vent the tank
vapor away to atmosphere
and to relieve vacuum
pressure within the tank.
The 3100 is a weight
loaded style.
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P.O. Box 6, Ellsworth, KS 67439-0006
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CAS-236A.indd 1
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
DECEMBER 2017
1/24/17 1:18 PM 21
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Chemical Engineering December 2017

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