Chemical Engineering June 2021 - 31

residual moisture
every 12 min. This
makes
TABLE 3. A SELECTION OF PAT APPLICATIONS
Example measurement task Operating principle Main parameter drivers
it possible
to quickly detect a
product that does
not meet specifications.
The real advantage,
however,
lies in the compliance
with specification
limits. As a rule,
specifications are
significantly undercut
without the use
of online measuring
equipment in order
to prevent rejection
by the customer in
Reactor monitoring for catalyst
poison
Online monitoring of the equilibrium
concentration of various
carboxylic acids
Distillation monitoring for feed
control
Residual moisture determination
of a powder
CO smoldering fire detection
End product control
Monitoring of inrush of current
for process control
any case. By exploiting the specification
limit, the ROI can now be
seen as less than 6 mo., depending
on the product price. In addition, energy
costs and the associated CO2
emissions are reduced.
These examples all refer to online
methods. By eliminating the need for
sampling and sample preparation for
analysis, inline methods once again
ensure lower costs and significantly
increased operational reliability with
comparable measurement accuracy.
For example, inline Raman spectroscopy
has been successfully used in
urea synthesis to optimize process
parameters. The productivity of the
plant, which has an annual output
of 495,000 tons, was increased by
0.5% as a result. The higher yield
from process optimization alone, as
well as the savings in energy consumption
and emissions, add up to
€700,000 to 800,000 annually.
Another question that also arises
in the decision-making process is
" When should one continue to rely
on laboratory analytical analysis, and
when to rely on PAT? " The advantages
of an analytical laboratory lie in
its flexibility. With the appropriate analytical
equipment and experienced
laboratory technicians, analyses that
are not part of the daily routine can
also be carried out there. However,
apart from extremely time-consuming
sample preparation and special
analyses, it makes more sense to automate
routine analyses.
According to NAMUR, the following
rule of thumb applies. From
around one analysis per day, pro30
Thermal
conductivity
measurement
Near infrared (NIR)
spectroscopy
NIR spectroscopy
Process improvement and reduction of
H2 losses
Investment ROI
€120,000 3 months
Stabilization of a crystallization process €675,000 12 months
Process improvement through automated
column control
Microwave absorption Reduction of drying time and improvement
of product quality
Nondispersive IR
NIR spectroscopy
Raman spectroscopy
Source: Ref. 2, with permission. Date: October 30, 2017
cess analytics is less expensive than
laboratory analytics. Further advantages
are that process analytics also
provide measurement results over
the weekend and holidays without
shift work. Current measured values
are available without any major
delay, and only this allows them to
be used in process control systems.
And sample falsification due to sampling
errors is ruled out. The main
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Chemical Engineering June 2021

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