Chemical Engineering April 2016 - 27

Emerson Process Management
company's model 888 sulfur-recovery
tail-gas analyzer (Figure 2) uses
UV technology to accurately monitor
the H2S and So2 concentrations in
sulfur-recovery tail-gas. model 888
provides reliability via automatic
flow control for proactive response
to adverse process conditions and
flange temperature alarms for early
warning of poor-quality steam, while
smart diagnostic models identify,
communicate and react to potential
problems, which helps reduce unscheduled
downtime.
Mass spectroscopy. Some of the
latest, non-optical technologies
also bring faster response times,
increased reliability and flexibility to
the table, notes Daniel merriman,
product manager for process analyzers
with Thermo Fisher Scientific
(Waltham, mass.; thermofisher.com).
" Some of the optical spectroscopy
methods and lasers don't support
all of the applications that conventional
process gas analyzers can, "
he says. " Lasers tend to provide discrete
measurements, but there are
applications where multi-component
measurements are required in different
sample streams. "
For these applications, he says,
being able to measure multiple
streams with different gas compositions
provides valuable and cost effective
data at process control levels.
However, even in these applications,
processors are still seeking higher
speeds. " Process mass spectrometers
are generally capable of measuring
complex gas-sample streams
within cycle times that are ten to
twenty times faster than traditional
gas chromatographs, " says merriman.
" They are also largely configured
by software so they are able
to provide gas analysis from multiple
sample streams where the gas
composition might vary significantly
between streams. Some of the processes
being controlled are very dynamic
so they benefit from fast gas
analysis. That enables process control
models to improve efficiency for
the process that can yield increased
productivity and reduced waste, resulting
in reduced rework, reduced
use of raw materials and lower energy
costs. That's really where the
value proposition of these advanced
Figure 4. Gas chromatograph software control of a gas chromatograph is easier with intuitive,
Windows-based pulldown menus and fill-in-the-blank tables. The software collects and organizes the
analyzed data from gas chromatographs, such as the 700XA model shown here
technologies lies. "
The Thermo Scientific Prima PRo
process mass spectrometer (Figure 3)
was developed to provide faster, more
complete, laboratory-quality online
gas-composition analysis of multiple
sample streams with different and
varying compositions in each stream.
The Prima PRo typically operates
up to 90 days between calibration
intervals, and it offers a fault-tolerant
design for availability of greater than
99.7% to facilitate ongoing operation
and enhance productivity.
Improving gas chromatography
" While we are seeing requests for
inline instruments and instantaneous
measurements, there are certainly
some obstacles to overcome with
spectroscopy over gas chromatography, "
notes yokogawa's Cathey.
" Gas chromatography is extremely
accurate because it measures the
components directly, whereas spectrography
provides an inferential
measurement based upon the optical
properties of what it is measuring.
So, there are some cases where
there are very good solutions for
spectrometers right now, but they
tend to be application-specific. What
this means is that the gas chromatograph
is still a very viable technology
for large numbers of applications. "
Siemen's Dean agrees: " Laser and
other analysis technologies are not
ChemiCal engineering www.Chemengonline.Com april 2016
taking over the analysis market. So,
for this reason, we are also working
to improve our traditional gas-chromatograph
technologies. "
He says a lot of effort has been
made to improve reliability, stability
and to include diagnostic systems
that will recognize an issue or
a potential problem. " There are now
smarter sampling systems that can
recognize issues like higher pressure
differentials and that can constantly
verify and validate measurements, as
well as recognize when maintenance
is needed, " says Dean.
In addition to these smarter systems,
providers of gas chromatographs
are working on ease of use
and simplified maintenance, says
Bonnie Crossland, product marketing
manager for gas chromatographs
with Emerson Process management's
Rosemount Analytical (Irvine,
Calif.; www.emersonprocess.com).
" Gas chromatographs have never
been viewed as an easy-to-use instrument, "
she says. " So we are
starting to work on ease-of-use with
features like interactive and intuitive
touchscreens and we now offer advanced
diagnostics so the machine
itself provides feedback and suggests
preventative maintenance to
correct problems before measurement
errors occur. "

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Chemical Engineering April 2016

Table of Contents for the Digital Edition of Chemical Engineering April 2016