Hydrocarbon Processing - August 2022 - 63

Gas Processing & LNG Industry Spotlight
TIGRON ACTUATORS
Raman spectroscopy. Various gas and
liquid analysis technologies have been
developed around the ability of lasers
to produce highly specific wavelengths
of light. Various molecules are affected
by this radiation at specific wavelengths,
in characteristic and measurable ways,
making it possible to detect and quantify
chemical components of interest.
One method for determining vibrational
modes of molecules is Raman
spectroscopy, which uses a laser to produce
light of visible or near-infrared
wavelengths. When various molecules
pass through this light, the light's energy
excites the vibrations of molecular bonds,
such as the bond between two hydrogen
atoms. Inelastic scattering results in emissions
of this excited energy, casting the laser
light into different wavelengths.
What started as a single laser-generated
color now becomes its own rainbow
spectrum because each molecule in
the sample produces a signal at a unique
wavelength, and the relative intensity indicates
the sample's molecular concentration.
A Raman analyzer looks for these
specific wavelengths and intensities to
create a chemical profile of the sample.
When this concept is applied to LNG
analysis, a probe is inserted into the
pipe to analyze the flowing liquid or gas
(FIG. 4). The probe is inserted into the
flowing LNG stream either directly or
via a bypass loop. Laser light is emitted
from the end of the probe into the LNG
sample, and the scattered Raman light is
collected back through the same probe
tip. The collected Raman light travels
through a second fiber-optic cable and
then enters a detector in the analyzer,
where the resulting individual wavelengths
are identified and quantified. All
electronic components are housed inside
the analyzer enclosure (FIG. 5).
This approach has several critical advantages
when compared to GC analysis,
including the following:
* The probe inserts directly into
the LNG stream so that it takes
the reading in situ, with the
moving liquid constantly
refreshing the sample.
* Measuring LNG in situ means
that there is no vaporizer and no
sample lines, valves, heaters or
regulators. This results in more
stable measurements from a Raman
analyzer, without the noise and
spikes that are characteristic of
vaporizer variability.
* The probe can handle pressures
up to 111 barg (1,610 psig)
for C276 alloy or 87.5 barg
(1,270 psig) for a hybrid metal
combo, and at temperatures
as low as -196°C (-320.8°F)
for both material options.
* The laser and detector are housed
within the analyzer, and the light is
carried to and from the probe via
fiber-optic cables over distances up
to 500 m. The probe contains only
the optical system and is rated for
installations in Class 1, Division 1
and Zone 0 hazardous areas.
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FIG. 4. A proprietary analyzerb
can take simultaneous readings from up to four probes located
in different parts of the process stream.
Hydrocarbon Processing | AUGUST 2022 63
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Hydrocarbon Processing - August 2022

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