Hydrocarbon Processing - November 2022 - 19

Process Controls, Instrumentation and Automation
FIG. 6. Moisture measurement related to process dryer swapping. The red line indicates the
moisture analyzer measurement, while the yellow lines indicate the moment of the dryer swap.
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FIG. 7. Moisture measurements relate to process dryer swapping (two drying cycles). The red line is
the moisture analyzer measurement, while the yellow lines indicate the moment of the dryer swap.
Summer season trend. In this summer
period, the OAT ranged between 20°C
and 40°C, with an average day/night
variation of 14°C (FIG. 4). The measurement
remained at 0.01 ppmv-0.08 ppmv.
A small inverse relationship between the
OAT and moisture measurements can be
seen when OAT varies widely. Despite
high variations in the OAT, moisture remained
within the expected values.
Measurement variations regarding
dryer swapping. The following analysis
used small process variations to check the
sensitivity of the analyzer. Using the QCM
analyzer, small variations in moisture
could be measured during dryer swaps.
In the two-column dryer dehydration
system (FIG. 5), one dryer dehydrates the
ethylene while the other is in regeneration.
When one dryer becomes saturated
with water vapor, it is swapped with the
other dryer. The saturated dryer is then
regenerated. The moisture analyzer was
installed at the outlet of both dryers.
Moisture measurements related to
process dryer swapping. A small variation
in the dryer's moisture measurement
(a drop of 0.03 ppmv) can be seen at each
dryer swap (FIG. 6). This variation was
expected, and it confirmed the sensitivity
of this analyzer to process changes. The
trend shown in FIG. 7 extended two drying
cycles to observe in more detail the
moisture variations after each dryer swap.
Takeaway. QCM moisture technology
has negligible influence due to the OAT.
Some variations can be seen (no more than
0.02 ppmv) with day/night temperature
changes (5°C-10°C). The lower detectable
limit for this analyzer is 0.02 ppmv, which
is consistent with what was observed.
In relation to the detection of low
moisture values, this analyzer has proven
to be very sensitive to small variations in
the process. With the analyzer's internal
National Institute of Standards and Technology
(NIST) traceable calibration/
verification system, it was possible to validate
the analyzer's performance during
testing. Because of this operation, the detection
of moisture changes during dryer
swapping has been transformed into valuable
information for monitoring dryer
performance and verifying ethylene quality.
QCM technology has been proven to
be suitable for this type of process.
HERMAN HECKER is an Electromechanical Technician
with a background in electronics and computers.
He has worked with analyzers at Dow Chemical
for 22 yr and is responsible for supporting analytical
projects and improvements in Latin America.
JUNG-IL KIM is a Product Manager with a background
in electrical engineering. He has worked at AMETEK
Process Instruments for 18 yr and is responsible
for the moisture measurement product line.
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Hydrocarbon Processing - November 2022

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