Hydrocarbon Processing - April 2022 - GP-22
PROCESS OPTIMIZATION
can be considered based on gas density. However, this requires
the gas temperature in the pressure piping.
To investigate the difference between the PDT reading and
the predicted pressure drop, the operation data of HP columns
in the ASU were collected and processed. It was determined the
deviation is caused by significant temperature difference between
the HP column and the differential pressure transmitter
piping. The PDT reading corresponds neither to the dynamic
pressure drop of packings nor the total pressure drop of the column.
GP
NOTES
a Sulzer's Sulcol™
b Sulzer MellapakPlus™ series
c YOKOGAWA EJA110E
LITERATURE CITED
1
2
FIG. 5. Density of gaseous N2
at different temperature and pressure.
3
In addition to the variation associated with the temperature
gradient along the piping, the location of the transmitter outside
the cold box-which is also project dependent-affects
the gas static head in the piping to a small extent. Specifically,
in the case investigated here, the gas in the upper piping is nearly
pure N2
with trace of oxygen (O2
gas in the lower piping consists of 37.8% O2
) and argon (Ar), and the
and 1.6% Ar. As
the gas density is a function of its composition, if the location
of the transmitter changes, then the gas static head in the piping
would also change, according to Eq. 3.
Inferences. Despite being a theoretical exercise, the calculations
in this paper are adequate to conclude that the deviation
between the predicted dynamic pressure drop and the PDT
reading is caused by the difference between the gas density in
the HP column and the gas density in the pressure piping due
to the great temperature difference. The larger the difference in
gas density, the greater the deviation.
This can also explain why only a 10%-30% deviation has
been observed with the LP and CAR columns. First, the gas
density difference is still the primary reason for the deviation.
Due to much lower operating pressure, the gas density in the
LP and CAR columns are in the range of 5 kg/m3
-8 kg/m3
;
therefore, the gas static head becomes a smaller portion of the
total pressure drop (the curves of static and total pressure drop
would shift downwards in FIG. 1 in such a case). Using gaseous
N2
, FIG. 5 illustrates the impact of column operating pressure
on the gas density at different temperatures.
Takeaway. Due to the temperature gradient along the piping
of the differential pressure transmitter and its varying position
in the cold box, it would be challenging-if not impossible-
to deduce from a PDT reading either the dynamic pressure
drop of packings or the total pressure drop of a column. Hence,
unlike in other applications, PDT readings in an ASU cannot
be used to judge how far the columns are from flooding, nor
can they provide any input to process simulation and upstream
equipment sizing, significantly limiting typical uses. To obtain
the correct pressure drop for ASU columns, zero calibration5
22 MARCH/APRIL 2022 | GasProcessingNews.com
Cai , T. J. and M. R. Resetarits, " Pressure drop measurements on distillation columns, "
Chinese Journal of Chemical Engineering, 2011.
Kehrer, F., L. Spiegel, E. Kolesnikov and P. Choo, " Experimental investigation and
modelling of Sulzer I-ring hydraulics, " Chemical Engineering Research and Design,
Vol. 84, Iss. 11, November 2006.
Yang, Q., J. J. Dong, F. J. Feng and X. D. Zhang, " Revamping an air separation unit, "
PTQ, 2019.
4 Kister, H. Z., " Distillation operation, " McGraw-Hill Inc., New York, 1990.
5
American Institute of Chemical Engineers (AIChE), Tray distillation columns: A
guide to performance evaluation, 2nd Ed., Wiley, New York, New York, 1987.
FENGJIE XU is a Senior Engineer at China National Air
Separation Engineering Co. Ltd., where he is responsible for
R&D of ASU processes and ASU energy-saving technologies.
He has been engaged in the field of air separation for 15 yr, and
holds a BE degree in energy and environmental engineering.
FENGHUA ZHOU is a Senior Engineer at China National
Air Separation Engineering Co. Ltd. She specializes in the
automation design and R&D of control technology for ASUs.
She has more than 19 yr of experience in the field of air
separation automatic control and holds an MA degree in
control engineering.
ZHIMING CAO is a Senior Project Manager at China National
Air Separation Engineering Co. Ltd. with responsibility over
equipment integration, construction, erection and project
management. His 21 yr of process project management
experience ranges from engineering design, equipment
installation to commissioning, etc., for ASU projects.
QUAN YANG is a Sulzer Senior Technical Expert, specializing
in mass transfer components. He is in charge of air separation
knowledge management within Sulzer Chemtech. Recently,
his field expanded to process optimization for DWC.
Dr. Yang holds a PhD in environmental engineering from
the National University of Singapore.
LAURENT ZUBER heads Process Innovation and Technology
Management at Sulzer Chemtech Ltd. in Winterthur,
Switzerland. He joined Sulzer in 1995 as a Process Engineer
for chemical and petrochemical separation units, and has
held different positions in application management. He has
a special interest in advanced distillation solutions and difficult
product separation. Dr. Zuber holds a PhD in chemical
engineering from the Swiss Institute of Technology of Zurich.
JIAO-JIAO DONG is a Principle APT Engineer at Sulzer
Chemtech China in Shanghai, China. In her 13 yr with Sulzer,
her main responsibilities have included driving ASU business
in the China market and advocating the best designs and
practices of column internals optimized for ASUs. She holds
an MS degree in chemical engineering from the East China
University of Science and Technology.
http://www.GasProcessingNews.com
Hydrocarbon Processing - April 2022
Table of Contents for the Digital Edition of Hydrocarbon Processing - April 2022
Contents
Hydrocarbon Processing - April 2022 - Cover1
Hydrocarbon Processing - April 2022 - Cover2
Hydrocarbon Processing - April 2022 - Contents
Hydrocarbon Processing - April 2022 - 4
Hydrocarbon Processing - April 2022 - 5
Hydrocarbon Processing - April 2022 - 6
Hydrocarbon Processing - April 2022 - 7
Hydrocarbon Processing - April 2022 - 8
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Hydrocarbon Processing - April 2022 - 88A
Hydrocarbon Processing - April 2022 - 88B
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Hydrocarbon Processing - April 2022 - Cover3
Hydrocarbon Processing - April 2022 - Cover4
Hydrocarbon Processing - April 2022 - GP-1
Hydrocarbon Processing - April 2022 - GP-2
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https://www.nxtbook.com/nxtbooks/gulfpub/hp_200907
https://www.nxtbook.com/nxtbooks/gulfpub/hp_200906
https://www.nxtbook.com/nxtbooks/gulfpub/hp_200905
https://www.nxtbook.com/nxtbooks/gulfpub/hp_200904
https://www.nxtbook.com/nxtbooks/gulfpub/hp_200903
https://www.nxtbook.com/nxtbooks/gulfpub/hp_200902
https://www.nxtbook.com/nxtbooks/gulfpub/hp_200901
https://www.nxtbookmedia.com