Hydrocarbon Processing - June 2021 - 28

Process Optimization
these guidelines provide valuable information for vapor velocity
criteria since they were based on test data. It is generally recognized
that the allowable vapor velocity without a demister is
lower than the vapor velocity with a demister. Therefore, the axial
vapor velocity for a horizontal separator without an internal
demister should be less than the vapor velocity recommended
by API 12J. Walas' guideline is generally considered conservative.
For horizontal flare KO drums, it is important to limit the
axial vapor velocity below the maximum velocity limit from Eq.
13 to permit the liquid droplets to settle down prior to leaving
the KO drums. In addition, the vapor residence time should be
greater than the liquid droplets' settling time.
Takeaway. Horizontal flare KO drums are used to separate
fine liquid droplets out of the flare vapor stream by gravity at
relatively low velocities and low turbulence. The function of
the flare KO drums is to remove liquid droplets in the range of
Method
TABLE 3. Comparisons of various axial vapor velocity guidelines
Axial vapor velocity, ft/s Froude number
API 521 sample calculations
CCPS (re-entrainment limit)
API 12J (K = 0.5 ft/s)
Walas (K = 0.14 ft/s × 1.25)
Eq. 13
12.76-24.3
18.76
6.54
2.29
5.41
30-108.9
64.91
7.89
0.97
5.4
300 µm-600 µm from the vapor feed stream to the flare burner.
Failures to remove these liquid droplets can cause smoke or
burning rain (a significant safety hazard).
The most effective way to prevent burning rain is to install a
properly designed KO drum. Although determining the maximum
wet vapor velocity in the horizontal flare KO drums is important
to ensure that the liquid droplets are removed, the wet
vapor velocity guidelines are not well defined. The comparison
of various axial vapor velocity guidelines in TABLE 3 shows that
the residence time method recommended by API 521 is not
conservative and could lead to undersized flare KO drums that
could fail to remove entrained liquid. The residence time method
should be supplemented by the proposed vapor velocity limit
guidelines for the horizontal flare KO drums. The vapor velocity
estimated with Eq. 13 provides a reasonable prediction of the
wet vapor velocity based on the API 521 indication. Flare vapor
velocities exceeding 9.8 ft/sec or 13.1 ft/sec could entrain liquid
droplets up to 1,000 µm in size, and liquid droplets 300 µm and
larger may drop out of the gas stream at less than 6.6 ft/sec. Eq.
13 predicts 9.9 ft/sec for 1,000-µm liquid droplets and 5.41 ft/
sec for 300-µm liquid droplets. The vapor velocity guidelines using
Eq. 13 are in good agreement with the indication of API 521,
Section 5.7.8.4. Consequently, the maximum axial vapor velocities
of dry (non-condensable) vapors and wet (condensable) vapors
in horizontal flare KO drums should be less than the calculated
values obtained using Eq. 8 and Eq. 13, respectively.
LITERATURE CITED
1
2
The Low NPSH Advantage
Roth Low NPSH Pumps
provide full curve
performance with only 1ft
(0.3m) of liquid required.
3
4
5
6
7
API, " Pressure-Relieving and Depressurizing Systems, " API Standard 521, 7th
Edition, June 2020.
Walas, S. M., " Chemical Process Equipment Selection and Design, " ButterworthHeinemann,
Houston, 1990.
API, " Specification for Oil and Gas Separators, " API Specification 12J, 8th
Edition, October 2008.
Gas Processors Suppliers Association, GPSA Engineering Data Book, Vol. 1, 12th
Ed., GPA, Tulsa, Oklahoma, 2004.
Ishii, M. and M. A. Grolmes, " Inception Criteria for Droplet Entrainment in TwoPhase
Concurrent Film Flow, " AIChE Journal, March 1975.
Center for Chemical Process Safety, Guidelines for Pressure Relief Effluent Handling
Systems, AIChE, New York, 1998.
Turner, R. G., M. G. Hubbard and A. E. Dukler, " Analysis and Prediction of
Minimum Flow Rate for the Continuous Removal of Liquids from Gas Wells, "
Journal of Petroleum Technology, 1969.
JUNG SEOB KIM is a Principal Pressure Safety Engineer at
Covestro. He has more than 35 yr of experience in different
roles within the petrochemical industry, including with
ioMosaic, SK E&C USA, Bayer Technology Services, Samsung
BP Chemicals, and Samsung Engineering. Mr. Kim is a member
of AIChE and is a registered Professional Engineer in the
State of Texas. He earned a BS degree in chemical engineering
from the University of Seoul in South Korea.
Roth chemical processing pumps include a
standard chemical duty, low NPSH, seal less
magnetic drive, and low NPSH multistage pump
options to pump an extensive array of chemicals
including liquefied gases.
HEATHER JEAN DUNSHEATH is an Explosion Safety Expert
at Covestro. She has more than 14 yr of experience in process
safety, including designing emergency relief systems and
facilitating process hazard analysis studies. Ms. Dunsheath
spent 3 yr in Covestro's Global Explosion Safety Group in
Leverkusen, Germany. She earned a BS degree in chemical
engineering from Rice University in Houston, Texas.
1-888-444-ROTH * www.rothpump.com
28 JUNE 2021 | HydrocarbonProcessing.com
JUAN P. LOPEZ is a Senior Pressure Safety Engineer at
Covestro. He has 8 yr of experience in process safety, including
designing emergency relief systems and participating in
process hazard analyses. He is a registered Professional
Engineer in the State of Texas, and earned a BS degree
in chemical engineering from Texas A&M University.
http://www.rothpump.com http://www.HydrocarbonProcessing.com

Hydrocarbon Processing - June 2021

Table of Contents for the Digital Edition of Hydrocarbon Processing - June 2021

Contents
Hydrocarbon Processing - June 2021 - Cover1
Hydrocarbon Processing - June 2021 - Cover2
Hydrocarbon Processing - June 2021 - Contents
Hydrocarbon Processing - June 2021 - 4
Hydrocarbon Processing - June 2021 - 5
Hydrocarbon Processing - June 2021 - 6
Hydrocarbon Processing - June 2021 - 7
Hydrocarbon Processing - June 2021 - 8
Hydrocarbon Processing - June 2021 - 9
Hydrocarbon Processing - June 2021 - 10
Hydrocarbon Processing - June 2021 - 11
Hydrocarbon Processing - June 2021 - 12
Hydrocarbon Processing - June 2021 - 13
Hydrocarbon Processing - June 2021 - 14
Hydrocarbon Processing - June 2021 - 15
Hydrocarbon Processing - June 2021 - 16
Hydrocarbon Processing - June 2021 - 17
Hydrocarbon Processing - June 2021 - 18
Hydrocarbon Processing - June 2021 - 19
Hydrocarbon Processing - June 2021 - 20
Hydrocarbon Processing - June 2021 - 21
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Hydrocarbon Processing - June 2021 - 24
Hydrocarbon Processing - June 2021 - 25
Hydrocarbon Processing - June 2021 - 26
Hydrocarbon Processing - June 2021 - 27
Hydrocarbon Processing - June 2021 - 28
Hydrocarbon Processing - June 2021 - 29
Hydrocarbon Processing - June 2021 - 30
Hydrocarbon Processing - June 2021 - 31
Hydrocarbon Processing - June 2021 - 32
Hydrocarbon Processing - June 2021 - 33
Hydrocarbon Processing - June 2021 - 34
Hydrocarbon Processing - June 2021 - 35
Hydrocarbon Processing - June 2021 - 36
Hydrocarbon Processing - June 2021 - 37
Hydrocarbon Processing - June 2021 - 38
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Hydrocarbon Processing - June 2021 - 40
Hydrocarbon Processing - June 2021 - 41
Hydrocarbon Processing - June 2021 - 42
Hydrocarbon Processing - June 2021 - 43
Hydrocarbon Processing - June 2021 - 44
Hydrocarbon Processing - June 2021 - 45
Hydrocarbon Processing - June 2021 - 46
Hydrocarbon Processing - June 2021 - 47
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Hydrocarbon Processing - June 2021 - 49
Hydrocarbon Processing - June 2021 - 50
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Hydrocarbon Processing - June 2021 - 55
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Hydrocarbon Processing - June 2021 - 57
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Hydrocarbon Processing - June 2021 - 60
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Hydrocarbon Processing - June 2021 - 65
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Hydrocarbon Processing - June 2021 - 86
Hydrocarbon Processing - June 2021 - 87
Hydrocarbon Processing - June 2021 - 88
Hydrocarbon Processing - June 2021 - 89
Hydrocarbon Processing - June 2021 - 90
Hydrocarbon Processing - June 2021 - Cover3
Hydrocarbon Processing - June 2021 - Cover4
Hydrocarbon Processing - June 2021 - GP-1
Hydrocarbon Processing - June 2021 - GP-2
Hydrocarbon Processing - June 2021 - GP-3
Hydrocarbon Processing - June 2021 - GP-4
Hydrocarbon Processing - June 2021 - GP-5
Hydrocarbon Processing - June 2021 - GP-6
Hydrocarbon Processing - June 2021 - GP-7
Hydrocarbon Processing - June 2021 - GP-8
Hydrocarbon Processing - June 2021 - GP-9
Hydrocarbon Processing - June 2021 - GP-10
Hydrocarbon Processing - June 2021 - GP-11
Hydrocarbon Processing - June 2021 - GP-12
Hydrocarbon Processing - June 2021 - GP-13
Hydrocarbon Processing - June 2021 - GP-14
Hydrocarbon Processing - June 2021 - GP-15
Hydrocarbon Processing - June 2021 - GP-16
Hydrocarbon Processing - June 2021 - GP-17
Hydrocarbon Processing - June 2021 - GP-18
Hydrocarbon Processing - June 2021 - GP-19
Hydrocarbon Processing - June 2021 - GP-20
Hydrocarbon Processing - June 2021 - GP-21
Hydrocarbon Processing - June 2021 - GP-22
Hydrocarbon Processing - June 2021 - GP-23
Hydrocarbon Processing - June 2021 - GP-24
Hydrocarbon Processing - June 2021 - GP-25
Hydrocarbon Processing - June 2021 - GP-26
Hydrocarbon Processing - June 2021 - GP-27
Hydrocarbon Processing - June 2021 - GP-28
Hydrocarbon Processing - June 2021 - GP-29
Hydrocarbon Processing - June 2021 - GP-30
Hydrocarbon Processing - June 2021 - GP-31
Hydrocarbon Processing - June 2021 - GP-32
Hydrocarbon Processing - June 2021 - GP-33
Hydrocarbon Processing - June 2021 - GP-34
Hydrocarbon Processing - June 2021 - GP-35
Hydrocarbon Processing - June 2021 - GP-36
Hydrocarbon Processing - June 2021 - GP-37
Hydrocarbon Processing - June 2021 - GP-38
Hydrocarbon Processing - June 2021 - GP-39
Hydrocarbon Processing - June 2021 - GP-40
Hydrocarbon Processing - June 2021 - GP-41
Hydrocarbon Processing - June 2021 - GP-42
Hydrocarbon Processing - June 2021 - GP-43
Hydrocarbon Processing - June 2021 - GP-44
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https://www.nxtbook.com/nxtbooks/gulfpub/refining_processes_handbook_2020
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https://www.nxtbook.com/nxtbooks/gulfpub/hp_202007
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https://www.nxtbook.com/nxtbooks/gulfpub/hp_200901
https://www.nxtbookmedia.com