Hydrocarbon Processing - October 2022 - 35

Plant Safety and Environment
of the plugging material are available. In
these cases, samples can be analyzed for
elemental breakdown by x-ray dispersive
spectrometry (EDS), which can immediately
identify the plugging components
(FIG. 3). Otherwise, if samples are not
available, the incident investigation usually
involves the determination of the
plugging location (from a detailed pressure
survey of the plant and visual examination
of all liquid sulfur rundown lines)
in combination with a review of the operating
conditions and history to determine
the most likely root cause.
Regarding the prevention of plugging,
the following recommendations are associated
with the most common root
causes (Note: A more detailed discussion
of plugging mechanisms and recommendations
on avoiding and reversing plugging
can be found in literature6
):
* Solid sulfur
° Prevent sulfur freezing through
proper design, insulation and
external heating. Ensure that
all insulation and external
heating elements are replaced
as soon as possible if they are
ever removed for inspection
or repair. Regularly check all
steam heating loops to be certain
that they are properly installed
and correctly operating.
° Conduct routine external
temperature scans to look for
cold spots. Add insulation or
external heating where required.
* Elemental carbon (soot)
° Always confirm stoichiometry
when the reaction furnace is
being fired on a fuel gas stream
or when any inline heaters (SRU
reheaters or TGU burners) are
initially being restarted with
fuel gas. Stoichiometry checks
involve measuring excess oxygen
as an indication of excess
stoichiometry operation
(a portable fuel-cell-style
oxygen analyzer is recommended
for this service) and directly
measuring process gas soot
using various simple filter tests.
Note: Damaged burners or
poorly designed or operated
burners can result in poor
mixing and create multiple
stoichiometry zones within
the same burner, resulting in
simultaneous soot and excess
oxygen measurements.
° Minimize baseline hydrocarbon
content, along with the frequency
and severity of hydrocarbon
spikes in the acid gas and SWS
gas streams, by optimizing the
design and operation of the
amine and SWS units. Detailed
recommendations for minimizing
hydrocarbons in these two
units are available in literature.
° Conduct sulfur wash procedures
to remove soot from catalyst
beds, where applicable. These
procedures are best applied
shortly after the soot has been
created (i.e., within days or
weeks), since experience has
indicated that the soot can
agglomerate and harden over
time, making it harder to remove.
* Iron corrosion products
° Prevent corrosion
by using the detailed
recommendations presented
in the Corrosion section.
* Alumina fines
° Conduct a preliminary removal
of any visible dust after catalyst/
refractory installation through
vacuuming and sweeping
of the affected vessels.
° Prior to restarting a plant after a
turnaround involving refractory
or catalyst changes, conduct a
thorough dust blow procedure.
This involves using the sulfur
plant air blower to blow dust
out of the affected vessel and
into the atmosphere (or to a
dust collection device). The
dust blow procedure is usually
done vessel by vessel, with
vessels reconnected to the next
downstream vessel as they are
cleaned. An exact procedure
depends on the ease and ability
of creating various breakpoints
in the process and should be
combined with buttoning-up
steps for the various vessels after
they have been entered during
turnaround. The dust blow
procedure has the additional
benefit of removing all other
lightweight contaminants,
such as loose corrosion scale,
soot and other light debris.
* Ammonia salts
° Keep ammonia-containing
SWS streams at or above
85°C (185°F) prior to
entering the reaction furnace.
° Ensure good reaction furnace
ammonia destruction
by maintaining furnace
temperatures at or above
1,250°C (2,282°F). This can be
achieved by various methods,
including acid gas bypass designs,
oxygen enrichment, feed gas
preheating and fuel gas co-firing.
° Properly tune acid gas-fired
reheaters to avoid SO3
formation.
This should involve metering
checks and analytical checks
to confirm stoichiometry.
Part 2. Part 2-which will focus on temperature
excursions, process fluid (gas/
liquid) releases and explosions-will be
published in the November issue.
NOTE
This article was first presented at the Laurance Reid
Gas Conditioning Conference in Norman, Oklahoma,
in February 2022.
LITERATURE CITED
1
Marriot, R. A., R. Sui, N. I. Dowling and C. B.
Lavery, " High Temperature Sulfidation of Carbon
Steel under Claus Waste Heat Boiler Conditions, "
Alberta Sulphur Research Limited Quarterly Bulletin,
July-September 2020.
2 Clark, P. D., N. I. Dowling and C. B. Lavery,
" Corrosion in Claus Tail Gas and Pit Off Gas
Lines, " Alberta Sulphur Research Limited Quarterly
Bulletin, July-September 2015.
3
Yeaw, J. S. and L. Shnidman, " Dew point of flue
gases of fuels containing sulfur, " Power Plant
Engineering, 1943.
4
Huchler, L. and E. Nasato, " Hidden Opportunity:
Maximise Reliability of the Waterside of Sulfur
Recovery Units, " CRU Sulphur Conference 2020.
5
Kiebert, J. and J. Sames, " Sulphur Plant Incinerators
Emission and Energy Conservation: A Balancing
Act, " 2013.
6
Bohme, G., " Why Sulphur Plants Plug, " Laurance
Reid Gas Conditioning Conference, February
2019.
GERALD E. BOHME has been
directly involved in all aspects of
the process engineering consulting
work conducted by Sulphur Experts
Inc. since 1988. He provides expert
advice and consulting services in
the areas of plant inspections,
testing and plant optimization for the sour gas and oil
refining industries-including working on plant
optimization projects in more than 200 operating
facilities around the world. He also has primary
responsibility for overseeing all of Sulphur Experts'
field crews and technical reports. His experience in
the field of sulfur recovery is global-he has worked
on projects in more than 50 countries.
Hydrocarbon Processing | OCTOBER 2022 35
Hydrocarbon Processing - October 2022

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