Hydrocarbon Processing - October 2022 - 33

Plant Safety and Environment
result in damaging temperatures
regardless of the reported values.
° Ensure proper external heat
release from the reaction furnace,
so that the shell temperature
will not increase significantly
beyond the temperature achieved
by the internal refractory. The
reaction furnace is the only vessel
that should not be insulated;
instead, a thermal shroud
should allow heat to escape
from the furnace shell without
wind, rain or snow having a
direct impact on the shell.
° Use proper boiler feedwater
chemistry and proper blowdown
procedures to minimize the
buildup of scale on boiler tube
surfaces and to ensure maximum
heat transfer and minimum
tube-wall temperatures.
° Consider the use of stainlesssteel
materials in locations
where the metal temperatures
cannot be maintained below the
recommended limit or where
the use of refractory materials
is impractical (i.e., catalyst bed
grating and support mesh).
° Conduct regular external piping
and vessel metal temperature
scans to look for temperatures
above the recommended
maximum. In cases where
internal refractory failures have
occurred, temporary external
cooling measures (i.e., steam or
air blowing on the metal surface)
can help limit corrosion until
the refractory can be repaired.
* Low-temperature solid sulfur/
liquid water contact corrosion
° Properly insulate all vessels
and pipes downstream of the
reaction furnace. Insulation
should be designed to keep
metal surface temperatures
hotter than 119°C (246°F).
° In addition to insulation,
consider the use of external
heating [typically, 50 psi
(345 kPa) steam heating] in the
areas that operate at the lowest
temperatures [usually anything
below 150°C (302°F)]. This type
of external heating is already in
common use in many areas of
sulfur plants (e.g., liquid sulfur
rundown lines, transfer lines
and seal/storage devices), but
it is also useful protection in
other areas, such as in condenser
outlets and long-tail gas lines.
° Replace all insulation and
external heating elements as
soon as possible if they are ever
removed for inspection or repair.
Regularly check all steam heating
loops-including all steam
traps-to ensure that they are
properly installed and operating.
° Conduct regular external piping
and vessel metal temperature
scans to look for temperatures
below the recommended
minimum and add insulation or
external heating where required.
° Include a proper sweep of
the SRU during shutdown
procedures to remove as much
sulfur as possible before the
unit is shut down and opened
to atmosphere. In cases where
the plant will be left shut down
for long periods, incorporate
further mechanical sulfurcleaning
steps in combination
with moisture-prevention steps
(i.e., nitrogen blanketing).
* SO3
corrosion
° Where possible, control SO3
formation in oxidizing locations
by minimizing both excess
oxygen levels and temperatures.
For acid gas-fired reheaters,
make routine flowmeter checks
and analytical checks to ensure
that they are being operated well
below stoichiometry (usually
60%-75% of stoichiometry). For
incinerators, these should ideally
be operated with 2%-3% excess
oxygen in the effluent gas, and, in
the worst case, with no more than
5% excess oxygen. Incinerators
should also be operated at
the lowest temperature that
achieves the required levels
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FIG. 2. Examples of SRU plugging.
Hydrocarbon Processing | OCTOBER 2022 33
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Hydrocarbon Processing - October 2022

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