Hydrocarbon Processing - December 2022 - 49

Process Optimization
tally as the world continues to transition
to renewable fuels that also contain sulfur
compounds that must be removed.
Most new oil and gas field discoveries
today are sour and do require a certain
amount of cleaning up as part of bringing
the products to market. Global sulfur
emissions standards, for both hydrocarbon
products and emissions from refineries,
gas plants and production facilities,
are continuing to tighten. Over the past
few decades, this has been evident with
some facilities upgrading Claus units and
now investigating further emissions reduction
with hydrogenation and aminebased
TGTUs. Additionally, operators
are looking to reduce their carbon footprint
to reflect the exponential increase
in carbon dioxide (CO2
) footprint as
SO2 emissions are reduced close to zero
in those types of TGTUs.
Claus process with conventional TGT.
The Claus process with conventional tail
gas treatment, shown in FIG. 1, typically
comprises a two-stage catalytic Claus
plant combined with a hydrogenation/hydrolysis
and amine-based TGTU, sometimes
referred to as a BSR/amine plant,
or SCOT plant. The offgases that contain
small amounts of H2
cally converted to SO2
S and COS are typiin
a thermal oxidizer
before venting to atmosphere.
Sulfur recoveries > 99.9% are possible
but at a relatively high CAPEX and OPEX.
It is in the last few percentage points where
costs escalate; the process is energy-intensive
and this is reflected in carbon footprint.
The conventional hydrogenation and
amine-based TGT was first patented by
the Ralph M Parsons Co. in 1971, with
other companies quickly following suit.
Incremental improvements have been
made throughout the years, but the process
largely remains the same. Improvements
with the amines used are related
to increased H2
S selectivity (often using
proprietary amines), but the process is
largely the same. Regardless, amine regeneration
is energy intensive.
Alternatives can offer lower CAPEX
and OPEX. One example would be Comprimo's
Claus tail gas direct oxidation
technologyb
that, when coupled with
caustic scrubbing, achieves very low sulfur
emissions. CAPEX is lower, but there
is an additional waste stream (spent caustic)
that has associated disposal costs.
However, this configuration is only appliFIG.
3. Claus reaction furnace chemistry: the fate of recycled H2
Research Ltd. (ASRL) and HEC Technologies.
SO4. Source: Alberta Sulphur
cable to relatively low-sulfur plant capacities,
and typically (but not exclusively)
to refinery plants with sulfur capacities <
300 tpd sulfur. Topsoe's WSA process also
offers an alternative TGT technology; to
date, some 165 units have been licensed.
The new sulfur recovery processa
technology (FIG. 2), using a WSA TGTU
with acid recycling, reduces energy intensity
but still maintains the sulfur recovery
of > 99.9%. Equipment count,
CAPEX and carbon footprint are all
reduced. The product is still sulfur, but
with enhanced operational benefits.
Enhanced sulfur recovery of >
99.95% is also achievable by the WSA
TGTU with double condensation. This
is a refined solution that consumes no
chemicals and produces no effluents.
Other alternatives exist, such as tail gas
scrubbing using chemicals like hydrogen
peroxide (H2
O2) or sodium hydroxide
(NaOH), which are cheaper than double
condensation but have chemical consumption
and, in the case of NaOH, an
effluent stream to be dealt with.
FIG. 2. A simplified process flow diagram of the new sulfur recovery processa
.
FIG. 4. The proprietary sulfur recovery processa
with SWS gas to the WSA section.
Hydrocarbon Processing | DECEMBER 2022 49
Hydrocarbon Processing - December 2022

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