Hydrocarbon Processing - December 2020 - 36

Plant Design, Engineering and Construction

Flue gas from
regenerator

tion drops in line with a reduction of
SRU tail gas flow (TABLE 4).

Flue gas to
atmosphere

CO
boiler
Orifice
chamber

FCC reactor and
regeneration system

Tail gas from SRU

Tail gas from
incinerator
Wet gas
scrubber

FIG. 9. Alternative option: CO boiler and wet gas scrubber at the FCCU.

TABLE 4. SRU capacity increases by application of oxygen enrichment
Enriched oxygen, %

21 (atmosphere)

25

50

100

100

113

170

226

Acid feed gas, kmol/hr
Oxygen, kmol/hr

50

57

85

113

Nitrogen, kmol/hr

189

169

84

0

Total flow to SRU, kmol/hr

339

339

339

339

Total flow to TGTU, kmol/hr

293

286

261

235

TABLE 5. Comparison between conventional SRU with SCOT and modified SRU with
caustic scrubbing

Item

Conventional SRU + SCOT process
(fixed catalytic beds)

Modified SRU + caustic scrubbing
system (switching reactors
with internal cooling)

Total capacity

200 tpd of sulfur production

200 tpd of sulfur production

Total investment cost

$80.5 MM

$56.8 MM

Configuration

2 trains of SRU and SCOT,
respectively

2 trains of SRU and 1 common
train caustic system

Overall sulfur
recovery efficiency

Min. 99.9%

Avg. 99.5%

SO2 emissions

Max. 250 ppmv

50 ppmv-250 ppmv

ryover in the SCOT unit. SO2 emissions
can be reduced by up to 50 ppm with the
correct scrubber design, and CO2 emissions will be substantially reduced compared to the SCOT unit due to no steam
consumption. For plant owners looking
for countermeasures against tight environmental regulations, the caustic scrubbing system is a good alternative choice.
In the refinery, which has an upgraded
secondary plant such as the fluidized catalytic cracking (FCC) unit, another option
with the modified SRU can be considered.
Instead of a dedicated caustic scrubber at
the TGTU, the tail gas from the SRU can
be directly connected upstream of the CO
boiler, or the tail gas from the incinerator
can be routed to the inlet of the wet gas
scrubber, as shown in FIG. 9.
The CO boiler performs complete
combustion of carbon monoxide (CO)
36

DECEMBER 2020 | HydrocarbonProcessing.com

with excess air; therefore, all minor sulfur
species of tail gas can be converted to SO2.
Alternatively, all SO2 from the incinerator
downstream of the modified SRU can
be treated in the wet gas scrubber, which
removes SO2 and particulate with caustic (NaOH) or magnesium hydroxide
[Mg(OH)2 ] in the flue gas from the CO
boiler. Significant cost savings are achievable with this modification.
Some sulfur plants apply oxygen
enrichment for the following benefits,
even though additional cost is required
to purchase high-purity oxygen: Greater
processing capacity for existing plants,
lower capital cost for smaller equipment
for new plants, smaller tail gas treating
equipment, and lower reheater and incinerator fuel costs. In an environmental
view, this technology is also beneficial to
CO2 emissions since fuel gas consump-

Takeaway. If a new Claus plant is being considered, the operating company
should endeavor to select the SRU/
TGTU processing scheme that will result
in the most reliable plant, built for the
minimum investment that can be operated in compliance with emissions regulations. The same considerations apply for
modifying or revamping existing facilities.
In the past, the Claus process was often
viewed as just a means for disposing of a
noxious and highly toxic byproduct of upstream processes. In that role, it did not receive much attention. Later, with the dramatic increase in environmental concerns,
the need to improve the operation and
design of the process has become a priority. Fortunately, the goals of improving the
sulfur yield and sulfur recovery efficiency,
and of reducing emissions, are one and the
same for the process.
For this review, sulfur recovery and
emissions were the top two priorities. The
process is a critical environmental facility,
so production benefit is subordinate. The
third and fourth priorities were process reliability and operation stability, because the
SRU can widely impact plant performance
and profit. Equipment and operational
costs were the next concerns. So far, the
commercialized and applicable processes
have been briefly identified and compared
and their best combinations have been researched. The overall performance of the
optimized combined SRU-TGTU processes are summarized in TABLE 5.
LITERATURE CITED
Goar, B. G., " Tail gas clean-up processes-A review, "
33rd Gas Conditioning Conference, Norman,
Oklahoma, March 1983.
2
Paskall, H. G., " Calculation methods for heat and material balances in sulfur plants, " Houston, March 1981.
3
Mehta, M., " Enhancing SRUs with oxygen-enriched
air, " PTQ , Q2 2005.
4
Park, G. W., " Optimize the design of amine treatment and sulfur recovery, " Hydrocarbon Processing,
May 2020.
1

GI WON PARK works in the
upstream division of Kuwait Oil Co.
in Kuwait. He has 25 yr of
experience in process design and
operation, and holds two U.S.
patents and one international
patent in process technology. He
has worked on various projects and revamps,
including three billion-dollar projects for grassroots
refining (SK Energy) and petrochemical plants as a
senior process engineer and engineering team leader.
Mr. Park holds a BS degree in chemical engineering
from Dong-A University in Busan, Korea.


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Hydrocarbon Processing - December 2020

Table of Contents for the Digital Edition of Hydrocarbon Processing - December 2020

Contents
Hydrocarbon Processing - December 2020 - Intro
Hydrocarbon Processing - December 2020 - Cover1
Hydrocarbon Processing - December 2020 - Cover2
Hydrocarbon Processing - December 2020 - Contents
Hydrocarbon Processing - December 2020 - 4
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Hydrocarbon Processing - December 2020 - 80A
Hydrocarbon Processing - December 2020 - 80B
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Hydrocarbon Processing - December 2020 - Cover3
Hydrocarbon Processing - December 2020 - Cover4
Hydrocarbon Processing - December 2020 - GP-1
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