Hydrocarbon Processing - December 2022 - 54

Process Engineering
in the two crude cases (Crudes A and B, as
shown in TABLE 2) were so widespread, a
two-stage SWS was implemented, which
would generate two separate products
from the SWS to be routed to the SRU-
namely the H2
NH3 gas stream with practically no H2
S-rich gas stream, and the
S
while running on Crude B.
The two-stage SWS design, as shown
in FIG. 4, takes advantage of the different
solubilities and affinities towards water
for the two components: H2
The H2
S and NH3
tively less when compared to NH3
first column (H2
.
S solubility in water is compara.
The
higher pressure, and almost the entire H2
TABLE 2. SRU feed gas compositions
Crude A
Parameter
Flow, kg/hr
S, mol
NH3,
mol
Capacity, tpd of sulfur
(NH3) : (NH3
+ H2
S)
Acid gas from amine
regineration unit (ARU)
H2
6,200
171.3
0.1
145
8.50%
Acid gas
from SWS
1,090
17.7
17.4
Crude B
Acid gas
from ARU
970
24.5
38
36%
Acid gas
from SWS
1,350
24.4
27.6
S stripper) operated at a
S
load would be dissoluted, leaving the NH3
in the water phase to the second column
(NH3 stripper). This requires operation at
a much lower pressure to enable the NH3
to be released from the aqueous phase.
As shown in FIG. 4, an additional H2
scrubber column may also be included in
the design to ensure that the H2
the NH3
S
S slip in
-rich gas stream is limited, mainly
to limit the sulfur oxide emissions issues
in the downstream SRU incinerator, as has
been described in the SRU design aspects.
The design of the downstream SRU
was also implemented to manage the
H2
S- and NH3
ment the two-SWS design. The H2
-rich streams to compleS-rich
stream
is routed in the front-end section
or the Claus section of the SRU for sulfur
recovery, whereas the NH3
-rich stream is
routed to the back end of the unit, to the
thermal incinerator, where it is burned off
and released to the atmosphere. The split
stream of NH3
-rich gas is routed to the
catalytic converter to manage the nitrogen
oxide emissions limits (FIG. 5).
This design allowed the refinery operation
to manage the two operating cases
with Crudes A and B. As indicated previously,
the two-stage SWS and the SRU
operation to manage the high NH3
are applicable
for Crude B of the high nitrogencontaining
crude.
However, when the refinery operates
with Crude A, the two-stage SWS would
operate as a normal single-stage SWS,
whereby the first stage stripping section
(H2
S stripper) would be bypassed, as indicated
by dotted lines in FIGS. 4 and 5.
In this operating condition, there would
be only a single SWS-rich gas sent to the
SRU. The SRU operates in its normal
mode, processing the amine acid and the
SWS gas, as the total NH3
in the SRU feed,
for this case, is in the manageable range for
the standard Claus furnace arrangement.
Takeaway. With the application for residue
upgrade projects in refineries, there
is an inherent increase in the sulfur load
in addition to an out-of-proportion increase
of NH3
load on the existing sulfur
FIG. 4. Simplified scheme for a two-stage SWS unit.
blocks. Depending on the nature of the
applied residue upgrade technology, the
refinery configuration and the crude diet,
the impact on the sulfur block also varies
widely. Existing sulfur blocks need a significant
overhaul or new SRU to meet the
additional loads. The varying operating
parameters of the revamped refinery add
additional complexity to the sulfur block
design. Therefore, proper design of the sulfur
block to meet the post-revamp requirements
for all operating scenarios is of utmost
importance and relevance, not only
to achieve a techno-economical optimum
refinery but also to overcome the environmental
requirements of the project.
DEBOPAM CHAUDHURI is a Senior Process Specialist
for Fluor in New Delhi, India and a subject matter
expert of sulfur recovery processes. He has more
than 21 yr of experience in petroleum refining,
petrochemical complexes and upstream projects.
Chaudhuri earned BTech degrees in chemistry and
chemical engineering from the University of Calcutta.
FIG. 5. SRU design for the management of sour gases from SWS.
54 DECEMBER 2022 | HydrocarbonProcessing.com
HANS VAN DE RUIT is a Technical Manager of Process
Technology for Fluor in Amsterdam, the Netherlands.
He has more than 34 yr of experience in refining
and petrochemical projects. Van de Ruit earned an
MS degree in chemical engineering from the Delft
University of Technology, the Netherlands.
http://www.HydrocarbonProcessing.com
Hydrocarbon Processing - December 2022

Table of Contents for the Digital Edition of Hydrocarbon Processing - December 2022
