Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~3~3~3:~l
IMPROVED THREE CATALYTIC REACTOR EXTENDED
CLAUS PROCESS AND APPARATUS
The invention relates to gas processing. In a
particular aspect, the invention relates to processing
gases containing hydrogen sulfide for the recovery of ele-
mental sulfur. In a further aspect, the invention relates
15 to such a process utilizing the Claus reaction in a Claus
thermal reaction zone (furnace) and two or more Claus
catalytic reaction zones, at least one o~ the two or mor~
Claus catalytic reaction zones being operated periodically
under conditions effective for forming and depositing ele-
~0 mental sulfur on the catalyst.
FIELD OF THE INVENTION
The conventional Claus process for sulfurrecovery from hydrogen sulfide containing gas is widely
practiced and accounts for a major portion of total world-
25 wide sulfur production. Such Claus processes utilize theClaus reaction for removing hydrogen sulfide from the acid
gas stream being processed:
H2S + 1/2 SO~ ~ 3/2 S + H~O
Typical Claus process sulfur recovery plants can
include a Claus thermal reaction zone or furna~e in which
the hydrogen sulfide containing gas can be combusted in
the presence of an oxidant such as oxygen or air to form
an effluent stream comprising unreacted hydrogen sulfide,
35 sulfur dioxide, and formed elemental sulfur, as well as
other compounds. This effluent stream can then be intro-
duced into a series of one, two, or more Claus ~atalytic
reaction zones typically operated so that the resulting
:~3~tP3~
--2--
formed sulfur is continuously removed in the vapor phaae,
that is, the reaction zones are operated above the temper-
ature at which significant sulfur deposition on the cata-
lyst occurs, for the further production of elemental
5 sulfur which can be continuously removed from the Claus
catalytic reaction zones in the vapor phase and removed
from the effluent streams by condensation at appropriate
points in the process. Recovery of sulfur from a hydrogen
sulfide containing stream in a properly designed and oper-
10 ated plant can be as high as, for example, about 96~ fortwo Claus catalytic reaction zone plants or about 97% for
three Claus catalytic reaction zone plants.
In many instances, however, this level of
recovery will be inadequate either because of economic or
15 because of environmental cGnsiderations. To meet the
higher levels of sulfur recovery which can be required, a
number of treatment processes have been developed to
increase the level of overall sulfur recovery. Certain of
these processes involve extensions of the Claus reaction
20 under conditions which favor additional removal of
hydrogen sulfide from the gas stream being processed.
Thus, the residual level of sulfur compounds can be sig-
nificantly reduced by operating one or more of the Claus
catalytic reaction zones under conditions of temperature,
25 pressure and composition such that the preponderance of
elemental sulfur, one of the Claus reaction products, is
deposited on the catalyst. Similarly, the Claus reaction
in one or more of the Claus reactors can likewise be
driven in the direction of removal of hydrogen sulfide and
30 sulfur dioxide from the process stream by removing water,
the other Claus reaction product, from the stream prior to
carrying out the Claus reaction in said one or more Claus
reactors.
It will be appreciated by those familiar with
35 this art area that other processes not involving an exten-
sion of the Claus reaction are also available and have
been utilized for the further removal of hydro~en sulfide
and other sulfur compounds from process gas strea~s~
.:
~3~ 3~
--3--
These other processes include such as the SCOT (Shell
Claus Off-gas Treating), BSRP (Beavon Sulfur Recovery Pro-
cess), the Beavon-Stretford Process, and the like. How-
ever, to the extent that it is economically and techni-
5 cally feasible, use of the Claus reaction either directlyor of the extended Claus reaction are preferred for rea-
sons of simplicity, ease of operation and maintenance,
diminished capital expense and operating expenditures, and
other similar reasons.
Two interrelated concerns are highly significant
in Claus process sulfur plant design. On the one hand, it
is highly desirable to minimize capital expenditure and
operating expense. In this regard, sulfur plant designs
which can eliminate the need for particular equipments
15 such as reactors, condensers, valves, and the like are
needed. On the other hand, it is highly desirable to max-
imize the sulfur recovery efficiency from the acid gas
stream being processed. In this regard, sulfur plant
designs which can maximize recovery without increasing
20 requirements for equipment are needed.
SUMMARY OF THE_ INVENTION
In accordance with the invention, there is pro-
vided a process for recovering sulfur from an acid gas
feed stream comprising hydrogen sulfide in a Claus process
25 sulfur recovery plant. The Claus process sulfur recovery
plant comprises a thermal reaction zone and three Claus
catalytic reaction zones Rl, R2, and R3. The process com-
prises successively passing the acid yas feed stream
through the Claus thermal reaction zone, a first position
30 Claus catalytic reaction zone, a second position Claus
catalytic reaction zone, and a third position Claus cata-
lytic reaction zone, the third position Claus catalytic
reaction zone being operated under conditions effective
for depositing a preponderance of the formed sulfur on the
35 catalyst. The processed gas stream can be passed through
the Claus catalytic reaction zones in a first and a second
mode, in the first mode the processed gas stream being
passed successively through Rl, R2, and R3 and in the
r 3 ~
-4
second mode the processed gas stream being passed
successively through the Claus catalytic reaction zones
Rl, R3, and R2. Periodically, flow is switched from the
first mode to the second mode and from the second mode to
5 the first mode. Prior to switching from the first mode to
the second mode and from the second mode to the first
mode, the Claus catalytic reaction zone in the second
position can be preconditioned by introducing thereinto a
cold stream having a temperature effective for condensing
10 sulfur on at least a portion of the catalyst and passing
the resulting stream through a remaining substantial por-
tion of the catalyst, thereby further preparing the cata-
lyst for adsorption-type operation in the third (final)
position. In accordance with anoth~r aspect of the inven-
15 tion, the Claus catalytic reaction zone in the secondposition can be preconditioned by passing a stream lean in
sulfur and sulfur compounds, at least as compared with the
regeneration streaml in contact with at least a substan-
tial portion of the catalyst therein for a period of time
20 effective for reducing an increase in emissions occurring
where a hot, freshly regenerated reactor is switched
without preconditioning into a final position of a series
of Claus catalytic reaction zones, prior to switching the
thus preconditioned second position catalytic reaction
25 zone into the third (final) position.
Further according to the invention, there is
provided apparatus for the recovery of sulfur from an acid
gas feed stream comprising hydrogen sulfide, the apparatus
comprising a Claus thermal reaction zone means, first,
30 second, and third catalytic reaction zone means Rl, R2,
and R3, at least two sulfur condensing means, means for
configuring the foregoing for processing the acid gas feed
stream in a first mode in which the acid gas stream is
passed successively through the Claus thermal reaction
35 zone, reactor Rl, reactor R~l and reactor R3, and in a
second mode in which the acid gas stream is passed succes-
sively through the Claus thermal reaction zone, reactor
Rl, reactor R3, and reactor R2, means for regenerating the
3~
--5--
catalyst in the second position reactor in each mode, and
means for preconditioning the reactor in the second posi-
tion prior to switching from the first mode to the second
mode and prior to switching from the second mode to the
5 first mode, said second position reactor being R2 in the
first mode and being R3 in the second mode.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be further understood and
appreciated from the following detailed description and
10 the drawings in which:
Figure 1 illustrates schematically a first mode
of the process and apparatus according to the instant
invention.
Figure 2 illustrates schematically a second mode
15 of the process and apparatus according to the instant
invention.
The invention will be further understood and
appreciated from the following detailed description and
the examples.
DETAILED DESCRIPTION OF THE INVENTION
As used herein, the symbols Rl~ R2, and R3 are
employed to refer to specific reactor equipment whereas
the terms first position Claus catalytic reactor, second
position, and the like, are employed to refer to the posi-
25 tion of the reactor relative to the process stream being
processed. ~rom the following description it will be
apparent that rea~tor Rl can always be the first position
reactor, while reactors R2 and R3 alt~rnate between being
second position and third position reactors. It will be
30 further appreciated that the term first position con-
denser, second position condenser, and the like, refer to
the condenser upstream of a correspondingly positioned
reactor. Thus, a first position sulfur condenser is
upstream of a first position Claus catalytic reaction
35 zone, a second position sulfur condenser is upstream of a
second position Claus catalytic reaction zone, and so
forth.
~ 3~ 3
--6--
In accordance with the invention, a process and
apparatus for the recovery of sulfur from an acid gas feed
stream comprising hydrogen sulfide utilizes a Claus pro-
cess sulfur recovery plant having a Claus thermal reaction
5 zone, three Claus catalytic reaction zones Rl, R2, and R3,
and at least two sulfur condensers. According to a pre-
ferred embodiment, the Claus process sulfur recovery plant
can have one reactor Rl which always functions in the
first position as a high temperature Claus catalytic reac-
10 tion zone from which formed elemental sulfur is continu-
ously removed in the vapor phase, and two other reactors
R2 and R3 which can be rotated between second position and
third position operation, the reactor being operated in
the third position being operated under conditions effec-
15 tive for forming and depositing the preponderance of ele-
mental sulfur on the catalyst.
The process and apparatus operate in two primary
or general modes which can be designated Mode A and
Mode B. In both modes, the acid gas feed stream can be
20 passed successively through the Claus thermal reaction
zone, the first position Claus catalytic reaction zone,
the second position Claus catalytic reaction zone, and the
third position Claus catalytic reaction zone. In both
modes, the first position Claus catalytic reaction zone
25 can comprise a dedicated reactor Rl, the remaining two
Claus catalytic reaction zones comprising two reactors R2
and R3 which are alternated between the second position
and the third position in the sequence described above.
Upstream of the first position Claus catalytic reaction
30 zone is a first position condenser, and upstream of the
second Claus catalytic reaction zone, is a second position
condenser. During Mode A, the reactor R2 operates as the
second position Claus catalytic reaction zone and the
reactor R3 operates as the third position Claus catalytic
35 reaction zone, whereas during Mode B the reactor R3 oper-
ates as the second position Claus catalytic reaction zone
and the reactor R2 operates as the third position Claus
catalytic reaction æone. During both Mode A and Mode B~
~3V3~
--7--
the reactor which was previously in the third position in
which sulfur has been deposited on the catalyst and which
has been moved into the second position undergoes regener
ation of the sulfur-laden catalyst therein while simulta-
5 neously functioning as a high temperature Claus reactionzone producing elemental sulfur from reaction of hydrogen
sulfide and sulfur dioxide in the gas stream passir.g ther-
ethrough in the presence of an effective Claus catalyst.
Suitable regeneration/Claus operating temperatur~s can be
10 generally in the range of from above about the sulfur con-
densation point to about 700F, preferably in the range of
from about 550 to about 650F.
Prior to switching the freshly regenerated
second position Claus catalytic reactor to the third posi~
15 tion, that is, prior to switching from Mode A to Mode B or
from Mode B to Mode A, the second position Claus catalytic
reaction zone can be preconditioned by introducing there-
into a cold stream having an inlet temperature effective
for condensing sulfur on at least a portion of the cata-
20 lyst therein and passing the resulting stream through asubstantial portion of the catalyst to reduce or minimize
any increase in sulfur emissions which otherwise can occur
when a hot freshly regenerated reactor is switched into
the third (final~ position. According to another aspect
25 of the invention, the preconditioning can be effected by
passing a stream lean in sulfur and sulfur compounds as
compar~d with the regeneration gas stream through at least
a substantial portion of the catalyst and reducing the
otherwise observed temporary increase in sulfur emissions
30 occurring where a hot, freshly regen~rated reactor is
switched without preconditioning into a final position of
a series of Claus catalytic reaction zones~ The tempera-
ture of the cold stream used for preconditioning can be
broadly about the sulfur condensation point, preferably in
35 the rang~ of about 160 to about 330F, and most preferably
in the range of about 250 to about 330F.
The preconditioning step can be conducted for a
relatively short period of time, on the order of a few
~31; 333~
8--
hours or less, for example, for a period of two hours or
even less than about one hour. Generally, the precondi-
tioning period can be continued for a period effective to
eliminate or significantly reduce the temporary rise in
5 sulfur emissions which otherwise occurs after switching a
freshly regenerated Claus catalytic reaction zone into a
final position. The minimum period of time can be readily
determined by the person skilled in the art by observing
the operation of a plant in accordance with the invention.
10 Thus, for example, the operator can observe emissions from
the plant, for example, with a Continuous Stack Emissions
Monitor (CSEM~, determine the occurrence and the time
frame of the temporary increase in sulfur emissions, and
can increase the preconditioning time until a significant
15 reduction in the temporary increase of sulfur emissions
occurs. Generally, a reduction in the temporary increase
by a factor of at least 10%, preferably by at least 50%,
and most preferably by 80% or more will be desired. From
the above, it will be apparent that a period from a few
20 minutes to a few hours, for example one or two hours, will
generally be effective for preconditioning the reactor
prior to switching. Preferably the preconditioning period
will be less than about 25% of the normal time period for
adsorption-type operation.
It will be appreciated by those skilled in the
art, that such a relatively short preconditioning period
will not generally be sufficient to precondition the cata-
lyst bed to the operating temperature required for adsorp-
tion. In fact, most of the cooling to adsorption-type
30 operating conditions will occur after switching. However,
a portion of the catalyst near the feed gas inlet end will
be cooled to a low temperature which is about the same as
the inlet gas, for example, about 260F. Then, in the
presence of the freshly regenerated catalyst a forward
35 Claus reaction can occur resulting in additional removal
of hydrogen sulfide and ~ulfur dioxide from the process
gas stream which will be deposited on the catalyst, pro-
ducing a sulfur-lean stream which can effect stripping of
~3~P~333~
g
residual sulfur loading on the catalyst to extremely low
levels, thereby minimizing and reducing any sulfur emis-
sions which might otherwise occur following switching of a
hot, freshly regenerated bed of catalyst into the third
5 position in ac~ordance with the invention.
From the above, it will be appreciated that the
preconditioning step in accordance with the invention can
be effected by passing a gas stream relatively lean in
sulfur and sulfur compounds in contact with at least a
10 substantial portion of the hot freshly regenerated cata-
lyst while in the second position for a period of time to
further reduce the level of residual sulfur loading in
such portion as can be determined by observing the reduc~
tion of the temporary increase in sulfur emissions
15 described above, and then switching the thus precondi-
tioned reactor into the third (final) position.
According to a preferred embodiment of one
aspect of the invention, the preconditioning step can be
accomplished by feeding the second position condenser
20 effluent at substantially its exit temperature, typically
about 260F, to the second position Claus catalytic reac-
tion zone, the second position condenser effluent other-
wise being reheated by appropriate means to a temperature
effective for regeneration and high temperature ~laus con-
25 version in the second position Claus catalytic reactionzone~
The thermal reaction zone which can be utilized
in accordance with the invented process and apparatus can
be any suitable thermal reaction zone such as, for
30 example, a muffle tube furnace, a fire-tube furnace, and
the like, which can be selected and designed in accordance
with principles familiar to those skilled in this art
area. Similarly, the Claus catalytic reaction zones can
comprise any suitable vessel for containing catalyst
35 facilitating the Claus reaction, whether in fixed-bed or
fluid/moving-bed format, and can be selected, sized, and
designed in accordance with principles well established in
this art areaO
~3~3~
--10--
In accordance with the invention, a reactor Rl
can be operated as a conventional first Claus catalytic
reaction zone in the first position with the temperature
being maintained at a temperature in the range of from
5 above about the sulfur condensation point to about 700F.
Preferably the temperature can be in the range of from
about 550 to about 650~F. The effluent from the first
Claus catalytic reaction zone Rl can be removed and pro
vided to a second position condenser and can then be
1~ reheated by a portion of the first position Claus cata-
lytic reaction zone effluent gas, or by other means
familiar to those skilled in this art area. The reheated
effluent gas from the first position Claus catalytic reac-
tion zone can then be provided to the second position
15 Claus catalytic reaction zone which can be operated for
high temperature Claus conversion and can simultaneously
and conc-~rrently be undergoing catalyst regeneration, the
reactor in the second position having been previously
rotated from the third position where it had been operated
20 under conditions effective for depositing a preponderance
of formed sulfur on the catalyst therein. The effluent
stream from the second position Claus catalytic reaction
zone can then be cooled in a third position condenser and,
in a preferred embodiment, the effluent gas from the third
25 position condenser can flow without reheating to the third
position Claus catalytic reaction zone which can be oper
ated as an adsorption-type ceactor. Broadly, the tempera-
ture in the third position Claus catalytic reaction zone
can be in the range of from about 160 to about 330F,
30 preferably in the range of from about 250 to about 330F,
and most preferably about 260~F at the inlet to about
270F at the outlet. The effluent from the third position
Claus catalytic reaction zone can then be provided to an
incinerator or to ~urther treatment if appropriate.
~uring regeneration of the second position Claus
catalytic reaction zone, ~hich occurs concurrently with a
high temperature Claus conversion, three distinct phases
can be identified, a first heat-up phase in which the
~3~;;1;~3~
--11--
catalyst having sulfur deposited thereon is being heated
to an effective temperature for vaporizing and removing
the sulfur from the catalyst, a second plateau phase at
approximately constant temperature in which the sulfur is
5 being rapidly vaporized and removed from the catalyst,
then a third phase of final temperature rise with further
removal of sulfur from the catalyst. These ~hases of
regeneration will be familiar to those skilled in this art
area and there~ore require no further explanation at thls
10 point. It will, however, be appreciated that during the
regeneration of the catalyst in the second position Claus
catalytic reactor, the catalyst surface is available for
catalyzing the high temperature Claus conversion of
hydrogen sulfide and sulfur dioxide in the process gas
15 stream being passed therethrough.
The instant invention provides an improved
method including a preconditioning step at the end of
regeneration when the Claus process sulfur recovery plant
comprises only three Claus catalytic reaction zones, and
20 the freshly regenerated Claus catalytic reaction zone is
to be rotated into the inal or third position. In a typ-
ical operation, the sulfur loading on the catalyst can be
as high as about 0.75 lbs of sulfur per pound of catalyst
at the start o~ regeneration and it may be reduced, for
25 example, to about 0.1 lbs of sulfur per pound of catalyst
at the end of the plateau phase and, for example, to about
0.01 lbs of sulfur per pound of catalyst at the end of the
final heating period. At this time, the remaining resi-
dual sulfur loading is relatively low; nevertheless, if
30 the hot freshly regenerated reactor is switched into the
third position immediately, it has been found that the gas
leaving the reactor and going to the tail gas line will
have a small but significant sulfur content which can
constitute an unacceptable increase in the sulfur emis-
35 sions level. We have found that this unacceptable rise insulfur emissions level can be prevented in accordance with
our process by leaving the freshly regenerated reactor in
the second position for an additional relatively short
- .
-` - ~L3~3~ ~
-12-
period of time during which preconditioning of the freshly
regenerated reactor can be effected, for example, by
introducing a cold gas stream into the reactor, the cold
gas stream having an inlet temperature effective for con-
5 densing sulfur on at least a portion of the catalyst orgenerally by passing a stream leaner in sulfur and sulfur
compounds in contact with at least a substantial portion
of the catalyst and further reducing the residual sulfur
loading thereof. In accordance with one aspect of the
lO invention, the inlet gas temperature to the second posi-
tion Claus catalytic reaction zone can be reduced to start
the process of preconditionin~ the catalyst. As indicated
above, the length of this time period can be determined
for each plant from data obtained during operation of the
15 plantl but it is envisioned that typically this period
would be no longer than one or two hours in length. We
have found that even though the cooled reactor feed gas
used in accordance with this step o our invention has
been processed through only one upstream Claus reactor,
20 that use of the gas can result in additional removal of
sulfur from the catalyst and can also reduce the tempera-
ture of the gas leaving the reactor sufficiently to reduce
the sulfur content of the effluent gas so that the reactor
can then be switched to the third (final) position without
25 causing the otherwise observed unacceptable rise in sulfur
emissions level. By preconditioning the reactor prior to
switching the temporarily increased sulfur emissions which
would have appeared in the tail gas stream after switchiny
can be removed in the third position Claus catalytic con-
30 version zone which functions as an adsorption type
reactor. After the time period has passed during which an
increase in sulfur emissions can occur, the preconditioned
reactor can be moved into the third (final) position.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring now to the drawings and in particular
to Figure l, Figure 1 represents a first mode of a pre
ferred embodiment of the instant invention in which flow
of acid gas passes successively through reactors Rl, R2
and R3 in sequence.
-13-
As shown in Figure 1, a Claus thermal reaction
zone can comprise a furnace 14 having an acid gas inlet to
which acid gas can be provided by line 10 and an oxidant
inlet to which an oxygen containing gas, for example, air~
5 can be provided by line 12. In the Claus thermal reaction
zone or furnace 14, the hydrogen sulfide in the acid gas
can be combusted in the presence of the oxidant to produce
a hot combustion product stream comprising hydrogen sul-
fide, sulfur dioxide, elemental sulfur and other com-
10 pounds. The hot effluent product stream from the furnacecan then be provided to a waste heat boiler 16, in the
illustrated embodiment, integrally constructed with the
furnace 14. Typically, the waste heat boiler 16 can be a
shell-and-tube exchanger having provision made for
15 removing cooled effluent products after 1, 2, or more
passes therethrough. Thus, for example, a first pass
effluent can be removed from waste heat boiler 16 by
line 24 at a temperature in the range of, for example,
about 800 to about 1200F. A second pass effluent can
20 also be removed, for example, after two passes through the
waste heat boiler 16 by line 18 at a temperature in the
range of~ for example, 550 to about 650F and can ~e pro-
vided to a first position condenser 20 (C1) in which ele-
mental sulfur can be condensed and removed by line 22.
25 The cooled sulfur denuded effluent stream from the first
condenser 20 can be removed and combined in line 30 with
the first pass effluent stream in line 24 to provide in
line 32 a reheated stream at a temperature effective for
high temperature Claus conversion. The temperature of the
30 reheated stream can be controlled by temperature cont-
rolled valve 24V in line 24 which receives a temperature
signal via control line 34 from line 32.
According to the invention, the first position
Claus catalytic reaction zone comprises a dedicated
35 reactor 36 (Rl) which can be operated continuously for
high temperature Claus conversion. Thus, hydrogen sulfide
and sulfur dioxide present in line 32 can be reacted in
the presence of a catalyst for facilitating the Claus
r ,f~
~3~r3~
-14-
reaction in first position reactor 36 and elemental sulfur
can be produced. The elemental sulfur can be continuously
removed in the vapor phase by line 42 and provided to
second position condenser 44 (C2) in which the gas stream
5 can be cooled and liquid sulfur condensed therefrom and
removed by line 46. The resulting cool sulfur-denuded
stream in line 48 can then be reheated to an appropriate
temperature in line 50 for high temperature Claus conver-
sion, for example, by bypass reheating using effluent from
10 the first position Claus catalytic reaction zone 36 via
line 38 having associated valve 38V, shown partly open~
Other means of reheat can, of course, also be utilized;
however, this method of reheat is preferred according to
the instant invention because the equipment configuration
lS facilitates cooling of the second position Claus catalytic
reaction zone as is hereinafter described.
The process gas stream in line 50 can then be
provided successively to the second position Claus cata-
lytic reaction zone, a third position sulfur condenser,
20 and to the third position Claus catalytic reaction æone,
the reactors R2 and R3 being alternately rotated between
the second position and the third position. According to
the illustrated configuration of Figure l, the reactor R2
is configured in the second position and the reactor R3 is
25 configured in the third position by having valves 52V in
line 52, 58V in line 58, 66V in line 66 and 72V in line 72
open and valves 54V in line 54, 60V in line 60, 64V in
line 64, and 70V in line 70 closed. It will be apparent
to those skilled in this art area that the reactors can be
30 configured in Mode B in which reactor R3 is in the second
position and reactor R2 is in the third position by
closing valves 52V, 58Vr 66V, and ~2V and opening valves
54V, 60V, 64V, and 70V. This configuration is illustrated
in Figure 2 in which the condition of these valves is
35 appropriately shown, the other reference numerals corre-
sponding to those of Figure 1 and therefore needing no
further explanation.
~ r Ir~ ~
-15-
Thusl in accordance with the configuration shown
in Figure 1, the process stream in line 50 can be provided
by line 52 and valve 52V to the second position Claus
catalytic reaction zonel in the illus~rated configuration,
5 reactor R2 (56) which is operated concurrently for regen-
eration and as a high temperature Claus catalytic reaction
zone. The effluent stream can then be removed from the
second position Claus catalytic reaction zone, for
example, by line 58 having associated valve 58V and pro-
10 vided by line 74 to the third position condenser 76 (C3)in which the effluent products can be cooled and elemental
sulfur removed therefrom by line 78. The cooled effluent
stream exiting the third position condenser 76 can then be
provided substantially at its effluent temperature to the
15 third position Claus catalytic reaction zone 68 (R3) which
can be operated under conditions effective or depositing
a preponderance of the sulfur on the catalyst therein, for
example, by line 80, line 66 and valve 66V to reactor 68
(R3). The effluent from the third position Claus cata-
Z0 lytic reaction zone can then be removed, by line 72,valve 72V, and line 62 to the incinerator.
Operation in the Mode A as shown in Figure 1 or
Mode B as shown in Figure 2 can be continued and sulfur
loading on the catalyst in the third position Claus cata-
25 lytic reaction zone increases. At some time prior to thetime at which the sulfur loading in the third position
Claus catalytic reaction zone reaches a level at which the
instantaneous recovery of sulfur starts to fall, the
second position Claus catalytic reaction zone ~an be pre-
30 conditioned in accordance with the invention preliminaryto moving the second position reactor into the third
(final) position, that is, switching from Mode A to Mode B
or from Mode B to Mode A~ According to a preferred embod-
iment of the invention, this preconditioning can be
35 effected by closing, or substantially closing, the bypass
valve 38V in line 38 thus sending all, or substantially
all, of the effluent of reactor 36 (R1) to the second
position condenser 44 ~C2~ and providing the effluent from
~ J',~ 3
-16-
the condenser 44 substantially without reheating typically
at about 260F to the second position Claus catalytic con-
version zone. After the second position Claus catalytic
conversion zone has been precondltioned in accordance with
5 the invention, then the second position Claus catalytic
reaction zone can be rotated into the third position as
hereinabove described, the valve 38V can be opened, and a
heated process gas stream can be provided to the reactor
newly switched into the second position Claus catalytic
10 conversion zone for regeneration and concurrent high tem-
perature Claus operation.
The invention will be further appreciated and
understood from the following Example.
EXAMPLE
The configuration illustrated in the Figures was
simulated by setting up three tubular reactors equipped
with Claus catalyst in series with the first two reactors
simulating the two reactors R2 and R3 and the third
tubular reactor simulating a catalytic incinerator. By
20 using two reactors simulating R2 and R3, rather than one,
it is considered that the dynamic behavior of the system
was accurately simulated. By using a reactor simulating a
catalytic incinerator, the sulfur species from the effl-
uent of the final reactor could be be converted into
25 sulfur dioxide so that a sulfur material balance around
the incinerator can be made to estimate sulfur vapor loss
from the system. By thus taking sulfur vapor loss into
account, it is believed that an accurate measurement of
the overall sulfur recovery was obtained.
3Q The reaction setup was operated for the periods
and with the results, shown as percent sulfur recovery
from original acid gas, set forth in the following Table:
-17-
TABLE
Period Computer
Length Simulation Laboratory Results
Period (Hr) Results Low High Avg
Heat-up 1.8 99.37% }
Plateau 3.0 98.91% } 98.~0% 99.24% 98.97%
Final Heat 0.2 98.18% }
lO Precool 2.0 99.33% 98.59% 99.30% 99.28%
Adsorb 2.5 99.59% 98.96% 99.42% 99.36%
Total or Avg 9.5 99.25% 99.14
The results indicate that recovery can range
15 from about 98.6 to about 99.4~ during the periods. The
results further indicate that an average recovery of about
99.1% can be achieved with such a three reactor system as
described in the instant application, or on the order of
about 99.25% based on those predicted by computer simula-
20 tion. It will be noted that computer simulation predictsvalues somewhat higher than those achieved in the labora-
tory setup. The lower values achieved in the laboratory
are attributed to H2S/SO2 being off-ratio due to some SO2
adsorption on the catalyst. It is expected that actual
25 recoveries will be in the range of about 99.1 to about
99.25 or slightly higher.
It will be appreciated from the foregoing that
there has been provided an improved apparatus and method
for carrying out the Claus sulfur recovery process in a
30 design utilizing a Claus thermal reaction zone and three
and only three Claus catalytic conversion zones. The
sulfur recovery process and apparatus when operated as
hereinabove described is indicated to be capable of giving
recoveries on the order of from about 99.1% to about
35 99.25% or slightly higher, and in comparison with certain
prior art processes and apparatus can achieve this level
of recovery efficiency while eliminating equipment such as
some reactors, some condensers, some reheat exchangers,
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and the like, as will be apparent from comparing the
process and apparatus according to the instant invention
with such prior art designs. Further, separate ducting
and valves for the regeneration gas can be eliminated by
5 utilizing first reactor effluent for reheat, and then pro-
viding second condenser effluent substantially without
reheating for the preconditioning step in accordance with
the invention. Finally, the pressure drop can be ~uch
less in accordance with the instant design as compared
lO with other three and four reactor designs, which can
reduce the investment and operating cost for the air
blower, which i9 commonly provided in line 12. Further,
it will be noted and appreciated that it will be possible
to modify an existing three reactor high temperature Claus
15 plant to t21e apparatus and process in accordance with the
invention and at a relative low cost, raise the recovery
from about 96 or 97% to about 99% or more.
Although the invention has been described herein
in accordance with preferred embodiments and giving spe-
20 cific temperatures and conditions of operation asrequired, it will be apparent ~hat persons skilled in this
art can make other variations and modifications and
methods of practicing the invention without departing from
the spirit or scope of the invention as set forth in the
25 claims appended hereto. Accordingly, the invention is not
to be restricted by the preferred embodiments described
herein but by the claims set out here below.
