Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
3~
IMPROVED FOUR CATALYTIC REACTOR EXTENDED
CLAUS PROCESS
The invention relates to gas processingO 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
process sulfur recovery plant comprising a Claus thermal
reaction zone and two or more Claus catalytic reaction
zones, at least one of the two or more Claus catalytic
reaction zones being operated periodically under condi-
20 tions effective for forming and depositing elemental
~i sulfur on the catalyst.
FIELD OF THE INVENTION
.
The conventional Claus process for sulfurrecovery from hydrogen sulfide containing gas is widely
25 practiced and accounts for a major portion of total world-
wide sulfur production. Such Claus processes utilize the
Claus reaction for the recovery of sulfur:
H2S + l/2 SO2 ~ 3/2 S + ~ o
Typical Claus process sulfur recovery plants can
include a Claus thermal reaction zone or furnace in which the
hydrogen sulfide containing gas can be combusted in the pres-
ence of an oxidant such as oxygen or air to form an effluent
stream comprising unreacted hydrogen sulfide, sulfur dioxide,
and formed elemental sulfur, as well as other compounds~
This effluent stream can then be in-troduced into a series of
\
~3~,P3
--2--
one, two, or more Claus catalytic reaction zones typically
operated so that the resulting formed sulfur is continuously
removed in the vapor phase, that is, the reaction zones are
operated above the temperature at which significant sulfur
deposition on the catalyst can occur. The elemental sulfur
can then be removed from the Claus catalytic reaction zone
effluent streams by condensation at appropriate points in the
process. Recovery of sulfur from a hydrogen sulfide con-
taining stream can be as high as about 96% for two 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 because of
environmental considerations. To meet the higher levels
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 under conditions whlch favor additional
removal of hydrogen sulfide from the gas stream being pro-
cessed. Thus, the residual level of sulfur compounds can be
significantly reduced by operating one or more of the Claus
catalytic reaction zones under conditions of temperature,
pressure, and composition such that the preponderance of
formed elemental sulfur is deposited on the catalyst. Simi-
larly, the Claus reaction in one or more Claus reactors can
likewise be driven ln the direction of removal of hydrogen
sulfide and sulfur dioxide from the process stream by
removing water 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 this
art area that other processes not involving an extension of
the Claus reaction are also available and have been utilized
for the further removal of hydrogen sulfide and other sulfur
compounds from process gas streams. These other processes
include such as the SCOT (Shell Claus Off-gas Treating)l, BSRP
(Beavon Sulfur Re~overy Process), the Beavon-Stretford Pro-
cess, and the like. However r to the extent that it is eco-
nomically and technically feasible, use of the Claus reaction
~3~33~
--3--
either directly or of the extended Claus reaction is
preferred for reasons of simplicity~ ease oE operation and
maintenance, and other similar reasons.
SWMMARY OF THE INVENTION
According to the invention, there is provided a
process for the recovery of sulfur from an acid gas stream
comprising hydrogen sulfide in a Claus process sulfur
recovery plant. ~he Claus process sulfur recovery plant can
comprise a Claus thermal reaction zone and four Claus cata-
lytic reaction zones Rl, R2, R3, and R4 and at least four
sulfur condensers Cl~ C2, C3, and C~. The process comprises
passing the acid gas stream successively through the Claus
thermal reaction zone and then successively through a first
position Claus catalytic reaction zone, a second position
Claus catalytic reaction zone, a third position Claus cata-
lytic reaction zone, and a fourth position Claus catalytic
reaction zone, at least the third and fourth position Claus
catalytic reaction zones being operated under conditions of
temperaturer pressure, and composition for depositing a pre-
ponderance of the sulfur on the catalyst therein. The pro-
cess further comprises rotating at least three of the reac-
tors Rl, R2, R3, and R4 through the third and fourth
positions operated under conditions effective for depositing
the preponderance of the sulfur on the catalyst and periodi-
cally regenerating such reactors with a process gas stream
derived from the sulfur recovery process upstream of the
second position Claus catalytic reaction zone. Following
regeneration, the freshly regenerated reactors can be precon-
ditioned by introducing thereinto a cold stream having an
inlet temperature effective for condensing sulfur on at least
a portion of the catalyst and passing the resulting stream
through at least a remaining substantial portion of the cata-
lyst prior to placing the freshly regenerated reactor in the
fourth position operated under conditions effective for depo-
siting a preponderance of the formed sulfur on the catalyst
therein. In another aspect of the invention, the freshly
regenerated second position Claus catalytic reaction zone can
be preconditioned by passing a stream lean in sulfur and
~3~3~
-4
sulfur compounds in contact with at least a substantial
portion of the catalyst in the freshly regenerated second
position Claus catalytic reaction zone for a period of time
effective for reducing an increase in sulfur emissions occur-
ring where a hot, freshly regenerated reactor is switched
into a final position of a series of Claus catalytic reaction
zones without preconditioning prior to switching the thus-
preconditioned Claus catalytic reaction zone into the fourth
(final) position.
In accordance with one aspect of the invention
there is provided such a process for the recovery of sulfur
from a feed stream comprising hydrogen sulfide by passing the
feed stream successively through a Claus thermal reaction
zone, a Claus catalytic reaction zone in a first position, a
Claus catalytic reaction zone in a second pOsitiOIl~ a Claus
catalytic reaction zone in a third position, and a Claus
catalytic reaction zone in a fourth position, the Claus cata-
lytic reaction zones in the third and fourth positions being
operated under conditions effective for depositing the pre-
ponderance of the formed elemental sulfur on the catalyst
therein. In accordance with this aspect of the invention,
the Claus catalytic reaction zone in the first position can
be a dedicated reaction zone which is operated at all times
as a high temperature Claus catalytic converter under condi-
tions of temperature and pressure and composition such that
the formed elemental sulfur is continuously removed from the
first position Claus catalytic reaction zone in the vapor
phase~ According to this aspect of the invention, the Claus
catalytic reaction zones in the second, third, and fourth
positions are rotated successively and sequentially for the
recovery of sulfur through the second positionJ the fourth
position, the third position, and back to the second posi-
tion, subject to in accordance with one method of the inven-
tion a temporary departure from this sequence for purposes of
preconditioning the freshly regenerated second position Claus
catalytic reaction zone by introducing a cold stream ther-
einto having a temperature effective for condensing sulfur on
at least a portion of the catalyst and passing the resulting
~3~3~
--5--
stream in contact with a remaining substantial portion of the
catalyst or b~ passing a stream lean in sulfur and sulfur
compounds, at least in comparison with the stream used for
regeneration, in contact with a substantial portion of the
catalyst in the hot, freshly regenerated catalytic reaction
zone and reducing an increase in sulfur emissions occurring
where a ~ot, 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 freshly regenerated catalytic reaction zone
into the fourth position. As will be appreciated from the
above, the freshly regenerated Claus catalytic reaction zone
after preconditioning will be rotated into the fourth posi-
tion operated as described under adsorption conditions
thereby placing the freshly regenerated Claus catalytic reac-
tion ~one which will have a substantial portion of the cata-
lyst therein having a very low residual sulfur loading in the
final adsorption position thus favoring the removal of
hydrogen sulfide and sulfur dioxide remaining in the process
gas stream to a very low level.
Further in accordance with this aspect of the
invention, it will be appreciated that a Claus catalytic
reaction zone previously loaded with sulfur by successive
operation in the fourth and then in the third position, can
be rotated into the second position for regeneration by the
effluent gas stream from the first position Claus catalytic
reaction zone. In this position, the laden sulfur can be
removed from the catalyst by heating with the effluent from
the first position Claus catalytic reaction zone and concur-
rently a high temperature, Claus catalytic reaction is facil-
itated in the second position catalytic reaction zone, the
reactor in the second position thus performing concurrently
regeneration and Claus sulfur recovery functions.
In accordance with another aspect of the invention,
regeneration of a reactor in the second position can be
effected at a temperature in the ranye of about 425 to about
550F and during a second period at a temperature in the
range of about 550 to about 650F prior to preconditioning.
~3~
In accordance with further aspects of the
invention, after regeneration, the freshly regenerated reac-
tors can be preconditioned prior to being rotated into the
fourth position either by reducing the temperature o~ the
feed gas to the freshly regenerated reactor, or by going tem-
porarily to a previous configuration of reactors as will be
discussed below in more detail, to effect preconditioning of
the freshly regenerated reactor prior to rotation into the
fourth position.
BR~EF D~SCRIPTION OF THE DRAWINGS
The invention will be further understood and appre-
ciated from the following detailed description and the draw-
ings in which:
Figure 1 illustrates schematically a first
mode (Mode A) of the process according to the instant
invention;
E'igure 2 illustrates schematically a second
mode (Mode ~) of the process according to the instant
invention; and
Figure 3 illustrates schematically a third
mode (Mode C) of the process according to the instant
invention.
The invention will be further understood and appre-
ciated from the following detailed description.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the invention, there is provided
a process for the recovery of sulfur from a feed stream com-
prising hydrogen sulfide which utilizes a Claus process
sulfur recovery plant comprising a thermal reaction zone and
four Claus catalytic reaction zones, Rl, R2, R3, and R4.
According to a pre~erred embodiment, the Claus process sulfur
recovery plant can have one reactor, Rl, which always func-
tions in the first position as a high temperature, Claus
catalytic reaction zone from which elemental sulfur is con-
tinuously being removed in the vapor phase, and three other
reactors, R2, R3, and R4, which can be rotated between second
position, third position, and fourth position operation, the
reactors in the third and fourth positions being operated
~ ~q ~
--7--
under conditions effective for forming and depositing the
preponderance of elemental sulfur on the surface of the cata-
lyst.
As used in the instant specification and claims,
the symbols Rl, R2, etc., Cl, C2, etc.~ shall refer to spe-
cific pieces of equipment whereas the notation first position
reactor, second position reactor, etc~, and first position
condenser, second position condenser, shall refer to equip-
ment position or location relative to the acid gas stream
being processed. Thus, a first position reactor is upstream
of a second position reactor, etc., and a first position con-
denser is upstream of a second position condenser, etc. Fur-
ther, a first position condenser will for purposes of this
specification refer to a condenser upstream of a first posi-
tion reactor, a second position condenser shall refer to a
condenser upstream of a second reactor, and so forth.
Salient features of the process according to the
invention are the following. (1) When a reactor previously
laden with sulfur by being rotated successively through the
fourth and third positions is being regenerated, it is simul-
taneously operating as a second stage Claus catalytic reac-
tion zone, preferably with the temperature being higher than
normal for a second stage Claus catalytic reaction zone, but
in accordance with one aspect of the invention, lower during
at least part of regeneration than is conventional during
regeneration of sulfur-laden catalyst. (2) The regeneration
period can preferably consist of two high temperature per-
iods, the first period being conducted at an effluent temper-
ature in the range of about 425 to about 550F, most prefer-
ably at a temperature in the range of about 500 to about
525F, and the second period being conducted at an effluent
temperature in the range of about 550 to about 650F, prefer-
ably 5~5 to 600F. (3) The reheat exchanger according to one
aspect of the invention can be eliminated upstream of the
second position reactor since hot effluent gas from the first
position Claus catalytic reaction zone can be bypassed around
the second condenser to reheat the feed to the second posi-
tion ~laus catalytic reaction zoneO (~) There can be two
~L3~-J~
catalytic reaction zones operated in series at all times
under conditions effective for depositing a preponderance of
the formed sulfur on the catalyst, so overall recovery can
remain high throughout the process. (5) Only nine switching
valves are required, with only six of those being required to
give positive shut-off.
The Claus thermal reaction zone which is utilized
in accordance with the invented method can be any suitable
Claus thermal reaction zone such as, for 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 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 estab-
lished in this art area.
In accordance with a preferred embodiment of the
invention, reactor Rl can be operated as a conventional first
stage Claus reactor in the first position. Broadly, the tem-
perature of reactor Rl can thus be in the range of from about
above the sulfur condensation point to about 700F, prefer-
ably in the range of ahout 550F to about 650F, most prefer-
ably in the range of about 575F to about 625F~ ~f neces-
sary, or appropriate, the temperature in the first Claus
catalytic reaction zone can be maintained at a higher temper-
ature, for example, at about 695F for maximum conversion of
organic sulfur compounds to H2S while minimizing sulfidiza-
tion of carbon steel. The efluent from the first position
Claus catalytic reactor can be removed and provided to a
second position condenser and can then be reheated, in accor-
dance with a preferred embodiment of the invention, by a por-
tion of the first position Claus catalytic reactor effluent
gas, or by other means familiar to those skilled in this art
area. The reheated effluent gas from the first position
Claus catalytic reactor can then be provided to the second
position Claus catalyti~ reactor which can be operated con-
currently for high temperature Claus conversion and simulta-
~3~33~
g
neously be undergoing catalyst regeneration, the secondposition Claus catalytic reactor previously having been
rotated successively for the recovery of sulfur through the
fourth and third positions. The effluent stream from the
second position Claus catalytic reactor can then be cooled in
a third position condenser and the gas can flow without
reheating to a third position Claus catalytic reactor which
can be operated as a Claus adsorption-type reactor with,
preferably, a slightly elevated temperature, for example,
320F inlet and 355F outlet, as compared with conventional
adsorption-type operation. Conventional operating tempera-
tures can, of course, also be employed. The effluent from
the third position Claus catalytic reactor can then be cooled
and sulfur condensed and removed in a fourth position sulfur
condenser and the cooled effluent gas therefrom can then be
provided to a fourth position Claus catalytic reaction zone
which can have an inlet temperature in the range from about
160 to about 330F preferably in the range of about 250 to
about 330F and most preferably having an inlet temperature
of about 260F but an effluent temperature of, for example,
only about 266F due to the low residual sulfur content of
the process gas stream entering the fourth position reactor.
It will be appreciated from the exemplary temperature rises
set forth above that most of the low temperature Claus cata-
lytic reaction in accordance with a preferred embodiment of
the invention occurs in the third position Claus catalytic
reactor and that the rate of sulfur deposition can therefore
be very low in the fourth position Claus catalytic reactor.
According to a preferred embodiment of the inven-
tion, the second position Claus catalytic reactor can be
regenerated during two high temperature periods, the first
period being conducted at a lower than usual regeneration
effluent temperature, for example, in the range of about 425
to about 550F, most preferably at about 500-525F, and a
second period having an effluent temperature preferably in
the range of about 550 to about 650F, p~eferably from about
575 to 600F. It will be appreciated by those skilled in the
art that the usual phases of regeneration will occur during
~3~3~
--10--
these two periods. These phases are outlined briefly as
follows. First occurs initial hea~ing of the catalyst to the
plateau temperature. Then the temperature remains essen
tially constant for a period of time as most of the sulfur
deposited on the catalyst is vaporized from the catalyst.
The third phase of regeneration is the final temperature
rise. ~hus, heat-up and plateau phases will typically occur
during the lower temperature period, and the final tempera
ture rise will occur during the high temperature period. As
indicated, after the low temperature regeneration period, the
inlet temperature to the second position Claus catalytic
reactor can be increased and held there until the reactor
configuration is changed. The higher temperature can prefer-
ably be achieved by bypassing more of the first position
Claus catalytic reactor effluent around the second position
condenser and directly to the second position Claus catalytic
reactor. The purpose of this higher temperature period of
regeneration is to desorb additional sulfur from the catalyst
to prepare the reactor for adsorption. Thus, with a given
sulfur concentration in the vapor, increasing the temperature
causes the residual sulfur loading to decrease. Thus, by
regenerating during a second period at a high temperature, a
lower residual sulfur loading can be accomplished; then by
preconditioning in a nonfinal position as hereinafter
described, residual sulfur loading on the catalyst can be
further lowered and a temporary increase in emissions during
final cooling of a freshly regenerated reactor in the final
position can be reduced or eliminated; and then by operating
the freshly regenerated and preconditioned reactor in the
fourth position at a low temperature, the equilibrium concen-
tration of sulfur in the vapor after it traverses the cata-
lyst bed of the fourth position Claus catalytic reactor will
be very low thus increasing the overall sulfur recovery effi-
ciency to about 99.5~ overall.
In accordance with a preferred aspect of the inven-
tion, after completion of the high temperature regeneration
of the reactor in the second position, it is desirable to
precondition the catalyst befGre switching the freshly regen-
~3~
11-
erated second position Claus catalytic reactor into the
fourth position for adsorption-type operation. If the reac-
tors were to be switched without preconditioning the catalyst
in the second position Claus catalytic reactor, then immedi-
ately after switching the catalyst in the freshly regenerated
reactor would still have a high temperature/ for example,
about 625F and, for example, the water content of the feed
gas could react with the sulfur still adsorbed on the cata-
lyst and could form hydrogen sulfide and sulfur dioxide by
the reverse Claus reaction which would flow clirectly into the
tail gas line. The resulting increase in sulfur emissions,
although temporary, can be significant in their effect on the
overall sulfur recovery efficiency, and can be substantially
reduced or prevented by preconditioning the freshly regener-
ated second position Claus catalytic reactor as hereinafter
described in detail prior to moving it into the fourth posi-
tion. Two procedures for preconditioning the freshly regen-
erated second position Claus catalytic reactor prior to
switching into the fourth position will be discussed. Others
methods of preconditioning will, of course, be apparent to
persons skilled in this art area in accordance with the ins-
tant invention.
In accordance with a specific aspect of the inven-
tion, preconditioning of the second position Claus catalytic
reactor can be efEected by introducing a cold stream ther-
einto, the cold stream preferably having an inlet temperature
effective for condensing sulfur on at least a portion of the
catalyst and passing the resulting stream in contact with a
remaining substantial portion of the catalyst for a period of
time effective to remove additional residual sulfur deposited
on the catalyst therefrom and, preferably, to achieve some
cooling of the catalyst. Alternatively, the preconditioning
can be effected by passing a stream lean in sulfur and sulfur
compounds in contact with at least a substantial portion of
the catalyst and further reducing the residual sulfur loading
level before switching into the final position~ The addi-
tional sulfur removed from the regenerated catalyst can then
react in the fourth position reactor and will not appear as
~3~
-12-
an increase in sulfur emissions. Thus, preferably the cold
stream will have a temperature below about 330~, preferably
in the range of about 160 to about 330F and most preferably
in the range of about 250 to about 330F, since a stream
having this temperature range is readily available in the
proce~s and avoids problems due to sulfur solidification and
water condensation which can occur at lower temperatures if a
process stream is utilized. The preconditioning period can
be continued for a period effective to eliminate or signifi-
cantly reduce the temporary rise in sulfur emissions which
otherwise would occur after switching the freshly regenerated
Claus catalytic reaction zone into the final position. The
minimum period of time can be readily determined by the
person skilled in the art by observing the operation of the
plant. Thus, the operator can observe emissions from the
plant in accordance with the invention, for example, with a
Continuous Stack Emissions Monitor (CSEM), determine the
occurrence and time frame of the temporary increase in emis-
sions occurring when a hot, freshly regenerated reactor is
switched into a final position, and can increase the precon-
ditioning time until the temporary increase has been signifi-
cantly ameliorated, for example, reduced by a factor of about
10~ or more, preferably by a factor of about 50% or more, and
most preferably by a factor of about ~0% or more. Based upon
our investigations, it appears that generally a relatively
short period of time will be effective, for example, on the
order of a few hours, preferably on the order of one or two
hours or less. Broadly, the period can range from a few
minutes to a few hours; preferably the preconditioning period
will not exceed about 25~ of the period of time ordinarily
required for adsorption~type operation of a reactor. It will
be appreciated by the person skilled in the art that most
cooling of a reactor will occur after switching into the
fourth ~final) position concurrently with adsorption-type
operation.
In accordance with one aspect of the invention,
preconditioning of the second position freshly regenerated
Claus catalytic reactor can be accomplished by leaving all
~3~33~
-13-
switching valves in the regenerating position as hereinafter
described in more detail, and reducing the temperature of the
feed gas to the second position Claus catalytic reactor. In
accordance with a second aspect of the invention, precondi-
tioning of the second position freshly regenerated Claus
catalytic reactor can be achieved by temporarily rotating the
reactors so that the freshly regenerated Claus catalytic
reactor assumes the position it occupied prior to regenera-
tion, that is, rotating the reactor to the third position,
for a brief period of preconditioning in accordance with the
invention, the time period being effective for reducing the
residual sulfur loading of at least a substantial portion of
the catalyst, and then rotating the preconditioned reactor
forward into the fourth position where adsorption continues
first in the Eourth position and then after switching modes
in the third position prior to regeneration in the second
position in accordance with the invention. During the brief
preconditioning period the reactor in the third position can
receive low temperature effluenk gas from the reactor which
previously was in the fourth position but now is temporarily
in the second position.
Thus, in accordance with a first preconditioning
method, the reheat gas flow from the first position Claus
catalytic reactor to the second position Claus catalytic
reactor can be eliminated and the temperature of the feed gas
to the second position Claus catalytic reactor can be reduced
by cooling in the second position condenser to less than
~bout, for example, 300F which can precondition the second
position reactor from, for example, about 625F to a lower
temperature, for example, about 400F in a few hours. How-
ever, because the regenerating gas is relatively rich in
sulfur species, the catalyst bed of the freshly regenerated
reactor can have a slightly higher residual sulfur loading
than will occur with a second preconditioning method herein-
after described.
In accordance with a second preconditioning methodl
following regeneration of the second position Claus catalytic
reactor, the reactor can be switched into the position it
?3~2~
~ 14-
occupied prior to regeneration~ that is, into the third
position. ~uring the preconditioning stepl regeneration gas
is no longer needed for the second position reactor, conse-
quently reheat gas to the second position Claus catalytic
reactor can be discontinued. During preconditioning, the
effluent from the second position Claus catalytic reactor and
the third position condenser can be provided to the third
position Claus catalytic reactor at a low temperature, for
example, as low as about 252F and can precondition the third
position reactor at the maximum possible rateO During pre~
conditioning, the effluent from the second position reactor
can then flow on to the third position, fourth position, and
the tail gas line. Thus, the temporary increase in sulfur
emissions which can occur during cooling of a freshly regen-
erated reactor can be remo~ed by a downstream reactor prior
to the freshly regenerated reactor belng switched into the
final position. This preconditioning method can result in
slightly faster preconditioning of the freshly regenerated
reactor temporarily in the third position than the first pre-
conditioning method and can moreover decrease the residual
loading level because the preconditioning is being effected
by a relatively low sulur content gas. However, the hourly
emissions rate can increase slightly because the fourth posi-
tion reactor during the coolin~ phase can be at a somewhat
higher temperature, for example, at about 355F, instead of
at about 266F as is preferred during normal operation for
sulfur recovery.
When a four Claus catalytic reaction zone plant is
operated in accordance with the invention, the overall
recovery of sulfur can be about 99.5%. The cycle time can be
varied depending upon the sulfur loading on the catalyst beds
in the third and fourth position reactors. The minimum time
between reactor rotation will be set by the required time to
regenerate the bed which, can be, for example, about 9 hours.
The maximum time can be determined by the maximum loading
allowed for the third position (first adsorption) reactor.
For an 18-hour period between rotation, or 54-hour full
cycle, the maximum loading on the catalyst in the third posi-
~L3~;?3~ '"~
-15-
tion can be, for example, about 0.66 lbs sulfur/lb catalyst
and about 0.15 lb/lb for the fourth position Claus catalytic
reactor. Calculation and determination of loading rates,
cycle times, and the like can be readily determined by per-
sons skilled in this art area in view of the instant specifi-
cation and claims~
The invention will be further understood and appre-
ciated by the following detailed description of the drawings.
DETAILED DESCRIPTION OF THE DRAW~NGS
Figures 1, 2, and 3, respectively, illustrate sche
matically three modes of operation in accordance with the
invention as follows: a first mode (Mode A) in which the
reactor flow sequence is Rl, R2, R3, and R4 wherein R2 is on
regeneration and R3 and R4 are on adsorption; a second mode
(Mode B) in which the reactor flow sequence is Rl, R3, R~, R2
wherein reactor R3 is on regeneration and reactors R4 and R2
are on adsorption; and a third mode (Mode C) in which the
reactor flow sequence is Rl, ~4, R2, and R3 and wherein
reactor R4 i5 on regeneration and reactors R2 and R3 are on
adsorption.
Referring now in particular to Figure 1, Figure 1
represents schematically a first mode (Mode A) of the process
according to the invention utilizing a Claus thermal reaction
zone, five condensers, Cl, C2, C3, C4, and C5, and fou~ reac-
tors, Rl, R2, R3 and R4, operated in series for the recovery
of sulfur from an acid gas feed stream, the reactors R2, R3,
and R4 being rotatable successively through the second,
fourth, and third positions. Thus, in Figure 1, valves 52V
in line 52, 92V in line 92, 90V in line 90 and 98V in line 9B
are shown open; and valves 64V in line 64, 78V in line 78,
94V in line 94, 88V in line 88 and 96V in line 96 are shown
closed.
Referring now to Figure 1 in detail, an acid gas
stream comprising hydrogen sulfide can be introduced by
line 10 into a Claus furnace (Claus thermal reaction zone)
14, as illustrated a muffle-tube furnace having an integrally
associated waste heat boiler 16. An oxidant, for example,
oxygen contained in air can be introduced by line 12 into the
~3~3~2~
-16-
furnace. In -the furnace, the hydrogen sulfide can be
combusted in the presence of the oxygen to produce a hot
effluent gas stream comprising hydrogen sulfide, sulfur
dioxide, and elemental sulfur, as well as other compounds.
The furnace (thermal reaction zone) effluent stream can be
provided to the waste heat boiler 16 for cooling and recovery
of heat. A portion of the effluent can be cooled by multiple
passes, for example, by a two pass sequence, in the waste
heat boiler 16 to a temperature in the range of about 550 to
about 650F and can be removed by line 18 to first position
condenser 20 (Cl) where the stream can be further cooled to
below, for example, about 260F and liquid sulfur can be
removed via line 22. A second portion of the effluent from
the Claus thermal reaction zone 14 can be removed from the
waste heat boiler 16 after, for example, a single pass ther-
ethrough at a temperature in the range of about 800 to about
1200F and can be passed through ]ine 2~ and associated valve
24V and combined with the effluent from the first position
condenser 20 to form a stream in lines 30 and 32 having an
inlet temperature in the range of about 400 to about 500F
for introduction into the first position Claus catalytic
reaction zone 36 (Rl) having an effluent temperature most
preferably in the range of about 575-625F. The amount of
bypass reheat provided by line 24 can be controlled by uti~
lizin~ a temperature controlled valve 24V, the valve being
controllable by a temperature dependent signal from line 30
as shown schematically by reference numeral 34, the valve
being illustrated as partly open.
In the first position Claus catalytic reaction zone
36, hydrogen sulfide and sulfur dioxide remaining in the
effiuent stream from the first position condenser Cl can be
further reacted in the presence of a Claus catalyst for
facilitating the Claus reaction preferably at a temperature
in the range of from about 550 to about 650F and elemental
sulfur can be produced which can be removed continuously from
the first position reactor Rl in the vapor phase, for
example, by line 42 and can be provided to a second position
sulfur condenser 44 (C2) where the effluent stream can be
cooled and sulfur removed by line 46.
~3~33~
-17-
The cooled sulfur-denuded stream can then be
removed from the second position condenser C2 by line 48 and
can be reheated by utilizing a portion of first position
Claus catalytic reaction zone effluent via line 38 and asso-
ciated valve 38V shown partly open, to produce in line 50 a
feed to the second position Claus catalytic reaction zone
having a temperature as in the ranges set forth above for
regeneration during the second position operation. It will
be appreciated that during the regeneration period, concur-
rently the forward Claus reaction is being catalyzed and ele-
mental sulfur is formed and removed in the vapor phase from
the second position reactor. In the illustrated embodiment
of FIGURE 1, valve 52V is shown as open and therefore the
reactor 54 (R2) occupies the second position, the reactor 68
~R3) occupies the third position, and the reactor 80 (R4)
occupies the fourth position. Thus r in accordance with this
configuration of the equipment, the effluent from the first
position Claus catalytic reactor can be introduced via
line 52 and associated valve 52V into the second position
Claus catalytic reactor which in this configuration comprises
reactor 54 (R2). The reactor in the second position has in
accordance with the invention previously been rotated for the
recovery of sulfur successively through the fourth position
and the third position prior to being rotated into the second
position. The inlet gas in line 52 can be adjusted to tem-
perature ranges in accordance with certain aspects of the
invention by which regeneration is accomplished at different
temperatures. Thus, during a first period of regeneration,
the temperature in line 52 to reactor 54 can be in the range
of about 425 to about 550F whereas in the second period of
regeneration, the temperature can be in the range of from
about 550 to about 650F. The effluent from the reactor in
the second position, in the illustrated configuration of
Figure 1, from reactor 54 (R2) can then be removed by line 56
to third position condenser 58 (C3) where sulfur can be con-
densed and removed by line 60.
The cooled sulfur-denuded effluent stream from the
third position condenser 58 (C3) can then be introduced via
~3`1~3~
-18-
line 62 and line 92 having associated valve 92V into the
third position Claus catalytic reactor, in the illustrated
configuration, reactor 68 (R3) at a temperature ir. the range
of from about 160 to about 330F, preferably at about 320F.
In the third position Claus catalytic reactor, the Claus con-
version can be accomplished under conditions of temperaturel
pressure, and composition such that the preponderance of the
formed sulfur is deposited on the catalyst. The effluent
stream from the third position Claus catalytic reaction zone
can then be removed, for example, by line 70 to fourth con-
denser 72 (C4) from which sulfur can be removed by line 74.
The resulting sulfur-denuded effluent stream from
the fourth position condenser 72 (C4) can then be provided to
the fourth position Claus catalytic reactor, in the illus-
trated configuration, reactor 80 (R4) via line 76, line 90,
and associated valve 90V for further conversion and removal
of elemental sulfur by depositing on the catalyst in the
fourth position Claus catalytic reactor. The effluent stream
from the fourth position Claus catalytic reactor can then be
removed by line 82 and provided to fifth position condenser
84 (C5) where elemental sulfur can be removed (if present,
for example, when the reactor R4 is in the second or the
third position - Cf. Figures 2 and 3, respectively), for
example, by line 86. The tail gas exiting the fifth position
condenser can then be provided to an incinerator by being
passed through line 98 having associated valve 98V to
line 100 and then to an incinerator (not shown).
Referring now in particular to Figure 2, Figure 2
represents schematically a second mode ~Mode B) of the pro-
cess according to the invention wherein valves 64V, 9~V, 88V
and 94V are shown open; and valves 52V, 92V, 78V, 96V and 98V
are shown closed. The other reference numerals of Figure 2
are as set forth in the discussion of Figure 1 and will not
be here repeated. It will be appreciated by observing the
flow sequence of the configuration of Figure 2 that the
reactor sequence will be Rl, R3~ R4, R2. It will be further
appreciated that the first, second, third, fourth, and fifth
position condensers will be Cl, C2, C4, C5 and C3, respec-
tively.
~3~3E32~
-19-
Referring now to Figure 3 in particular, Figure 3
represents a third mod~ ~Mode C) according to the invention
wherein the valving is such that the reactor flow sequence is
Rl, R4, R2, and R3. Thus, valves 7~V, 88V, 92V, and 96V are
shown open; and valves 52V, 6~V, 90V, 94V, and 98V are shown
closed. The other reference numerals of Figure 3 are as set
forth in Figure 1 and will not be here repeated. Similarly,
it will be appreciated that the first position, second posi-
tion, third position, fourth position, and fifth position
condensers are respectively Cl, C2, C5, C3~ and C4.
By referring to the drawings of Figures 1, 2, and
3, it will be noted that the normal rotation sequence for the
recovery of sulfur in accordance with the invention will be
from Mode A (Figure 1) to Mode B (Figure 2) to Mode C
~Figure 3). In accordance with one method of preconditioning
according to the invention, this rotation sequence can be
departed from temporarily to permit preconditioning of the
freshly regenerated reactor which has been regenerated in the
second position. In accordance with this aspect of the
invention, the rotational sequence would be as follows:
Mode A (regenerate R2), Mode C transition (precondition R2),
Mode B (regenerate R3), Mode A transition (precondition R3),
Mode C (regenerate R4), and Mode B transition (precondition
R4) r then return to Mode A (regenerate R2) and so forth.
Typically, the time required for a preconditioning mode will
be on the order of a few hours or less, for example, on the
order of about 1 or ~ hours or less. It will be appreciated
that this period of time will not be long enough to reduce
the temperature of the preconditloned reactor to an ultimate
value desired for fourth position adsorption-type operation;
calculations can, however, be made by one skilled in the art
which will show that the regeneration mode just completed can
reduce the residual sulfur loading of the catalyst to a low
level so that a relatively short preconditioning time period
can result in removing substantially all o~ the remaining
deposited residual sulfur as well as providing adequate ini-
tial preconditioning of the catalyst.
~L3~ 2~3
-20-
It will be evident from the above that regeneration
of a reactor in the second position (R2 of Mode A) can reduce
the residual sulfur loading on the catalyst to a low level,
and that then the loading will further be reduced during the
preconditioning step in which the same reactor (R2) can
operate in the third position. During successive modes, B
and C, when the same reactor R2 operates in the fourth posi-
tion and then in the third position, the sulfur loading grad-
ually increases~ slowly during Mode B, then rnore rapidly
during Mode C. Prior to the time when the sulfur loading on
the catalyst while operating in the third position Claus
catalytic reactor exceeds a predetermined maximum allowable
level, preferably less than that at which the instantaneous
recovery of sulfur starts to drop, the reactor in the second
position can be cooled in accordance with either of the two
methods described above. Thus, referring to the Figures 1,
2, and 3, the valve 38V can be closed to eliminate or reduce
reheat gas flow from the effluent from the first position
Claus catalytic reactor to the inlet to the second position
Claus catalytic reactor and, simultaneously, if desired,
steam generation in the second position condenser can be
reduced, for example, from about 60 psig to about 15 psig.
This can reduce the temperature of the feed gas to the second
position reactor to less than about, for example, 300F and
can cool the second position reactor from about 625F to a
lower temperature, for example, about 400F. Alternatively,
the other preconditloning method described above can be used.
It will be appreciated that there has been provided
an improved four Claus catalytic reaction zone process for
the recovery of sulfur which is capable of recoveries on the
order of about 99.5%. It will be further appreciated that
the invention is not limited by the preferred embodiment
described herein but will also be applicable to other four
Claus catalytic reactor plants for the recovery of sulfur in
which a reactor can be regenerated in the second position and
can be rotated for adsorption-type operation successively
into the fourth (final) position and then into the third
position prior to regeneration. The invention therefore
~3i~
-21--
should not be considered limited by the detailed description
of the preferred embodiment set forth herein as required, but
by the claims appended hereto.
