CA1303331C - Three catalytic reactor extended claus process and apparatus - Google Patents
Three catalytic reactor extended claus process and apparatusInfo
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- CA1303331C CA1303331C CA000489548A CA489548A CA1303331C CA 1303331 C CA1303331 C CA 1303331C CA 000489548 A CA000489548 A CA 000489548A CA 489548 A CA489548 A CA 489548A CA 1303331 C CA1303331 C CA 1303331C
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- sulfur
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- catalytic reaction
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Abstract
ABSTRACT
Sulfur is recovered in a Claus process sulfur recovery plant comprising a thermal reaction zone and three Claus catalytic conversion zones, the first Claus catalytic conversion zone being operated as a high temper-ature Claus converter, and the second and third Claus catalytic reaction zones being operated alternately as high temperature converters and as adsorption-type con-verters. After regeneration, the freshly regenerated reaction zone is preconditioned to further reduce residual sulfur loading of at least a substantial portion of the catalyst therein and then is switched into the final posi-tion where the low sulfur loading on such portion facili-tates a high average recovery of sulfur on the order of about 99.1% to 99.25%.
Sulfur is recovered in a Claus process sulfur recovery plant comprising a thermal reaction zone and three Claus catalytic conversion zones, the first Claus catalytic conversion zone being operated as a high temper-ature Claus converter, and the second and third Claus catalytic reaction zones being operated alternately as high temperature converters and as adsorption-type con-verters. After regeneration, the freshly regenerated reaction zone is preconditioned to further reduce residual sulfur loading of at least a substantial portion of the catalyst therein and then is switched into the final posi-tion where the low sulfur loading on such portion facili-tates a high average recovery of sulfur on the order of about 99.1% to 99.25%.
Description
~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~
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~
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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 ~
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~
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 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~
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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~
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
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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~
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 - .
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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.
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~
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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.
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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 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:
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.
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~
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~
.:
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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 ~
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~
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 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~
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~
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~
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~
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~ ~
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.
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~
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.
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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 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:
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.
Claims (11)
1. Process for recovering sulfur from an acid gas feed stream comprising hydrogen sulfide in a Claus proc-ess sulfur recovery plant:
wherein the Claus process sulfur recovery plant comprises a thermal reaction zone and three and only three Claus catalytic reaction zones R1, R2, and R3, the process comprising:
successively passing the acid gas stream through the Claus thermal reaction zone, a first posi-tion Claus catalytic reaction zone, a second position Claus catalytic reaction zone, and a third position Claus catalytic reaction zone, the first position Claus catalytic reaction zone and the second position Claus catalytic reaction zone, except for preconditioning as hereinafter set forth, being operated above the sulfur condensation point, and the third position Claus cata-lytic reaction zone being operated under conditions effective for depositing a preponderance of the formed sulfur on the catalyst therein, the acid gas stream being passed through the Claus catalytic reaction zones in a first and a second mode, in the first mode the acid gas being passed successively through the Claus catalytic reaction zones according to the sequence R1, R2, R3 and in the second mode the acid gas being passed successively through the Claus catalytic reaction zones in the sequence R1, R3, and R2;
periodically switching flow from the first mode to the second mode and from the second mode to first mode by steps comprising:
preconditioning the Claus catalytic reaction zone in the second position by introducing thereinto a cold effluent stream from the first position Claus cat-alytic reaction zone, and cooling a portion, but not all, of the catalyst in the freshly regenerated reactor in the second position to a temperature effective for forming and depositing sulfur thereon and passing the resulting stream lean in sulfur and sulfur compounds therethrough in contact with the remaining portion of the catalyst prior to switching from the first mode to the second mode and from the second mode to the first mode; and then switching from one mode to another and cool-ing the remaining portion of catalyst in the thus pre-conditioned freshly regenerated Claus catalytic reactor in the third position to a temperature effective for forming and depositing sulfur thereon, and continuing operation in the third position under such conditions.
wherein the Claus process sulfur recovery plant comprises a thermal reaction zone and three and only three Claus catalytic reaction zones R1, R2, and R3, the process comprising:
successively passing the acid gas stream through the Claus thermal reaction zone, a first posi-tion Claus catalytic reaction zone, a second position Claus catalytic reaction zone, and a third position Claus catalytic reaction zone, the first position Claus catalytic reaction zone and the second position Claus catalytic reaction zone, except for preconditioning as hereinafter set forth, being operated above the sulfur condensation point, and the third position Claus cata-lytic reaction zone being operated under conditions effective for depositing a preponderance of the formed sulfur on the catalyst therein, the acid gas stream being passed through the Claus catalytic reaction zones in a first and a second mode, in the first mode the acid gas being passed successively through the Claus catalytic reaction zones according to the sequence R1, R2, R3 and in the second mode the acid gas being passed successively through the Claus catalytic reaction zones in the sequence R1, R3, and R2;
periodically switching flow from the first mode to the second mode and from the second mode to first mode by steps comprising:
preconditioning the Claus catalytic reaction zone in the second position by introducing thereinto a cold effluent stream from the first position Claus cat-alytic reaction zone, and cooling a portion, but not all, of the catalyst in the freshly regenerated reactor in the second position to a temperature effective for forming and depositing sulfur thereon and passing the resulting stream lean in sulfur and sulfur compounds therethrough in contact with the remaining portion of the catalyst prior to switching from the first mode to the second mode and from the second mode to the first mode; and then switching from one mode to another and cool-ing the remaining portion of catalyst in the thus pre-conditioned freshly regenerated Claus catalytic reactor in the third position to a temperature effective for forming and depositing sulfur thereon, and continuing operation in the third position under such conditions.
2. The Process of Claim 1 comprising:
removing an effluent stream from the first posi-tion Claus catalytic reaction zone, providing the thus removed stream to a sulfur condenser, and cooling and con-densing elemental sulfur therefrom, then reheating the thus cooled sulfur-denuded effluent stream with a portion of first position Claus catalytic reaction zone effluent to an effective temperature for high temperature Claus conversion, and passing the thus heated sulfur-denuded stream to the second position Claus catalytic reaction zone.
removing an effluent stream from the first posi-tion Claus catalytic reaction zone, providing the thus removed stream to a sulfur condenser, and cooling and con-densing elemental sulfur therefrom, then reheating the thus cooled sulfur-denuded effluent stream with a portion of first position Claus catalytic reaction zone effluent to an effective temperature for high temperature Claus conversion, and passing the thus heated sulfur-denuded stream to the second position Claus catalytic reaction zone.
3. The Process of Claim 2 wherein:
the preconditioning step is effected by pro-viding the effluent from the sulfur condenser substan-tially without reheating to the second position Claus catalytic reaction zone.
the preconditioning step is effected by pro-viding the effluent from the sulfur condenser substan-tially without reheating to the second position Claus catalytic reaction zone.
4. The Process of Claim 1 wherein:
the Claus process sulfur recovery plant fur-ther comprises first and second position condensers upstream of the first position Claus catalytic reaction zone and the second position Claus catalytic reaction zones, respectively.
the Claus process sulfur recovery plant fur-ther comprises first and second position condensers upstream of the first position Claus catalytic reaction zone and the second position Claus catalytic reaction zones, respectively.
5. The Process of Claim 4 further comprising:
substantially bypassing the second position condenser during regeneration and Claus conversion; and substantially flowing the entire process acid gas stream through the second position condenser during preconditioning.
substantially bypassing the second position condenser during regeneration and Claus conversion; and substantially flowing the entire process acid gas stream through the second position condenser during preconditioning.
6. The Process of Claim 1 wherein:
The preconditioning is conducted for a period of time less than 2 hours.
The preconditioning is conducted for a period of time less than 2 hours.
7. The Process of Claim 1 wherein:
the preconditioning is conducted for a period of time less than 1 hour.
the preconditioning is conducted for a period of time less than 1 hour.
8. The Process of Claim 1 wherein:
most of the cooling of a freshly regenerated reactor occurs after switching into the third position.
most of the cooling of a freshly regenerated reactor occurs after switching into the third position.
9. The Process of Claim 1 wherein:
the entire acid gas stream is passed succes-sively through the first position catalytic reaction zone, the second position Claus catalytic reaction zone, and the third position Claus catalytic reaction zone at all times.
the entire acid gas stream is passed succes-sively through the first position catalytic reaction zone, the second position Claus catalytic reaction zone, and the third position Claus catalytic reaction zone at all times.
10. The Process of Claim 1 wherein:
the catalytic reaction zone previously in the third position in which sulfur has been deposited on the catalyst area after being moved into the second position undergoes regeneration of the sulfur-laden catalyst therein while simultaneously functioning as a high temperature Claus reaction zone producing ele-mental sulfur from reaction of hydrogen sulfide and sulfur dioxide.
the catalytic reaction zone previously in the third position in which sulfur has been deposited on the catalyst area after being moved into the second position undergoes regeneration of the sulfur-laden catalyst therein while simultaneously functioning as a high temperature Claus reaction zone producing ele-mental sulfur from reaction of hydrogen sulfide and sulfur dioxide.
11. The Process of Claim 1 wherein:
the preconditioning period during which sulfur is deposited on catalyst in the second position Claus catalytic reaction zone is less than about 25% of an adsorption period for such reactor, the remaining portion of the adsorption period for such reactor occurring in the third position after switching.
the preconditioning period during which sulfur is deposited on catalyst in the second position Claus catalytic reaction zone is less than about 25% of an adsorption period for such reactor, the remaining portion of the adsorption period for such reactor occurring in the third position after switching.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US64886584A | 1984-09-07 | 1984-09-07 | |
| US648,865 | 1984-09-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1303331C true CA1303331C (en) | 1992-06-16 |
Family
ID=24602543
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000489548A Expired - Lifetime CA1303331C (en) | 1984-09-07 | 1985-08-28 | Three catalytic reactor extended claus process and apparatus |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1303331C (en) |
-
1985
- 1985-08-28 CA CA000489548A patent/CA1303331C/en not_active Expired - Lifetime
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