CA1286481C - Method for controlling claus furnace with variable hydrocarbon feed composition - Google Patents
Method for controlling claus furnace with variable hydrocarbon feed compositionInfo
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- CA1286481C CA1286481C CA000541113A CA541113A CA1286481C CA 1286481 C CA1286481 C CA 1286481C CA 000541113 A CA000541113 A CA 000541113A CA 541113 A CA541113 A CA 541113A CA 1286481 C CA1286481 C CA 1286481C
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- hydrogen sulfide
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Abstract
ABSTRACT
Oxygen feed to a Claus plant is controlled by calibrating a hydrocarbon-representative response signal, but not a hydrogen sulfide representative response signal, responsive to the ratio of hydrogen sulfide:sulfur dioxide in effluent from the Claus plant.
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Oxygen feed to a Claus plant is controlled by calibrating a hydrocarbon-representative response signal, but not a hydrogen sulfide representative response signal, responsive to the ratio of hydrogen sulfide:sulfur dioxide in effluent from the Claus plant.
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Description
6~
Reed/Holdeman METHOD FOR CONTROLLING CLA~S FURNACE WITH
VARIABLE HYDROCARBON FEED COMPOSITION
FIELD OF THE INVENTION
The invention relates to a method for cont-rolliny a Claus furnace. In a particular aspect, the 15 invention relates to a method for controlling a Claus fur-nace responsive to detecting variations in hydrogen sul-fide and hydrocarbon concentration and composition in the feed(s) to the furnace. In a further aspect, the inven-tion relates to a method for controlling a Claus furnace 20 in a Claus sulfur recovery plant in which a signal repre-sentative of hydrocarbon concentration in feed gases to the furnace is corrected responsive to the composition of effluent from the sulfur recovery plant.
SETTING OF THE I~ TION
The recovery of elemental sulfur from yaseous streams containing hydroyen sul~ide is a common industrial process. Such recovery of elemental sulfur can be accom-plished by a process according to the followincJ reactions:
( 1 ) 2H2S t 32 ~ 2H2 t 2SO
(H S Oxldation) (2) 2H2S t S2 ~- 3S t 2H 0 (Claus reaction) (3) H2S ~ 1/2O2 ~ S ~ H O
(Overall Claus Reaction) ,~;,, ~
~z~
Thus, elemental sulfur can be produced from gaseous streams containing hydrogen sulfide by the Claus process according to reaction (2).
The gaseous stream containing hydrogen sulfide 5 (acid gas) can be provided to the combustion chamber of a furnace where a portion of the hydrogen sulfide can be converted into sulfur dioxide by thermal oxidation in the presence of oxygen or an oxygen containing gas stream. A
hot combustion furnace effluent is produced which can con-10 tain unreacted hydrogen sulfide, sulfur dioxide, water,formed elemental sulfur and other organic sulfide com-pounds formed by the reaction with hydrocarbon combustion products where hydrocarbons are present in the acid gas feedstream. The mixture can be passed to one or more 15 catalytic reactors, optionally after passing the mixture through a sulfur condenser for removal of elemental sulfur. In the Claus catalytic reactors, additional sulfur and water can be formed. ~he gas mixture leaving the condenser can then be reheated and passed to a Claus 20 catalytic reactor where additional elemental sulfur and water can be formed from the reaction of hydrogen sulfide and sulfur dioxide in the presence of an effective Claus catalyst, for example, activated alumina or bauxite. The effluent from each catalytic reactor can be cooled and the 25 elemental sulfur can be removed as condensate. Alterna-tively, one or more of the catalytic reactors can be oper-ated under conditions, includincJ temperature, effective for depositing a preponderance of sulfur formed on cata-lyst therein with periodic regeneration of the catalyst as 30 is known in the art.
C].ose control oE the ratio between hydrogen sul-fide and sulfur dioxide must be maintained to obtain optimum performance of a sulfur recovery plant. In plants based on the Claus reaction, conversion to elemental 35 sulfur and overall plant recovery is maximized when the ratio of hydrogen sulfide to sulfur dioxide is about 2:1.
In some plants, it may be desirable to maintain hydrogen sulfide to sulfur dioxide ratios other than 2:1 at some sacrifice in conversion efficiency and sulfur recovery.
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As indicated, a portion of the hydrogen sulfide in the acicl yas feedstream can be converted to sulfur dioxide by thermal o~idation. Air is the usual source of oxygen, although air enriched with oxygen or even pure 5 oxygen may be used. The rate of oxygen feed must be cont-rolled to achieve a desired amount of oxidation of hydrogen sulfide to sulfur dioxide. If hydrogen sulfide is the only combustible compound in the acid gas feed to the sulfur plant, and if both the acid gas flow rate and 10 combustion are constant, or if changes occur slowly, then control of the air or oxygen can be readily effected by those skilled in the art; thus, the hydrogen sulfide to sulfur dioxide ratio can be maintained at a desired value.
Control of the rate of oxygen feed is made dif-15 ficult by large variations in composition of the feed to the furnace. The gas feed to the furnace can contain for example, in addition to hydrogen sulfide, other combust-ible compounds such as aliphatic, olefinic, aromatic, naphthenic, and other hydrocarbons.
The oxygen feed to a Claus sulfur plant can be controlled responsive to analysis of effluent (tail gas) from the plant to determine the hydrogen sulfide to sulfur dioxide ratio. When this ratio deviates from the desired ratio, an analyzer generates a signal for use in 25 increasing or decreasing the rate of oxygen feed to the furnace of the Claus plant. Variations in the flow rate and composition of the acid gas stream containing hydrogen sulfide and other combustibles such as hydrocarbons and the like result in off~ratio operation until analysis of 30 the resultin~ effluent gas is completed and a corrected siynal i5 generated. This feedback system, however, results in the Claus plant operating off-ratio and thus inefficiently until effluent representative of a new feed composition to the Claus plant reaches the analyzer and a 35 new control setting is called for.
The oxygen feed to a Claus sulfur plant can also be controlled by analyzing the acid gas feed to the plant and determininy the amount of o~ygen needed to effect a desired ratio of air to acid gas, and also analyzing the tail gas from the plant to send a corrected siynal to adjust the air to acid gas ratio. This type of process control, howev~r, also results in inefficien-t Claus plant 5 off-ratio operation as it fails to compensate for other combustible compounds in the gas feed to the Claus fur-nace, such as hydrocarbons, until effluent representative of a new feed gas composition provided to the Claus plant reaches the tail-gas analyzer and a new control setting is 10 called for.
Another method of process control is described in Andral, et al., U.S. 3,871,831 (1975). Andral, et al., regulates the control of gas containing oxygen fed to a unit producing sulfur via oxidation of hydrogen sulfide by 15 generating signals representing the hydrogen sulfide and methane composition of the gas fed to the unit, and by generating a signal representative of the hydrogen sul-fide:sulfur dioxide ratio in effluent from the unit.
Andral, et al., specifically disclose the pre-20 ferential use of gas chromatographs for analysis of bothfeed gas and effluent gas from the unit. Gas chromato-graphs, however, are relatively slow analyzers. In this regard, gas chromatographic analysis of the acid gas feed for methane concentration only, as in Andral, et al., con-25 siderably shortens the chromatographic an~lytical responsetime. By way of comparison, a chromatographic analysis of an acid gas feed to obtain, for example, pentane concen-tration requires much longer than where the analysis is for methane only. However, methane is not the only pos-30 sible hydrocarbon in gaseous feedstreams to Claus plants,and it is the heavier hydrocarbons which are usually responslble for air control problems in a furnace.
Acld gas streams can typically contain 1 to 2%
methane and smaller amounts of heavier hydrocarbons. For 35 purposes of illustration, assume a particular acid gas contains 0.2% total hydrocarbons heavier than methane, expressed as pentane, plus 1% methane, and, for example, 60% hydrogen sulfide. ~t steady state, the moles of oxygen required per 100 moles of acid gas are:
~i ~8~
H S: 60 H S + 30 o -~ 60 S ~ 60 ~1 o 2 ~ 2 2 CH : 1 CH -~ 1.5 0 -~ 1 C0 -~ 2 H 0 5 C H : 0.2 C H + 1.1 0 -~ 1 C0 -~ 1.2 H o Total 0 : 32.6 0 10 Assuming that the hydrocarbon concentration doubles, without any change in acid gas concentration, and both the air and acid gas flow rates stay constant, then:
15 CH :2 CH ~ 3.0 0 -~ 2 C0 + ~ H 0 C H :0.4 C5Hl -1- 2.2 0 -~ 2 C0 -~ 2.4 H 0 H S (By60 H S -~ 27.g 0 -~ 54.8 S + 54.8 H 0 -~ 5.2 H S
20 Difference):
Total 0 :32.6 0 Thus, the minor change in hydrocarbon reduces the sulfur 25 recovery by nearly 10% (from 60 moles to 5~.8 moles) during the period tha-t oxygen feed is not ad~usted. If methane were the only hydrocarbon causing problems, the loss would not be so great (rom 50 moles to 57 moles).
While there are many other factors to be considered in 30 determ:Lning C:Laus plant su.Lfur recovery than o~ygen feed, this illustrates the larye effect on sulfur recovery of a small amo~mt o~ hydrocarbons in tha acid gas, especially those heavier than methane, and further illustrates the significant effect on sulfur recovery of a change in com-35 position of the hydrocarbon components. Thus, it is appa-rent that rapid adjustment of the oxygen feed to a Claus plant in response to changing feed stream concentration and composition is highly desirable.
.~
It has been suggested to employ an infrared (IR) analyzer on the feedstreams to a Claus plant. (See, for example, sec}~man and Company, Industrial Bulletin ~OlC, "Models 864/865 Nondispersive Infrared Analyzers" (19~4).) 5 Since the IR analyzer responds to carbon-hydrogen bonds, the signal strength from an IR analyzer is proportional to the total amount of carbon hydrogen bonds and therefore to total hydrocarbons and to the amount of oxygen required to combust the total amount of hydrocarbons. An IR online 10 analyzer can also give a rapid response in comparison, for example, to the relatively slow response from a gas chro-matographic analyzer. However, if the hydrocarbon compo-sition of the acid gas feedstream varies, the IR analyzer may not give a signal accurately representing the amount 15 of oxygen necessary to combust the hydrocarbons to carbon dioxide or carbon monoxide and water. The reason for this is that although the IR signal is proportional to the number of carbon hydrogen bonds, the amount of oxygen required for combustion will vary not only with the number 20 of carbon hydrogen bonds, but also with the relative pro-portions of saturated (aliphatic), unsaturated (olefinic), and cyclic (aromatic, naphthenic, etc.) hydrocarbons, all of which have differing carbon-hydrogen ratios.
Accordingly, it is desirable to achieve the 25 advantages of operation obtainecl by employing analyzer~ on Claus plant acid gas feedstreams containing hydrogen sul-fide and hyclrocarbons, and to analyze the feed for hydro~
carbon composition, particularly where the composition inclucles compounds other than methane. It is also desi 30 rable to generate a rapid response to adjust the oxygen flow rate into the Claus furnace, and to compensate for the presence of other combustible compounds besides hydrogen sulfide in the Claus furnace. In addition to the above, it i~ also cle~irable, when employing an IR analyzer 35 on Claus plant acid gas feedstreams containing hydrocar-bons, to adjust the analyzer output to compensate for sig-nificant changes in the hydrocarbon composition of the Claus plant acid gas feedstreams.
, . ~
Reed/Holdeman METHOD FOR CONTROLLING CLA~S FURNACE WITH
VARIABLE HYDROCARBON FEED COMPOSITION
FIELD OF THE INVENTION
The invention relates to a method for cont-rolliny a Claus furnace. In a particular aspect, the 15 invention relates to a method for controlling a Claus fur-nace responsive to detecting variations in hydrogen sul-fide and hydrocarbon concentration and composition in the feed(s) to the furnace. In a further aspect, the inven-tion relates to a method for controlling a Claus furnace 20 in a Claus sulfur recovery plant in which a signal repre-sentative of hydrocarbon concentration in feed gases to the furnace is corrected responsive to the composition of effluent from the sulfur recovery plant.
SETTING OF THE I~ TION
The recovery of elemental sulfur from yaseous streams containing hydroyen sul~ide is a common industrial process. Such recovery of elemental sulfur can be accom-plished by a process according to the followincJ reactions:
( 1 ) 2H2S t 32 ~ 2H2 t 2SO
(H S Oxldation) (2) 2H2S t S2 ~- 3S t 2H 0 (Claus reaction) (3) H2S ~ 1/2O2 ~ S ~ H O
(Overall Claus Reaction) ,~;,, ~
~z~
Thus, elemental sulfur can be produced from gaseous streams containing hydrogen sulfide by the Claus process according to reaction (2).
The gaseous stream containing hydrogen sulfide 5 (acid gas) can be provided to the combustion chamber of a furnace where a portion of the hydrogen sulfide can be converted into sulfur dioxide by thermal oxidation in the presence of oxygen or an oxygen containing gas stream. A
hot combustion furnace effluent is produced which can con-10 tain unreacted hydrogen sulfide, sulfur dioxide, water,formed elemental sulfur and other organic sulfide com-pounds formed by the reaction with hydrocarbon combustion products where hydrocarbons are present in the acid gas feedstream. The mixture can be passed to one or more 15 catalytic reactors, optionally after passing the mixture through a sulfur condenser for removal of elemental sulfur. In the Claus catalytic reactors, additional sulfur and water can be formed. ~he gas mixture leaving the condenser can then be reheated and passed to a Claus 20 catalytic reactor where additional elemental sulfur and water can be formed from the reaction of hydrogen sulfide and sulfur dioxide in the presence of an effective Claus catalyst, for example, activated alumina or bauxite. The effluent from each catalytic reactor can be cooled and the 25 elemental sulfur can be removed as condensate. Alterna-tively, one or more of the catalytic reactors can be oper-ated under conditions, includincJ temperature, effective for depositing a preponderance of sulfur formed on cata-lyst therein with periodic regeneration of the catalyst as 30 is known in the art.
C].ose control oE the ratio between hydrogen sul-fide and sulfur dioxide must be maintained to obtain optimum performance of a sulfur recovery plant. In plants based on the Claus reaction, conversion to elemental 35 sulfur and overall plant recovery is maximized when the ratio of hydrogen sulfide to sulfur dioxide is about 2:1.
In some plants, it may be desirable to maintain hydrogen sulfide to sulfur dioxide ratios other than 2:1 at some sacrifice in conversion efficiency and sulfur recovery.
,~,`'~
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As indicated, a portion of the hydrogen sulfide in the acicl yas feedstream can be converted to sulfur dioxide by thermal o~idation. Air is the usual source of oxygen, although air enriched with oxygen or even pure 5 oxygen may be used. The rate of oxygen feed must be cont-rolled to achieve a desired amount of oxidation of hydrogen sulfide to sulfur dioxide. If hydrogen sulfide is the only combustible compound in the acid gas feed to the sulfur plant, and if both the acid gas flow rate and 10 combustion are constant, or if changes occur slowly, then control of the air or oxygen can be readily effected by those skilled in the art; thus, the hydrogen sulfide to sulfur dioxide ratio can be maintained at a desired value.
Control of the rate of oxygen feed is made dif-15 ficult by large variations in composition of the feed to the furnace. The gas feed to the furnace can contain for example, in addition to hydrogen sulfide, other combust-ible compounds such as aliphatic, olefinic, aromatic, naphthenic, and other hydrocarbons.
The oxygen feed to a Claus sulfur plant can be controlled responsive to analysis of effluent (tail gas) from the plant to determine the hydrogen sulfide to sulfur dioxide ratio. When this ratio deviates from the desired ratio, an analyzer generates a signal for use in 25 increasing or decreasing the rate of oxygen feed to the furnace of the Claus plant. Variations in the flow rate and composition of the acid gas stream containing hydrogen sulfide and other combustibles such as hydrocarbons and the like result in off~ratio operation until analysis of 30 the resultin~ effluent gas is completed and a corrected siynal i5 generated. This feedback system, however, results in the Claus plant operating off-ratio and thus inefficiently until effluent representative of a new feed composition to the Claus plant reaches the analyzer and a 35 new control setting is called for.
The oxygen feed to a Claus sulfur plant can also be controlled by analyzing the acid gas feed to the plant and determininy the amount of o~ygen needed to effect a desired ratio of air to acid gas, and also analyzing the tail gas from the plant to send a corrected siynal to adjust the air to acid gas ratio. This type of process control, howev~r, also results in inefficien-t Claus plant 5 off-ratio operation as it fails to compensate for other combustible compounds in the gas feed to the Claus fur-nace, such as hydrocarbons, until effluent representative of a new feed gas composition provided to the Claus plant reaches the tail-gas analyzer and a new control setting is 10 called for.
Another method of process control is described in Andral, et al., U.S. 3,871,831 (1975). Andral, et al., regulates the control of gas containing oxygen fed to a unit producing sulfur via oxidation of hydrogen sulfide by 15 generating signals representing the hydrogen sulfide and methane composition of the gas fed to the unit, and by generating a signal representative of the hydrogen sul-fide:sulfur dioxide ratio in effluent from the unit.
Andral, et al., specifically disclose the pre-20 ferential use of gas chromatographs for analysis of bothfeed gas and effluent gas from the unit. Gas chromato-graphs, however, are relatively slow analyzers. In this regard, gas chromatographic analysis of the acid gas feed for methane concentration only, as in Andral, et al., con-25 siderably shortens the chromatographic an~lytical responsetime. By way of comparison, a chromatographic analysis of an acid gas feed to obtain, for example, pentane concen-tration requires much longer than where the analysis is for methane only. However, methane is not the only pos-30 sible hydrocarbon in gaseous feedstreams to Claus plants,and it is the heavier hydrocarbons which are usually responslble for air control problems in a furnace.
Acld gas streams can typically contain 1 to 2%
methane and smaller amounts of heavier hydrocarbons. For 35 purposes of illustration, assume a particular acid gas contains 0.2% total hydrocarbons heavier than methane, expressed as pentane, plus 1% methane, and, for example, 60% hydrogen sulfide. ~t steady state, the moles of oxygen required per 100 moles of acid gas are:
~i ~8~
H S: 60 H S + 30 o -~ 60 S ~ 60 ~1 o 2 ~ 2 2 CH : 1 CH -~ 1.5 0 -~ 1 C0 -~ 2 H 0 5 C H : 0.2 C H + 1.1 0 -~ 1 C0 -~ 1.2 H o Total 0 : 32.6 0 10 Assuming that the hydrocarbon concentration doubles, without any change in acid gas concentration, and both the air and acid gas flow rates stay constant, then:
15 CH :2 CH ~ 3.0 0 -~ 2 C0 + ~ H 0 C H :0.4 C5Hl -1- 2.2 0 -~ 2 C0 -~ 2.4 H 0 H S (By60 H S -~ 27.g 0 -~ 54.8 S + 54.8 H 0 -~ 5.2 H S
20 Difference):
Total 0 :32.6 0 Thus, the minor change in hydrocarbon reduces the sulfur 25 recovery by nearly 10% (from 60 moles to 5~.8 moles) during the period tha-t oxygen feed is not ad~usted. If methane were the only hydrocarbon causing problems, the loss would not be so great (rom 50 moles to 57 moles).
While there are many other factors to be considered in 30 determ:Lning C:Laus plant su.Lfur recovery than o~ygen feed, this illustrates the larye effect on sulfur recovery of a small amo~mt o~ hydrocarbons in tha acid gas, especially those heavier than methane, and further illustrates the significant effect on sulfur recovery of a change in com-35 position of the hydrocarbon components. Thus, it is appa-rent that rapid adjustment of the oxygen feed to a Claus plant in response to changing feed stream concentration and composition is highly desirable.
.~
It has been suggested to employ an infrared (IR) analyzer on the feedstreams to a Claus plant. (See, for example, sec}~man and Company, Industrial Bulletin ~OlC, "Models 864/865 Nondispersive Infrared Analyzers" (19~4).) 5 Since the IR analyzer responds to carbon-hydrogen bonds, the signal strength from an IR analyzer is proportional to the total amount of carbon hydrogen bonds and therefore to total hydrocarbons and to the amount of oxygen required to combust the total amount of hydrocarbons. An IR online 10 analyzer can also give a rapid response in comparison, for example, to the relatively slow response from a gas chro-matographic analyzer. However, if the hydrocarbon compo-sition of the acid gas feedstream varies, the IR analyzer may not give a signal accurately representing the amount 15 of oxygen necessary to combust the hydrocarbons to carbon dioxide or carbon monoxide and water. The reason for this is that although the IR signal is proportional to the number of carbon hydrogen bonds, the amount of oxygen required for combustion will vary not only with the number 20 of carbon hydrogen bonds, but also with the relative pro-portions of saturated (aliphatic), unsaturated (olefinic), and cyclic (aromatic, naphthenic, etc.) hydrocarbons, all of which have differing carbon-hydrogen ratios.
Accordingly, it is desirable to achieve the 25 advantages of operation obtainecl by employing analyzer~ on Claus plant acid gas feedstreams containing hydrogen sul-fide and hyclrocarbons, and to analyze the feed for hydro~
carbon composition, particularly where the composition inclucles compounds other than methane. It is also desi 30 rable to generate a rapid response to adjust the oxygen flow rate into the Claus furnace, and to compensate for the presence of other combustible compounds besides hydrogen sulfide in the Claus furnace. In addition to the above, it i~ also cle~irable, when employing an IR analyzer 35 on Claus plant acid gas feedstreams containing hydrocar-bons, to adjust the analyzer output to compensate for sig-nificant changes in the hydrocarbon composition of the Claus plant acid gas feedstreams.
, . ~
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SUMMARY OF THE INVENTION
In accordance wi.th the present invention, an improved method and apparatus for controlling the produc-tion of free sul*ur from hydrogen sulfide is provided. A
5 control system is utilized -to obtain improved per~ormance from a sulfur plan-t by controlliny the amount of oxygen needed to combust hydrogen sulfide and other combustibles including hydrocarbons varying in concentration and compo-sition in yaseous feedstreams to a Claus furnace.
In accordance with the invention, there is pro-vided a method for controlling a Claus furnace in a sulfur recovery plan-t comprising such Claus furnace and at least one downstream Claus catalytic reaction zone. In accor-dance with the invention, the flow rate and concentration 15 of hydrogen sulfide in the feed(s) to the Claus furnace is sensed and a first control signal is produced for cont-rolling the flow of oxygen to the Claus furnace for com-busting the hydrogen sulfide and producing a first ratio of hydrogen sulfide to sulfur dioxide in feed to the at 20 least one downstream Claus catalytic reaction zone. A
second control signal is then generated for controlling the flow of oxygen to the Claus furnace by steps com-prising: (1) generatin0 a first response signal represen-tative of carbon-hydrogen bonds of hydrocarbons in the 25 feed(s) to the Claus furnace; (2) responsive to a second ratio of hydrogen sulfide to sulfur dioxLcle in effluent from the at least one downstream Claus catalytic reaction zone, the second ratio differing from the firs-t ratio, a second response signal 1~ generated representative of a 30 changed hydrocarbon compos:Ltion in hydrocarbons in feed(s) to the C.l.aus furnace. Then, tho f:L~st and seconcl response signals are combined and a third response signal represen-tative of carbon-hydrogell boncls and the chan0ed hydro-~carbon composition in the feed(s) to the Claus furnace is 35 generated. A fourth response signal representative of the flow rate of the feed(s) having hydrocarbons therein is also generated and the thus generated fourth response signal is combined with the third response signal for pro-8~
ducing the second control signal for controlling the flowof oxygen to the Claus furnace. The flow of oxygen to the Claus furnace is thus controlled responsive to the first control signal and to the second control signal, the 5 second control signal being representative of hydrocarbon concentration and composition.
By practicing the invention, those skilled in the art will appreciate that the signal representative both of carbon-hydrogen bonds and composition of the 10 hydrocarbon in the feed(s) is advantageous where the flow rate increases, but the relative composition of hydrocar-bons in the hydrocarbon fraction remains substantially the same because the carbon-hydrogen bond analyzer can then accomplish appropriate adjustment of the oxygen feed to 15 the Claus plant by feed forward control. Where the re].a-tive composition changes, an initial adjustment can be made by feed forward control, and then feedback control in accordance with the invention from the tail gas can be utilized to complete adjustment for the change in composi-20 tion. Thus, by generating a con-trol signal representative of both carbon-hydrogen bonds and the relative composition of h~drocarbons in -the feed(s) to the Claus plant in accordance with the invention, more rapid response is achieved even where composition changes; and where compo-25 sition of hydrocarbons does not change, varia-tions in the hydrocarbon concentration can be compensated for entirely in a feecl forward mode, -thus decreasing the response time and improving the overall operation of the plant, including the recovery of sulfur therefrom.
Other advantayes w:ill be apparent to tho~e slsilled :in the art from -the following description of the drawings and claims.
BRIEF DESCRIPTIO~ OF THE DRAWING
The FIGURE illustrates schematically the 35 invented process.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the invention, one or more acid gas feedstreams containing hydrogen sulfide and other combustible compounds including a variable hydrocarbon composition can be introduced into the thermal combustion zone of a Claus furnace in the presence of an oxidant such as, for example, air, oxygen enriched air, or pure mole-5 cular oxygen. ~uch feedstreams can be combusted in thefurnace, as is known, to produce a hot gaseous effluent stream which can contain formed elemental sulfur, sulfur dio~ide, unreacted hydrogen sulfide and other organic sul-fide compounds formed where hydrocarbons or carbon dioxide 10 are present in the acid gas.
The Claus furnace which is utilized with the invention can be any suitable furnace such as, for example, a muffle-tube furnace, a fire-tube furnace and the like, which can be selected and designed in accordance 15 with principles familiar to those skilled in the sulfur recovery arts. Combustion of hydrogen sulfide in the fur-nace can generally be carried out, as is known in the art, for example, at furnace temperatures in the range of about 1800F to about 2600F.
In using the invention, one or more gaseous feedstreams containing hydrogen sulfide are introduced into the thermal combustion zone of a Claus furnace. The feedstreams to the furnace can contain combus-tible com-pounds, in addition to hydrogen sulfide, which vary in 25 concentration as well as composition, such as aliphatic hydrocarbons, olefins, aromatics, naphthenics, and other compounds containing carbon-hydrocJen bonds such as alco-hols, ketones, aldohydes, mercaptans, and the li~e. Thus, gaseous feedstreams in accordance w.Lth the :Lnvention can 30 typically contaln up to 2% methane and smaller amounts of hydrocarbons heavier than methane. Broadly, the hydro-carbon concentra-tion of the gaseous ~eedstreams can vary from about 0.5% to about 5%. However, the hydrocarbon concentration :is not limitecl to these ranges.
In accordance with the invention, a first con-trol siynal is generated representative of the amount of oxygen recluired to combust hydrogen sulfide in the feed~s) to the Claus furnace for producing a first ratio of hydrogen sulfide -to sulfur dioxide in effluent from the Claus furnace. The flow rate and concentration of hydrogen sulfide in the feeds can be determined by any method known to those skilled in the art. Preferably, the 5 flow rate can be determined, for example, by an orifice meter, or other state-of-the-art ecluipment, and concentra-tion of hydrogen sulfide can be determined using, on the acid gas feedstream, an ultraviolet (UV) analyzer such as is known to those skilled in this art.
Also in accordance with the invention, a second control signal for controlling the oxygen feed to the Claus furnace can be generated by the following steps.
The first response signal representative of carbon-hydrogen bonds of hydrocarbons in the feed(s) to the Claus 15 furnace can be yenerated. Then, responsive to a second ra-tio of hydrogen sulfide to sulfur dioxide in effluent from the at least one downstream Claus catalytic reaction zone, the second ratio differing from the first ratio, a second response signal can be generated representative of 20 a change in hydrocarbon composition of hydrocarbons in the feed(s) to the Claus furnace. Then the first and second response signals can be combined and a third signal repre-sentative of carbon-hydrogen bonds and the change in hydrocarbon composition in the feed(s) to the Claus fur-25 nace can be yerlerated. A fourth response siynal represen-tative of flow rate of the feed(s) haviny hydrocarbons therein can also be yenerated and comb:ined with the thus generated third response siynal representative of carbon-hydrogen bonds and -the changed hydrocarbon compositlon in 30 the feed(~) to the Clau~ furnace to procluce the second control signal for controlling the flow of oxygen to the Claus Eurrlace. Finally, responslve to the first control si.ynal and to the second control siynal, the flow of oXycJen feed to the Claus furnace can be controlled.
In accordance with the invention, the first response signal representative of carbon hydrogen bonds of hydrocarbons in the feed(s) to the Claus furnace is pref-erably determined using an infrared analyæer. Hydrocarbon ~2~
compounds adsorb infrared radiation due to stretchiny and bending of characteristic bonds such as the carbon-hydrogen bond. The carbon-hydrogen bond strongly absorbs in the 2-4 micron range for saturated, olefinic, and aro-5 matic compounds. The carbon-hydrogen bond stretch region occurs in the region of about 2850 to 29~0 cm . The source can be a broadband infrared source such as a hok wire, a Nernst glower, and the like. The gases flow through the sample flow cell and absorb their character-10 istic infrared radiation wave length characteristic of thequantity of carbon-hydrogen bonds in the feed(s). The detector can be, for example, of the type consisting of two gas-filled cells, one in an analyzing beam and one in a reference beam, separated by a diaphragm where adsorp-15 tion of energy results in expansion of the gas which issensed by a capacitive system. Alternatively, the detector can be of the type consisting of two thermal piles or bolometers, one in each of the two radiation beams, where the absorption of infrared radiation is meas-20 ured by a differential thermocouple output for aresistant-thermometer (bolometer) grid circuit. Other types of infrared sources and detectors for produciny a signal representative of carbon-hydrogen bonds can also be utilized. Further, filters restricting absorption of the 25 infrared radiati.on to a suitable range can al80 be used.
~ second response siynal is generated represen-ta-tive of the hydrocarbon composition :Ln the feed(s) to the Claus furnace. In accordance with the invention, this second response siynal :ls preferably determined by cont-30 rol.tiny the oxygen flow to the Claus furnace responsive toa signal represen-tatlve of the amoun-t of oxyyen required for combusting hydrogen sulfide and produciny a first ratio of hydroyen sulfide to sulfur dioxide in effluent from the Claus furnace. By thus controlling oxyyen in 35 response to the hydrogen sulfide in the feed(s) to the Claus furnace, a deviation from the desired first ratio is representa-tive of a change in hydrocarbon or other com-bustible composition of the feed(s) to the Claus plant.
,.
Thus, a siynal representative of a change in hydrocarbon composi-tion in the feed(s) to the Claus furnace can be genera-ted. The signal representative of composition of hydrocarbon in the feed(s) to the Claus furnace can be 5 ~enerated by determining the ratio of hydrogen sulfide to sulfur dioxide in the effluent from the at least one down-stream Claus catalytic reaction zone, determining the deviation of the second ratio from the first ratio, and generating a second response signal representative of the 10 deviation of the second ratio from the first ratio.
The first and second response signals can then be combined and a third response signal representative of carbon-hydrogen bonds and the changed hydrocarbon composi-tion in the feed(s) to the Claus furnace can then be gen-15 erated. Then, by combininy the third response signal with a fourth response signal representative of flow rate of the feed(s) having hydrocarbons therein, the second con-trol signal can be produced for controlling the flow of oxygen to the Claus furnace.
By adjusting the output from the infrared ana-lyzer to be representative of flow rate and composition of hydrocarbons in feed(s) to the Claus furnace significant advantages are obtained. For example, where the composi-tlon remains stable but the flow rate or concentration 25 changes, adjustment in the control can be by the feed for-ward mechanism which offers signlfiLcant advantage in response ti.me. Even where the composition changes, a por-tion of the change of composition will be sensed in the feed forward control and a f:Lnal adjustment can be made by 30 feed back control from the determination of the ratio of hydrogen sulide to sulfur dioxide in the effluent from the at least one downstream Claus catalytic reaction zone.
The process according to the invention can fur-ther inclucle a first microprocessor means to recei~e the 35 first and second response signals representative of the carbon-hydrogen bonds in the hydrocarbon feed(s) to the furnace and also representative of the hydrogen sulfide and sulfur dioxide in effluent from the furnace, and to ~enerate .~rom the fi~st and second response signals the third response signal representative of carbon-hy~rogen bonds and the changed hydrocarbon composition in -the feed(s) to the furnace.
Another microprocessor means can also be included -to receive the first and second control signals and produce an output control signal using a specific reg-ulating algorithm adapted to the dynamics of the unit as is known to those skilled in the ar-t. ~he output control 10 signal represents -the flow rate of oxygen containing gas to the furnace necessary to maintain the instantaneous level of the ratio of hydrogen sulfide to sulfur dioxide in the furnace a-t a desired ratio. The output control signal can then, for example, operate a servomechanism to 15 adjust the set-ting of an air inlet valve thereby cont-rolling the flow rate of oxygen containing gas to the fur-nace.
In one aspec-t of the invention, the effluent stream from the Claus furnace can be cooled to a tempera-20 ture in the r~nge of from about the sulfur condensationpoint to abou-t 700F, preferably in the range of about 350F to about 575F, and can be introduced into one or more Claus catalytic reaction zones in the presence of a catalyst for facilitating -the Claus reaction (2). In -the 25 presence of such catalyst, the hydrogen sulfide and sulfur dLoxide remaininy in the gaseous stream can be further converted to elemental sulfur and an effluent stream con-taining elemental sulfur :in a vapor stage, as well as unreacted hydrogen slllf:Lde and sulfur dioxide can be pro-30 duced which can be provided to a sulfur condenser wheresuch effluent stream i.s cooled, for example to about 260E', ancl elemental sulfur can be removed therefrom in the liquid state to produce a sulfur-lean Claus catalytic reaction zone effluent stream. A second response signal 35 representative of the hydrogen sulfide and sulfur dioxide concentration in the Claus catalytic reaction zone effluent stream can then be generated, in accordance with ,~ the invention, and provided to the ~irst microprocessor ,, ~ .
~Z~L81 means along wi-th the first response signal representakive of the carbon-hydrogen bonds in the hydrocarbons in the feed(s) to the Claus furnace to generate the third response signal represerltative of the changed hydrocarbon 5 composition in feed(s) to the Claus furnace.
The resulting sulfur-lean Claus catalytic reac-tion zone effluent stream can be introduced without heating into a second Claus catalytic reaction zone at temperatures such that a predominant portion of the pro-10 duced elemental sulfur is deposited on the catalyst. Sucha process is prefer ably the Claus cold hed absorption (CBA) process, although other such processes may be used in accordance with the invention. In the CBA process, further Claus ca-talytic conversion occurs which further 15 reduces the level of sulfur compounds in the effluent stream therefrom. The CBA reaction zone can be operated under conditions of temperature such that sulfur deposi-tion occurs, preferably in the range of about 250-330F.
In accordance with the invention, the second response 20 signal representative of the hydrogen sulfide and sulfur dioxide concentration in the effluent from the CBA process can then be generated, and provided to the first micropro-cessor means along with the first response signal repre-sentative of the carbon-hydrogen bonds in the feed(s) to 25 the Claus furnace to generate the third response signal representative of the changed hydrocarbon composition in the feed(~) to the Clau~ furnace. The Claus catalytic reac-tion efluent stream can alternatively be provided to other known Claus plant ta:Ll gas cleanup processes a :~ur-30 ther sulfur removal. In such event, the hyclroyensulfides-sulfur dioxide analysis can occur upstream of such a tail gas cleanup unit.
DETAILED DESCRIPTION OF T~IE DRAWING
The invention will be further understood and 35 appreciated from the followincJ detailed description, illustrated by the accompanying FIGURE, without being in any way confined to this embodiment.
The FIGURE shows schematically, a Claus plant including a thermal reactor (furnace 30~ and a Claus cata-lytic ~one 32.
Referring now in detail to the FIGURE, gaseous 5 feed streams containing hydrogen sulfide (acid gas streams), and which also contain methane and heavier hydrocarbons, are fed by conduit means 1 to furnace 30. A
sample of effluent from the tail gas 29 passes through a conduit means 28 to an ultraviolet analyzer 27 where the 10 hydrogen sulfide and sulfur dioxide concentrati.on of the furnace effluent is measured and a signal representative of such is fed by line 26 to a first microprocessor means 15. The sample inlet device on analyzer 27 can be an adjustable inlet tap which is placed in a heated insulated 15 enclosure, the temperature of which is above the solidifi-cation point of sulfur.
A sampling device 11, connected to conduit means 1, tal~es a sample of the acid gas feedstream. This sample passes along a conduit means 12 to an infrared analyzer 20 13. Analyzer 13 measures the carbon-hydrogen bond concen-tration of the acid gas feedstreams fed to furnace 30 and a siyrlal representative of such is then provided by line 14 to microprocessor means 15 where said signal is cor-rected in response to the signal provided by line 26 to 25 the first microprocessor means 15 which represents the hydrogen sulficle and su.lfur dioxide concentration in the furnace effluent, thus compensating for siynificant changès of hydrocarbon concentration itl the acicl gas feed-streams. The corrected siynal represelltative o:E the total 30 hydrocarbon concentration of the acid gas feedstreams is then provided by line 16 to a siynal summing means 17.
A sampling clevice 6, connected to conduit means 1 also ta]ces a ~ample of the acid gas feedstreams fed to furnace 30. This sample passes along conduit means 7 to 35 an ultraviolet analyzer 8 where the hydrogen sulfide con-centration of the acid gas feed streams fed to furnace 30 is measured. A signal representative of such is then pro-vlded by line 9 into signal summing means 17. A combined signal representative of the corrected total hydrocarbon concentration and compo~ition in the acid gas feedstream to ~urnace 30 and the hydrogen sulfide concentration of said feedstreams is then provided by line 18 to a second 5 microprocessor means 19.
A signal representing the flow rate of acid gas streams fed to furnace 30 obtained by a suitable device such as orifice meter 2 is provided by line 3 to flow sensor 4 and then by line 5 to the second microprocessor 10 means 19 which in conjunction with the combined signal provided by line 18 to the second microprocessor means is then used to determine a control signal representative of the flow ra-te of oxygen containing gas to furnace 30 needed to maintain the ratio of hydrogen sulfide to sulfur 15 dioxide in said furnace at an instantaneous operating par-ameter.
Oxygen-containing gas can be provided by conduit means 22 on which is fi-tted a flow meter or recorder 23 to which a signal is provided by orifice meter 10 and 20 line 24. The signal representative of oxygen flow is pro-vided to the second microprocessor means 19 by line 20.
From microprocessor 19, another signal representative of the value of the control siynal is provided :by line 25 to a valve 21 which controls the flow rate of oxygen-25 containiny gas to the furnace 30.
E~AMPLE - E'EEDBACK CONTROL RESPONSIyE TQ,H~DROCARBON
COMPOSITlOyL___NGES
The principles underlying the invention can be further understood and appreciated by considering a typ-30 ical condition where both hydroyen ~ulfide and hydrocar-bons are present in the acid ga~ feedstream to the Claus furllace. In such a case, as illustrated in the FIGURE, the acid gas volume V can be sensed by ori:Eice meter 2 aa and flow recorder ~; t~e flow rate of air tmolecular 35 oxyyen) can be sensed by orifice meter 10 and flow recorder 23; the hydrogen sulfide concentration [H S] can be measured by ultraviolet analyzer 8; the carbon-hydrogen bond concentration [C-H] can be measured by infrared ana-lyzer 13; and the hydrogen sulfide and sul~ur dioxide in the tailgas line 29 can be measured by ultraviolet ana-lyzer 27. The output signal from the tailgas ultraviolet analyzer 27 can then be sent as a linear relationship 5 -[SO ] - 1/2 [H S]- to microprocessor 15, which also receives the carbon-hydrogen bond concentration [C-H] from infrared analyzer 13. Then, the oxygen demand will be proportional to V -[H S] ~ K' [C-H]-ag 2 where K' is a correction factor applied to the infrared analyzer output 14 based on an excess or defi-ciency of S0 in the tailgas line expressed as a linear 15 signal from the tailgas analyzer 27 provided by line 26 to microprocessor 15. From the above equation, it will be appreciated that the correction factor scales (is multi-plied with) the infrared analyzer output, but not the ultraviolet analyzer 8 output. It will be appreciated 20 that K' will be proportional to the change in the ratio of hydrogen sulfide to sulfur dioxide in the tail gas from the Claus catalytic reaction zone 32 due to hydrocarbon composition changes, that is, where the desired hydrogen sulfide:sulfur dioxide ratio is 2:1, K' will be propor-25 tional to -[S0 1 - 1/2 [H S]- which is the signal provided by tail gas analyzer 27.
Air flow rate control presents no problem if the acid gas flow rate and the acid gas composition are con-stant. Adju~tment, however, :Ls re~uired when one or more 30 of the following occurs:
(1) acid gas flow rate, V changes;
(2) hydrogen sulfide concentration [H2S
changes;
(3) hydrocarbon concentration of the acid gas changes, but the distribution of the hydrocarbon compounds within the hydrocarbon fraction is unchanged;
~L2~8~
(4) composition of the hydrocarbon fraction of the aci.d gas changes even though the hydrocarbon concentration (percent hydrocarbon) may not change.
As illus-trated in the FIGURE, the air (oxygen~
5 flow valve 21 can be controlled by a combination of sig-nals from the acid gas flowmeter 4 and the two acid gas analyzers 8 and 13. The signal from at least one of these analyzers 8 and 13 can be reset by the signal from the tail gas ultraviolet analyzer 27. Therefore, for each of 10 the occurrences (1)-(4), consideration of two base cases will suffice:
(A) the signal from the tail gas ultra-violet analyzer 27 calibrates (resets) the acid gas ultraviolet analyzer 8;
(B) the signal from tail yas ultraviolet analyzer 27 calibrates (resets) the acid gas infrared analyzer 13 only.
Those skilled in the art will recognize that :Eor changes in the acid gas flow rate, changes in H S concen-20 tration, and changes in hydrocarbon concentration but notcomposition, it makes litkle or no difference whether the signal from the tailyas ultraviolet analyzer 27 calibrates the acid gas ultraviolet analyzer 8 or the acid gas infrared analyzer 13. However, where the composition of 25 the hydrocarbon fraction chan0es, even though the total hydrocarbon concentration does not change, it i.s recluired in accordance with the .invention that the siynal from tailyas analyzer 27 calibrate the acid gas infrared ana-lyzer 13. The aclvantayes can be seen from the followi.ny 30 cases:
_SE 1 - ~ ECT OE'E~ A BON COMPOSITIO~ CHANGE WHERE
ANALYZ~F~ RESETS ANALYZER 8 In this case, the hydrocarbon concentration of the acid gas does not change, but the distribution of the 35 hydrocarbolls (composition) within the hydrocarbon fraction changes and the tail gas ultraviolet analyzer 27 cali-brates the signal from the acid gas ultraviole-t ana-lyzer 8. For illustrative purposes, the plant operation 3~
is considered to be stable and to be processing an acid gas having the following composition:
Acid Gas Composition A:
S H2S 70.00%
C2 24.00%
H2O 3.00%
CH4 1.50%
C2H6 0.60~
C2H4 0.40%
C3H~ 0.20%
C3H6 0.10%
4 10 0.20%
(3.0% Hydrocarbon) Then, the acid gas composition (but, for illus-trative purposes, not the rate) changes to the following:
Acid Gas Composition B:
H2S 70.00%
C2 24.00%
H2O 3.00%
CH~ 1.00%
C2~6 0.70%
C2H~ 0.50%
C3H8 0.30%
C3H6 0.20~
C H -~ 0.30%
(3.0% Total Hydrocarbon) Thus, both acid gas compositions contains the same concentration (percentage) Oe hydrocarbons, but the compositi.on oE the hydrocarbon fraction differs. The change from composition A to composition B wiLl require 35 that more oxygen be provided to the furnace to combust the hydrocarbons to carbon dioxide since the total number of carbon-hydrogen bonds has increased. The acid gas infrared analyzer 13, which detects primarily the C-H
~;~86~
single bonds will detect an increase, but because of the hydrocarbon composition change, the signal from the infrared analyzer 13 will not initially be proportional to the air rate required. In this event, the H2S:SO2 ratio 5 in the tail gas will depart from the desired ratio, for e~ample, 2:1. It can be set on ratio again by the tail gas ultraviolet analyzer 27 adjusting the air rate by calibrating the signal from the acid gas ultraviolet ana-lyzer 8. However, this is disadvantageous in that the 10 tail gas ultraviolet analyzer 27 would be recalibrating the acid gas ultraviolet analyzer 8 so that a given meas-ured amount of H2S would correspond to a different air rate. Then, if later, a change in the H2S concentration of the acid gas occurs, the ultraviolet analyzer 8 would 15 change the air rate, but the change would not be correct because of the changed calibration, so the plant will again be off ratio until the tail gas ultraviolet analyzer again corrects the air rate.
Similarly, if the change from acid gas composi-20 tion A to acid gas composition B as described above occurs, and the tail gas ultraviolet analyzer 27 adjusts the air rate by calibrating the signal from the acid gas ultraviolet analyzer 8, and then a change in the acid gas hydrocarbon concentration occurs (for illustrative pur-25 poses, assuming no change in the composition of the hydro-carbon fraction), the acid gas infrared analyzer 13 will change the air rate. However, the air rate change will not maintain the ~12S:SO2 ratio at the desired ratio since the infrared analyzer 13 was calibrated according to the 30 previous hydrocarbon composition (that is, acid gas compo-sition A), and changes in the air rate are based on this composition. Therefore, the plant would again be operated ofe ratio untiL the tail gas ultraviolet analyzer 27 can again correct the air rate. Thus, providing a signal from 35 tail gas analyzer 27 to calibrate ultraviolet analyzer 8 leads to an iterative searching for the desired air rate when these changes occur in the acid gas concentration.
~28~
CASE 2 - EF~`ECT OE~' HYDP~OCA~BON_C ~IPOSITION CHANCE WHERE
ANALYZER 27 CALIBR~TES ANALYZER 13 _ . __ _ __ _ . __ _ _ _ ___ ___ In this case also, the hydrocarbon concentration of the acid gas does not change, but the distribution of 5 the hydrocarbons (composition) within the hydrocarbon fraction changes. However, unlike Case 1, the tail gas ultraviolet analyzer 27 calibrates the signal from the acid gas inErared analyzer 13. The change from acid gas composition A to acid gas composition B is as described 10 above. This change will again require more oxygen be pro-vided to the ~urnace. The acid gas infrared analyzer 13, which detects primarily the C-H single bonds will detect an increase, but because of the hydrocarbon composition change, the signal from the infrared analyzer 13 will not 15 initially be proportional to the air rate required. In this event, again the H2S:SO2 ratio in the tail gas will depart from desired ratio. The ratio is reset to the desired ratio, for example, 2:1, by the tail gas ultra-violet analyzer 27 adjusting the air rate by calibrating 20 the signal from the acid gas .n~rared analyzer 13. This is, in essence, recalibrating the acid gas infrared ana-lyzer for the new hydrocarbon composition. Consider now the two cases considered in Case 1 above. If, a~ter the change in hydrocarbon fraction composition, a change in 25 the H2S concentration of the acid gas occurs, the ultra-violet analyzer 8 will change the air rate. Because the acid gas ultraviolet analyzer 8 signal has not been modi-fied/ it is still proportional to the amount Oe air required by the H2S, so that the air rate can change in 30 response to ultraviolet analyzer 8 without changing the H2S:SO2 ratio in the tail gas. Therefore, iterative cor-rection from the tail gas analyzer 27 is not re~uired.
Similarly, i~ the change from acid gas composition A to acid gas composition 8 as described above occurs and the 35 tail gas ultraviolet analyzer 27 adjusts the air rate by calibrating the signal from the acid gas infrared ana-lyzer 13, and then a change in the acid gas hydrocarbon concentration occurs (assuming for illustration purposes, no change in composition of the hydrocarbon fraction), the acid gas infrared analyzer will change the air rate as required based on the hydrocarhon composition of the new acid gas (acid gas composition b), as the tail gas ultra-5 violet analyzer has recalibrated it for the new composi-tion. Again, the plant will continue to operate on ratio and no further modification of the acid gas analyzers 8 or 13 by the tail gas ultraviolet analyzer 27 should be required. Thus, it is apparent that the signal from tail 10 gas analyzer 27 should be used to calibrate or reset the output of analyzer 13 rather than of analyzer 8.
While the invention has been described in -terms of the presently preferred embodiment, reasonable varia-tions and modifications are possible, by those skilled in 15 the art of sulfur recovery, within the scope of the described invention and the appended claims.
,. . .
SUMMARY OF THE INVENTION
In accordance wi.th the present invention, an improved method and apparatus for controlling the produc-tion of free sul*ur from hydrogen sulfide is provided. A
5 control system is utilized -to obtain improved per~ormance from a sulfur plan-t by controlliny the amount of oxygen needed to combust hydrogen sulfide and other combustibles including hydrocarbons varying in concentration and compo-sition in yaseous feedstreams to a Claus furnace.
In accordance with the invention, there is pro-vided a method for controlling a Claus furnace in a sulfur recovery plan-t comprising such Claus furnace and at least one downstream Claus catalytic reaction zone. In accor-dance with the invention, the flow rate and concentration 15 of hydrogen sulfide in the feed(s) to the Claus furnace is sensed and a first control signal is produced for cont-rolling the flow of oxygen to the Claus furnace for com-busting the hydrogen sulfide and producing a first ratio of hydrogen sulfide to sulfur dioxide in feed to the at 20 least one downstream Claus catalytic reaction zone. A
second control signal is then generated for controlling the flow of oxygen to the Claus furnace by steps com-prising: (1) generatin0 a first response signal represen-tative of carbon-hydrogen bonds of hydrocarbons in the 25 feed(s) to the Claus furnace; (2) responsive to a second ratio of hydrogen sulfide to sulfur dioxLcle in effluent from the at least one downstream Claus catalytic reaction zone, the second ratio differing from the firs-t ratio, a second response signal 1~ generated representative of a 30 changed hydrocarbon compos:Ltion in hydrocarbons in feed(s) to the C.l.aus furnace. Then, tho f:L~st and seconcl response signals are combined and a third response signal represen-tative of carbon-hydrogell boncls and the chan0ed hydro-~carbon composition in the feed(s) to the Claus furnace is 35 generated. A fourth response signal representative of the flow rate of the feed(s) having hydrocarbons therein is also generated and the thus generated fourth response signal is combined with the third response signal for pro-8~
ducing the second control signal for controlling the flowof oxygen to the Claus furnace. The flow of oxygen to the Claus furnace is thus controlled responsive to the first control signal and to the second control signal, the 5 second control signal being representative of hydrocarbon concentration and composition.
By practicing the invention, those skilled in the art will appreciate that the signal representative both of carbon-hydrogen bonds and composition of the 10 hydrocarbon in the feed(s) is advantageous where the flow rate increases, but the relative composition of hydrocar-bons in the hydrocarbon fraction remains substantially the same because the carbon-hydrogen bond analyzer can then accomplish appropriate adjustment of the oxygen feed to 15 the Claus plant by feed forward control. Where the re].a-tive composition changes, an initial adjustment can be made by feed forward control, and then feedback control in accordance with the invention from the tail gas can be utilized to complete adjustment for the change in composi-20 tion. Thus, by generating a con-trol signal representative of both carbon-hydrogen bonds and the relative composition of h~drocarbons in -the feed(s) to the Claus plant in accordance with the invention, more rapid response is achieved even where composition changes; and where compo-25 sition of hydrocarbons does not change, varia-tions in the hydrocarbon concentration can be compensated for entirely in a feecl forward mode, -thus decreasing the response time and improving the overall operation of the plant, including the recovery of sulfur therefrom.
Other advantayes w:ill be apparent to tho~e slsilled :in the art from -the following description of the drawings and claims.
BRIEF DESCRIPTIO~ OF THE DRAWING
The FIGURE illustrates schematically the 35 invented process.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the invention, one or more acid gas feedstreams containing hydrogen sulfide and other combustible compounds including a variable hydrocarbon composition can be introduced into the thermal combustion zone of a Claus furnace in the presence of an oxidant such as, for example, air, oxygen enriched air, or pure mole-5 cular oxygen. ~uch feedstreams can be combusted in thefurnace, as is known, to produce a hot gaseous effluent stream which can contain formed elemental sulfur, sulfur dio~ide, unreacted hydrogen sulfide and other organic sul-fide compounds formed where hydrocarbons or carbon dioxide 10 are present in the acid gas.
The Claus furnace which is utilized with the invention can be any suitable furnace such as, for example, a muffle-tube furnace, a fire-tube furnace and the like, which can be selected and designed in accordance 15 with principles familiar to those skilled in the sulfur recovery arts. Combustion of hydrogen sulfide in the fur-nace can generally be carried out, as is known in the art, for example, at furnace temperatures in the range of about 1800F to about 2600F.
In using the invention, one or more gaseous feedstreams containing hydrogen sulfide are introduced into the thermal combustion zone of a Claus furnace. The feedstreams to the furnace can contain combus-tible com-pounds, in addition to hydrogen sulfide, which vary in 25 concentration as well as composition, such as aliphatic hydrocarbons, olefins, aromatics, naphthenics, and other compounds containing carbon-hydrocJen bonds such as alco-hols, ketones, aldohydes, mercaptans, and the li~e. Thus, gaseous feedstreams in accordance w.Lth the :Lnvention can 30 typically contaln up to 2% methane and smaller amounts of hydrocarbons heavier than methane. Broadly, the hydro-carbon concentra-tion of the gaseous ~eedstreams can vary from about 0.5% to about 5%. However, the hydrocarbon concentration :is not limitecl to these ranges.
In accordance with the invention, a first con-trol siynal is generated representative of the amount of oxygen recluired to combust hydrogen sulfide in the feed~s) to the Claus furnace for producing a first ratio of hydrogen sulfide -to sulfur dioxide in effluent from the Claus furnace. The flow rate and concentration of hydrogen sulfide in the feeds can be determined by any method known to those skilled in the art. Preferably, the 5 flow rate can be determined, for example, by an orifice meter, or other state-of-the-art ecluipment, and concentra-tion of hydrogen sulfide can be determined using, on the acid gas feedstream, an ultraviolet (UV) analyzer such as is known to those skilled in this art.
Also in accordance with the invention, a second control signal for controlling the oxygen feed to the Claus furnace can be generated by the following steps.
The first response signal representative of carbon-hydrogen bonds of hydrocarbons in the feed(s) to the Claus 15 furnace can be yenerated. Then, responsive to a second ra-tio of hydrogen sulfide to sulfur dioxide in effluent from the at least one downstream Claus catalytic reaction zone, the second ratio differing from the first ratio, a second response signal can be generated representative of 20 a change in hydrocarbon composition of hydrocarbons in the feed(s) to the Claus furnace. Then the first and second response signals can be combined and a third signal repre-sentative of carbon-hydrogen bonds and the change in hydrocarbon composition in the feed(s) to the Claus fur-25 nace can be yerlerated. A fourth response siynal represen-tative of flow rate of the feed(s) haviny hydrocarbons therein can also be yenerated and comb:ined with the thus generated third response siynal representative of carbon-hydrogen bonds and -the changed hydrocarbon compositlon in 30 the feed(~) to the Clau~ furnace to procluce the second control signal for controlling the flow of oxygen to the Claus Eurrlace. Finally, responslve to the first control si.ynal and to the second control siynal, the flow of oXycJen feed to the Claus furnace can be controlled.
In accordance with the invention, the first response signal representative of carbon hydrogen bonds of hydrocarbons in the feed(s) to the Claus furnace is pref-erably determined using an infrared analyæer. Hydrocarbon ~2~
compounds adsorb infrared radiation due to stretchiny and bending of characteristic bonds such as the carbon-hydrogen bond. The carbon-hydrogen bond strongly absorbs in the 2-4 micron range for saturated, olefinic, and aro-5 matic compounds. The carbon-hydrogen bond stretch region occurs in the region of about 2850 to 29~0 cm . The source can be a broadband infrared source such as a hok wire, a Nernst glower, and the like. The gases flow through the sample flow cell and absorb their character-10 istic infrared radiation wave length characteristic of thequantity of carbon-hydrogen bonds in the feed(s). The detector can be, for example, of the type consisting of two gas-filled cells, one in an analyzing beam and one in a reference beam, separated by a diaphragm where adsorp-15 tion of energy results in expansion of the gas which issensed by a capacitive system. Alternatively, the detector can be of the type consisting of two thermal piles or bolometers, one in each of the two radiation beams, where the absorption of infrared radiation is meas-20 ured by a differential thermocouple output for aresistant-thermometer (bolometer) grid circuit. Other types of infrared sources and detectors for produciny a signal representative of carbon-hydrogen bonds can also be utilized. Further, filters restricting absorption of the 25 infrared radiati.on to a suitable range can al80 be used.
~ second response siynal is generated represen-ta-tive of the hydrocarbon composition :Ln the feed(s) to the Claus furnace. In accordance with the invention, this second response siynal :ls preferably determined by cont-30 rol.tiny the oxygen flow to the Claus furnace responsive toa signal represen-tatlve of the amoun-t of oxyyen required for combusting hydrogen sulfide and produciny a first ratio of hydroyen sulfide to sulfur dioxide in effluent from the Claus furnace. By thus controlling oxyyen in 35 response to the hydrogen sulfide in the feed(s) to the Claus furnace, a deviation from the desired first ratio is representa-tive of a change in hydrocarbon or other com-bustible composition of the feed(s) to the Claus plant.
,.
Thus, a siynal representative of a change in hydrocarbon composi-tion in the feed(s) to the Claus furnace can be genera-ted. The signal representative of composition of hydrocarbon in the feed(s) to the Claus furnace can be 5 ~enerated by determining the ratio of hydrogen sulfide to sulfur dioxide in the effluent from the at least one down-stream Claus catalytic reaction zone, determining the deviation of the second ratio from the first ratio, and generating a second response signal representative of the 10 deviation of the second ratio from the first ratio.
The first and second response signals can then be combined and a third response signal representative of carbon-hydrogen bonds and the changed hydrocarbon composi-tion in the feed(s) to the Claus furnace can then be gen-15 erated. Then, by combininy the third response signal with a fourth response signal representative of flow rate of the feed(s) having hydrocarbons therein, the second con-trol signal can be produced for controlling the flow of oxygen to the Claus furnace.
By adjusting the output from the infrared ana-lyzer to be representative of flow rate and composition of hydrocarbons in feed(s) to the Claus furnace significant advantages are obtained. For example, where the composi-tlon remains stable but the flow rate or concentration 25 changes, adjustment in the control can be by the feed for-ward mechanism which offers signlfiLcant advantage in response ti.me. Even where the composition changes, a por-tion of the change of composition will be sensed in the feed forward control and a f:Lnal adjustment can be made by 30 feed back control from the determination of the ratio of hydrogen sulide to sulfur dioxide in the effluent from the at least one downstream Claus catalytic reaction zone.
The process according to the invention can fur-ther inclucle a first microprocessor means to recei~e the 35 first and second response signals representative of the carbon-hydrogen bonds in the hydrocarbon feed(s) to the furnace and also representative of the hydrogen sulfide and sulfur dioxide in effluent from the furnace, and to ~enerate .~rom the fi~st and second response signals the third response signal representative of carbon-hy~rogen bonds and the changed hydrocarbon composition in -the feed(s) to the furnace.
Another microprocessor means can also be included -to receive the first and second control signals and produce an output control signal using a specific reg-ulating algorithm adapted to the dynamics of the unit as is known to those skilled in the ar-t. ~he output control 10 signal represents -the flow rate of oxygen containing gas to the furnace necessary to maintain the instantaneous level of the ratio of hydrogen sulfide to sulfur dioxide in the furnace a-t a desired ratio. The output control signal can then, for example, operate a servomechanism to 15 adjust the set-ting of an air inlet valve thereby cont-rolling the flow rate of oxygen containing gas to the fur-nace.
In one aspec-t of the invention, the effluent stream from the Claus furnace can be cooled to a tempera-20 ture in the r~nge of from about the sulfur condensationpoint to abou-t 700F, preferably in the range of about 350F to about 575F, and can be introduced into one or more Claus catalytic reaction zones in the presence of a catalyst for facilitating -the Claus reaction (2). In -the 25 presence of such catalyst, the hydrogen sulfide and sulfur dLoxide remaininy in the gaseous stream can be further converted to elemental sulfur and an effluent stream con-taining elemental sulfur :in a vapor stage, as well as unreacted hydrogen slllf:Lde and sulfur dioxide can be pro-30 duced which can be provided to a sulfur condenser wheresuch effluent stream i.s cooled, for example to about 260E', ancl elemental sulfur can be removed therefrom in the liquid state to produce a sulfur-lean Claus catalytic reaction zone effluent stream. A second response signal 35 representative of the hydrogen sulfide and sulfur dioxide concentration in the Claus catalytic reaction zone effluent stream can then be generated, in accordance with ,~ the invention, and provided to the ~irst microprocessor ,, ~ .
~Z~L81 means along wi-th the first response signal representakive of the carbon-hydrogen bonds in the hydrocarbons in the feed(s) to the Claus furnace to generate the third response signal represerltative of the changed hydrocarbon 5 composition in feed(s) to the Claus furnace.
The resulting sulfur-lean Claus catalytic reac-tion zone effluent stream can be introduced without heating into a second Claus catalytic reaction zone at temperatures such that a predominant portion of the pro-10 duced elemental sulfur is deposited on the catalyst. Sucha process is prefer ably the Claus cold hed absorption (CBA) process, although other such processes may be used in accordance with the invention. In the CBA process, further Claus ca-talytic conversion occurs which further 15 reduces the level of sulfur compounds in the effluent stream therefrom. The CBA reaction zone can be operated under conditions of temperature such that sulfur deposi-tion occurs, preferably in the range of about 250-330F.
In accordance with the invention, the second response 20 signal representative of the hydrogen sulfide and sulfur dioxide concentration in the effluent from the CBA process can then be generated, and provided to the first micropro-cessor means along with the first response signal repre-sentative of the carbon-hydrogen bonds in the feed(s) to 25 the Claus furnace to generate the third response signal representative of the changed hydrocarbon composition in the feed(~) to the Clau~ furnace. The Claus catalytic reac-tion efluent stream can alternatively be provided to other known Claus plant ta:Ll gas cleanup processes a :~ur-30 ther sulfur removal. In such event, the hyclroyensulfides-sulfur dioxide analysis can occur upstream of such a tail gas cleanup unit.
DETAILED DESCRIPTION OF T~IE DRAWING
The invention will be further understood and 35 appreciated from the followincJ detailed description, illustrated by the accompanying FIGURE, without being in any way confined to this embodiment.
The FIGURE shows schematically, a Claus plant including a thermal reactor (furnace 30~ and a Claus cata-lytic ~one 32.
Referring now in detail to the FIGURE, gaseous 5 feed streams containing hydrogen sulfide (acid gas streams), and which also contain methane and heavier hydrocarbons, are fed by conduit means 1 to furnace 30. A
sample of effluent from the tail gas 29 passes through a conduit means 28 to an ultraviolet analyzer 27 where the 10 hydrogen sulfide and sulfur dioxide concentrati.on of the furnace effluent is measured and a signal representative of such is fed by line 26 to a first microprocessor means 15. The sample inlet device on analyzer 27 can be an adjustable inlet tap which is placed in a heated insulated 15 enclosure, the temperature of which is above the solidifi-cation point of sulfur.
A sampling device 11, connected to conduit means 1, tal~es a sample of the acid gas feedstream. This sample passes along a conduit means 12 to an infrared analyzer 20 13. Analyzer 13 measures the carbon-hydrogen bond concen-tration of the acid gas feedstreams fed to furnace 30 and a siyrlal representative of such is then provided by line 14 to microprocessor means 15 where said signal is cor-rected in response to the signal provided by line 26 to 25 the first microprocessor means 15 which represents the hydrogen sulficle and su.lfur dioxide concentration in the furnace effluent, thus compensating for siynificant changès of hydrocarbon concentration itl the acicl gas feed-streams. The corrected siynal represelltative o:E the total 30 hydrocarbon concentration of the acid gas feedstreams is then provided by line 16 to a siynal summing means 17.
A sampling clevice 6, connected to conduit means 1 also ta]ces a ~ample of the acid gas feedstreams fed to furnace 30. This sample passes along conduit means 7 to 35 an ultraviolet analyzer 8 where the hydrogen sulfide con-centration of the acid gas feed streams fed to furnace 30 is measured. A signal representative of such is then pro-vlded by line 9 into signal summing means 17. A combined signal representative of the corrected total hydrocarbon concentration and compo~ition in the acid gas feedstream to ~urnace 30 and the hydrogen sulfide concentration of said feedstreams is then provided by line 18 to a second 5 microprocessor means 19.
A signal representing the flow rate of acid gas streams fed to furnace 30 obtained by a suitable device such as orifice meter 2 is provided by line 3 to flow sensor 4 and then by line 5 to the second microprocessor 10 means 19 which in conjunction with the combined signal provided by line 18 to the second microprocessor means is then used to determine a control signal representative of the flow ra-te of oxygen containing gas to furnace 30 needed to maintain the ratio of hydrogen sulfide to sulfur 15 dioxide in said furnace at an instantaneous operating par-ameter.
Oxygen-containing gas can be provided by conduit means 22 on which is fi-tted a flow meter or recorder 23 to which a signal is provided by orifice meter 10 and 20 line 24. The signal representative of oxygen flow is pro-vided to the second microprocessor means 19 by line 20.
From microprocessor 19, another signal representative of the value of the control siynal is provided :by line 25 to a valve 21 which controls the flow rate of oxygen-25 containiny gas to the furnace 30.
E~AMPLE - E'EEDBACK CONTROL RESPONSIyE TQ,H~DROCARBON
COMPOSITlOyL___NGES
The principles underlying the invention can be further understood and appreciated by considering a typ-30 ical condition where both hydroyen ~ulfide and hydrocar-bons are present in the acid ga~ feedstream to the Claus furllace. In such a case, as illustrated in the FIGURE, the acid gas volume V can be sensed by ori:Eice meter 2 aa and flow recorder ~; t~e flow rate of air tmolecular 35 oxyyen) can be sensed by orifice meter 10 and flow recorder 23; the hydrogen sulfide concentration [H S] can be measured by ultraviolet analyzer 8; the carbon-hydrogen bond concentration [C-H] can be measured by infrared ana-lyzer 13; and the hydrogen sulfide and sul~ur dioxide in the tailgas line 29 can be measured by ultraviolet ana-lyzer 27. The output signal from the tailgas ultraviolet analyzer 27 can then be sent as a linear relationship 5 -[SO ] - 1/2 [H S]- to microprocessor 15, which also receives the carbon-hydrogen bond concentration [C-H] from infrared analyzer 13. Then, the oxygen demand will be proportional to V -[H S] ~ K' [C-H]-ag 2 where K' is a correction factor applied to the infrared analyzer output 14 based on an excess or defi-ciency of S0 in the tailgas line expressed as a linear 15 signal from the tailgas analyzer 27 provided by line 26 to microprocessor 15. From the above equation, it will be appreciated that the correction factor scales (is multi-plied with) the infrared analyzer output, but not the ultraviolet analyzer 8 output. It will be appreciated 20 that K' will be proportional to the change in the ratio of hydrogen sulfide to sulfur dioxide in the tail gas from the Claus catalytic reaction zone 32 due to hydrocarbon composition changes, that is, where the desired hydrogen sulfide:sulfur dioxide ratio is 2:1, K' will be propor-25 tional to -[S0 1 - 1/2 [H S]- which is the signal provided by tail gas analyzer 27.
Air flow rate control presents no problem if the acid gas flow rate and the acid gas composition are con-stant. Adju~tment, however, :Ls re~uired when one or more 30 of the following occurs:
(1) acid gas flow rate, V changes;
(2) hydrogen sulfide concentration [H2S
changes;
(3) hydrocarbon concentration of the acid gas changes, but the distribution of the hydrocarbon compounds within the hydrocarbon fraction is unchanged;
~L2~8~
(4) composition of the hydrocarbon fraction of the aci.d gas changes even though the hydrocarbon concentration (percent hydrocarbon) may not change.
As illus-trated in the FIGURE, the air (oxygen~
5 flow valve 21 can be controlled by a combination of sig-nals from the acid gas flowmeter 4 and the two acid gas analyzers 8 and 13. The signal from at least one of these analyzers 8 and 13 can be reset by the signal from the tail gas ultraviolet analyzer 27. Therefore, for each of 10 the occurrences (1)-(4), consideration of two base cases will suffice:
(A) the signal from the tail gas ultra-violet analyzer 27 calibrates (resets) the acid gas ultraviolet analyzer 8;
(B) the signal from tail yas ultraviolet analyzer 27 calibrates (resets) the acid gas infrared analyzer 13 only.
Those skilled in the art will recognize that :Eor changes in the acid gas flow rate, changes in H S concen-20 tration, and changes in hydrocarbon concentration but notcomposition, it makes litkle or no difference whether the signal from the tailyas ultraviolet analyzer 27 calibrates the acid gas ultraviolet analyzer 8 or the acid gas infrared analyzer 13. However, where the composition of 25 the hydrocarbon fraction chan0es, even though the total hydrocarbon concentration does not change, it i.s recluired in accordance with the .invention that the siynal from tailyas analyzer 27 calibrate the acid gas infrared ana-lyzer 13. The aclvantayes can be seen from the followi.ny 30 cases:
_SE 1 - ~ ECT OE'E~ A BON COMPOSITIO~ CHANGE WHERE
ANALYZ~F~ RESETS ANALYZER 8 In this case, the hydrocarbon concentration of the acid gas does not change, but the distribution of the 35 hydrocarbolls (composition) within the hydrocarbon fraction changes and the tail gas ultraviolet analyzer 27 cali-brates the signal from the acid gas ultraviole-t ana-lyzer 8. For illustrative purposes, the plant operation 3~
is considered to be stable and to be processing an acid gas having the following composition:
Acid Gas Composition A:
S H2S 70.00%
C2 24.00%
H2O 3.00%
CH4 1.50%
C2H6 0.60~
C2H4 0.40%
C3H~ 0.20%
C3H6 0.10%
4 10 0.20%
(3.0% Hydrocarbon) Then, the acid gas composition (but, for illus-trative purposes, not the rate) changes to the following:
Acid Gas Composition B:
H2S 70.00%
C2 24.00%
H2O 3.00%
CH~ 1.00%
C2~6 0.70%
C2H~ 0.50%
C3H8 0.30%
C3H6 0.20~
C H -~ 0.30%
(3.0% Total Hydrocarbon) Thus, both acid gas compositions contains the same concentration (percentage) Oe hydrocarbons, but the compositi.on oE the hydrocarbon fraction differs. The change from composition A to composition B wiLl require 35 that more oxygen be provided to the furnace to combust the hydrocarbons to carbon dioxide since the total number of carbon-hydrogen bonds has increased. The acid gas infrared analyzer 13, which detects primarily the C-H
~;~86~
single bonds will detect an increase, but because of the hydrocarbon composition change, the signal from the infrared analyzer 13 will not initially be proportional to the air rate required. In this event, the H2S:SO2 ratio 5 in the tail gas will depart from the desired ratio, for e~ample, 2:1. It can be set on ratio again by the tail gas ultraviolet analyzer 27 adjusting the air rate by calibrating the signal from the acid gas ultraviolet ana-lyzer 8. However, this is disadvantageous in that the 10 tail gas ultraviolet analyzer 27 would be recalibrating the acid gas ultraviolet analyzer 8 so that a given meas-ured amount of H2S would correspond to a different air rate. Then, if later, a change in the H2S concentration of the acid gas occurs, the ultraviolet analyzer 8 would 15 change the air rate, but the change would not be correct because of the changed calibration, so the plant will again be off ratio until the tail gas ultraviolet analyzer again corrects the air rate.
Similarly, if the change from acid gas composi-20 tion A to acid gas composition B as described above occurs, and the tail gas ultraviolet analyzer 27 adjusts the air rate by calibrating the signal from the acid gas ultraviolet analyzer 8, and then a change in the acid gas hydrocarbon concentration occurs (for illustrative pur-25 poses, assuming no change in the composition of the hydro-carbon fraction), the acid gas infrared analyzer 13 will change the air rate. However, the air rate change will not maintain the ~12S:SO2 ratio at the desired ratio since the infrared analyzer 13 was calibrated according to the 30 previous hydrocarbon composition (that is, acid gas compo-sition A), and changes in the air rate are based on this composition. Therefore, the plant would again be operated ofe ratio untiL the tail gas ultraviolet analyzer 27 can again correct the air rate. Thus, providing a signal from 35 tail gas analyzer 27 to calibrate ultraviolet analyzer 8 leads to an iterative searching for the desired air rate when these changes occur in the acid gas concentration.
~28~
CASE 2 - EF~`ECT OE~' HYDP~OCA~BON_C ~IPOSITION CHANCE WHERE
ANALYZER 27 CALIBR~TES ANALYZER 13 _ . __ _ __ _ . __ _ _ _ ___ ___ In this case also, the hydrocarbon concentration of the acid gas does not change, but the distribution of 5 the hydrocarbons (composition) within the hydrocarbon fraction changes. However, unlike Case 1, the tail gas ultraviolet analyzer 27 calibrates the signal from the acid gas inErared analyzer 13. The change from acid gas composition A to acid gas composition B is as described 10 above. This change will again require more oxygen be pro-vided to the ~urnace. The acid gas infrared analyzer 13, which detects primarily the C-H single bonds will detect an increase, but because of the hydrocarbon composition change, the signal from the infrared analyzer 13 will not 15 initially be proportional to the air rate required. In this event, again the H2S:SO2 ratio in the tail gas will depart from desired ratio. The ratio is reset to the desired ratio, for example, 2:1, by the tail gas ultra-violet analyzer 27 adjusting the air rate by calibrating 20 the signal from the acid gas .n~rared analyzer 13. This is, in essence, recalibrating the acid gas infrared ana-lyzer for the new hydrocarbon composition. Consider now the two cases considered in Case 1 above. If, a~ter the change in hydrocarbon fraction composition, a change in 25 the H2S concentration of the acid gas occurs, the ultra-violet analyzer 8 will change the air rate. Because the acid gas ultraviolet analyzer 8 signal has not been modi-fied/ it is still proportional to the amount Oe air required by the H2S, so that the air rate can change in 30 response to ultraviolet analyzer 8 without changing the H2S:SO2 ratio in the tail gas. Therefore, iterative cor-rection from the tail gas analyzer 27 is not re~uired.
Similarly, i~ the change from acid gas composition A to acid gas composition 8 as described above occurs and the 35 tail gas ultraviolet analyzer 27 adjusts the air rate by calibrating the signal from the acid gas infrared ana-lyzer 13, and then a change in the acid gas hydrocarbon concentration occurs (assuming for illustration purposes, no change in composition of the hydrocarbon fraction), the acid gas infrared analyzer will change the air rate as required based on the hydrocarhon composition of the new acid gas (acid gas composition b), as the tail gas ultra-5 violet analyzer has recalibrated it for the new composi-tion. Again, the plant will continue to operate on ratio and no further modification of the acid gas analyzers 8 or 13 by the tail gas ultraviolet analyzer 27 should be required. Thus, it is apparent that the signal from tail 10 gas analyzer 27 should be used to calibrate or reset the output of analyzer 13 rather than of analyzer 8.
While the invention has been described in -terms of the presently preferred embodiment, reasonable varia-tions and modifications are possible, by those skilled in 15 the art of sulfur recovery, within the scope of the described invention and the appended claims.
,. . .
Claims (2)
1. A method for controlling a Claus furnace in a sulfur recovery plant comprising a Claus furnace and at least one downstream Claus catalytic reaction zone com-prising:
sensing flow rate and concentration of hydrogen sulfide in feed(s) to the Claus furnace and producing a first control signal for controlling the flow of oxygen to the Claus furnace for combusting hydrogen sulfide and producing a first ratio of hydrogen sulfide to sulfur dioxide in feed to the at least one downstream Claus catalytic reaction zone;
generating a second control signal for controlling the flow of oxygen to the Claus furnace by steps comprising:
(1) generating a first response signal representative of carbon-hydrogen bonds of hydrocarbons in the feed(s) to the Claus fur nace;
(2) responsive to a second ratio of hydrogen sulfide to sulfur dioxide in effluent from the at least one downstream Claus catalytic reaction zone, the second ratio differing from the first ratio, generating a second response signal representative of a changed hydrocarbon composition of hydrocarbons in feed(s) to the Claus furnace;
(3) combining the first and second response signals and generating a third response signal representative of carbon-hydrogen bonds and the changed hydrocarbon composition in the feed(s) to the Claus furnace;
(4) generating a fourth response signal representative of flow rate of the feed(s) having hydrocarbons therein and com-bining the thus generated signal with the third response signal and producing the second control signal representative of carbon-hydrogen bonds and composition of the hydrocarbons in the feed(s) to the Claus furnace and producing the second control signal for controlling the flow of oxygen to the Claus furnace; and responsive to the first control signal and to the second control signal controlling the flow of oxygen feed to the Claus furnace.
sensing flow rate and concentration of hydrogen sulfide in feed(s) to the Claus furnace and producing a first control signal for controlling the flow of oxygen to the Claus furnace for combusting hydrogen sulfide and producing a first ratio of hydrogen sulfide to sulfur dioxide in feed to the at least one downstream Claus catalytic reaction zone;
generating a second control signal for controlling the flow of oxygen to the Claus furnace by steps comprising:
(1) generating a first response signal representative of carbon-hydrogen bonds of hydrocarbons in the feed(s) to the Claus fur nace;
(2) responsive to a second ratio of hydrogen sulfide to sulfur dioxide in effluent from the at least one downstream Claus catalytic reaction zone, the second ratio differing from the first ratio, generating a second response signal representative of a changed hydrocarbon composition of hydrocarbons in feed(s) to the Claus furnace;
(3) combining the first and second response signals and generating a third response signal representative of carbon-hydrogen bonds and the changed hydrocarbon composition in the feed(s) to the Claus furnace;
(4) generating a fourth response signal representative of flow rate of the feed(s) having hydrocarbons therein and com-bining the thus generated signal with the third response signal and producing the second control signal representative of carbon-hydrogen bonds and composition of the hydrocarbons in the feed(s) to the Claus furnace and producing the second control signal for controlling the flow of oxygen to the Claus furnace; and responsive to the first control signal and to the second control signal controlling the flow of oxygen feed to the Claus furnace.
2. The Method of Claim 1 further comprising:
generating the first response signal repre-sentative of carbon hydrogen bonds by irradiating a portion of the feed(s) containing hydrocarbons with a source of infrared radiation, and detecting absorp-tion in at least the 2 to 4 micron range of wave lengths;
generating the second response signal using an ultraviolet analyzer and detecting the amount of hydrogen sulfide and the amount of sulfur dioxide in the tail gas from the at least one downstream Claus catalytic reaction zone;
generating a signal representative of the change in oxygen level needed for returning the ratio of hydrogen sulfide:sulfur dioxide to a desired ratio;
utilizing the signal representative of the amount of oxygen necessary to return the hydrogen sulfide:sulfur dioxide ratio to a desired level for adjusting the first response signal representative of carbon hydrogen bonds of hydrocarbons in the feed(s) to the Claus furnace to take into account a change of hydrocarbon composition.
generating the first response signal repre-sentative of carbon hydrogen bonds by irradiating a portion of the feed(s) containing hydrocarbons with a source of infrared radiation, and detecting absorp-tion in at least the 2 to 4 micron range of wave lengths;
generating the second response signal using an ultraviolet analyzer and detecting the amount of hydrogen sulfide and the amount of sulfur dioxide in the tail gas from the at least one downstream Claus catalytic reaction zone;
generating a signal representative of the change in oxygen level needed for returning the ratio of hydrogen sulfide:sulfur dioxide to a desired ratio;
utilizing the signal representative of the amount of oxygen necessary to return the hydrogen sulfide:sulfur dioxide ratio to a desired level for adjusting the first response signal representative of carbon hydrogen bonds of hydrocarbons in the feed(s) to the Claus furnace to take into account a change of hydrocarbon composition.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US89146086A | 1986-07-29 | 1986-07-29 | |
| US891,460 | 1986-07-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1286481C true CA1286481C (en) | 1991-07-23 |
Family
ID=25398231
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000541113A Expired - Lifetime CA1286481C (en) | 1986-07-29 | 1987-07-02 | Method for controlling claus furnace with variable hydrocarbon feed composition |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1286481C (en) |
-
1987
- 1987-07-02 CA CA000541113A patent/CA1286481C/en not_active Expired - Lifetime
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