KR20070118690A - Treatment of fuel gases - Google Patents

Abstract

Fuel gas, such as coke oven gas, is used to remove hydrogen sulfide and ammonia impurities in the absorption columns 12, 18. The absorbent is regenerated in the stripping column 32. The gaseous stream containing hydrogen sulfide and ammonia is passed from the stripping column to the same combustion bed or furnace 48 of the Claus plant 44. Combustion is carried out under conditions which essentially remove all ammonia. The combustion is supported by a gas stream containing at least 40 volume percent oxygen. Residual amounts of sulfur dioxide and sulfur in the tail gas from the Claus plant 44 are catalytically reduced in the reactor 73 and the resulting gas is recycled to the absorption column 12.

Description

Treatment of Fuel Gases {TREATMENT OF FUEL GAS}

The present invention relates to a method for treating fuel gas containing hydrogen sulfide impurities. One example of such a fuel gas is a coke oven gas.

Industrial gases such as coke oven gas, natural gas and various artificially produced fuel gases are used to produce useful products in industrial plants or are burned in suitable combustion apparatus to generate heat. These gases are mixtures of many different components. Primarily one or more major combustible components, typically carbon monoxide, or hydrogen, or aliphatic hydrocarbons such as methane; Secondly one or more non-combustible components such as carbon dioxide, nitrogen and argon; Thirdly, there are a wide range of impurities, including hydrogen sulfide. Other impurities that may be present include ammonia, nitrogen oxides, sulfur oxides, hydrogen cyanide and carbonyl sulfide. In addition, aromatic hydrocarbons and higher aliphatic hydrocarbons may be present.

The method according to the invention relates to a method for treating fuel gas containing both hydrogen sulfide and ammonia impurities.

US-A 085 199 discloses a process for desulfurizing a fuel gas containing hydrogen and hydrogen sulfide without releasing any sulfur-containing tail gas. Hydrogen sulfide is separated from the fuel gas by an absorption-desorption method using a liquid absorbent of hydrogen sulfide such as monoethanolamine (MEA). Hydrogen sulphide is passed to the Claus reaction zone with an appropriate stoichiometric amount of sulfur dioxide. Tail gas containing sulfur compounds is released from the Klaus reaction zone. Portions of the feed gas bypass the separation and Klaus reaction zone and react with the tail gas within the catalytic hydrogenation zone. As a result, kinds such as sulfur dioxide, carbonyl sulfide, carbon disulfide and elemental sulfur which may be present in the tail gas are reduced to hydrogen sulfide. The final hydrogenated tail gas is recycled to the absorption process to remove hydrogen sulfide therefrom.

A particular example of this method, presented in US-A 085 199, is the desulfurization of coke oven gas. The coke oven gas typically contains a significant amount of ammonia. However, US-A 085 199 does not mention treatment of ammonia impurities. The reason for this lack of mention is simple. Ammonia is usually removed completely from hydrogen sulfide completely.

The method according to the invention is capable of removing both hydrogen sulfide and ammonia impurities from a fuel gas having hydrogen sulfide.

1 is a flow chart schematically showing a plant for the treatment of coke oven gas.

According to the present invention, there is provided a method for treating a feed stream of a fuel gas containing both hydrogen sulfide and ammonia as impurities, comprising extracting at least 70% hydrogen sulfide impurities from the feed stream in an absorbent, the hydrogen sulfide from the formed hydrogen sulfide-filled absorbent. Stripping to form a combustible gas stream containing hydrogen sulfide, forming sulfur from the combustible gas stream, recovering the formed sulfur, and a tail gas stream containing residual amounts of hydrogen sulfide, sulfur vapor, and sulfur dioxide. Reducing the residual amount of sulfur dioxide and sulfur vapor in the tail gas stream to hydrogen sulfide, and combining the reduced tail gas stream with the feed stream upstream of the extraction of hydrogen sulfide impurities; Combustible Gas The hydrogen sulfide portion of the trim is burned to form sulfur dioxide, which includes one or more combustion steps that react with unburned hydrogen sulfide to form sulfur vapors, wherein ammonia impurities are also extracted from the feed gas by the absorbent and the flow of ammonia Produced by stripping ammonia from the ammonia-filled absorbent formed, the flow of the ammonia is passed to the combustion stage, and the combustion of hydrogen sulfide is carried out under essentially all removal of ammonia, and the combustion is at least 40% by volume (preferably Preferably at least 80% by volume) of oxygen molecules supported by a gas stream.

Thus, the process according to the invention eliminates the need for complete individual extraction and treatment of ammonia impurities from the feed stream, which can reduce the ammonia level to less than 100 ppm per volume, which ultimately breaks down the plant in which the method is carried out. Is considered below the level that results in the downstream formation of the ammonia salt blocking the passage of gas.

The process according to the invention is particularly suitable for the treatment of coke oven gases, but can be used to treat other fuel gases containing both hydrogen sulfide and ammonia as impurities.

In order to remove all ammonia in the combustion step, it is required to keep the flame temperature therein high. The effluent gas leaving the combustion step has a temperature of 1300 ° C. or higher, and the arrangement of the burners is configured such that the conditions in the flame are generally suitable to thermally decompose ammonia into nitrogen and hydrogen after all the ammonia is applied to a high flame temperature. One of the particular advantages of supplying ammonia stripped from the ammonia-filled absorbent to the combustion stage of the plant to recover sulfur from hydrogen sulfide is the known removal and separation of the ammonia stream under oxidative conditions resulting in the formation of nitrogen oxides. Unlike the method, ammonia can be removed with minimal formation of nitrogen oxides therein.

Supplying a combustion support gas containing at least 40% by volume of oxygen to the combustion stage promotes the creation of high flame temperature conditions and promotes thermal decomposition of ammonia therein. The combustion support gas is preferably industrial pure oxygen (i.e. oxygen containing impurities of less than 5% by volume, preferably less than 1.5% by volume, most preferably less than 1% by volume) and the oxygen-rich air is this combustion It is preferred to be fed to the step. A further advantage of using pure oxygen or oxygen-rich air contained above 40% by volume to support combustion in the combustion step is that the tail gas stream can be kept low in size. It is important to keep the size of the tail gas stream low because the dilution of the fuel gas using the tail gas has the effect of reducing its caloric value. If the tail gas stream is made small, the reduction in calorie value is significantly smaller.

Combining the tail gas stream with the feed stream removes residual hydrogen sulfide impurities from the tail gas, thereby eliminating the need for a separate tail gas treatment plant. A further advantage of keeping the tail gas stream low in size is that the hydrogen sulfide and ammonia absorption unit (s) can be kept low in size. It is also possible to keep the size of any equipment used for further treatment of the treated fuel gas low. For example, such equipment may be required for washing aromatic hydrocarbon impurities such as benzene, toluene and xylene from the treated fuel gas. However, for example, if an existing coke oven gas treatment plant is switched to operation by the method according to the invention, it may not be advantageous to replace the aromatic hydrocarbon impurity scrubber with a smaller one. Nevertheless, there will be an opportunity to prevent the scrubber from acting as a limit on the maximum achievable output of treated fuel gas.

In the process according to the invention the order in which ammonia and hydrogen sulfide impurities are extracted from the feed stream is not critical. Single or multiple absorbents can be used. Preferably, most of the hydrogen sulfide is absorbed in aqueous liquids having a pH above 7. Preferably, most of the ammonia is absorbed in aqueous liquids having a pH of less than 7.

Once the individual absorbents of hydrogen sulfide and ammonia impurities are selected, the hydrogen sulfide-filled absorbent is preferably stripped separately from the ammonia-filled absorbent and the resulting hydrogen sulfide combustible gas stream is stripped from the ammonia-filled absorbent. The ammonia may be supplied to the combustion stage separately, or may be combined with stripped ammonia upstream of the combustion stage.

Preferably, the recovery of sulfur comprises a plurality of combustion stages where the hydrogen sulfide portion of the combustible gas stream is combusted. Preferably, pure oxygen or oxygen-rich air containing at least 80% by volume of oxygen is supplied to all of these combustion stages.

Preferably, the reduction of the tail gas is carried out using a gas mixture containing hydrogen or pure hydrogen on the catalyst as the reducing agent. The source of reducing agent may be cleaned coke oven gas. The catalyst is typically cobalt and manganese on the support, and the reduction reaction is preferably carried out at a temperature of 320 to 400 ° C.

Preferably, the reduced tail gas has water vapor condensed therefrom upstream that merges with the feed gas by indirect heat exchange with the coolant and / or by direct contact with water.

The method according to the invention is described below by way of example with reference to the accompanying drawings, which are a flow chart schematically showing a plant for the treatment of coke oven gas.

The drawings are not to scale.

Referring to FIG. 1, the coke oven gas is typically recovered from one or more coke ovens 2 at elevated temperatures of about 1100 ° C. or higher, and cooled by direct contact with an aqueous solution of ammonia in the first cooler 4 to tar from the gas. And other heavy hydrocarbons. Some of the ammonia of the coke oven gas can be extracted in the first cooler (4). Uncondensed gas flows from the first cooler 4 to an electrostatic precipitator 6 which is operated to remove particulate contaminants from the coke oven gas. The flow of coke oven gas is produced by the operation of the blower 8 located downstream of the electrostatic settler. The arrangement, configuration and operation of the first cooler 4 and the electrostatic precipitator 6 are well known in the field of treating coke oven gas and need not be further described herein.

The treated coke oven gas discharged from the blower 8 typically contains hydrogen, methane and carbon monoxide. It may also contain various unwanted gas impurities, including carbon dioxide, nitrogen, gaseous hydrocarbons containing two or more carbon atoms, and ammonia, hydrogen sulfide, carbonyl sulfide and typical hydrogen cyanide. According to the present invention, the coke oven gas is treated by scrubbing to remove ammonia, hydrogen sulfide, carbonyl sulfide and hydrogen cyanide impurities. Typically, upstream of the scrubbed, the coke oven gas passes from the blower 8 through the second cooler 10 to reduce its temperature below 100 ° C. The final cooled coke oven gas is introduced into the first absorption column 12, typically at a pressure of 1.2 to 2 bar (absolute). The first absorption column 12 includes a member or device (not shown) suitable for initial contact with the downwardly flowing gas. Typically, the first absorption column 12 comprises a packing for this purpose, such as a structured packing. The flow of absorbent is passed up to one or more spray nozzles 14 located above the column 12 and is discharged from the nozzle 14 down the column 12. The absorbent is typically an alkali, such as a caustic soda solution or an aqueous solution of ammonia. This ammonia solution can be produced in another part of the plant, for example in the first cooler 4. As the alkaline absorbent solution descends from column 12, it contacts the upwardly coking oven gas. The alkaline absorbent solution absorbs hydrogen sulfide, hydrogen cyanide and carbon dioxide from the coke oven gas. The relative mole fractions of carbon dioxide, hydrogen cyanide and hydrogen sulfide in the coke oven gas are typically such that they gradually become more acidic as water is moved down the first absorption column 12.

The coke oven gas essentially free of hydrogen sulfide, carbon dioxide and hydrogen cyanide leaves the top of the first absorption column 12 through the outlet 16 and flows to the bottom region of the second absorption column 18. Ammonia and trace amounts of carbonyl sulfide are absorbed from the coke oven gas in the second absorption column 18 by a neutral or acidic aqueous absorbent. Liquor from the bottom of the first absorption column 12 may be used as an absorbent in the second absorption column 18. Pump 20 is operated to recover liquid from the bottom of column 12 through outlet 22 and pass it to one or more spray nozzles 24 at the top of second absorption column 18. Similar to the first absorbent column 12, the second absorbent column 18 includes a packing (eg, a structured packing) to initially contact the upstream gas with the descending alkaline liquid discharged from the spray nozzle 24. do. As a result of the initial contact, ammonia is gradually absorbed from the coke oven gas as it rises from the second absorption column 18. Treated coke oven gas, which is currently essentially free of environmentally unacceptable gaseous impurities, in particular hydrogen sulfide, ammonia and hydrogen cyanide, flows from the second absorption column 18 through the outlet 26 to its top and generates power or It can be used as a fuel for heating.

The liquid at the bottom of the second absorption column 18 contains ammonia absorbed as flow from the first absorption column 12 and trace amounts of other impurities as described above. This liquid is withdrawn continuously through the outlet 28 at the bottom of the second absorption column 18 by the operation of the pump 30. The liquid recovered from the second absorption column 18 by the operation of the pump 30 flows to the top of the stripping column 32. Typically, the liquid is heated to a temperature near the boiling point of water in an additional heat exchanger 34 upstream of the column 32. Similar to the absorption columns 12, 18, the stripping column 32 may include a packing (eg, structured packing) or other such that the liquid absorbent is initially contacted with an upwardly gas or vapor as he moves down the column 32. Liquid-gas contact means, including stripping hydrogen sulfide, ammonia, carbon dioxide and hydrogen cyanide therefrom. Liquid absorbents are typically introduced into the top of column 32 through one or more spray nozzles 36. The bottom of the stripping column 32 is provided with an internal or external boiler 38 to boil the liquid portion at the bottom of the stripping column 32. Boiler 38 is typically heated by an external source of superheated steam. The steam produced by the operation of the boiler 38 is moved up in the column, stripping hydrogen sulfide, ammonia, carbon dioxide and hydrogen cyanide from the downward liquid. A gas stream comprising water vapor, carbon dioxide, hydrogen cyanide, ammonia and hydrogen sulfide flows from the stripping column 32 through the outlet 40 at the top thereof. Although the hydrogen sulfide content of the untreated coke oven gas may be less than 2% by volume, the gas leaving from the top of the stripping column 32 will contain substantially more hydrogen sulfide. Typically, it will contain more than 20 volume percent hydrogen sulfide. In addition, it typically contains a similar volume of ammonia. Since this gas mixture contains hydrogen sulfide and ammonia in this ratio, it is combustible.

The portion of the liquid absorbent that does not boil in the boiler 38 is typically discharged continuously from the plant shown in FIG. 1 through the outlet 42. It may typically be supplied to the effluent treatment plant to be suitable for discharge to the environment.

The gaseous stream containing hydrogen sulfide and ammonia generated from the stripping column 32 is used as feed to the Claus plant 44. If desired, this may be the only hydrogen sulfide-containing gas stream sent to the Claus plant 44. Alternatively, however, there may be a second feed of the hydrogen sulfide-containing gas stream from separate sources. Klaus plant 44 is arranged and arranged to essentially remove all ammonia and hydrogen cyanide in its feed gas, and the ammonia concentration is reduced to less than 100 ppm per volume. The characteristics of the Klaus plant 44 are characterized by the combustion of hydrogen sulfide, ammonia and hydrogen cyanide fractions using commercial pure oxygen (typically containing more than 99% by volume of oxygen) or oxygen-rich air containing more than 88% by volume of oxygen. I support it. In particular, air directly from the atmosphere does not typically need to be used to support combustion. By this means, it is possible to preferentially create combustion conditions that do not allow any ammonia to pass through the catalyst stages of the Clause plant and at the same time leave the gas stream leaving the Clause plant which is recycled to the absorption columns 12, 18 according to the invention. The amount of diluent gas in the tank is kept low.

Both the flow of hydrogen sulfide-containing gas from the stripping column 32 and the flow of commercial pure oxygen are fed, the latter through the pipe 45 into the furnace 48 (which forms part of the claus plant 44). To burner 46, which burns in a direction or tangentially. The burner is preferably formed of a corrosion resistant iron alloy such as stainless steel. Burner 46 is preferably in the form of a tip-mixed structure, which is a mixture of oxygen and combustion gases containing hydrogen sulfide, ammonia and hydrogen cyanide that occur downstream of the distal end of burner 46. Burner 46 may have a configuration of passages that enable initial mixing of combustion gas and oxygen. For example, this may be a shell-and-tube arrangement (not shown), typically with combustion gas provided to the tube and oxygen provided to the shell. In another arrangement, there are two sets of tubes. One set of tubes is supplied with combustion gas and the other set of tubes is provided with some oxygen. Residual oxygen is supplied to the shell. This arrangement can be used to produce a temperature sufficient for the decomposition of ammonia without causing damage to the fire resistant lining of the furnace 48. Typically, when pure oxygen is used to support combustion, sparks may be generated in the local region of 2000 ° C. or higher. This high flame temperature promotes thermal decomposition of ammonia, which facilitates its decomposition and minimizes the formation of incidental nitrogen oxides. The relative flow of combustible gas and oxygen to burner 46 causes about two thirds of the hydrogen sulfide to remain unburned. Various reactions occur in the furnace 48. Part of the hydrogen sulfide is oxidized with sulfur dioxide and water vapor. Some hydrogen sulfides are thermally decomposed into hydrogen and sulfur vapors. Hydrogen cyanide is completely oxidized. As mentioned above, some ammonia is thermally decomposed into nitrogen and hydrogen. In addition, ammonia is burned to form nitrogen and water vapor. Part of the sulfur dioxide formed by the combustion of hydrogen sulfide reacts with the remaining hydrogen sulfide to form sulfur vapor and water vapor. Various other reactions can also occur in the furnace 48, such as the formation of carbon monoxide, carbon oxysulfide and carbon disulfide. The effluent gas stream flows directly from the furnace 48 into the waste heat boiler 50 or directly into another type of heat exchanger that is cooled to a temperature of 250 to 400 ° C. During the passage of the gas stream through the waste heat boiler 50, there is a tendency for some hydrogen to recombine with sulfur to form hydrogen sulfide.

The cooled effluent gas stream passes from the waste heat boiler 50 to the sulfur condenser 52, where it is further cooled to a temperature of 120 to 160 ° C., and the sulfur vapor is condensed and extracted through the outlet 54. The final liquid sulfur is typically passed up to a sulfur seal pit (not shown). The final sulfur vapor-depleted gas stream (now typically containing only traces of sulfur vapor) is downstream of the sulfur condenser 52, for example by indirect heat exchange using superheated steam or hot gas in reheater 56. Heated to a temperature of 250-350 ° C., typically about 300 ° C.

This reheated sulfur vapor-depleted gas stream is flowed into the first catalytic cloud reactor 60. The first catalytic Klaus reactor 60 comprises one or more conventional catalysts of Klaus reactions (ie, reactions between hydrogen sulfide and sulfur dioxide forming sulfur vapor and water vapor). Typically, the catalyst is activated alumina, titanium dioxide or bauxite. Most of the sulfur dioxide in the sulfur vapor-depleted gas stream reacts on this catalyst to form sulfur vapor and water vapor. However, the reaction is not carried out completely, which results in one or more additional catalytic steps of the Klaus reaction. However, first the gas flowing from the first catalytic cloud reactor 60 flows to another sulfur condenser 62 where the gas stream is cooled to a temperature of 120 to 160 ° C. and sulfur vapors are condensed. Condensate is extracted through the outlet 64 leading from the condenser 62 to a sulfur sealed pit (not shown). The final sulfur vapor-depleted gas stream (now typically containing only traces of sulfur vapor) is 250 by indirect heat exchange downstream of condenser 62, for example using superheated steam or hot gas in reheater 66. Reheat to a temperature of from about 350 ° C., typically about 300 ° C. This reheated sulfur vapor-depleted gas stream is flowed into a second catalytic cloud reactor 68. The second catalytic Claus reactor 68 is similar in all essential respects to the first catalytic Claus reactor 60. Most of the remaining sulfur dioxide reacts with hydrogen sulfide on the catalyst to form sulfur vapor and water vapor. The final gas mixture leaves the second catalyst Claus reactor 68 and is passed into another sulfur condenser 70 where it is cooled to a temperature of 120 to 160 ° C. to condense its sulfur vapors. Sulfur vapor is extracted through outlet 72 and flows to a sulfur sealed pit (not shown). The final gas stream still contains a small amount of sulfur dioxide and may also contain traces of carbon disulfide, carbon oxysulfide and sulfur vapors. To convert these compounds to hydrogen sulfide, the final gas stream is reheated in reheater 71 and is about 350 using hydrogen as reducing agent on a suitable catalyst, typically supported cobalt-molybdenum catalyst, in reactor 73. Reduced at a temperature of < RTI ID = 0.0 > Typically, the final gas mixture contains sufficient hydrogen for this purpose. However, if desired, an external source of hydrogen, such as a hydrogen generator, can be used. The reduced gas stream then has most of its water content (typically at least 85% by volume) removed by passing through condenser 74, where it is typically cooled to a temperature of 50-95 ° C. The condenser 74 is preferably in direct contact with the column, where the reduced gas stream is in contact with the flowing water. Indirect heat exchangers may alternatively be used. The composition of the gas stream exiting the condenser is typically from 4 to 8% H ₂ , based on the dry state; 40 to 70% of N ₂ ; 22 to 45% CO ₂ ; And 4-7% H ₂ S (all are volume percent). The precise amount of water vapor present depends on the outlet temperature of the reduced gas stream from condenser 74. Downstream of the condenser 74, the gas stream is combined with the cooled coke oven gas stream. This combination occurs at a location downstream of the second cooler 10 but upstream of the inlet for the coke oven gas with respect to the absorption column 12. The size of the gas stream recycled from the cloud plant 44 is limited by the fact that oxygen-rich air or essentially pure oxygen containing at least 40% by volume of oxygen is used to support the combustion therein. Thus, the treated coke oven gas has an acceptable calorie value.

Various modifications to the plant shown in FIG. 1 may be possible depending on the composition of the gas released from the stripping column 32. If the proportion of combustible species in this gas is too high, combustion of one third of its hydrogen sulfide in the furnace 48 results in the production of a temperature high enough to damage its refractory lining. In this case, combustion can occur in two thermal stages, which is less than one third of the hydrogen sulfide content of the gas occurring in the furnace 48. Thus, a second furnace can be used downstream of the sulfur condenser 52. The operation of the second furnace is similar to that of the furnace 48, and about one third of the hydrogen sulfide content of the gas released from the stripping column 32 can be completely oxidized to hydrogen disulfide in the two furnaces. However, this is still important so that sufficient temperature is maintained in the furnace 48 for the decomposition of ammonia and preferably all ammonia is decomposed in the furnace 48 without entry of the second furnace. In another variant, two passages can be created in the waste heat boiler 50 that communicate with each other through the chamber where additional oxygen is supplied (with the accompanying waste heat boiler and sulfur condenser). The temperature in the middle of the two passages is sufficient to occur in the chamber for self-burning of some of the residual hydrogen sulfide and to react with the residual hydrogen sulfide for the final sulfur dioxide to form additional sulfur vapors. In this way, the advantage of having two separate hydrogen sulfide combustion zones is that they can be obtained with a minimum of additional equipment without the need for additional burners and sulfur condensers. The furnace or each furnace may be operated at an outlet gas outlet temperature of 1300-1600 ° C. If the gas supporting combustion in the furnace is a combination of commercial pure oxygen and air, the temperature can be controlled by adjusting the relative ratio of air and commercial pure oxygen.

In a further variant, the acidic gas stripped from the liquid absorbent may be heated above its dew point, typically above 10 ° C., and by, for example, an insulated and / or heated pipeline upstream of the Claus plant to prevent condensation at this temperature. Can be maintained.

Klaus plant 44 is required to be able to convert at least 95% of the incoming hydrogen sulfide to sulfur. The conversion achieved in each catalyst cloud stage depends in part on the concentration of hydrogen sulfide on the catalyst.

Various changes, improvements and modifications to the uptake of impurities from the coke oven gas and subsequent stripping from the absorbent are possible. For example, if the pH is properly controlled therein, a single absorption column can perform the function of columns 12,18. In another variation, the gas-filled liquid from the absorption column 12 is stripped separately from the gas-filled liquid from the absorption column 18. The advantage of such individual stripping is that the amount of residual hydrogen sulfide and ammonia retained in the absorbent can be minimized, thereby facilitating downstream wastewater treatment. Stripping of hydrogen sulfide is facilitated by acidifying the gas-loaded absorbent (eg by dilute sulfuric acid), and stripping of ammonia is promoted by further alkalizing the gas-loaded absorbent (eg by caustic soda). In yet other variations, selective absorbers of hydrogen sulfide may be used. Preferred selective absorbents include alkanolamines, in particular ethanolamine. Monoethanolamine is particularly preferred. If such a selective absorbent is used, it is desirable to remove the upstream ammonia from the gas stream.

In summary, the plant shown in the figure can remove ammonia, hydrogen sulfide and hydrogen cyanide impurities from the coke oven gas. Thus, it is possible to considerably simplify a conventional purification plant that treats ammonia completely completely from hydrogen sulfide.

Claims (12)

A process for treating a feed stream of fuel gas containing both hydrogen sulfide and ammonia as impurities, Extracting at least 70% hydrogen sulfide impurities of the feed stream in an absorbent, Stripping hydrogen sulfide from the formed hydrogen sulfide-filled absorbent to form a combustible gas stream containing hydrogen sulfide, Forming sulfur from the combustible gas stream, Recovering the formed sulfur and a tail gas stream containing residual amounts of hydrogen sulfide, sulfur vapor and sulfur dioxide, Reducing the residual amount of sulfur dioxide and sulfur vapor in the tail gas stream to hydrogen sulfide, and Combining the reduced tail gas stream with the feed stream upstream of the extraction of hydrogen sulfide impurities Including but not limited to: The sulfur forming step comprises one or more combustion steps in which the hydrogen sulfide portion of the combustible gas stream is combusted, Ammonia impurities are also extracted from the feed gas by the absorbent, a flow of ammonia is produced by stripping ammonia from the formed ammonia-filled absorbent, the flow of ammonia is passed through to the combustion stage, and the combustion of the hydrogen sulfide Carried out under conditions which essentially remove all ammonia, the combustion being supported by a gas stream containing at least 40% by volume of oxygen Characterized by the above. The method of claim 1, Effluent gas leaves at a temperature of at least 1300 ° C. in said combustion step. The method according to claim 1 or 2, Oxygen-rich air or pure oxygen containing at least 50% by volume of oxygen is supplied to the combustion stage, therein generates a hot flame zone, and pyrolyzes ammonia within the hot flame zone, but effluent from the combustion stage A method in which there is essentially no nitrogen oxide in the gas. The method according to any one of claims 1 to 3, The extraction of the ammonia is carried out downstream of the extraction of hydrogen sulfide. The method according to any one of claims 1 to 4, Absorbing said ammonia separately from hydrogen sulfide. The method of claim 5, And separately stripping said hydrogen sulfide-filled absorbent from the ammonia-filled absorbent. The method according to any one of claims 1 to 6, Wherein the recovery of sulfur comprises a plurality of combustion stages in which the hydrogen sulfide portion of the combustible gas stream is combusted. The method of claim 7, wherein Supplying pure oxygen or oxygen-rich air containing at least 80% by volume of oxygen to all of said combustion stages. The method according to any one of claims 1 to 8, The feed gas is a coke oven gas. The method according to any one of claims 1 to 9, Reduction of the tail gas using hydrogen as a reducing agent over a catalyst. The method according to any one of claims 1 to 10, The reduced tail gas which merges with the feed gas upstream has water condensed therefrom. The method of claim 11, Condensation by direct contact with water.

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