MXPA99011904A - Method for desulfurizing off-gases - Google Patents

Abstract

The invention relates to a method for removing H2S from off-gases which contain at least 20%by volume of water vapor, comprising treating the off-gases at a temperature above the water dew point of the off-gases with an aqueous, alkaline solution under absorption of the H2S, followed by subjecting the sulfide-containing solution formed to a biological oxidation of the sulfide.

Description

METHOD FOR DESULFURING DISCHARGE GASES DESCRIPTION OF THE INVENTION This invention relates to a method for desulfurizing discharge gases which contain a high water vapor content. More specifically, the invention comprises a method for reducing the total sulfur content of the discharge gases from the sulfur recovery plants. The preparation of elemental sulfur from hydrogen sulfide (H2S) by partial oxidation thereof by means of oxygen or an oxygen-containing gas such as air, followed by the reaction of sulfur dioxide (S02) formed from Hydrogen sulfide, with the residual part of the hydrogen sulfide, in the presence of a catalyst, is known as the Claus process. This process is frequently used both in refineries and for the processing of hydrogen sulphide recovered from natural gas. A conventional Claus plant consists of a burner with a combustion chamber, the so-called thermal stage, followed by a number of - usually two or three - reactors which are filled with a catalyst. These last stages constitute the so-called catalytic stages. In the combustion chamber, the gas flow rich in incoming H2S is burned with an amount of air at a temperature REF: 32331 of about 1200 ° C. The amount of air is set so that one third of the H2S is burned to S02 according to the reaction: 2H2S + 302? 2H20 + 2S02 (1) After this partial combustion of the H2S, the part of the unreacted H2S (that is approximately two thirds of the amount presented) and the S02 formed react additionally for a considerable part according to the Claus reaction: 4H2S + 2S02 < - > 4H20 + 3S2 .2) Description this mode, in the thermal stage, approximately 60% of the H2S is converted to elemental sulfur. The gases from the combustion chamber are cooled to approximately 160 ° C in a sulfur condenser, in which the sulfur formed is condensed, which then flows via a siphon to a sulfur reservoir. The non-condensed gases, in which the molar ratio of H2S to S02 is still 2: 1, are subsequently heated to approximately 250 ° C and passed through a first catalytic reactor, in which the equilibrium is again established 4H2S + 2S02 < - > 4H20 + 6 / nSn.

The gases coming from this catalytic reactor are then cooled again in a sulfur condenser, where subsequently the liquid sulfur formed is recovered and the residual gases, after reheating, are passed to a second catalytic reactor. Depending on the number of catalytic stages, the recovery percentage of sulfur in a conventional Claus plant constitutes 94-97%. Consequently, an amount of H2S and S02 is left. One of the important limitations of the Claus process is the increase in water content in the process gas as the conversion of H2S to sulfur proceeds. The Claus reaction is limited by thermodynamically by this increase in water vapor content and simultaneously by the decrease in the concentration of H2S and S02, with the result that the equilibrium of the reaction of Claus (2) moves to the left . The condensation of water vapor in the process gas would be desirable to remove this limitation as much as possible. However, since the water spray point is well below the solidification point of sulfur, the condensation of water vapor in the Claus process meets insurmountable problems, such as clogging due to solidification of sulfur and corrosion due to the formation of sulfurous acid. In the past, the discharge gases from the Claus process were burned in a subsequent burner. However, in view of the increasingly stringent environmental requirements, this is no longer allowed. This has led to improvements in the Claus process and the development of Claus discharge gas removal processes. An improvement of the Claus process is known as the SUPERCLAUS® process, in which the efficiency of the Claus process was increased from 94-97% to more than 99%. The SUPERCLAUS® process is described in "SUPERCLAUS®, the response to the limitations of the Claus plant", publ. 38th Canadian Chem. Eng. Conference, October 25, 1988, Edmonton, Alberta. Glen. In the SUPERCLAUS®-99 process, the reaction (2) in the thermal stage and in the Claus reactors is operated with an excess of HS, so that in the gas of the last Claus reactor the H2S content is approximately 1. % in volume and the content of S02 is approximately 0.02% by volume. In a next stage of the reactor, the H2S is selectively oxidized to elemental sulfur according to the reaction: 2H2S + 02 - > 2H20 + 2 / nSn (3) In the presence of a special selective oxidation catalyst. These catalysts are described, for example, in European Patents 0242920 and 0409353. As stated, the increasingly stringent environmental requirements have led not only to improvements of the Claus process but also to the development of processes for Claus waste gases for additional desulfurization of discharge gases from sulfur recovery plants. The majority of waste gas processes in Claus uses a hydrogenation reactor, also known as a reduction reactor, in which S02, carbonyl sulphide (COS), carbon disulfide (CS2), sulfur vapor and any trapped sulfur droplets (sulfur mist) are converted. with hydrogen (H2) or a reducing gas, which contains, for example, hydrogen monoxide and carbon, to hydrogen sulfide. The hydrogen sulphide is then removed by absorption in a solution or by conversion in the gas phase to elemental sulfur, using a catalyst. Only a few residual gas processes have been developed which, after the combustion of Claus residual gases, absorb S02 from the flue gas. These processes will not be discussed anymore. Most well known among Claus residual gas processes which, after hydrogenation, absorb the resulting H2S in a solution are SCOT, BSR-Stretford, BSR-MDEA, Trencor-M and Suften. These processes are described in a publication of B.G. Goar: "Residual Gas Cleaning Processes, a review", presented at the 33rd Annual Gas Conditioning Conference, Norma, Oklahoma, March 7-9, 1983 and in Hydrocarbon Processing, February 1986. The best known process, and to date the most effective, to desulfurize residual gases is the SCOT process described in Maddox "Gas and Liquid Mercaptization" (1977). The SCOT process achieves a sulfur recovery of 99.8 to 99.9%. Of the residual gas processes which, after hydrogenation, convert the resulting H2S into the gas phase using a catalyst, only a few processes have been created and known, such as MODOP, CLINSULF, BSR-Selectox, Sulfreen , SUPERCLAUS-99.5. These processes are described in the aforementioned publication of B.G. Goar, in the Journal C & EN of May 11, 1987, the Journal Sulfur January / February 1995, and in the DE-A 2648190. In all those residual gas processes of Claus, after hydrogenation, the water formed in the reaction of Claus (2) and in the selective oxidation reaction (3) is condensed, because the presence of water has an adverse effect on the subsequent removal of H2S in a absorption liquid or in the catalytic conversion of H2S to elemental sulfur. The absorption liquids used in the aforementioned processes are secondary or tertiary alkanolamine solutions such as Diisopropanolamine (DIPA) or Methyldiethanolamine (MDEA) or complex Redox solutions. Without the removal of water, the absorption process would be completely disturbed, viz, either by too high temperatures at which no or only slight absorption occurs, or because water condenses in the absorbent during absorption and the circulating solution it is continuously diluted, so that no more absorption can take place. In the conversion of the H2S in the gas phase using a catalyst, without water removal the thermodynamic conversion of the H2S according to the Claus reaction (2) is strongly reduced and a situation comparable to that of the last reactor stage is obtained. Claus process, so that the total sulfur recovery efficiency of more than 99.5% is impossible to achieve. Although the use of a selective oxidation catalyst such as that used in the SUPERCLAUS process results in greater efficiency, when the SUPERCLAUS-99.5 also, it has been found that it is impossible in practice to achieve a sulfur recovery efficiency of more than 99.5%. In general, it can be established that the disadvantage of Claus waste gas processes, in which, after hydrogenation, the H2S in the gas phase is converted to elemental sulfur using a catalyst, is that the current requirements of a total efficiency Sulfur recovery of more than 99.90% can not be satisfied. Claus waste gas processes with hydrogenation are carried by condensation of water after the H2S is absorbed in an absorption liquid such as, for example, in the SCOT process, to achieve total sulfur recovery efficiencies of more than 99.90. %, but has a greater disadvantage that investment costs and energy costs are tremendously high. Newer versions of the SCOT process, such as the SUPERSCOT and LS-SCOT, achieve a total sulfur recovery efficiency of 99.95%, but are even more expensive. Another disadvantage of these processes is that the condensate containing acid hydrogen sulfide must be discharged and treated, for example in an Acid Water Separator, whereby the dissolved acid gas is separated with steam. This is too expensive.

The environmental requirements have had influence not only on the development of the Claus processes and Claus waste gases, but also on the development of the flue gas processes, also known as flue gas combustion processes, for power plants. Energy. Several processes are known for the "flue gas desulfurization" (FGD), in which the S02 is converted with gypsum calcination slurry (Ca2S04). Because a surplus of gypsum has been formed, processes have been sought, in which the S02 can be converted to elemental sulfur. The process of ellman Lord, described in Gas Purification, fourth edition 1985, A. L. Kohl, F. C. Riesenfeld, p. 351-356, is an example, where SO2 is eventually released as a concentrated gas. After two thirds of the SO2 are converted to H2S in a hydrogenation step, the H2S and gaseous SO2 can be converted to elemental sulfur in a Claus plant. This process route, too, is expensive. Another development in this field is the biological desulfurization of flue gases or chimney. The biological desulphurization of flue gases or chimney is described in the journal Lucht, number 4, December 1994. The BIO-FGD process described there is to remove S02 from stack gases from power stations and consists of an absorber where S02 It is dissolved in a solution of sodium hydroxide diluted according to the reaction.

S02 + NaOH? NaHS03 (4) This solution is subsequently treated in two stages of biological reactor. In the first biological step, in an anaerobic reactor, the sodium bisulfite (NaHS03) formed is converted with an electron donor to sodium sulfide (NaHS).

NaHS03 + 3H2 NaHS + 3H20 (5) Suitable electron donors are, for example, hydrogen, ethanol, hydrogen and glucose. In the second step, in an aerobic reactor, the sodium sulfide is oxidized to elemental sulfur, which is separated.

NaHS + Oz? NaOH + S (6) The flue gases contain, after combustion of coal or fuel oil, a slight amount of water vapor. The water content is typically between 2-15% by volume, which corresponds to a water dew point of 20-55cC. If the BIO-FGD process is used for the desulphurisation of Claus discharge gases that have subsequently been burned and therefore all the sulfur components have been converted to S02, the gas must be cooled due to the high vapor content of the gas. discharge water from Claus. This is done to prevent the water vapor from condensing in the sodium hydroxide solution, as a result of which part of the sodium hydroxide solution would have to be constantly discharged. The Claus discharge gases must, therefore, be cooled, so that an acid condensate is formed and must be discharged. In the desulphurisation of discharge gases from a coal or oil-fired power plant, this problem does not occur because the water spray point is below the operating temperature in the absorbent. The cooling of these discharge gases can, therefore, be carried out in only one way without the condensation of the water occurring. A first object of the invention is to provide a method for desulphurizing discharge gases with a high water vapor content of 20 to 40% by volume in which the condensation of this water is not necessary, thus preventing the formation of a condensate containing acid hydrogen sulfide, which will subsequently have to be discharged. A second object of the invention is to provide a second method in which the H2S formed after the hydrogenation can be absorbed into an absorption liquid at a temperature above the dew point of the water in the gas, so that also during absorption of the H2S does not occur water condensation. A following object of the invention is to provide a method by which a total efficiency of sulfur recovery greater than 99.90% is achieved without the aforementioned disadvantages occurring. The invention is based on the surprising observation that it is possible to absorb the H2S of such a gas with a water content of 20 to 40% by volume at a temperature above the dew point of the water, in an alkaline solution, so that the solution containing sulfide formed is subjected to aerobic biological oxidation. The invention is accordingly related to a method for removing H 2 S from discharge gases which contain at least 20% by volume of water vapor, which comprises treating the discharge gases at a temperature above the dew point of the discharge gases. with an aqueous alkaline solution, under the absorption of H2S4 followed by the subjection of the sulfur-containing solution formed to a biological oxidation of the sulfide. Surprisingly, it has now been found that the HS dissolved in the alkaline solution, preferably a sodium hydroxide solution, can be oxidized to elemental sulfur with air in a biological aerobic reactor at a temperature which is preferably the same at which absorption has taken place. Such gases with a water content of 20-40% by volume have a dew point in water of 60-80 ° C, which means that in practice biological oxidation will occur at a temperature of at least 65 ° C, more specific way at a temperature of 70 to 90 ° C. It is particularly surprising that it is possible to carry out an efficient and appropriate biological oxidation at such high temperatures. In the method according to the invention, the total sulfur content of the discharge gases is first reduced by raising the temperature of those discharge gases to a temperature higher than 200 ° C and subsequently by passing them along with the hydrogen-containing gas and / or carbon monoxide on a metal catalyst of group Vi / sulfurized group VIII on an inorganic oxidizing support, whereby the sulfur components such as SO2, sulfur vapor and sulfur mist are converted with hydrogen or other gas reducer which contains, for example, hydrogen and carbon monoxide, to hydrogen sulfide, according to the reactions: S02 + 3H2? H2S + H20 (7! S + H2? H2S (8) If oxygen is present in the exhaust gases, a catalyst from the previous group is used which also has the property of hydrogenating the oxygen according to the reaction 02 + 2H2? 2H20 or: Preferably, a catalyst of the above group is used which also has the property of hydrolyzing COS and CS2 according to the reactions COS + H20 - > H2S + C02 (10) CS2 + 2H20 - > 2H2S + C02 (11) In the method according to the invention, the discharge gases of the hydrogenation reactor are cooled just above the dew point of the water vapor present in the gas, so that condensation does not occur. Preferably, the cooling proceeds from 3 to 5 ° C above the dew point. The discharge gases, specifically the discharge gases from a Claus refrigeration plant, with a water vapor content of 20 to 40 vol.%, Have a dew point between 60-80 ° C. In an absorbent, these discharge gases are subsequently contacted directly with a dilute alkaline solution, preferably sodium hydroxide solution, with a pH between 8 and 9, so that the H2S is present in the gas and It dissolves according to the reaction: H2S + NaOH - > NaHS + H20 (12) The non-absorbed part of the mentioned discharge gases is optionally after combustion, discharged into the air. Because the regenerated alkaline solution does not contain H2S, the H2S present in the exhaust gases is completely absorbed in this way a total sulfur recovery efficiency of more than 99.90% can be achieved. In the method according to the invention, the solution is passed to the biological aerobic reactor at a temperature, preferably at the same temperature at which the absorption has taken place, so that no heat needs to be supplied or removed. In the aerobic reactor an amount of air is supplied, so that the H2S is partially oxidized with oxygen of air, to form elemental sulfur according to the reaction: H2S + i / 2 02 - > S + H20 (13) Subsequently, in a sulfur separator, preferably again at the same temperature, the sulfur is separated from the sodium hydroxide solution, after obtaining the solution it is recirculated to the absorbent. It is possible to cool the sodium hydroxide solution having the H 2 S absorbed therefrom before it is fed to the biological aerobic reactor. After separation of the sulfur, however, the solution is then heated again before being supplied to the absorbent. The invention will now be elucidated with reference to the d-B figures in which the method according to the invention is described in the form of a block diagram. In Figure 1 a general process diagram is represented. The discharge gas from a sulfur recovery plant, not shown, is passed via line 1, with the addition of hydrogen or other reducing gas via line 2, and is adjusted to the desired hydrogenation temperature with heater 3, before of passing through line 4 to the hydrogenation reactor 5. In the hydrogenation reactor 5, the sulfur dioxide, water vapor and organic sulfur compounds present in the gas are converted with H2 to H2S. If oxygen is present in the gas, it is converted to H20. The COS and CS2, if present, are converted with the water vapor present, to H2S and C02. The gas from the hydrogenation reactor 5 is adjusted via the. line 6 at the desired absorption temperature with the cooler 7, before being passed via line 8 to the absorbent 9 of a bioplant. In the absorbent, the H2S is washed off the gas with a dilute solution of sodium hydroxide, which is then passed via line 10 to an aerobic biological reactor 11, which H2S with the addition of oxygen from the air supplied via the line 12, is converted to elemental sulfur. The line 13 line the sodium hydroxide solution is passed to the sulfur separator 14, from which the sulfur formed is discharged via line 15. The solution is recirculated via line 16 to the absorber. The absorbent gas, which now contains only a low H2S content, is passed via line 17 to the back burner 18 before the gas is discharged via chimney 19. In Figure 2, a diagram is given for a plant according to the invention in which the discharge gas of a Claus plant with a high H2S / S02 ratio is directly absorbed, without intermediate hydrogenation. The discharge gas from the three-stage Claus plant 100 is added via line 101 to the absorbent 102. The Claus 100 plant is operated so that the molar ratio of H2S / S02 is at least 100. In the absorbent 102, the H2S is washed off the gas with a dilute solution of sodium hydroxide, which is then passed via line 103 to a biological reactor 104, in which the H2S, with the addition of oxygen from the air supplied via the line 105, is converted to elemental sulfur. Via line 106, pump 107 and line 108, a portion of the sodium hydroxide solution is passed to a sulfur separator 109, from which the sulfur formed is discharged via line 110. The solution is recirculated via the line 111 and 112 to the absorbent, with a small discharge via line 113. The absorbent gas, which now contains only a low H2S content, is passed via line 114 to a subsequent burner, not shown, before the gas is discharged via a chimney, it is also not illustrated.

EXAMPLE 1 An acid gas quantity of 9700 Nm3 / h from a gas purification plant has the following composition at 45 ° C and 1.6 bar absolute. 60. 0 Vol.% Of H2S 3.0 Vol.% Of NH3 30.0 Vol.% Of C02 5.0 Vol.% Of H20 2.0 Vol.% Of CH4 This acid gas was fed to a Claus plant with two Claus reactors. The sulfur formed in the sulfur recovery plant was, after the thermal stage and the catalytic reactor stages, condensed and discharged. The amount of sulfur was 7768 kg / h. The sulfur recovery efficiency of the Claus plant, based on acid gas, was 93.3%. The amount of discharge gas was 29749 Nm3 / h from the Claus plant had the following composition of 16 ° C and a pressure of 1.14 bar absolute. 0. 47 Vol,% of H2S 0.24 Vol,% of S02 0.03 Vol,% of COS 0.04 Vol,% of CS2 0.01 Vol,% of S6 0.04 Vol,% of S8 1.38 Vol,% of CO 1.53 Vol,% of H2 11.37 Vol ,% of C02 55.96 Vol,% of N2 0.66 Vol,% of Ar 28.27 Vol,% of H20 This discharge gas was supplied with 103 Nm3 / h of hydrogen as a reducing gas and then heated to 280 ° C to hydrogenate all the sulfur dioxide (S02) and the sulfur vapor (S6, S8) present to H2S, and also to hydrolyze the carbonyl sulphide (COS) and carbon sulfide (CS2) to H2S in the hydrogenation reactor which contains a Group VI metal catalyst and / or sulfurized Group VIII, in this case a Co-Mo catalyst. The amount of discharge gas from the hydrogenation reactor was 31574 Nm3 / h and had the following composition at 367 ° C and 1.10 bar absolute. 1. 24 Vol,% of H2S 28 ppm of COS 2 ppm of CS2 2.02 Vol,% of H2 12.64 Vol,% of C02 56.62 Vol,% of N2 0.67 Vol,% of Ar 26.80 Vol,% of H20 The discharge gas was then cooled to 72 ° C, a temperature which is 3 ° C higher than the spray point of the water vapor present in the discharge gas. Then the cold discharge gas was treated in a bioplant at 12 ° C, without condensation of water from the discharge gas taking place. In the absorber of the bioplant, the H2S was flushed from the discharge gas with diluted sodium hydroxide solution, after which the solution with the absorbed H2S was passed to an aerobic biological reactor in which the H2S was converted to sulfur elementary. No heat was supplied or removed in the bioplant, so that the absorption of the HS and the conversion to elemental sulfur occurred at the same temperature of 72 ° C. To the aerobic reactor an amount of 945 Nm3 / h of air was supplied for the selective oxidation of H2S to sulfur. The amount of gas in the absorbent was 31189 Nm3 / h and had the following composition at 72 ° C and 1.05 bar absolute. 250 ppm of H2S 28 ppm of COS 2 ppm of CS2 2.04 Vol,% of H2 12.80 Vol,% of C02 57.32 Vol,% of N2 0.68 Vol,% of Ar 27.13 Vol, of H? 0 Via a later combustion, this gas was passed to the chimney. The amount of sulfur formed in the biplanta was 551 kg / h. The total amount of sulfur produced in the recovery plant and the bioplant was 8319 kg / h, which increased the total desulfurization efficiency, based on the original acid gas to 99.87%.

EXAMPLE 2 An acid gas quantity of 6481 Nm3 / h from a gas purification plant had the following composition at 45 ° C and 1.6 bar absolute. 90. 0 Vol,% of H2S 3.0 Vol,% of NH3 5.0 Vol,% of H20 2.0 Vol,% of CH4 This acid gas was supplied to a plant SUPERCLAUS® with two Claus reactors and a selective oxidation reactor. The sulfur formed in the sulfur recovery plant was, after the thermal stage and the catalytic reactor stages, condensed and discharged. The amount of sulfur was 8227 kg / h. The sulfur recovery efficiency of the Claus plant, based on acid gas, was 98.5%. The amount of discharge gas of 21279 Nm3 / h from the Claus plant had the following composition at 129 ° C and a pressure of 1.14 bar absolute 0. 03 Vol, o. or of H2S 0.20 Vol, or. c of S02 20 ppm of COS 30 ppm of CS2 10 ppm of S6 0.01 Vol, o of S8 0.15 Vol, of CO 1.72 Vol, of H2 1.14 Vol, of C02 62.45 Vol, or. 0 of N2 0.74 Vol, or o of Ar 33.05 Vol, or. or of H20 0.50 Vol. of 02 This discharge gas was supplied with 133 Nm3 / h of hydrogen as a reducing gas and then heated to 280 ° C to hydrogenate all of the sulfur dioxide (S02), sulfur vapor (S6, • S8) present to H2S and H20, and in addition to hydrolyze the carbonyl sulfide (COS) and carbon sulfide (CS2) to H2S in the hydrogenation reactor which contains a metal catalyst of group VI and / or sulfurized group VIII, in this case a Co-catalyst. Mo. The amount of discharge gas from the hydrogenation reactor was 22863 Nm3 / h and had the following composition at 367 ° C and 1.10 bar absolute. 0. 37 Vol,% H2S 2 ppm COS 0.82 Vol,% H2 1.90 Vol,% C02 62.89 Vol,% N2 0.75 Vol,% Ar 33.27 Vol,% H20 The discharge gas was then cooled to 76 ° C, a temperature which is 3 ° C higher than the dew point of the water vapor present in the discharge gas. Then the cold discharge gas was treated in a bioplant at 76 ° C, without condensation of water from the discharge gas taking place. In the absorber of the bioplant, the H2S was flushed from the discharge gas with a dilute solution of sodium hydroxide, after which the solution with the absorbed H2S was passed to an aerobic biological reactor in which the H2S was converted to elemental sulfur. In the bioplant, heat was not supplied or removed, so that the absorption of H2S and the conversion to elemental sulfur occurred at the same temperature of 76 ° C. The aerobic reactor was supplied with an amount of 205 Nm3 / h of air for the partial oxidation of H2S to sulfur. The absorbent gas was 22780 Nm3 / h and had the following composition at 76 ° C and 1.05 absolute bar. 75 ppm of H2S 2 ppm of COS 0.82 Vol,% of H2 1.91 Vol,% of C02 63.12 Vol,% of N2 0.75 Vol,% of Ar 33.39 Vol,% of H20 Via a later combustion, this gas was passed to the chimney. The amount of sulfur formed in the bioplant was 119 kg / h. The total amount of sulfur produced in the sulfur recovery plant and the bioplant was 8346 kg / h, which increased the total efficiency of desulfurization, based on the original acid gas, to 99.97%.

EXAMPLE 3 An acid gas quantity of 3500 Nm3 / h from a gas purification plant had the following composition at 40 ° C and 1.7 bar absolute. 88. 0 Vol,% H2S 6.1 Vol,% C02 1.5 Vol,% CH4 4. 4 Vol,% of H20 This acid gas was supplied to a Claus plant with three Claus reactors. The air supply to this Claus plant was set according to the reaction (2) in the thermal stage in the Claus reactors was operated with excess H2S, so that the content of H2S: S? 2 after the third stage of reactor is greater than 100 to 1, so that the content of S02 would be less than 0.009 vol.%. The sulfur formed in the sulfur recovery plant, after the thermal stage and the catalytic reactor stages, was condensed and discharged. The amount of sulfur was 4239 kg / h. The sulfur recovery efficiency of the Claus plant, based on acid gas, was 96.4%. The amount of discharge gas of 10001 Nm3 / h from the Claus plant had the following composition of 130 ° C and a pressure of 1.15 bar absolute. 0.93 Vol.% Of H2S 0.009 Vol.% Of S02 0.04 Vol.% Of COS 0.04 Vol.% Of CS2 0.001 Vol.% Of S5 0.01 Vol,% of S8 0.36 Vol.% Of CO 1.83 Vol.% Of H2 2.79 Vol .% of C02 59.68 Vol.% of N2 0.60 Vol.% of Ar 33.71 of Vol.% of H20 The discharge gas was then cooled to 78 ° C, at a temperature at which 3 ° C higher than the dew point of the water vapor present in the discharge gas. Then the cooled discharge gas was treated in a bioplant at 13 ° C, without condensation of water from the discharge gas taking place. In the absorber of the biplanta, the H2S was flushed from the discharge gas with dilute sodium hydroxide solution, after which the solution with the absorbed H2S was passed to an aerobic biological reactor in which the H2S was converted to elemental sulfur. In the bioplant, no heat was supplied or removed so that the absorption of H2S and the conversion to elemental sulfur occurred at the same temperature of 73 ° C. The aerobic reactor was supplied with an amount of 320 Nm3 / h of air for the selective oxidation of H2S to sulfur. The amount of gas in the absorbent was 9901 Nm3 / h and had the following compositions at 73 ° C and 1.05 bar absolute. 190 ppm H2S 7 ppm COS 9 ppm CS2 1.85 Vol.% H2 0.36 Vol.% CO 2.82 Vol.% C02 60.28 Vol.% N2 0.61 Vol.% Ar 34.06 Vol.% H20 Via a later combustion, this gas was passed to the chimney. The amount of sulfur formed in the bioplant was 156 kg / h. The total amount of sulfur produced in the sulfur recovery plant and the bioplant was 4395 kg / h, which increased the total desulfurization efficiency, based on the original acid gas, to 99.93%.

The small amount of S02 was converted to sulphate in the lye solution. No combination of sulphates was obtained, a small amount of 85 kg / h of bleach solution was replaced with a corresponding discharge amount. It is noted in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (8)

1. CLAIMS Having described the invention as above, the following claims are claimed as content property: 1. A method for removing H2S from discharge gases which contain from 20 to 40% of water vapor volume, characterized in that it comprises gas treatment discharge at a temperature above the dew point of the discharge gases with an aqueous, alkaline solution, under the absorption of the H2S, followed by the subjection of the sulfur-containing solution formed to a biological sulfide oxidation.
2. 2. The method ading to claim, characterized in that the absorption and oxidation occur substantially at the same temperature.
3. 3. The method ading to claim 1 or 2, characterized in that the discharge gases to be treated come from a sulfur removal plant.
4. 4. The method of compliance with the claim 3, characterized in that the discharge gases are hydrogenated before absorption.
5. 5. The method ading to claims 1-3, characterized in that the discharge gases have a molar ratio of H2S / S02 of at least 100 and preferably comes from a Claus plant.
6. 6. The method ading to claims 1-5, characterized in that the sulfides are converted into aerobic biological oxidation to elemental sulfur.
7. 7. The method ading to claims 1-6, characterized in that the sulfur, after biological oxidation, is separated from the liquid.
8. 8. The method ading to claim 7, characterized in that the liquid, after separation of the sulfur, is recirculated as an absorption liquid.