MXPA97003369A

MXPA97003369A - Procedure to treat gas currents quecontienen

Info

Publication number: MXPA97003369A
Application number: MXPA/A/1997/003369A
Authority: MX
Inventors: A Hammond Charles
Original assignee: The Dow Chemical Company
Priority date: 1994-11-09
Filing date: 1995-11-07
Publication date: 1997-08-01

Abstract

The present invention relates to a process comprising a condensation vapor containing a minor amount of H2S and other non-condensable gases in a condensation zone with an aqueous solution containing a ferric chelator under conditions to convert H2S to sulfur, and chelator ferrous ferrous chelator, leaving a stream of non-condensable gas containing the volume of H2S in the vapor, dividing or separating said stream of non-condensable gas to a first stream containing H2S containing the volume of H2S containing a smaller portion of H2S in the non-condensable gas stream, oxidizing the H2S in the first stream containing H2S in a thermal oxidation zone to produce a gaseous stream that comrpenses SO2, and removing the SO2 from the gas stream comprising SO2, and removing the SO2 from the gaseous current by contacting said gas stream with an alkaline solution, concurrently contacting the second stream containing H2S with an aqueous solution of ferric chelator in an area of aqueous liquid oxidation under conditions to convert H2S in said second stream containing H2S to sulfur in the solution producing a current of purified waste gas and removing sulfur in the oxidation zone liquid water

Description

PROCEDURE TO TREAT GAS CURRENTS CONTAINING H, S DESCRIPTION OF THE INVENTION The invention relates to the processing of gas streams containing H 2 S to remove H 2 S and, in preferred aspects, to the processing of gas streams comprising steam and H 2 S to condense the vapor and remove H 2 S. The invention is particularly suitable for treating streams containing H2S from the escape of a steam turbine, especially the exhaust steam from a turbine using geothermal steam as the working fluid. Industrial and natural sources produce a wide variety of gas streams that contain significant amounts of H2S concentrations. In some cases, the gas streams will also contain or will be composed primarily of steam, with H2S and other non-condensable gaseous materials being pre-shipped as contaminants. Geothermal steam, for example, comprises or is composed of current with varying lower concentrations or quantities of non-condensable gases, such as H2S, CO2, CH4, N H3, H, and N2. Since the processing equipment, which uses or deposits such gases, is commonly constructed of special materials that resist the corrosive nature of H2S, downstream use or requirements may require the removal of H2S. For example, H2S interferes with many chemical reactions and can not be tolerated in a reactive gas. Again, even if it is tolerated in some operations, the gas containing H2S can not be allowed to escape into the environment. For example, exhaust gases from a kettle that contain significant amounts of H2S must be treated before being sent to the stack. In the case of the use of geothermal steam, before the condensate derived from the spent steam can be processed for distribution, the H2S in the condensate must be eliminated. A variety of procedures have been employed to treat or purify gases contaminated with H2S. In some cases, if the stream comprises mainly non-condensable materials, for example, those mentioned above, with a significant concentration of H2S, ie 200 ppm by volume or more, the stream can be incinerated to produce SO2 from the H2S. In such cases, the SO2 can then be removed from the non-condensable stream by purification, the remaining non-condensable gases being vented or further processed. When the non-condensable gases contain minor amounts of H2S, aqueous reactive systems are preferred, which comprise regenerable reagents that react with the H2S to produce free solid sulfur. Suitable reagents include polyvalent metal ions, such as iron, vanadium, copper, manganese, and nickel, and include polyvalent metal chelators. Preferred reagents are coordination complexes, in which the polyvalent metals form chelating agents with specific organic acids. When the gas rich in sulfur-containing products or containing H2S comprises or is composed mainly of steam, condensation of the vapor can not be taken into account in any removal procedure. Thus, in a preferred system during use for the geothermal exhaust steam, the exhaust vapor is condensed in an H2S removal zone of combination condensation, with removal of the H2S from the vapor and / or condensate by an aqueous solution. oxidation iron chelator. The solubility of H2S in the condensate or condensate / chelator combination solution is determined enormously by the type of condensation used and, if direct contact of the vapor with the aqueous solution of the iron chelator is practiced, by the pH of the aqueous solution oxidation of the iron chelator. In general, condensation of the vapor is carried out under conditions, so that the volume of dissolved H2S is less than 50% by weight of the H2S in the vapor. Dissolved H2S reacts with the Fe +++ chelator to form particulate sulfur, the remaining H2S as a non-condensable gas being thermally incinerated to SO2. The SO2 is also treated with an alkaline solution to convert the SO2 to be distributed easily or to use additionally ions of HSC3-and / or SO3"2 in solution.The procedure also characterizes the regeneration of the Fe ++ chelator derivative in the condensate / chelator solution to the Fe +++ chelator, and, importantly, it uses sulfur from the condensate and other byproducts of the process to generate thiosulfate ions in solution, the latter being easily and safely discarded without environmental contamination, since the prior art schemes present many advantages, they still admit an improvement, for example, if the gas containing H2S contains a large proportion of H2S, or if H2S is divided in an increasing way, for example, up to 95% or by weight of the stream, to the incineration reactor, there will be increased costs in energy and in chemistry (alkaline solution) The invention, therefore, is aimed at providing a more cost-efficient factor for processing streams with a high H2S content or for increasing the volume of the non-condensable polluting H2S division of the steam condensation processes. Accordingly, the invention relates to the removal of H 2 S from gas streams rich in sulfur-containing products, the removal of H 2 S from gas streams rich in sulfur-containing products comprising or consisting mainly of vapor which is a preferred aspect of the invention. In the case of non-condensable streams containing high concentrations of H2S, the reduction of by-products is achieved in an integrated record, which returns the important values to the procedure. Accordingly, in one embodiment, the invention relates to a method for removing H2S from a non-condensable gas stream containing H2S and other non-condensable gases comprising dividing or separating the non-condensable gas stream into a first stream containing H2S, containing the volume of the H2S in the gas stream (ie, greater than 50% by weight), and a second stream containing H2S containing a smaller portion of the H2S in a non-condensable gas stream; oxidizing the H2S in the first stream containing H2S in a thermal oxidation zone to produce a gaseous stream comprising SO2, and removing the SO2 from the gas stream by contacting said gas stream with an alkaline solution in a purification zone with a alkaline solution under conditions that produce a purified gas stream and a purification zone solution containing bisulfite and / or sulfite ions; contacting the second stream containing H2S concurrently with an aqueous solution of ferric chelator in an aqueous liquid oxidation zone under conditions to convert the H2S in said second stream containing H2S to sulfur in said solution, producing a stream of purified waste gas , and removing the sulfur from said aqueous liquid oxidation zone. In addition, according to this embodiment, the solution of the purification zone containing sulfite is combined with sulfur from the aqueous liquid oxidation zone in a mixing zone under conditions to convert the sulfur and produce a solution containing a thiosulfate ion and ions. residues of bisulfite and / or sulfite. As used herein, the term "and / or", as applied in the indication of ions in solution derived from the reaction of the alkaline solution with S02, is understood to include three possibilities, ie, all or substantially all of the bisulfite ions, the bisulfite and sulphite ions, or all or substantially all of the ions in its lily. In a second embodiment, the invention relates to a process for condensing vapor containing a lower concentration or amount of H2S and other non-condensable gases. The procedure provides for an effective conversion of H2S from the aqueous solution of ferric chelator, which dissolves in the condensate or in the treatment solution in the condensation zone, while simultaneously dividing a larger portion of the H2S from the condensation zone as a non-condensable gas stream, with an efficient and cost-effective arrangement of H2S in the stream. The reduction in the amount of sulfur produced in the combined aqueous-condensate iron chelator, since the larger portion of H2S is distributed to the non-condensable gas stream, allows for improved handling of the sulfur in the cooling section and regeneration associated with the condensation-removal zone. Up to this point, the efficient removal of H2S in the non-condensable stream is achieved through an additional separation or division of this stream containing H2S, and the effective treatment of the divided streams, as described above. That is, the stream containing H2S from the condensation zone is divided into a first portion or stream containing H2S, or primary, which is subjected to thermal oxidation and to the treatment of the current containing H2S produced, and a second portion or smaller current from which the H2S is oxidized concurrently to the elemental sulfur through an aqueous solution of ferric chelator. The use of an aqueous ferric chelator solution system for the removal of H2S from the second portion allows for reduced costs in the incineration and caustic scrubbing, as well as the production of the sulfur byproduct, which is easily recovered or used with an additional advantage, as underlined in the preferred embodiments of the invention described above. More particularly, in this embodiment, the invention relates to a process comprising condensing the vapor containing a lower amount of H2S and other non-condensable gases in a condensation zone, and removing the H2S from the vapor and condensate through a direct contact with an aqueous solution containing ferric chelator under conditions to convert V to sulfur, and ferric chelator to ferrous chelator, leaving a stream of non-condensable gas containing the volume of H2S in the vapor; dividing or separating said non-condensable gas stream in a first stream containing H2S containing the volume of H2S in said gas stream, and a second stream containing H2S containing a minor portion of H2S in the non-condensable gas stream; oxidizing the H2S in a first stream containing H2S in a thermal oxidation zone to produce a gaseous stream comprising SO, and removing the SO from the gas stream by contacting said gas stream with an alkaline solution; contacting the second stream containing H2S concurrently with an aqueous solution of the ferric chelator in an aqueous liquid oxidation zone under conditions to convert H2S into said second stream containing H2S to sulfur in said solution, producing a stream of purified waste gas , and removing the sulfur from the aqueous liquid oxidation zone. Alternatively, in a further embodiment, the vapor containing the smaller amount of H2S, is condensed, and the ferric chelator solution is combined with the condensate to remove the dissolved H2S, the volume of H2S in the vapor being divided as a stream of H2S. non-condensable gas and treated as previously written. In preferred and more specific embodiments, the SO2 produced in the thermal oxidation zone is removed by means of purification with an alkaline solution in a purification zone under conditions to produce a solution of the purification zone containing bisulfite ions and / or sulfite, and the solution of the purification zone is combined with sulfur from the aqueous liquid oxidation zone in a mixing zone under conditions to react and produce a solution containing a thiosulfate ion and residual bisulfite and / or sulphite ions . In a further preferred aspect, the aqueous iron chelator solution containing the ferrous chelator and the sulfur is removed from the condensation zone and combined with the solution containing thiosulfate and residual sulphite and / or sulphite ions from the area. of mixing. And, in a highly preferred embodiment, the H 2 S content of the first stream containing H 2 S is greater than the total amount of H 2 S removed in the condensation zone and the second stream containing H 2 S, so that the mixing of the sulfur in a wet process with the current containing bisulfite and / or sulfite allows the total removal of the derivative sulfur from the system. Figure 1 illustrates schematically one embodiment of the ntion, wherein the alkaline solution of a SO2 purification step, containing bisulfite ion and / or the sulfite ion, is mixed with the sulfur produced in an aqueous liquid oxidation zone through the oxidation of the aqueous ferric H2S chelator in a non-condensable gas divided. Figure 2 schematically illustrates one embodiment of the ntion, wherein a turbine exhaust gas containing H2S is treated through the condensation and partial removal of the H2S in a combination zone of condensation and oxidation of aqueous solution, the H2S not dissolved or unreacted, passing from the zone with other non-condensable gases and being divided or separated into primary and secondary portions, which are oxidized through specific oxidation processes. Figure 3 illustrates schematically a highly preferred embodiment of the ntion, wherein the alkaline solution of a S0 removal step, containing the bisulfite ion and / or the sulfite ion, is mixed with the sulfur produced through the oxidation of the H2S aqueous ferric chelator in the secondary portion of the aqueous liquid oxidation zone, and the mixture formed is further mixed with the sulfur-containing aqueous-condensed iron chelator, containing liquid from the condensation zone. As indicated, the ntion is suitable for the processing of a variety of gas streams containing H2S. The particular type of non-condensable stream treated according to the first mentioned modalityis not critical, the term "non-condensable" is understood herein in the sense that the gas or components thereof will not condense to any significant degree under the conditions existing in the H2S incineration zone or in the zone of oxidation of the aqueous ferric chelator. Accordingly, such streams may contain a wide variety of "condensable" components, such as propane, butane, etc. , and they can be saturated. As will be apparent to those skilled in the art, practically speaking, the only requirements are that the treated gas comprising H2S will be, instead of H2S, non-reactive or substantially unreactive and of limited solubility (ie, insoluble or substantially insoluble). in the solution of aqueous ferric chelator. Suitable gas streams include naturally occurring gases, fuel gases, vent gases, hydrocarbon gases, flue gases, and gases produced, for example, after the condensation of a desired compound such as a hydrocarbon or vapor. Other gases to which the invention can be applied are described more fully in the patent of E. U.A. 4,705,676, and, giving the teachings herein, can be readily selected by those skilled in the art. The concentrations of H2S in the treated streams may vary from trace or minimum to heavy, but, in no way as a limitation here, commonly encountered streams ranging from 200 ppm in volume to 50 volume%, preferably 0.5% in volume. Volume at 10% in volume. Typically, steam contaminated with H 2 S treated in accordance with preferred aspects of the invention will contain lower concentrations or amounts of H 2 S and other non-condensable gases. The source of said steam is a matter of choice, but the invention is particularly suited to the treatment of steam exhaust from turbines, using geothermal steam as the working fluid. In general, the steam processed according to the invention will contain H2S and other non-condensable fluids in totally minor amounts, ie 15% by weight. Normally, the H2S will be presented in an amount less than 5 or 6% by weight, more commonly less than 3% by weight. The conditions of temperature and pressure and their relation to condense the vapor are well known to those skilled in the art, and need not be presented here. The volume or concentration of H2S removed in the condensation zone, that is, the H2S that does not remain as a non-condensable gas, varies considerably depending on the type of condensation used and possibly to a certain degree in the pH of the iron chelator solution. of oxidation. If the direct contact of the chelating solution with the steam and condensate is used, the amount of H2S removed corresponds substantially to that which is dissolved in the condensate and an aqueous solution of iron chelator supplied. If indirect condensation is achieved, either with the chelator solution used as the heat exchanger fluid, or with some other cooler (or both), the amount of H2S removed is that which is absorbed or dissolved in the condensate. In the first case, the amount absorbed is an additional function of many variables, including the pressure and temperature of the zone, the volume and temperature of the aqueous chelator solution supplied, and the pH of the liquid phase in the zone. In the second case, as indicated, only the variables relevant to the condensation of the vapor matter, and less volume of liquid are present for the dissolution of H2S. Generally, the pH of the iron chelator solution, supplied to the condensation zone, will vary from 4 or 4.5 to 10, preferably from 7 to 10. Those skilled in the art can adjust the conditions and equipment in the area of condensation to obtain the desired division of H2S, between liquid and non-condensable gas, as illustrated, for example, through the separation described in the patent of E. U.A. 4,468,929. According to the invention, the division of the H2S to or as a non-condensable stream will be greater than 50%, that is, the volume of the H2S in the vapor, preferably from 75% to 95%, by weight. This provides a non-condensable gas stream for the removal of H2S, which corresponds to that described in relation to the first mentioned modality. As stated, supra, the gas or non-condensable stream of the condensation zone is separated or divided into first and second streams, which are treated separately. Generally, the non-condensable stream will be separated so that 50 to 95% by volume, preferably 60 to 90% by volume, of the stream, goes to the thermal oxidation zone, the rest goes to the oxidation zone liquid chelator of watery iron. The various embodiments of the invention wherein the contaminating H2S derivatives, produced in the oxidation step or steps, are used for the production of safely disposed material, it is important that the volume of the H2S sent to the thermal oxidation step be separated. properly. Thus, in the first mentioned embodiment of the invention, if a complete elimination of the sulfur produced in the oxidation step of aqueous ferric chelator is desired, the volume separated from the thermal oxidation step must be greater than 50% by volume of the H2S in the stream to the aqueous liquid oxidation zone. In the case where the removal of sulfur in the steam condensate is desired, the volume separated from the thermal oxidation must be greater than 50% of the total volume of the H2S in the treated steam.

The specific details of the thermal oxidation step and the oxidation method of the aqueous iron chelator, used with respect to the second portion, are not, per se, part of the invention. Whenever the procedures achieve, in the first case, the substantially complete conversion of H2S to produce SO2, and, in the second case, a ventilation gas or substantially pure product and solid sulfur that can be removed from the solution, it can be employ any suitable procedure of these types. The liquid oxidation process of aqueous iron chelator is understood to be a cyclic process carried out in a liquid aqueous oxidation zone, said zone including the provision for the generation of the ferrous chelator, with the appropriate removal of sulfur formed from a suitable site in the aqueous liquid oxidation zone. For example, the procedures employed in the U.S.A. patent may be used. 4, 830, 838 and the patent of E.U.A. 4,774,071. The general reaction for thermal oxidation can be shown as follows: 2H2S + 3O2 > 2SO 2 + 2H 2 O Merely by way of example, the temperatures in the thermal reaction zone may vary from 648 ° C to 1093 ° C, preferably from 760 ° C to 1093 ° C. In the condensation zone and in the aqueous liquid oxidation zone, the reactions for the conversion of H2S by the ferric chelator and the regeneration of the chelator can be summarized as follows: 2Fe + 3quelator + H2S > 2Fe + 2quelator + S ° + 2H + water and 2Fe + 2quelator + 2H ++ 1/2 O2 > 2Fe + 3quelator + H2O Any suitable iron chelator system can be used. Preferred iron chelators are coordination complexes where the iron forms chelators by reaction with an aminocarboxylic acid, an aminocarboxylic acid, a polyamino carboxylic acid or a polyamino polycarboxylic acid. A preferred class of coordination complexes is one in which the iron forms a chelator with an acid having the formula: (A) 3.n-N »Bn wherein n is two or three, A is a lower alkyl or hydroxyalkyl group; and B is a lower alkylcarboxylic acid group. A second class of preferred acids used to form the iron chelators employed are acids having the formula: X X V / N-R-N / X X where from two to four of the X groups are selected from lower alkylcarboxylic acid groups, from zero to two of the X groups is selected from the group consisting of lower alkyl groups, lower hydroxyalkyl groups, and, Y / -CH2-CH2- N \ Y wherein Y is selected from lower alkylcarboxylic acid groups, and R is a divalent organic group containing from 2 to 8 carbon atoms, preferably from 2 to 6 carbon atoms. Representative divalent organic groups include ethylene, propylene or isopropylene, or, alternatively, cyclohexane or benzene, wherein the two hydrogen atoms replaced by nitrogen are in the 1, 2 position. Iron chelators are present in the solution as solubilized species, for example, solubilized ammonium or alkali metal salts (or mixtures thereof) of the iron chelators. Accordingly, as used herein, the term "chelator" is meant herein to include mixtures of the aforementioned chelators, and references to "iron chelator" or "Fe +++ chelator", etc. , in solution indicate dissolved iron chelators, either as a salt or salts of the cation or cations mentioned above, or in some other form, where the chelator or iron chelators exist in solution. Iron chelators useful in the invention are easily formed in aqueous solution by reacting an appropriate salt, oxide, or hydroxide of iron and the aminocarboxylic acid present in the acid form or as an alkali or ammonium salt thereof.

Examples of aminocarboxylic acids include, (1) aminoacetic acids derived from ammonia or 2-hydroxyalkylamines, such as glycine, diglycine; 2-hydroxyalkyl glycine, hydroxyalkyl glycine, and (2) nitrilotriacetic acid; and (3) aminoacetic acids derived from ethylenediamine, diethylenetriamine, 1,2-propylenediamine, and 1,3-propylenediamine, such as ethylenediaminetetraacetic acid, 2-hydroxyethylethylaminetriacetic acid, diethylenetriaminepentaacetic acid; and (4) aminoacetic acids derived from cyclic 1,2-diamines, such as 1,2-diaminocyclohexane N, N-tetraacetic acid, and 1,2-phenylenediamine-N acid. N-tetracetic. Iron chelators of 2-hydroxyethyl ethylenediaminetriacetic acid and nitrilotriacetic acid are preferred. The ferrous chelating solutions will be supplied respectively to the condensation zone and the aqueous liquid oxidation zone in effective amounts, ie, at least a sufficient amount of each, on a stoichiometric basis, to convert the H2S removed or present in the treated stream. The conditions, proportions and parameters suitable for the removal of iron chelator of H2S are described very well in the literature of patents, especially the patent of E. U.A. 4,705,676, and, per se, do not form part of the present invention. An important advantage of the distribution of the stream containing H2S to a liquid oxidation zone of iron chelator, is the reduction of the volume or amount of the SO2 formed, and, consequently, the volume of the non-recoverable alkaline solution required for the conversion of SO2. As used herein, the term "alkaline solution" is understood to refer to an aqueous solution of an ammonium or alkali metal hydroxide or hydroxides, and mixtures thereof, and said solutions will preferably contain from 1% to 50%. % by weight of the hydroxide or dissolved hydroxides, most preferably from 10% to 25% by weight. According to the invention, the alkaline solution is supplied with the alkali metal or ammonium in an equivalent or stoichiometric excess with respect to SO2 in the gas of the thermal oxidation zone. The conditions can be regulated to convert SO2 to bisulfite according to the general reaction: 2 MeOH + 2 S02 > 2 MeHSO3 wherein Me is an alkali metal or ammonium. With stoichiometric excess, sulfite is also formed, according to the reaction: 2 MeOH + 2 SOz > 2 MeHS03 + H20 where Me is also an alkali metal or ammonium. A greater excess provides almost, if not all, sulfite. A relatively dilute solution of alkali metal or ammonium bisulfite and / or sulphite is produced, which is easily used or distributed. However, as noted above, in one of the unique and preferred aspects of the invention, the solution containing bisulfite and / or sulfite ions is removed from the contact or purification zone of S02 and combined or mixed with the sulfur removed from the liquid oxidation zone of an aqueous iron chelator. This combination can be carried out suitably at prevailing temperatures and pressures, for example, 21 ° C to 71 ° C, and atmospheric pressure to 5 atmospheres or more. The pH in the combined mixture is maintained at a suitable scale, for example, from 4.5 to 10, by the addition of an alkaline solution, if necessary, the sulfur will be converted to the thiosulfate ion, as follows: S ° + HSO 3 - > S2O3 2 + H + The resulting solution will be a solution containing thiosulfate which still contains bisulfite and / or sulfite. If this solution is then combined, in the mentioned modes, with the sulfur-containing condensate from the H2S-condensation removal zone, under similar conditions, that is, from 21 ° C to 71 ° C, and from atmospheric pressure to 5 ° C. atmospheres, the resulting additional reaction will substantially reduce or totally eliminate the sulfur derivative from the system. In addition, as discussed above, the solution can also provide a source of chelated iron for the reaction of the condensation zone. The following illustrations are given to understand more the reaction. All values are calculated or are illustrative. Accordingly, in Figure 1, a gas containing H2S, for example a vent gas rich in sulfur containing 1% H2S and 99% or more other non-condensable gases, both percentages are by weight, in line 1 it is shown divided into A, so that a volume of gas comprising 60% by weight of the H2S in the gas goes via line 2 to the thermal oxidizer 3, while the rest is sent through line 4. In the thermal oxidant 3, the H2S is oxidized with air at, for example, 871 ° C, as previously described, to produce on line 5 a gas stream comprising SO2 and leaving non-condensable gases. The SO-containing stream is contacted or purified in zone 6, which comprises, for example, a conventional scrubber, with a stoichiometric excess (1.5 to 1) of 25% by weight of the NaOH solution aqueous supplied via line 7. As further described in the patent of E. U.A. 4,834,959, the depuration produces, under suitable conditions, a diluted solution containing mainly bisulfite ions and sulfite ions, the solution being removed from zone 6 via line 8. The remaining non-condensable gases exit through line 9. Concurrently, the stream containing H2S in line 4, enters the aqueous liquid oxidation zone 10, where it is contacted with a stoichiometric excess of an aqueous solution containing 0.8 M of ferric chelating agent of sodium of ethylenediamine triacetate chelator of N- (2-hydroxyethyl). As indicated, other preferred ferric chelator solutions, of chelator-like concentrations, such as those containing a sodium or ammonium nitriloacetate chelator or a sodium ethylenediaminetetraacetate chelator can be used. The H2S becomes a form known to those skilled in the art, as illustrated in the aforementioned patents. A purified ventilation stream of remaining non-condensable gases is removed via line 1 1, and the sulfur is shown to be removed from the aqueous liquid oxidation zone on line 12. Provision is made for the generation and recirculation of the iron chelator solubilized in the system or zone (not shown). The dilution liquid diluted in line 8, containing the bisulfite and sulfite ions, is sent to the zone or mixing tank 13, which is maintained at atmospheric pressure, the pressure in the tank stabilizing on a scale of 21 ° C at 87.7 ° C. The sulfur in line 12 is combined or mixed in the zone or tank 13 with the diluted bisulfite / sulfite solution. As discussed above, the sulfur that comes from 12 contains some iron chelator residue. In tank 13, the sulfur reacts with bisulfite / sulfite ions to form thiosulfate, effectively solubilizing all of the sulfur in zone 10. The alkaline solution can be provided through line 14 to maintain an appropriate pH, which generally must to be maintained between 4.5 and 10. By doing this, the separate distribution of the sulfur in the oxidation zone of the aqueous iron chelator is avoided. The values of the iron chelator residue are recovered in the mixing solution, and if desired, the mixing solution with the thiosulfate can be returned to the aqueous liquid oxidation zone through line 15, or it can be used or distributed in another form (line 16). In Figure 2, a vapor containing H2S, for example, a geothermal vapor containing 1% H2S and 9% and more other non-condensable gases, both percentages by weight, leaves a turbine via line 21 to a direct contact condensation zone or condenser 22. The capacitor 22 may comprise a large, single spray tower, or may comprise multiple zones of condensation, as described, for example, in the U.S.A. 4,468, 929. From line 23, cooling water or a solution containing ferric chelating agent of N- (2-hydroxyethyl) ethylenediaminetriacetate chelator, at a concentration of 1% by weight and at a pH of 8, is sprayed in the condenser 22 to condense the vapor and convert the H2S in or from the vapor to sulfur. Concurrently, the iron chelator is converted, through the conversion reaction of H S, to the ferrous chelator. Approximately 95% by weight of the H2S in the vapor, together with other non-condensable gases, such as N, CO, and O, is removed from the condensation zone 22 in line 24. An aqueous or liquid solution, comprising a mixture of condensate, ferric and ferrous chelator of the aforementioned acid, dissolved residual HS, and sulfur, is removed through line 25, and sent to cooling tower 26. To avoid any development of sulfur in the system, the Sulfur can be removed from the liquid before or after the cooling tower, preferably before the tower, providing a settling deposit arrangement as indicated in 25a. In the cooling tower 26, oxygen (as air) is blown through the solution to oxidize the ferrous chelator to ferric chelator, the spent air coming out at 27. In order to prevent the release of any unreacted H2S, dissolved , in the liquid sent to tower 26, an amount of ferric chelator is added to the circulation solution at 28, to maintain a concentration of ferric chelator in the solution, which is greater than that required to convert the H2S removed in the solution. Zone 22. In this way, any remaining dissolved H2S is effectively oxidized before the condensate / chelator solution enters the top of the cooling water 26. The air flow and the contact time between the air and the solution in tower 26, is sufficiently long that the ferrous chelator, which results from the oxidation of hydrogen sulfide, is oxidized to the active ferric state as it passes below the t cooling pad 26. Line 23 provides for the return of the solution to the condensation zone 22, while the outlet line 29 is provided for the blowing of the solution, for example, to an injection well. The amount of fresh chelator solution, added at 28, is further regulated or increased to compensate for any loss of iron chelator at 29. The volume of H2S and other non-condensable gases on the line 24, it is divided, so that a gas volume, comprising 60% of the H2S in the geothermal vapor, travels via the line 30 to the thermal oxidant 31, while the rest is sent through the line 32. In the thermal oxidant 31, the H2S is oxidized with air at, for example, 871 ° C, as previously described, to produce on line 33 a gas stream comprising SO2 and remaining non-condensable gases. The stream containing SO2 is contacted or purified in zone 34, which comprises, for example, a conventional scrubber, with a stoichiometric excess of * 25% by weight of the aqueous NaOH solution supplied via line 35. As described in the patent of E. U.A. 4,834,959, the depuration produces, under suitable conditions, a diluted solution containing mainly bisulfite ions and sulfite ions, the solution being removed from zone 34 via line 36. This diluted stream of bisulfite and sulfite is easily discarded, if If desired, the remaining non-condensable gases exit through line 37. Similar to the previous example, the stream containing H2S on line 32 enters contact zone 38, where it is contacted with a stoichiometric excess of a solution aqueous containing 0.8 M of sodium ferric chelating agent of N- (2-hydroxyethyl) ethylenediaminetriacetate chelator. As indicated, other preferred ferric chelator solutions of similar chelator concentrations can be used, such as those containing sodium or ammonium nitrilotriacetate chelator or sodium ethylenediamine tetraacetate chelator. The H2S is converted into a form known to those skilled in the art, and a purified exhaust stream of remaining non-condensable gases is removed through line 39, the sulfur being removed at 40. Provision is made for generation and recirculation of the iron chelator solubilized in the system (not shown). With respect to Figure 3, the numbers used in it, which are identical to those used in Figure 2, correspond to the same equipment or to an analogous equipment. In this way, elements 21 to 24, 26 to 35, and 37 to 39 of Figure 3, correspond to the same aspects of Figure 2. However, the only integration of components and process streams shown in Figure 3 provides advantages and important results. More particularly, similar to the procedure of Figure 1, the dilution liquid diluted in line 41, containing the bisulfite ion (and part of the sulfite ion) is sent to the mixing zone or tank 42, which is maintained at atmospheric pressure, the temperature in the tank stabilizing on a scale of 21 ° C to 71 ° C. Concurrently, the sulfur is removed from the liquid oxidation zone 38 of the aqueous iron chelator through line 43. Then, the sulfur is combined or mixed in the zone or tank 42 with the diluted bisulfite / sulfite solution. As discussed above, the sulfur of 38 contains some of the iron chelator residue. In tank 42, sulfur reacts with bisulfite and sulfite to form thiosulfate, effectively solubilizing all of the sulfur in zone 38. The alkaline solution can be supplied through line 44 to maintain an appropriate pH, which generally must to be maintained between 4.5 and 10. By doing this, waste separated from the sulfur in the oxidation zone of the aqueous iron chelator is avoided, and the iron chelator residue values are recovered in the mixing solution. In addition according to the invention, the mixture solution containing in excess bisulfite, sulfite, and thiosulfate, is removed from tank 42 via line 45. This stream combines, as shown, with liquid on line 46, which it comprises a condensate-reagent mixture containing sulfur removed from the condenser 2. The line 46 may or may not comprise a container (not shown) with the function of the element 25a. Sulfur and hydrosulfide in the condensate-reagent mixture are converted through an excess of bisulfite and sulfite at line 45 to form thiosulfate. If a stoichiometric excess of bisulfite / sulfite is present (allowed by the proper division of H2S to the thermal oxidant), all the sulfur produced in the wet oxidation processes can be converted. The combined liquid is sent via line 47 to the cooling tower 26, where it can be treated, in the manner described above with respect to that of line 25. As noted above, the iron chelator values remaining in the Sulfur from zone 38, are recovered and can be used in the reactive liquid of the condenser, so that the requirements of the Fe * 3 chelator can be reduced or eliminated towards the condenser-reactant liquid in line 3. Optionally, if maintains a closed stoichiometric control, the alkaline solution in line 16 can be divided or separated (not shown) between 42 and 46.

As will be understood by those skilled in the art, the solutions or mixtures employed may contain other materials or additives for given purposes. For example, the patent of E. U.A. 3,933, 993 discloses the use of pH regulating agents, such as phosphate and carbonate pH regulators. Similarly, the patent of E.U.A. No. 4,009,251 describes various additives, such as sodium oxalate, sodium formate, sodium thiosulfate and sodium acetate, which are beneficial, and other additives, such as anti-foaming agents and / or wetting agents, can be used.

Claims

1 .- A process comprising a condensation vapor containing a lower amount of HS and other non-condensable gases in a condensation zone with an aqueous solution containing a ferric chelator under conditions to convert H2S to sulfur, and ferric chelator to chelator ferrous, leaving a stream of non-condensable gas containing the volume of H2S in the vapor; dividing or separating said non-condensable gas stream to a first stream containing H2S containing the volume of H2S in said gas stream, and a second stream containing H2S containing a minor portion of H2S in the non-condensable gas stream; oxidizing the H2S in the first stream containing H2S in a thermal oxidation zone to produce a gaseous stream comprising SO2, and removing the SO2 from the gas stream by contacting said gas stream with an alkaline solution; concurrently contacting the second stream containing H2S with an aqueous solution of ferric chelator in an aqueous liquid oxidation zone under conditions to convert H2S in said second stream containing H2S to sulfur in the solution, producing a stream of purified waste gas, and removing sulfur from the aqueous liquid oxidation zone.

2. A process comprising a condensation vapor containing a minor amount of H2S and other non-condensable gases in a condensation zone, producing a condensate and a non-condensable gas stream containing the volume of H2S in the vapor, and contacting the condensate with an aqueous solution containing a ferric chelator under conditions to convert H2S to sulfur, and an iron chelator to a ferrous chelator; dividing or separating the non-condensable gas stream to a first stream containing H2S containing the volume of H2S in the gas stream, and a second stream containing H2S containing a minor portion of the H2S in the non-condensable gas stream; oxidizing the H2S in the first stream containing H2S in a thermal oxidation zone to produce a gaseous stream comprising SO2, and removing the SO2 from the gas stream by contacting said gas stream with an alkaline solution; concurrently contacting the second stream containing H2S with an aqueous solution of ferric chelator in an aqueous liquid solution under conditions to convert H2S in said second stream containing H2S to sulfur in the solution, produce a stream of purified waste gas, and remove the sulfur in the aqueous liquid oxidation zone.

3. The process according to claim 1 or 2, wherein the SO2 is removed by purification in a purification zone with an alkaline solution under conditions to produce a solution of purification zone containing bisulfite and / or sulfite ions. , and the solution of the purification zone is combined with the sulfur of the aqueous liquid oxidation zone in a mixing zone under conditions to convert the sulfur and to produce a solution containing a thiosulfate ion and residual bisulfite ions and / or sulfite.

4. The process according to claim 3, wherein the aqueous iron chelator solution containing ferrous chelator and sulfur is removed from the condensation zone and combined with the solution containing thiosulfate and residual bisulfite ions and / or sulfite from the mixing zone.

5. The method of claim 4, wherein the H2S content of the first stream containing H2S is greater than the total amount of H2S removed in the condensation zone and of the second stream containing H2S.

6. The process according to any of claims 1-5, wherein the ferric chelator is the chelator of an organic acid having the formula: (A) 3. "- N - Bn where n is two or three, A is a lower alkyl or hydroxyalkyl group; and B is a lower alkylcarboxylic acid group; or an organic acid having the formula: XX \ / NRN / \ XX where from two to four of the X groups are selected from lower alkylcarboxylic acid groups, from zero to two of the X groups is selected from the group consisting of lower alkyl groups, lower hydroxyalkyl groups, and, Y / -CH2-CH2-N \ Y wherein Y is selected from lower alkylcarboxylic acid groups, and R is a divalent organic group containing from 2 to 8 carbon atoms.

7. The process according to claim 6, wherein the ferric chelator is selected from the ferric chelating agents of 2-hydroxyethyl ethylenediaminetriacetic acid, nitrilotriacetic acid, and ethylenediamine tetraacetic acid.