Process for continuously treating hydrogen sulfide-containing gas and sulfur regeneration equipment

Abstract

The process for continuously treating a hydrogen sulfide-containing gas includes the steps of: (a) contacting the hydrogen sulfide-containing gas with an aqueous alkaline liquid containing sulfide-oxidizing bacteria and elemental sulfur particles, thereby producing a loaded aqueous liquid containing dissolved sulfides, polysulfide compounds, sulfide-oxidizing bacteria and elemental sulfur particles, and a gas having a lower content of hydrogen sulfide, and passing the loaded aqueous liquid through a polysulfide reactor zone comprising one or more plug flow reactor zones; (b) contacting the loaded aqueous liquid with an oxidizing agent to enable the sulfide-oxidizing bacteria to oxidize sulfides to elemental sulfur, thereby producing a concentrated aqueous liquid containing an increased amount of elemental sulfur particles; and (c) separating the elemental sulfur particles from the concentrated aqueous liquid, wherein the residence time between the preparation of the loaded aqueous liquid in step (a) and its feeding to step (b) is between 3 and 45 minutes, and the content of elemental sulfur as part of polysulfide compounds in the loaded aqueous liquid fed to step (b) is between 3 and 45 minutes. 0 exceeds 0.7 mM.

Description

[Technical field]

[0001] The present invention relates to a process for continuously treating a hydrogen sulfide-containing gas, the process comprising the steps of: (a) contacting the hydrogen sulfide-containing gas with an aqueous alkaline liquid further comprising sulfide-oxidizing bacteria and elemental sulfur particles, thereby producing a loaded aqueous liquid; (b) contacting the loaded aqueous liquid with an oxidizing agent, wherein the sulfides are oxidized to elemental sulfur by the sulfide-oxidizing bacteria, thereby producing a concentrated aqueous liquid comprising an increased amount of elemental sulfur particles; and (c) separating the elemental sulfur particles from the concentrated aqueous liquid. The present invention also relates to a sulfur regeneration process facility. [Background technology]

[0002] Such a biological desulfurization process is described in WO 92 / 10270. The process as described therein has already been applied in more than 250 commercial installations worldwide. However, separation of sulfur particles remains a challenge; the proportion of sulfur particles is often too small for liquid-solid separation by conventional separation techniques.

[0003] Sulfur is the 10th most abundant element in the universe and plays a key role in Earth's ecosystems through the (bio)chemical sulfur cycle, which converts the atmosphere from its most reduced state (-2), hydrogen sulfide (H2S), to its most oxidized state (+6), sulfate (SO4 2-), elemental sulfur (S with oxidation state 0) can be recovered from hydrogen sulfide-containing gas using the process described in WO 92 / 10270. The main advantage of this process compared to chemical and physical alternatives is that it operates without toxic chemicals at ambient pressure and temperature. In the process of WO 92 / 10270, H2S is absorbed into a moderately alkaline solution where it reacts to soluble bisulfides and is subsequently oxidized to elemental sulfur by a mixed culture of sulfide-oxidizing bacteria. Elemental sulfur exists primarily in the form of orthorhombic α-S8. Following the formation of elemental sulfur, oxidation by-products such as sulfate and thiosulfate are formed upon excessive exposure to dissolved oxygen, sulfate being formed biologically and thiosulfate being formed abiotically. These compounds are undesirable as they result in acidification and thus the addition of chemicals is required to neutralize the process solution.

[0004] Although the above biological desulfurization processes have been intensively studied, sulfur settleability remains a major challenge. Sulfur has been shown to settle poorly, and the settleability of sulfur produced in commercial processes varies over time. Poorly settleable sulfur can accumulate in the system and interfere with process operation. Sulfur accumulation can cause problems such as clogged pumps and pipes, and at high concentrations can also cause foaming. Furthermore, small sulfur particles have a large relative surface area, making them prone to side reactions such as oxidation. Summary of the Invention [Problem to be solved by the invention]

[0005] The object of the present invention is to provide a process and a sulfur regeneration installation which does not have the aforementioned problems of low and variable sulfur deposition. [Means for solving the problem]

[0006] This is provided by the following process: A process for continuously treating a hydrogen sulfide-containing gas, comprising: (a) contacting a hydrogen sulfide-containing gas with an aqueous alkaline liquid further comprising sulfide-oxidizing bacteria and elemental sulfur particles, thereby producing a loaded aqueous liquid comprising dissolved sulfides, polysulfide compounds, sulfide-oxidizing bacteria and elemental sulfur particles, and a gas having a lower content of hydrogen sulfide, and passing the loaded aqueous liquid through a polysulfide reactor zone comprising one or more plug flow reactor zones; (b) contacting the loaded aqueous liquid with an oxidizing agent to enable the sulfide-oxidizing bacteria to oxidize sulfide to elemental sulfur, thereby producing a concentrated aqueous liquid containing an increased amount of elemental sulfur particles; (c) separating the elemental sulfur particles from the concentrated aqueous liquid; Including, The residence time of the loaded aqueous liquid between its preparation in step (a) and its feeding to step (b) is 3 to 45 minutes, and the content of elemental sulfur as part of polysulfide compounds in the loaded aqueous liquid fed to step (b) [S x 2- Medium S 0 ] is greater than 0.7 mM, a process. [Brief description of the drawings]

[0007] [Figure 1] An example will be given. [Diagram 2] Typical particle size distributions (PSDs) of sulfur particulate samples taken from the microaerobic reactor during the experiment are shown. [Diagram 3] 1 illustrates the effect of the polysulfide reactor zone on agglomerate formation. [Figure 4] An example will be given. [Diagram 5] 1 shows a sulfur regeneration process installation in which the process according to the invention can be carried out. [Figure 6] 6 shows a sulfur regeneration process installation similar to that shown in FIG. [Figure 7]FIG. 1 shows a sulfur regeneration process installation (1a) including a first absorption column (35) with an inlet (36) for a hydrogen sulfide-containing gas (4), an outlet (37) at its upper end (39) for an intermediate gas (38) having a lower content of hydrogen sulfide, an inlet (40) for a portion (8c) of an aqueous alkaline liquid (8) further comprising sulfide-oxidizing bacteria, and an outlet (41) for a first intermediate-loaded aqueous liquid at a lower height. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The applicants have found that the implementation of the claimed process significantly improves the settling of elemental sulfur. The results show that although the agglomeration of sulfur particles is promoted, the presence of very small single particles is low compared to the prior art process conditions. It is surprising that a high content of polysulfide compounds in the loaded aqueous liquid is beneficial, since polysulfide formation in the bioreactor of step (b) is considered undesirable and is an indication of poor operating conditions. Furthermore, polysulfides are known to be more sensitive to peroxidation than sulfides, reducing the efficiency of elemental sulfur formation / regeneration of the undesirable caustic. The applicants believe that the improvement in the retention of elemental sulfur is due to the fact that, prior to carrying out steps (a) and (b), very small sulfur particles are removed as a result of the presence of polysulfides. It is believed that due to polysulfide formation, the remaining smallest particles in the liquid have a higher tendency to agglomerate, improving the retention of elemental sulfur.

[0009] Without wishing to be bound by the following theory, applicants believe that the improved retention of elemental sulfur may be explained by the following equilibrium between polysulfides and S8 rings: HS - +(x-1) / 8S8<->S x 2- +H + (1).

[0010] Polysulfide content [S x2- When the saturation ratio of the dissolved S8 rings is high, the formation of dissolved S8 rings is also promoted, resulting in so-called supersaturation of the dissolved S8 rings, which then form the desired aggregates under so-called polysulfide conditions. These polysulfide conditions are described by the following equation (2): [S x 2- Medium S 0 ]≧1.7*[HS - ]*10 (-9.17+pH) (2) In the formula, [S x 2- Medium S 0 ] is the amount of polysulfide compounds [S x 2- ] and the content of elemental sulfur as a fraction of [S x 2- Medium S 0 ] is the content of elemental sulfur as part of polysulfide compounds in the loading aqueous liquid fed to step (b), expressed in mM S, [HS - ] is the sulfide concentration, expressed in mM, of the loaded aqueous liquid provided in step (b) and pH is the pH of the loaded aqueous liquid provided in step (b).

[0011] Even more preferably, the polysulfide conditions are represented by the following formula (3): [S x 2- Medium S 0 ]≧2.8*[HS - ]*10 (-9.17+pH) (3).

[0012] Typically, [S x 2- Medium S 0 ]≦6.0*[HS - ]*10 (-9.17+pH) (4)

[0013] The content of elemental sulfur as part of polysulfide compounds in the loaded aqueous liquid fed to step (b) [S x 2- Medium S 0] is greater than 0.7 mM, preferably greater than 1 mM, and even more preferably greater than 1.5 mM.

[0014] The content of elemental sulfur as part of polysulfide compounds in the loaded aqueous liquid [S x 2- Medium S 0 ] is the polysulfide content [S x 2- ] and depends on the average chain length x according to the formula: [S x 2- Medium S 0 ]=(x-1)*[S x 2- ] (3).

[0015] For example, the following expression SSSS 2 - According to x=4, [S x 2- ] concentration, the content of elemental sulfur as part of the polysulfide compound [S x 2- Medium S 0 ]teeth, (4-1) x 1.5 mM = 4.5 mM It is.

[0016] Polysulfides are formed by the reaction of bisulfides with elemental sulfur. Polysulfides themselves may also react with elemental sulfur. Due to the high surface-to-volume ratio of very small elemental sulfur particles, these particles are thought to be selectively consumed. This chemical reaction apparently also occurs in prior art processes. In prior art processes, however, the concentration of polysulfides does not reach the levels achieved in the present process, which result in improved sulfur precipitation. For this reason, the process according to the invention is carried out over a period of at least one week, measuring the daily average content of elemental sulfur as part of polysulfide compounds in the loaded aqueous liquid fed to step (b) [S x 2- Medium S 0

[0036] is greater than 0.7 mM, preferably greater than 1 mM, even more preferably greater than 1.5 mM. More preferably, the process according to the invention is operated under polysulfide conditions as represented by equation (2) above for a period of at least 1 week.

[0017] The hydrogen sulfide-containing gas can be any gas containing such compounds. The hydrogen sulfide-containing gas can also contain carbon dioxide, nitrogen, hydrogen, small amounts of oxygen, water vapor and gaseous hydrocarbons such as methane, ethane, propane and / or higher boiling point hydrocarbons as well as mercaptans and / or other sulfur compounds such as carbonyl sulfide. Such gases can be natural gas, such as biogas from anaerobic wastewater treatment units, refinery off-gas, synthesis gas, geothermal gas, landfill gas or acid gases obtained in amine gas treatment processes. The present invention is particularly suitable for gases having a carbon dioxide content of more than 20% by volume and a hydrogen sulfide content of 0.1-3% by volume. When such gases are treated by the prior art processes, sulfur settleability is a particular challenge. With hindsight, it is believed that the low content of sulfur as part of polysulfides at the resulting lower pH and lower bisulfide content causes poor fixation of elemental sulfur as also shown in Example B. When such gases are treated by the process of the present invention, improved settleability of elemental sulfur is observed.

[0018] In step (a), the hydrogen sulfide-containing gas is contacted with an aqueous alkaline liquid further comprising sulfide-oxidizing bacteria at a temperature preferably between 15 and 48°C, more preferably between 35 and 45°C. Such processes are also called absorption processes and are typically carried out in an absorption or contact column in which gas and liquid flow countercurrently. Suitably, step (a) is carried out in a vertical column, in which the hydrogen sulfide-containing gas is continuously fed to the column at a lower position in the column and the aqueous liquid comprising the sulfide-oxidizing bacteria is continuously fed to a higher position in the column, such that a substantially upwardly flowing gas stream is in contact with a substantially downwardly flowing aqueous stream. The column further comprises an outlet at its lower end for the loaded aqueous liquid and an outlet at its upper end for the treated gas.

[0019] The aqueous alkaline liquid may be any liquid alkaline absorbent known to be suitable for absorbing hydrogen sulfide. Examples of suitable liquid alkaline absorbents are carbonate, bicarbonate and / or phosphate solutions, more preferably the aqueous liquid is a buffer further comprising sodium carbonate and sodium bicarbonate or potassium carbonate and potassium bicarbonate or mixtures thereof. The pH of the liquid aqueous alkaline liquid is preferably in the range of 7 to 10, more preferably 7.5 to 9.5. It will be appreciated that down the column the pH of the absorbing liquid will decrease due to the absorption of hydrogen sulfide and carbon dioxide. The pH of the loaded aqueous liquid produced in step (a) is typically lower than the pH of the aqueous liquid fed to the absorption column. The pH of the loaded aqueous liquid produced in step (a) may be as low as 6.5, preferably in the range of 6.5 to 9.0.

[0020] The pressure in step (a) may be up to 100 bara, preferably between atmospheric pressure and 80 bara.

[0021] In step (a), the concentration of oxygen, in particular dissolved oxygen, is low. The concentration of molecular oxygen in the loaded aqueous liquid produced in step (a) is at most 10 μM, preferably at most 1 μM, more preferably at most 0.1 μM. To achieve these low oxygen contents, the oxygen content in the hydrogen sulfide-containing gas is suitably less than 3% by volume, preferably less than 1% by volume.

[0022] The sulfide oxidizing bacteria present in step (a) may be any sulfide oxidizing bacteria, preferably sulfide oxidizing bacteria of the genera Halothiobacillus, Thioalkalimicrobium, Thioalkalispira, Thioalkalibacter, Thioalkalivibrio, Alkalilimnicola and related bacteria. Such sulfide oxidizing bacteria present in step (a) may be provided by recycling the concentrated aqueous liquid from step (b) and / or by recycling the aqueous liquid obtained after removal of the elemental sulfur particles in step (c). It has been found that when such sulfide oxidizing bacteria are present in the aqueous alkaline liquid under the above conditions, a very effective absorption of hydrogen sulfide occurs. The content of sulfide oxidizing bacteria based on the nitrogen content in the aqueous alkaline liquid in step (a) is preferably more than 5 mg N / L and less than 1000 mg N / L, more preferably 25 to 200 mg N / L.

[0023] The loaded aqueous liquid produced in step (a) comprises dissolved bisulfides, elemental sulfur particles and sulfide-oxidizing bacteria. The combined concentration (expressed as sulfur) of bisulfides, polysulfide compounds, sulfur in the sulfide-oxidizing bacteria and elemental sulfur in the loaded aqueous liquid produced in step (a) may be up to 20 grams per liter. Preferably, this combined concentration in the loaded aqueous liquid is in the range of 100 mg / L to 15 g / L, more preferably 150 mg / L to 10 g / L. The aqueous liquid may comprise trace compounds such as iron, copper or zinc as nutrients for the sulfide-oxidizing bacteria.

[0024] The elemental sulfur particles in the aqueous alkaline liquid of step (a) may suitably be provided by recycling at least a portion of the concentrated aqueous liquid of step (b) to step (a). In a particularly preferred embodiment, the majority of the aqueous alkaline liquid provided in step (a) consists of the recycled concentrated aqueous liquid from step (b). More preferably, at least 90% by volume of the alkaline liquid provided in step (a) consists of the recycled concentrated aqueous liquid from step (b).

[0025] In step (b), the loaded aqueous liquid of step (a) is contacted with an oxidizing agent, and the sulfides are oxidized to elemental sulfur by the sulfide-oxidizing bacteria. Preferably, the amount of oxidizing agent fed to the bioreactor capable of carrying out step (b) is at least about the stoichiometric amount required to oxidize the sulfides of steps (a) and / or (b) to elemental sulfur. In this way, the protons produced by the bacteria when forming elemental sulfur are consumed, thereby regenerating the bacteria. This step is therefore also called caustic regeneration. The regenerated sulfide-oxidizing bacteria thus obtained can then be reused in step (a). Any suitable oxidizing agent may be used, for example nitrates or molecular oxygen, preferably molecular oxygen. The oxidizing agent may be fed in any suitable manner, preferably by feeding a gas stream containing molecular oxygen to the bioreactor. The gas stream containing molecular oxygen may be any suitable gas, including oxygen, preferably air.

[0026] Preferably, the temperature in step (b) is in the range of 10 to 48° C., more preferably 35 to 45° C., and the pressure is in the range of 0 bara to 10 bara, more preferably atmospheric pressure to 5 bara, even more preferably atmospheric pressure.

[0027] The elemental sulfur particles in the concentrated aqueous liquid formed in step (b) are separated in step (c). Such separation may be performed after step (b) is completed and / or may be performed simultaneously with step (b). This separation of elemental sulfur may be performed by any means known in the art, such as, for example, settling or other means for solid-liquid separation. Preferably, elemental sulfur is recovered by taking a portion of the aqueous solution obtained in step (b) and separating elemental sulfur therefrom to obtain a sulfur-depleted effluent. A portion of the sulfur-depleted effluent may be recycled to step (b) and a portion of the sulfur-depleted effluent may be purged. Another portion of the aqueous solution obtained in step (b) may be used as the aqueous alkaline solution of step (a).

[0028] The content of elemental sulfur as part of polysulfide compounds in the loaded aqueous liquid [S x 2- Medium S 0 ] is measured according to the following method. First, the total concentration of polysulfides is measured spectrophotometrically at a wavelength of 285 nm, as described by Kleinjan, WE; De Keizer, A.; Janssen, AJH, Equilibrium of the reaction between dissolved sodium sulphide and biologically produced sulphur. Colloids and Surfaces B: Biointerfaces 2005, 43, (3-4), 228-237. Then, the average chain length is determined by thermodynamics, as described by Alexey Kamyshny, Jenny Gun, Dan Rizkov, Tamara Voitsekovski, and Ovadia Lev in Environ. Sci. Technol. 2007, 41, 7, 2395-2400. Here, the content of elemental sulfur as part of polysulfide compounds [S x 2- Medium S 0 ] can be calculated.

[0029] Required content of elemental sulfur as part of polysulfide compounds in the loaded aqueous liquid [S x 2- Medium S 0 ] or polysulfide conditions can be achieved in the process by influencing temperature, residence time and pH or a combination of these means. Higher sulfide concentration, higher temperature, longer residence time and higher pH favor the formation of polysulfides. Locally high contents of polysulfides and small elemental sulfur particles can also further result in a higher polysulfide content at a similar reaction time due to the autocatalytic effect. Thus, a person skilled in the art can select various means for achieving the process conditions of the present invention in order to carry out a process with good and stable sulfur precipitation.

[0030] One way of influencing the temperature is to increase the temperature of the aqueous alkaline liquid by indirect heat exchange with the loaded aqueous liquid and / or an external heat source, thereby obtaining the heated aqueous alkaline liquid used in step (a). The loaded aqueous liquid suitably has a higher temperature than the loaded aqueous liquid fed to step (a), for example just prior to being used in step (b). Suitably, the loaded aqueous liquid may have a temperature of 35-50° C. By using this relatively warm stream to increase the temperature of the aqueous alkaline liquid used in step (a), the required content of elemental sulfur as part of the polysulfide compounds in the loaded aqueous liquid or polysulfide conditions according to the invention [S x 2- Medium S 0 ] can be achieved.

[0031] In order to achieve a high content of elemental sulfur as part of polysulfide compounds in the loaded aqueous liquid fed to step (b), it is necessary to provide the loaded aqueous liquid with sufficient residence time. By increasing the residence time of the loaded aqueous liquid between its preparation in step (a) and its feeding to step (b), the amount of elemental sulfur [S x 2- Medium S0 This residence time is also called the sulfide retention time (SuRT). The residence time SuRT is preferably 3 to 45 minutes, more preferably 5 to 15 minutes.

[0032] The desired residence time is achieved by a process in which step (a) includes passing the loaded aqueous liquid stream through a polysulfide reactor zone, where polysulfide compounds are formed by reaction of dissolved sulfides with elemental sulfur particles. The polysulfide reactor zone includes one or more plug flow reactor zones. Backmixing is minimized in these plug flow reactor zones. The polysulfide reactor zones result in different polysulfide contents in different regions of the polysulfide reactor zone. This is beneficial because higher average polysulfide concentrations and higher polysulfide concentrations in the effluent of the polysulfide reactor zone are achieved as a result of the autocatalytic nature of the reaction. As used herein, the term "plug flow reactor zone" refers to a zone in a tube through which a fluid flows, where the velocity of the fluid is substantially constant across any cross section of the tube perpendicular to the axis of the tube, assuming no boundary layer adjacent the inner wall of the tube.

[0033] The polysulfide reactor zone may be, for example, a vertically or horizontally extending vessel having an interior in which liquid flows in a zigzag flow pattern through the vessel. Such a polysulfide reactor zone thus has an upstream region and a downstream region. Furthermore, the loaded aqueous liquid has a higher polysulfide content in the downstream region compared to the upstream region.

[0034] Required content of elemental sulfur as part of polysulfide compounds in the loaded aqueous liquid [S x 2- Medium S 0] or polysulfide conditions may be achieved in the polysulfide reactor zone by recycling a portion of the loaded aqueous liquid having a higher polysulfide content from a downstream region of the polysulfide reactor zone to an upstream region of the polysulfide reactor zone where the loaded aqueous liquid has a lower polysulfide content for the purpose of increasing the polysulfide content of the upstream region. It has been found that the presence of polysulfide compounds enhances the rate of formation of more polysulfide compounds. Thus, by such recycling, this autocatalytic effect is enhanced and the conditions of the invention are further achieved. Suitably, 5 to 50% by weight of the loaded aqueous liquid as discharged in the downstream region is recycled to the upstream region.

[0035] Preferably, the portion of the loaded aqueous liquid having a higher polysulfide content that is recycled is not immediately added, such as by conduit and pump, to an upstream region of the polysulfide reactor zone. By not immediately adding this portion, additional residence time for this portion is created, thereby allowing more polysulfides to form in this portion. By adding this polysulfide enriched portion to an upstream region of the polysulfide reactor zone, there is a greater autocatalytic effect. Suitably, the portion of the loaded aqueous liquid separated from the downstream region flows through a zone having a residence time of 5 to 45 minutes before it is recycled to the upstream region in the polysulfide reactor zone. Preferably, the residence time in this zone is 5 to 15 minutes.

[0036] Required content of elemental sulfur as part of polysulfide compounds in the loaded aqueous liquid [S x 2- Medium S 0] or polysulfide conditions may be achieved by feeding a portion of the aqueous alkaline liquid further comprising sulfide oxidizing bacteria directly to the polysulfide reactor zone. This portion thus bypasses the absorption, i.e. contacting portion of step (a) and is mixed directly with the loaded aqueous liquid in the polysulfide reactor zone. Preferably, a portion of the aqueous alkaline liquid is added to an upstream region of the polysulfide reactor zone. Suitably, 5-20 wt. % of the aqueous alkaline liquid is fed directly to the polysulfide reactor zone and the remaining portion is used to contact the hydrogen sulfide containing gas.

[0037] Increasing the polysulfide content of the portion of the loaded aqueous liquid which is recycled to the upstream region in the polysulfide reactor zone may also be achieved by increasing the temperature of this portion. Preferably, the portion of the loaded aqueous liquid having the higher polysulfide content is heated before being recycled to the upstream region of the polysulfide reactor zone. Preferably, the temperature is increased to 35-50°C.

[0038] As also described above, step (a) is preferably carried out in a vertical column, where hydrogen sulfide-containing gas is continuously fed to the column at a lower position in the column and aqueous liquid containing sulfide-oxidizing bacteria is continuously fed to a higher position in the column, such that a substantially upwardly flowing gas stream contacts a substantially downwardly flowing aqueous stream. Preferably, a portion of the aqueous liquid containing sulfide-oxidizing bacteria is continuously fed to a higher position in the column for contact with the ascending gas stream in a first contacting zone producing an intermediate load aqueous liquid. In the first contacting zone, the gas is polished to its required low level of hydrogen sulfide. A portion of the aqueous liquid containing sulfide-oxidizing bacteria is continuously fed to an intermediate position in the column to contact the intermediate load aqueous liquid, and the ascending gas stream is in a second contacting zone. In this second contacting zone, a portion of the aqueous liquid containing sulfide-oxidizing bacteria is contacted with fresh feed gas, together resulting in a higher polysulfide concentration in the load aqueous liquid. By mixing this loaded aqueous liquid with the intermediate loaded aqueous liquid, any small sulfur particles present in the intermediate loaded aqueous liquid are reacted and removed by the polysulfides. Preferably, 5-50% by weight of the total aqueous liquid containing the sulfide oxidizing bacteria is fed to this second contact zone. This embodiment may be carried out in a single absorption vessel.

[0039] In step (a), in another preferred embodiment, a portion of the aqueous liquid containing sulfide-oxidizing bacteria is continuously contacted with hydrogen sulfide-containing gas in step (a1) to obtain a first intermediate-loaded aqueous liquid and an intermediate gas having a lower intermediate content of hydrogen sulfide, and another portion of the aqueous liquid containing sulfide-oxidizing bacteria is continuously contacted with an intermediate gas having a lower intermediate content of hydrogen sulfide in step (a2) to obtain a second intermediate-loaded aqueous liquid and a gas having a lower content of hydrogen sulfide. Step (a2) can be considered as a polishing step in which the required low level of hydrogen sulfide is achieved. In step (a1), a portion of the aqueous liquid containing sulfide-oxidizing bacteria is contacted with fresh feed gas, resulting in a higher polysulfide concentration in the first intermediate-loaded aqueous liquid. By combining the first intermediate-loaded aqueous liquid with the second intermediate-loaded aqueous liquid, any small sulfur particles present in the second intermediate-loaded aqueous liquid are reacted out by the polysulfides. Preferably, 5-50 wt. % of the total aqueous liquid containing the sulfide-oxidizing bacteria is fed to step (a1). The first intermediate loaded aqueous liquid is combined with the second intermediate loaded aqueous liquid to obtain a loaded aqueous liquid. The residence time of the first and second intermediate loaded aqueous liquids between step (a) and step (b) is suitably 5-45 minutes, preferably 5-15 minutes.

[0040] Preferably, each of the first and second intermediate load aqueous liquids produced in steps (a1) and (a2) flows through separate first and second polysulfide reactor zones, respectively. In the polysulfide reactor zones, polysulfide compounds are formed by reaction of dissolved sulfides with elemental sulfur. Preferably, the polysulfide reactor zones include one or more plug flow reactor zones which avoid backmixing as described above. Preferably, a portion of the first intermediate load aqueous liquid rich in polysulfides is fed to the second polysulfide reactor zone to increase the polysulfide content in the second intermediate load aqueous liquid. When the polysulfide reactor zone has upstream and downstream regions, it is preferred to feed a portion of the first intermediate load aqueous liquid rich in polysulfides to the upstream region of the second polysulfide reactor zone to increase the polysulfide content in the second intermediate load aqueous liquid.

[0041] Steps (a1) and (a2) may be carried out in the same or preferably separate absorption columns, more preferably steps (a1) and (a2) are carried out in separate absorption columns, each including a lower end where the respective polysulfide reactor zone resides.

[0042] This process determines the content of elemental sulfur as part of polysulfide compounds in the loaded aqueous liquid [S x 2- Medium S 0 ] or by utilizing measurement and control in which the polysulphide conditions in the loaded aqueous liquid supplied to step (b) are measured and, if the measured content falls below a threshold value, the temperature and / or residence time are targeted to increase said content, as described above, by affecting recirculation.

[0043] The present invention will be described with reference to Figures 1 to 7. Figures 1 to 4 relate to an embodiment.

[0044] FIG. 5 shows a sulfur regeneration process installation in which the process according to the invention can be carried out. The invention also relates to this sulfur regeneration process installation. The sulfur regeneration process installation (1) comprises an absorption column (2) with an inlet (3) for a hydrogen sulfide-containing gas (4) and an outlet (5) at its upper end for a gas (6) with a lower content of hydrogen sulfide, an inlet (7) for an aqueous alkaline liquid (8) further comprising sulfide-oxidizing bacteria and a first outlet (9) at a lower height for a loaded aqueous liquid (10). Furthermore, a polysulfide reactor zone (11) is shown. This polysulfide reactor zone (11) is part of a separate vessel (12). Alternatively, the polysulfide reactor zone (11) can also be located at the lower end (2a) of the absorption column (2) or a combination of these two embodiments. The polysulfide reactor zone (11) comprises a plug flow reactor zone, said polysulfide reactor zone (11) comprising an upstream end (13) and a downstream end (14). The upstream end (13) of the polysulfide reactor zone (11) is fluidly connected to a first outlet (9) for the load aqueous liquid (10). The downstream end (14) of the polysulfide reactor zone (11) is provided with a second outlet (16) for the load aqueous liquid (17) and a recycle stream (18) for a portion of the load aqueous liquid to the upstream end (13) of the polysulfide reactor zone (11). This recycle stream (18) achieves that the content of elemental sulfur as part of polysulfides is increased in the load aqueous liquid as it is fed to the aerobically operated bioreactor (19). This content can be increased or decreased by increasing or decreasing the recycle fraction. The content of elemental sulfur as part of the polysulfides can also be increased by increasing the temperature of the recycle stream (18), increasing the temperature at the bottom end (2a) of the absorption column (2), increasing the temperature in the separate vessel (12), and / or increasing the time between separating a portion of the aqueous fraction loaded from the downstream region (14) and feeding this portion to the upstream region (13).

[0045] A second outlet (16) for the load aqueous liquid (17) is fluidly connected to an aerobically operated bioreactor (19) for carrying out step (c) of the process. The aerobically operated bioreactor (19) is fed with air (20) and discharges spent air (21). The aerobically operated bioreactor (19) is fluidly connected via a conduit (23) to an inlet (7) for the aqueous alkaline liquid (8) of the absorption column (2) and to an elemental sulfur recovery unit (22). Alternatively, the recovery unit (22) can be part of the bioreactor (19). The elemental sulfur recovery unit (22) is provided with an outlet (24) for elemental sulfur and an outlet (25) for a liquid effluent (26) lean in elemental sulfur. This liquid effluent is partially purged and partially returned to the aerobically operated bioreactor (19) as shown.

[0046] FIG. 6 shows a sulfur regeneration process installation similar to FIG. 5, with the following differences: instead of a separate vessel (12), the polysulfide reactor zone (11) is placed at the bottom (2b) of the absorption column (2) as a so-called sump (30). The sump (30) is a volume of loaded aqueous liquid (17) that is bounded at its upper end by a liquid level (31). This liquid level (31) can be at the same or different height as the liquid level (32) in the aerobically operated bioreactor (19) and the liquid level (33) in the elemental sulfur recovery unit (22), as shown. An inlet (3) for hydrogen sulfide-containing gas (4) is located above the liquid level (31) of the sump (30). The sump (30) as polysulfide reactor zone (11) comprises one or more plug flow reactor zones, said polysulfide reactor zones comprising an upstream end (13) and a downstream end. A portion of the loaded aqueous liquid (17) is recycled to the upstream region (13) of the sump (30) via recycle stream (18a). As shown, this portion may also be fed to the absorption column (2) at a location (34) above the liquid level (31) of the sump (30) as recycle stream (18a). This recycle stream (18a) may be combined with a portion (8b) of the aqueous alkaline liquid (8). Another portion (8a) of the aqueous alkaline liquid (8) is provided to an inlet (7) at the top of the column (2).

[0047] This recycle stream (18a) achieves that the content of elemental sulfur as part of polysulfides is increased in the load aqueous liquid (17) before it is fed to the aerobically operated bioreactor (19). This content can be increased or decreased by increasing or decreasing the fraction (18a) that is recycled. The content of elemental sulfur as part of polysulfides can also be increased by increasing the temperature of the recycle stream (18a), increasing the temperature in the sump (30), and / or increasing the time between separating a portion of the load aqueous fraction from the downstream region (14) and feeding this portion to the upstream region (13) or position (34).

[0048] 7 shows a sulfur regeneration process installation (1a) including a first absorption column (35) with an inlet (36) for the hydrogen sulfide-containing gas (4), an outlet (37) at its upper end (39) for an intermediate gas (38) having a lower content of hydrogen sulfide, an inlet (40) for a portion (8c) of the aqueous alkaline liquid (8) further comprising sulfide-oxidizing bacteria, and an outlet (41) for the first intermediate load aqueous liquid at a lower level. A second absorption column (55) is also shown with an inlet (56) for the intermediate gas (38) having a lower content of hydrogen sulfide, an outlet (57) at its upper end (58) for the gas (6) having a lower content of hydrogen sulfide, an inlet (59) for a portion (8a) of the aqueous alkaline liquid (8) further comprising sulfide-oxidizing bacteria, and an outlet (60) for the second intermediate load aqueous liquid at a lower level.

[0049] The polysulfide reactor zone (42) is part of the first absorption column (35) and is located at the lower end (43) of the first absorption column (35). The polysulfide reactor zone (62) is part of the second absorption column (55) and is located at the lower end (63) of the second absorption column (55). The polysulfide reactor zones (42, 62) include one or more plug flow reactor zones, the sulfide reactor zones (42, 62) including upstream ends (44, 64) and downstream ends (45, 65).

[0050] The upstream end (44) of the polysulfide reactor zone (42) of the first absorption column (35) is fluidly connected to the first intermediate loaded aqueous liquid outlet (41), and the upstream end (64) of the polysulfide reactor zone (62) of the second absorption column (55) is fluidly connected to the second intermediate loaded aqueous liquid outlet (60). The downstream end (45) of the polysulfide reactor zone (42) of the first absorption column (35) is fluidly connected to the upstream end (64) of the polysulfide reactor zone (62) of the second absorption column (55) via stream (66). In this way, a fraction containing a high content of polysulfides is added to the polysulfide reactor zone (62). The resulting loaded aqueous liquid (17) has the properties claimed. This loaded aqueous liquid (17) is fed to an aerobically operated bioreactor (19) for the oxidation of sulfides to elemental sulfur. To this end, the downstream end (65) of the polysulfide reactor zone (62) of the second absorption column (55) is fluidly connected to an aerobically operated bioreactor (19) for regeneration of the sulfide oxidizing bacteria.

[0051] A portion of the contents of the polysulfide reactor zone (42) of the first absorption column (35) may be fed directly to the bioreactor (19) (not shown). A portion (8b) of the aqueous alkaline liquid (8), further comprising sulfide oxidizing bacteria, is added to the first and second absorption columns (35, 55) to further promote the formation of polysulfides. The first absorption column may have a simple design, not necessarily equipped with contacting internals. The above step (a1) may be carried out in the first absorption column (35). The second absorption column (55) is suitably equipped with contacting internals to optimize gas-liquid contact to achieve optimal absorption of hydrogen sulfide. The above step (a2) may be carried out in the second absorption column (55).

[0052] The aerobically operated bioreactor (19) is fluidly connected to an inlet (59) for a portion (8a) of the aqueous alkaline liquid (8) of the second absorption column and to an inlet (40) for a portion (8c) of the aqueous alkaline liquid (8) of the first absorption column. An elemental sulfur recovery unit (22) is provided with an inlet fluidly connected to the aerobically operated bioreactor (19), an outlet (24) for elemental sulfur, and an outlet (25) for liquid effluent lean in elemental sulfur.

[0053] The polysulfide reactor zones (11, 2b, 42, 62) of Figures 5-7 may be provided with means for increasing the temperature of the liquid contents of the polysulfide reactor zones (11, 2a, 42, 62). This may be, for example, by indirect heat exchange in which a hot heat transfer medium flows through tubes to exit the polysulfide reactor zones (11, 2b, 42, 62), thereby heating the liquid contents of these zones.

[0054] The invention is illustrated by the following non-limiting experiments. EXAMPLES

[0055] Here, we report the effect of a novel sulfurization reactor inserted into a conventional process setup. The sulfurization reactor is defined as conditions where dissolved oxygen is less than 1 μM O2 and sulfide is greater than 0.5 mM. We analyzed the sulfur particles produced in continuous long-term laboratory-scale reactor runs under various sulfide concentrations and sulfide retention times. Analysis was performed using laser diffraction particle size analysis and optical microscopy.

[0056] Two identical lab-scale reactor setups were used with an absorber (A) with a liquid volume of 0.4 L and a microaerobic gas lift reactor (C) with a liquid volume of 3.7 L (as shown in Figure 1). Two additional reactor compartments can be added: a polysulfide reactor zone (B) with a liquid volume of 3.5 L between the absorber (A) and the microaerobic gas lift reactor (C) and a settler (D) with a liquid volume of 1.5 L after the microaerobic gas lift reactor.

[0057] A settler with the highest H2S loading rate was included in the experiment to prevent sulfur accumulation in the system, i.e. to avoid operational problems such as foaming and clogging due to sulfur accumulation. Experiments at lower H2S loading rates were performed without a settler, without removing particles with a settler, in order to collect samples in which all particles produced under the specific experimental conditions are present. The polysulfide reactor zone (B) is the zone with the retention time of the reactor contents (culture medium, microorganisms and sulfur particles) under anaerobic (poly)sulfide pressure. The presence of the polysulfide reactor zone (B) increases the retention time of sulfides (SuRT).

[0058] The experiments carried out under various conditions are numbered as Examples 1-3 and Comparative Experiment A. A summary of the operating conditions per experiment is given in Table 1. The gas stream was recirculated over the headspace of the microaerophilic gas lift reactor equipped with a vacuum pump to prevent the release of H2S gas and to reach low oxygen concentrations. Gas was introduced using porous stones at the bottom of the inner column of the microaerophilic gas lift reactor (C) to ensure proper oxygen transfer and mixing. Pure H2S gas and oxygen were supplied by mass flow controllers. In case of pressure increase, excess gas was vented through a water lock saturated with zinc acetate to capture any H2S potentially present. The reactor was operated at 35 °C using a thermostatic bath and a climate-controlled cabinet.

[0059] [Table 1]

[0060] The medium was 6.6 g L in demineralized water at pH 8.5. -1 Na2CO3 and 69.3 g L -1The buffer consisted of a 100 mL / L demineralized water solution containing NaHCO3. Fresh buffer was fed at a constant flow rate to maintain sufficient alkalinity in the system. In addition, for biological growth, the buffer consisted of (in g per L demineralized water): K2HPO4, 0.1; MgCl26H2O, 0.0203; NaCl, 0.6; CH4N2O, 0.06 and 2 mL L -1 The strains were supplied with a nutrient stock containing a trace element solution similar to that of Pfennig, N., Lippert, K.D., 1966. Über das Vitamin B12-bedurfnis phototropher Schwefelbacterien. Arch. Microbiol. 55, 245-256.

[0061] Comparative experiment A was inoculated with centrifuged microorganisms (to remove excess sulfur) from a laboratory-scale sulfur-producing gas-lift bioreactor operated under continuous conditions similar to those applied in these experiments. The original inoculum for this reactor was obtained from the applicant's well-characterized industrial-scale Thiopaq process. To remove sulfur, the reactor contents were centrifuged at 4500 RPM for 20 minutes (using FirLabO, Froilabo, Paris, France). A pellet was formed with two layers: a bottom layer of elemental sulfur and a pellet with microorganisms on top. The pellet containing the microorganisms was carefully washed away. Example 3 was inoculated with centrifuged microorganisms taken directly from the Thiopaq process described above. Experiments 1 and 2 were inoculated with the microorganism-rich process solution from Comparative experiment A and Example 3.

[0062] The reactors (B, C) were filled with media and inoculated. In all experiments, the setup was operated in continuous mode without interruption. Throughout all experiments, the H2S loading was kept constant for that experiment. The H2S loading was used to set the total sulfide concentration in the polysulfide reactor zone. To keep the sulfide to sulfur conversion efficiency high, the oxidation-reduction potential (ORP) was set at -360 mV vs. Ag / AgCl, a typical set point for industrial reactors. The ORP set point was controlled by a proportional-integral (PI) controller. The PI controller adjusted the oxygen feed rate. Samples (well-mixed reactor contents containing sulfur particles, medium and microorganisms) were taken for analysis at the central sampling port of the polysulfide reactor zone (B) (experiments 2 and 3) and the microaerobic gas lift reactor (C) (all experiments). The sampling tubes from the reactors were flushed three times before sampling to obtain representative samples.

[0063] The reactor was equipped with sensors for temperature and ORP (triple junction, platinum rod, glass electrode with internal Ag / AgCl reference electrode (ProSense, Oosterhout, The Netherlands)). Particle size distributions (PSD) are expressed both volumetrically and numerically. In a volumetric particle size distribution, larger particles have a heavier weight because due to their size they often constitute a larger percentage of the total solid volume. In a numerically based distribution, each particle has an equal weight, independent of particle size. According to common convention, if the PSD must be represented by a single value, the median of the PSD (D50) was reported to indicate the evolution of particle size over time. The median has a better way of representing the central location of the data in a non-normal distribution than the mean.

[0064] The process selectivity for elemental sulfur was calculated by mass balance based on the H2S feed and measurements of the dissolved sulfur products formed. - The term "HS" refers to the fact that most of the dissolved sulfide is present at pH 8.5. - Total dissolved sulfide (HS, HS - and S 2-)

[0065] In Experiment A and Examples 1, 2, and 3, sulfide was successfully converted to elemental sulfur and sulfur particles were present in the reactor solution. Typical particle size distributions (PSDs) of sulfur particle samples taken from the microaerobic reactor during these experiments are shown in Figure 2.

[0066] The sulfur particles formed under the various experimental conditions had distinctly different morphologies as observed by optical microscopy, as shown in Figure 3. The sulfur particles can be distinguished in optical micrographs as light, emitting particles (single particles) or darker patches with light, emitting edges (aggregated particles). The dark dots in the background are microorganisms.

[0067] In the photograph of Comparative Experiment A, many small individual (sub)micron sized sulfur particles are visible, which is in good agreement with the particle size distribution shown in Figure 2. In Comparative Experiment A, large agglomerates (approximately 20 μm) are also present in low apparent concentrations, too low to be visible in the number-based particle size distribution. In Comparative Experiment A, the particles appear to be primarily spherical (rough and smooth) and approximately 1 μm in size.

[0068] However, in Example 1, the small (sub)micron particles are barely visible (Figure 3(b)). Also, in Example 2, these particles do not seem to be present in large numbers, at least not as many as in Comparative Experiment A (Figure 3(c)). In the photographs of Examples 1 and 2, larger aggregated sulfur particles can be observed. In both examples, larger aggregates of 20-30 μm are visible, but also smaller aggregates of 5-10 μm. The centers of the aggregates appear dark due to the thickness of the sample and could be observed while focusing the microscope. Microorganisms attached to the aggregates were not observed, as they were easily identifiable as small black spots of about 1 μm in the sample. It is possible that mixing during the PSD measurement slightly destroyed the larger aggregates and therefore were not measured. In addition, since the PSD is number-based, the smaller particles are as heavy in the distribution as the larger ones, and there are clearly larger particles in terms of numbers than the larger ones. However, the larger ones are more visible in the micrographs. From the rough, clumpy edges of the aggregates, it can be observed that they are composed of many small constituent crystals.

[0069] Figure 3 shows the effect of the polysulfide reactor zone on the formation of agglomerates. Additionally, optical micrographs show that the smallest particles were almost absent in Example 1 and only to some extent in Examples 2 and 3.

[0070] The removal of the smallest particles in Examples 1, 2 and 3 is related to the formation of polysulfides in the polysulfide reactor zone. Polysulfides are yellow to orange in colour and the yellow colour of the sulfidation reactor allowed one to deduce that polysulfides were indeed formed.

[0071] The bisulfide content, polysulfide content, average chain length and content of elemental sulfur as part of polysulfides were measured according to the method of the present invention. These measurements were found to fit well with the mathematical model. The model inputs were the volume-based average PSD of the four experiments and the operating conditions under which these particles were produced. From these PSDs, the volume fraction of particles less than 1 μm in diameter was calculated. The total concentration of particles less than 1 μm was calculated by multiplying this volume fraction by the average measured concentration of elemental sulfur in the experiments. Three outputs were then obtained: polysulfide (S), expressed in mM; x 2- ), the equilibrium fraction S x 2- and the absolute content of elemental sulfur as part of polysulfides (S x 2- The mean S0) was calculated.

[0072] Our modeling results support the experimental findings that the smallest sulfur particles dissolve in the polysulfide reactor zone for polysulfide formation to the extent that conditions permit. In Examples 1, 2 and 3, the equilibrium S between sulfur, sulfides and polysulfides is x 2- (See Figure 4). In Comparative Experiment A, slight polysulfide formation was expected due to the short SuRT, which is consistent with the large amount of submicron particles found in the corresponding laboratory experiment. The modeling results support this. These particles were the ones most prone to react with polysulfides due to their high surface-to-volume ratio.

[0073] These results from these experiments and models illustrate the invention and show that if the sulfur absorption column is equipped with a reactor that promotes the correct degree of mixing and residence time and / or has a higher starting sulfide concentration, a higher (or overall) equilibrium is achieved between polysulfides and sulfides, allowing for reactive removal of the small elemental sulfur particles that are fed to the sulfide chamber to form polysulfides. The steady state obtained in the system (e.g., as measured in a bioreactor) is the absence of smaller sulfur particles (less than 1 μm) and / or enrichment in larger particles.

Claims

1. A process for continuously treating a hydrogen sulfide-containing gas, comprising: (a) contacting the hydrogen sulfide-containing gas with an aqueous alkaline liquid containing sulfide-oxidizing bacteria and elemental sulfur particles, thereby producing a loaded aqueous liquid containing dissolved sulfide, polysulfide compounds, sulfide-oxidizing bacteria and elemental sulfur particles, and a gas having a lower content of hydrogen sulfide, and passing the loaded aqueous liquid through a polysulfide reactor zone comprising one or more plug-flow reactor zones; (b) contacting the loaded aqueous liquid with an oxidizing agent to enable the sulfide-oxidizing bacteria to oxidize sulfide to elemental sulfur, thereby producing a concentrated aqueous liquid containing an increased amount of elemental sulfur particles; (c) separating elemental sulfur particles from the concentrated aqueous liquid; wherein the residence time between the preparation of the loaded aqueous liquid in step (a) and its supply to step (b) is 3 to 45 minutes; The content of elemental sulfur [S ｘ ２－ in S ０ as a part of the polysulfide compound in the load aqueous liquid supplied to step (b) is a process exceeding 0.7 mM.

2. The content of elemental sulfur [S ｘ ２－ as S ０ in the load aqueous liquid supplied to step (b) is more than 1 mM, the process according to claim 1.

3. The one-day average content of elemental sulfur [S ｘ ２－ in S ０ as part of said polysulfide compound in said loaded aqueous liquid supplied to step (b) over a period of at least one week is greater than 0.7 mM, process according to claim 1.

4. The content of elemental sulfur as part of the polysulfide compounds in the loaded aqueous liquid is subject to the following conditions: [S ｘ ２－ in S ０ ≥ 1.7 * [HS － * 10 （－９．１７＋ｐＨ） which is satisfied, wherein [S ｘ ２－ S in ０ is the content of elemental sulfur as part of the polysulfide compound in the loaded aqueous liquid supplied to step (b), represented in mM, [HS － is the sulfide concentration of the loaded aqueous liquid supplied to step (b), represented in mM, and pH is the pH of the loaded aqueous liquid supplied to step (b), the process according to claim 1 or 2.

5. [S ｘ ２－ in S ０ ≥ 2.8 * [HS － * 10 （－９．１７＋ｐＨ） is the process according to claim 4.

6. The hydrogen sulfide-containing gas has a hydrogen sulfide content of 0.1 to 3% by volume and a carbon dioxide content of more than 20% by volume, according to the process of claim 1 or 2.

7. The aqueous alkaline liquid is heated by indirect heat exchange with the loaded aqueous liquid and / or an external heat source, thereby obtaining the heated aqueous alkaline liquid used in step (a), according to the process of claim 1 or 2.

8. Step (a) includes passing the loaded aqueous liquid through a polysulfide reactor zone comprising one or more plug-flow reactor zones, the polysulfide reactor zone having an upstream region and a downstream region, according to the process of claim 1 or 2.

9. A part of the aqueous alkaline liquid containing sulfide-oxidizing bacteria is directly supplied to the upstream region of the polysulfide reactor zone, according to the process of claim 8.

10. In the polysulfide reactor zone, a part of the loaded aqueous liquid is recycled from the downstream region to the upstream region within the polysulfide reactor zone, according to the process of claim 8.

11. A portion of the loaded aqueous liquid flows through a zone having a residence time of 5 to 45 minutes when separated from the downstream region and before it is recycled to the upstream region within the polysulfide reactor zone, the process according to claim 10.

12. A portion of the loaded aqueous liquid recycled from the downstream region is heated before being recycled to the upstream region within the polysulfide reactor zone, the process according to claim 10.

13. Step (a) is carried out in a vertical column, the hydrogen sulfide-containing gas is continuously supplied to the column at a lower position of the column, and the aqueous liquid containing the sulfide-oxidizing bacteria is continuously supplied to a higher position of the column, whereby a gas stream flowing substantially upward contacts an aqueous stream flowing substantially downward, the process according to claim 1 or 2.

14. A portion of the aqueous liquid containing the sulfide-oxidizing bacteria is continuously supplied to a higher position of the column and contacts the rising gas stream in a first contact zone to produce an intermediate-loaded aqueous liquid, and a portion of the aqueous liquid containing the sulfide-oxidizing bacteria is continuously supplied to an intermediate position of the column and contacts the rising gas stream together with the intermediate-loaded aqueous liquid in a second contact zone, the process according to claim 13.

15. As part of step (a), in step (a1), a portion of the aqueous liquid containing the sulfide-oxidizing bacteria is continuously contacted with the hydrogen sulfide-containing gas to obtain a first intermediate-loaded aqueous liquid and an intermediate gas having a lower intermediate hydrogen sulfide content. As part of step (a), in step (a2), another portion of the aqueous liquid containing the sulfide-oxidizing bacteria is continuously contacted with the intermediate gas having a lower intermediate hydrogen sulfide content to obtain a second intermediate-loaded aqueous liquid and the gas having a lower hydrogen sulfide content. The first intermediate-loaded aqueous liquid is combined with the second intermediate-loaded aqueous liquid to obtain the loaded aqueous liquid, the process according to claim 1 or 2.

16. Each of the first and second intermediate-loaded aqueous liquids flows through a respective first and second polysulfide reactor zones, in which polysulfide compounds are formed by reaction of the dissolved sulfide with the elemental sulfur, the process according to claim 15.

17. The process according to claim 16, wherein the first and second polysulfide reactor zones each comprise one or more plug flow reactor zones.

18. The process according to claim 16, wherein a portion of the first intermediate loading aqueous liquid rich in polysulfide is fed to the second polysulfide reactor zone to increase the polysulfide content in the second intermediate loading aqueous liquid.

19. The process according to claim 17, wherein the portion of the first intermediate loading aqueous liquid rich in polysulfide is fed to an upstream region of the second polysulfide reactor zone to increase the polysulfide content in the second intermediate loading aqueous liquid.

20. The process according to claim 1 or 2, wherein at least a portion of the concentrated aqueous liquid in step (b) is recycled to step (a).

21. A sulfur regeneration process facility (1), - An absorption column (2) having an inlet (3) for a hydrogen sulfide-containing gas (4), an outlet (5) at its upper end for a gas (6) having a lower content of hydrogen sulfide, an inlet (7) for an aqueous alkaline liquid (8) further containing sulfide-oxidizing bacteria, and a first outlet (9) for a loaded aqueous liquid (10) at a lower height. - A polysulfide reactor zone (11) which is part of the absorption column (2) and is arranged at the lower end (2a) of the absorption column (2) and / or is part of a separate container comprising The polysulfide reactor zone (11) comprises one or more plug flow reactor zones, the polysulfide reactor zone (11) comprises an upstream end (13) and a downstream end (14), The upstream end (13) of the polysulfide reactor zone (11) is fluidly connected to the first outlet (9) for the loaded aqueous liquid (10). The downstream end (14) of the polysulfide reactor zone (11) comprises a second outlet (16) for the loaded aqueous liquid (17) and a recycle stream (18) for a portion of the loaded aqueous liquid to the upstream end (13) of the polysulfide reactor zone (11). The second outlet (16) for the loaded aqueous liquid (17) is fluidly connected to an aerobic bioreactor (19) for oxidizing sulfide to elemental sulfur. The aerobic bioreactor (19) is fluidly connected to the inlet (7) for the aqueous alkaline liquid (8) of the absorption column (2), and The sulfur regeneration process facility (1) includes an element sulfur recovery unit (22) having an inlet fluidly connected to the aerobic bioreactor (19), and an outlet (24) for elemental sulfur and an outlet (25) for liquid effluent poor in elemental sulfur. Sulfur regeneration process facility (1).

22. The sulfur regeneration process facility according to claim 21, wherein the recirculation flow includes a container for increasing the residence time in recirculation.

23. The polysulfide reactor zone (11, 42, 62) is provided with means for raising the temperature of the liquid content of the polysulfide reactor zone (11, 42, 62). Sulfur regeneration process facility.

24. The sulfur regeneration process facility according to claim 21 or 22, comprising sulfide-oxidizing bacteria.

25. A sulfur regeneration process facility (1a), - A first absorption column (35), having an inlet (36) for a hydrogen sulfide-containing gas (4), an outlet (37) at its upper end (39) for an intermediate gas (38) having a lower content of hydrogen sulfide, and an aqueous alkaline liquid (8) further comprising sulfide-oxidizing bacteria. A first absorption column (35) having an inlet (40) for a part (8c) and an outlet (41) for a first intermediate-loaded aqueous liquid at a lower height. - A second absorption column (55), having an inlet (56) for the intermediate gas (38) having a lower content of hydrogen sulfide, an outlet (57) at its upper end (58) for a gas (6) having a lower content of hydrogen sulfide, and an aqueous alkaline liquid (8) further comprising sulfide-oxidizing bacteria. A second absorption column (55) having an inlet (59) for a part (8a) and an outlet (60) for a second intermediate-loaded aqueous liquid at a lower height. - A polysulfide reactor zone (42) as part of the first absorption column (35) and disposed at the lower end (43) of the first absorption column (35), and / or as part of a separate container. - A polysulfide reactor zone (62) as part of the second absorption column (55) and disposed at the lower end (63) of the second absorption column (55), and / or as part of a separate container. comprising The polysulfide reactor zone (42, 62) includes a plug flow zone, and the sulfide reactor zone (42, 62) includes an upstream end (44, 64) and a downstream end (45, 65). The upstream end (44) of the polysulfide reactor zone (42) of the first absorption column (35) is fluidly connected to the outlet (41) for the first intermediate loaded aqueous liquid, and the upstream end (64) of the polysulfide reactor zone (62) of the second absorption column (55) is fluidly connected to the outlet (60) for the second intermediate loaded aqueous liquid. The downstream end (45) of the polysulfide reactor zone (42) of the first absorption column (35) is fluidly connected to the upstream end (64) of the polysulfide reactor zone (62) of the second absorption column (55). The downstream end (65) of the polysulfide reactor zone (62) of the second absorption column (55) is fluidly connected to an aerobic bioreactor (19) for oxidizing sulfide to elemental sulfur. The aerobic bioreactor (19) is fluidly connected to the inlet (59) for a portion (8a) of the aqueous alkaline liquid (8) of the first absorption column and to the inlet (40) for a portion (8c) of the aqueous alkaline liquid (8) of the second absorption column, and The sulfur regeneration process facility (1a) includes an elemental sulfur recovery unit (22) having an inlet fluidly connected to the aerobic bioreactor (19) and having an outlet (24) for elemental sulfur and an outlet (25) for liquid effluent poor in elemental sulfur.

26. The sulfur regeneration process facility according to claim 25, wherein the polysulfide reactor zone (11, 42, 62) comprises means for raising the temperature of the liquid content of the polysulfide reactor zone (11, 42, 62).

27. The sulfur regeneration process facility according to claim 25 or 26, comprising sulfide-oxidizing bacteria.

28. The process according to claim 10, implemented in the sulfur regeneration process facility according to claim 21.

29. The process according to claim 15, implemented in the sulfur regeneration process facility according to claim 25.

Images