System and method for degassing sulfur

Abstract

The present invention relates to systems and methods for degassing sulfur, and in particular to a contemplated system and method for removing polysulfides and hydrogen sulfide from liquid sulfur in a Claus plant, comprising (a) physically separate steps of catalytic decomposition of polysulfides and gas stripping, or (b) using the stripping gas as a continuous phase in a packed column with a decomposition catalyst to avoid catalyst loss.

Description

[0001] This application is a divisional application of the invention patent application with application number 201580083667.5 (PCT / US2015 / 054015) and application date October 5, 2015. Technical Field

[0002] The field of the invention is the degassing of liquid sulfur and it relates in particular to the catalytic decomposition of polysulfides to hydrogen sulfide and the removal of the hydrogen sulfide from the liquid sulfur. Background Art

[0003] The Background Description includes information that may be useful for understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[0004] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.

[0005] Since the Claus process is an equilibrium process, the presence of hydrogen sulfide in the liquid sulfur in and downstream of the sulfur condenser is unavoidable. Unfortunately, dissolved hydrogen sulfide tends to spontaneously outgas from the liquid into the headspace of conduits, vessels, wells and other containers where it may eventually reach toxic or explosive levels. In addition, the liquid sulfur will also contain appreciable amounts of polysulfides (H2S X , where x is typically between 8 and several hundred), polysulfides can then decompose into hydrogen sulfide, sulfur dioxide, and sulfur, increasing hazardous conditions.

[0006] Therefore, many systems and methods for removing hydrogen sulfide and polysulfide from liquid sulfur have been developed. For example, GB2203732B teaches the use of a decomposition catalyst in a storage tank provided for liquid sulfur recycling, and uses a purge gas nozzle to discharge hydrogen sulfide. A similar process with different treatment zones is described in US4729887A, while US7081233B2 uses a static mixer and well treatment of liquid sulfur. Alternatively, as described in US20140377165A1, a process gas is used to stir the liquid sulfur in the well and thus discharge hydrogen sulfide, while WO2014035614A1 uses a bubbling pad to discharge hydrogen sulfide from the sulfur in the well. US4755372A uses a degassing zone with a catalyst and further degassing in a sulfur rundown pit with a purge gas.

[0007] Hydrogen sulfide can also be removed kinetically from liquid sulfur, as described, for example, in EP2607304B1, where a relatively fine spray of liquid sulfur is formed in the presence of an oxidizing gas in a first compartment, and where the sulfur droplets thus treated coalesce into a liquid which is then discharged into a second compartment. In a similar manner, US6010677A uses an accelerating nozzle to discharge liquid sulfur against an impact target to remove hydrogen sulfide. Alternatively, US8084013B2 teaches the use of a gas-liquid ejector, using liquid sulfur as ejector power and ambient purge air as an active degassing agent, in combination with a static mixer and a packed bed.

[0008] In order to make the removal of polysulfide and hydrogen sulfide more compact, sulfur from a Claus device can be treated in a single tower, as described in US4844720A. Here, a decomposition catalyst is arranged in a tower purged with an oxygen-containing purge gas. In order to further increase the reaction rate, a high-pressure oxidizing gas in countercurrent contact with liquid sulfur can be used, as described in EP851836B1 and US5632967A. On the other hand, in the case where the purge gas is hypoxic or an inert gas, sulfur can be degassed using a catalyst on a specific tower packing, which increases the contact of bubbles and liquid sulfur, as shown in US8361432B2. Similar catalyst structures are also discussed in US8663596B2. Similarly, WO2013006040A1 teaches the use of catalyst modules with high void volumes to avoid catalyst loss, while relatively fast and efficient mass transfer can also be achieved by using stripping gas in the form of small bubbles in the presence of a strong Bronsted-Lowry base, as described in WO9506616A1.

[0009] However, despite these various systems and methods, there are still many difficulties. For example, in the case where the catalyst material is used in a container with sulfur and air flowing in a cocurrent upward direction for decomposing polysulfides into hydrogen sulfide and removing hydrogen sulfide from sulfur, the catalyst bed usually becomes fluidized due to the very similar density of sulfur and catalyst, resulting in catalyst loss due to particle abrasion. On the other hand, in the case of using a countercurrent flowing oxygen-containing stripping gas, water and sulfur dioxide products tend to condense in cooler locations and cause corrosion. In addition, in the case where the catalyst is fixed on a packing structure, high pumping speeds and relatively slow reaction rates are often encountered. Similarly, in the case of desulfurization in an overflow well, slow reaction times and high circulation rates are usually required.

[0010]

[0006] Therefore, while many sulfur processing methods are known in the art, a need remains for improved systems and methods for removing polysulfides and hydrogen sulfide from liquid sulfur. Summary of the invention

[0011] The present subject matter relates to various apparatus, systems and methods for processing liquid sulfur that utilize catalyst and stripping gas in a configuration that permits high efficiency and low catalyst loss. Most typically, these advantages are achieved by pre-treating the sulfur prior to introducing an inert or low oxygen concentration or air stripping gas, or by employing a fixed catalyst bed utilizing a trickle bed concept in which the sulfur flows across the bed from top to bottom while an upward flowing stripping gas serves as the continuous phase.

[0012] In one aspect of the inventive subject matter, a method for treating liquid sulfur comprising polysulfides and hydrogen sulfide comprises: a step of contacting the liquid sulfur with a decomposition catalyst under conditions effective to convert the polysulfides to hydrogen sulfide to thereby produce a liquid sulfur stream rich in hydrogen sulfide, and another step of stripping the liquid sulfur stream rich in hydrogen sulfide with a stripping gas to thereby produce an acid gas stream and a liquid sulfur product stream.

[0013] In some aspects of the subject matter of the present invention, the steps of contacting the liquid sulfur and stripping are carried out in two separate sections of a common container, wherein the decomposition catalyst can be arranged above the stripping section and can be configured as a ring. In other aspects, the steps of contacting the liquid sulfur and stripping are carried out in two separate containers fluidly connected to each other, for example in a trickle bed tower with a stripping gas as a continuous phase (for example in a countercurrent flow mode). Although not limited to the subject matter of the present invention, it is preferred that the stripping gas is an inert gas or a low-oxygen gas, and / or the decomposition catalyst comprises a Claus or Claus-type catalyst. As used herein, and unless the context indicates otherwise, the term "connected to" is intended to include both direct connections (wherein two elements connected to each other are in contact with each other) and indirect connections (wherein at least one additional element is located between the two elements). Therefore, the terms "connected to" and "connected to..." are used synonymously.

[0014] Therefore, viewed from another perspective, the inventors have also contemplated a method for treating liquid sulfur containing polysulfides and hydrogen sulfide, wherein in one step the liquid sulfur is contacted with a decomposition catalyst (a Claus catalyst or a Claus-type catalyst, such as alumina or a metal oxide supported on alumina) in a trickle bed reactor under conditions effective to convert the polysulfides into hydrogen sulfide, to thereby produce hydrogen sulfide from the polysulfides. In another step, the hydrogen sulfide is purged from the trickle bed reactor with a stripping gas as a continuous phase, to thereby form an acid gas stream and a liquid sulfur product stream.

[0015] Most typically, the stripping gas is an inert gas or a low oxygen gas, and / or the purge step is in a countercurrent flow regime. Likewise, it is contemplated that the trickle bed reactor may contain a fixed bed catalyst, and / or feed the acid gas stream to an incineration unit or Claus plant.

[0016] Therefore, the inventors also contemplate a processing plant for treating liquid sulfur containing polysulfides and hydrogen sulfide. In a particularly contemplated plant, a Claus plant produces a liquid sulfur stream containing polysulfides and hydrogen sulfide, and the Claus unit is connected to (a) a liquid sulfur contact unit having a decomposition catalyst for converting polysulfides into hydrogen sulfide to thereby produce a liquid sulfur stream rich in hydrogen sulfide, and a stripping unit for stripping the liquid sulfur stream rich in hydrogen sulfide with a stripping gas to thereby produce an acid gas stream and a liquid sulfur product stream; or (b) a trickle bed reactor having a decomposition catalyst to contact the liquid sulfur stream containing polysulfides and hydrogen sulfide with a stripping gas as a continuous phase in countercurrent to thereby form a liquid sulfur product stream and an acid gas stream. In such a plant, a vessel is then fluidly connected to the stripping unit or the trickle bed reactor to receive the liquid sulfur product stream.

[0017] In some embodiments, the liquid sulfur contact unit is configured as a catalytic reactor fluidly connected to a stripping unit, while in other embodiments, the liquid sulfur contact unit and the stripping unit are arranged in a single vessel. Most typically, the stripping gas is an inert gas or a low-oxygen gas, and the decomposition catalyst comprises a Claus catalyst.

[0018] Various objects, features, aspects, and advantages of the present subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawings, in which like numerals represent like parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is an exemplary sulfur processing system according to the present subject matter, wherein liquid sulfur flows through a packed bed of polysulfide decomposition catalyst before being subjected to a stripping gas in a stripping column.

[0020] Figure 2 is another exemplary sulfur processing system according to the present inventive subject matter, wherein liquid sulfur is processed in a combined tower by passing the sulfur through a packed bed polysulfide decomposition catalyst section separate from a stripping section.

[0021] Figure 3 is another exemplary sulfur processing system according to the present subject matter, wherein liquid sulfur is subjected to a packed bed of polysulfide decomposition catalyst and a stripping gas as the continuous phase. DETAILED DESCRIPTION

[0022] The present inventors have discovered that liquid sulfur, which normally originates from a Claus plant, can be treated in a conceptually simple and effective manner to decompose polysulfides and remove hydrogen sulfide without encountering the difficulties common to hitherto known systems and processes.

[0023] More specifically, the contemplated systems and methods employ Claus catalysts or Claus-type catalysts, processes or configurations for avoiding catalyst loss, by pre-treating the sulfur prior to the introduction of a stripping gas (e.g., an inert or low oxygen concentration gas or air) or by utilizing a fixed catalyst bed with a trickle bed concept, in which the sulfur flows across the bed from top to bottom and the upwardly flowing stripping gas serves as the continuous phase. Most typically, the catalyst is or comprises a granular Claus catalyst or a Claus-like catalyst material (alumina or a metal oxide supported on alumina or a similar catalytic material) coating of a metal or ceramic support to enhance the decomposition of polysulfides. The hydrogen sulfide so produced is then stripped from the sulfur at moderate pressure, typically utilizing an inert gas or air stripping gas of low oxygen concentration. Thus, oxidation of sulfur-containing species to corrosive sulfur dioxide, which causes catalyst loss via friction and / or fluidization (due to the stripping gas in the catalyst section where sulfur is the continuous phase).

[0024] In one aspect of the inventive subject matter, Figure 1 As schematically shown in FIG. 1 , a processing apparatus 100 for processing liquid sulfur receives an undegassed liquid sulfur stream 110 comprising polysulfides and hydrogen sulfide from a Claus plant (not shown). The stream 110 is then fed to a liquid sulfur contact unit 120, which includes a decomposition catalyst 122 in a fixed bed, the decomposition catalyst 122 being active to convert polysulfides into hydrogen sulfide to thereby produce a liquid sulfur stream rich in hydrogen sulfide. A stripping unit 130 having a packed bed 132 is fluidly connected to the liquid sulfur contact unit 120 and is configured to strip the hydrogen sulfide-rich liquid sulfur stream from the contact unit 120 with a stripping gas 140 in a countercurrent manner to thereby produce an acid gas stream 142 and a liquid sulfur product stream 114, which is then fed to an overflow well or other container (not shown) to at least temporarily store the sulfur. As from Figure 1 As should be readily apparent from the drawings, the apparatus physically separates the step of decomposing the polysulfides to hydrogen sulfide from the step of stripping the hydrogen sulfide from the liquid sulfur and thus avoids fluidization of the catalyst bed.

[0025] In another aspect of the inventive subject matter, as in Figure 2 As schematically shown in FIG. 2 , a processing unit 200 for processing liquid sulfur receives an undegassed liquid sulfur stream 210 containing polysulfides and hydrogen sulfide from a Claus unit (not shown). Figure 1In contrast, polysulfide decomposition and stripping are integrated into a single vessel 230 having a decomposition section 231 and a stripping section 232. Stream 210 enters vessel 230 and first contacts the annular catalyst bed of decomposition section 231 to decompose polysulfides into hydrogen sulfide. The hydrogen sulfide-rich liquid sulfur stream thus formed passes downward through the fixed bed into stripping section 232, which has a packed bed and is configured to strip hydrogen sulfide from the hydrogen sulfide-rich liquid sulfur stream in a countercurrent manner with a stripping gas 240. Acid gas stream 242 leaves vessel 230 after passing through the annular opening of the annular fixed bed, while liquid sulfur product stream 214 leaves the bottom section of the vessel and flows to an overflow well or other container (not shown) to at least temporarily store the sulfur. As previously mentioned, it will be appreciated that in this configuration, the steps of decomposing the polysulfides to hydrogen sulfide and stripping the hydrogen sulfide from the liquid sulfur are physically separated, and again fluidization of the catalyst bed (caused by the central opening in the annular catalyst bed, as the stripping gas will preferentially pass through such opening) is avoided. Figure 1-2 In the example of the stripping section, the catalyst bed can be appropriately sized to achieve the desired degree and rate of decomposition in a manner that is substantially independent of design considerations of the stripping section.

[0026] Or, if Figure 3 Schematically shown in FIG, a treatment unit 300 for treating liquid sulfur receives an undegassed liquid sulfur stream 310 comprising polysulfides and hydrogen sulfide from a Claus plant (not shown). The stream 310 is then fed to a trickle bed reactor 330, which contains a decomposition catalyst 322 in a fixed bed, the decomposition catalyst 322 being active to convert polysulfides into hydrogen sulfide to thereby produce a liquid sulfur stream rich in hydrogen sulfide, from which the stripping gas removes the hydrogen sulfide. Here, the catalyst is configured to allow the liquid sulfur to flow downward over (and into) the catalyst while the stripping gas 340 passes through the catalyst as a continuous phase. It should also be noted that although Figure 3 The trickle bed reactor is depicted as a tower in which the stripping gas is fed countercurrent to the catalyst bed, other flow patterns (e.g., cocurrent downward flow) are also considered suitable. Regardless of the flow pattern, the trickle bed reactor 330 produces an acid gas stream 342 and a liquid sulfur product stream 314, which is fed to an overflow well or other container (not shown) to at least temporarily store the sulfur. Once again, it should be recognized that such a configuration and method allows the processing of liquid sulfur containing polysulfides in a manner that avoids catalyst loss.

[0027] With regard to the type of catalyst used, it should be understood that all catalysts (and combinations thereof) that catalyze the decomposition of polysulfides in liquid sulfur to hydrogen sulfide are considered suitable. For example, suitable catalysts include particulate Claus or Claus-like catalyst materials, and in particular porous alumina or metal oxides supported on alumina, unpromoted or promoted activated alumina, and titania catalysts and alumina-titania composites, all of which may be structured or coated onto metal or ceramic supports to enhance the decomposition of polysulfides to hydrogen sulfide and allow stripping of hydrogen sulfide from sulfur at typically low to moderate pressures with or without the use of a stripping gas.

[0028] It is further contemplated that the catalyst may be arranged in a catalytic reactor in a fixed bed, a packed bed, a loose collection of contact bodies supported by a large retaining structure, or the like, depending on the specific configuration. Likewise, the decomposition may be carried out in a single stage or in multiple stages, which may or may not be interspersed with one or more stripping stages. Regardless of the type of catalyst and the arrangement of the catalyst bed, it is generally preferred that the apparatus include sufficient catalyst to reduce the polysulfide content by at least 50%, at least 70%, at least 80%, at least 90% or at least 95% (compared to the polysulfide content of the undegassed sulfur entering the apparatus). Viewed from various perspectives, the catalyst will be present in an amount effective to reduce the polysulfide content in the liquid sulfur to equal to or less than 100 ppm, equal to or less than 50 ppm, equal to or less than 20 ppm, or equal to or less than 10 ppm.

[0029] The decomposition of polysulfides is most preferably carried out at a pressure and temperature at which sulfur is liquid, the temperature being typically at least 140°C, or at least 160°C, or at least 200°C, or at least 250°C, or at least 300°C, or at least 340°C, and less than 440°C, and the pressure being between about 1 atm and 50 atm, and more typically between 1 atm and 20 atm. It is further contemplated that the decomposition of polysulfides can be carried out in the presence of an oxidant or gas (e.g., atmospheric air, an oxygen-containing gas), but can also be carried out in the absence of air or an oxidant or gas (e.g., no agent or gas, or using an inert gas). Therefore, the decomposition of polysulfides may exist in the absence of any gas flow. Unless the context dictates otherwise, all ranges set forth herein should be interpreted as including their endpoints, and open ranges should be interpreted as including commercially viable values. Similarly, unless the context indicates otherwise, all listed values ​​should be deemed to include intermediate values.

[0030] Most typically, the decomposition of polysulfides is carried out in a separation stage which may be located at a Figure 1 In a separate container as exemplified in Figure 2In addition, the decomposition of polysulfides can also be carried out in a thin film or in a cavity on the surface of the catalyst, which is usually supported on a structured filler or other support with a high surface area. Therefore, it should be noted that after the decomposition of polysulfides in a given volume of sulfur has been carried out to a relatively large extent (for example, at least 70%, at least 80%, at least 90% or at least 95%), the sulfur treated in this way is contacted with the stripping gas. It should also be noted that, for example, in the case where the decomposition catalyst is in a different container, such a volume can be relatively large (for example, at least 0.1m 3 , at least 0.5m 3 , at least 1.0m 3 , at least 5.0m 3 or in the case where the decomposition catalyst is in a separate portion of the same container, such volume may be relatively modest (e.g. at least 0.05 m 3 , at least 0.1m 3 , at least 0.0m 3 , at least 1.0m 3 In the case of a catalyst in a trickle bed reactor, this volume may be relatively small (e.g., at least 0.01 m 3 , at least 0.05m 3 , at least 0.1m 3 , at least 0.5m 3 wait).

[0031] Suitable gas streams for removing hydrogen sulfide from a hydrogen sulfide-rich liquid sulfur stream (stream after contact with a decomposition catalyst) generally include inert gases or gases with reduced oxygen concentrations (relative to ambient air). For example, the stripping gas will contain nitrogen, argon, combustion exhaust (preferably after decarbonization), etc. However, air is also considered suitable for use, and even oxygen-rich gas streams are also so. Regarding the flow rate of the stripping gas, it is generally preferred that the flow rate is sufficient to reduce the hydrogen sulfide concentration in the liquid sulfur to equal to or less than 100ppm, equal to or less than 50ppm, equal to or less than 20ppmv, or equal to or less than 10ppmv. Alternatively, stripping can be carried out using stirring, kinetic treatment or by recycling liquid sulfur through a bubbling zone. Therefore, depending on the specific method, the stripping gas can be pumped, injected or bubbled into the sulfur and / or tower packing being treated. In the case where the tower is a trickle bed tower, it is generally preferred that the tower be constructed and operated so that the stripping gas serves as a continuous phase. Therefore, the stripping gas can contact the sulfur or liquid sulfur being treated in a co-current or countercurrent flow mode.

[0032] It is obvious to those skilled in the art that, without departing from the inventive concept of this article, in addition to those already described, there may be many other modifications. Therefore, the subject matter of the present invention is not limited to the scope of the appended claims. Moreover, when interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. Specifically, the terms "include" and "comprise" should be interpreted as referring to elements, components or steps in a non-exclusive manner, indicating that the elements, components or steps mentioned may exist, or be utilized, or be combined with other elements, components or steps not explicitly mentioned. In the case where the present specification claims relate to at least one thing selected from the group consisting of A, B, C... and N, the text should be interpreted as requiring only one element from the group, rather than A+N or B+N, etc. Finally, and as used herein and throughout the subsequent claims, unless the context clearly indicates otherwise, the meaning of "one", "one" and "the" includes plural objects.

Claims

1. A method for treating liquid sulfur containing polysulfides and hydrogen sulfide, comprising: contacting the liquid sulfur with a decomposition catalyst in a fixed bed of a trickle bed reactor under conditions effective to convert polysulfides to hydrogen sulfide to thereby produce a liquid sulfur stream rich in hydrogen sulfide; stripping the hydrogen sulfide-rich liquid sulfur stream with a stripping gas as a continuous phase to thereby produce an acid gas stream and a liquid sulfur product stream, wherein: (a) the step of contacting liquid sulfur and the step of stripping are carried out in two separate sections of a common vessel, or (b) wherein the step of contacting liquid sulfur and the step of stripping are carried out in two separate vessels fluidly connected to each other.

2. The process according to claim 1, wherein the step of contacting liquid sulfur and the step of stripping are carried out in two separate sections of a common vessel.

3. The method according to claim 2, wherein the decomposition catalyst is arranged above the stripping section and is configured as a ring.

4. The method according to claim 1, wherein the stripping is carried out in a countercurrent flow manner. The method according to claim 1 , wherein the stripping gas is an inert gas or a low-oxygen gas.

6. The method of claim 1, wherein the decomposition catalyst comprises a Claus catalyst.

7. The method of claim 1, wherein the decomposition catalyst comprises a Claus-like catalyst.

8. The process according to claim 7, wherein the Claus-like catalyst is alumina or a metal oxide supported on alumina.

9. The method of claim 1, further comprising feeding the acid gas stream to an incineration unit or a Claus plant.

10. A processing device for treating liquid sulfur containing polysulfides and hydrogen sulfide, the device comprising: A Claus plant configured to produce a liquid sulfur stream comprising polysulfides and hydrogen sulfide, wherein the Claus plant is further connected to: a liquid sulfur contacting unit comprising a decomposition catalyst active to convert polysulfides to hydrogen sulfide to thereby produce a liquid sulfur stream rich in hydrogen sulfide; and a stripping unit connected to the liquid sulfur contacting unit and configured to strip the hydrogen sulfide-rich liquid sulfur stream with a stripping gas to thereby produce an acid gas stream and a liquid sulfur product stream; and a vessel fluidly connected to the stripping unit to receive a liquid sulfur product stream; wherein the liquid sulfur contact unit and the stripping unit are arranged in a single vessel, or Wherein the liquid sulfur contact unit and the stripping unit comprise two separate vessels fluidly connected to each other.

11. The treatment plant according to claim 10, wherein the liquid sulfur contact unit is configured as a catalytic reactor fluidly connected to the stripping unit.

12. The processing device according to claim 10, wherein the stripping gas is an inert gas or a low-oxygen gas.

13. The treatment device of claim 10, wherein the decomposition catalyst comprises a Claus catalyst.

14. The treatment device of claim 10, wherein the decomposition catalyst comprises a Claus-like catalyst.

15. The process of claim 14, wherein the Claus-like catalyst is alumina or a metal oxide supported on alumina.

16. The process plant according to claim 10, further comprising one or more lines for feeding the acid gas stream from the stripping unit to an incineration unit and / or a Claus unit.

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