Process and plant for the treatment of h 2s

Abstract

Chemical plant for the treatment of H2S comprising: a first unit (A) for decontaminating a gaseous process / feed stream contaminated by H2S (A1) and obtaining a first gaseous waste stream (A2) containing the separated H2S and a gaseous decontaminated process / feed stream (A3), a second unit (B) for recovering elemental sulphur from H2S and obtaining a second liquid stream of elemental sulphur (B3) and a final gaseous stream containing H2O (B2), a third unit for recovering H2 from H2S, wherein said third unit sequentially comprises a second line (2) in fluid communication with the first line (1), which is detached from said first line (1), to convey at least in part said first gaseous waste stream (A2), a chemical reactor (R) for heating and decomposing at high temperature the H2S according to the endothermic reaction (I), resulting in a gaseous H2-enriched stream, at least one heat exchanger (E) to cool said H2-enriched stream and to condense the elemental sulphur, a first separator (S1) for separating said condensed elemental sulphur from said H2-enriched stream, forming a first liquid stream of elemental sulphur, a fifth line (5) for conveying said gaseous H2-enriched stream exiting said first separator (S1) a sixth line (6) for conveying said first liquid stream leaving said first separator (S1), and wherein said third unit forms a loop circuit with a portion of said first line (1) or with a portion of said first line (1) and said first unit (A).

Description

[0001] “PROCESS AND PLANT FOR THE TREATMENT OF H2S”

[0002] DESCRIPTION

[0003] Field of the invention

[0004] The present invention concerns chemical, petrochemical and natural gas plants wherein the process streams or feed streams of the plants must be decontaminated from hydrogen sulphide (H2S), by means of chemical-physical washing units, or from sulphur, by means of hydro-desulphurisation units.

[0005] In particular, the present invention relates to the treatment of H2S, e.g. from washing or hydro-desulphurisation units, by means of the decomposition reaction H2S^H2+0.5S2 useful for the recovery of H2 from H2S.

[0006] State of the art

[0007] When gaseous process or feed streams, such as natural gas streams, are contaminated with H2S, they are generally decontaminated by physical -and chemical - washing.

[0008] Specifically, the gaseous stream to be decontaminated is contacted with a solution capable of retaining H2S (washing), after which the decontaminated gaseous stream continues in the synthesis process. The H2S-laden washing solution is subjected to treatment or stripping so that H2S is released from the solution and sent to a treatment or inertisation unit.

[0009] When gaseous process or feed streams, such as natural gas streams, are contaminated with sulphur, they are generally decontaminated by hydro-desulphurisation, i.e. by treatment with hydrogen. The gaseous stream to be decontaminated is mixed with hydrogen in the presence of a catalyst so that the sulphur is converted to H2S. Once the hydrogenation reaction has taken place, the gaseous stream is passed over an adsorbent material capable of retaining H2S. Subsequently, the decontaminated gaseous stream continues in the synthesis process. Instead, H2S is desorbed and sent to a treatment or inertisation unit.

[0010] H2S from conventional decontamination units, often in the presence of other sulphur chemicals, CO2 and CH4, is usually sent to a sulphur recovery unit in which H2S is inertised first by oxidation with air / oxygen and then by reaction with SO2. H2S is converted to elemental sulphur, which is extracted in the liquid phase, and to water, which is extracted in the vapour phase.

[0011] The general process described above, whereby the process / feed streams are conventionally subjected to chemical-physical washing or hydro-desulphurisation and the separated H2S is inertised by an oxidative process for recovering sulphur, is well known and adopted in most chemical, petrochemical and natural gas plants.

[0012] Some technologies for the recovery of H2 from H2S are described by the following patent documents.

[0013] WO2014073966A describes a process in which the heat of reaction to decompose H2S is provided in a direct manner, by injecting a gas containing oxygen into the H2S stream. In other words, the heat of reaction is obtained by the heat generated by the oxidation of a portion of H2S with oxygen. Consequently, H2S undergoes both decomposition to hydrogen and sulphur and oxidation to hydrogen, sulphur and water.

[0014] US2022380212 describes a chemical reactor for the high-temperature decomposition of H2S by thermal or thermo-catalytic means. The reactor is characterised in that there are two different process circuits, or coils, in it, in one of which the waste stream containing the H2S separated by means of a washing or hydro-desulphurisation unit flows. The document also describes a process in which the high-temperature decomposition of H2S is integrated into a process for the production of syngas; the document of the prior art does not describe a process in which the high-temperature decomposition of H2S is integrated into a process for the inertisation of H2S by oxidation.

[0015] SGI 1202010926TA describes a plant and process according to which the thermo- catalytic decomposition of H2S in a first reactor, the condensation and separation of elemental sulphur in heat exchangers and separators, the hydrogenation of sulphur species in a second reactor, and the separation of H2 from most other species by means of chemicalphysical washing is carried out in sequence. The waste stream from the chemical-physical washing is recycled to a point directly upstream of the first decomposition reactor. The feed stream is introduced directly upstream of the first decomposition reactor, and mixed with the recycle stream.

[0016] US2005191237 describes a process / plant for the high-temperature decomposition of H2S; the decomposition of H2S is not integrated with an operation for the inertisation of H2S by oxidation. The document also describes recycling of residual H2S that is not fed upstream of the washing / hydrodesulphurisation unit, but is fed at an intermediate point between the washing / hydrodesulphurisation unit and the final hydrogen separator.

[0017] US2002025292 describes a loop process / plant relating to the inertisation of a portion of H2S by oxidation in a furnace and the endothermic decomposition of a portion of H2S in the same furnace so as to exploit the exothermicity of the oxidation.

[0018] US2020353409 describes a process wherein H2S from washing operations and liquid / vapour separation undergoes oxidation.

[0019] Disadvantages of the prior art

[0020] The process of the prior art has some disadvantages:

[0021] 1) The hydrogen contained in the H2S, through oxidation in the sulphur recovery unit, is incorporated into the water; 2) Industrial demand for elemental sulphur is lower than in the past;

[0022] 3) The plant is operationally inflexible.

[0023] The first disadvantage is that a high-value chemical species, such as hydrogen, is not recovered. This translates into a disadvantage for the community in terms of environmental sustainability and a disadvantage for the production plant in terms of economic revenue.

[0024] The second disadvantage arises when the market value of elemental sulphur decreases. On the other hand, the sulphur recovery unit is essential as H2S cannot be released into the atmosphere. Hence, when the market value of elemental sulphur decreases, the conventional sulphur recovery unit puts the production plant at a disadvantage in terms of increased costs.

[0025] The third disadvantage occurs when there is a need to decrease the load of the sulphur recovery unit or to stop the sulphur recovery unit. In this case, in conventional plants, it is necessary to act upstream and decrease the plant’s production or even stop the plant.

[0026] Summary of the invention

[0027] The purpose of the present invention is to make available a process, and related plant, useful for the recovery of H2 from H2S from conventional chemical-physical washing and hydro-desulphurisation units.

[0028] Specifically, the purpose of the present invention is to make available a process, and related plant, for the treatment of H2S that is an alternative and an improvement over conventional plants based solely on washing / hydro-desulphurisation and sulphur recovery units.

[0029] The main purpose of the present invention is therefore to provide an innovative and alternative process and plant technology configured to at least partially replace elemental sulphur recovery from H2S with hydrogen recovery from H2S.

[0030] Another purpose of the present invention is to make available a plant unit, related to the process for the recovery of H2 from H2S, which is configured to be installed in existing conventional plants relatively quickly and inexpensively, i.e. in such a way as to minimise plant modifications and intervention times.

[0031] It is an object of the present invention to provide a process for treating H2S and obtaining an H2-enriched stream, or a stream substantially consisting of H2 comprising at least the following operational steps:

[0032] - Decontamination from H2S or sulphur of a process / feed stream by means of a chemical / physical washing or hydro-desulphurisation unit,

[0033] Conveyance of the gaseous waste stream containing the separated H2S to one or more H2S treatment units;

[0034] Heating of at least a portion of the waste stream containing the separated H2S and the high-temperature decomposition of H2S by thermal or thermo-catalytic means according to the reaction H2S^H2+0.5S2 to form a gaseous H2-enriched stream;

[0035] Cooling of the gaseous H2-enriched stream and condensation of elemental sulphur;

[0036] Separation of condensed elemental sulphur from the gaseous H2-rich stream;

[0037] Possible introduction of a portion of the gaseous waste stream containing the separated H2S into a sulphur recovery unit.

[0038] The plant which is further subject matter of the present invention wherein the above operations are carried out may comprise process units including: - A first unit corresponding to the chemical-physical washing or hydrodesulphurisation unit;

[0039] - A second unit corresponding to the unit for recovering sulphur from H2S;

[0040] - A third unit corresponding to the unit for recovering hydrogen from H2S; wherein the first and second units are connected to each other by means of a first line so as to convey the gaseous waste stream from the first unit to the second unit, and wherein the third unit is connected to the first line by means of a second line so as to tap at least a portion of the waste stream.

[0041] Alternatively, but not according to the present invention, the process units may be:

[0042] - A first unit corresponding to the chemical-physical washing or hydrodesulphurisation unit;

[0043] - A third unit corresponding to the unit for recovering hydrogen from H2S; wherein the first and third units are connected to each other via a second line connected to the first line leaving the first unit and configured to convey the gaseous waste stream from the first unit to the third unit.

[0044] Preferably, the first unit corresponds to a conventional washing and stripping unit, or a conventional hydro-desulphurisation and adsorption unit. Alternatively, the first unit can correspond to a conventional hydro-desulphurisation and washing-stripping unit.

[0045] For the purposes of the present invention, a conventional washing-stripping unit (hereinafter referred to as “A”) comprises two columns: a washing column and a stripping column. In the washing column, the gaseous process / feed stream contaminated with H2S is contacted with a washing solution that retains the H2S, while in the stripping column, the H2S is removed from the washing solution so that the latter is recycled back to the washing column. Thus, two streams essentially leave the washing-stripping unit: the gaseous process / feed stream decontaminated from H2S and a gaseous polluting and toxic waste stream containing the separated H2S.

[0046] For the purposes of the present invention, a conventional hydro-desulphurisation and adsorption unit (hereafter still referred to as “A”) comprises a catalytic reactor wherein the process or feed stream contaminated with elemental sulphur is mixed with hydrogen. The conversion from elemental sulphur to H2S takes place in the reactor. The gaseous stream containing H2S is passed through an adsorbent material that retains the H2S and lets the gaseous process / feed stream decontaminated from sulphur pass through. The adsorber is then regenerated by desorbing the H2S and thus generating a waste stream. Thus the adsorption unit essentially has two streams leaving it: the gaseous process / feed stream decontaminated from elemental sulphur and a gaseous polluting and toxic waste stream containing the separated H2S.

[0047] Alternatively, for the purposes of the present invention, a conventional hydrodesulphurisation and washing-stripping unit (hereafter still referred to as “A”) comprises a catalytic reactor wherein the process or feed stream contaminated with elemental sulphur is mixed with hydrogen. The conversion from elemental sulphur to H2S takes place in the reactor. The gaseous stream containing H2S is washed using a washing solution as described above. Thus the washing-stripping unit essentially has two streams leaving it: the gaseous process / feed stream decontaminated from elemental sulphur and a gaseous polluting and toxic waste stream containing the separated H2S.

[0048] Preferably, the second unit corresponds to a conventional elemental sulphur recovery unit (hereafter referred to as “B”) and comprises at least one furnace, wherein a portion of H2S reacts with oxygen to form SO2 and H2O, and one or more catalytic reactors, wherein the remaining H2S reacts with SO2 to form elemental sulphur and H2O. Therefore, two streams essentially leave the elemental sulphur recovery unit: a liquid stream of elemental sulphur and a gaseous stream containing H2O.

[0049] The third unit comprises a series of equipment and lines as follows:

[0050] - A second line that conveys at least a portion of the gaseous waste stream containing separated H2S leaving the first unit (A) and is in fluid communication with the first line;

[0051] - A chemical reactor, receiving the stream from the second line, to heat the stream and decompose H2S at high temperature to form a gaseous Ho-enriched stream;

[0052] - One or more heat exchangers, connected to the reactor via a third line, to cool the H2-enriched stream and condense the elemental sulphur;

[0053] - A first separator, connected to the heat exchangers via a fourth line, adapted to separate the condensed elemental sulphur from the gaseous Hi-rich stream;

[0054] - A fifth line adapted to convey the Hi-enriched stream;

[0055] - A sixth line adapted to convey the condensed sulphur.

[0056] The third unit can optionally include a second separator, connected to the first separator via the fifth line. The second separator is adapted to separate the H2 from the remaining gaseous chemical species, so as to obtain a gaseous stream substantially consisting of H2 and a second gaseous polluting and toxic waste stream containing the residual H2S, i.e. not decomposed in the reactor.

[0057] Further details of the third unit are described in the following discussion.

[0058] Preferably, where the plant of the present invention comprises first, second and third units, i.e., where the third unit is connected to the first line via the second line, a first flow control valve is installed on said first line downstream of the detachment of the second line, adapted to regulate the flow in the first line, and a second flow control valve is installed on said second line (or on said third or fourth line), adapted to regulate the flow in the second line. Flow control valves allow the flow rate of the waste stream, leaving the first unit (A), to be split between the second unit (B) and the third unit. In other words, the two control valves are intended to divide the flow of H2S between the sulphur recovery unit and the H2 recovery unit.

[0059] It should be emphasised that, when it includes the first, second and third units, the plant according to the present invention may be a new plant or a modified existing plant. In the case of an existing plant, the modification consists of adding the third unit to the first and second units, which already exist. Therefore, the invention described here lends itself to implementation on existing plants to improve their economic viability and operational flexibility.

[0060] It should be emphasised that, when it only includes the first and the third units, the plant according to the present invention may be a new plant or a modified existing plant.

[0061] In the case of an existing plant, the modification consists of adding the third unit to the first, already existing unit and splitting or removing the second unit, if already existing. Thus, it lends itself to be implemented on existing plants to eliminate the sulphur recovery section and replace it with the H2 recovery section, and thus to improve the economic sustainability of the plant.

[0062] In accordance with the present invention, the modification of an existing plant having the first and second units mainly includes the following operations:

[0063] - Installation of the third unit;

[0064] - Connection of the second line of the third unit to the first line connecting the first unit (A) to the second unit (B);

[0065] - Installation of the first and second flow control valves on the first and second lines, respectively.

[0066] The connection between the new third unit and the other two existing units thus requires a relatively simple and quick intervention to be implemented in the field. Advantages of the invention

[0067] Advantageously, the process and the plant of the present invention enable the recovery of H2 contained in at least a portion of H2S sent from the decontamination units to the elemental sulphur recovery units, thus improving the environmental sustainability and economic viability of the production plant.

[0068] Advantageously, the process and plant of the present invention enable the conventional plant, comprising an H2S or sulphur decontamination unit and an elemental sulphur recovery unit, to be operationally more flexible, i.e. capable of reducing the load of the elemental sulphur recovery unit without reducing the load of the upstream plant.

[0069] Advantageously, the process and plant of the present invention makes it possible to simplify the modification of an existing plant, including a decontamination and elemental sulphur recovery unit, to implement the recovery of H2 from H2S. The modification of the existing plant should, if possible, minimise downtime (to limit non-production costs), minimise impacts on the existing washing, hydro-desulphurisation and elemental sulphur recovery units (to limit labour and material costs), and ensure efficient control of the H2S treatment / inertisation process.

[0070] LIST OF FIGURES

[0071] The detailed description of the present invention is accompanied by the following figures, which are attached hereto:

[0072] Fig. A shows a diagram of a plant related to the prior art;

[0073] Fig. 1 shows a diagram of a first embodiment of a plant according to an embodiment of the present invention;

[0074] Fig. 2 shows a diagram of a second embodiment of a plant according to an embodiment of the present invention;

[0075] Fig. 3 shows a diagram of a third embodiment of a plant according to an embodiment of the present invention;

[0076] Fig. 4 shows a diagram of a fourth embodiment of a plant according to an embodiment;

[0077] Fig. 5 shows a diagram of a fifth embodiment of a plant according to an embodiment.

[0078] DETAILED DESCRIPTION

[0079] For the purposes of the present invention the definition “comprising” if referring to the plant does not exclude the presence of further equipment and / or operating units not expressly listed if referring to the process does not exclude the presence of further operating steps not expressly listed after this definition.

[0080] For the purposes of the present invention the definitions of “consisting of’ or “made up of ...” exclude the aforesaid presence.

[0081] For the purposes of the present invention, the term “gaseous mixture essentially consisting of hydrogen” means that the molar fraction of hydrogen in said gaseous mixture is at least 95%.

[0082] The diagram in Fig. A shows a plant related to the prior art. In particular, the diagram in Fig. A represents a conventional H2S treatment plant installed in a chemical, petrochemical or natural gas plant.

[0083] In accordance with Fig. A, a gaseous process / feed stream contaminated with H2S or sulphur (Al) enters the first unit (A) to be decontaminated by chemical / physical washing or hydro-desulphurisation. Out of the first unit (A) comes the decontaminated gaseous process / feed stream (A3) and a gaseous waste stream containing separated H2S (A2). The waste stream (A2) is conveyed into a first line (1) that connects the first unit (A) to a second unit (B) adapted for the inertisation of H2S and the recovery of elemental sulphur. In the second unit (B), H2S is inertised by oxidation with air / Ch and then by reaction with SO2 to obtain a liquid stream of elemental sulphur (B3) and a final gaseous stream containing H2O (B2).

[0084] Therefore, according to the diagram in Fig.A, the plant is configured to separate H2S, inertise H2S and recover elemental sulphur without the possibility of recovering H2 contained in H2S. In addition, if the second unit (B) has operational or maintenance problems, the entire upstream plant must undergo load reduction or shutdown.

[0085] The chemical plant covered by the present invention for the treatment of H2S preferably comprises, in sequence: a first unit (A) to decontaminate a gaseous process / feed stream contaminated with H2S or sulphur (Al) and obtain a first gaseous waste stream (A2) containing the separated H2S and a decontaminated process / feed gaseous stream (A3), a third unit for the recovery of H2 from H2S.

[0086] The first unit (A) comprises:

[0087] - washing and stripping columns, or a hydro-desulphurisation reactor and an adsorbent system, or a hydro-desulphurisation reactor and washing and stripping columns, -a first line (1) to convey the first waste stream (A2),

[0088] The third unit comprises in sequence:

[0089] -a second line (2) in fluid communication with the first line (1) to convey at least part of the first gaseous waste stream (A2),

[0090] -a chemical reactor (R), connected to the second line (2), to heat and decompose at high temperature the H2S according to the endothermic reaction H2SBH2+O.5S2, to obtain a gaseous IB-enriched stream, -at least one heat exchanger (E), connected to the reactor (R) via a third line (3), to cool the Hi-enriched stream and to condense the elemental sulphur,

[0091] -a first separator (SI), connected to or forming part of the exchanger (E) via a fourth line (4) or being part of said exchanger (E), to separate the condensed elemental sulphur from the Hi-enriched stream, forming a first liquid stream of elemental sulphur,

[0092] -a fifth line (5) to convey the gaseous Hi-enriched stream leaving said first separator (SI),

[0093] -a sixth line (6) to convey the first liquid stream leaving the first separator (SI).

[0094] In accordance with a preferred embodiment, the third unit also comprises:

[0095] -a second separator (S2), connected to the first separator (SI) via the fifth line (5), to separate the Hi from the remaining gaseous chemical species and to obtain a gaseous stream essentially consisting of Hi and a second gaseous waste stream containing the residual H2S,

[0096] -a seventh line (7) to convey the gaseous stream substantially consisting of H2,

[0097] -an eighth or ninth line (8,9) to convey the second gaseous waste stream.

[0098] Preferably, the fifth line (5) or the ninth line (9) is connected upstream of the first unit (A) to the contaminated process / feed stream (Al) in order to recycle and inject the H2- enriched stream or the second waste stream into it.

[0099] Preferably, a fan or compressor (C) is installed on the fifth line (5) or ninth line (9) to raise the pressure of the stream flowing in the line (5,9).

[0100] In accordance with a preferred embodiment, a device is installed on the second, fifth, eighth or ninth line (2,5, 8,9) to heat the stream flowing in the line (2,5, 8,9). Preferably, the heating device corresponds to a heat exchanger (E) installed between the reactor (R) and the first separator (SI).

[0101] In accordance with a preferred embodiment, the reactor (R) is a coil furnace, into which the first gaseous waste stream (A2) flows, and wherein the coil reactor comprises burners or electrical devices to indirectly release the heating heat and the heat of reaction to H2S through the walls of the coil.

[0102] In accordance with a preferred embodiment, the heat exchanger (E) directly installed downstream of the reactor (R) is a water or smoke tube boiler that rapidly cools the Hi-enriched stream by boiling pressurised water.

[0103] The plant further comprises:

[0104] -a second unit (B) to recover elemental sulphur from H2S and to obtain a second liquid stream of elemental sulphur (B3) and a final gaseous stream containing H2O (B2),

[0105] - a first and a second flow control valve (VI, V2) mounted on the first line (1) and the second or third line (2,3) respectively.

[0106] The second unit (B) comprises in sequence:

[0107] -a furnace to oxidise a portion of H2S with air / Ch and obtain SO2 and H2O,

[0108] -a reactor to react the remaining portion of H2S with SO2,

[0109] It should be noted that the first line (1) is connected to the second unit (B). The first control valve (VI) is installed downstream of the detachment of the second line (2).

[0110] In accordance with a preferred embodiment, the eighth line (8) connects to the first line (1) downstream of the first control valve (VI).

[0111] Preferably, on the first line (1), downstream of the first control valve (VI) and upstream of the connection to the eighth line (8), a lamination valve (V3) is installed, which equalises the pressure of the first line (1) with respect to the pressure of the eighth line (8).

[0112] In accordance with a preferred embodiment, the first liquid stream (6) is connected to the second liquid stream (B3), preferably by hydraulic connection.

[0113] It should be noted that the third unit forms a closed or loop circuit with a portion of said first line (1) or with a portion of the first line (1) and the first unit (A). It is further subject matter of the present invention to provide a process for the treatment of H2S produced in the chemical plant. It should be noted that it will be clear how the process steps are carried out in the relevant parts of the plant described above.

[0114] The chemical process for treating H2S according to the present invention comprises in sequence the operations or steps of: decontamination (A) of a gaseous process / feed stream contaminated with H2S or sulphur (Al) to obtain a first gaseous waste stream (A2) containing the separated H2S and a decontaminated process / feed gaseous stream (A3),

[0115] -recovery of H2 from H2S.

[0116] Specifically, the decontamination (A) comprises the operational steps:

[0117] -one of the following operational steps selected from washing and stripping, hydrodesulphurisation and adsorption, or hydro-desulphurisation and washing and stripping,

[0118] - conveying the first gaseous waste stream in a first line (1) towards said recovery of elemental sulphur from H2S (B); while, the operation to recover H2 from H2S sequentially comprises the operations of:

[0119] -tapping at least a portion of the first gaseous waste stream (A2) from the first line (1),

[0120] -heating and high-temperature decomposition of H2S contained in the tapped stream in a chemical reactor (R) according to the endothermic reaction H2S^H2+0.5S2, resulting in a gaseous IB-enriched stream,

[0121] -cooling (E) of the IE-enriched stream and condensation of elemental sulphur,

[0122] -an initial separation operation (SI) to separate the condensed elemental sulphur from the H2-enriched stream, forming a first liquid stream of elemental sulphur,

[0123] -conveyance of the IE-enriched gaseous stream obtained through the first separation into a line (5), -conveyance of the first liquid stream into a line (6).

[0124] In accordance with a preferred embodiment, the process also comprises:

[0125] - a second separation operation (S2) performed on the gaseous Ho-enriched stream (5) obtained by the first separation (SI) to separate the H2 from the remaining gaseous chemical species and to obtain a gaseous stream substantially consisting of H2 and a second gaseous waste stream containing the residual H2S,

[0126] - conveyance of the gaseous stream basically consisting of H2 into a line (7),

[0127] - conveying the second gaseous waste stream into a line (8,9).

[0128] The process also includes the operations of:

[0129] - flow regulation (VI, V2) of said first gaseous waste stream (A2), wherein the flow regulation is operated on said first line (1), performed between the decontamination step and the step of H2 recovery from H2S. Preferably, this flow control operation (VI, V2) is performed downstream of said tapping and on said at least one portion of the first gaseous waste stream (A2) tapped from the first line;

[0130] - recovery of elemental sulphur from H2S (B) to obtain a second liquid stream of elemental sulphur (B3) and a final gaseous stream containing water (B2), downstream of the H2 recovery from H2S, and on said stream tapped from the first line (1).

[0131] Specifically, the recovery of elemental sulphur from H2S (B) sequentially comprises the operations of:

[0132] -oxidation of a portion of H2S with air / Ch to obtain SO2 and H2O,

[0133] -reaction of the remaining portion of H2S with SO2 to obtain elemental sulphur and H2O.

[0134] Preferably, it should be noted that the first waste stream (A2) conveyed by the first line (1) undergoes elemental sulphur recovery from H2S (B).

[0135] Preferably, the process comprises the operation of raising the pressure (C) of the Hi-enriched stream (5) or the second waste stream (9), recycling upstream of the decontamination (A) of the H2 -enriched stream (5) or the second waste stream (9), and mixing the H2-enriched stream (5) or the second waste stream (9) with the contaminated process / feed stream (Al).

[0136] In accordance with a preferred embodiment, the chemical process further comprises the operations of:

[0137] - conveying the second waste stream (8) to elemental sulphur recovery (B).

[0138] Preferably, the chemical process further comprises the operations of:

[0139] -pressure regulation (V3) of the first waste stream (A2) conveyed by the first line (1) to the elemental sulphur recovery (B) to match the pressure of the second waste stream (8) conveyed to elemental sulphur recovery (B);

[0140] -possible mixing (Bl) of the first waste stream (A2) conveyed from the first line (1) to elemental sulphur recovery (B) with the second waste stream (8) conveyed to elemental sulphur recovery (B).

[0141] In accordance with a preferred embodiment, the chemical process also comprises the heating of the tapped stream (2), the IB-enriched stream (5), or the second waste stream (8,9). Preferably, the heating of the fifth line (5) of the eighth (8) and the ninth line (9) is carried out using the hot gaseous IB-enriched stream leaving the reactor (3) and entering the exchanger.

[0142] In accordance with an alternative embodiment, the chemical process includes a cooling operation of the IB-enriched stream (5).

[0143] In accordance with a preferred embodiment, the chemical process also includes the operation of feeding the first liquid stream (6) into the second liquid stream (B3).

[0144] In accordance with a preferred embodiment, the chemical process further comprises the operational steps of conveying the tapped stream into a coil placed inside the reactor (R), generating heat within the reactor (R) by means of burners or electrical devices, and indirectly transferring the heat, through the coil wall, to the H2S to perform heating and decomposition.

[0145] Preferably, the cooling operation comprises rapid cooling by boiling pressurised water directly downstream of the reactor (R).

[0146] Finally, according to an alternative and preferred embodiment, the gaseous stream essentially consisting of H2 (7) is subjected to compression.

[0147] It should be noted that the residual H2S not decomposed in said reactor (R) is recycled and fed into said contaminated gaseous process / feed stream (Al) or sent to said elemental sulphur recovery (B).

[0148] The following is a more detailed description of the chemical plant for the treatment of H2S and the related processes.

[0149] First embodiment of process and plant Pl (illustrated in Figure 1)

[0150] Figure 1 shows an initial embodiment of the plant (Pl). Specifically, the plant (Pl) comprises: a first washing or hydro-desulphurisation unit (A) receiving a process or feed stream contaminated with H2S or sulphur (Al). The stream (Al) is gaseous and may contain hydrocarbons or correspond to a natural gas stream. The decontaminated process / feed stream (A3) and a first gaseous waste stream (A2) containing separate H2S flow out of the first unit (A). The first waste stream (A2) is partly conveyed into a first line (1).

[0151] The first line (1) connects the first unit (A) with a second elemental sulphur recovery unit (B) in order to transfer the first waste stream (A2) from the first unit (A) to the second unit (B).

[0152] A third waste stream (Bl) containing H2S enters the second unit (B). The third waste stream (Bl) can correspond to a portion of the first waste stream (A2). The second unit (B) is configured to inertise H2S. A liquid stream of elemental sulphur (B3) and a final gaseous stream containing water (B2) leave the second unit (B).

[0153] Preferably, as illustrated in Figure 1, a second line (2) is placed in fluid communication with the first line (1), preferably the second line (2) is detached from the first line (1). The second line (2) taps a portion of the first gaseous waste stream (A2) from the first line (1). The second line (2) is connected to a chemical reactor (R) in which the tapped stream is heated and the H2S decomposition reaction takes place at high temperature to obtain an H2-rich gaseous stream. The IB-rich stream flowing out of the reactor (R) flows in a third line (3) to one or more heat exchangers (E) for cooling the stream and condensing the elemental sulphur produced by the decomposition of IBS. The IB-enriched stream, once cooled and partially condensed, is sent via a fourth line (4) to a first phase separator (SI), which separates the liquid sulphur, conveyed in a sixth line (6), from the IB-enriched gaseous stream. The gaseous IB-enriched stream, after separation from the elemental sulphur, is sent via a fifth line (5) to a second separator (S2) that separates IB from the other gaseous chemical species. From the second separator (S2), then, a gaseous stream exits substantially consisting of IB, conveyed into a seventh line (7), and a second gaseous waste stream containing residual IBS not decomposed in the reactor (R), conveyed into an eighth line (8).

[0154] In accordance with the embodiment shown in Figure 1, the reactor (R), heat exchangers (E), separators (S1,S2) and the related connecting lines (2, 3, 4, 5, 6, 7, 8) define the third unit adapted to recover H2 from IBS, this third unit being part of the plant Pl.

[0155] It should be noted that the second waste stream conveyed into the eighth line (8) is fed into the first line (1), downstream of the detachment of the second line (2), i.e. the tapping of the first gaseous waste stream (A2). The second waste stream is then sent to the second unit (B) for the inertisation of residual H2S. In the first line (1), any portion of the first waste stream (A2) that has not been tapped from the second line (2) is mixed with the second waste stream. A third gaseous waste stream (Bl) containing H2S then enters the second unit (B), which may correspond to the second waste stream from the second separator (S2) or to the mixture formed by the second waste stream and the first waste stream (A2).

[0156] Preferably, the liquid sulphur leaving the first separator (SI) and conveyed into the sixth line (6) is sent to the liquid sulphur line (B3) leaving the second unit (B).

[0157] Preferably, the first and second lines (1,2) are provided with a first and second flow control valve (VI, V2), respectively. The first valve (VI) is installed on the first line (1) downstream of the detachment of the second line (2) and upstream of the connection to the eighth line (8). The control valves (VI, V2) are required to split the flow of the first waste stream (A2) between the relevant lines (1, 2) and thus to control the recovery process of H2 from H2S and the recovery process of elemental sulphur from H2S.

[0158] Alternatively, the first control valve (VI) can be installed on the third line (3). In addition, the first line (1), downstream of the first flow control valve (VI) and upstream of the connection to the eighth line (8), is also provided with a lamination valve or pressure control valve (V3). The lamination valve (V3) is connected with a signal line (SL) to the eighth line (8). The lamination valve (V3) is required to equalise the pressure of the streams flowing in the first line (1) and the eighth line (8) at the connection point.

[0159] The process implemented in the plant (Pl) comprises the following steps:

[0160] -Decontamination of the gaseous process / feed stream (Al) by H2S or sulphur via the first unit (A) to obtain a decontaminated gaseous process / feed stream (A3) and a first gaseous waste stream (A2) containing the separated H2S conveyed into the first line (1);

[0161] -Opening / closing of the first and / or second flow control valve (VI, V2); -Tapping at least a portion of the first waste stream (A2) from the first line (1) via the second line (2);

[0162] -Heating the tapped stream and high-temperature decomposition of H2S in the reactor (R) to produce a gaseous Ho-enriched stream (3);

[0163] -Cooling of the Hi-enriched stream and condensation of the elemental sulphur;

[0164] -A first separation to separate the condensed elemental sulphur from the gaseous Hi-enriched stream (5) to form a first liquid stream of elemental sulphur (6);

[0165] -A second separation, downstream of the first separation, to separate the H2 from the other gaseous chemical species in order to obtain a gaseous stream basically consisting of H2 (7) and a second gaseous waste stream (8) containing the residual H2S;

[0166] -Opening / closing the lamination valve (V3);

[0167] -Injection of the second waste stream (8) into the first line (1), downstream of the lamination valve (V3);

[0168] -Possible mixing, in the first line (1), of the second waste stream (8) with a portion of the first waste stream (A2);

[0169] -Injection of a third waste stream (Bl) corresponding to or containing the second waste stream, via the first line (1), into a second unit (B);

[0170] -Inertisation of H2S in the second unit (B) to obtain a second liquid stream of elemental sulphur (B3) and a final gaseous stream containing water (B2). This enables the recovery of elemental sulphur from H2S (B) to obtain a second liquid stream of elemental sulphur (B3) and a final gaseous stream containing water (B2);

[0171] -Injection of the first liquid sulphur stream (6) into the second liquid sulphur stream (B3).

[0172] Preferably, to increase the tapping from the first line (1) and thus the recovery of

[0173] H2, the first flow control valve (VI) is at least partially closed and the second flow control valve (V2) is at least partially open. Conversely, to decrease the tapping from the first line (1) the first flow control valve (VI) is at least partially open and the second flow control valve (V2) is at least partially closed. One of the two flow control valves (VI, V2) may be superfluous for splitting the first waste stream (A2). However, as a person skilled in the art can understand, it is preferable to have the two valves (VI, V2) as they allow, when operated together, accurate and effective biasing under all operating conditions.

[0174] It should be noted that in order to equalise the pressure in the first line (1) with respect to the pressure in the eighth line (8), the lamination valve (V3) opens or closes. In practice, the pressure of the stream flowing in the first line (1) must be equal to the pressure of the stream flowing in the eighth line (8) at the point of reconnection. Preferably, the lamination valve (V3) and the pressure signal collected on the eighth line (8) are close to the point where the two lines (1, 8) rejoin.

[0175] Second embodiment of process and plant P2 (illustrated in Figure 2)

[0176] A second embodiment of the plant (P2) is illustrated in Figure 2. Specifically, the plant (P2) is substantially equivalent to the plant (Pl). The plant diagram in Fig.2 is similar to the plant diagram in Fig.1 except for the eighth line and the lamination valve which are both absent in the plant (P2) as shown in Figure 2. Therefore, the process carried out in the plant (P2) is similar to the process carried out in the plant (Pl), except that the operational step of feeding the second waste stream into the first line and the subsequent opening / closing of the lamination valve are not performed.

[0177] As illustrated in Figure 2, the plant P2 provides for a gaseous stream substantially consisting of H2 to flow from the second separator (S2), which is conveyed into the seventh line (7), and a second gaseous waste stream containing residual H2S, which is conveyed into a ninth line (9). The second waste stream undergoes heating in at least one heat exchanger (E) and a pressure increase by a fan or compressor (C). The second waste stream is then recycled upstream of the first unit (A) and mixed with the contaminated process / feed stream (Al). It should be noted that the pressure increase is necessary to feed the stream into an upstream point of the plant where the pressure is higher. Heating is recommended to avoid possible condensation of the stream during the pressure increase. The third waste stream (Bl) entering the second unit (B) corresponds to the portion of the first waste stream (A2) that may not have been tapped by the second line (2).

[0178] In accordance with the diagram in Fig.2, the reactor (R), heat exchangers (E), separators (SI, S2), fan (C) and the related connecting lines (2, 3, 4, 5, 6, 7, 9) define the third unit adapted to recover H2 from H2S part of the plant (P2)

[0179] Consequently, the process carried out in the plant (P2) comprises the recycling operation of the second waste stream, after pressure increase upstream of the first unit (A) and mixing with the contaminated process / feed stream (Al).

[0180] The plant P2 and its process have the advantage that the first control valve (VI) can be completely closed and the second unit (B) isolated and taken out of service. This can be useful in case of maintenance on the second unit (B) or in order to maximise hydrogen recovery. Residual H2S, i.e. non-decomposed H2S in the reactor (R), recycled upstream via the ninth line (9), is separated again in the first unit (A) and fed back into the first waste stream (A2).

[0181] Third embodiment of process and plant P3 (illustrated in Figure 3)

[0182] A third embodiment of the plant (P3) is illustrated in Figure 3. Specifically, the plant (P3) is substantially equivalent to the plant (P2) shown in Figure 2. The diagram of plant P3 in Fig.3 is similar to the plant diagram in Fig.2, except for the absence of the second separator, the seventh line and the ninth line in plant P3. Consequently, the process carried out in the plant (P3) is therefore similar to the process carried out in the plant (P2), except that the second separation is not performed.

[0183] As illustrated in Figure 3, plant P3 has the gaseous Ho-enriched stream flowing out of the first separator (SI), conveyed into the fifth line (5), and the first liquid sulphur stream, conveyed into the sixth line (6). The IE-enriched stream undergoes heating in at least one heat exchanger (E) and a pressure increase by means of a fan or compressor (C). The Hi-enriched stream is then recycled upstream of the first unit (A) and mixed with the contaminated process / feed stream (Al). The pressure increase is necessary to feed the stream to an upstream point of the plant where the pressure is higher. Heating is recommended to avoid possible condensation of the stream during the pressure increase. The third waste stream (Bl) entering the second unit (B) corresponds to the portion of the first waste stream (A2) that may not have been tapped by the second line (2).

[0184] It should be noted that the reactor (R), the heat exchangers (E), the first separator (SI), the fan (C) and the related connecting lines (2, 3, 4, 5, 6) define the third unit adapted to recover H2 from H2S, part of the plant (P3).

[0185] Consequently, the process carried out in the plant (P3) comprises the recycling operation of the H2-enriched stream, after pressure increase, upstream of the first unit (A) and mixing with the contaminated process / feed stream (Al).

[0186] Advantageously, the plant (P3) and the related process allow the first control valve (VI) to be completely closed and the second unit (B) to be isolated and taken out of service. This can be useful in case of maintenance on the second unit (B) or in order to maximise hydrogen recovery. Residual H2S, i.e. non-decomposed H2S in the reactor (R), recycled upstream via the fifth line (5), is separated again in the first unit (A) and fed back into the first waste stream (A2).

[0187] It should therefore be emphasised that: -processes and plants (Pl, P2) advantageously enable the recovery of H2 from H2S, and specifically the extraction of H2 from the plant by means of a stream substantially consisting of H2, conveyed into the seventh line (7);

[0188] -the process and plant (P3) advantageously allow the recovery of H2 from H2S, and specifically to extract H2 from the plant already mixed with the decontaminated process / feed stream (A3).

[0189] It should be noted that the plants (Pl, P2, P3) may refer to new or existing plants.

[0190] In the case of existing plants, i.e. if the first unit (A) and the second unit (B), connected by the first line (1), are existing, the third unit of the plants (Pl, P2, P3) can be added to the first and second units (A, B) and connected to the existing lines.

[0191] It is emphasised that the plants (Pl, P2, P3) allow better operational flexibility than conventional plants, i.e. plants comprising only the first and second units (A, B).

[0192] Advantageously, by operating the control valves (VI, V2), the load of the second and third units can be varied, i.e. hydrogen recovery can be increased or decreased, and above all, by completely closing the first control valve (VI), hydrogen recovery can be maximised.

[0193] Advantageously, the third unit, by completely closing the second control valve (V2), can be sectioned off or stopped in the event of operational or maintenance problems, conveying all the first waste stream (A2) to the second unit (B).

[0194] Fifth embodiment of process and plant P4 (illustrated in Figure 4)

[0195] A fourth embodiment of the plant (P4) not covered by the present invention is illustrated in Figure 4. Specifically, the plant (P4) comprises the first and third units.

[0196] Specifically, the plant (P4) comprises a first chemical-physical or hydrodesulphurisation washing unit (A) receiving a process or feed stream contaminated with HoS or sulphur (Al). The contaminated process / feed stream (Al) is gaseous and may contain hydrocarbons or correspond to a natural gas stream. From the first unit (A) flows the decontaminated process / feed stream (A3) and a first gaseous waste stream (A2) containing the separated H2S via a first line (1) configured to convey said first waste stream (A2). The first waste stream (A2) is conveyed, preferably at least in part, into a second line (2) via a dynamic fluid connection with the first line (1). Preferably, the second line (2) is detached from the first line (1), more preferably it is the continuation of the first line (1). This second line (2) is connected to a chemical reactor (R) in which the first waste stream (A2) is heated and the high-temperature decomposition reaction of H2S takes place to obtain an IE-rich gaseous stream. The Fh-rich stream flowing out of the reactor (R) flows in a third line (3) to one or more heat exchangers (E) for cooling the stream and condensing the elemental sulphur produced by the decomposition of H2S. The IE-enriched stream, once cooled and partially condensed, is sent via a fourth line (4) to a first phase separator (SI), which separates the liquid sulphur, conveyed in a sixth line (6), from the IE-enriched gaseous stream. The gaseous IE-enriched stream, after separation from the elemental sulphur, is sent via a fifth line (5) to a second separator (S2) that separates IE from the other gaseous chemical species. From the second separator (S2), then, a gaseous stream exits, substantially consisting of IE, conveyed into a seventh line (7), and a second gaseous waste stream containing residual FES not decomposed in the reactor (R), conveyed into a ninth line (9).

[0197] Preferably, the second waste stream undergoes heating in at least one heat exchanger (E) and a pressure increase by a fan or compressor (C). The second waste stream is then recycled upstream of the first unit (A) and mixed with the contaminated process / feed stream (Al). It should be noted that pressure build-up is necessary to feed the stream into an upstream point of the plant, where the pressure is higher. Heating is recommended to avoid possible condensation of the stream during pressure build-up.

[0198] The reactor (R), the heat exchangers (E), the separators (SI, S2), the fan (C) and the related connecting lines (2, 3, 4, 5, 6, 7, 9) define the third unit adapted to recover H2 from H2S part of the plant (P4).

[0199] The process implemented in the plant (P4) comprises the following steps:

[0200] -Decontamination of the gaseous process / feed stream (Al) by H2S or sulphur via the first unit (A) to obtain a decontaminated gaseous process / feed stream (A3) and a first gaseous waste stream (A2) containing the separated H2S conveyed into the second line (2);

[0201] -Heating the first waste stream (A2) and high-temperature decomposition of H2S in the reactor (R) to produce a gaseous H2-enriched stream (3);

[0202] -Cooling of the H2-enriched stream and condensation of the elemental sulphur;

[0203] -A first separation to separate the condensed elemental sulphur from the gaseous H2-enriched stream (5) to form a first liquid stream of elemental sulphur (6);

[0204] -A second separation, downstream of the first separation, to separate H2 from the other gaseous chemical species in order to obtain a gaseous stream substantially consisting of H2 (7) and a second gaseous waste stream (9) containing residual, undecomposed H2S;

[0205] -Heating and raising the pressure of the second waste stream (9);

[0206] -Recirculation of the second waste stream (9) upstream of the first unit (A) and mixing it with the contaminated process / feed stream (Al).

[0207] Fifth embodiment of process and plant P5 (illustrated in Figure 5)

[0208] A fifth embodiment of the plant (P5) not covered by the present invention is illustrated in Figure 5. Specifically, the plant (P5) is similar to the plant (P4) except for the absence of the second separator, the seventh line and the ninth line, which are absent in the plant (P5). The process carried out in the plant (P5) is therefore similar to the process carried out in the plant (P4) except that the second separation is not performed.

[0209] As illustrated in Figure 5, plant P5 has the gaseous Ho-enriched stream flowing out of the first separator (SI), conveyed into the fifth line (5), and the liquid sulphur stream, conveyed into the sixth line (6). The IE-enriched stream undergoes heating in at least one heat exchanger (E) and a pressure increase by means of a fan or compressor (C). The H2- enriched stream is then recycled upstream of the first unit (A) and mixed with the contaminated process / feed stream (Al). The pressure increase is necessary to feed the stream to an upstream point of the plant where the pressure is higher. Heating is recommended to avoid possible condensation of the stream during the pressure increase.

[0210] It should be noted that the reactor (R), the heat exchangers (E), the first separator (SI), the fan (C) and the related connecting lines (2, 3, 4, 5, 6) define the third unit adapted to recover H2 from H2S part of the plant (P5).

[0211] Consequently, the process carried out in the plant (P5) comprises the recycling operation of the H2-enriched stream, after pressure increase, upstream of the first unit (A) and mixing thereof with the contaminated process / feed stream (Al).

[0212] It should therefore be emphasised that:

[0213] -the process and the plant (P4) advantageously allow the recovery of H2 from H2S, and specifically the extraction of H2 from the plant by means of a stream substantially consisting of H2, conveyed into the seventh line (7);

[0214] -the process and plant (P5) enable the recovery of H2 from H2S, and specifically to extract H2 from the plant already mixed with the decontaminated process / feed stream (A3).

[0215] The plants (P4, P5) are preferably new plants and are implemented when the elemental sulphur recovery unit is not desired. The plants (P4, P5) are designed to maximise the recovery of H2 from H2S. It should be noted that the plants (P4, P5) are also obtainable from existing plants, e.g. by eliminating the second elemental sulphur recovery unit (B) of the plants (P2, P3) related to Figs. 2 and 3.

[0216] It should be noted again that a common feature of the plants (P1-P5) in the diagrams of Figs. 1-5 is the presence of a closed circuit or loop, which is absent in the diagram of the prior art of Fig. A.

[0217] In the plant (Pl), the closed or loop circuit is formed by the third unit and a portion of the first line (1). The first and second units (A,B) are not included in the circuit. Furthermore, the first unit (A) and the second unit are placed upstream and downstream of the closed circuit, respectively.

[0218] In the plant (P2, P3) the closed or loop circuit is formed by the first unit (A), a portion of the first line (1) and the third unit. The second unit (B) is excluded from the circuit and placed downstream of the closed circuit. In addition, the contaminated process / supply stream (Al) enters a point in the closed circuit between the third unit and the first unit (A) in the flow direction of the recycle stream (5,9), so that it is injected directly into the first unit (A).

[0219] In the plant (P4, P5), the closed or loop circuit consists of the first unit (A) and the third unit. In addition, the contaminated process / feed stream (Al) enters a point in the closed circuit between the third unit and the first unit (A) in the flow direction of the recycle stream (5,9), so that it is injected directly into the first unit (A). This makes the present process / plant 1 substantially different from the one disclosed in the prior art SGI 1202010926TA.

[0220] It should be noted that the endothermic decomposition reaction FbS^Hi+O.SSi is carried out in a reactor (R) preferably corresponding to a coil furnace. The first waste stream (A2) leaving the first unit (A) flows into the coil pipes. The coil furnace can be equipped with a convection section, or a radiant section, or both. The heating heat and heat of reaction is transferred indirectly to the stream flowing in the coil pipes. Heat can be provided by burners or by devices that convert electrical energy into heat, e.g. radiative heaters or electromagnetic induction devices. Consequently, the burner system or electric heating devices can be designed to indirectly supply heating heat and heat of reaction to H2S through the coil wall in order to reach the required decomposition temperatures.

[0221] If the decomposition reaction is conducted thermally, it is preferable that the temperature at which the decomposition reaction of H2S is carried out is greater than 700°C in the reactor R, and more preferably greater than 800°C.

[0222] If the reaction is carried out thermo-catalytically, the decomposition reaction is carried out in the presence of a catalyst loaded into the coil pipes. The pipes are preferably placed vertically. The temperature at which the reaction is conducted by thermo-catalytic means is preferably greater than 500°C, and even more preferably greater than 600°C. The active part of the catalyst is preferably molybdenum / molybdenum-disulphide-based.

[0223] In accordance with a preferred embodiment, the chemical decomposition reaction preferably reaches equilibrium along the pathway in the reactor (R). In other words, the gaseous H2-enriched stream (3) flowing out of the reactor (R) is preferably in thermodynamic equilibrium according to the operating conditions.

[0224] Downstream of the reactor (R), in accordance with the present invention, rapid cooling of the H2-enriched gaseous stream (3) is preferable in order to freeze the chemical composition flowing out of the reactor (R) and thus prevent any retrogradation reactions. Consequently, a water or fume pipe boiler is preferably installed directly downstream of the chemical reactor (R) to rapidly cool the hot stream by boiling pressurised water. Subsequently, other heat exchangers can be installed to cool the H2 -enriched stream (3) and, in particular, one or more sulphur condensers adapted to condense the elemental sulphur produced in the decomposition of H2S.

[0225] In accordance with a preferred embodiment, the first separator (SI) corresponds to a phase separator. The first separator (SI) can be a stand-alone device, such as a cylindrical vessel, or it can be a part of a heat exchanger. For example, the first separator (SI) may correspond to the outlet box of a sulphur condenser where a mat is optionally installed to separate sulphur droplets from the Fh-enriched gaseous stream.

[0226] In accordance with a preferred embodiment, the second separator (S2) is preferably a membrane separator. The membrane, which is preferably made of ceramic or polymer material, is permeable to H2 and not to other chemical species. Alternatively, the second separator (S2) corresponds to a chemical-physical washing or adsorption unit.

[0227] With reference to the plants (Pl, P2 and P4), an alternative and preferred embodiment (not shown in the figures) is for the H2 -enriched gaseous stream exiting the first separator (SI) to undergo heating. In this case, the recirculated stream upstream of the first unit (A) can avoid being subjected to heating.

[0228] With reference to the plants (Pl, P2 and P4), another alternative and preferred embodiment (not shown in the figures) is for the FF-enriched gaseous stream exiting the first separator (SI) to undergo cooling.

[0229] With reference to the plants (Pl, P2 and P4), an alternative and preferred embodiment (not shown in the figures) is for the gaseous stream consisting essentially of H2 leaving the second separator (S2) to be subjected to compression.

[0230] With reference to the plant (Pl), an alternative and preferred embodiment (not shown in the figures) is that the second gaseous waste stream exiting the second separator (S2) is advantageously subjected to heating, to avoid condensation along the eighth line (8).

[0231] In accordance with a preferred embodiment, the heating of the H2 -enriched stream (5) exiting the first separator (SI) or of the second waste stream (5,8,9) exiting the second separator (S2) is preferably and advantageously carried out in a heat exchanger (E) wherein the hot Hi-enriched stream (3) exiting the reactor (R) is used as heating fluid. Alternatively, heating can be achieved with a hot auxiliary fluid or another heating device.

[0232] In accordance with a preferred embodiment, with reference to the plants (P1-P5), the first waste stream (A2) flowing in the second line (2) can also be heated upstream of the chemical reactor (R). Accordingly, in accordance with an alternative and preferred embodiment (not shown in the figures) of the present process and plant, the first waste stream (A2) flowing in the second line (2) is heated upstream of the reactor (R) by means of a heat exchanger. Preferably, the heat exchanger can be part of the heat exchangers (E) located downstream of the reactor (E) and thus the waste stream (A2) is heated using the hot H2 enriched gaseous stream (3) flowing out of the reactor (R) as the heating fluid. Consequently, it is emphasised that the waste stream (A2) flowing in the second line (2), according to the present invention, can be heated upstream of the reactor (R), or in the reactor (R), or both upstream of the reactor (R) and in the reactor (R).

[0233] Preferably, with reference to processes and plants (P2,P3,P4,P5), wherein there is recycling upstream of the first unit (A), it is emphasised that the first unit (A) must separate an amount of H2S equivalent to the sum of H2S contained in the recycle stream and H2S contained in the contaminated process / feed stream (Al). Therefore, a person skilled in the art will understand that if the first unit (A) is part of an existing plant, the addition of a new third unit for hydrogen recovery can be implemented if the first unit (A) is able to separate a higher quantity of H2S than the quantity present in the contaminated process / feed stream alone (Al). Otherwise, the first unit (A) must be upgraded.

[0234] As a person skilled in the art can understand, with reference to the diagrams in Figs. 1-5, other components are present in the plant described here, such as pumps, valves, instruments, tanks, which are not shown in the accompanying figures because they are not relevant to the inventive concepts disclosed here.

[0235] From the foregoing, it is clear that the present invention achieves its intended purposes and, specifically, the process and plant described herein make it possible to:

[0236] -recover the H2 from at least a portion of H2S separated in the decontamination unit (A);

[0237] -split the amount of H2S between the elemental sulphur recovery unit (B) and the H2 recovery unit;

[0238] -reduce the load of the elemental sulphur recovery unit (B) or isolate and shut down the elemental sulphur recovery unit (B) without the need for upstream load reduction or plant shutdown;

[0239] -install the H2 recovery unit in an existing plant by modifying the process lines and thus minimising implementation time and costs.

[0240] The process and the associated plant for the treatment of H2S, as conceived and described, is in any case open to numerous modifications and variations, all of which can be attributed to the same inventive concept. Furthermore, all the details can be replaced by other technically equivalent elements.

[0241] It is further subject matter of the present invention to provide a method for modifying an existing chemical / petrochemical plant, for example a plant illustrated in Figure 1, comprising a first unit (A) and a second unit (B) placed in series and connected by a first line (1).

[0242] More specifically, as previously described, the first unit (A) is adapted to receive and decontaminate from H2S or from sulphur a gaseous process / feed stream (Al) in order to obtain a decontaminated process / feed stream (A3) and a first waste stream (A2) containing the separated H2S conveyed in said first line (1), while the second unit (B) is adapted to receive said first waste stream (A2) via said first line (1) and to inertise the H2S and recover elemental sulphur from H2S. It should be noted that the first unit (A) comprises chemical-physical washing and / or hydro-desulphurisation operations and the second unit (B) comprises oxidation operations of H2S with air / Ch. The method comprises the operations of installing a third unit for the recovery of H2 from H2S with the existing plant operating or switched off of the type described above in accordance with one of the embodiments in Figures 1- 3 comprising at least one in sequence of: a second line (2) equipped with a second flow control valve (V2), at least one reactor (R) connected to said second line (2) adapted to heat and decompose at high temperature the H2S according to the endothermic reaction H2S^H2+0.5S2, at least one heat exchanger (E) connected to said reactor (R), at least one separator (S1,S2) connected to said heat exchanger (E) and connected either to said first line (1) via said eighth line (8) or to said contaminated process / feed stream (Al) via said fifth or ninth line (5,9).

[0243] It should be noted that further elements of the third unit are described in the embodiments and can be included in the installation of the third unit.

[0244] The method comprises the step of: installing the third unit at the existing plant with the existing plant operating or switched off; possibly shutting down and reclaiming the existing plant; providing an initial fluid-dynamic connection between said third unit and said first line (1) by means of a second line (2), providing a second fluid-dynamic connection either between said third unit and said first line (1) by means of an eighth line (8) downstream of said first connection, or between said third unit and said contaminated process / feed stream (Al) by means of a fifth or ninth line (5,9) upstream of said first unit (A); installing a first flow control valve (VI) on said first line (1), downstream of said first connection. The first and second connections form a loop circuit with their units connected to each other.

[0245] Preferably, the installation of the third unit on an existing plant according to the method of the present invention involves connecting the third unit described in accordance with the embodiments, and in particular the embodiments shown in Figures 1-3, to the first and second units to obtain the plant (Pl, P2, P3).

Claims

CLAIMS1. A chemical plant for the treatment of H2S comprising: a first unit (A) to decontaminate a gaseous process / feed stream contaminated with H2S (Al) and obtain a first gaseous waste stream (A2) containing the separated H2S and a decontaminated process / feed gaseous stream (A3), a second unit (B) to recover elemental sulphur from H2S and obtain a second liquid stream of elemental sulphur (B3) and a final gaseous stream containing H2O (B2), a third unit for the recovery of H2 from H2S, a first and a second flow control valve (V 1 , V2), wherein said first unit (A) comprises: operating units selected from: washing and stripping columns; a hydrodesulphurisation reactor and an adsorbent system; a hydro-desulphurisation reactor and washing and stripping columns, a first line (1) to convey said first waste stream (A2), wherein said second unit (B) comprises in sequence: a furnace to oxidise a portion of H2S with air / Ch and obtain SO2 and H2O, a reactor to react the remaining portion of H2S with SO2, wherein said third unit comprises: a second line (2) in fluid communication with the first line (1), which is detached from said first line (1), to convey at least part of said first gaseous waste stream (A2), a chemical reactor (R), connected to said second line (2), to heat and decompose at high temperature the H2S according to the endothermic reaction H2S^H2+0.5S2, obtaining a gaseous H2-enriched stream,at least one heat exchanger (E), connected to said reactor (R) via a third line (3), to cool said Hi-enriched stream and to condense the elemental sulphur, a first separator (SI), connected to or forming part of said exchanger (E) via a fourth line (4) or being part of said exchanger (E), to separate the condensed elemental sulphur from said Ho-enriched stream, forming a first liquid stream of elemental sulphur, a fifth line (5) to convey said gaseous Ho-enriched stream leaving said first separator (SI), a sixth line (6) to convey said first liquid stream leaving said first separator (SI), wherein: said first line (1) is connected to said second unit (B), said first and second control valves (VI, V2) are mounted on said first line (1) and said second or third line (2,3) respectively, said first control valve (VI) is mounted downstream of the detachment of said second line (2), and wherein said third unit forms a loop circuit with a portion of said first line (1) or with a portion of said first line (1) and said first unit (A).

2. The chemical plant according to claim 1, wherein said third unit further comprises: a second separator (S2), connected to said first separator (SI) via said fifth line (5), to separate the H2 from the remaining gaseous chemical species and to obtain a gaseous stream essentially consisting of H2 and a second gaseous waste stream containing the residual H2S, a seventh line (7) to convey said gaseous stream substantially consisting ofan eighth or ninth line (8,9) to convey said second gaseous waste stream.

3. The chemical plant according to claim 1 or 2, wherein said fifth line (5) or said ninth line (9) is connected, upstream of said first unit (A), to said contaminated process / feed stream (Al) to recycle and inject said H2 enriched stream or said second waste stream into it.

4. The chemical plant according to claim 3, wherein a fan or compressor (C) is installed on said fifth line (5) or said ninth line (9) to raise the pressure of the stream flowing in the line(5.9).

5. The chemical plant according to any one of claims 2 to 4, wherein a device is installed on said second, fifth, eighth or ninth line (2, 5, 8, 9) to heat the stream flowing in the line(2.5.8.9).

6. The chemical plant according to claim 5, wherein said heating device corresponds to a heat exchanger (E), installed between said reactor (R) and said first separator (SI), which serves to cool the stream in the line (3) leaving the reactor R.

7. The chemical plant according to any one of claims 1 to 6, wherein said reactor (R) is a coil furnace, into which said first gaseous waste stream (A2) flows, and wherein said coil reactor comprises burners or electrical devices for indirectly yielding heating and reaction heat to H2S through the walls of the coil.

8. The chemical plant according to any of claims 1 to 7, wherein the heat exchanger (E)directly installed downstream of the reactor (R) is a water or fume pipe boiler that rapidly cools said Ho-enriched stream by boiling pressurised water.

9. The chemical plant according to any one of claims 1 to 8, wherein said eighth line (8) is connected to said first line (1) downstream of said first control valve (VI).

10. The chemical plant according to claim 9, wherein on said first line (1), downstream of said first control valve (VI) and upstream of said connection to said eighth line (8), there is installed a lamination valve (V3) which equalises the pressure of said first line (1) with respect to the pressure of said eighth line (8).

11. The chemical plant according to any one of claims 7 to 10, wherein said first liquid stream (6) is connected to said second liquid stream (B3).

12. A chemical process for the treatment of H2S comprising in sequence the operations of: decontamination (A) of a gaseous process / feed stream contaminated with H2S (Al) to obtain a first gaseous waste stream (A2) containing the separated H2S and a decontaminated process / feed gaseous stream (A3),- flow regulation (VI, V2) of said first gaseous waste stream (A2),- recovery of H2 from H2S,- recovery of elemental sulphur from H2S (B) to obtain a second liquid stream of elemental sulphur (B3) and a final gaseous stream containing water (B2), wherein decontamination (A) comprises the operational steps: at least one of the following operational steps selected from washing and stripping, hydro-desulphurisation and adsorption, or hydro-desulphurisation and washingand stripping; conveying said first gaseous waste stream (A2) into a first line (1) to said elemental sulphur recovery from H2S (B), wherein said recovery of elemental sulphur from H2S (B) comprises the operational steps in sequence: oxidation of a portion of H2S with air / Ch to obtain SO2 and H2O, reaction of the remaining portion of H2S with SO2 to obtain elemental sulphur and H2O, wherein said recovery of H2 from H2S comprises in sequence the operations of: tapping at least a portion of said first gaseous waste stream (A2) from said first line (1), heating and high-temperature decomposition of H2S contained in said tapped stream in a chemical reactor (R) according to the endothermic reaction H2SBH2+O.5S2, resulting in a gaseous H2-enriched stream, cooling (E) of said IB-enriched stream and condensation of elemental sulphur, a first separation operation (SI) to separate said condensed elemental sulphur from said IB-enriched stream, forming a first liquid elemental sulphur stream, conveyance of said gaseous IB-enriched stream obtained by said first separation into a line (5), conveyance of said first liquid stream into a line (6), wherein said flow regulation is operated on said first line (1), downstream of said tapping, and on said stream tapped from the first line (1).

13. The chemical process according to claim 12, further comprising the operations of:a second separation operation (S2) performed on the gaseous Ho-enriched stream (5) obtained by said first separation (SI) to separate the H2 from the remaining gaseous chemical species and to obtain a gaseous stream substantially consisting of H2 and a second gaseous waste stream containing the residual H2S, conveyance of said gaseous stream substantially consisting of H2 into a line(7), conveyance of said second gaseous waste stream into a line (8,9).

14. The chemical process according to claim 12 or 13, comprising the operation of raising the pressure (C) of said Ho-enriched stream (5) or said second waste stream (9), recycling upstream of said decontamination (A) of said Hi-enriched stream (5) or said second waste stream (9), and mixing said Hi-enriched stream (5) or said second waste stream (9) with said contaminated process / feed stream (Al).

15. The chemical process according to any one of claims 12 to 14, comprising the operation of conveying said second waste stream (8) to said elemental sulphur recovery (B).

16. The chemical process according to claim 15, comprising-possible pressure regulation (V3) of the first waste stream (A2) conveyed by said first line (1) to the elemental sulphur recovery (B) to match the pressure of said second waste stream(8) conveyed to elemental sulphur recovery (B), and-possible mixing (Bl) of said first waste stream (A2) conveyed by said first line (1) to the elemental sulphur recovery (B) with said second waste stream (8) conveyed to the elemental sulphur recovery (B).

17. The chemical process according to any one of claims 12 to 16, comprising a heating operation of said tapped stream, of said IE-enriched stream (5), or of said second waste stream (2, 5, 8, 9).

18. The chemical process according to claim 17, wherein the heating of the fifth line (5) and the eighth (8) and ninth line (9) is carried out by the use of the hot gaseous IE-enriched stream leaving said reactor (3) and entering the exchanger (E).

19. The chemical process according to any one of claims 12 to 18, comprising the operation of feeding said first liquid stream (6) into said second liquid stream (B3).

20. The chemical process according to any one of claims 12 to 19, comprising operational steps of conveying said tapped stream into a coil located within said reactor (R), generating heat within said reactor (R) by means of burners or electrical devices, and indirectly transferring the heat, through the wall of the coil, to the H2S to perform said heating and said decomposition.

21. The chemical process according to any of claims 12 to 20, wherein said cooling includes rapid cooling by boiling pressurised water performed directly downstream of said reactor (R).

22. A method for modifying an existing chemical / petrochemical plant comprising a first unit (A) and a second unit (B) placed in series and connected by a first line (1), wherein said first unit (A) is adapted to receive and decontaminate from H2S a gaseous process / feed stream (Al) to obtain a decontaminated process / feed stream (A3) and a first waste stream(A2) containing the separated H2S conveyed in said first line (1), wherein said second unit (B) is adapted to receive said first waste stream (A2) via said first line (1) and to inertise the H2S and to recover elemental sulphur from H2S, wherein said first unit (A) comprises chemical / physical washing and / or hydro-desulphurisation operations, wherein said second unit (B) comprises oxidation operations of H2S with air / Ch, said method comprising the operations of:- installing a third unit for the recovery of H2 from H2S with the existing plant operating or switched off,- installing the third unit at the existing plant with the existing plant operating or switched off- possibly shutting down and reclaiming the existing plant;- providing an initial fluid-dynamic connection between said third unit and said first line (1) by means of a second line (2),- providing a second fluid-dynamic connection either between said third unit and said first line (1) by means of an eighth line (8) downstream of said first connection, or between said third unit and said contaminated process / feed stream (Al) by means of a fifth or ninth line (5,9) upstream of said first unit (A),- installing a first flow control valve (VI) on said first line (1), downstream of said first connection, wherein said first and second connections form a loop circuit, and wherein said third unit comprises in sequence: said second line (2) equipped with a second flow control valve (V2), at least one reactor (R) connected to said second line (2) adapted to heat and decompose at a high temperature the H2S according to the endothermic reactionH2S^H2+0.5S2,at least one heat exchanger (E) connected to said reactor (R), at least one separator (S1,S2) connected to said heat exchanger (E) and connected either to said first line (1) via said eighth line (8) or to said contaminated process / feed stream (Al) via said fifth or ninth line (5,9).

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