Plant and method for treating sulphide-containing gases and for recovering sulphur by high-temperature electrolysis unit coupling

Abstract

The invention relates to a plant for treating gases containing hydrogen sulphide (H2S), the plant comprising: - a Claus-type sulphur recovery unit (1), the sulphur recovery unit (1) receiving, as input: a first stream comprising a gas containing H2S and a second stream comprising a gas that comprises O2; - a high-temperature steam electrolysis unit receiving, as input, a first stream comprising water vapour and supplying, as output, a second stream comprising O2 gas and a third stream comprising H2 gas. The invention is characterised in that the plant further comprises a water vapour forming unit (3) comprising means for recovering the heat from the sulphur recovery unit (1), this heat being used to produce at least some of the water vapour of the first stream received by the electrolysis unit.

Description

Installation and process for treating sulfur gases and recovering sulfur by coupling a high-temperature electrolysis unit

[0001] The present invention relates to the field of treatment of gases containing hydrogen sulfide (H2S). In refineries, these gases, known as acid gases, have a composition of 90% to 95% H2S, approximately 5% water, and 0 to 5% carbon dioxide (CO2).

[0002] Regulations regarding the sulphur and hydrocarbon content of emitted gases are becoming increasingly strict and it is important to be able to offer treatment facilities that are both more efficient in reducing the sulphur content of emitted gases, that allow the sulphur to be recovered in a valuable form and that also produce low CO2 emissions. State of the art

[0003] Thus, in order to treat acid gases both to reduce their sulfur content and also to recover this sulfur, it is conventional to use a sulfur recovery process such as that known as the Claus process.

[0004] This process allows the recovery of sulfur from H2S in two stages: - a first purely thermal stage of oxidation of a fraction of H2S to obtain oxygen sulfide (SO 2) , and conversion of the SO2 formed with the remaining H2S, according to the following chemical reactions:2 H2S + 3 O2-> 2 SO2+ 2 H2O2 H2S + SO2-> 3 S + 2 H2O, and- a second stage of reaction of the remaining fraction of H2S with the SO2 produced in the first stage in several catalytic stages, which allows the recovery of the sulfur according to the following reaction:2 H2S + SO2-> 3 S + 2 H2O.

[0005] Thus, during the thermal stage of the Claus process, approximately 60 to 70% of the sulfur is recovered and the temperature during this thermal stage reaches approximately 925°C. The remaining sulfur is then recovered during the catalytic stages in which the remaining hydrogen sulfide (H2S) reacts with the sulfur dioxide (SO2) formed during the thermal stage. The temperature during this catalytic phase is between 150°C and 400°C, and preferably between 180°C and 340°C.

[0006] A Claus process typically uses air to carry out the combustion stage. Studies have shown that O2-enriched air promotes the operation of the thermal stage.

[0007] Document WO-A-2023 / 161611 describes a sulfur recovery system comprising a sulfur recovery unit in which oxygen-containing gas is supplied at the inlet of the unit to enable a Claus process to be carried out. In order to provide this O2 enrichment, the sulfur recovery unit is coupled to at least one solid oxide electrolysis cell known by the acronym SOEC corresponding to the English name "Solid Oxide Electrolysis Cell".

[0008] Such a SOEC comprises an anode, a cathode and an electrolyte. Water is introduced into this cell, particularly in the form of steam, which produces dioxygen, more commonly known as oxygen, O2, and dihydrogen, more commonly known as hydrogen, H2, according to the following reactions: 2 H2O -> 2 H2+ O2 and the oxygen-enriched gas from the SOEC is then led to the sulfur recovery unit for the implementation of the thermal stage of the Claus process. This improves the operation of the sulfur recovery unit to treat even more sulfur dioxide. Such an installation makes it possible to increase the sulfur recovery treatment but remains expensive in terms of energy to produce the oxygen-enriched gas.

[0009] Therefore, it is also appropriate to propose a sulfur gas treatment and sulfur recovery facility with improved energy and ecological impact.

[0010] To this end, the invention relates to an installation for treating gases containing hydrogen sulfide (H2S) comprising:- a Claus-type sulfur recovery unit, said sulfur recovery unit receiving at the inlet: a first flow comprising a gas containing H2S and a second flow comprising a gas comprising O2,- a high-temperature steam electrolysis unit: receiving at the inlet a first flow comprising water vapor and supplying at the outlet a second flow comprising O2 gas and a third flow comprising H gas 2, characterized in that said installation further comprises a water vapor formation unit comprising means for recovering the heat from the sulfur recovery unit, this heat being used to produce at least part of the water vapor from the first flow received by the electrolysis unit.

[0011] Thus, advantageously, the installation according to the invention makes it possible to limit energy costs by using the heat produced in the sulfur recovery unit at the thermal and catalytic stages so as to recover this heat to produce high-temperature water vapor which is then used in the high-temperature electrolysis unit.

[0012] According to a preferred embodiment, the second flow at the outlet of the high temperature water vapor electrolysis unit comprising O2 gas is connected to the second flow comprising a gas comprising O2 received en entrée de l’unité de récupération du soufre.

[0013] The invention therefore relates to an installation for treating sulphur gases and recovering sulphur by coupling a high-temperature electrolysis unit.

[0014] Advantageously, the installation according to the invention thus makes it possible to produce pure O2 gas, at the outlet of the water vapor electrolysis unit to supply the sulfur recovery unit with this O2 gas, either directly or by mixing with ambient air, thus improving the efficiency of the sulfur recovery unit.

[0015] The heat recovery means of the water vapor formation unit comprise at least one heat transfer device such as a heat exchanger.

[0016] According to an alternative embodiment, the high-temperature electrolysis unit can receive a fourth air flow at the inlet, the second flow at the outlet of said high-temperature electrolysis unit then comprising an O2-rich gas at the outlet.

[0017] According to one embodiment, the second flow at the outlet of the electrolysis unit comprising pure O2 gas (100% O2) or O2-rich gas (<100% O2) is connected to a flow comprising air to form, by mixing with the air, the second flow comprising air (gas) enriched with oxygen at the inlet of the sulfur recovery unit.

[0018] Alternatively, the second stream at the outlet of the electrolysis unit comprising O2 gas is conducted directly to the sulfur recovery unit, in particular in a combustion sub-unit, to constitute the second stream comprising the O2 gas at the inlet of said sulfur recovery unit.

[0019] According to one embodiment, the heat recovery means of the water vapor formation unit comprise at least one heat transfer device such as a heat exchanger.

[0020] Preferably, the high temperature steam electrolysis unit is a solid oxide electrolyser known by the English acronym SOEL corresponding to “Solid Oxide Electrolyser”.

[0021] The Claus-type sulfur recovery unit comprises a combustion subunit and a catalysis subunit. The water vapor formation unit comprises means for collecting heat from said combustion subunit and / or from said catalysis subunit. These heat collection means are preferably means for collecting the water vapor produced in said combustion subunit and / or from said catalysis subunit.

[0022] According to one embodiment, the water vapor formation unit comprises:- a first circuit configured to receive a so-called outlet fluid comprising water in the form of a gaseous flow,- a second circuit configured to receive a heat transfer fluid,- a third circuit configured to receive a so-called inlet fluid at the inlet,- a first heat transfer device configured to be able to transfer heat from said inlet fluid to said heat transfer fluid in order to increase the temperature of said heat transfer fluid,- a second heat transfer device configured to be able to transfer heat from said heat transfer fluid to a flow of said outlet fluid in the gaseous state in order to increase the temperature of this gaseous flow,the so-called inlet fluid consisting of a flow of water vapor at the outlet of the sulfur recovery unit;and- the so-called outlet fluid of said water vapor production unit constituting the first flow comprising water vapor at the inlet of the high-temperature electrolysis unit.;

[0023] Said water vapor formation unit further comprises a water inlet, a degasser for removing gases dissolved in the water, an evaporator for converting the water to a gaseous state, in the form of saturated water vapor, a superheater device as a second heat transfer device for transferring heat from the heat transfer fluid to the water vapor and thus increasing the temperature of the water vapor at the outlet.

[0024] The installation according to the invention has many advantages. Thus, H2 and solid sulfur are produced as recoverable products. The waste gases leaving the installation are gases rich in H2O, therefore less harmful and requiring less treatment.

[0025] In addition, the treatment of NOx in waste gases is simplified depending on the reduction or absence of N2 in the gas supplying the combustion, this NO content x which can be reduced to near zero when the flue gas consists only of O2.

[0026] The efficiency of the Claus-type sulfur recovery process is also improved, since using more O2 promotes the following reaction in the thermal step: 2 H2S + 3 O2-> 2 SO2 + 2 H2O.

[0027] In addition, smaller catalytic units can be used to process the same amount of H2S-rich gas or process more gas with existing units, for example. Finally, H2 is produced at high efficiency (thermal recovery).

[0028] According to a second embodiment of the installation according to the invention, said installation further comprises a hydrodesulfurization unit receiving at its inlet a flow of H2 gas, consisting of the flow of H2 gas at the outlet of the high-temperature electrolysis unit, said hydrodesulfurization unit further receiving at its inlet a flow of sulfur-rich hydrocarbons and providing, at its outlet, a flow of sulfur-poor hydrocarbons and a flow of a gas rich in hydrogen sulfide (H2S), which, in turn, is led to the inlet of the sulfur recovery unit.

[0029] Thus, advantageously, in this hydrodesulfurization unit, the H2 gas from the electrolysis unit is used to react with sulfur-rich hydrocarbons to form H2S, and a sulfur-poor hydrocarbon stream.

[0030] The reactor operating conditions are approximately 350-400 °C, under a pressure of 30-80 bar. Advantageously, the heat produced in the hydrodesulfurization unit can be recovered to feed the heat recovery unit for the production of water vapor.

[0031] Advantageously, this embodiment of the installation according to the invention has additional advantages to those already described above.

[0032] This facility therefore makes it possible to produce low-sulfur hydrocarbons with a low carbon footprint.

[0033] In addition, the production of H2 gas has a very high efficiency with recoverable heat. Indeed, the production of low-sulfur hydrocarbons has a low carbon footprint since the H2 gas used does not come from fossil raw materials but from the electrolyser which uses water vapor supplied by the installation itself.

[0034] The invention also relates to a method for treating gas containing hydrogen sulfide (H2S) intended to be implemented in an installation according to the invention, comprising: a step of recovering sulfur in a Claus-type sulfur recovery unit receiving at the inlet a first flow comprising a gas containing H2S and a second flow comprising O2 gas, a step of high-temperature electrolysis of water vapor in a high-temperature electrolysis unit to produce O2 gas and H2 gas, a step of forming water vapor by recovering heat from the sulfur recovery unit, this heat being used to produce at least part of the water vapor received at the inlet of the electrolysis step.

[0035] The water vapor received at the inlet of the high-temperature electrolysis unit is a stream of water vapor produced at the outlet of the water vapor formation unit in which the temperature of a stream of water vapor is increased by heat transfer from a heat transfer fluid whose temperature has been increased by heat transfer from a stream of water vapor at the inlet of said water vapor formation unit, collected at the outlet of the sulfur recovery unit.

[0036] The method according to the invention may further comprise a hydrodesulfurization step comprising the reaction of a sulfur-rich hydrocarbon stream with H2 gas to form at the outlet a sulfur-poor hydrocarbon stream and a H2S-rich gas stream, the inlet H2 gas stream being constituted by the H2 gas stream at the outlet of the high-temperature electrolysis of water vapor and the H2S stream generated by the hydrodesulfurization step being treated in the sulfur recovery step.

[0037] The invention will be well understood and other aspects and advantages will appear clearly on reading the following description, given by way of example with reference to the attached drawing plate in which the figures represent:

[0038] a schematic representation of the invention according to a first embodiment; and

[0039] a schematic representation of the invention according to a second embodiment.

[0040] As can be seen in the, the installation according to the invention comprises: a sulfur recovery unit 1 of the Claus type comprising a combustion sub-unit 11 and a catalytic treatment sub-unit 12 allowing respectively the implementation of the thermal stage and the catalytic stage of the Claus process.

[0041] The combustion sub-unit 11 comprises a gas inlet EG containing H2S to be treated, an air inlet EA and an O2EO inlet. This O2 inlet is made either directly into the combustion sub-unit 11 or into the air inlet EA to enrich the air with O2.

[0042] The thermal step implemented in the combustion sub-unit 11 allows the following reactions to be carried out: 2 H2S + 3 O2-> 2 SO2 + 2 H2O, 2 H2S + SO2-> 3 S + 2 H2O. In this combustion sub-unit 11, approximately 60 to 70% of sulfur S is recovered at the outlet 13a of said combustion sub-unit 11. Then the gas remaining after cooling enters the catalytic treatment sub-unit 12 which may comprise several condensers implementing the catalytic steps in which the H2S reacts with the SO2 in several steps, between the condensers. The temperature at the catalytic stage is between 180 and 340 °C.

[0043] The remainder of the sulfur is thus recovered at outlet 13b of the sulfur recovery unit 1 in the catalytic stages.

[0044] In order to enrich the air entering the combustion unit 11 with O2, the installation comprises an O2 gas production unit consisting of a high-temperature water vapor electrolysis unit comprising at least one SOEL solid oxide electrolyser 2. The electrolysis unit thus carries out high-temperature electrolysis of water vapor, for example electrolysis of steam at a temperature between 650°C and 850°C. In particular, the electrolysis unit comprises a stack of electrolysis cells, arranged in an enclosure, forming the electrolyser. The stack is maintained at a temperature between 650°C and 850°C.

[0045] Such an electrolyser 2 comprises a plurality of cells comprising an anode, a cathode and an electrolyte as well as at least one water vapour inlet 21. This electrolyser under the effect of an electric current 25 makes it possible to decompose the water vapour molecules into H2 gas and O2 gas. The H2 gas is then evacuated through an outlet 23 while the O2 gas is conducted from an outlet 24 to the combustion sub-unit 11 either to be admitted directly into a combustion chamber or to be mixed with air through the EO inlet at the EA inlet.

[0046] In the Claus-type sulfur recovery process, a large amount of VP water vapor is produced during the thermal step at the combustion subunit 11 and the catalytic step at the catalysis subunit 12. This VP water vapor is collected to form a stream at the outlet of the sulfur recovery unit 1 which is conducted to a water vapor supply / formation unit 3.

[0047] The water vapor supply unit 3 thus comprises means for recovering heat, preferably contained in the water vapor, from the sulfur recovery unit 1, this heat being used to produce high-temperature water vapor to supply said water vapor and feed the high-temperature electrolyzer 2.

[0048] This water vapor formation unit thus comprises, as heat recovery means: - a first circuit supplied by a so-called outlet fluid; - a second circuit configured to receive a heat transfer fluid; - a third circuit supplied by an inlet of so-called inlet fluid consisting of the water vapor VP collected at the outlet of the sulfur recovery unit 1.

[0049] The water vapor VP entering the water vapor formation unit 3 is calorific, that is to say loaded with heat, and this heat is transferred to the heat transfer fluid of the second circuit in order to increase the temperature of said heat transfer fluid by means of a first heat transfer device.

[0050] A second heat transfer device then transfers the heat from the heat transfer fluid to the flow of the so-called outlet fluid consisting of water which is in a gaseous state in order to increase its temperature.

[0051] The so-called outlet fluid consists of water brought into the steam formation unit via an inlet 32. When the water arrives in the liquid state via the inlet 32, for example coming from a water treatment unit (not shown), it is first brought to a degasser which makes it possible to eliminate gases such as oxygen (O2) dissolved in the water. The water thus treated is conveyed to an evaporator which makes it possible to pass into the gaseous state, in the form of saturated steam. This steam is then conducted to a superheating device constituting the second heat transfer device, so as to constitute the hot gas flow at the outlet.The inlet and heat transfer fluids circulating in a heat recovery sub-unit have respective temperatures such that the superheater transfers heat from the heat transfer fluid to the outlet fluid (water vapor) which circulates in the superheater in the form of a gaseous stream, thus increasing the temperature of this gaseous stream.

[0052] Thus, the VP water vapor produced in the sulfur recovery unit 1 is then sent to the heat recovery sub-unit. This heat is then used to heat the water vapor formed in the water vapor formation unit. This high-temperature VPHT water vapor is connected at the outlet of the water vapor formation unit 3 to the electrolyzer 2, to form H2 and O2 then used in the sulfur recovery unit 1.

[0053] Preferably, an additional water vapor inlet is provided at the electrolyser 2 in order to start or complete the water vapor inlet into said electrolyser 2.

[0054] A second installation according to the invention is shown in which the entire installation described in is repeated but also comprises a hydrodesulfurization unit 4 connected to the H2 outlet of the electrolyser 2.

[0055] In this hydrodesulfurization unit 4, the H2 from the electrolyzer 2 is led to the inlet 41 to react with sulfur-rich hydrocarbons brought to the inlet 42. At the end of the reaction, a stream of H2S is formed at the outlet 44 and a stream of sulfur-poor hydrocarbons at the outlet 43. The operating conditions of the reactor are approximately 320-400 °C and under a pressure of 20-200 bars, preferably at a temperature between 350-400 °C and under a pressure between 30-80 bars.

[0056] In this configuration, the hydrodesulfurization unit uses the H2 produced by the electrolyzer 2. Advantageously, the heat produced in the hydrodesulfurization unit is recovered to supply the water vapor formation unit.

[0057] The installation includes conduits forming the circuit for conveying fluid flows between the units of said installation.

Claims

Installation for treating gases containing hydrogen sulfide (H2S) comprising:- a sulfur recovery unit (1) of the Claus type, said sulfur recovery unit (1) receiving at the inlet:a first flow comprising a gas containing H2S anda second flow comprising a gas comprising O2,- a high-temperature steam electrolysis unit (2):receiving at the inlet a first flow comprising water vapor andproviding at the outlet a second flow comprising O2 gas and a third flow comprising H gas 2, characterized in that said installation further comprises a water vapor formation unit (3) comprising means for recovering the heat from the sulfur recovery unit (1), this heat being used to produce at least part of the water vapor of the first flow received by the electrolysis unit. Installation according to claim 1, characterized in that the second flow at the outlet of the high temperature water vapor electrolysis unit (2) comprising O2 gas is connected to the second flow comprising a gas comprising O2 received at the inlet of the sulfur recovery unit (1). Installation according to claim 1 or 2, characterized in that the heat recovery means of the water vapor formation unit (3) comprise at least one heat transfer device such as a heat exchanger. Installation according to one of claims 1 to 3, characterized in that the sulfur recovery unit (1) comprises a combustion sub-unit (11) and a catalysis sub-unit (12), and in that the water vapor formation unit (3) comprises means for collecting heat from said combustion sub-unit (11) and / or from said catalysis sub-unit (12). Installation according to one of claims 1 to 4, characterized in that the high-temperature water vapor electrolysis unit (2) is a solid oxide electrolyser. Installation according to one of claims 1 to 5, characterized in that the second flow at the outlet of the high-temperature water vapor electrolysis unit (2) comprising O2 gas is connected to a flow comprising air to form the second flow comprising O2-enriched gas at the inlet of the sulfur recovery unit. Installation according to one of claims 1 to 5, characterized in that the second flow at the outlet of the high-temperature steam electrolysis unit (2) comprising O2 gas is conducted to the sulfur recovery unit to constitute the second flow comprising pure O2 gas at the inlet of said sulfur recovery unit (1). Installation according to one of claims 1 to 7, characterized in that the water vapor formation unit (3) comprises - a first circuit configured to receive a so-called outlet fluid comprising water in the form of a gaseous flow, - a second circuit configured to receive a heat transfer fluid, - a third circuit configured to receive at the inlet a so-called inlet fluid, - a first heat transfer device configured to be able to transfer heat from said inlet fluid to said heat transfer fluid in order to increase the temperature of said heat transfer fluid, - a second heat transfer device configured to be able to transfer heat from said heat transfer fluid to a flow of said outlet fluid in the gaseous state in order to increase the temperature of this gaseous flow, the so-called inlet fluid consisting of a flow of water vapor at the outlet of the sulfur recovery unit;and- the so-called outlet fluid of said water vapor production unit constituting the first flow comprising water vapor at the inlet of the high-temperature electrolysis unit.; Installation according to claim 8, characterized in that the water vapor formation unit (3) comprises a water inlet (32), a degasser for removing gases dissolved in the water, an evaporator for converting the water to the gaseous state, in the form of saturated water vapor, a superheating device as a second heat transfer device for transferring heat from the heat transfer fluid to the water vapor and thus increasing the temperature of the water vapor at the outlet. Installation according to one of claims 1 to 9, characterized in that it further comprises a hydrodesulfurization unit receiving at its inlet a flow of H2 gas, consisting of the flow of H2 gas leaving the high-temperature electrolysis unit, said hydrodesulfurization unit also receiving at its inlet a flow of sulfur-rich hydrocarbons and providing, at its outlet, a flow of sulfur-poor hydrocarbons and a flow of a gas rich in hydrogen sulfide (H2S), conducted at the inlet of the sulfur recovery unit. A method for treating gas containing hydrogen sulfide (H2S) intended to be implemented in an installation according to one of claims 1 to 10, said method comprising: a step of recovering the sulfur in a sulfur recovery unit (1) of the Claus type receiving at the inlet a first flow comprising a gas containing H2S and a second flow comprising a gas comprising O 2,a high-temperature electrolysis step of water vapor to produce O2 gas and H2 gas, a step of forming water vapor by recovering heat from the sulfur recovery unit (1), this heat being used to produce at least part of the water vapor received at the inlet of the electrolysis step. The method of claim 11, further comprising a hydrodesulfurization step comprising reacting a sulfur-rich hydrocarbon stream with H2 gas to form at the outlet a sulfur-poor hydrocarbon stream and a H2S-rich gas stream, the inlet H2 gas stream consisting of the H2 stream output from the high-temperature electrolysis of water vapor and the H2S stream generated by the hydrodesulfurization step being treated in the sulfur recovery step.

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