WO2016102900A1

WO2016102900A1 - Thermal reduction of sulfur

Info

Publication number: WO2016102900A1
Application number: PCT/FR2015/053737
Authority: WO
Inventors: Benoit Grand; Jacques Mulon; Xavier Paubel; Rémi Tsiava
Original assignee: L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude
Priority date: 2014-12-23
Filing date: 2015-12-22
Publication date: 2016-06-30
Also published as: RU2017123787A; CA2971982A1; CA2971982C; RU2696477C2; RU2017123787A3; FR3030302B1; FR3030302A1

Abstract

The invention relates to a method and a device for the thermal reduction of sulfur dioxide present in a gas to be treated and particularly in industrial gaseous effluents, wherein an oxygen-rich oxidant and a fuel gas are injected into a reaction zone (201) in order to generate an oxy-fuel flame (202) in the reaction zone (201), and wherein the gas to be treated (5) is injected around the oxy-fuel flame (202), a reducing gas (7) being injected in the gas to be treated (5) in or upstream of the reaction zone (201).

Description

Thermal reduction of sulfur

The present invention relates to the thermal reduction of sulfur dioxide and in particular the thermal reduction of sulfur dioxide present in industrial waste gases.

Sulfur dioxide (SO ₂ ) is a pollutant that is very harmful to health and the environment. It is mainly generated by refineries during the desulphurisation of fuels and by the extraction mines of non-ferrous ores (nickel, copper, lead, etc.).

For example, the extraction of one ton of nickel emits 4 tons of SO ₂ and the extraction of copper produces 1 ton of SO ₂ .

To treat these huge volumes of SO ₂ , the thermal reduction is particularly interesting because it can be integrated into the SO ₂ emitter upstream process.

In addition, at the end of the thermal reduction process, the sulfur is recovered mainly elemental form (Sx), and, in combination with a Claus-type process, almost all of the sulfur is recovered in elemental form. Thermal reduction is particularly interesting when SO ₂ sources do not have a sulfuric acid market nearby.

The implementation of the thermal reduction requires the mixing of a reducing agent with the SO ₂ , and optionally water vapor, at high temperature.

The reactions which take place between 1000 ° C. and 1500 ° C. with, for example, methane as reducing agent, are:

CH ₄ + 2SO ₂ = CO ₂ + 2H ₂ O + 1 / x Sx (formation of elemental sulfur)

4CH ₄ + 4SO ₂ = 2CO + 4H ₂ + 2H ₂ S + S ₂ + 2CO ₂ + 2H ₂ O

(formation of H ₂ S, elemental sulfur and syngas)

The goal is to obtain an H ₂ S / SO ₂ flux in a 2: 1 ratio in order to be able to recover a maximum of sulfur present in these two compounds in solid form via a Claus type catalytic process. Thermal reduction of SO2 is described in reference books such as Ullmann's Encylopedia of Industrial Chemistry.

It is also included in the processes described in FR-A-2212290, US-A-4117101, US-A-4207304, WO-A-2012/177281 and WO-A-2013/190335.

US-A-4117101 more particularly discloses a process for the production of sulfur from SO2-containing gases _. . According to this known method, a fuel with a sub-stoichiometric amount of an oxygen-containing gas is burned in a combustion zone in the absence of the gas containing SO 2.

In this way, downstream of the combustion zone, a zone of thermal reduction is carried out at a temperature between 95 ° C. and 1250 ° C. essentially free of oxygen and containing the gaseous effluent of the combustion, this effluent being a reducing gas. The SO2-containing gas is introduced into this reduction zone downstream of the combustion zone so as to effect a thermal reduction of the SO2-containing gas by means of the aforementioned effluent of the combustion.

In this way, a product containing elemental sulfur and other sulfur compounds such as carbonyl sulphide or carbon disulfide is obtained. This product is then contacted with a catalyst at a temperature of 200 ° C to 460 ° C to convert the sulfur carbonyl or carbon disulfide to hydrogen sulfide. Said hydrogen sulfide may in turn be converted to elemental sulfur by reaction with SO2 in a Claus reactor. According to one embodiment, a gas containing hydrocarbon, such as in particular coke oven gas, is also introduced into the reduction zone downstream of the combustion zone.

The present invention aims to provide an improved method of thermal reduction of SO2 and means for its implementation. The present invention more particularly aims to allow a particularly effective thermal reduction of SO2 limiting the amount of soot and generated gaseous by-products, and this by means of a flexible process and easy to implement. To this end, the present invention provides a method of injecting reactants into a reaction zone in which the thermal reduction of SO2 occurs.

Indeed, the realization of the mixture of reactants directly impacts the performance of the heat reduction process such as, in particular, the conversion rate of SO2 into H ₂ S and the rate of production of soot (harmful pollutant for the catalysts in the downstream process) Claus) or finally the quantity of by-products such as COS, CO and H ₂ generated.

According to the injection method according to the invention, the following reagents are injected into the reaction zone:

A gaseous oxidant having an oxygen content of 50% vol to 100% vol,

• a gaseous fuel,

• a gas to be treated containing sulfur dioxide and

"A hydrogenated reducing gas.

The oxidant and the fuel are injected into the reaction zone so as to generate, by combustion of the fuel with the oxidant, an oxy-fuel flame having a longitudinal axis. The gas to be treated is injected into the reaction zone and this around the oxy-fuel flame, and the reducing gas is injected into the gas to be treated inside or upstream of the reaction zone.

In the first case, the hydrogenated reducing gas comes into contact with the gas to be treated in the reaction zone at or downstream of the injection point of the gas to be treated in the reaction zone.

In the latter case, the reducing gas comes into contact with the gas to be treated before the injection of the gas to be treated into the reaction zone.

In the present context, "oxy-fuel flame" is understood to mean a flame generated by the combustion of a fuel with a gaseous oxidant (oxidant) having an oxygen content of at least 50% vol.

The reduction reaction between the SO2 of the gas to be treated and the hydrogenated reducing gas is promoted by the heat generated by the oxy-fuel flame around which the gas to be treated is injected. The reduction reaction between the SO 2 of the gas to be treated and the hydrogenated reducing gas is also promoted by the injection of the reducing gas into the gas to be treated, which ensures an intimate contact between the gas to be treated and the reducing gas and thus improves the effectiveness of the thermal reduction of SO ₂ .

According to an advantageous embodiment, at least some, or all, of the oxidant is injected around the fuel.

Different injection orientations can be envisaged for the injection of the various reactants into the reaction zone: parallel to the longitudinal axis of the flame, convergent with respect to this axis or diverging with respect to this axis.

It has however been found that the efficiency of the thermal reduction can be improved when at least one of the oxidant and the fuel and preferably both are injected into the reaction zone at a divergent angle to the axis. of the oxy-fuel flame, particularly when fuel injection is surrounded by an oxidant injection.

According to an alternative embodiment, the fuel is injected into the reaction zone around a first portion of the oxidant and a second portion of the oxidant is injected into the reaction zone around the fuel. In this case, the fuel and / or the second part of the oxidant and preferably both are advantageously injected into the reaction zone at a divergent angle with respect to the longitudinal axis of the flame.

Other injection configurations for the fuel and the oxidant are, however, conceivable.

The injection speeds of the fuel gas and oxygen are advantageously chosen between 30 and 60 m / s

In order to intensify the contact between the gaseous fuel and the oxidant, the fuel can be injected by means of a multitude of fuel injection openings.

This multitude of fuel injection openings advantageously comprises a series of these injection openings positioned around the longitudinal axis of the oxy-fuel flame, in particular on a circular contour around the longitudinal axis and preferably concentric with the longitudinal axis.

In this geometry and without central oxidant injection inside the fuel injections, it is preferable to add a central injection of combustible gas along the longitudinal axis to limit the soot deposition on the nose of the injection and thus to increase the service life.

The efficiency of the thermal reduction can also be improved by the injection of the gas to be treated into the reaction zone with a rotational movement about the longitudinal axis of the oxy-fuel flame.

Advantageously, the hydrogenated reducing gas is injected through a plurality of reducing gas injection openings which are disposed about the longitudinal axis of the oxy-fuel flame. Said reducing gas injection openings are preferably positioned axisymmetrically with respect to said longitudinal axis.

The gas to be treated may in particular be injected into the reaction zone through a passage, said main passage, which ends in an annular injection opening concentric with the longitudinal axis of the oxyfuel flame. In this case, said annular injection opening of the gas to be treated corresponds to the aforementioned point of injection of the gas to be treated.

In this case, the reducing gas may more particularly be injected through a plurality of reducing gas injection lances, these lances being disposed in the aforementioned main passage and ending:

• Inside the main passage so that the reducing gas comes into contact with the gas to be treated before its injection into the reaction zone through the annular injection opening of the main passage, or

• In the annular injection opening of the main passage for the reducing gas contacts the gas to be treated during the injection of the gas to be treated in the reaction zone.

The lances are advantageously arranged around the longitudinal axis of the oxy-fuel flame, preferably axisymmetrically.

Advantageously, the injection speed of the gas to be treated will be chosen between 5 and 15 m / s, preferably 5 to 10 m / s while the injection rate of the reducing gas will be chosen between 10 and 50 m / s, preferably between 20 and 40 m / s.

The injection method according to the invention is generally part of a process for the recovery of sulfur from the sulfur dioxide-containing process gas.

In this case, the gas to be treated is subjected to a partial reduction of SO 2 by the injection method according to any one of the embodiments described above.

A treated gas containing H ₂ S and SO _{2 is} thus obtained. The treated gas is cooled downstream of the reaction zone, which makes it possible to recover, on the one hand, condensed sulfur and, on the other hand, a cooled gas containing H ₂ S and SO ₂ .

The treated gas can be cooled in a boiler, said recovery boiler, which captures and exploit a portion of the thermal energy of the treated gas from the reaction zone, for example by transforming it into the mechanical or electrical energy or to supply steam to other installations. It is also possible to exploit the captured thermal energy to heat one or more of the reagents before their injection into the reaction zone.

The cooled gas is advantageously subjected to a desulfurization process in a Claus reactor. This makes it possible to recover more sulfur and a desulfurized and therefore less polluting gas.

The injection method according to the invention has the important advantage that it makes it possible to regulate the H2S / SO2 ratio of the treated gas simply by regulating the flow rate of the reducing gas injected into the reaction zone without impacting the flow of fuel gas.

Thus, the release of heat from the flame to the gas to be treated is not affected by this regulation which allows greater flexibility in operation. In particular, when the treated gas is intended to be sent to a Claus reactor, the flow rate of the reducing gas will preferably be adjusted so as to obtain in the treated gas a molar ratio of H 2 S 2 SO 2 between 1, 9 and 2.1, a molar ratio of 2.0 being optimal for the Claus reaction. For better regulation of said ratio, the ratio H2S / SO2 is advantageously determined in the treated gas (before cooling) or in the cooled gas. It is then possible to regulate the flow rate of the reducing gas injected into the reaction zone as a function of the ratio thus determined, preferably so that the molar ratio of H2S / SO2 is between 1, 9 and 2.1.

The processes according to the invention make it possible to treat a large number of gases containing sulfur dioxide, in particular gaseous effluents resulting from industrial processes.

The invention provides in particular a simple means for the partial thermal reduction of SO2 present in SO2-containing gases:

• from petrochemical refineries, including the desulphurisation of petrochemicals such as fuels and other petrochemicals; and

· From melting furnaces (smelters) for non-ferrous ores, and in particular smelting furnaces for nickel, copper or lead ores, etc. such as found near the mines, for example).

The oxygen content of the gaseous oxidant injected into the reaction zone is preferably greater than 80% vol, more preferably greater than 90% vol, or even greater than 95% vol.

The gaseous fuel injected into the reaction zone is advantageously chosen from methane, ethane, propane, hydrogen, a mixture of hydrogen and carbon monoxide and mixtures of at least two of these gaseous fuels. such as natural gas. The hydrogen or the mixture of hydrogen and CO can in particular be derived from the gasification of biomass or waste.

The more hydrogen the fuel contains, the lower the soot formation. The presence of hydrogen in the gaseous fuel, in the form of H ₂ or in chemically bound form in the case of a hydrogenated gaseous fuel, is therefore generally desired.

By hydrogenated reducing gas is meant a gas capable of reacting with SO2 at a temperature between 1000 ° C and 1500 ° C with formation of elemental sulfur and H ₂ S. The hydrogenated reducing gas is preferably selected from the gases listed above in connection with the gaseous fuel.

The more the reducing gas contains hydrogen, the more effective the thermal reduction reaction will be.

H ₂ is the most appropriate reducing gas but generally also the most expensive. It is therefore wise and more environmentally friendly to use as a reducing gas H ₂ or a gas containing H ₂ from alternative sources such as gasification of waste or biomass.

The reducing gas and the gaseous fuel may be identical and come from the same source. The reducing gas may also be different from the combustible gas. In this case, the reducing gas may comprise or not comprise a gas having the same composition as the fuel or vice versa: for example methane and natural gas.

It may sometimes be advantageous to add water vapor (H ₂ O) to the reaction zone to further limit the formation of soot if for example the type of fuel or reducing gas contains a lot of carbon. This addition of water vapor can be done by mixing the steam with the reducing gas and / or by mixing it with the sulfur dioxide-containing gas to be treated.

The invention, however, has the advantage that the formation of soot is particularly low, which is particularly important when the thermal reduction is followed by a Claus-type process, even without the addition of steam to the reducing gas and / or to the gas to be treated.

The oxy-fuel flame advantageously has a richness

(In English: "fuel-oxidant equivalent ratio") from 0.5 to 2.0, preferably from 0.80 to 1, 50 and even more preferably from 0.90 to 1, 10.

Wealth is defined as the ratio between, on the one hand, the actual ratio between the fuel flow and the oxidant flow, and on the other hand, the strictly stoichiometric ratio between the flow rate of this fuel and the flow rate of this oxidant. .

The adjustment of the richness is a setting parameter of the injection of the oxidant and the fuel on the release of heat by the flame oxy-fuel and thus the performance of the thermal reduction reaction.

According to a first embodiment, the oxy-fuel flame is stoichiometric (richness = 1).

According to another embodiment, the oxy-fuel flame is low in oxygen (rich in fuel), that is to say with a richness greater than 1, preferably greater than 1 and less than or equal to 2. In this case, In this case, the combustion of the fuel in the oxy-fuel flame is a partial combustion and (unburnt thus formed such as H ₂ present in) the combustion gases generated by the oxy-fuel flame can act as an additional reducing gas for the thermal reduction. SO2.

In yet another embodiment, the oxy-fuel flame is rich in oxygen (low in fuel), i.e., with a richness of less than 1, preferably greater than 0.5, and less than 1.0 . In this case, the residual oxygen that did not participate in the combustion due to lack of fuel will burn the hydrogenated reducing gas to release more heat energy in the heart of the reaction zone.

The temperature of the gases in the reaction zone is typically from 1000 ° C to 1400 ° C, preferably from 1100 ° C to 1300 ° C.

The injection method according to the invention fits perfectly in other steps to be part of a process for the recovery of elemental sulfur gas to be treated.

The present invention therefore also covers a process for recovering sulfur from a sulfur dioxide-containing process gas in which the gas to be treated is subjected to a partial thermal reduction of SO 2 as described above. The gas resulting from the reaction zone thus obtained, having therefore undergone a partial thermal reduction of the SO 2, is hereinafter called the "treated gas".

The treated gas contains H ₂ S and SO 2. This treated gas is cooled to recover condensed sulfur and a cooled gas still containing the H ₂ S and SO 2 of the uncooled treated gas. The treated gas may more particularly be cooled in a heat recovery boiler located downstream of the reaction zone. This allows a thermal energy recovery of the treated gas in the form of steam, or in the form of mechanical or electrical energy.

After separation of the elemental sulfur produced by the thermal reduction, the cooled gas is directed to a catalytic reactor of the Claus type, with recovery of sulfur and a desulphurized gas.

The sulfur recovered in elemental form in the Claus process is derived from the residual sulfur present in the cooled gas. The gas recovered from the Claus process is essentially desulphurized and therefore significantly less polluting than the gas to be treated initially.

The present invention more particularly allows the partial thermal reduction of SO2 in gases to be treated and in particular gaseous effluents:

• from petrochemical refineries, in particular during the desulphurisation of fuels or other petrochemical products, or · from smelting furnaces for non-ferrous ores, and in particular smelting furnaces for nickel ores, copper, lead, etc. such as found near mines, for example.

Such a gaseous effluent may be subjected to a purification treatment, dedusting, etc. before being subjected to the process according to the invention for recovering elemental sulfur from said gases.

The present invention also relates to an injection assembly adapted for implementing the injection method according to the invention.

The injection assembly includes a central burner, a peripheral injector and at least one additional injector.

The central burner is adapted for injecting an oxidant and a fuel into a reaction zone downstream of the injection assembly. It is capable of generating, by combustion of the fuel with the oxidant, a flame having a longitudinal axis.

The central burner itself generally has a longitudinal axis called "burner" which coincides with the longitudinal axis of the flame. Unless otherwise indicated, reference to a "longitudinal axis" is a reference to the longitudinal axis of the flame. The peripheral injector of the injection assembly is suitable for injecting a gas to be treated containing sulfur dioxide into the reaction zone and this around the oxy-fuel flame generated by the central burner.

The at least one additional injector of the injection assembly is adapted for injecting a hydrogenated reducing gas inside the peripheral injector, at an injection opening of the peripheral injector or still in the reaction zone.

The at least one additional injector may open into the peripheral injector, at the or an injection opening of the peripheral injector and / or be positioned inside the peripheral injector so that the hydrogenated reducing gas mixes with the gas to be treated injected by the peripheral injector, in particular before or at the point of injection of the gas to be treated. The central burner advantageously comprises an oxidant injector and a fuel injector for injection into the reaction zone of the oxidant and the fuel, respectively.

In one embodiment, the oxidant injector surrounds the fuel injector.

According to another embodiment, the central burner comprises a first oxidant injector surrounded by the fuel injector and a second oxidant injector surrounding the fuel injector.

Other configurations are however possible for the fuel injector (s) and the oxidizer nozzle (s) of the central burner.

For the operation of the injection assembly, the oxidant injector or injectors are connected to an oxidant source and more particularly to a source of an oxidant having an oxygen content of 50% vol to 100% vol. the fuel injector (s) being connected to a source of a gaseous fuel.

In the present context, two elements are "connected" when they are connected so as to allow the flow of a fluid from one of the two elements to the other of the two elements, for example by means of a pipe for the transporting said fluid. The oxidant and fuel injectors are preferably such that at least a portion of the oxidant and / or fuel is injected into the downstream reaction zone with a direction of injection diverging with respect to the longitudinal axis.

Thus, when the central burner comprises a fuel injector that surrounds the oxidant injector, the fuel injector and / or the oxidant injector advantageously have an injection nozzle diverging with respect to the longitudinal axis in the directions of injection.

When, on the other hand, the central burner comprises two oxidant injectors, one of which (the first) is surrounded by the fuel injector and the other (the second) surrounds the fuel injector, the injector fuel and the second oxidant injector are advantageously provided with such a diverging nozzle.

The central burner, and more particularly the fuel injector, preferably has a multitude of fuel injection openings. In this case, at least some of said fuel injection openings are advantageously positioned on a substantially circular contour around the longitudinal axis.

In this geometry and without central injector of oxidant, it is preferable to add a central injector of combustible gas along the longitudinal axis to avoid the deposition of soot on the injector.

The peripheral injector advantageously comprises a gyration device adapted for rotating around the longitudinal axis of the gas to be treated injected by the peripheral injector into the reaction zone. The turning device may in particular comprise rotating valves.

The peripheral injector terminates in an injection opening, said injection opening being preferably an annular injection opening concentric with the longitudinal axis.

In order to improve the efficiency of the thermal reduction of the effluent, the injection assembly advantageously comprises a multitude of additional injectors as described above. The additional injectors of this multitude thus open: i. inside the peripheral injector, and / or

ii. in the injection opening of the peripheral injector, that is to say in the same plane perpendicular to the longitudinal axis.

The additional injectors preferably open axisymmetrically about the longitudinal axis.

For the use of the assembly according to the invention in a process of thermal reduction of a gas to be treated containing sulfur dioxide:

The central burner is connected to a source of an oxidant having an oxygen content of 50% vol to 100% vol and a source of a gaseous fuel;

• the peripheral injector is connected to a source of the gas to be treated containing sulfur dioxide; and

The at least one additional injector is connected to a source of a hydrogenated reducing gas.

As already indicated above with respect to the process according to the invention:

The sulfur-containing gas to be treated may be a gaseous effluent from a petrochemical refinery or a non-ferrous ore smelter;

The gaseous fuel is advantageously chosen from methane, ethane, propane, hydrogen or mixtures of hydrogen and carbon monoxide, which may in particular be derived from biomass or waste, and the mixtures of minus two of these fuels such as natural gas;

The oxidant, which has an oxygen content of at least 50% vol, preferably contains more than 80% vol of oxygen, more preferably more than 90% vol, or even more than 95% vol; and

The hydrogenated reducing gas is preferably chosen from methane, ethane, propane, hydrogen or mixtures of hydrogen and carbon monoxide, and mixtures of at least two of these gases, such as, for example, natural gas. The reducing gas and the gaseous fuel may be identical. The reducing gas may also be different from the combustible gas. In this case, the reducing gas may comprise or not comprise a gas of the same composition as the fuel or vice versa.

The injection assembly typically also includes controllers for regulating the flow rates of the different fluids to the injection assembly.

When the reducing gas has the same composition as the gaseous fuel or comprises a gas having this composition (in combination with other components such as, for example, water vapor), the central burner (or even the fuel injector) this) and the at least one additional injector are advantageously connected to the same fuel source.

The injection assembly is normally provided with a controller regulating the flow rates of fuel, oxidant, the gas to be treated and the hydrogenated reducing gas injected by the injection assembly. The controller therefore also regulates the richness of the flame (oxy-fuel flame) generated by the central burner. When the fuel and the reducing gas come from the same fuel source, the controller also regulates the ratio between:

(i) the fuel flow to the central burner and

(ii) the flow rate to the at least one additional fuel injector to be injected as the hydrogenated reducing gas and,

(iii) the ratio between the two flows.

The present invention also relates to an installation for the recovery of sulfur from a gas called "gas to be treated" containing sulfur dioxide.

The plant according to the invention comprises a sulfur dioxide thermal reduction chamber equipped with an assembly according to any one of the embodiments described above. Said thermal reduction chamber comprises an outlet for the evacuation of the treated gas, that is to say the gas having undergone a thermal reduction of SO2.

The installation advantageously also comprises a cooling device for cooling the treated gas. For this purpose the cooling device is connected to the treated gas outlet of the reduction chamber. The cooling device in turn comprises an outlet for evacuating the cooled gas from the cooling device and a sulfur outlet for discharging the condensed sulfur into the cooling system. The cooling device is advantageously a recovery boiler.

The plant according to the invention advantageously also comprises an installation for further desulfurization of the cooled treated gas.

Thus, the plant preferably comprises a Claus reactor for the desulfurization of cooled gas from the cooling device and for recovering the sulfur thus obtained. For this purpose, the Claus reactor is connected to the cooled gas outlet of the cooling device.

The plant according to any one of the embodiments described above conveniently comprises control equipment. Said regulating equipment includes a detection device for determining the ratio between the H ₂ S and the SO 2 in the treated gas at the treated gas outlet of the thermal reduction chamber or in the gas cooled at the cooled gas outlet of the cooling device.

The regulation equipment then advantageously also comprises a flow controller adapted to regulate the flow rates of the fluids supplied to the injection assembly, said flow controller preferably being able to regulate the flow of hydrogenated reducing gas supplied to the assembly. injection according to the ratio between H ₂ S and SO 2 determined by the aforementioned detection device. The flow controller advantageously regulates the flow rates supplied to the injection assembly and in particular the flow rate of hydrogenated reducing gas supplied to the injection unit so that the H2S / SO2 ratio detected is 1, 9 to 2.1, preferably 2.0.

The invention makes it possible to better control the reactions of the thermal reduction by uncoupling at least partially (a) the release of the heat necessary for the thermal reduction and (b) the mixing of the gas to be treated containing sulfur dioxide with the reducing gas hydrogen. This also reduces the formation of soot. Indeed, the invention makes it possible to create a first heat-generating zone produced by an oxy-fuel flame (combustion zone), which can notably be close to stoichiometry (see above), and a second zone in which the gas to be treated containing SO2 is mixed with the products of combustion of the oxy-fuel flame and with the hydrogenated reducing gas and in which the SO2 present in the gas to be treated reacts with the reducing gas with formation of elemental sulfur among others.

It should be noted that the injection configuration of the method according to the invention and the structure of the injection assembly according to the invention have the advantage of allowing a particularly compact and easy to control system, for example with the together injections into the reaction zone on one side of a thermal reduction reactor.

The present invention and its advantages will be better understood in the light of the example below, reference being made to FIGS. 1 and 2 in which:

• Figure 1 is a schematic representation in longitudinal section of an injection assembly according to the invention.

FIG. 2 is a schematic representation of the use of the injection assembly according to the invention in an installation for recovering sulfur from a gas to be treated.

The injection assembly 10 has a longitudinal axis X-X. It is composed in the center of an oxy-fuel central burner 20 for stoichiometric combustion (or non-stoichiometric, see above) of a gaseous fuel, such as natural gas with an oxygen-rich oxidant (> 50% flight). The central burner comprises a first passage 21 located in the center of the burner and allowing the transport of a fuel and more particularly methane or natural gas to a first injection nozzle 22.

This injection nozzle has a first central injection opening 22a surrounded by a ring of injection openings 22b. The central burner also comprises a second passage 25 of annular section which surrounds the first passage 21 and which allows the transport of an oxidant rich in oxygen and more particularly oxygen purity industrial (95% vol 0 ₂ ) to a second injection nozzle 26 which surrounds the first injection nozzle 22.

In the illustrated example, the injection direction of the first and second injection nozzles is parallel to the longitudinal axis X-X.

It may, however, be preferable to use first and / or second nozzles 22, 26 such that the directions of injection of the fuel and oxidant jets injected by said nozzles 22, 26 into the reaction zone 1 are divergent relative to each other. to the axis XX (in the direction of injection of said jets).

The gas to be treated containing SO ₂ is fed to the reaction zone 1 by a peripheral injector 30 terminating in a ring-shaped peripheral injection opening. The peripheral injector 30 comprises rotating fins 31 of the gas jet to be treated containing SO ₂ before it is injected into the reaction zone 1.

Through this peripheral injector 30, additional injectors 40 of hydrogenated reducing gas are arranged axisymmetrically with respect to the longitudinal axis X-X.

The whole is surrounded by a refractory block 50. Such a refractory block facilitates the integration of the injection assembly into one of the walls surrounding the reaction zone in a thermal reduction reactor.

The swirling motion (often referred to by the English origin word "swirlé") given to the jet of the gas to be treated containing SO ₂ allows at least partly to dilute the combustion zone, that is to say the oxy flame. - fuel 2 with the gas to be treated containing SO ₂ , thus limiting the formation of soot by lowering the temperature peaks.

This desirable effect can be enhanced by injecting the gas to be treated with an injection speed whose component parallel to the longitudinal axis (called "longitudinal component") is less than or equal to the longitudinal component of the oxy-fuel flame speed. .

In the illustrated case, an excess of the gaseous fuel injected by the central burner is injected as a hydrogenated reducing gas through the additional injectors 40. The injection direction of said reducing gas is parallel to the longitudinal axis XX and its speed of rotation. injection (and therefore the longitudinal component of this speed) is greater than the longitudinal component of the speed of the gas to be treated. These two elements help to maximize the dilution of the reducing gas with the gas to be treated containing SO2 downstream and around the combustion zone, that is to say downstream and around the oxy-fuel flame 2 and thus limit the concentration of fuel in high temperature areas responsible for soot formation.

As indicated above, the hydrogenated reducing gas corresponds to an excess of fuel. The mixture between the gas to be treated containing SO 2 and the hydrogenated reducing gas not being upstream, in or by means of the central burner, the present invention allows a great flexibility of operation on the ratio between, on the one hand, the SO2 present in the gas to be treated and secondly, the reducing gas and in particular the hydrogen present in the reducing gas while providing the necessary heat input for SO2 thermal reduction reactions and this even for variable flow rates of gas to be treated and / or for variable SO2 contents of the gas to be treated. The SO2 / hydrogen ratio drives the H2S / SO2 ratio at the outlet of the reaction zone.

As illustrated in FIG. 2, an injection assembly 210 according to the invention can be installed in a thermal reduction reactor 200 having inside a reaction zone 201.

The injection assembly 210 and supplied with gas to be treated containing 5

SO2 _, oxygen-rich oxidant 6 and natural gas 7. A portion of the natural gas supplied to the injection assembly 210 is the fuel supplied to the central burner of the injection assembly 210 to generate the oxy-fuel flame. fuel 202 and another portion of the natural gas is supplied to the injection assembly 210 as a hydrogenated reducing gas.

As described above, it is also possible in some cases to supply the injection assembly with water vapor, particularly when the nature of the gas to be treated and / or the fuel is likely to promote the formation of water. soot.

The injection assembly 210, and more particularly its central burner, is operated so as to maintain the reaction zone 201 at a temperature between 1300 ° C and 1500 ° C suitable for the thermal reduction of SO ₂ . The treated gas 220 from the reactor 200, which contains SO 2 and H ₂ S, is directed to an energy recovery boiler 250 into which thermal energy is recovered from the treated gas 220, the gases being there cooled and the elemental sulfur Sx obtained by the thermal reduction in the reactor 200 is recovered.

Downstream of the energy recovery boiler 250, the cooled gas 230 is directed to a catalytic reactor of the Claus 260 type for the recovery of elemental sulfur Sx by reaction of SO2 with H ₂ S present in the cooled treated gas 230 of in order to obtain a final gas 240, downstream of the Claus reactor 260 which is essentially free of sulfur.

Thanks to the present invention, the production of soot in the thermal reduction reactor 200 is very limited, which greatly prolongs the longevity of the catalyst in the Claus 260 reactor and limits the consumption of natural gas and oxygen per unit of gas to be treated. (better efficiency thanks to the absence of steam acting as a heat sink)

The method and the injection assembly according to the invention have been tested in an installation as illustrated in FIG. 2 under different conditions.

Example

An injection assembly according to the invention was installed in a cylindrical reactor for the thermal reduction of SO2. The injection assembly used was equipped with a device for gyration / rotation of the gas stream containing SO 2 gas to be treated injected into the reactor by means of the peripheral injector. The multiples (8 in number) of reducing gas injectors, called additional injectors, were distributed over a circumference of said peripheral injector and their respective outlet faces were situated in the same plane as the injection opening of the peripheral injector. the gas to be treated.

The reactor in which the injection assembly was installed consisted of two successive zones of volume and equivalent length and separated by a flow restriction between the two successive zones. The injection assembly was mounted at the inlet of the first reaction zone and set back relative to the internal refractory wall of the reactor. In the case of In this example, this shrinkage was approximately equal in length to the diameter of the aperture block of the injection assembly.

The central burner of the injection assembly and the additional injectors of hydrogenated reducing gas were fed with natural gas (hereinafter GN) of the following composition:

Mol Component

C1 91.93

C2 3.54

C3 1 .98

C4 0.52

C5 + 0

N2 1 .51

CO ₂ 0.52

Table 1

The oxygen supplying the central burner of the injection unit had a purity of 91% vol.

The gas to be treated consists of 99.9% vol of SO2.

Following ignition of the burner and reactor heating, the reactant flow rates were set as follows:

Oxygen = 39.5 Nm3 / h (at 91% purity)

GN to the central burner (combustible gas) = 17 Nm3 / h

Gas to be treated containing SO ₂ = 122 Nm3 / h preheated to 140 ° C

GN (Hydrogenated reducing gas to additional injectors) =

70 Nm3 / h preheated to 50 ° C

The temperature in the two zones of the reactor was of the order of 1150 ° C.

In the reactor, the SO2 contained in the gas to be treated was partially reduced to H ₂ S and small amounts of other by-products such as COS and CS2. Another part of SO2 was directly reduced to elemental sulfur in gaseous form. The flow of reaction products from the reactor then passed through an energy recovery boiler which allows to lower their temperature and thus isolate the elemental sulfur by condensation.

The composition (in% by volume) of the gaseous flow at the outlet of the boiler is given in Table 2.

This stream was then injected into a conventional CLAUS reactor to react the SO2 with the H ₂ S and to recover the remainder of sulfur in elemental form.

Under these operating conditions, no soot was measured or suspected either in the thermal reduction reactor or in the Claus reactor.

It has thus been found that the invention surprisingly allows the thermal reduction of the SO 2 present in a gas to be treated with a good constant quality of the recovered sulfur and essentially without the production of soot, even without the addition of water vapor to the reducing gas. , and this in particular thanks to the specific injection configuration used.

Note also the high sulfur recovery rate and the low content of COS & CS2 in the gas leaving the reaction zone / thermal reduction reactor (COS <4% & CS2 <2% by volume).

Claims

claims

1. Injection method for thermal reduction of sulfur dioxide in a reaction zone (1, 201), wherein a gaseous oxidant (6) having an oxygen content of 50% vol to 100 vol% is injected, a gaseous fuel (7), a gas to be treated (5) containing sulfur dioxide and a hydrogenated reducing gas (7) and wherein:

The oxidant (6) and the fuel (7) are injected into the reaction zone (1, 201) so as to generate an oxy-fuel flame (2, 202) having a longitudinal axis X-X,

The gas to be treated (5) is injected around the oxy-fuel flame (2, 202) into the reaction zone (1, 201), and

The reducing gas (7) is injected into the gas to be treated (5) in or upstream of the reaction zone (1, 201).

2. The method of claim 1, wherein at least a portion of the oxidant (6) is injected around the fuel (7).

A process as claimed in any one of the preceding claims, wherein the fuel (7) is injected by means of a plurality of fuel injection openings (22a, 22b), at least some of said fuel injection openings fuel (22b) being advantageously positioned on a circular contour around the longitudinal axis XX, with preferably also a fuel injection opening (22a) at the center of the circular contour.

4. Method according to one of the preceding claims, wherein the gas to be treated (5) is injected into the reaction zone (1, 201) with a rotational movement about the longitudinal axis XX of the oxy-fuel flame (2, 202).

5. Method according to one of the preceding claims, wherein the gas to be treated (5) is injected into the reaction zone (1, 201) through a passage of the gas to be treated (30) ending in an opening of concentric annular injection with the longitudinal axis XX of the oxy-fuel flame (2).

6. A method according to claim 5, wherein the reducing gas (7) is injected through a plurality of reducing gas injection lances (40) disposed in the passage of the gas to be treated (30), said lances (40). terminating within the passage of the gas to be treated (30) and / or in the annular injection opening, said lances (40) being preferably axially symmetrical about the longitudinal axis XX of the oxy flame. fuel (2).

7. A process according to any one of the preceding claims, wherein the gas to be treated (5) is a gas containing sulfur dioxide from a petrochemical refinery or a non-ferrous ore melting furnace.

Injection assembly comprising:

A central burner (20) for the injection of an oxidant (6) and a fuel (7) into a reaction zone (1, 201), said burner (20) being capable of generating a flame having a longitudinal axis XX by the combustion of the fuel with the oxidant,

A peripheral injector (30) adapted for injecting a gas (5) containing sulfur dioxide around the flame (2, 202) into the reaction zone (1, 201), and

At least one additional injector (40) opening into or located in the peripheral injector (30) and adapted for the injection of a hydrogenated reducing gas (7) inside the peripheral injector (30) or in the reaction zone (1, 201) downstream of the peripheral injector (30).

9. The assembly of claim 8, wherein the central burner (20) comprises an oxidant injector (25) and a fuel injector (21), the oxidant injector (25) preferably surrounding the injector fuel (21).

10. The assembly of claim 8, wherein the central burner (20) comprises a first oxidant injector, a fuel injector surrounding the first oxidant injector and a second oxidant injector surrounding the fuel injector.

1 1. Assembly according to one of Claims 8 to 10, in which the peripheral injector (30) comprises a gyration device (31) adapted for rotation around the longitudinal axis XX in the reaction zone (1, 201 ) of the gas to be treated (5) injected by said peripheral injector (30).

12. Assembly according to one of claims 8 to 1 1, comprising a plurality of additional injectors (40) opening (i) inside the peripheral injector (30) and / or (ii) with the injector peripheral (30) in the same plane perpendicular to the longitudinal axis XX, said additional injectors (40) preferably opening axisymmetrically about the longitudinal axis XX.

An assembly according to any one of claims 8 to 12, wherein:

• the central burner (20) is connected to a source of an oxidant (6) having an oxygen content of 50% vol to 100% vol and a source of a gaseous fuel;

• the peripheral injector (30) is connected to a source of a gas to be treated (5) containing sulfur dioxide; and

The at least one additional injector (40) is connected to a source of a hydrogenated reducing gas (7).

14. Installation for the recovery of sulfur from a gas to be treated containing sulfur dioxide, installation comprising:

A sulfur dioxide thermal reduction chamber (200) equipped with an assembly (210) according to any of claims 8 to 13 and including a treated gas outlet (220), and

A cooling device (250) for cooling the treated gas (220) connected to the treated gas outlet (220) of the reduction chamber (200), said cooling device (250) having a cooled gas outlet ( 230) and a sulfur outlet for discharging condensed sulfur into the cooling system (250).

15. Plant according to claim 14, comprising a Claus reactor (260) for the desulfurization of cooled gas (230) from the cooling device (250) and for the recovery of the sulfur thus obtained, said Claus reactor (260) being connected to the cooled gas outlet (230) of said cooling device (250).