Method and facility for treating combustion gases originating in particular from a fluidised-bed catalytic cracking (FCC) process regenerator operating in complete combustion mode

Abstract

The invention relates to a method for treating combustion gases originating from the combustion of coke deposited on catalytic particles, the method comprising: (a) a step of regenerating the catalytic particles in a regenerator (10), during which the coke present on the catalytic particles is combusted in the presence of an oxidising gas containing dioxygen under complete combustion conditions, and combustion gases containing at least CO2 and CO are produced; (b) a step of recovering the heat from the combustion gases of the regenerator (10); (c) a step of purifying the combustion gases cooled in step (b) that is carried out in a purification unit (30). Furthermore, dioxygen is added to the oxidising gas used in step (a), which contains a portion of the purified combustion gases leaving the purification unit (30) in step (c).

Description

[0001] DESCRIPTION

[0002] TITLE: PROCESS AND PLANT FOR TREATING COMBUSTION GAS, IN PARTICULAR FROM A FLUIDIZED BED CATALYTIC CRACKING (FCC) PROCESS REGENERATOR OPERATING IN TOTAL COMBUSTION MODE

[0003] Field of invention

[0004] The present invention lies in the field of capturing carbon dioxide emitted by fumes from the regeneration of catalytic particles in catalytic cracking units (abbreviated as FCC).

[0005] Prior art

[0006] Catalytic cracking units generate combustion fumes from the regeneration of the catalyst carried out in a reactor, called a regenerator. These combustion fumes contain CO2, but also generally SOx (sulfur oxides) and / or NOx (nitrogen oxides). The CO2 contained in these fumes is usually recovered by a capture process comprising various pretreatment systems to remove SOx and / or NOX (for example basic scrubbing systems, amine scrubbing systems), dust separation systems and CO2 liquefaction systems, thus allowing its storage. These different systems consume energy and also water vapor, the production of which also generates CO2. The overall energy consumption of CO2 capture processes is therefore generally very sensitive to the CO2 content of the combustion fumes.

[0007] Additionally, FCC regenerators sometimes operate in partial combustion mode. One problem associated with operating regenerators in partial combustion mode is the formation of dilute flue gas containing both CO and CO2. While CO2 can be removed from the flue gas stream by amine scrubbing, reducing CO emissions would require multiple downstream treatment units or changes in the operation of the FCC regenerator to effectively reduce CO emissions. For this reason, flue gas from a regenerator operating in partial combustion mode is typically sent to a CO burner to oxidize the CO to CO2, thereby concentrating the flue gas to CO2 while recovering energy from the treated flue gas by producing steam.When regenerators operate in full combustion mode, all of the coke is burned, and the flue gases leaving the regenerator are typically CO-free. Therefore, there is no need to burn the flue gases and the burner downstream of the regenerator is replaced by a heat recovery system to produce steam.

[0008] Despite a high CO2 content in the flue gases of the regenerator operating in total combustion, there is still a need to concentrate these gases more in CO2 and to optimize the size of a downstream CO2 capture and storage unit and / or to allow the recovery of fumes from other emitters of a petrochemical site whose fumes would be more diluted in CO2 in addition to the FCC fumes. In this mode of operation, the fumes leaving the regenerator already contain an excess of oxygen, typically from 0.5% vol O2 to 1.5% vol O2.

[0009] Summary of the invention

[0010] In order to overcome all or part of the aforementioned drawbacks, a method is proposed for treating combustion gases originating from the combustion of coke deposited on catalytic particles, comprising:

[0011] (a) a step of regenerating catalytic particles in a regenerator, during which the combustion of the coke present on the catalytic particles is carried out in the presence of an oxidizing gas containing dioxygen under total combustion conditions and combustion gases containing at least CO2 and free of CO are produced,

[0012] (b) a step of recovering heat from the combustion gases leaving the regenerator of step (a),

[0013] (c) a step of purifying the combustion gases cooled in step (b), carried out in a purification unit.

[0014] The process according to the invention is characterized in that: the oxidizing gas used during step (a) contains, in particular consists of, a portion of the purified combustion gases leaving the purification unit of step (c) to which dioxygen is added.

[0015] This recirculation makes it possible to operate the regenerator of step (a) in an oxycombustion mode, which makes it possible to increase its combustion temperature and therefore the energy released, and to produce fumes consisting of water vapor and concentrated carbon dioxide (more than 80% by volume). Advantageously, the added oxygen can advantageously be mixed with the purified combustion gases leaving the purification unit of step (c) before they enter the regenerator of step (a).

[0016] Advantageously, the purification step (c) can implement one or more treatments chosen from a particle removal treatment, a sulfur oxide removal treatment, a nitrogen oxide removal treatment.

[0017] In a preferred embodiment, the purification step (c) may implement the following treatments from upstream to downstream with respect to the circulation of the cooled combustion gases leaving step (b): a treatment for removing nitrogen oxides, in particular in an SCR device for catalytic reduction of NOx, followed by a treatment for removing particles, in particular via an electrostatic precipitator, preferably dry, followed by a treatment for removing sulfur oxides, in particular in a washing device with a basic solution.

[0018] Advantageously, in particular in order to limit corrosion, the volume ratio of oxygen / purified combustion gases entering the regenerator of step (a) may be 15 to 28%, preferably 15 to 20%, more preferably 17 to 19%.

[0019] A dioxygen / purified combustion gas volume ratio at the inlet of the regenerator of step (a) of 15 to 20% or 17 to 19% has many advantages. Such a ratio makes it possible to limit the operating costs linked to the production of dioxygen. In addition, this ratio makes it possible to maintain hydrodynamic operating conditions (surface velocity) of the regenerator identical to those obtained in the absence of CO2 recycle and therefore to avoid having to completely modify the operation of the regenerator. Finally, the metallurgical constraints of the gas distribution members in the regenerator can be kept identical and / or similar to those of a regenerator operating without CO2 recycle: this makes it possible to avoid having to modify the distribution members.Thus, such a dioxygen ratio makes it possible to implement the method of the present invention without having to modify the structure and operation of a regenerator normally operating without CO2 recycle. An existing regenerator can thus be used without major modification, the only modification to be made being the addition of a CO2 recycle line to the inlet of the regenerator.

[0020] The steam produced may in particular be used for downstream purification treatments using steam, for example NOx treatment, and / or for the various CO2 compression / absorption systems used in a treatment facility implementing the method of the present invention, and / or for other units on the site where the method according to the invention is implemented.

[0021] Advantageously, other combustion gases containing CO2, in particular combustion gases containing CO2 from other combustion systems, such as those from steam production or other petrochemical units, may be added to the cooled combustion gases in step (b), or to the purified combustion gases leaving the purification unit in step (c).

[0022] The invention also relates to a flue gas treatment installation, in particular for implementing the method according to the invention, the installation comprising: a regenerator of a fluid catalytic cracking unit comprising an oxidizing gas supply line, a supply line for coked catalytic particles to be regenerated, a discharge line for the regenerated catalytic particles and a flue gas discharge line, a heat recovery device comprising a supply line connected to the flue gas discharge line of the regenerator and a cooled flue gas discharge line, a purification unit comprising an inlet connected to the discharge line of the heat recovery device and a purified gas discharge line.

[0023] According to the invention, the installation further comprises: a recirculation pipe connecting the discharge pipe of the purification unit to the oxidizing gas supply pipe of the regenerator or to a dedicated inlet of the regenerator, a dioxygen supply pipe connected to the inlet of the regenerator or to the second recirculation pipe, a system for controlling the dioxygen / combustion gas volume ratio at the inlet of the regenerator of step (a) configured to set this ratio at a value ranging from 15 to 20%, preferably from 17 to 19%.

[0024] This purification unit may include one or more purification systems such as particle separation systems, NOx removal systems and SOx removal systems.

[0025] In a preferred embodiment, the purification unit may comprise, from upstream to downstream with respect to the circulation of the cooled combustion gases leaving the heat recovery device: a nitrogen oxide removal system, such as an SCR device for catalytic reduction of NOx, followed by a particulate removal system, such as an electrostatic precipitator, preferably dry, followed by a sulfur oxide removal system, such as a washing device with a basic solution.

[0026] Advantageously, the installation may comprise a combustion gas supply line from another unit connected to the combustion gas discharge line of the heat recovery device or to the purified gas discharge line of the purification unit.

[0027] The invention also relates to a fluid catalytic cracking process comprising a step of fluid catalytic cracking of a hydrocarbon feedstock in the presence of catalytic particles producing a cracked hydrocarbon feedstock and coked catalytic particles, and a step of regenerating the coked catalytic particles, the process implementing the treatment process according to the invention.

[0028] The invention also relates to a fluid catalytic cracking unit comprising a fluid catalytic cracking reactor in which a step of fluid catalytic cracking of a hydrocarbon feedstock is carried out in the presence of catalytic particles producing a cracked hydrocarbon feedstock and coked catalytic particles, the unit further comprising the treatment installation according to the invention, the regenerator of which receives the coked catalytic particles coming from the fluid catalytic cracking reactor.

[0029] Definitions

[0030] By "hydrocarbon feedstock" or "hydrocarbon stream" is meant a mixture of hydrocarbon compounds, a hydrocarbon compound containing carbon and hydrogen, and possibly heteroatoms such as sulfur, nitrogen, metals, etc.

[0031] The notation “SOx” designates all the sulfur oxides possibly present in combustion fumes (e.g. SO2, SO3).

[0032] The term “NOx” refers to all nitrogen oxides that may be present in combustion fumes (e.g. NO, NO2).

[0033] The term "coked catalyst" or "coked catalyst particles" means any solid catalytic material on which coke is deposited, typically in amounts of 0.5 to 1% by mass. Preferably, the coked catalyst particles are produced during a fluid catalytic cracking step. The term "particle fines" means particles whose average diameter has been reduced by abrasion, due to the particles rubbing against each other, in other words by attrition. Such particles therefore have an average diameter smaller than the average diameter of the particles before attrition.

[0034] The term "average diameter" means the diameter of a spherical particle of the same mass. This average diameter can be determined by any suitable technique, in particular by optical diffraction techniques (e.g. laser diffraction).

[0035] Downstream and upstream refer to the directions of circulation of fluids within the different areas of the installation.

[0036] Detailed description of the invention

[0037] Regeneration step (a)

[0038] In this step, the coke present on catalytic particles is burned in the presence of an oxidizing gas containing dioxygen under total combustion conditions and combustion gases containing at least CO2 and free of CO are produced.

[0039] The coked catalytic particles typically originate from a fluid catalytic cracking step carried out in one or more suitable reactors. This regeneration step thus makes it possible to regenerate the catalyst and return it to the fluid catalytic cracking step in a manner known per se.

[0040] The regeneration step is carried out in a regenerator, in particular a regenerator of an FCC unit, comprising an oxidizing gas supply line, a supply line for coked catalytic particles to be regenerated, a discharge line for the regenerated catalytic particles and a combustion gas discharge line.

[0041] Typically, catalytic particles enter the regenerator with a coke content of 0.5 to 1% by mass and exit with a coke content of 0.1 to 0.05% by mass, or even less than 0.01% by mass.

[0042] In total combustion, the regenerator is typically operated at a temperature of 680°C to 760°C and a pressure of 1.5 to 2.5 barg.

[0043] Flue gases generated by the total combustion of coke typically contain predominantly CO2, are CO-free, and generally also contain NOx and SOx depending on the cracked feedstock. They also generally include particulate fines.

[0044] According to the invention, the oxidizing gas comprises, in particular consists of, purified combustion gases enriched in dioxygen, these purified combustion gases coming from a subsequent purification step (c) described below.

[0045] The regenerator then operates using oxycombustion, which increases its combustion temperature and therefore the energy released, and produces fumes made up of water vapor and concentrated carbon dioxide.

[0046] The volume ratio of oxygen / purified combustion gases at the inlet of the regeneration step (a) may advantageously be from 15 to 28%, preferably from 15 to 20%, more preferably from 17 to 19%. This volume ratio may be regulated by means of a system for controlling the volume ratio of oxygen / combustion gases at the inlet of the regenerator of step (a) configured to set this ratio at a value ranging from 15 to 20%, preferably from 17 to 19%. This control system may be a mixing valve or any other mixing device capable of controlling the ratio of a mixture of oxygen flows and purified combustion gas flows.

[0047] The oxygen used to enrich the purified flue gases entering the regenerator may be pure oxygen or oxygen with a purity of 90% by volume or more.

[0048] Dioxygen can advantageously be added to the combustion gases before they enter the regenerator.

[0049] Heat recovery step (b)

[0050] In this step, the heat from the combustion gases produced in step (a) is recovered in a heat recovery device, which cools the combustion gases.

[0051] Step (b) of heat recovery is thus typically implemented in a device generally called a “boiler” or “waste heat boiler” in English, comprising a series of tubes filled with water between which the combustion gases circulate.

[0052] Thus, according to one embodiment, the heat recovered during step (b) is used to produce steam from water.

[0053] Purification step (c)

[0054] The cooled combustion gases leaving the heat recovery step (b) are sent to a purification step (c), in particular to remove the particles and / or NOx and / or SOx still present. The purified gases leaving step (c) thus have a reduced content of particles and / or NOx and / or SOx compared to the cooled combustion gases leaving step (b).

[0055] According to the invention, part of the purified combustion gases leaving step (c) are recycled so that they form part of the oxidizing gas used in step (a). These purified combustion gases are preferably taken directly from the outlet of purification step (c) and returned directly to step (a), optionally after compression, without having undergone any other treatment.

[0056] Typically, the purified flue gases exiting purification step (c) and returned to step (a) may have one or more of the following characteristics:

[0057] - A particle content of less than 50 mg / Nm 3 , or even less than 10 mg / Nm 3 , for example from 0.01 to 50 mg / Nm 3 ,

[0058] - A NOx content of less than 250 ppm vol, for example from 1 to 250 ppm vol,

[0059] - A SOx content of less than 400 ppm vol, for example from 1 to 400 ppm vol.

[0060] This purification step may in particular comprise, or consist of, one or more treatments chosen from a particle removal treatment, a sulfur oxide removal treatment, a nitrogen oxide removal treatment.

[0061] The purification step can be implemented in a purification unit, comprising for example, or consisting of, a particle removal device, generally an electrostatic precipitator, in particular dry (operating without adding liquid), a SOx removal device, for example a washing device with a basic solution, a NOx removal device, for example an SCR (Selective Catalytic Reduction) device for catalytic reduction of NOx or an ozone injection device for NOx reduction. The invention is of course not limited by the number and nature of these devices, which are otherwise well known to those skilled in the art.

[0062] The SCR device for catalytic reduction of NOx typically operates in the presence of a reducing agent, and optionally a catalyst, in order to transform the NOx present in the fumes into N2 and water. This reducing agent can be urea or NH3 in the gaseous or aqueous phase, preferably NH3 in the gaseous phase (ammonia). The usual catalysts are based on tungsten and vanadium in oxidized form: tungsten (III) oxide W2O3 or vanadium (V) oxide V2O5. The catalyst is generally deposited on a support based on titanium oxide (TiCh). The invention is of course not limited to a specific catalyst and any catalyst usually used to catalyze the selective reduction of nitrogen oxides can be considered.

[0063] In a preferred embodiment, the purification unit implementing the purification step may advantageously comprise, or consist of, from upstream to downstream: an SCR device for catalytic reduction of NOx, an electrostatic precipitator (in particular dry) and a device for washing with a basic solution. The purified combustion gases returned in step (a) are then preferably taken at the outlet of the washing device with a basic solution.

[0064] The purification unit may further comprise an additional dust removal device, for example of the cartridge filter type, arranged downstream of the washing device with a basic solution, in particular downstream of the sampling point for the purified combustion gases recycled in step (a), to further purify the combustion gases before the optional capture and storage step and to protect the equipment implementing this step, and in particular the compressor(s) present.

[0065] Air may also be injected only at the start of the process to initiate combustion, and then to stop this injection. For example, air can be injected into the purified combustion gases leaving the purification unit before they are returned to the regenerator.

[0066] Optional capture and storage step

[0067] Downstream of the heat recovery device implementing step (b) or the purification unit implementing step (c), the method according to the invention may further comprise a CO2 capture and storage step, which may comprise at least one CO2 liquefaction step, typically by compression, and a liquefied CO2 storage step. The liquefaction step may optionally be preceded by a drying step and / or a pressure swing adsorption step or PSA (from the English acronym Pressure Swing Adsorption).

[0068] This step can be implemented in a CO2 capture and storage unit comprising at least one liquefaction system, typically by compression, and at least one liquefied CO2 storage system. This capture and storage unit can also comprise, upstream of the liquefaction system, a drying system, and / or a pressure inversion adsorption system to further concentrate the gases into CO2.

[0069] Typically, if the CO2 content at the inlet of the capture and storage unit is less than 45-50% by volume, a PSA is advantageously used to concentrate the fumes. If the CO2 content is greater than 45-50% by volume, a PSA is not useful.

[0070] CO2 capture and storage can also be carried out, not in the liquid phase but in the gas phase or supercritical phase, typically at room temperature and pressure between 20 barg and 170 barg. In this configuration, the CO2 liquefaction step, allowing in particular the ultimate purification of CO2, can either be maintained with a CO2 revaporization step, or carried out by alternative treatments such as absorption by amine solvents.

[0071] The CO2 capture and storage unit may then comprise at least one liquefaction system followed by a revaporization system, or at least one CO2 extraction system, typically using an amine solvent, followed by a water and oxygen extraction system, and a compression system in gaseous or supercritical form.

[0072] The method according to the invention can make it possible to obtain combustion gases having a CO2 content in dry fumes of 20 to 30% by volume, typically 25% by volume, at the outlet of step (b) or (c).

[0073] The implementation of the method according to the invention thus makes it possible to produce combustion gases with a higher concentration of CO2, which then makes it possible to reduce the size of the purification unit implementing step (c) and / or of the capture and storage unit implementing the capture and storage step, and consequently to reduce their operating cost.

[0074] Alternatively, the method according to the invention may receive, downstream of the heat recovery device implementing step (b) or of the purification unit implementing step (c), and in particular upstream of a CO2 capture and storage step, combustion gases containing CO2 originating from other petrochemical units. Insofar as the present invention makes it possible to enrich the combustion gases produced by the regenerator with CO2, it is possible to envisage adding external combustion gases without having to modify the dimensions and / or conditions of implementation of a purification step and / or a CO2 capture and storage step located downstream.In particular, the CO2 content of the dry gases entering a capture and storage unit can advantageously be 15 to 20% CO2 by volume on a dry basis. It will thus be possible to adjust the ratios of the combustion gases from step (b) or (c) and the combustion gases from other units to obtain a CO2 content of this order. For example, combustion gases from furnaces typically contain 7 to 10% CO2 by volume.

[0075] Treatment facility

[0076] The method according to the invention can be implemented in a treatment installation as previously described.

[0077] Furthermore, this installation may include a CO2 capture and storage unit as described above.

[0078] As previously described with reference to the process, this installation can receive combustion gases from other units via dedicated pipes. These pipes can be connected to the installation downstream of the heat recovery device or downstream of the purification unit, and in particular upstream of the CO2 capture and storage unit.

[0079] Description of figures

[0080] The invention is now described with reference to the accompanying non-limiting drawings, in which:

[0081] [Fig. 1] Figure 1 represents an exemplary embodiment of an installation implementing the method according to an embodiment of the invention.

[0082] Figure 1 schematically represents a treatment installation 1 according to one embodiment of the invention. The installation shown comprises a regenerator 10, a heat recovery device 20, a purification unit 30, and in the example shown a CO2 capture and storage unit 40.

[0083] The regenerator 10 has a coked catalytic particle feed line 101, an oxidizing gas feed line 102, a combustion gas discharge line 103, and a regenerated catalytic particle discharge line 104. The coked catalytic particles come from a catalytic cracking reactor (not shown) into which the regenerated catalytic particles are returned.

[0084] The heat recovery device 20 comprises a supply line 201 connected to the flue gas discharge line 103 of the regenerator, and a discharge line 202 for cooled flue gas. The heat recovery device 20 further comprises an inlet 20a for water and an outlet 20b for steam. Such a heat recovery device 20 is generally called a "boiler".

[0085] The purification unit 30 comprises an inlet 301 connected to the discharge pipe 202 of the heat recovery device, and a discharge pipe 302 for the purified gases.

[0086] According to the invention, a recirculation line 303 connects the discharge line 302 of the purification unit to the oxidizing gas supply line 102 of the regenerator. In addition, a dioxygen supply line 106 is connected to the oxidizing gas supply line 102 of the regenerator.

[0087] Thus, the oxidizing gas entering the regenerator 10 consists of the cooled and purified combustion gases brought via the pipe 303 and of oxygen brought via a pipe 106.

[0088] The installation typically comprises a control system 108 of the oxygen / combustion gas volume ratio at the inlet of the regenerator of step (a) configured to set this ratio at a value ranging from 15 to 20%, preferably from 17 to 19%. This is typically a mixing device such as a mixing valve.

[0089] In the example shown, the installation also comprises a compressor 2 between the heat recovery device 20 and the purification unit 30, a compressor 3 on the line 302 between the purification unit 30 and the recirculation line 303, and another compressor 4 on the line 302 between the recirculation line 303 and the CO2 capture and storage system 40. The invention is of course not limited by the number and position of the compressors, which may vary depending on the needs of the installation. The different lines may also be equipped with valves and / or pumps for circulating the fluids.

[0090] The capture and storage unit 40 typically comprises a CO2 liquefaction system and a liquefied CO2 storage system. This capture and storage unit may also correspond to an extraction of CO2 by an amine solvent followed by a step of extraction of water and oxygen and final compression of the CO2 in the form of gas or supercritical fluid.

Claims

CLAIMS 1. Method for treating combustion gases from the combustion of coke deposited on catalytic particles, comprising: (a) a step of regenerating catalytic particles in a regenerator (10), during which the combustion of the coke present on the catalytic particles is carried out in the presence of an oxidizing gas containing dioxygen under total combustion conditions and combustion gases containing at least CO2 and free of CO are produced, (b) a step of recovering heat from the combustion gases leaving the regenerator (10) of step (a), (c) a step of purifying the combustion gases cooled in step (b), implemented in a purification unit (30), characterized in that: the oxidizing gas used during step (a) contains a portion of the purified combustion gases leaving the purification unit (30) of step (c) to which dioxygen is added, and in that the volume ratio of dioxygen / purified combustion gases entering the regenerator of step (a) is 15 to 20%.

2. Treatment method according to claim 1, characterized in that the added oxygen is mixed with the purified combustion gases leaving the purification unit (30) of step (c) before they enter the regenerator of step (a).

3. Treatment method according to claim 1 or 2, characterized in that step (c) implements one or more purification treatments chosen from a particle removal treatment, a sulfur oxide removal treatment, a nitrogen oxide removal treatment.

4. Treatment method according to any one of claims 1 to 3, characterized in that step (c) implements the following treatments from upstream to downstream with respect to the circulation of the cooled combustion gases leaving step (b): a treatment for removing nitrogen oxides, in particular in an SCR device for catalytic reduction of NOx, followed by a treatment for removing particles, in particular via an electrostatic precipitator, preferably dry, followed by a treatment for removing sulfur oxides, in particular in a washing device with a basic solution.

5. Treatment method according to any one of claims 1 to 4, characterized in that the volume ratio of oxygen / purified combustion gases entering the regenerator of step (a) is 17 to 19%.

6. Treatment method according to any one of claims 1 to 5, characterized in that other combustion gases containing CO2 are added to the cooled combustion gases in step (b), or to the purified combustion gases leaving the purification unit of step (c).

7. Fluid catalytic cracking process comprising a step of fluid catalytic cracking of a hydrocarbon feedstock in the presence of catalytic particles producing a cracked hydrocarbon feedstock and coked catalytic particles, and a step of regenerating the coked catalytic particles, characterized in that it implements the treatment process according to any one of claims 1 to 6.

8. Installation (1) for treating combustion gases comprising: - a regenerator (10) of a fluid catalytic cracking unit comprising a supply line (102) for oxidizing gas, a supply line (101) for coked catalytic particles to be regenerated, a discharge line (104) for the regenerated catalytic particles and a discharge line (103) for combustion gas, - a heat recovery device (20) comprising a supply line (201) connected to the combustion gas discharge line (103) of the regenerator and a cooled combustion gas discharge line (202), - a purification unit (30) comprising an inlet connected to the discharge pipe (202) of the heat recovery device and a discharge pipe (302) for the purified gases, characterized in that it further comprises: - a recirculation pipe (303) connecting the discharge pipe (302) of the purification unit to the oxidizing gas supply pipe (102) of the regenerator or to a dedicated inlet of the regenerator, - a dioxygen supply line (106) connected to the inlet of the regenerator or to the recirculation line, - a control system (108) of the oxygen / combustion gas volume ratio at the inlet of the regenerator of step (a) configured to set this ratio at a value ranging from 15 to 20%, preferably from 17 to 19%.

9. Treatment installation (1) according to claim 8, characterized in that it comprises a combustion gas supply line coming from another unit connected to the combustion gas discharge line. combustion of the heat recovery device or to the purified gas discharge line of the purification unit.

10. Treatment installation (1) according to claim 8 or 9, characterized in that the purification unit comprises, from upstream to downstream with respect to the circulation of the cooled combustion gases leaving the heat recovery device: a nitrogen oxide removal system, such as an SCR device for catalytic reduction of NOx, followed by a particle removal system, such as an electrostatic precipitator, preferably dry, followed by a sulfur oxide removal system, such as a washing device with a basic solution.

11. Fluid catalytic cracking unit comprising a fluid catalytic cracking reactor in which a step of fluid catalytic cracking of a hydrocarbon feedstock is carried out in the presence of catalytic particles producing a cracked hydrocarbon feedstock and coked catalytic particles, characterized in that it further comprises the treatment installation according to any one of claims 7 to 10, the regenerator of which receives the coked catalytic particles coming from the fluid catalytic cracking reactor.

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