Method for chemical looping combustion of a fuel comprising a high volatile content

Abstract

The invention relates to a method for chemical looping combustion of a fuel which comprises a high volatile content in which an oxygen carrier (1) circulates, the method comprising at least: - a first reaction zone (Z1) operating in a dilute upward fluidised bed; - a second reaction zone (Z2) located vertically above the first reaction zone (Z1), the second reaction zone (Z2) operating in a dense fluidised bed; - a third zone (Z3) operating in a dilute fluidised bed, located vertically above the second reaction zone (Z2); - an oxidation zone in which the particles of the oxygen carrier (1) are re-oxidised before the re-oxidised particles are returned towards the first reaction zone (Z1). The invention also relates to an installation suitable for implementing this method.

Description

[0001] CHEMICAL LOOP COMBUSTION PROCESS OF A FUEL COMPRISING A HIGH VOLATILE CONTENT

[0002] technical field

[0003] The field of the invention is that of chemical loop combustion (CLC) for the production of energy, syngas, and / or hydrogen. More particularly, the invention relates to the chemical loop combustion of a fuel containing a high content of volatile compounds. The fuel may, in particular, include biomass and / or solid recovered fuel (SRF) and / or RDF (Refuse Derived Fuels).

[0004] Previous technique

[0005] In a context of increasing global energy demand, carbon capture and storage (CCS) has become an essential necessity to limit the emission of greenhouse gases that are harmful to the environment. The CLC process makes it possible to produce thermal energy from hydrocarbon fuels while simultaneously facilitating the capture of carbon dioxide emitted during combustion.

[0006] A chemical loop combustion process generally includes one or more reaction zones in which a fuel is combusted by contact with an oxygen-carrying solid which is then reoxidized in at least one oxidation zone by contact with air or water vapor before being returned to the combustion (or reduction) zone(s).

[0007] Chemical loop combustion involves bringing a gaseous, liquid, and / or solid hydrocarbon feedstock into contact with an oxygen-carrying solid, such as a metal oxide, within a high-temperature chamber. The oxygen carrier releases some of its oxygen, which then participates in the combustion of the hydrocarbons.

[0008] At the end of combustion, the fumes mainly contain carbon oxides, water, and possibly hydrogen. Indeed, it is not necessary to bring the hydrocarbon fuel into contact with air, and the fumes are therefore primarily composed of combustion gases and possibly a dilution gas used for transport and fluidization of the particles (for example, water vapor).

[0009] Thanks to the chemical closed-loop combustion process, it is possible to produce energy, in the form of steam or electricity, by placing heat exchange surfaces in the circulation loop of the oxygen carrier or on the gaseous effluents downstream of the combustion or oxidation reactions. This allows for the production of flue gases that are mostly free of nitrogen and contain high CO2 levels (> 90% vol.), making it possible to consider capturing and then storing this CO2. The oxygen carrier that participated in the combustion is then transported to another reaction chamber where it is brought into contact with air to be reoxidized.

[0010] It should be noted that, generally speaking, the terms oxidation and reduction are used in relation to the oxidized or reduced state, respectively, of the oxygen carrier. An oxidation reactor is one in which the oxygen carrier is oxidized, and a reduction reactor (also called a combustion reactor) is one in which the oxygen carrier is reduced.

[0011] US patent 5,447,024 describes a chemical loop combustion process comprising a first reactor for reducing an oxygen carrier using a reducing gas and a second oxidation reactor for restoring the oxygen carrier to its oxidized state through an oxidation reaction with humid air. Circulating fluidized bed technology is used to enable the continuous cycle of the oxygen carrier between its oxidized and reduced states.

[0012] The oxygen carrier, alternately changing from its oxidized form to its reduced form and vice versa, describes a redox cycle.

[0013] Thus, in the reduction reactor, the oxygen carrier M x O y is first reduced to state M x Oy-2n-m / 2, via a hydrocarbon C n H m , which is correspondingly oxidized into CO2 and H2O, according to reaction (1), or possibly into a mixture of CO + H2 depending on the proportions used.

[0014] In the oxidation reactor, the oxygen carrier is restored to its oxidized state M x O y upon contact with the air according to reaction (2), before returning to the first reactor.

[0015] MxOy-2n-m / 2 + (n+m / 4) O2M x O y (2)

[0016] In equations (1) and (2) above, M can, for example, represent a metal.

[0017] The efficiency of the circulating fluidized bed chemical loop combustion (CLC) process depends to a large extent on the physico-chemical properties of the oxygen carrier.

[0018] The reactivity of the redox couple(s) involved, as well as the associated oxygen transfer capacity, are parameters that influence reactor sizing and particle flow rates. Particle lifetime, in turn, depends on the particles' mechanical strength and chemical stability.

[0019] Numerous studies with gas feedstocks (mainly methane or syngas) and solid feedstocks have been conducted and have shown the feasibility of the chemical combustion loop for this type of fuel.

[0020] The principle of chemical loop combustion of redox in fluidized bed of liquid feedstocks has some specific features and is described for example in patents FR 2.930.771 and FR 2.936.301.

[0021] Biomass is an interesting solid fuel because the carbon dioxide (CO2) generated during its closed-loop combustion can be sequestered, leading to negative greenhouse gas emissions. This is known as BECCS, an acronym for "Bioenergy with Carbon Capture and Storage."

[0022] Applicant WO2011 / 151535's patent application describes a chemical loop combustion process fed with a solid fuel, enabling near-total or even total combustion of the solid feedstock. However, the applicant has observed that when the solid fuel is biomass, this type of implementation is unsuitable and leads to poor combustion of the gaseous effluents produced when the biomass particles come into contact with the metal oxide particles in the first reaction zone operating in a dense fluidized bed. Indeed, because biomass contains a very high quantity of volatiles (compared to traditional fossil feedstocks such as petcoke, i.e., petroleum coke), these volatiles are released almost instantaneously upon injection of the biomass particles into the dense bed, which is at a high temperature, typically exceeding 700°C.This rapid release of volatile gases from biomass occurs in the form of gas pockets within the dense fluidized bed, causing pressure instabilities on the one hand, and significantly reducing the contact of these volatiles with oxygen carrier particles on the other. Consequently, these gases are only minimally oxidized by contact with the oxygen carrier, and the gas phase exiting the combustion reactor then contains, in addition to CO2 and water vapor, a significant amount of unburned gases such as methane, CO, and H2.

[0023] Figure 1 illustrates test results carried out by the applicant on a CLC process based on patent application WO2011 / 151535 using a biomass fuel. The biomass is first injected into a dense fluidized bed reaction zone. Diagram a) (upper part) illustrates the evolution of the CO / CO2 ratio, in moles, between CO and CO2 (represented by circles), the evolution of the CH4 / CO2 ratio, in moles, between CH4 and CO2 (represented by squares), and the evolution of the H2 / CO2 ratio, in moles, between H2 and CO2 (represented by triangles), as a function of time T in hours. The right-hand axis represents the H2 / CO2 ratio, and the left-hand axis represents the other two ratios. The biomass injection (Inj) is shown at a time corresponding to the vertical dashed line.

[0024] Diagram a) shows the formation of significant quantities of unburned CH4, carbon monoxide CO, and hydrogen H2 in the gaseous effluents exiting the combustion reactor. It also shows the significant variations in these ratios over time.

[0025] Diagram b) (lower part) illustrates the evolution of the bed density Dlit in kg / m³ 3 Circles represent the evolution of the gas flow rate Qgas in NL / h (normal liters per hour), triangles the evolution of the reactor pressure P in mbar, and squares the evolution of the reactor pressure as a function of time T in hours. Biomass injection is represented at a time corresponding to the vertical dashed line. The right-hand axis represents the reactor pressure, and the left-hand axis represents the other two parameters.

[0026] Diagram b) shows significant variations in bed density Dlit, gas flow rate Qgaz, and pressure P. Furthermore, it can be observed that pressure P is affected by gases released during biomass devolatilization, which are generated in a relatively erratic manner. This results in an overall decrease in bed density, as well as significant variability due to the difficulty in controlling the test equipment under such conditions.

[0027] Patent application CN114961997 proposes a chemical loop combustion process for biomass fuel. The fuel reactor contains several internal components, which appears difficult to implement in practice at typical reactor temperatures. Furthermore, the biomass entering the lower section is fed into a bubbling fluidized bed, and therefore into a dense phase, which risks generating gas pockets. This could lead to pressure instabilities and / or reduced contact between the released volatiles and the oxygen carrier.

[0028] Summary of the invention

[0029] The aim of the invention is to provide a chemical loop combustion process suitable for fuels with a high volatile compound content (at least 50% volatile compounds, preferably at least 60%, and even more preferably at least 70% volatile compounds) in order to achieve satisfactory fuel combustion and improved performance. The invention relates to a chemical loop combustion process for a fuel comprising at least 50% volatile compounds, with particles of an oxygen carrier circulating in said chemical loop. Preferably, the fuel comprises biomass and / or SRF and / or RDF. Furthermore, said process comprises at least:

[0030] - a step of bringing the fuel into contact, in a first reaction zone operating in an upward transported dilute fluidized bed, with the particles of the oxygen carrier, this contact generating a first gaseous effluent and char;

[0031] - a combustion / gasification stage, in a second reaction zone located vertically above the first reaction zone, the second reaction zone operating in a dense fluidized bed, in which:

[0032] * combustion of the gaseous effluents from the first reaction zone is carried out in the presence of the oxygen carrier particles;

[0033] * gasification of the char followed by combustion of the gases resulting from this gasification of the char are produced;

[0034] - a stage of circulating the gases produced in the combustion / gasification stage and the particles of the oxygen carrier, in a third zone operating in a dilute fluidized bed, located vertically above the second reaction zone;

[0035] - an oxidation step, in an oxidation zone, in which a reoxidation of the oxygen carrier particles occurs before returning said reoxidized particles to the first reaction zone.

[0036] Preferably, the fluid exiting the first reaction zone is distributed via a distributor to enter the second reaction zone, preferably the distributor comprising a substantially vertical cylindrical part closed at the top, and lateral openings.

[0037] According to one implementation of the process of the invention, the process does not include separation of unburned particles and oxygen carrier particles.

[0038] Advantageously, the cross-sectional area in the second reaction zone is strictly greater than that in the first reaction zone.

[0039] Advantageously, the passage cross-section in the third zone is greater than or equal to the passage cross-section in the second reaction zone.

[0040] Preferably, the first reaction zone and / or the second reaction zone are supplied with a fluidizing gas.

[0041] According to one configuration of the invention, the fluidization gas comprises a portion of the gas exiting the third zone, optionally purified, preferably the fluidization gas comprises CO2 and / or recycled water vapor.

[0042] Preferably, the average residence time of solid particles in the first reaction zone is between 0.5 and 10 seconds, the average residence time of solid particles in the second reaction zone being between 0.25 and 60 minutes, preferably between 1 and 30 minutes.

[0043] Advantageously, the surface velocity of the gas in the first reaction zone is between 0.5 and 20 m / s, the surface velocity of the gas in the second reaction zone being between 0.02 and 3 m / s.

[0044] Advantageously, the volume fraction of solid in the first reaction zone is less than or equal to 0.1, preferably less than or equal to 0.05, and even more preferably less than 0.02.

[0045] According to one embodiment of the invention, the temperature in the second reaction zone is greater than 700°C, preferably greater than 800°C, and even more preferably between 900 and 1000°C.

[0046] According to one variant of the invention, at the exit of the third zone, the gas stream containing the fuel particles and a fraction of oxygen carrier particles is sent to at least one gas-solid separation stage to recover almost all of the particles contained in the gas stream from the third zone, the recovered particles being recycled to the first reaction zone.

[0047] The invention also relates to an installation for carrying out the combustion of a fuel comprising at least 50% volatile compounds, preferably fuel comprising biomass and / or RDF, according to the process as described above, said installation comprising at least:

[0048] - a combustion reactor comprising three successive zones:

[0049] * a first reaction zone operating in dilute phase, comprising a fuel supply, an oxygen carrier particle supply and preferably a fluidizing gas supply and,

[0050] * a second reaction zone receiving, via a feed, gases and particles coming directly from the first reaction zone,

[0051] * a third zone operating in dilute phase receiving, via its inlet, a gaseous combustion effluent from the second reaction zone,

[0052] - an oxidation reactor comprising an oxidation zone, a supply of oxygen carrier particles exiting the second reaction zone and a supply of oxidizing gas.

[0053] Preferably, the first reaction zone has a passage cross-section strictly smaller than the passage cross-section of the second reaction zone, and / or the third zone has a passage cross-section greater than or equal to the passage cross-section of the second reaction zone.

[0054] List of figures Other features and advantages of the process and installation according to the invention will become apparent from the following description of non-limiting examples of implementations, with reference to the figures attached and described below.

[0055] Figure 1 (already described) represents test results of a prior art CLC process with a biomass-type fuel.

[0056] Figure 2 represents an example of a CLC process and installation according to the invention.

[0057] Figure 3 represents an example of a distributor for the CLC process according to the invention.

[0058] Figure 4 shows an example of a distributor for the CLC process according to the invention. The figures are highly schematic; components or flows retain the same reference from one figure to another, with Figure 2 representing the installation in its spatial operating positioning.

[0059] Description of the implementation methods

[0060] The invention relates to a chemical loop combustion process for a fuel comprising at least 50% (by mass) volatile compounds. The mass content of volatile compounds in the fuel can be determined, for example, by thermogravimetric analysis (TGA) under nitrogen. Particles of an oxygen carrier circulate in the chemical loop. Preferably, the fuel can comprise biomass and / or waste, in particular SRF (Solid Recovered Fuel) and / or RDF (Refuse-Derived Fuel). Solid recovered fuels can include, in particular, various types of household waste. Thus, this type of fuel can encompass a wide variation in the feedstock introduced into the process.This type of fuel, particularly biomass or RDF, generally includes a large quantity (at least 50%, or even more than 60% or 70%, by mass) of volatile species, compared to traditional fossil fuels such as petcoke.

[0061] A volatile compound is a compound produced by the thermal degradation of fuel; this compound is in a gaseous state under the pressure and temperature conditions of the combustion reactor. Volatile compounds can include, in particular, methane, carbon monoxide, carbon dioxide, water vapor, dihydrogen, and hydrocarbons.

[0062] The oxygen carrier can, for example, be a metal oxide, and the particles involved can be composed of a redox couple or set of redox couples chosen from among CuO / Cu, Cu2O / Cl, NiO / Ni, Fe2Os / Fe3O4, FeO / Fe, FesO / FeO, MnO2 / Mri2O3, Mr s / MrisC / MnsO / MnO, MnO / Mn, Co3O4 / CoO, CoO / Co, and a binder providing the necessary physicochemical stability. Interactions with supports, such as Al2O3, are possible.

[0063] The process includes at least:

[0064] 1) a step of bringing into contact, in a first reaction zone operating in an upward transported dilute fluidized bed, the fuel particles with the particles of the oxygen carrier, this contact generating a first gaseous effluent and char;

[0065] 2) a combustion / gasification step, in a second reaction zone located vertically above the first reaction zone, the second reaction zone operating in a dense fluidized bed, in which: a) combustion of the gaseous effluents from the first reaction zone in the presence of the oxygen carrier particles is carried out; b) gasification of the char and then combustion of the gases from this gasification are produced;

[0066] 3) a gas circulation stage for the gases produced in the combustion / gasification stage and the oxygen carrier particles, in a third zone operating as a dilute fluidized bed, located vertically above the second reaction zone. This third zone serves to limit the entrainment of the oxygen carrier towards the combustion gas outlet; for this purpose, the third zone may include a sufficient vertical height and / or may include a disengagement zone;

[0067] 4) an oxidation step, in an oxidation zone in which reoxidation of the oxygen carrier particles occurs before returning said reoxidized particles to the first reaction zone.

[0068] By "dense fluidized bed" or "dense phase" we mean a fluidized bed in which the volume fraction of solid is between 0.2 and the volume fraction corresponding to a packed (non-fluidized) bed close to 0.5.

[0069] By "diluted fluidized bed" or "diluted phase", we mean a fluidized bed generally having a solid volume fraction generally strictly less than 0.2, or even less than 0.1.

[0070] The term "transported dilute fluidized bed" or "transported dilute phase" refers to solid particles being transported by the gas (carried along by the gas) within the dilute fluidized bed. The solid volume fraction for such a transported dilute fluidized bed is less than 0.1, or even less than 0.05, and preferably less than 0.02.

[0071] It is understood that the sum of the volume fraction of gas and the volume fraction of solid is equal to 1. In this description, char refers to the residual carbonaceous residue, one of the products of the fuel gasification stage.

[0072] The first, second and third reaction zones can advantageously be contained in a combustion reactor, while the oxidation zone can be contained in an oxidation reactor.

[0073] In the combustion reactor, the oxygen carrier particles and the feedstock flow advantageously vertically from bottom to top, carried by the fluidizing gas and the product gases. The feedstock and the oxygen carrier particles therefore flow in co-current with each other and in co-current with the fluidizing gas (the gas that fluidizes and carries the particles from one reactor to the other (from the combustion reactor to the oxidation reactor and vice versa).

[0074] In the oxidation reactor, the oxygen carrier particles advantageously flow vertically from bottom to top, carried along by the oxidation gas (the gas that oxidizes the oxygen carrier, for example air or dioxygen). The oxygen carrier particles therefore flow in co-current with the oxidation gas.

[0075] According to one embodiment of the invention, the fluid (composed of various gases, oxygen carrier particles, and char) exiting the first reaction zone can be distributed via a distributor that allows the fluid to enter the second reaction zone. The distributor can, in particular, be a "mushroom distributor," used in the field of Fluid Catalytic Cracking (FCC). This ensures a homogeneous distribution of the fluid within the dense fluidized bed.

[0076] In the context of the invention, the "fluid" may comprise one or more gases and preferably contain solid particles suspended in them, the solid particles being, for example, carried along with the gas(s). Preferably, the distributor may comprise a substantially vertical cylindrical portion closed at the top, with lateral openings for distributing the fluid laterally around the distributor, which terminates in the lower part of the second reaction zone. For example, the distributor may be of the "bubble cap" or "mushroom distributor" type.

[0077] Advantageously, the process may not involve separating the unburned particles from the oxygen carrier particles (either in the upper part of the combustion reactor or at the combustion reactor outlet). In other words, the process may involve keeping the unburned particles and the oxygen carrier particles circulating. Indeed, when the temperature in the second reaction zone is above 700°C, preferably above 800°C, and preferably between 900 and 1000°C, the time required to gasify the char is reduced, thus avoiding the need for a separation zone.

[0078] First reaction zone

[0079] In the first reaction zone, the feedstock, comprising a majority of volatile compounds (at least 50%, preferably at least 60%, and even more preferably at least 70%), is brought into contact with the oxygen carrier particles. The fuel may consist of biomass and / or SRF and / or RDF. The oxygen carrier particles and the feedstock (also called "fuel") are fed in via a feed located in the lower part of the first reaction zone (specifically, in the lower part of the combustion reactor).

[0080] The fuel can be injected in various ways, for example, with a screw conveyor or a pneumatic device. Preferably, the fuel can be injected at several points (this is called multi-point injection) for better fuel vaporization and improved contact with the carrier. Even more preferably, the fuel can be injected at at least three points, ideally distributed around the reaction zone. In this first reaction zone, the volatiles from the charge are rapidly released and react with the oxygen carrier present (some of the gases are oxidized in this first reaction zone upon contact with the oxygen carrier). This process forms char and the gases released in the first reaction zone. The char and these gases are carried by an upward flow to the second reaction zone.

[0081] Advantageously, the volume fraction of solid in the first reaction zone can be less than or equal to 0.1, preferably less than or equal to 0.05, and even more preferably less than 0.02, to promote the creation of a transported dilute phase.

[0082] Second reaction zone

[0083] In this second reaction zone, the gases and char from the first reaction zone enter. This second reaction zone operates in a dense fluidized bed to increase the residence time of the particles and char. Several reactions can occur in this second reaction zone:

[0084] - Combustion of unconverted gaseous effluents (which have not reacted with the oxygen carrier in the first reaction zone) from the first reaction zone, with the particles of the oxygen carrier.

[0085] - Slow gasification of the char: this is possible, in particular, due to the use of a dense phase which allows for a longer residence time. - Combustion of some of the gases produced by the gasification of the char upon contact with the particles of the oxygen carrier.

[0086] Advantageously, the cross-sectional area in the second reaction zone can be strictly larger than that in the first reaction zone. Therefore, generating a dense phase in the second reaction zone and a dilute phase in the first reaction zone is facilitated because the fluid velocity in the second reaction zone is lower than the fluid velocity in the first reaction zone.

[0087] According to one embodiment of the invention, the average residence time of the solid particles in the first reaction zone can be between 0.5 and 10 seconds, and the average residence time of the solid particles in the second reaction zone can be between 0.25 and 60 minutes, preferably between 1 and 30 minutes. As a result, the first reaction zone can form a dilute transported phase and the second reaction zone can form a dense phase.

[0088] According to the invention, "solid particles" means particles comprising the oxygen carrier particles, the fuel particles and possibly the ash (which are solid residues of combustion).

[0089] According to one configuration of the invention, the surface velocity of the gas in the first reaction zone can be between 0.5 and 20 m / s, and the surface velocity of the gas in the second reaction zone can be between 0.02 and 3 m / s. The surface velocity in the second reaction zone is strictly lower than the surface velocity in the first reaction zone. This difference in velocity between the two zones promotes the formation of a dense phase in the second reaction zone and the formation of a dilute phase transported in the first reaction zone.

[0090] The definitions of surface gas velocities, for the different targeted regimes (different reaction zones) depend in particular on the size and density of the solid particles.

[0091] Preferably, the temperature in the second reaction zone can be above 700°C, preferably above 800°C, and even more preferably between 900 and 1000°C. This minimizes the time required to gasify the char and thus eliminates the need for a separation zone downstream of the third zone, in the direction of fluid flow. Furthermore, this allows for the conversion of tars, as unconverted tars can clog the downstream section due to condensation below approximately 350-400°C. Tars are heavy hydrocarbons (with more than 6 carbon atoms) that are contained with the volatiles but are more difficult to convert than the lighter products (which contain fewer carbon atoms than tars). Advantageously, the first and / or second reaction zone can be supplied with a fluidizing gas.This facilitates the generation of the dilute phase transported from the first reaction zone. In the second reaction zone, the injection of a fluidizing gas fluidizes the entire cross-section of the second zone (the gas from the first zone representing a limited cross-section in the second reaction zone).

[0092] When a fluidizing gas is fed (injected) into the first reaction zone and into the second reaction zone, the fluidizing gas in the first reaction zone may be the same as or different from the fluidizing gas in the second reaction zone.

[0093] Preferably, the fluidization gas can include a portion of the gas exiting the third zone (of the combustion reactor), gas which can optionally be purified.

[0094] Preferably, the fluidizing gas may include CO2 and / or recycled water vapor.

[0095] The purification process may include a step where remaining solid particles (particularly fine particles) are removed and / or a step where water vapor is separated from CO2. Therefore, the water vapor and / or CO2 used as a fluidizing gas have a high level of purity.

[0096] Third zone

[0097] The third zone is a dilute phase zone used to limit the entrainment of oxygen-carrying solid particles towards the combustion gas outlet.

[0098] Preferably, the cross-sectional area of ​​the third zone can be greater than or equal to the cross-sectional area of ​​the second reaction zone. When the cross-sectional area of ​​the third zone is strictly greater than the cross-sectional area of ​​the second reaction zone, this third zone acts as a disengagement zone (reduction of the gas surface velocity due to the increase in cross-sectional area).

[0099] According to one aspect of the invention, at the exit of the third zone, the gas stream containing fuel particles (light, for example) and a fraction of oxygen carrier particles is sent to at least one gas-solid separation stage to recover almost all of the particles contained in the gas stream from the third zone. The recovered particles are then recycled back to the first reaction zone. This allows for the recovery of the unconverted feedstock and the oxygen carrier for reuse.

[0100] Oxidation zone

[0101] In the oxidation zone, the oxygen in the oxygen-carrying solid is restored. Indeed, upon exiting the combustion reactor (the second reaction zone), the oxygen carrier is in a reduced state. It is then sent to the oxidation reactor where it comes into contact with an oxidizing gas (air, for example) and exits the oxidation reactor in an oxidized (or partially oxidized) state. It can then be sent back to the combustion reactor.

[0102] Furthermore, the invention also relates to an installation for burning a fuel containing a high content of volatile compounds (at least 50%, or even 60% or 70% volatile compounds), according to the process described in one of the preceding variants or combinations thereof. Preferably, the fuel may comprise biomass and / or waste, particularly of the RDF or SRF type.

[0103] The said installation includes at least:

[0104] - a combustion reactor comprising three successive zones (in the direction of gas flow):

[0105] * a first reaction zone operating in dilute phase, comprising a fuel supply, a fluidizing gas supply and an oxygen carrier particle supply,

[0106] * a second reaction zone receiving, via a feed, gases and particles coming directly from the first reaction zone,

[0107] * a third zone operating in dilute phase receiving, via its inlet, a gaseous combustion effluent from the second reaction zone,

[0108] - an oxidation reactor comprising an oxidation zone, a supply of oxygen carrier particles exiting the third zone and an air supply.

[0109] Thus, the reactor is configured so that the charge and oxygen carrier particles circulate successively first in the first reaction zone, then in the second reaction zone, and then in the third zone.

[0110] Thus, the combustion reactor comprises, successively in the direction of the gas flow, a first reaction zone, a second reaction zone and then a third zone located above the second reaction zone.

[0111] For the purposes of this invention, a "reaction zone" is understood as a zone where a major chemical reaction occurs: this chemical reaction may be a combustion or gasification reaction. The term "major chemical reaction" refers to the fact that this zone is designed primarily for this chemical reaction, as opposed to a zone designed for another effect (major effect), and in which unforeseen / undesired chemical reactions or secondary chemical reactions (i.e., reactions for a secondary effect) could nevertheless occur.

[0112] Naturally, piping can be installed between the combustion reactor and the oxidation reactor, and this piping may include various components such as valves, including L-valves, and / or siphons, which can be used to regulate the flow rate of the oxygen carrier. In other words, the reactors are connected via fluids, specifically through pipes equipped with appropriate valves.

[0113] Such an installation is suitable for the implementation of the process described above and is particularly suitable for biomass or RDF type loads, comprising a significant amount (at least 50% or even 70% or 80%) of volatiles.

[0114] Preferably, the first reaction zone may have a passage cross-section strictly smaller than the passage cross-section of the second reaction zone, and / or the third zone may have a passage cross-section greater than or equal to the passage cross-section of the second reaction zone to promote the creation of a dense phase in the second reaction zone and the creation of a dilute phase in the first reaction zone.

[0115] Figure 2 illustrates, schematically and without limitation, an example of a CLC process for a fuel comprising at least 50% volatile compounds according to the invention.

[0116] The process includes an AR oxidation reactor and an FR combustion reactor.

[0117] In the AR oxidation reactor, an oxygen carrier 8, in particulate form, and an oxidizing gas 1, which can be air, are injected. The oxidizing gas 1 will oxidize the oxygen carrier 8 particles in the AR oxidation reactor. The oxygen carrier 8 particles move vertically from bottom to top in the AR oxidation reactor and in co-current with the oxidizing gas 1.

[0118] Downstream of the AR oxidation reactor, there is a first cyclone S1 which separates oxygen-depleted gas 2 and the oxygen carrier particles which are sent to the lower part of the FR combustion reactor by the oxygen carrier feed 5.

[0119] The FR combustion reactor comprises three reaction zones situated one above the other:

[0120] - A first reaction zone Z1 which is a dilute phase;

[0121] - A second reaction zone Z2 which is a dense phase;

[0122] - A third zone Z3 which is a diluted phase.

[0123] In addition to the oxygen carrier which is introduced by the feed 5 located in the lower part, the FR combustion reactor includes a feed 6 in charge (here biomass or CSR or RDF or any other fuel including a high quantity of volatiles) and a feed G1 in a fluidization gas.

[0124] In the first reaction zone Z1, the volatiles of the charge are released and char is produced. The volatiles can react with the oxygen carrier.

[0125] In the second reaction zone Z2, the produced char is gasified, and some of the resulting gases react with the oxygen carrier. In the third zone Z3, the combustion and fluidization gases exit to join the second cyclone S2, and this third zone serves to limit the entrainment of solid particles.

[0126] The oxygen carrier exits through outlet 4 to join the oxygen carrier supply 8 of the oxidation reactor AR. As shown, outlet 4 is located at the bottom of the second reaction zone Z2, but it could be located elsewhere, notably at the top of the combustion reactor FR.

[0127] In the FR combustion reactor, the charge and the oxygen carrier move globally from bottom to top, driven by the fluidizing gas.

[0128] In the second reaction zone Z2, a G2 fluidizing gas supply can be used.

[0129] The fluid, exiting the third zone Z3 and the combustion reactor FR, which includes the fluidization gas from the first reaction zone Z1, the second reaction zone Z2, and the reaction gases (gasification and reaction of volatiles with the oxygen carrier) and entrained solid particles, enters a second cyclone S2. The gas, consisting mainly of carbon dioxide CO2 and water vapor H2O, exits through outlet 3, while the solid particles recovered by the second cyclone S2 are rerouted through conduit 7 to the bottom of the first reaction zone Z1 for recycling.

[0130] The cross-sectional area in the second reaction zone Z2 is strictly greater than that in the first reaction zone Z1 and the cross-sectional area in the third zone Z3 is equal to the cross-sectional area in the second reaction zone Z2.

[0131] The fluidizing gas entering feeds G1 and / or G2 may be a portion of the gas exiting outlet 3, including CO2 and / or steam, possibly purified. Figures 3 and 4 illustrate, schematically and without limitation, examples of distributors for the CLC process according to the invention.

[0132] Figure 3 illustrates the distributor installed in the combustion reactor in a two-dimensional plan view, while Figure 4 represents the distributor alone in a three-dimensional view.

[0133] In Figure 3, the distributor 20 is positioned at the outlet of the first reaction zone Z1 to distribute the fluid exiting this reaction zone into the second reaction zone Z2. As shown, the distributor 20 comprises a cylindrical, substantially vertical section which is an extension of the wall of the first reaction zone Z1. The distributor 20 therefore has the same cross-sectional area as the first reaction zone Z1 (although it could have a different cross-sectional area). The distributor 20 is located in the lower part of the second reaction zone so that the fluid enters this lower section and flows upwards within this second reaction zone.

[0134] The distributor 20 is closed at the top by a plug 22 (or cap) so as to prevent the fluid from exiting through the top and to force it to exit through the lateral openings 21 positioned in the cylindrical part.

[0135] Figure 4 provides a clearer visualization of the distributor 20, which comprises the substantially vertical cylindrical portion as shown, a cap 22 for closing the top of this cylindrical portion, and lateral openings 21 positioned on the cylindrical portion, preferably evenly distributed around it to distribute the fluid homogeneously in the second reaction zone. The lateral openings 21 are shown here in a substantially circular shape, but other shapes could be used.

Claims

Demands 1. Chemical loop combustion process of a fuel comprising at 50% volatile compounds, preferably fuel comprising biomass and / or RDF and / or RDF, particles of an oxygen carrier (1) circulating in said chemical loop, said process comprising at least: - a step of bringing the fuel into contact, in a first reaction zone (Z1) operating in an upward transported dilute fluidized bed, with the particles of the oxygen carrier (1), this contact generating a first gaseous effluent and char; - a combustion / gasification stage, in a second reaction zone (Z2) located vertically above the first reaction zone (Z1), the second reaction zone (Z2) operating as a dense fluidized bed, in which: * combustion of the gaseous effluents from the first reaction zone (Z1) in the presence of the oxygen carrier particles (1) is carried out; * gasification of the char followed by combustion of the gases resulting from this gasification of the char are produced; - a stage of circulating the gases produced in the combustion / gasification stage and the particles of the oxygen carrier, in a third zone (Z3) operating in a dilute fluidized bed, located vertically above the second reaction zone (Z2); - an oxidation step, in an oxidation zone, in which a reoxidation of the oxygen carrier particles (1) occurs before returning said reoxidized particles to the first reaction zone (Z1).

2. A method according to claim 1, wherein the fluid exiting the first reaction zone is distributed via a distributor to enter the second reaction zone (Z2), preferably the distributor comprising a substantially vertical cylindrical part closed at the top, and lateral openings.

3. A method according to any one of the preceding claims, wherein the method does not include separation of unburned particles and oxygen carrier particles (1).

4. A method according to any one of the preceding claims, wherein the passage cross-section in the second reaction zone (Z2) is strictly greater than that in the first reaction zone (Z1).

5. A method according to any one of the preceding claims, wherein the passage section in the third zone (Z3) is greater than or equal to the passage section in the second reaction zone (Z2).

6. A method according to any one of the preceding claims, wherein the first reaction zone (Z1) and / or the second reaction zone (Z2) are supplied with a fluidizing gas.

7. A method according to claim 6, wherein the fluidizing gas comprises a portion of the gas exiting the third zone (Z3), optionally purified, preferably the fluidizing gas comprises CO2 and / or recycled water vapor.

8. A method according to any one of the preceding claims, wherein the average residence time of the solid particles in the first reaction zone is between 0.5 and 10 seconds, the average residence time of the solid particles in the second reaction zone being between 0.25 and 60 minutes, preferably between 1 and 30 minutes.

9. A method according to any one of the preceding claims, wherein the surface velocity of the gas in the first reaction zone (Z1) is between 0.5 and 20 m / s, the surface velocity of the gas in the second reaction zone (Z2) being between 0.02 and 3 m / s.

10. A method according to any one of the preceding claims, wherein the volume fraction of solid in the first reaction zone (Z1) is less than or equal to 0.1, preferably less than or equal to 0.05, and even more preferably less than 0.

02.

11. A method according to any one of the preceding claims, wherein the temperature in the second reaction zone (Z2) is greater than 700°C, preferably greater than 800°C, and even more preferably between 900 and 1000°C.

12. A method according to any one of the preceding claims, wherein at the exit of the third zone (Z3), the gas stream containing the fuel particles and a fraction of oxygen carrier particles (1) is sent to at least one gas-solid separation stage (S2) to recover almost all of the particles contained in the gas stream from the third zone (Z3), the recovered particles being recycled to the first reaction zone (Z1).

13. Installation for carrying out the combustion of a fuel comprising at least 50% volatile compounds, preferably fuel comprising biomass and / or SRF, according to the process according to any one of claims 1 to 12, said installation comprising at least: - a combustion reactor (FR) comprising: * a first reaction zone (Z1) operating in dilute phase, comprising a fuel supply (6), an oxygen carrier particle supply (5) and preferably a fluidization gas supply (G1), * a second reaction zone (Z2) receiving gases and particles originating directly from the first reaction zone (Z1), * a third zone (Z3) operating in dilute phase receiving through its inlet a gaseous combustion effluent from the second reaction zone (Z2), - an oxidation reactor (AR) comprising an oxidation zone, a feed of oxygen carrier particles (1) exiting the second reaction zone (Z2) and a feed (8) of oxidizing gas.

14. Installation according to claim 14, wherein the first reaction zone (Z1) has a passage section strictly smaller than the passage section of the second reaction zone (Z2), and / or wherein the third zone (Z3) has a passage section greater than or equal to the passage section of the second reaction zone (Z1).

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