Method and device for drying and torrefaction of a carbon-based feedstock

Abstract

A method and device for drying and torrefaction of a carbon-based feedstock, comprising: drying the feedstock (§1) with air (§3) originating solely from a makeup of ambient air in order to produce an at least partially dried solid effluent (§5); treating said solid effluent with a gaseous combustion effluent (§15) to produce a torrefied solid effluent (§7) and a gaseous torrefaction effluent (§8); treating said gaseous torrefaction effluent in a combustion unit (§9) with an oxygen-containing gas stream (§10) to produce combustion flue gases (§12), a portion of the heat generated by combustion being used to heat one or more stream(s) entering the combustion unit; cooling combustion flue gases to produce partially cooled combustion flue gases (§14), at least a first portion of which is recycled to the torrefaction unit (§6), as gaseous combustion effluent.

Description

[0001] Method and apparatus for drying and roasting a carbonaceous feedstock

[0002] technical field

[0003] The present invention relates to a process and device for drying and roasting a carbon feedstock preferably containing at least a fraction of biomass for the production of liquid hydrocarbons, biofuels, and possibly the production of petrochemical bases and / or chemical bases and / or hydrogen.

[0004] Previous technique

[0005] US patent application US2010 / 0083530 describes a device and method for roasting a water-containing lignocellulosic material, said method using a single gas circulation loop for both drying and roasting operations. Raw biomass is fed into the top of the kiln and flows by gravity to the bottom. The drying operation takes place in the first section of the kiln. The temperature in this top zone is between 200°C and 260°C. Once the biomass is dried, the roasting operation takes place on the lower trays, and the roasting gases and drying water are extracted from the top of the kiln. The temperature in the kiln zone where the roasting operation is carried out is typically between 200°C and 300°C, and preferably between 260°C and 280°C. Part of the gases extracted at the top of the furnace are recycled to the bottom of the furnace after being reheated by passing through a heat exchanger.The remaining portion of these gases is first sent to a condensing zone. The gases exiting this section are then sent to a combustion zone, where they are utilized and hot flue gases are generated. These flue gases then pass through a heat exchanger, reheating the portion of the roasting gases recycled both at the top and bottom of the oven, in the drying and roasting zones. The energy supplied to the oven therefore comes from the combustion of these roasting gases. The roasted biomass is extracted from the bottom of the oven. In this process, the hot flue gases generated by the combustion of a portion of the roasting gases are used to reheat the remaining portion of the roasting gases recycled within the oven. These hot flue gases are not recycled to the top of the oven in the drying zone, nor to the bottom of the oven in the roasting zone.

[0006] US patent application 2013 / 228443 proposes a thermochemical treatment of biomass within a vertical, multi-stage furnace featuring several independent chambers with controlled temperature and pressure environments. Each chamber can be connected to a control zone containing at least one combustion zone, a valve, and a pump. The control zone is connected to a gas inlet and outlet for each chamber. The control zone(s) thus supply the necessary energy to each chamber by introducing hot gas generated in the control zone via the combustion zone, and reintroducing this hot gas into the inlet of the chamber(s) at a temperature ranging from 40 to 370°C. LIS2013 / 228443 specifically describes a multi-stage furnace with five independent chambers, each connected to its own control unit.Each control unit has the characteristics described above. Biomass is introduced into the first chamber, which operates under an aerobic atmosphere, where it is dried by a flow of gas heated in the control zone connected to that chamber and introduced into the chamber at a temperature between 94 and 204°C. The dried biomass is then transferred from one chamber to the next via a gas-tight valve and is heated to progressively higher temperatures, thus promoting torrefaction as it is transferred to the different chambers, which operate under an anaerobic atmosphere. In this configuration, each chamber within the furnace is independent with respect to the gas phase.

[0007] Patent application W02005 / 056723 describes a process for producing solids from biomass raw material, preferably lignocellulosic biomass, in which the biomass, generally with a moisture content between 30% and 60% by weight, is sent to a drying stage to reduce its moisture content to below 15% by weight. The dry biomass is then sent to a torrefaction zone, from which gases called torrefaction gases and a solid called torrefied biomass are extracted. This solid is then cooled and can be processed in a pelletizing stage before transport and / or storage. A portion of the torrefaction gases emitted during the torrefaction operation is sent to a heat exchanger after a step designed to increase their pressure.The remaining roasting gases are used in a combustion chamber to generate hot flue gases, which are cooled by passing through a heat exchanger before being recycled to the drying stage to provide the required energy. The portion of the roasting gases compressed at the end of the stage to increase their pressure is then sent to the heat exchanger to be reheated by exchanging heat with the hot flue gases from the combustion chamber. The hot roasting gases exiting the heat exchanger are then recycled back into the roasting area to provide the thermal energy needed for this operation.In this case, the hot fumes generated by the combustion of part of the roasting gases are used to heat the other part of the roasting gases before they are recycled in the roasting area and the fumes, cooled, are then recycled, alone, in the drying stage.

[0008] US patent application 2012 / 137538 describes a device and method for drying and roasting a material comprising carbon and preferably biomass in a multi-stage furnace including a drying zone and a roasting zone, said zones having two separate gas circulation loops. The biomass is fed into a drying zone located in the upper section of the furnace to remove almost all of its water content. The dried biomass is then fed into the roasting zone, from which gases called roasting gases and the roasted biomass are extracted.The drying gases, consisting mainly of water vapor, extracted from the drying zone circulate in an independent loop and are partially sent to a heat exchanger where they are heated to a temperature between 150 and 300°C before being recycled back into the drying zone to provide the thermal energy required for drying. The roasting gases extracted from the roasting zone are sent to a combustion chamber to generate hot combustion gases or fumes, which are cooled to a temperature above 300°C by passing through the heat exchanger with the drying gases circulating in the drying loop, before being partially recycled back into the roasting zone to provide the energy required for roasting.This heat exchanger thus allows the reheating of the recycled gas from the drying loop and the cooling of the gas from the roasting loop.

[0009] Patent application WO2015 / 091492 describes a process for roasting a carbon feed comprising at least one step of drying the biomass and a step of roasting the dried carbon feed producing roasting gases and a roasted carbon feed, wherein at least a portion of the roasting gases from the roasting step is sent to a combustion step producing combustion gases at a temperature at least above 700°C, at least a portion of which is recycled without an intermediate cooling step, in the drying step, mixed with at least one gaseous effluent, the temperature of the gaseous mixture recycled in the drying step being between 200 and 900°C.

[0010] The processes described above propose to send to the drying stage either roasting gases, or fumes from the combustion of roasting gases and / or other fuels, or to recycle part of the gas from the drying unit.

[0011] Summary of the invention

[0012] A first object of the present invention is to provide a drying and roasting process and device that allows for more efficient control of roasting yield, independent of the feed moisture content. The use of a process and device according to the invention makes it possible to improve the material yield of a stand-alone roasting plant, reducing consumption and even eliminating the need for fossil fuels or fuels from an external source. The process and device according to the invention are particularly well-suited for integration into a process chain for producing advanced fuels.

[0013] A second object of the present invention is to provide a drying and roasting process and device that reduces the fuel consumption required for the combustion unit.

[0014] According to a first aspect, the aforementioned objects, as well as other advantages, are obtained by a drying and roasting process of a carbon feed comprising the following steps: treating the carbon feed (§1) in a drying unit (§2) with air (§3) coming only from an ambient air supply to produce air charged with water vapor (§4) and a solid effluent at least partially dried (§5); treating the solid effluent at least partially dried (§5) with a combustion gaseous effluent (§15) in a roasting unit (§6) to produce a roasted solid effluent (§7) and a roasting gaseous effluent (§8) containing the combustion gaseous effluent (§15) and gases formed by roasting;treat the roasting gaseous effluent (§8) in a combustion unit (§9) with at least one oxygen-containing gas stream (§10) to produce combustion fumes (§12), part of the heat generated in the combustion unit (§9) being used to reheat at least part of at least one of the streams entering the combustion unit (§9); cool at least part of the combustion fumes (§12) in a first cooling unit (§13) to produce partially cooled combustion fumes (§14); recycle at least a first part of the partially cooled combustion fumes (§14) to the roasting unit (§6), as the combustion gaseous effluent (§15).

[0015] An advantage of the present invention is that it reduces the consumption of auxiliary fuel required to dry and roast a given hourly dry flow rate of carbon feedstock with a given material yield. The process according to the invention is particularly suitable for installation integrated into a process for the production of liquid hydrocarbons by gasification, Fischer-Tropsch synthesis, and the valorization, for example by hydroconversion, of the effluents from the Fischer-Tropsch synthesis, the production of gaseous effluents by these latter installations being in excess of the auxiliary fuel required for said drying and roasting steps.

[0016] An advantage of the present invention is to provide a process for treating in a given installation a carbonaceous load having a variable moisture content without varying the consumption of auxiliary fuel, or affecting the dry hourly flow rate treated or the material yield of the operation.

[0017] An advantage of the present invention is that it provides a process for drying and roasting a carbonaceous feedstock that can operate autonomously without fossil fuels or in a decentralized manner, as opposed to a process for transforming the roasted solid effluent in a plant for the production of liquid hydrocarbons, biofuels, and potentially petrochemical and / or chemical bases and / or hydrogen. The invention improves the material yield of roasting in this scenario compared to the prior art, regardless of the feedstock's moisture content. According to one or more embodiments, a supplementary fuel supply (§11) is sent to the combustion unit (§9).

[0018] According to one or more embodiments, part of the heat generated in the combustion unit (§9) is used to heat at least part of the fuel (§11).

[0019] According to one or more embodiments, the fuel (§11) comprises residual gas from a Fischer-Tropsch synthesis unit or a Fischer-Tropsch effluent recovery unit.

[0020] According to one or more embodiments, part of the heat generated in the first cooling unit (§13) is used to heat at least part of at least one (of the) stream(s) or flow entering the combustion unit (§9) and / or to heat the air (§3) entering the drying unit (§2).

[0021] According to one or more embodiments, the process includes cooling a second part (§16) of the partially cooled combustion fumes (§14) in a second cooling unit (§17) to produce cooled combustion fumes (§18).

[0022] According to one or more embodiments, the second part (§16) represents the remainder of the first part of the partially cooled combustion gases (§14). According to one or more embodiments, the cooled combustion gases (§18) exiting the second cooling unit (§17) have a temperature between 100°C and 300°C, preferably between 150°C and 250°C, and preferably between 160°C and 210°C.

[0023] According to one or more embodiments, one or more secondary gas streams containing oxygen are injected into the combustion unit (§9).

[0024] According to one or more embodiments, at least a portion of the oxygen-containing gas stream (§10) and optionally of the secondary oxygen-containing gas streams entering the combustion unit (§9) is heated by a portion of the heat generated in the combustion unit (§9).

[0025] According to one or more embodiments, the oxygen-containing gas stream (§10) and optionally one or more secondary oxygen-containing streams entering the combustion unit (§9) are separated into several streams injected (into different zones) into the combustion unit (§9).

[0026] According to one or more embodiments, at least one oxygen-containing gas stream (§10) entering the combustion unit (§9) comprises air, oxygen or an oxygen-enriched gas stream (e.g. air).

[0027] According to one or more embodiments, the oxygen in the oxygen-containing gas stream (§10) is produced by a water electrolysis unit or by an air separation unit. According to one or more embodiments, the process includes at least one of the following operating conditions: the drying operation is carried out at a temperature between 100°C and 300°C, preferably between 100°C and 200°C and preferably between 100°C and 150°C; the residence time of the carbon feedstock (§1) in the drying unit (§2) is between 5 minutes and 180 minutes, preferably between 5 minutes and 120 minutes and even more preferably between 5 minutes and 60 minutes; the drying operation is carried out at an absolute pressure between 0.05 MPa and 0.2 MPa and preferably between 0.08 MPa and 0.15 MPa;the roasting operation is carried out at a temperature between 200°C and 450°C, preferably between 250°C and 425°C and preferably between 300°C and 400°C; the residence time of the at least partially dried solid effluent (§5) in the roasting unit (§6) is between 5 minutes and 600 minutes, preferably between 10 minutes and 180 minutes and even more preferably between 10 minutes and 90 minutes; the roasting operation is carried out at an absolute pressure between 0.05 MPa and 0.2 MPa and preferably between 0.08 MPa and 0.15 MPa; the combustion operation of organic compounds of the roasting gaseous effluent (§8) produces combustion fumes (§12) having a temperature greater than or equal to 700°C, preferably greater than or equal to 750°C, preferably greater than or equal to 800°C, such as being between 800°C and 850°C;the partially cooled combustion fumes (§14) exiting the first cooling unit (§13) have a temperature between 200°C and 450°C, preferably between 250°C and 425°C and preferably between 300°C and 400°C.;

[0028] According to a second aspect, the aforementioned objects, as well as other advantages, are obtained by a device for drying and roasting a carbonaceous load comprising the following units: a drying unit (§2) adapted to treat the carbonaceous load (§1) with air (§3) coming only from an ambient air supply to produce air charged with water vapor (§4) and a solid effluent at least partially dried (§5); a roasting unit (§6) adapted to treat the solid effluent at least partially dried (§5) with a combustion gaseous effluent (§15) to produce a roasted solid effluent (§7) and a roasting gaseous effluent (§8) containing the combustion gaseous effluent (§15) and gases formed by roasting; a combustion unit (§9) adapted to treat the roasting gaseous effluent (§8) with a gas stream containing oxygen (§10) to produce combustion fumes (§12);at least one heat exchanger suitable for reheating at least part of at least one of the streams entering the combustion unit (§9) with part of the heat generated in the combustion unit (§9); a first cooling unit (§13) suitable for cooling at least part of the combustion fumes (§12) to produce partially cooled combustion fumes (§14); a recycling duct suitable for recycling at least a first part of the partially cooled combustion fumes (§14) to the roasting unit (§6), as the combustion gaseous effluent (§15).

[0029] Methods of implementing the process and device according to the aforementioned aspects as well as other characteristics and advantages will appear upon reading the description that follows, given for illustrative purposes only and not as a limitation, and with reference to the following drawings.

[0030] List of figures

[0031] Figure 1 shows a schematic representation of a drying and roasting process according to the present invention.

[0032] Figure 2 shows a schematic representation of a reference drying and roasting process.

[0033] Description of the implementation methods

[0034] Embodiments of the method and device according to the invention will now be described in detail. In the following detailed description, numerous specific details are presented to provide a more thorough understanding of the method and device according to the invention. However, it will be apparent to those skilled in the art that the method and device according to the invention can be implemented without these specific details. In other cases, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0035] In this description, the term "include" is synonymous with (means the same as) "include" and "contain," and is inclusive or open-ended and does not exclude other unstated elements. It is understood that the term "include" includes the exclusive and closed term "consist." Furthermore, when used in this description, the terms "essentially," "substantially," or "approximately" in relation to a reference value correspond to an approximation of ±10%, preferably ±5%, most preferably ±2%, or even more preferably ±1% of that reference value, which may be, for example, a temperature, pressure, compound content, etc.

[0036] The present invention relates to a process and device for drying and roasting a carbon feedstock preferably containing at least a fraction of biomass for the production of liquid hydrocarbons, biofuels, and possibly the production of petrochemical bases and / or chemical bases and / or hydrogen.

[0037] The drying and roasting process and device according to the present invention are described below with reference to Figure 1.

[0038] A carbonaceous load §1 is treated in a drying unit §2 with air §3 to produce air charged with water vapor §4 and an effluent of solid at least partially dried §5. Advantageously, the air §3 comes only from an ambient air supply.

[0039] The at least partially dried solid effluent §5 obtained from the drying unit §2 is treated with a combustion gas effluent §15 in a roasting unit §6 to produce a roasted solid effluent §7 and a roasted gas effluent §8. The roasted gas effluent §8 includes, in particular, the introduced combustion gas effluent §15 and additional gases formed by roasting the at least partially dried solid effluent §5. The roasted solid effluent §7 is extracted from the process and can be stored or sent to a downstream treatment unit such as a gasification unit.

[0040] The roasting gaseous effluent §8 exiting the roasting unit §6 is treated in a combustion unit §9 by reaction with at least one oxygen-containing gas stream §10 to produce combustion fumes §12. Advantageously, a portion of the heat generated in the combustion unit §9 is used to reheat at least a portion of at least one of the streams entering the combustion unit §9. Optionally, a fuel stream §11 is sent as a make-up to the combustion unit §9.

[0041] At least part of the combustion fumes §12 exiting the combustion unit §9 is treated in a first cooling unit §13 to produce partially cooled combustion fumes §14.

[0042] At least a first part of the partially cooled combustion fumes §14 is sent to the roasting unit §6, as combustion gaseous effluent §15.

[0043] According to one or more embodiments, a second part §16 of the partially cooled combustion fumes §14 is cooled in a second cooling unit §17 to produce cooled combustion fumes §18. Advantageously, heat can be recovered to cover a possible energy requirement, such as to heat a process stream according to the invention.

[0044] It is understood that the heating of the process streams according to the invention is not shown in Figure 1 because many possibilities (e.g., heat exchanger) known to those skilled in the art are conceivable. For example, it is envisaged to heat at least one of the following streams or flows: air §3; the roasting gas effluent §8; at least a portion of the oxygen-containing gas stream §10 and optionally at least one secondary oxygen-containing gas stream feeding the combustion unit §9; the fuel stream §11.

[0045] The process according to the invention can advantageously be implemented in a decentralized drying and roasting installation, away from the units for the valorization of the roasted biomass, making it possible to provide a roasted solid effluent §7 with a concentrated energy content, with a yield and a quality that can be controlled independently of the moisture content of the load §1.

[0046] The process according to the invention also has the advantage of reducing the fuel consumption §11 required by the combustion unit §9 and thus potentially using only fuel from the feed §1 of the process and obtained in units located downstream of the roasting (e.g. waste gas from a Fischer-Tropsch unit or a Fischer-Tropsch effluent recovery unit), or even not using any fuel §11 (flow §11 equal to zero).

[0047] Carbon footprint

[0048] The carbon feed §1 used in the drying and roasting process according to the present invention is preferably a solid feed comprising or consisting of biomass.

[0049] The biomass treated in the drying and roasting process according to the invention can advantageously vary according to its origin.In one or more embodiments, biomass comprises at least one compound selected from the following: wood or wood by-products, such as waste and residues produced by forestry (forest residues) or papermaking, forestry products, residues from sawmills and wood processing industries, recycled wood such as packaging wood from the recovery of pallets, crates and boxes, end-of-life wood from industry, construction, furniture, DIY and agriculture; carbon compounds from industry such as sludge or agri-food waste; carbon compounds from traditional agriculture, such as residues selected from straw, coppice, bagasse, as well as crops dedicated to energy production (miscanthus, short-rotation coppice...); organic waste, such as urban waste, for example sewage sludge, household waste.

[0050] Preferably, the biomass used in the present invention comprises or consists of lignocellulosic biomass or cellulose, and preferably the biomass is lignocellulosic biomass. Lignocellulosic biomass essentially contains three natural constituents present in varying quantities depending on its origin: cellulose, hemicellulose, and lignin. Lignocellulosic biomass is preferably used in its raw form, that is, in its entirety, consisting of these three constituents: cellulose, hemicellulose, and lignin. Preferably, the lignocellulosic biomass comprises a water content of between 5% and 70% by weight relative to the total mass of the biomass.

[0051] In one or more embodiments, the carbon content §1 comprises a plastic fraction including, for example, one or more polymers, and may contain other compounds, such as additives of organic or inorganic origin and / or impurities resulting, for example, from the life cycle of plastic materials and objects, and / or from the waste collection and sorting process. For example, impurities resulting from use may be metallic, organic, or mineral; they may include packaging residues, food residues, or compostable residues (biomass). Impurities resulting from use may also include glass, wood, cardboard, paper, household, chemical, or cosmetic products, used oils, and water.

[0052] The drying unit

[0053] According to the invention, the drying unit (or dryer as described below) §2 is adapted to treat the carbon load §1 with air §3 to produce air charged with water vapor §4 and an effluent of solid at least partially dried §5.

[0054] According to the invention, the airflow §3 introduced into the dryer §2 comes solely from ambient air supply. The airflow §3 is therefore not recirculated from another airflow. For example, the air §3 is not recirculated from the drying unit §2 and / or the roasting unit §6 and / or the combustion unit §9 and / or the cooling unit(s) §13 and / or §17.

[0055] Advantageously, the dryer §2 allows the water content of the carbon load §1 to be reduced. According to one or more embodiments, the effluent of at least partially dried solid §5 has a water content of less than 25% by weight, preferably less than 15% by weight, and preferably less than 12% by weight, relative to the total weight of the effluent of at least partially dried solid §5, at the outlet of the dryer §2.

[0056] According to one or more embodiments, the dryer §2 comprises at least one of the following devices: a belt tunnel dryer (also called a belt dryer), a trolley and rack or swing tunnel dryer, a tray dryer, a drum dryer, a fluidized bed dryer, a pneumatic dryer, a disc or screw dryer.

[0057] According to one or more embodiments, the drying operation is carried out with air §3 entering the dryer §2 at a temperature between 100°C and 300°C, preferably between 100°C and 200°C, and most preferably between 100°C and 150°C. According to one or more embodiments, the residence time of the carbonaceous load §1 in the dryer §2 is between 5 minutes and 180 minutes, preferably between 5 minutes and 120 minutes, and even more preferably between 5 minutes and 60 minutes. According to one or more embodiments, the drying operation is carried out at an absolute pressure between 0.05 MPa and 0.2 MPa, and most preferably between 0.08 MPa and 0.15 MPa.

[0058] The roasting unit

[0059] According to the invention, the roasting unit §6 (or roaster) is adapted to treat the at least partially dried solid effluent §5 with the combustion gaseous effluent §15 to produce a roasted solid effluent §7 and a roasting gaseous effluent §8 containing the combustion gaseous effluent §15 and gases formed in the roasting unit §6.

[0060] According to one or more embodiments, the roasting unit §6 comprises at least one oven, such as at least one of the following devices: a tray oven, a multi-deck oven, a multi-stage oven comprising one or more trays through which the solid charge flows from an upper tray to the lower trays by gravity, a rotary drum reactor, a screw reactor, a fluidized bed reactor, a moving bed reactor, a vibrating grid or belt reactor, a cyclone reactor.

[0061] According to one or more embodiments, the roasting operation is carried out at a temperature of the incoming gas phase (combustion gas effluent §15) between 200°C and 450°C, preferably between 250°C and 425°C, and preferably between 300°C and 400°C. According to one or more embodiments, the residence time of the at least partially dried solid effluent §5 in the roasting unit §6 is between 5 minutes and 600 minutes, preferably between 10 minutes and 180 minutes, and even more preferably between 10 minutes and 90 minutes. According to one or more embodiments, the roasting operation is carried out at an absolute pressure between 0.05 MPa and 0.2 MPa, and preferably between 0.08 MPa and 0.15 MPa.

[0062] According to one or more embodiments, at the end of the roasting step, the effluent of roasted solid §7 is sent to a cooling step (known to those skilled in the art) before storage or transport to another operation.

[0063] According to one or more embodiments, the roasting gaseous effluent §8 comprises, at the end of the roasting step, at least one of the following compounds: carbon monoxide (CO), carbon dioxide (CO2), acetic acid, methanol, furfural, nitrogen, water, oxygen.

[0064] The combustion unit

[0065] According to the invention, the combustion unit §9, comprising for example or consisting of a burner and a combustion chamber, is adapted to treat the roasting gaseous effluent §8 with at least one oxygen-containing gas stream §10 and optionally a fuel supplement §11 to produce combustion fumes §12, part of the heat generated in the combustion unit §9, for example in the combustion fumes §12, being used to reheat at least part of at least one of the streams entering the combustion unit §9, such as at least one of the streams §8, §10 and §11.

[0066] According to one or more embodiments, the oxygen-containing gas stream §10 and optionally one or more secondary oxygen-containing streams can be separated into several streams injected at the burner or combustion chamber.

[0067] According to one or more embodiments, at least one of the oxygen-containing gas streams entering the combustion unit comprises air, oxygen-enriched air or oxygen, or any other oxygen-enriched gas stream.

[0068] According to one or more particular embodiments, the oxygen used as the gas stream entering the combustion unit or to enrich the oxygen-containing gas stream §10 is produced by electrolysis of water or by an air separation unit.

[0069] In one or more embodiments, the fuel §11 comprises or consists of gas of biogenic origin or derived from the carbon feedstock §1 and produced in a downstream step of the roasting step. In one or more embodiments, the fuel comprises or consists of gas produced by a Fischer-Tropsch synthesis unit or a Fischer-Tropsch effluent recovery unit in a process sequence as described in patent application WO2014068253A1. In one or more embodiments, the fuel comprises or consists of residual gas from a Fischer-Tropsch synthesis unit or a Fischer-Tropsch effluent recovery unit. According to one or more embodiments, the fuel §11 comprises unconverted synthesis gas, carbon dioxide and gaseous hydrocarbons such as C1 to C10 paraffins (predominantly), C2 to C10 olefins, and C1 to C5 oxygenated compounds.According to one or more embodiments, the unconverted synthesis gas essentially comprises or consists of carbon monoxide and hydrogen and optionally of water vapor and / or methane and / or carbon dioxide.

[0070] Advantageously, depending on the quantity of roasting gases generated during the roasting operation and their calorific value, depending on the severity of the roasting operation, a supplementary fuel §11 can be introduced into the combustion unit §9 in order to cover all the energy needs of the process and in particular to provide the energy required for the roasting unit §6.

[0071] According to one or more embodiments, the roasting gaseous effluent §8 is sent with the oxygen-containing gas stream §10 and with the fuel supplement §11 into the combustion unit §9.

[0072] According to one or more embodiments, the oxygen-containing gas stream §10 is separated into two or more streams which can be injected with the roasting gas effluent §8 and optionally with the fuel supplement §11 at the combustion chamber or burner of the combustion unit §9.

[0073] Advantageously, the combustion unit §9 allows for the conversion, at least in part, of the organic compounds present in the roasting flue gas §8 and possibly the fuel §11 into CO2 and H2O. The combustion flue gas stream §12 consists mainly of carbon dioxide CO2, water H2O, residual oxygen O2 and, if at least one oxygen-containing gas stream §10 injected into the combustion unit §9 contains air, nitrogen N2.

[0074] Advantageously, the combustion of organic compounds from the roasting gaseous effluent §8 makes it possible to produce combustion fumes (or gases) §12 having a temperature greater than or equal to 700°C, preferably greater than or equal to 750°C, preferably greater than or equal to 800°C, such as being between 800°C and 850°C.

[0075] Advantageously, the heat produced by the combustion unit §9 can be at least partly used to reheat all or part of the oxygen-containing gas stream §10 and optionally oxygen-containing secondary feed streams and / or all or part of the roasting gas effluent §8 and / or the fuel §11.

[0076] The first cooling unit

[0077] According to the invention, the first cooling unit §13 is adapted to cool at least part of the combustion fumes §12 and thus produce partially cooled combustion fumes §14.

[0078] According to one or more embodiments, the first cooling unit §13 comprises or consists of at least one heat exchange device suitable for cooling the combustion fumes §12 and heating at least a part of at least one of the following streams: the roasting gaseous effluent §8; the oxygen-containing gaseous stream §10; the fuel top-up §11.

[0079] According to one or more embodiments, the first cooling unit §13 further includes one or more heat exchange devices for heating the air §3.

[0080] According to one or more embodiments, the first cooling unit §13 further includes one or more heat exchange devices for generating hot utility (e.g. steam, hot water) by cooling the combustion fumes §12. For example, part of the hot utility generated in the first cooling unit §13 can be used to heat the air §3.

[0081] Advantageously, the first cooling unit §13 can thus contribute to heating at least part of the loads of the combustion unit §9, thereby leading to a reduction in fuel consumption §11. According to one or more embodiments, the partially cooled combustion fumes §14 exiting the first cooling unit §13 have a temperature between 200°C and 450°C, preferably between 250°C and 425°C and preferably between 300°C and 400°C.

[0082] Furthermore, according to the invention, at least a first part of the partially cooled combustion fumes §14 is recycled to the roasting unit §6, as combustion gaseous effluent §15. Advantageously, at least a first part of the partially cooled combustion fumes §14 provides the thermal energy required for the roasting stage.

[0083] According to one or more embodiments, the second part §16 (e.g. the remainder) of the partially cooled combustion fumes §14 can be sent to a second cooling unit §17.

[0084] The second cooling unit

[0085] The second cooling unit §17 is adapted to cool the second part §16 of the partially cooled combustion fumes §14 to produce cooled combustion fumes §18.

[0086] According to one or more embodiments, the second cooling unit §17 comprises or consists of at least one heat exchange device suitable for cooling the second part §16 of the partially cooled combustion fumes §14 and heating at least a part of at least one of the following streams: air §3; roasting gaseous effluent §8; oxygen-containing gas stream §10; fuel top-up §11.

[0087] According to one or more embodiments, the second cooling unit §17 further comprises one or more heat exchange devices for generating hot utility (e.g., steam, hot water). For example, part of the hot utility generated in the second cooling unit §17 can be used to heat the air §3.

[0088] Advantageously, the second cooling unit §17 can thus contribute to heating at least part of the loads of the combustion unit §9, thereby leading to a reduction in fuel consumption §11.

[0089] The cooling units §13 and §17 may include heat exchangers or any other device enabling heat exchange between two streams, or even at least three streams such as multi-service heat exchangers. According to one or more embodiments, the cooled combustion gases §18 exiting the second cooling unit §17 have a temperature between 100°C and 300°C, preferably between 150°C and 250°C, and preferably between 160°C and 210°C.

[0090] Examples

[0091] Examples 1 and 2 illustrate the performance of a biomass drying and torrefaction process with a combustion unit §9 powered by an auxiliary fuel §11, respectively, according to the prior art and the invention. The units described are integrated into a process chain for producing advanced fuels by gasification and Fischer-Tropsch synthesis.

[0092] Examples 3 and 4 illustrate the performance of an autonomous biomass drying and roasting process, i.e. with a combustion unit §9 having as its sole fuel the roasting gaseous effluent §8 exiting the roasting unit §6 (fuel flow §11 equal to zero) respectively according to the prior art and according to the invention.

[0093] Example 1 (according to the art of interiority)

[0094] Example 1 according to the prior art, shown in Figure 2, is described in patent US2012 / 0137538 and includes a drying step and a roasting step.

[0095] Wet biomass is sent as carbon feedstock §1 to a dryer §2 to remove all or part of its water content. The at least partially dried biomass (stream §5) exits the drying stage at 100°C and is then sent to a torrefyer §6 to be converted into torrefied biomass (stream §7) and torrefaction gaseous effluent §8. The torrefaction gaseous effluent §8 exiting the torrefaction stage is at 169°C and is sent to a combustion unit §9 with air at 20°C (stream §10) and fuel (stream §11) to generate combustion fumes §12 at 753°C.

[0096] The drying gas §30 entering the drying stage is at 180°C and consists mainly of water vapor. The drying gas effluent §40 exiting the dryer §2 is at 140°C. A portion of the drying gas effluent §40 exiting the drying stage is released into the air, and the other portion is sent to the first cooling unit §13, a heat exchanger type unit, to be heated by heat exchange with the hot combustion gases §12 exiting the combustion unit §9. In the heat exchanger, the combustion gases §12 are cooled from 753°C to 383°C, and the drying gas effluent is heated from 140°C to 180°C. The drying gaseous effluent exiting the heat exchanger at 180°C is recycled into the dryer §2 as drying gas §30 to provide the thermal energy required for drying.

[0097] Part (flow 15) of the combustion fumes partially cooled to 383°C (flow §14) is recycled to the roaster §6 to provide the thermal energy required for roasting. The other part (flow §16) of the combustion fumes partially cooled §14 is released into the air.

[0098] The energy required for the drying stage is entirely supplied by cooling the combustion fumes. The drying and roasting stages have two separate gas circulation loops.

[0099] The process of example 1 is not in accordance with the invention in that, on the one hand, the drying gas §30 used for drying is a recycling of part of the gas exiting the dryer §2 heated by heat exchange with the combustion fumes §12 and, on the other hand, no current supplying the combustion unit §9 (flow §8, §10 or §11) is heated by heat exchange with the combustion fumes §12.

[0100] In this example, the load for the drying and torrefaction process consists of wood chips with a moisture content at the inlet of dryer §2 of either 45% by weight or 20% by weight, representing two characteristic cases: forest biomass for the former and recycled wood for the latter. The equipment is sized for a maximum moisture content of 45% by weight. The hourly throughput of dry biomass at the inlet of dryer §2 is set at 9375 kg / h for each type of biomass.

[0101] The roasting yield, defined as the ratio of the dry biomass mass flow rates between the roasted solid effluent §7 and the at least partially dried solid effluent (§5), is set at 80%. The roasted solid effluent §7 exiting the roasting stage is completely dry.

[0102] Table 1 below gives the main operating conditions and energy requirements of the drying and combustion stages as a function of the water content contained in the biomass at the process input.

[0103] Table 1 The moisture content of the biomass entering the torrefyer §6 is 10% in the case of forest biomass and corresponds to the moisture content obtained by using the energy obtained by cooling the combustion fumes §12 from 753°C to 383°C.

[0104] The moisture content of the biomass entering the torrefyer §6 is 0% in the case of recycled wood because the biomass can be completely dried with the energy available by cooling the combustion fumes §12 from 753°C to 383°C.

[0105] The fuel available for roasting, derived from wood chips, is gas produced by Fischer-Tropsch units and Fischer-Tropsch effluent recovery units. The available quantity of this fuel is 4500 kW and corresponds to the available fuel flow rate multiplied by its lower heating value (LHV).

[0106] The quantity of fuel §11 required for the combustion chamber with air at 20°C is 5700 kW for forest biomass and 5000 kW for recycled wood, and corresponds to the required fuel flow multiplied by its lower heating value (LHV).

[0107] This quantity of fuel required under Section 11 is therefore greater than the quantity of fuel available in the Fischer-Tropsch and Fischer-Tropsch effluent recovery units. A supplementary supply of fossil fuel (e.g., natural gas) is therefore necessary.

[0108] Example 2 according to the invention

[0109] Example 2 is an example conforming to the invention in that the gas used for drying is air §3, sourced solely from ambient air supply, and therefore not from recirculation. Part of the heat from the combustion gases §12 is recovered to preheat the oxygen-containing gas stream §10 feeding the combustion unit §9. Example 2 is shown in Figure 1.

[0110] The wet biomass is fed as a carbon feedstock §1 into a dryer §2 to remove some of its water content. The air §3 entering the drying stage is at 120°C and contains mainly nitrogen and oxygen. This air §3 has been preheated from ambient temperature to 120°C by heat exchange with low-pressure steam.

[0111] The air laden with water vapor (§4) exiting the drying stage is at 52°C and contains mainly nitrogen, oxygen, and water vapor. This gas is not recycled in the drying stage (§2).

[0112] The at least partially dried biomass (flow §5) exits the drying stage at 50°C and is then sent to a torrefyer §6 to be converted into torrefied biomass (flow §7) and torrefaction gaseous effluent §8. The torrefaction gaseous effluent §8 is at 169°C and is sent to a combustion unit §9 with air at 600°C (flow §10) and fuel (flow §11) to generate combustion fumes §12 at 753°C. The combustion fumes §12 exiting the combustion unit §9 at 753°C are sent to the first cooling unit §13, which comprises two heat exchangers in series: a first heat exchanger A and then a second heat exchanger B.

[0113] The combustion gases §12 first enter the first heat exchanger A to be cooled by heat exchange with the air (flow §10) required for combustion. The air (flow §10) required for the combustion unit §9 is thus heated from 314°C to 600°C through heat exchange with the combustion gases §12 in the exchanger A.

[0114] Next, the combustion fumes exiting the first heat exchanger A are sent to the second heat exchanger B to be cooled to 383°C while generating high-pressure steam.

[0115] The partially cooled combustion fumes §14 exit the first cooling unit §13 at 383°C. A portion of the partially cooled combustion fumes §14 is recycled to the roaster §6 (flow §15) to provide the thermal energy required for roasting.

[0116] The second part (§16) of the partially cooled combustion gases (§14) is sent to the second cooling unit (§17), which includes a third heat exchanger (C), to be cooled to 200°C by heat exchange with the air (flow (§10) required for combustion. The air (flow (§10) required for the combustion unit (§9) is thus heated from ambient temperature to 314°C through heat exchange with the partially cooled combustion gases (§16) in exchanger C.

[0117] Finally, the cooled combustion fumes §18 exiting the third heat exchanger C of the second cooling unit §17 are released into the air.

[0118] The carbon load §1 of the process in example 2 is identical to that of example 1 in terms of type and flow rate: forest biomass containing 45% moisture by weight or recycled wood containing 20% ​​moisture by weight, hourly flow rate of dry biomass at the inlet of the dryer §2 of 9375 kg / h. The equipment is sized for a maximum moisture content of 45% by weight.

[0119] The roasting yield, defined by the ratio of the mass flow rates of dry biomass between the roasted solid effluent §7 and the at least partially dried solid effluent §5, is set at 80% as in example 1. The roasted solid effluent §7 exiting the roasting stage is completely dry as in example 1.

[0120] Table 2 below shows the main operating conditions and energy requirements of the drying and combustion stages as a function of the moisture content of the biomass entering the process. Table 2

[0121] The water content of the at least partially dried solid effluent §5 at the outlet of the drying stage is fixed at 10% by weight for both types of biomass. Unlike example 1, the residual moisture of the biomass (flow §5) at the inlet of the torrefyer §6 (flow §5) can be fixed at 10% by weight independently of the moisture of the biomass (flow §1) at the inlet of the dryer §2 by adjusting the air flow rate §3.

[0122] The fuel §11 available for roasting and derived from wood chips is gas produced by the Fischer-Tropsch downstream units and the Fischer-Tropsch effluent recovery (e.g., hydroconversion) facilities. As in Example 1, the available quantity of this fuel, which depends only on the roasted solids effluent §7, is 4500 kW and corresponds to the available fuel flow rate multiplied by its lower heating value (LHV).

[0123] For a given roasting yield of 80% and a residual moisture content of 10% by weight at the roaster inlet (§6), and under the temperature and thermal integration conditions of the invention described above, with air (flow §10) preheated to 600°C at the inlet of the combustion unit (§9), the quantity of fuel (§11) required for the combustion chamber is 3500 kW. This required quantity of fuel is therefore less than the quantity of fuel available in Fischer-Tropsch units and Fischer-Tropsch effluent recovery systems. Therefore, a supplementary supply of fossil fuel gas (natural gas, for example) is not necessary in the process according to the invention, unlike in Example 1 of the prior art.

[0124] The ambient air §3 used for drying is heated from 20°C to 120°C by low pressure steam, within a heat exchanger, the power required for this exchanger being 7200 kW in case 1 and only 1640 kW in case 2.

[0125] In both cases, low pressure (LP) steam can be at least partly produced by expanding the high pressure (HP) steam produced by exchanger B, which covers 78% of the requirements for case 1 and more than 3 times the required flow rate in case 2. In case 1, additional LP steam can be supplied by available steam produced in the downstream gasification units or in the Fischer-Tropsch unit.

[0126] Reference Example 3

[0127] Example 3 according to the prior art, shown in Figure 2, is described in US patent 2012 / 0137538 and comprises a drying stage and a roasting stage that are decentralized because they are located at a geographically distant site from the biofuel production facility using biomass gasification and Fischer-Tropsch synthesis. The combustion unit in Section 9 therefore cannot use fuel in Section 11 from Fischer-Tropsch units or from the hydroconversion of Fischer-Tropsch effluents from the latter.

[0128] To limit greenhouse gas emissions related to the production of torrefied biomass, the aim is to operate the unit in a way that avoids the use of fossil gas as fuel. To meet this requirement, the torrefaction efficiency is adjusted.

[0129] The description of the drying and roasting stages is identical to that of reference example 1, with the exception of the hourly fuel flow rate §11 in steady state which is equal to zero, the installation not consuming gaseous fuel from Fischer Tropsch units or hydroconversion of Fischer Tropsch effluents from the latter nor natural gas or other fossil fuel.

[0130] The process of example 3 is not in accordance with the invention in that, on the one hand, the drying gas §30 used for drying is a recycling of part of the gas exiting the dryer §2 heated by heat exchange with the combustion fumes §12 and, on the other hand, no current supplying the combustion unit §9 (flow §8 or §10) is heated by heat exchange with the combustion fumes §12.

[0131] The process feed (flow 1) is identical to that of example 1 in terms of type and flow rate: forest biomass containing 45% moisture by weight or recycled wood containing 20% ​​moisture by weight, hourly flow rate of dry biomass at the inlet of dryer §2 of 9375 kg / h. The equipment is sized for a maximum moisture content of 45% by weight.

[0132] The §7 roasted solid effluent exiting the roasting stage is completely dry as in example 1. The roasting yield, defined by the ratio of the dry biomass mass flow rates between the §7 roasted solid effluent and the at least partially dried solid effluent (§5), is adjusted contrary to example 1 to have a §11 fuel flow rate equal to zero.

[0133] Table 3 below gives the main operating conditions and energy requirements of the drying stage and associated roasting yield as a function of the water content contained in the biomass at the process input.

[0134] Table 3

[0135] As in example 1, the moisture content of the biomass entering the torrefyer is 10% in the case of forest biomass and corresponds to the moisture content obtained by using the energy obtained by cooling the combustion fumes §12 from 753°C to 383°C.

[0136] As in example 1, the moisture content of the biomass entering the torrefyer is 0% in the case of recycled wood because the biomass can be completely dried with the energy available by cooling the combustion fumes §12 from 753°C to 383°C.

[0137] The roasting yield obtained without using §11 fuel for forest biomass and recycled wood is 64% and 66% respectively.

[0138] Example 4 according to the invention

[0139] Example 4 conforms to the invention in that the gas used for drying is air §3, sourced solely from ambient air supply, and therefore not from recycling. Part of the heat from the combustion flue gases §12 is recovered to preheat the air supplying the combustion unit §9. Example 4 is shown in Figure 1. In this example, as in Example 3, the drying and torrefaction stages are decentralized because they are located at a geographically distant site from the biofuel production facility using biomass gasification and Fischer-Tropsch synthesis. The combustion unit §9 therefore cannot use fuel §11 from Fischer-Tropsch units or from the hydroconversion of Fischer-Tropsch effluents from the latter.

[0140] In this example, as in example 3, to limit greenhouse gas emissions related to the production of torrefied biomass, the aim is to operate the unit in a way that avoids the use of fossil gas as fuel. To meet this constraint, the torrefaction efficiency is adjusted.

[0141] The description of the drying and roasting stages is identical to that of Example 2 according to the invention, with the exception of the hourly fuel flow rate §11 in steady state which is equal to zero, the installation not consuming gaseous fuel from Fischer Tropsch units or hydroconversion of Fischer Tropsch effluents from the latter nor natural gas or other fossil fuel.

[0142] The process load (flow 1) is identical to that of the previous examples in terms of type and flow rate: forest biomass containing 45% moisture by weight or recycled wood containing 20% ​​moisture by weight, hourly flow rate of dry biomass at the inlet of dryer §2 of 9375 kg / h. The equipment is sized for a maximum moisture content of 45% by weight.

[0143] The roasted solid effluent §7 exiting the roasting stage is completely dry, as in all the other examples. The roasting yield, defined as the ratio of the dry biomass mass flow rates between the roasted solid effluent §7 and the at least partially dried solid effluent (§5), is adjusted as in Example 3 to have a fuel flow rate §11 equal to zero.

[0144] Table 4 below gives the main operating conditions and energy requirements of the drying stage and associated roasting yield as a function of the water content contained in the biomass at the process input.

[0145] Table 4 As in Example 2, the moisture content of the at least partially dried solid effluent (§5) exiting the drying stage is set at 10% by weight for both types of biomass. The moisture content of the biomass entering the torrefyer (flow §5) can be set at 10% by weight independently of the moisture content of the biomass entering the dryer (flow §1) by adjusting the air flow rate (§3). The torrefaction efficiency obtained without using fuel (§11) for forest biomass and recycled wood is 70%.

[0146] The roasting yield obtained in the process according to the invention is 4 to 6 points higher than that obtained in the process according to the prior art (example 3) in the case of an autonomous process, i.e. with a combustion unit §9 having as its sole fuel the roasting gaseous effluent §8 exiting the roasting unit §6 (fuel flow §11 equal to zero).

[0147] Furthermore, the roasting yield obtained in the process according to the invention is independent of the moisture content of the biomass in the process, unlike the process according to the prior art (example 3), in the case of an autonomous process, i.e. with a combustion unit §9 having as its sole fuel the gaseous roasting effluent §8 exiting the roasting unit §6 (fuel flow §11 equal to zero).

Claims

25 Demands 1. A process for drying and roasting a carbon feedstock comprising the following steps: treating the carbon feedstock (§1) in a drying unit (§2) with air (§3) coming solely from an ambient air supply to produce air charged with water vapor (§4) and a solid effluent that is at least partially dried (§5); treating the solid effluent that is at least partially dried (§5) with a combustion gaseous effluent (§15) in a roasting unit (§6) to produce a roasted solid effluent (§7) and a roasting gaseous effluent (§8) containing the combustion gaseous effluent (§15) and gases formed by roasting;treat the roasting gaseous effluent (§8) in a combustion unit (§9) with an oxygen-containing gas stream (§10) to produce combustion fumes (§12), part of the heat generated in the combustion unit (§9) being used to reheat at least part of at least one of the streams entering the combustion unit (§9); cool at least part of the combustion fumes (§12) in a first cooling unit (§13) to produce partially cooled combustion fumes (§14); recycle at least a first part of the partially cooled combustion fumes (§14) to the roasting unit (§6), as the combustion gaseous effluent (§15).

2. Method according to claim 1, wherein a fuel supplement (§11) is sent into the combustion unit (§9).

3. Method according to claim 2, wherein a part of the heat generated in the combustion unit (§9) is used to reheat at least a part of the fuel (§11).

4. A process according to claim 2 or claim 3, wherein the fuel (§11) comprises residual gas from a Fischer-Tropsch synthesis unit or a Fischer-Tropsch effluent recovery unit.

5. A method according to any one of the preceding claims, wherein a portion of the heat generated in the first cooling unit (§13) is used to reheat at least a portion of at least one stream entering the combustion unit (§9) and / or to reheat the air (§3) entering the drying unit (§2).

6. A method according to any one of the preceding claims, comprising cooling a second part (§16) of the partially cooled combustion fumes (§14) in a second cooling unit (§17) to produce cooled combustion fumes (§18).

7. Method according to claim 6, wherein the second part (§16) represents the remainder of the first part of the partially cooled combustion fumes (§14).

8. A method according to claim 6 or claim 7, wherein the cooled combustion fumes (§18) exiting the second cooling unit (§17) have a temperature between 100°C and 300°C, preferably between 150°C and 250°C and preferably between 160°C and 210°C.

9. A method according to any one of the preceding claims, wherein one or more secondary gas streams containing oxygen are injected into the combustion unit (§9).

10. A method according to any one of the preceding claims, wherein at least a portion of the oxygen-containing gas stream (§10) and optionally of the oxygen-containing secondary gas streams entering the combustion unit (§9) is heated by a portion of the heat generated in the combustion unit (§9).

11. A method according to any one of the preceding claims, wherein the oxygen-containing gas stream (§10) and optionally one or more secondary oxygen-containing streams entering the combustion unit (§9) are separated into several streams injected into the combustion unit (§9).

12. A method according to any one of the preceding claims, wherein the at least one oxygen-containing gas stream (§10) entering the combustion unit (§9) comprises air, oxygen, or an oxygen-enriched gas stream.

13. A method according to any one of the preceding claims, wherein the oxygen from the oxygen-containing gas stream (§10) is produced by a water electrolysis unit or by an air separation unit.

14. A method according to any one of the preceding claims, comprising at least one of the following operating conditions: the drying operation is carried out at a temperature between 100°C and 300°C, preferably between 100°C and 200°C and preferably between 100°C and 150°C; the residence time of the carbon charge (§1) in the drying unit (§2) is between 5 minutes and 180 minutes, preferably between 5 minutes and 120 minutes and even more preferably between 5 minutes and 60 minutes; the drying operation is carried out at an absolute pressure between 0.05 MPa and 0.2 MPa and preferably between 0.08 MPa and 0.15 MPa; the roasting operation is carried out at a temperature between 200°C and 450°C, preferably between 250°C and 425°C and preferably between 300°C and 400°C; the residence time of the at least partially dried solid effluent (§5) in the roasting unit (§6) is between 5 minutes and 600 minutes, preferably between 10 minutes and 180 minutes and even more preferably between 10 minutes and 90 minutes; the roasting operation is carried out at an absolute pressure between 0.05 MPa and 0.2 MPa and preferably between 0.08 MPa and 0.15 MPa; the combustion operation of organic compounds of the roasting gaseous effluent (§8) produces combustion fumes (§12) having a temperature greater than or equal to 700°C, preferably greater than or equal to 750°C, preferably greater than or equal to 800°C, such as between 800°C and 850°C; the partially cooled combustion fumes (§14) exiting the first cooling unit (§13) have a temperature between 200°C and 450°C, preferably between 250°C and 425°C and preferably between 300°C and 400°C.

15. Device for drying and roasting a carbon feed comprising the following units: a drying unit (§2) adapted to treat the carbon feed (§1) with air (§3) coming only from an ambient air supply to produce air charged with water vapor (§4) and a solid effluent at least partially dried (§5); a roasting unit (§6) adapted to treat the solid effluent at least partially dried (§5) with a combustion gaseous effluent (§15) to produce a roasted solid effluent (§7) and a roasting gaseous effluent (§8) containing the combustion gaseous effluent (§15) and gases formed by roasting; a combustion unit (§9) adapted to treat the roasting gaseous effluent (§8) with a gas stream containing oxygen (§10) to produce combustion fumes (§12);at least one heat exchanger suitable for reheating at least part of at least one of the streams entering the combustion unit (§9) with part of the heat generated in the combustion unit (§9); a first cooling unit (§13) suitable for cooling at least part of the combustion fumes (§12) to produce partially cooled combustion fumes (§14); a recycling duct suitable for recycling at least a first part of the partially cooled combustion fumes (§14) to the roasting unit (§6), as the combustion gaseous effluent (§15).

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