Method for calcining carbonic acid ore in parallel-flow heat storage type kiln and implementation kiln

Abstract

A parallel flow regenerative kiln, in which each shaft comprises means for injecting a heating gas (6) into the shaft (1) during calcination at the top of the calcination zone (B), and means for removing (21, 23), from the kiln, cooling air heated in contact with the calcination material, the level of which is lower than the cross channel (4).

Description

Technical Field

[0001] The invention relates to a method for calcining carbonate ore in a parallel flow regenerative kiln (PFRK) comprising at least two shafts interconnected by a cross channel. In each shaft, the stone is introduced at the top and follows a downward gravitational displacement, during which it is successively preheated, calcined and then cooled in order to be collected in the lower part of each shaft. Background Art

[0002] According to the present invention, the term "stone, carbonate ore, limestone" refers to pieces of carbonate raw material having an average particle size d50 between 20 mm and 20 cm, preferably above 25 mm, preferably below 18 cm, more preferably below 16 cm, and typically between 3 and 15 cm.

[0003] The carbonate ore according to the present patent application is typically calcium magnesium carbonate, also known as limestone.

[0004] Parallel flow regenerative kilns typically have two or three circular or rectangular shafts, which do not operate continuously. In standard operation, fuel is injected into the calcining zone of one shaft via lances during periods typically lasting 12 to 20 minutes, where it is burned in the presence of combustion air. The descending calcined product is then cooled in the cooling zone by heat exchange with cooling air introduced at the shaft's base. The flue gas consists of combustion gases, decarburization gases, and heated cooling air. This flue gas is drawn into the other shaft through a cross-channel, then passes through the stones in that shaft before exiting the kiln. Thus, in this "preheat" shaft, the existing stones are preheated by the exhaust flue gas. Therefore, during this period, the shaft where combustion occurs operates in calcining mode, while the shaft where the flue gas is drawn through the stones operates in preheating mode. After this, there is a period, typically between 30 seconds and two minutes, called the reversal period, during which the air and fuel circuits are restored. The shaft operating in calcining mode now operates in preheating mode, and the shaft operating in preheating mode now operates in calcining mode.

[0005] A classical method for calcining carbonate ores in a parallel flow regenerative kiln having at least two shafts interconnected by a cross channel, which in standard operation comprises:

[0006] -Carbonate ore is loaded on top of each shaft,

[0007] - Preheating of these loaded ores in the preheating zone,

[0008] - calcining these preheated ores in a calcining zone to produce decarbonized calcined material,

[0009] - cooling the calcined material with cooling air in the cooling zone, forming heated cooling air by heat exchange,

[0010] - discharge the calcined material from the bottom of the shaft,

[0011] - discharge of gaseous effluent from the kiln,

[0012] - Each shaft operates alternately in calcining mode and preheating mode, one shaft operating in calcining mode for a predetermined period of time, during which at least one other shaft operates in preheating mode; and vice versa,

[0013] -The calcination method includes:

[0014] o Carry out the step of loading carbonate ore on the top of the kiln shaft,

[0015] o the calcining step of producing the decarbonized calcined material by increasing the temperature inside the preheated carbonate ore and releasing a gas flow co-current with the calcined material, and

[0016] o the passage of the air flow towards at least one shaft operating in preheating mode, through the cross channel,

[0017] -The preheating method includes:

[0018] o subjecting the carbonate ore charge to said preheating step by heat exchange with said gas stream from the cross-channel, said gas stream rising and passing countercurrently through the carbonate ore charge, and

[0019] o said exhaust step of exhausting said gas stream as a gaseous effluent in a preheated manner at the top of said at least one shaft,

[0020] The cooling step comprises supplying cooling air to the bottom of each of the shafts or only to the bottom of the shafts operating in calcining mode,

[0021] In the calcining zone of a conventional kiln, fuel is injected into the stone to be calcined below the preheated stone and burned in a calcining mode to benefit from the flue gas heat transferred to the stone in the preheating zone. In the preheating mode, the stone introduced into the kiln is at ambient temperature, and the flue gas temperature discharged from the kiln is approximately 150°C, limiting energy losses.

[0022] According to the present invention, standard operation means that the kiln produces calcined material in a continuous manner. This operation does not involve start-up, shutdown or maintenance phases of the kiln.

[0023] According to the invention, carbonate ore is in particular calcareous stone (limestone), dolomite (dolomite or unburned dolomite) and / or magnesite ore calcined in quicklime, raw dolomite and / or magnesia.

[0024] The reaction of calcining limestone into quicklime is:

[0025] CaCO3 (solid) + heat → CaO (solid) + CO2 (gas)

[0026] The reaction is endothermic and reversible. Below 850 to 900°C, lime and CO2 readily recombine. However, starting at temperatures around 900°C, the raw stone releases significant amounts of CO2 during decarbonization. To achieve this decarbonization, the temperature in the calcination zone must be significantly increased. Today, this increase is primarily achieved by burning fuel (usually fossil fuels) in the presence of an oxidant such as air. This fuel combustion, in turn, leads to the release of significant amounts of CO2. Globally, current calcination methods are exacerbating the greenhouse effect.

[0027] During fuel combustion, direct contact between the flame and the preheated carbonate ore can also lead to localized overheating in the calcination zone, and flue gas or fuel ash can contaminate the calcined material. Maintaining the high quality of the calcined material requires careful fuel selection, particularly avoiding high-sulfur fuels. Even with selected fossil fuels, the reactivity of the calcined material can be affected by fuel ash and minor contaminants. Thermal and fuel NOx can also be generated during high-temperature combustion due to the potential presence of nitrogen in the fuel and the high nitrogen content of the combustion air.

[0028] This very common calcination process also has the disadvantage that it recommends using air to burn the fuel and cool the calcined product. This results in a gaseous effluent released at the top of the kiln with high levels of diatomic nitrogen N2 and relatively low levels of CO2 (about 20% to 27% by volume of dry gas). Due to the high nitrogen content in the air, capturing the CO2 is very difficult and expensive.

[0029] Variants of the common calcination process have been proposed to improve CO2 capture, for example in WO2022 / 002869 or WO2022229120. Summary of the Invention

[0030] The present invention aims to address the significant CO₂ emissions from PFRK kilns without substantially altering their cycle function or making any or no changes to their structure. Another aim is to minimize overheating of the calcined material and the introduction of impurities into it. Another aim is to more easily capture the CO₂ in the gaseous effluent from the kiln. Obviously, the primary purpose of the calciner must be maintained: producing high-quality and high-purity calcined material.

[0031] In order to solve these problems, according to the present invention, the method as described above further includes:

[0032] recirculating in preheated form a portion of the gaseous effluent discharged from the top of said at least one shaft,

[0033] heating the recycled portion of said gaseous effluent outside the kiln by means of at least one device capable of heating the gas,

[0034] injecting a heated portion of the recycled gaseous effluent into a shaft operating in calcining mode, at a level situated at the top of the calcining zone, in order to obtain said temperature increase allowing calcination of the carbonate ore, and

[0035] Heated cooling air is extracted from each shaft, where the cooling air is supplied at a level located below the cross channel,

[0036] The gaseous effluent from the kiln is concentrated into CO2.

[0037] According to the present invention, the term CO2-concentrated or CO2-concentrated gaseous effluent, or a gaseous effluent concentrated in CO2 means that the content of CO2 in the dry gas is at least 65%, in particular at least 70%, more preferably at least 80% by volume, preferably at least 90% by volume, most preferably at least 95% by volume.

[0038] The present invention primarily relies on an external energy supply, while also utilizing a heating device capable of heating the gas to heat the circulating gas. The gas entering such a device has a predetermined temperature and leaves at a higher temperature. Such a device may be, for example, a furnace equipped with at least one plasma torch, an induction heating device, a radiant panel, a microwave oven, a solar heating device, or a combination thereof. Devices capable of releasing hot gases generated by reactions such as combustion are not included in the gas heating device of the present invention.

[0039] In a variant embodiment, such a device can be a combination of an oven equipped with at least one plasma torch, an induction heating device, a radiant panel, a microwave oven, a solar heating device with a combustion oven (indirect combustion heating, oxygen-enriched combustion, etc.), with a switch provided between the two. In this way, the switch can be operated between the oven combinations, depending on the availability and price of the energy source.

[0040] In another embodiment, such means may be any heating means capable of heating a gas to provide heated gas to be supplemented with oxygen prior to feeding the calcining zone of the kiln where oxidative combustion will occur, thereby reducing further heat generated by the oxidative combustion.

[0041] The injection system of the kiln of the present invention is optimized to obtain a good heat distribution. As a result, the quality of the calcined material is extensively improved.

[0042] Combustion in the kiln still requires neither fuel nor air. Consequently, no or limited additional pollutants are emitted, apart from the slight amounts contained in the stone. No ash is produced, resulting in a purely decarbonized material. Since the gas stream contains no or low levels of nitrogen, no or virtually no NOx is produced, enabling the plant to comply with stricter regulations. Direct contact of the stone with the flame is no longer a concern. The appropriate temperature of the heated gas from the heating device is easily controlled, resulting in high-quality lime. According to the invention, heated recirculated gas is introduced into the shaft in a calcining manner at the top of the calcining zone, just below the preheating zone, maintaining all the regenerative features of the kiln.

[0043] By recycling the CO2-based gas, and in the absence of combustion air, the system will enrich the gaseous effluent from the kiln with CO2, making it easier to capture the CO2 and / or making the CO2 cleaning process of the kiln flue gas before capture (with cleaner and more concentrated CO2) simpler and more energy-efficient than with standard CO2 concentrations in the flue gas.

[0044] As in the method according to the invention, the extraction of heated cooling air from the shaft takes place at a level located below the cross-channel, and the gaseous effluent discharged from the kiln consists almost entirely of a CO2-based gas stream resulting from decarburization and a CO2-based gas injected by calcination and optionally in the cross-channel. Thus, the gaseous effluent discharged from the furnace has a concentrated CO2 content, generally at least 80% by volume on dry gas, preferably at least 90% by volume on dry gas, and most preferably at least 95% by volume on dry gas.

[0045] This gaseous effluent can be used or stored under favorable conditions, thus reducing its contribution to the greenhouse effect of the kiln.

[0046] While kiln combustion still requires neither fuel nor air, according to the present invention, it is also possible to combine the heating of the gaseous effluent with the addition of oxygen to provide a heated gas mixture suitable for kiln oxycombustion. In this case, the calcination zone in the kiln will be airless or virtually airless, since, compared to combustion with combustion air, more than 90%, preferably more than 95%, by volume of nitrogen in the dry gas will be replaced by CO2. In fact, this combination also allows the recycling of CO2-based gases in the absence of combustion air, thereby enriching the gaseous effluent discharged from the kiln with CO2, making CO2 capture easier, and / or making the CO2 purification process of the kiln flue gas before capture (CO2 is cleaner and more concentrated) simpler and more energy-efficient than with standard CO2 concentrations in the flue gas.

[0047] According to one embodiment of the invention, before the heating step, at least one heat exchange is carried out between the heated cooling air extracted from outside the kiln and the recycled portion of the gaseous effluent by means of a heating device. This heat exchange allows heat to be recovered from the extracted cooling air before the heating step, and the air released into the atmosphere is closer to the ambient temperature.

[0048] Advantageously, the process of the invention consists in introducing into a cross-channel a first portion of said recycled portion of the gaseous effluent, which has been heated outside the kiln by said means capable of heating the gases, and a second portion which has not been heated by said means, so as to obtain a regulated temperature, generally ranging from 900 to 1100° C., above the recarbonation temperature of the calcined ore but below the temperature of said gases allowing the calcination of the carbonated ore, preferably ranging from 1100 to 1500° C.

[0049] Alternatively, the gas stream introduced into the cross channel is said second portion of said portion, which is not heated by said means, heated by separate heating means to a conditioning temperature below said temperature allowing calcination of carbonated ore but above the recarbonation temperature of the calcined ore.

[0050] The term "adjustment temperature below the temperature allowing calcination of carbonate ore but above the recarbonation temperature of the calcined ore" means that according to the present invention, the temperature is below 1100°C, preferably in the range of 900°C to 1100°C, more preferably in the range of 950°C to 110°C.

[0051] According to the present invention, the term "temperature allowing calcination of carbonate ore" refers to a temperature within the range of 1100°C to 1500°C.

[0052] According to a preferred embodiment of the invention, a portion of the recycled portion of the CO2-based gaseous effluent which has not been heated is injected in a calcined manner into the top of each shaft.

[0053] In a preferred embodiment according to the invention, the temperature of the heated portion of the recycled gaseous effluent injected into the shaft in a calcining manner at a level situated at the top of the calcining zone is between 1100°C and 1500°C, said temperature being between 1100°C and 1500°C allowing the calcination of the carbonate ore.

[0054] In a variant embodiment according to the invention, the temperature of the heated portion of the recycled gaseous effluent injected in a calcining manner into the shaft at a level situated at the top of the calcining zone is lower than 1100° C. and oxygen is supplemented before and / or in the calcining zone, said increase in temperature allows calcining the carbonate ore by oxycombustion in the presence of said heated portion of the recycled gaseous effluent supplemented with oxygen.

[0055] In certain cases, the process is carried out in a twin-shaft kiln.

[0056] The present invention also relates to a parallel flow regenerative kiln. The kiln comprises at least two shafts connected to each other by a cross channel.

[0057] Each axis includes the following positions when in use or out of use:

[0058] - at least one inlet for loading carbonate ore at the top of the shaft,

[0059] - at least one outlet for discharging the decarburized calcined material at the bottom of the shaft,

[0060] - removal of the piping for the removal of the CO2-based gaseous effluent from the top of the shaft, and

[0061] - Cooling air supply device located at the bottom of the shaft for cooling the decarburized calcined material to be discharged,

[0062] The kiln further includes a reversing system arranged to alternately drive the use and stop positions of each shaft in calcining operation and preheating operation, wherein a shaft is in calcining operation for a predetermined period of time while at least another shaft is in preheating operation and is driven in reverse according to control of the reversing system.

[0063] The shaft in the calcination process includes a preheating zone, a calcination zone and a cooling zone from top to bottom, and the interconnected cross channel is located at the bottom of the calcination zone.

[0064] According to the invention, each shaft comprises means for injecting heated gas into the shaft when calcining is carried out at the top of the calcining zone and means for removing from the kiln cooling air heated by contact with the calcined material, at a level below the cross-channels,

[0065] The kiln further comprises an external recirculation loop comprising:

[0066] - a separation body for withdrawing a portion of said gaseous effluent from said removal duct,

[0067] - heating means capable of heating a gas, said heating means being connected to said separation body and being arranged to heat a portion of said gaseous effluent, and

[0068] - said means for injecting heated CO2-based gas into the shaft during calcination operation, connected to the heating means and injected into said heating section, to provide said gaseous effluent at a temperature equal to or higher than the calcination temperature of the charged ore.

[0069] The term "injected into said heating portion to provide said gaseous effluent at a temperature equal to or higher than the calcination temperature of the charged ore" means that according to the present invention, either said heating portion of said gaseous effluent is injected at a temperature equal to or higher than the calcination temperature of the charged ore, or said gaseous effluent is injected at a temperature higher than or equal to the calcination temperature of the charged ore, for example by using an additional device to provide the calcination temperature of the charged ore, such as an additional oxygen-enriched combustion device or step.

[0070] As mentioned above, the PFRK kiln has a cyclic operation, where each shaft runs in calcining mode for a predetermined time, then after a reversal time, usually between 30 seconds and 2 minutes, runs in preheating mode, etc. During the reversal time, the reversal system synchronizes all changes required to go from one mode to the other, such as by opening devices to inject gas into the shaft operating in calcining mode and closing them when the shaft switches to preheating mode.

[0071] The turnover system therefore controls not only numerous flaps and valves, but also the operation of the loading and unloading equipment and even the operation of various suction, pumping or injection elements.

[0072] Advantageously, at the bottom of each shaft, at a level below the cross-channel, said means for removing the heated cooling air from the kiln may comprise a central collector element communicating with external extraction means.

[0073] According to some embodiments of the kiln, each shaft has a circular cross-section and is provided with a peripheral channel at the bottom of the calcining zone, and cross-channels interconnecting the peripheral channels of the shafts to allow gas to flow from one shaft to another. At a level below the peripheral channels and cross-channels, the means for removing heated cooling air from the kiln may include an annular collector in communication with an external extraction device.

[0074] According to other kilns, each shaft has a rectangular cross-section, with the sides of one shaft facing the other, and a cross-channel interconnecting the shafts directly between the facing sides. The means for removing the heated cooling air from the kiln comprise, on at least some of the sides of each shaft, at a level below the cross-channel, at least one collector communicating with external extraction means.

[0075] According to one embodiment of the kiln according to the invention, each shaft comprises a top opening for introducing a portion of said unheated CO2-based gaseous effluent.

[0076] According to another embodiment of the kiln according to the invention, at least one heat exchanger is arranged on said external recirculation loop, which heat exchanger is supplied with heated cooling air extracted from the kiln.

[0077] In a preferred embodiment of the invention, the kiln comprises a mixing chamber connected to a recirculation circuit situated below the heating means for collecting a first portion of said recirculating fraction of said CO2-based gaseous effluent that has been heated, and to a separation body arranged on the recirculation circuit above the heating means and capable of conveying a second portion of said recirculating fraction of said CO2-based gaseous effluent that has not been heated by said heating means into said mixing chamber in order to obtain a gaseous mixture having a regulated temperature that is lower than the temperature allowing calcination of carbonate ore, said mixing chamber being connected by a gaseous mixture conduit to a cross-channel for injecting said gaseous mixture therein or by a gaseous mixture conduit to a device for injecting heated gas so as to inject said gaseous mixture into the top of the calcining zone when the shaft is in preheating mode.

[0078] When the gaseous mixture is injected into the cross channel, the temperature is adjusted to be lower than 1100° C., preferably between 900° C. and 1100° C., more preferably between 950° C. and 1100° C. When the gaseous mixture is injected into the top of the calcining zone where the shaft is in a preheated state, the temperature is adjusted to be lower than 1100° C., preferably between 500° C. and 1100° C., more preferably between 550° C. and 950° C.

[0079] Alternatively, the gas stream (mixture) introduced into the cross channel via the gaseous mixture conduit is heated by a separate heating device to a conditioning temperature below the temperature allowing calcination of the carbonate ore but above the recarbonation temperature of the calcined ore.

[0080] In another alternative embodiment, while the shaft is in the preheated state, the gaseous mixture introduced through the gaseous mixture conduit at the top of the calcining zone is heated by a separate heating device to a conditioning temperature below the temperature allowing calcination of the carbonate ore but above the recarbonation temperature of the calcined ore.

[0081] When the gaseous mixture is injected into the cross channel, the temperature is adjusted to be lower than 1100° C., preferably between 900° C. and 1100° C., more preferably between 950° C. and 1100° C. When the gaseous mixture is injected into the top of the calcining zone where the shaft is in a preheated state, the temperature is adjusted to be lower than 1100° C., preferably between 500° C. and 1100° C., more preferably between 550° C. and 950° C.

[0082] In some embodiments of the present invention, the device for injecting heated gas is connected to a heated CO2-based gas source and a gaseous mixture conduit located outside the shaft, and the device for injecting heated gas has a non-operating position and an operating position for the heated CO2-based gas, and a non-operating position and an operating position for the gaseous mixture conduit. In other words, this means that during the calcination process, the device for injecting heated gas is usually in the operating position for the heated CO2-based gas (allowing the entry of the heated CO2-based gas) and in the non-operating position in the gaseous mixture conduit (closing the entry of the gaseous mixture), and in the preheating state (closing the entry of the heated CO2-based gas) the device for injecting heated gas is usually in the non-operating position for the heated CO2-based gas and in the operating position in the gas mixture conduit (allowing the entry of the gaseous mixture).

[0083] It can be seen that the kiln according to the present invention has only some structural modifications to the exterior of the furnace.

[0084] In certain cases, the kiln is a twin-shaft kiln.

[0085] Further embodiments according to the invention are mentioned in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0086] Other characteristics and advantages of the invention will emerge from the following non-limiting description with reference to the accompanying drawings and examples.

[0087] In the accompanying drawings, Figure 1 A first embodiment of a kiln according to the invention is shown.

[0088] Figure 2 A second embodiment of a kiln according to the invention is shown.

[0089] In the drawings, the same reference numerals are assigned to the same or similar elements. DETAILED DESCRIPTION

[0090] like Figure 1 As shown, the PFRK kiln shown comprises two shafts 1 and 2, which have a circular cross-section and are provided with peripheral channels 3 interconnected by a cross channel 4. Conventionally, shaft 1, shown on the left, operates in calcining mode, and shaft 2, shown on the right, operates in preheating mode. The shafts are divided into three zones in height: a preheating zone A, in which the carbonate is preheated before calcining, a calcining zone B, in which the preheated carbonate is decarburized, and a cooling zone C, in which the decarburized calcined material is cooled.

[0091] Carbonate stone is introduced into the top of the shaft through an open inlet 5. Due to gravity, the stone gradually descends within the shaft. When the shaft is operating in calcining mode, a device is provided at the top of calcining zone B, directly below preheating zone A, for injecting gas at a temperature equal to or higher than the stone calcination temperature, for example, between 1100 and 1500°C. In the illustrated kiln, these devices are represented by holes 6 in the shaft housing, which allow gas injection from outside the shaft at various radial locations within the shaft. Advantageously, several injection points are required in a horizontal layer to achieve the correct heat distribution. Several other injection systems are also conceivable, including horizontal lances, vertical lances, inner barrels, and crossbeams. Consequently, the stone is decarburized, resulting in decarburized calcined material, which continues to descend within the shaft and is fed by a gas stream 7 co-current with the calcined material.

[0092] Cooling air is introduced into the bottom of the shaft through a supply pipe 8 and an open feed port 9. The cooling air flows countercurrently with the calcined material to cool it. The cooled calcined material is discharged into an unloading device 10 through an open outlet 11.

[0093] The gas stream 7 is composed of the CO2 released during the decarburization process and the heated CO2-based gas injected into the interior of the shaft. This gas stream passes through the peripheral channel 3, through the cross channel 4, and then into the interior of the shaft 2 operating in preheating mode.

[0094] When a shaft is operating in preheating mode, here shaft 2, the CO2-based gas injection device, such as orifice 6, is deactivated. Meanwhile, the cooling air inlet 9 and the calcined material outlet 11 remain open. In shaft 2, the gas flow from the cross channel 4 proceeds to the top of the shaft in countercurrent to the preheated stone. Through the open outlet 12, the gaseous effluent is discharged from the kiln via a removal duct 13 and chimney 14. When shaft 1 is operating in calcining mode, the outlet 12 of the removal duct 13 is closed.

[0095] The kiln also includes a schematically shown reversing system 15. This system directly or remotely synchronizes the operation of the axes during reversal. The system is arranged to alternately drive each axis between the working position and the non-working position during calcination and preheating operations.

[0096] Outside the kiln, on the removal line 13, a separator 16 is provided which is capable of withdrawing a portion of the gaseous effluent from the kiln and introducing it into a recirculation circuit 17. In this circuit, part of the gaseous effluent is advantageously treated in a treatment unit 18, where it can be cooled, filtered, and / or dried, for example. The recirculation circuit 17 also comprises an external heating device 19 capable of heating the gas. This heating device, which can be driven by the reversing system 15, is used to supply a CO2-based gas of suitable temperature, which is injected through the orifice 6 of the shaft operating in calcining mode and achieves thermal decomposition of the preheated stone.

[0097] A portion of the gaseous effluent is taken from a recirculation loop 17 upstream of the furnace 19. In the kiln shown, the temperature of this exhaust gas is close to ambient temperature (preferably below 200° C.) and is advantageously introduced into the shaft 1 in a calcining manner through its top opening 20. This opening is closed in the shaft 2 operating in preheat mode. It is necessary to inject cold gas at a slightly higher pressure at the top of the shaft 1 in order to maintain the benefits of regeneration.

[0098] In the kiln shown, the heated cooling air is sucked in through a central collecting element 21 communicating with external extraction means 22 for removing from the kiln, at a level below the cross-channel 4, the cooling air heated by contact with the decarburized calcined material. For the same purpose, each circular shaft can also be equipped with an annular collector 23, also communicating with said extraction means 22.

[0099] Advantageously, at least one heat exchanger is arranged on the external recirculation loop 17 and is supplied with heated cooling air extracted from the kiln. In the kiln shown, the heated cooling air drawn by the extraction device 22 is supplied to the heat exchanger 24, where it exchanges heat with the cold air leaving the treatment unit 18. The air, which has a temperature close to that of the ambient temperature, is released to the atmosphere through an outlet 25, possibly after dust removal or other treatment, with energy recovery upstream of the heating device 19.

[0100] The kiln shown also comprises means for advantageously injecting heated gas 26 into the cross channel 4. This gas is supplied from a mixing chamber 27 connected to the recirculation circuit 17 situated below the heating device 19, in order to collect a first portion of said recirculated portion of the gaseous effluent that has been heated, and to a separator 28 arranged on the recirculation circuit 17 situated above the heating device 19 and capable of transferring a second portion of said recirculated portion of the gaseous effluent that has not been heated by said heating device into the mixing chamber 27. Thus, a gas mixture is obtained whose temperature is adjusted to lie within the range of 900 to 1100° C., which is above the recarbonation temperature for calcining the ore but below the temperature that allows calcining the carbonated ore, advantageously lying within the range of 1100 to 1500° C., and which can be injected into the cross channel 4 through the connection 26 in order to compensate for the heated cooling air extracted from the kiln.

[0101] In another embodiment, a gaseous mixture having a regulated temperature in the range of 900 to 1100° C. is injected into the cross channel 4 to compensate for the extraction of heated cooling air from the kiln, the gaseous mixture being generated by a separate heating device, heating a second portion of the recycled portion of the CO2-based gaseous effluent not heated by the heating device 19 to a temperature in the range of 900 to 1100° C. for direct injection into the cross channel through the connection 26. Figure 1 This embodiment is not shown in FIG.

[0102] In the kiln shown, the gas flow entering shaft 2 consists almost exclusively of the CO2 released during the decarburization of shaft 1, heated CO2-based gas injected into shaft 1 at the top of calcination zone B via device 6, and heated CO2-based gas injected into the cross-channel via device 26. This gas flow is no longer diluted by air. In fact, air is no longer required for combustion, and cooling air is extracted from the kiln. Consequently, the gaseous effluent leaving the kiln is highly concentrated in CO2.

[0103] like Figure 2 The kiln shown (PFRK) is Figure 1 The kiln is similar to the kiln of the present invention in that it also comprises two shafts 1 and 2 of circular cross-section, provided with peripheral channels 3 interconnected by cross-channels 4. Conventionally, shaft 1, shown on the left, operates in calcination mode, while shaft 2, shown on the right, operates in preheating mode. The shafts are divided into three zones in height: a preheating zone A, in which the carbonate is preheated before calcination; a calcination zone B, in which the preheated carbonate is decarbonized; and a cooling zone C, in which the decarbonized calcined material is cooled.

[0104] Carbonate stone is introduced into the top of the shaft through an open inlet 5. Due to gravity, the stone gradually descends into the shaft. When the shaft is operating in calcining mode, a gas injection device is provided at the top of the calcining zone B, directly below the preheating zone A. These devices are represented by holes 6 in the shaft housing. These holes allow gas to be injected from outside the shaft at various radial locations within the shaft. Advantageously, several horizontal layers of injection points are required to achieve the correct heat distribution. Gas is injected to provide a gas temperature equal to or higher than the calcining temperature of the stone in the calcining zone, for example, a gas temperature of 1100 to 1500°C. This gas will mix with gas 20 injected at the top of the kiln. The gas 20 injected at the top of the kiln is cooler than the heated gas injected from outside the kiln. The temperature of the gas injected from outside the kiln is taken into account when setting the temperature of the gas injected from outside the kiln to provide a gas temperature equal to or higher than the calcining temperature of the stone in the calcining zone, for example, a gas temperature of 1100 to 1500°C.

[0105] Several other injection systems are also conceivable: horizontal lances, vertical lances, inner cylinders, crossbeams. Thus, the stone is decarburized, resulting in a decarburized calcined material which continues to descend in the shaft and is subjected to a gas stream 7 co-current with the calcined material.

[0106] Cooling air is introduced into the bottom of the shaft through a supply pipe 8 and an open feed port 9. The cooling air flows countercurrently with the calcined material to cool it. The cooled calcined material is discharged into an unloading device 10 through an open outlet 11.

[0107] The gas stream 7 is composed of the CO2 released during the decarburization process and the heated CO2-based gas injected into the interior of the shaft. This gas stream passes through the peripheral channel 3, through the cross channel 4, and then into the interior of the shaft 2 operating in preheating mode.

[0108] When a shaft is operating in preheating mode, here shaft 2, the device for injecting heated CO2-based gas from an external source to provide a temperature equal to or higher than the stone calcination temperature in the calcining zone is deactivated. On the other hand, the cooling air inlet 9 and the calcined material outlet 11 remain open. In shaft 2, the gas flow from the cross channel 4 proceeds to the top of the shaft in countercurrent to the preheated stone. Through the open outlet 12, the gaseous effluent is discharged from the kiln via a removal duct 13 and chimney 14. In shaft 1 operating in calcining mode, the outlet 12 of the removal duct 13 is closed.

[0109] The kiln also includes a schematically shown reversing system 15. This system directly or remotely synchronizes the operation of the axes during reversal. The system is arranged to alternately drive each axis between the working position and the non-working position during calcination and preheating operations.

[0110] Outside the kiln, on the removal pipe 13, a separator 16 is provided which is able to discharge a portion of the gaseous effluent from the kiln and introduce it into a recirculation circuit 17. In this circuit, part of the gaseous effluent is advantageously treated in a treatment unit 18, where it can, for example, be filtered and / or dried.

[0111] The recirculation circuit 17 also comprises external heating means 19 capable of heating the gas. This heating means can be driven by the reversing system 15 and is used to supply CO2-based gas of suitable temperature, which is injected through the orifice 6 of the shaft working in calcining mode.

[0112] In the kiln shown, the temperature in the calcining zone is achieved by injecting a combination of heated gas concentrated in CO2, to which oxygen is added via an oxygen addition 29. The oxygen can come from an oxygen tank, an oxygen production unit, or a separator 30 to which air is supplied via a feed inlet 31. In the latter case, nitrogen, which is the main component of the air, is separated from it and leaves the separator via an outlet 32. As previously described, the heated gas concentrated in CO2, to which oxygen is added, is provided in the calcining zone (top) provided with the existing combustion lances 33 and burners. Figure 2The burner in the embodiment shown operates under oxygen-rich conditions, wherein the combustion of the fuel takes place in a gaseous mixture consisting primarily of oxygen and CO2.

[0113] If preferred, oxygen can be added to the heated gas concentrated in CO2 via a mixing chamber.

[0114] Oxygen can also be added through the top opening 20 instead of or in addition to the oxygen addition 29 .

[0115] Compared to combustion operations using air, the CO2 present in the gaseous mixture typically replaces more than 90%, preferably more than 95%, of the nitrogen.

[0116] The oxygen content in the gaseous mixture is preferably in excess relative to the stoichiometric conditions of combustion, preferably 5 to 50% by volume, in particular 10 to 30% by volume, advantageously 15 to 25% by volume relative to the stoichiometric requirement of the combustion reaction.

[0117] In this case, the combustion of the fuel can reach the temperature required for thermal decomposition of the preheated stone, which is between 900°C and 1500°C.

[0118] Within the meaning of the present invention, a fuel may be any solid, liquid or gaseous combustible, such as natural gas, hydrogen, biogas, fuel oil, oil, powdered coal or coke, solid biomass such as sawdust, recycled solid combustibles such as plastics, cellulosic materials, etc.

[0119] Advantageously, in the case of a solid fuel, it is introduced into the calcining shaft in the form of particles or powder, using as carrier gas a portion of the gaseous effluent discharged from the kiln. CO2 from any other source can also be provided as carrier gas.

[0120] A portion of the gaseous effluent is withdrawn from the recirculation loop 17 upstream of the heating device 19. In the kiln shown, the temperature of this exhaust gas is close to that of the environment and is advantageously introduced into the shaft 1 in a calcining manner through its top opening 20. This opening is closed in the shaft 2 operating in preheating mode. It is necessary to inject cold gas at a slightly higher pressure at the top of the shaft 1 in order to maintain the benefits of regeneration.

[0121] In the kiln shown, the heated cooling air is sucked in through a central collecting element 21 communicating with external extraction means 22 for removing from the kiln, at a level below the cross-channel 4, the cooling air heated by contact with the decarburized calcined material. For the same purpose, each circular shaft can also be equipped with an annular collector 23, also communicating with said extraction means 22.

[0122] Advantageously, at least one heat exchanger is arranged on the external recirculation loop 17, which is supplied with heated cooling air extracted from the kiln. In the kiln shown, the heated cooling air drawn by the extraction device 22 is supplied to the heat exchanger 24, where it exchanges heat with the cold air leaving the treatment unit 18. The air, at a temperature close to that of the ambient temperature, is released into the atmosphere through the outlet 25, with energy recovery upstream of the heating device 19.

[0123] The kiln shown also comprises means for advantageously injecting heating gas 26 into the cross channel 4 .

[0124] This gas is supplied from a mixing chamber 27 connected to the recirculation circuit 17 below the heating device 19 to collect a first portion of said recirculation fraction of the gaseous effluent that has been heated and to a separation body 28 arranged on the recirculation circuit 17 above the heating device and capable of transferring a second portion of said recirculation fraction of the gaseous effluent that has not been heated by said heating device to the mixing chamber 27.

[0125] Thus, a gas mixture is obtained whose temperature is adjusted in the range of 900 to 1100°C, above the recarbonation temperature of the calcined mineral stone, but below the temperature that allows the carbonated mineral stone to be calcined, advantageously in the range of 1100 to 1500°C, and which can be injected into the cross channel 4 through the connection 26 to compensate for the heated cooling air extracted from the kiln.

[0126] The kiln shown also comprises means for advantageously injecting heated gas 26 into the cross channel 4. This gas is supplied from a mixing chamber 27 connected to the recirculation circuit 17 situated below the heating device 19, in order to collect a first portion of said recirculated portion of the gaseous effluent that has been heated, and to a separator 28 arranged on the recirculation circuit 17 situated above the heating device 19 and capable of transferring a second portion of said recirculated portion of the gaseous effluent that has not been heated by said heating device into the mixing chamber 27. Thus, a gas mixture is obtained whose temperature is adjusted to lie within the range of 900 to 1100° C., which is above the recarbonation temperature for calcining the ore but below the temperature that allows calcining the carbonated ore, advantageously lying within the range of 1100 to 1500° C., and which can be injected into the cross channel 4 through the connection 26 in order to compensate for the heated cooling air extracted from the kiln.

[0127] In another embodiment, a gaseous mixture having a regulated temperature in the range of 900 to 1100° C. is injected into the cross channel 4 to compensate for the extraction of heated cooling air from the kiln, the gaseous mixture being generated by a separate heating device, heating a second portion of the recycled portion of the CO2-based gaseous effluent not heated by the heating device 19 to a temperature in the range of 900 to 1100° C. for direct injection into the cross channel through the connection 26. Figure 2 This embodiment is not shown in FIG.

[0128] In the kiln shown, the gas stream entering shaft 2 consists almost exclusively of CO2 released during the decarburization of shaft 1, heated CO2-based gas injected into shaft 1 at the top of calcining zone B via device 6, and heated CO2-based gas injected into the cross-channel via device 26. The supplemental oxygen used for oxycombustion is primarily consumed by the oxycombustion. This gas stream is no longer diluted by air, even though it may contain residual oxygen. In fact, air is no longer required for combustion, and cooling air is extracted from the kiln. Consequently, the gaseous effluent exiting the kiln is highly concentrated in CO2.

[0129] Example

[0130] The kiln in this embodiment Figure 1 The kilns shown can produce between 150 and 760 tons of lime per day. All gas flow rates mentioned are in Nm of lime produced on dry gas. 3 / t indicates.

[0131] At the top of the shaft 1 working in calcining mode, 270 to 1400 tons / day (t / d) of calcareous stone can be loaded through the inlet 5. At the same time, the top opening 20 introduces 300 to 500 Nm of heat at a temperature below 200 ° C. 3 / t of recirculated gas to benefit from the regeneration and not obtain too high a temperature at the kiln outlet.

[0132] The gas injection device 6 introduces hot gas at the top of the calcination zone B in order to obtain a temperature of 1050-1250°C at the beginning of calcination. This temperature corresponds to the temperature of the mixture of the cold gas recycled at the top of the shaft and the hot gas injected at the top of the calcination zone. The temperature obtained is then much higher than 900°C and thus causes the stone to decarbonize, releasing 360-390 Nm 3 / t of CO2, and the formation of 950-1400Nm in the calcination zone 3 / tA gas flow co-current with the calcined material.

[0133] 250 to 450 Nm is introduced at the bottom of each shaft through the feed port 10 3 / t of cooling air. After heat exchange with the calcined material, the heated cooling air is extracted from the kiln by the collector elements 11 and 13. In order to compensate for this extraction, 0 to 600 Nm 3 The temperature of the kiln is based on the continuous introduction of CO2 gas at 900-1000°C into the cross channel 4. This introduction can avoid the cooling of the kiln.

[0134] After passing through the cross channel 4, the air flow is sucked towards the outlet 16 of the shaft 2 and simultaneously preheats the stones stored therein. 2000-2100 Nm 3 / t of gaseous effluent is discharged from the kiln at a temperature of 150-200°C.

[0135] 1500 to 1800 Nm 3 A portion of the gaseous effluent of 100 Nm / t is taken from the removal pipe 13 by the separator 16 and now flows along the recirculation loop 17, while 300 to 500 Nm 3 / t is discharged from the chimney 14. Before entering the treatment unit 22, the temperature of the discharged gas portion is 120 to 140°C, and the temperature after treatment is 30 to 50°C.

[0136] A separation element 34 divides the gaseous part taken out into two parts. The first part is sent to the kiln top (250-500Nm 3 / ton), and the second part is transferred to a heating device 19, such as a plasma torch, which heats the gas flow to a temperature of 1300 to 1500 ° C.

[0137] exist Figure 1 In the embodiment of the kiln shown, 900 to 1200 Nm 3 / t of this hot gaseous mixture is injected into shaft 1 and simultaneously 0 to 600 Nm 3 / t another part is transferred to the mixing chamber 27. There, the gas flow is mixed in a controlled manner with the cold third part of the gaseous effluent to obtain a regulated temperature of 900 to 1000 ° C. As described above, 0 to 600 Nm 3 / t of this mixture is injected into the cross channel 4.

[0138] 300 to 500 Nm discharged from chimney 18 3 The CO2 content of the gaseous effluent of 100 t / t is greater than 95% by volume, preferably 98% by volume (calculated on dry gas).

[0139] It will be understood that the invention is not limited to the described embodiments and that variations may be applied without departing from the scope of the appended claims.

Claims

1. A method for calcining carbonate ore in a parallel flow regenerative kiln having at least two shafts interconnected by a cross channel, the method comprising, in standard operation: -Carbonate ore is loaded on top of each shaft, - Preheating of these loaded ores in the preheating zone, - calcining these preheated ores in a calcining zone to produce decarbonized calcined material, - cooling the calcined material with cooling air in the cooling zone, forming heated cooling air by heat exchange, - discharge the calcined material from the bottom of the shaft, - discharge of gaseous effluent from the kiln, - Each shaft operates alternately in calcining mode and preheating mode, one shaft operating in calcining mode for a predetermined period of time, during which at least one other shaft operates in preheating mode; and vice versa, -The calcination method includes: o Carry out the step of loading carbonate ore on the top of the kiln shaft, o the calcining step of producing the decarbonized calcined material by increasing the temperature inside the preheated carbonate ore and releasing a gas flow co-current with the calcined material, and o the passage of the air flow towards at least one shaft operating in preheating mode, through the cross channel, -The preheating method includes: o subjecting the carbonate ore charge to said preheating step by heat exchange with said gas stream from the cross-channel, said gas stream rising and passing countercurrently through the carbonate ore charge, and o said exhaust step of exhausting said gas stream as a gaseous effluent in a preheated manner at the top of said at least one shaft, The cooling step comprises supplying cooling air to the bottom of each of the shafts or only to the bottom of the shafts operating in calcining mode, Characterized in that the method further comprises: - recirculating in preheated form a portion of the gaseous effluent discharged from the top of said at least one shaft, - heating the recycled portion of said gaseous effluent outside the kiln by means of at least one device capable of heating the gas, - injecting the heated portion of the recycled gaseous effluent into a shaft operating in calcining mode, at a level situated at the top of the calcining zone, in order to obtain said temperature increase allowing calcination of the carbonate ore, and - Heated cooling air is extracted from each shaft, where the cooling air is supplied at a level located below the cross-channels, and the gaseous effluent from the kiln is concentrated into CO2.

2. The method according to claim 1, further comprising, before said heating step, carrying out at least one heat exchange between heated cooling air extracted from outside the kiln and a recycled portion of said gaseous effluent by said device capable of heating the gas.

3. The process according to claim 1 or 2, further comprising introducing into a cross-channel a first portion of said recycled portion of the gaseous effluent and a second portion of said portion, said first portion having been heated outside the kiln by said means capable of heating the gas, and said second portion not having been heated by said means, in order to obtain a conditioning temperature allowing the calcination of the carbonated ore and above its recarbonation temperature.

4. The method according to any one of claims 1 to 3, wherein A portion of the recycled portion of the unheated gaseous effluent is injected in a calcined manner into the top of each shaft.

5. The method according to any one of claims 1 to 4, wherein The temperature of the heated portion of the recycled gaseous effluent injected in a calcining manner into the shaft at a level situated at the top of the calcining zone is between 1100° C. and 1500° C., said temperature being between 1100° C. and 1500° C. allowing the carbonate ore to be calcined.

6. The method according to any one of claims 1 to 4, wherein The temperature of the heated portion of the recycled gaseous effluent injected in a calcining manner into the shaft at a level situated at the top of the calcining zone is lower than 1100° C. and oxygen is supplemented before and / or in the calcining zone, said increase in temperature allowing calcination of the carbonate ore by oxy-combustion in the presence of said heated portion of the recycled gaseous effluent supplemented with oxygen.

7. A parallel flow regenerative kiln comprising at least two shafts (1, 2) interconnected by a cross channel (4), - Each axis includes the following when in use or out of use: - at least one inlet (5) for loading carbonate ore at the top of the shaft, - at least one outlet (11) for discharging the decarburized calcined material at the bottom of the shaft, - removal of the pipe (13) for the discharge of the CO2-based gaseous effluent from the top of the shaft, and - a cooling air supply device (8) at the bottom of the shaft for cooling the decarburized calcined material to be discharged, The kiln further comprises a reversing system (15) arranged to alternately drive the use and stop positions of each shaft in calcining operation and preheating operation, wherein the shaft (1) is in calcining operation for a predetermined period of time, while at least another shaft (2) is in preheating operation and is driven in reverse according to the control of the reversing system (15). The shaft (1) in the calcining operation comprises, from top to bottom, a preheating zone (A), a calcining zone (B) and a cooling zone (C), wherein the interconnected cross channel (4) is located at the bottom of the calcining zone (B). Characterized in that each shaft comprises means for injecting heated gas (6) into the shaft (1) during calcination at the top of the calcination zone (B) and means for removing (21, 23) the cooling air heated in contact with the calcined material from the kiln, at a level below the cross channel (4), The kiln further comprises an external recirculation loop (17), comprising: a separation body (16) for withdrawing a portion of the gaseous effluent from the removal duct (13), - heating means (19) capable of heating the gas, said heating means being connected to said separation body (16) and being arranged to heat a portion of said gaseous effluent, and - said means for injecting heating gas (6) into the shaft (1) during calcination operation, connected to the heating means (19) and injected into said heating section, to provide said gaseous effluent at a temperature equal to or higher than the calcination temperature of the charged ore.

8. The parallel flow thermal storage kiln according to claim 7, characterized in that: At the bottom of each shaft, at a level below the cross-channels (4), the means for removing the heated cooling air from the kiln comprise a central collecting element (21) communicating with external extraction means (22).

9. The parallel flow thermal storage kiln according to claim 7 or 8, characterized in that: Each shaft has a circular cross-section and is provided with a peripheral channel (3) at the bottom of the calcining zone (B), said cross-channels (4) interconnecting the peripheral channels (3) of the shafts to allow the flow of gas from one shaft to another, and at a level below the peripheral channels and the cross-channels, said means for removing heated cooling air from the kiln comprise an annular collector (23) communicating with an external extraction device (22).

10. The parallel flow thermal storage kiln according to any one of claims 7 or 8, characterized in that: Each shaft has a rectangular cross-section, the sides of one shaft facing the other shaft, cross-channels interconnecting the shafts directly between said facing sides, and at a level below the cross-channels, said means for removing heated cooling air from the kiln comprise, on at least some of the sides of each shaft, at least one collector communicating with external extraction means.

11. The parallel flow thermal storage kiln according to any one of claims 7 to 10, characterized in that: The heating device (19) is a furnace equipped with at least one plasma torch, an induction heating device, a radiation plate, a microwave oven or a solar heating device.

12. The parallel flow regenerative kiln according to any one of claims 7 to 11, wherein each shaft comprises a top opening (20) for introducing a portion of the unheated CO2-based gaseous effluent.

13. The parallel flow thermal storage kiln according to any one of claims 7 to 12, characterized in that: At least one heat exchanger (24) is arranged on the external recirculation loop (17), which is supplied with heated cooling air extracted from the kiln.

14. A parallel flow regenerative kiln according to any one of claims 7 to 13, comprising a mixing chamber (27) connected to the recirculation circuit (17) below the heating means for collecting a first portion of the recirculation fraction of the gaseous effluent that has been heated, and to a separation body (28) arranged on the recirculation circuit (17) above the heating means (19) and capable of conveying a second portion of the recirculation fraction of the gaseous effluent that has not been heated by the heating means into the mixing chamber in order to obtain a gaseous mixture having a regulated temperature that is lower than the temperature allowing calcination of carbonate ore, the mixing chamber being connected (26) to a cross-channel for injecting the gaseous mixture therein, Alternatively, it is connected to a device (6) for injecting heated gas so that the gaseous mixture is injected into the shaft when it is in preheating mode.

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