Method for calcining carbonate ores in a parallel-flow regenerative calciner and embodied calciner - Patent Application 20070122999

Abstract

A parallel-flow regenerative calciner, each shaft comprising means (6) for injecting heated gas into the shaft (1) in the calcining operation at the top of the calcination zone (B), and means (21, 23) for removing cooling air heated in contact with the calcined material from the calciner at a height lower than the crossover channel (4).

Description

[Technical Field]

[0001] The present invention relates to a method for calcining carbonate ores in a parallel flow regenerative kiln (PFRK). Such kilns comprise at least two shafts interconnected by a crossover channel. In each shaft, stone is introduced at the top and moves downward by gravity while it is successively preheated, calcined, and then cooled and collected at the bottom of each shaft. [Background technology]

[0002] The term "stone, carbonate ore, limestone" means, according to the present invention, a mineral having an average particle size d 50 By "fracture" is meant fragments of raw carbonate mineral having a size between 20 mm and 20 cm, preferably larger than 25 mm, preferably smaller than 18 cm, more preferably smaller than 16 cm, typically comprised between 3 and 15 cm.

[0003] Carbonate minerals according to the present patent application are typically calcium magnesium carbonates, 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 calcination zone of one shaft by a lance and burned in the presence of combustion air, usually every 12 to 20 minutes. The descending calcined product is then cooled in the cooling zone by heat exchange with cooling air introduced at the bottom of the shaft. Flue gases consist of combustion gases, decarbonated gases, and heated cooling air. These flue gases enter another shaft through a crossover channel, then pass through the stones present in this shaft and are then drawn out of the kiln. Thus, in this "preheat" shaft, the stones are preheated by the escaping flue gases. As a result, during this period, the shaft where combustion takes place operates for calcination, while the shaft through which flue gas is drawn operates for preheating. A period, usually between 30 seconds and 2 minutes, is then provided to reverse the air and fuel circuits, known as the reversal period. The shaft operated in the calcination mode then operates in the preheat mode, and the shaft operated in the preheat mode then operates in the calcination mode.

[0005] The classical method of calcining carbonate ores in a parallel-flow regenerative calciner having at least two shafts interconnected by a crossover channel, in standard operation, involves: - loading carbonate ore at the top of each shaft; - preheating these loaded stones in a preheating zone; - calcining these preheated stones in a calcination zone to produce a decarbonated calcine; - cooling the calcinate with cooling air in a cooling zone by heat exchange to produce heated cooling air; - discharging the calcinate from the bottom of the shaft; - venting the gaseous effluent from the kiln; - each shaft operates alternately in a calcination mode and a preheating mode, such that one shaft operates in the calcination mode for a predetermined period of time while at least another shaft operates in the preheating mode, and vice versa; - Calcination mode loading carbonate ore at the top of the shaft of the kiln; a calcination step, wherein the temperature rise in the preheated carbonate ore results in the production of a decarbonated calcinate and the release of a gaseous stream flowing cocurrently with the calcinate; and passing the gaseous stream through a crossover channel toward at least one shaft operating in a preheat mode; - Preheat mode preheating the charged carbonate ore by heat exchange with a gaseous stream coming from the crossover channel, the gaseous stream rising and flowing countercurrently through the charged carbonate ore; and discharging the gaseous stream as a gaseous exhaust at the top of the at least one shaft in a preheat mode; The cooling step involves supplying cooling air at the bottom of each of the shafts, or only at the bottom of the shafts operating in calcination mode.

[0006] In the calcination zone of a classical kiln, fuel is injected and burned beneath the preheated stones in the calcination mode to utilize the heat of the flue gases transferred to the stones in the preheating zone. In the preheating mode, the stones introduced into the kiln are at room temperature, and the flue gases drawn in from outside the kiln are at about 150°C, minimizing energy loss.

[0007] According to the present invention, normal operation means that the kiln continuously produces calcined material, which operation does not involve start-up, shutdown or maintenance phases of the kiln.

[0008] According to the invention, carbonate ores are understood in particular to mean calcareous stones (limestones), dolomitic stones (dolomite or uncalcined dolomite) and / or magnesite stones, which are calcined to give quicklime, quicklime and / or magnesia.

[0009] The calcination reaction in which limestone turns into quicklime is CaCO3 (solid) + heat → CaO (solid) + CO2 (gas) is.

[0010] This reaction is endothermic and reversible. At temperatures below 850-900°C, lime and CO2 can easily recombine. However, from temperatures around 900°C, the raw stone releases large amounts of CO2 during decarbonation. To achieve this, the temperature must be significantly increased in the calcination zone. Today, this temperature increase is primarily achieved by burning fuels, often fossil fuels, in the presence of an oxidizing agent such as air. Burning fuels in this way also releases large amounts of CO2. Globally, current calcination methods actively contribute to the greenhouse effect.

[0011] During fuel combustion, direct contact of the flame with the preheated carbonate ore can also cause local overheating in the calcination zone, resulting in flue gas or fuel ash contaminating the calcinate. To maintain high calcination quality, careful fuel selection is required, particularly avoiding fuels with high sulfur content. Even with the selection of fossil fuels, the reactivity of the calcinate can be affected by fuel ash and minor contaminants. During high-temperature combustion, thermally and fuel-borne NOx are produced due to the high nitrogen content of the combustion air, as well as the nitrogen that may be present in the fuel.

[0012] This very common calcination process also has the disadvantage that the fuel is burned with air and the calcined product is cooled with air. As a result, a gaseous effluent rich in diatomic nitrogen (N2) and relatively low in CO2 (approximately 20%-27% volume concentration of dry gas) is released at the top of the calciner. This high nitrogen content in air makes CO2 capture very difficult and expensive.

[0013] For example, WO2022 / 002869 , DE102021204175, WO2022 / 238384 Alternatively, modifications of the general calcination process have been proposed to improve CO2 capture, such as in WO2022 / 229120. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] WO2022 / 002869 [Patent Document 2] DE102021204175 [Patent Document 3] WO2022 / 238384 [Patent Document 4] WO2022 / 229120 Summary of the Invention [Problem to be solved by the invention]

[0015] The objective of the present invention is to improve the significant CO2 emissions problem of the PFRK kiln without substantially altering the cyclical function of the kiln and with little or no modification to its design. Another objective is to avoid, as much as possible, overheating the calcined product and the introduction of impurities into the calcined product. Another objective of the present invention is to make it easier to recover CO2 in the gaseous effluent from the kiln. It is clear that the primary objective of the calciner, i.e., the production of high-quality, high-purity calcined product, must be maintained. [Means for solving the problem]

[0016] To solve these problems, according to the present invention, the method as described above is in a preheat mode, recirculating a portion of the gaseous effluent discharged from the top of the at least one shaft; withdrawing heated cooling air from each shaft, the cooling air being supplied at an elevation located below the crossover channel, and the gaseous effluent from the kiln being CO 2 is enriched in

[0017] The method comprises: heating the recirculated portion of the gaseous effluent outside the calciner by at least one heating device capable of heating the gas; injecting a heated recycle portion of the gaseous effluent into a shaft operating in a calcination mode at a height located at the top of a calcination zone to obtain a temperature increase enabling calcination of the carbonate ore; removing a portion of the gaseous effluent from the recirculation circuit upstream of a device capable of heating the gas and introducing the portion into a shaft at its top opening in a calcining state; Also includes It is characterized by:

[0018] The terms CO2-enriched or CO2-enriched gaseous effluent or CO2-enriched gaseous effluent mean according to the present invention that the CO2 content is at least 65% by volume of dry gas, in particular at least 70% by volume, more preferably at least 80% by volume, preferably at least 90% by volume of dry gas, most preferably at least 95% by volume of dry gas.

[0019] The present invention relies largely on externalizing the energy supply and heating the recirculated gas with a heating device capable of heating the gas. The gas enters such a device at a defined temperature and exits 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. Also, devices capable of releasing heated gases resulting from a reaction, e.g., from combustion, are not included in the meaning of the heating device capable of heating the gas according to the present invention.

[0020] In one variation of the embodiment, such a device can be a combination of a furnace with at least one plasma torch, induction heating device, radiant panel, microwave oven, solar heating device, and a combustion furnace (indirect combustion, oxy-fuel, etc.), which can be switched between, so that the combined furnaces can be operated alternately depending on the availability and price of energy.

[0021] In a further embodiment, such a device can be any heating device that heats gas and provides heated gas supplemented with oxygen before feeding it into the calcination zone of a kiln where oxy-combustion takes place, thereby reducing the additional heat generated by oxy-combustion.

[0022] The injection system of the calciner of the present invention is optimized to provide good heat distribution, thus significantly improving the quality of the calcinate.

[0023] Neither fuel nor air is required for combustion in the calciner. As a result, no or limited pollutants are generated, except for minor contaminants contained in the stones. No ash is produced, resulting in a pure decarbonated product. Because there is no or low levels of nitrogen in the gas stream, no or very little NOx is produced, allowing the plant to comply with stricter regulations. There is no risk of the stones coming into direct contact with the flame. It is very easy to control the appropriate temperature of the heated gas from the heating device, thereby producing high-quality lime. According to the present invention, the heated recycle gas is introduced into the calcining shaft from the top of the calcination zone, just below the preheating zone, thereby maintaining all of the heat storage functions of the calciner.

[0024] By recirculating the CO2-based gas in the absence of combustion air, the system enriches the CO2 in the gaseous effluent from the calciner, making CO2 capture easier and / or making the CO2 purification process (which purifies and enriches the CO2) of the calciner flue gas prior to capture easier and more energy-efficient compared to standard flue gas enrichment. In the method according to the invention, the heated cooling air from the shaft is withdrawn at a height below the crossover channel, so that the gaseous effluent removed from the calciner is formed almost exclusively from the CO2-based gaseous stream resulting from the decarbonation reaction and the CO2-based gas injected into the calcining shaft and, optionally, into the crossover channel. As a result, the gaseous effluent discharged from the kiln typically has an enriched CO2 content of at least 80% by volume dry gas, preferably at least 90% by volume dry gas, and most preferably at least 95% by volume dry gas.

[0025] Such gaseous emissions can be used or sequestered under favorable conditions, thus reducing the kiln's contribution to the greenhouse effect.

[0026] Although neither fuel nor air is required for combustion in the calciner, the present invention also contemplates combining heating of the gaseous effluent with oxygen addition to provide a heated gas mixture compatible with oxy-combustion in the calciner. In such cases, there is little or no air in the calcination zone of the calciner, since the nitrogen in the dry gas is replaced by more than 90% by volume, preferably more than 95% by volume, of CO, compared to combustion with combustion air. In fact, this combination allows for the recirculation of CO-based gases in the absence of combustion air to enrich the CO in the gaseous effluent leaving the calciner, thereby facilitating CO capture and / or making the CO purification process of the calciner flue gas prior to capture (to purify and enrich the CO) simpler and more energy-efficient than standard flue gas enrichment.

[0027] According to one embodiment of the present invention, at least one heat exchange is carried out between the heated cooling air extracted outside the calciner and the recycled part of the gaseous effluent before the heating step by the heating device, such heat exchange allowing to recover heat from the extracted cooling air before the heating step, so that the air released into the atmosphere is closer to the ambient temperature.

[0028] Advantageously, the process of the invention comprises introducing into a crossover channel a gaseous mixture of a first part of the recycled gaseous effluent, which has been heated outside the calciner by a device capable of heating the gas, and a second part which has not been heated by the device, in order to obtain a gas temperature which is higher than the temperature for recarbonation of the calcined ore but which allows the calcination of the carbonate ore, preferably a temperature lower than the range of 1100-1500°C, typically a temperature in the range of 900-1100°C.

[0029] Alternatively, the gaseous stream introduced into the crossover channel is a second portion of the portion not heated by the device that has been heated by another heating device to a regulated temperature that is lower than the temperature that allows for calcination of the carbonate ore but higher than the temperature for recarbonation of the calcined ore.

[0030] The term "adjusted temperature below the temperature that allows the calcination of the carbonate ore but above the temperature for recarbonation of the calcined ore" means, according to the present invention, a temperature below 1100°C, preferably in the range of 900°C to 1100°C, preferably 950°C to 1100°C.

[0031] The term "temperature allowing the calcination of carbonate ore" means, according to the invention, a temperature in the range of 1100°C to 1500°C.

[0032] According to a preferred embodiment of the present invention, a portion of the recycled portion of the unheated CO2-based gaseous effluent is injected at the top of each calcining shaft.

[0033] In a preferred embodiment according to the invention, the heated portion of the recycled gaseous effluent injected into the shaft operating in calcination mode at a height located at the top of the calcination zone has a temperature comprised between 1100°C and 1500°C, the temperature comprised between 1100°C and 1500°C allowing the calcination of carbonate ores.

[0034] In one variant of the embodiment according to the invention, the heated portion of the recycled gaseous effluent injected into the shaft operating in calcination mode at a height located at the top of the calcination zone has a temperature below 1100°C, oxygen is supplemented before and / or in the calcination zone, and the temperature increase enabling the calcination of the carbonate ore is provided by oxy-combustion in the presence of the heated portion of the recycled gaseous effluent supplemented with oxygen.

[0035] In certain cases, the process is carried out in a two-shaft kiln.

[0036] The present invention also relates to a parallel-flow regenerative calciner, comprising at least two shafts interconnected by a crossover channel, Each shaft, in its actuated or inactive position, - at least one inlet opening at the top of the shaft for loading carbonate ore; - at least one outlet opening at the bottom of the shaft for discharging the decarbonated calcinate; - an extraction duct for discharging CO2-based gaseous emissions from the top of the shaft; - a cooling air supply at the bottom of the shaft for cooling the decarbonated calcined product being discharged; The kiln further comprises an inversion system configured to alternately drive each shaft between an operating position and a non-operating position to place the shaft in a calcination operating state and a preheating operating state, wherein one shaft is operated in a calcination operating state for a predetermined time while at least another shaft is operated in a preheating operating state, and vice versa under the control of the inversion system; The shaft operating in calcination comprises, successively from top to bottom, a preheating zone, a calcination zone, and a cooling zone, with an interconnecting crossover channel located at the bottom of the calcination zone.

[0037] According to the invention, each shaft comprises means for injecting heated gas into the shaft during calcination at the top of the calcination zone, and means for removing cooling air heated in contact with the calcined material from the kiln at a height lower than the crossover channel; The calciner further includes an external recirculation circuit, the external recirculation circuit comprising: - a separator for removing a portion of the gaseous emissions from the extraction duct; Equipped with each shaft comprises means for injecting heated gas into the shaft operating in the calcination zone at the top of the calcination zone and a top opening for introducing a portion of the removed portion of the unheated gaseous effluent, the external recirculation circuit comprising: a heating device connected to the separator and configured to heat a portion of the gaseous effluent, the heating device being capable of heating the gas; - means for injecting heated CO2-based gas into the shaft operating in the calcination operation, connected to the heating device and injecting the heated portion to provide a gaseous effluent at a temperature above the calcination temperature of the ore charged; - introducing a removed portion of the gaseous effluent from the recirculation circuit at the top opening, upstream of the heating device; It is characterized by: do.

[0038] The term "injecting a heated portion to provide a gaseous effluent at a temperature above the calcination temperature of the loaded ore" means, according to the present invention, either injecting a heated portion of a gaseous effluent at a temperature above the calcination temperature of the loaded ore, or injecting a heated portion to provide a gaseous effluent at a temperature above the calcination temperature of the loaded ore using additional means to provide the calcination temperature of the loaded ore, such as, for example, an additional oxy-combustion means or step.

[0039] As explained above, the PFRK kiln operates in a cyclical cycle, with each shaft operating in calcination mode for a predetermined time, then operating in preheat mode after a reversal period, typically between 30 seconds and 2 minutes. During the reversal period, the reversal system synchronizes and controls all the changes necessary to move from one state to another, for example, by opening the means for injecting gas into the shaft operating in calcination mode and closing it when the shaft is switched to preheat mode. Thus, the reversal system not only controls many flaps and valves, but also the operation of loading and unloading equipment, or even the operation of various suction, pumping, or injection elements.

[0040] Advantageously, at the bottom of each shaft, at a height lower than the crossover channels, the means for extracting heated cooling air from the kiln may comprise a central collecting element communicating with an external extraction device.

[0041] According to some embodiments of the calcination furnace, each shaft has a circular cross section and includes a peripheral channel at the bottom of the calcination zone, with crossover channels interconnecting the peripheral channels of the shafts for passing gases from one shaft to another. The means for removing heated cooling air from the calcination furnace can include an annular collector at a height lower than the peripheral and crossover channels and in communication with an external extraction device.

[0042] According to another kiln, each shaft has a rectangular cross section, the sides of one shaft face the sides of another shaft, and crossover channels directly interconnect the shafts between the opposing sides. The means for removing heated cooling air from the kiln comprise at least one collector on at least some sides of each shaft, at a height below the crossover channels, in communication with an external extraction device.

[0043] According to one embodiment of the kiln of the present invention, each shaft is provided with a top opening for introducing a portion of the removed portion of the unheated CO2-based gaseous effluent.

[0044] According to another embodiment of the calciner of the invention, at least one heat exchanger supplied with heated cooling air extracted from the calciner is arranged in the external recirculation circuit.

[0045] In a preferred embodiment of the present invention, the calciner comprises a mixing chamber connected to a recirculation circuit below the heating device for collecting a first portion of the heated CO2-based recycled gaseous effluent, and connected to a separator arranged in the recirculation circuit above the heating device for transferring a second portion of the recycled CO2-based gaseous effluent that has not been heated by the heating device to the mixing chamber, thereby enabling the calciner to obtain a gaseous mixture having a regulated temperature lower than that allowing the calcination of carbonate ore. The mixing chamber is further connected to the crossover channel for injecting the gaseous mixture through the gaseous mixture conduit into the crossover channel, and also connected to a means for injecting heated gas for injecting the gaseous mixture through the gaseous mixture conduit at the top of the calcination zone when the shaft is in the preheat mode.

[0046] When the gaseous mixture is injected into the crossover channel, the temperature adjusted is below 1100° C., preferably between 900° C. and 1100° C., more preferably between 950° C. and 1100° C. When the gaseous mixture is injected at the top of the calcination zone when the shaft is in preheat mode, the temperature adjusted is below 1100° C., preferably between 500° C. and 1100° C., more preferably between 550° C. and 950° C.

[0047] Alternatively, the gaseous stream (mixture) introduced into the crossover channel through the gaseous mixture conduit is heated by a separate heating device to a regulated temperature below that which allows for calcination of the carbonate ore, but above the temperature for recarbonation of the calcined ore.

[0048] In yet another alternative embodiment, when the shaft is in preheat mode, the gaseous mixture introduced at the top of the calcination zone through the gaseous mixture conduit is heated by a separate heating device to a regulated temperature below that which will enable calcination of the carbonate ore, but above that which will enable recarbonation of the calcined ore.

[0049] When the gaseous mixture is injected into the crossover channel, the temperature adjusted is below 1100° C., preferably between 900° C. and 1100° C., more preferably between 950° C. and 1100° C. When the gaseous mixture is injected at the top of the calcination zone when the shaft is in preheat mode, the temperature adjusted is below 1100° C., preferably between 500° C. and 1100° C., more preferably between 550° C. and 950° C.

[0050] In some embodiments of the invention, the means for injecting heated gas is connected to a source of heated CO2-based gas external to the shaft and to the gaseous mixture conduit, and the means for injecting heated gas has an inactive position and an active position for the heated CO2-based gas and an inactive position and an active position for the gaseous mixture conduit. This means that the means for injecting heated gas is typically in an active position for the heated CO2-based gas (where the heated CO2-based gas can enter) and in an inactive position for the gaseous mixture conduit (where the gaseous mixture inlet is closed) during the calcination mode, and the means for injecting heated gas is typically in an inactive position for the heated CO2-based gas (where the heated CO2-based gas inlet is closed) and in an active position for the gaseous mixture conduit (where the gaseous mixture can enter) during the preheat mode.

[0051] As can be seen from the above, the firing furnace according to the present invention requires only slight structural changes to the exterior of the furnace.

[0052] In certain cases, the kiln is a two-shaft kiln.

[0053] Other embodiments according to the invention are set forth in the accompanying claims.

[0054] Other features and advantages of the invention will become apparent from the following non-limiting description and by reference to the drawings and examples. [Brief explanation of the drawings]

[0055] [Figure 1] 1 is a diagram of a first embodiment of a calcination furnace according to the present invention; [Figure 2] FIG. 2 is a diagram of a second embodiment of a calcination furnace according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0056] In the drawings, the same reference numbers are assigned to the same or similar elements.

[0057] As seen in Figure 1, the illustrated PFRK kiln has two shafts 1, 2 having circular cross-sections with peripheral channels 3 interconnected by crossover channels 4. Conventionally, shaft 1, shown on the left, operates in a calcination mode, while shaft 2, shown on the right, operates in a preheating mode. The shafts are divided in height into three zones: preheating zone A, where the carbonate stone is preheated before calcination; calcination zone B, where the preheated carbonate stone is decarbonated; and cooling zone C, where the decarbonated calcinate is cooled.

[0058] The carbonate rock is introduced at the top of the shaft through the inlet opening 5, which is in the open position. The rock gradually descends through the shaft due to gravity. When the shaft is operating in calcination mode, at the top of the calcination zone B, and thus immediately below the preheating zone A, there are provided means for injecting gas having a temperature above the calcination temperature of the rock during operation, for example, a gas having a temperature between 1100 and 1500 °C. In the illustrated kiln, these means are represented by holes 6 in the shaft shell, which allow gas to be injected from the outside of the shaft at various radial positions within the shaft; several horizontal, layered injection points are advantageously required to obtain the correct heat distribution. Several other injection systems are also conceivable, such as horizontal lances, vertical lances, inner barrels, beams, etc. Thus, the rock is decarbonated, resulting in a decarbonated calcinate that continues to descend through the shaft, and a gaseous stream 7 that flows cocurrently with the calcinate.

[0059] Cooling air is introduced into the bottom of the shaft via a supply pipe 8 and a supply opening 9 in the open position. The cooling air flows countercurrently to the calcinate to cool it. The cooled calcinate is discharged through an outlet opening 11 in the open position to an unloading device 10.

[0060] Gaseous stream 7 is composed of the CO2 released during decarbonation and the heated CO2-based gas injected into the shaft. This gaseous stream passes through the surrounding channel 3, the crossover channel 4 and then into shaft 2, which is operating in preheat mode.

[0061] When a shaft is operating in preheating mode, in this case shaft 2, the means for injecting CO2-based gas, such as holes 6, are not used. Meanwhile, the cooling air supply opening 9 and the calciner outlet opening 11 remain open. In this shaft 2, the gas flow coming from the crossover channel 4 advances to the top of the shaft in countercurrent with the stones, preheating them. The gaseous effluent leaves the kiln through outlet opening 12, which is open in this case, and through the discharge duct 13 and chimney 14. In shaft 1 operating in calcination mode, the outlet opening 12 of this discharge duct 13 is closed.

[0062] The kiln also includes a reversal system 15, shown diagrammatically, which synchronizes and controls the operation of the shafts, either directly or remotely, during reversal times. The system is configured to alternately drive each shaft between an active and inactive position to establish a calcination operating state and a preheat operating state.

[0063] Outside the kiln, a separator 16 is provided in the outlet duct 13, which can remove a portion of the gaseous effluent discharged from the kiln and introduce it into a recirculation circuit 17. In this circuit, a portion of the gaseous effluent can be advantageously treated in a treatment device 18, for example cooled, filtered, and / or dried. The recirculation circuit 17 also comprises an external heating device 19 capable of heating the gas. This heating device may be driven by the reversal system 15 to provide a CO2-based gas injected through the bore 6 of the shaft operating in calcination mode and having a temperature suitable for pyrolyzing the preheated stone.

[0064] A portion of the gaseous effluent is withdrawn from the recirculation circuit 17 upstream of the furnace 19. This withdrawn gas has a temperature close to ambient temperature (preferably below 200°C) and is advantageously introduced into shaft 1 in calcination mode, as in the illustrated kiln, through a top opening 20. This opening is closed in shaft 2, which is operating in preheating mode. To maintain the heat storage effect, cold gas must be injected at a slightly higher pressure at the top of shaft 1.

[0065] In the illustrated kiln, the heated cooling air is drawn at a height below the crossover channels 4 through a central collecting element 21 which communicates with an external extraction device 22 for removing the cooling air heated in contact with the decarbonated calcinate from the kiln. For the same purpose, each circular shaft may also be provided with an annular collector 23 which also communicates with the extraction device 22.

[0066] At least one heat exchanger, supplied with the heated cooling air extracted from the calciner, is advantageously arranged in the external recirculation circuit 17. In the calciner shown, the heated cooling air extracted by the extraction device 22 is fed to a heat exchanger 24, where it exchanges heat with the cold gas leaving the treatment device 18. The air, which is at a temperature close to ambient temperature, is discharged into the atmosphere by an outlet 25, possibly after treatment such as dedusting, with energy recovery upstream of the heating device 19.

[0067] The illustrated calciner also comprises means 26 for advantageously injecting heated gas into the crossover channel 4. This gas is supplied from a mixing chamber 27. The mixing chamber 27 is connected to the recirculation circuit 17 below the heating device 19 in order to collect a first portion of the recycled portion of the heated gaseous effluent, and is connected to a separator 28 arranged in the recirculation circuit 17 above the heating device 19 and capable of transferring a second portion of the recycled portion of the gaseous effluent not heated by the heating device to the mixing chamber 27. A gaseous mixture having a regulated temperature in the range of 900-1100°C, which is higher than the temperature for recarbonation of the calcined ore but lower than the temperature allowing the calcination of carbonate ores (advantageously in the range of 1100-1500°C), is thus obtained and can be injected into the crossover channel 4 by means of the connection 26 to compensate for the withdrawal of heated cooling air from the calciner.

[0068] In another embodiment, to supplement the withdrawal of heated cooling air from the calciner, the gaseous mixture having a temperature adjusted to the range of 900-1100°C that is injected into the crossover channel 4 is generated by a separate heating device that heats a second portion of the recycled portion of the CO2-based gaseous effluent that was not heated by the heating device 19 to the range of 900-1100°C and is injected directly into the crossover channel by connection 26. This embodiment is not shown in FIG.

[0069] In this illustrated calciner, the gaseous stream entering shaft 2 consists essentially solely of CO released during decarbonation in shaft 1, heated CO-based gas injected into shaft 1 at the top of calcination zone B by means 6, and heated CO-based gas injected into the crossover channel by means 26. This gaseous stream is not diluted with air. Virtually no air is required for combustion, and cooling air is withdrawn from the calciner. As a result, the gaseous effluent leaving the calciner has a high CO content.

[0070] As can be seen in FIG. 2, the illustrated calciner (PFRK) is similar to the calciner of FIG. 1 in that it also has two shafts 1, 2, each having a circular cross section and a peripheral channel 3. The peripheral channels are interconnected by a crossover channel 4. Conventionally, shaft 1, shown on the left, operates in a calcination mode, while shaft 2, shown on the right, operates in a preheating mode. The shafts are divided in height into three zones: a preheating zone A, where the carbonate stone is preheated before calcination; a calcination zone B, where the preheated carbonate stone is decarbonated; and a cooling zone C, where the decarbonated calcinate is cooled.

[0071] The carbonate stone is introduced at the top of the shaft through the inlet opening 5, which is in the open position. The stone gradually descends down the shaft by gravity. When the shaft operates in calcination mode, at the top of the calcination zone B, and therefore just below the preheating zone A, means for injecting gas during operation are provided. These are represented by holes 6 in the outer shell of the shaft, which allow gas to be injected from the outside of the shaft at various radial positions within the shaft; several horizontal, layered injection points are advantageously required to obtain the correct heat distribution. The gas is injected to achieve a temperature above the calcination temperature of the stone in the calcination zone, for example, between 1100 and 1500°C. This gas mixes with the gas 20 injected at the top of the kiln. The gas 20 injected at the top of the kiln is at a lower temperature than the heated gas injected from outside the kiln, and the temperature of the gas injected at the top is taken into consideration in setting the temperature of the gas injected from outside the kiln to a temperature above the calcination temperature of the stones in the calcination zone, for example, 1100 to 1500°C.

[0072] Several other injection systems are possible, such as horizontal lances, vertical lances, inner barrels, beams, etc. In this way, the rock is decarbonated, resulting in a decarbonated calcinate that continues to descend in the shaft, and a gaseous stream 7 that flows cocurrently with the calcinate.

[0073] Cooling air is introduced into the bottom of the shaft via a supply pipe 8 and a supply opening 9 in the open position. The cooling air flows countercurrently to the calcinate to cool it. The cooled calcinate is discharged through an outlet opening 11 in the open position to an unloading device 10.

[0074] Gaseous stream 7 is composed of the CO2 released during decarbonation and the heated CO2-based gas injected into the shaft. This gaseous stream passes through the surrounding channel 3, the crossover channel 4 and then into shaft 2, which is operating in preheat mode.

[0075] When a shaft is operating in preheating mode, in this case shaft 2, the means for injecting heated CO2-based gas from the outside to achieve a temperature above the calcination temperature of the stones in the calcination zone are not used. Meanwhile, the cooling air inlet 9 and the calcination outlet 11 remain open. In this shaft 2, the gas flow coming from the crossover channel 4 advances countercurrently to the top of the shaft to preheat the stones. The gaseous effluent leaves the kiln through the outlet 12, which is open in this case, and through the discharge duct 13 and chimney 14. In shaft 1 operating in calcination mode, the outlet 12 of this discharge duct 13 is closed.

[0076] The kiln also includes a reversal system 15, shown diagrammatically, which synchronizes and controls the operation of the shafts, either directly or remotely, during reversal times. The system is configured to alternately drive each shaft between an active and inactive position to establish a calcination operating state and a preheat operating state.

[0077] Outside the calciner, a separator 16 is provided in the withdrawal duct 13, which allows a portion of the gaseous effluent discharged from the calciner to be withdrawn and introduced into a recirculation circuit 17. In this circuit, a portion of the gaseous effluent is advantageously treated in a treatment device 18, where it can be, for example, filtered and / or dried.

[0078] The recirculation circuit 17 also includes an external heating device 19 capable of heating the gas. This heating device may be driven by the reversing system 15 to provide a CO2-based gas having a suitable temperature to be injected through the shaft bore 6 operating in calcination mode.

[0079] In the illustrated kiln, the temperature of the calcination zone is achieved by injecting heated CO2-enriched gas in combination with the addition of oxygen through oxygen addition section 29. Oxygen can be supplied from an oxygen tank, an oxygen production unit, or from a separator 30 to which air is supplied through supply inlet 31. In the latter case, nitrogen, the main component of air, leaves the separator through outlet 32. The heated CO2-enriched gas, to which oxygen has been added, is supplied to the calcination zone (top) where the existing combustion lance 33 and burner are provided, as previously described. The burner in the embodiment shown in Figure 2 operates under oxy-combustion conditions, where combustion of fuel takes place in a gas mixture containing primarily oxygen and CO2.

[0080] Oxygen can be added to the heated CO2 enriched gas through a mixing chamber if desired.

[0081] Oxygen can also be added through top opening 20 instead of or in addition to oxygen addition 29 .

[0082] The CO2 present in the gas mixture typically replaces more than 90%, preferably more than 95%, of the nitrogen compared to combustion operation using air.

[0083] The content of oxygen in the gas mixture is preferably in excess of the stoichiometric conditions of combustion, preferably 5 to 50% by volume, in particular 10 to 30% by volume, advantageously 15 to 25% by volume in excess of the stoichiometric amount required for the combustion reaction.

[0084] In this state, the fuel can be burned to reach the temperatures required for pyrolysis of the preheated stone, between 900°C and 1500°C.

[0085] The fuel may be any solid, liquid or gaseous combustible within the meaning of the present invention, such as natural gas, hydrogen, biogas, fuel oil, oil, powdered coal or coke, solid biomass such as sawdust, recycled solid combustibles such as plastic materials, cellulosic materials, etc.

[0086] Advantageously, in the case of solid fuel, it is introduced into the calcination shaft in the form of granules or powder, using as carrier gas a portion of the gaseous effluent discharged from the calciner. CO2 from any other source can also be supplied as carrier gas.

[0087] A portion of the gaseous effluent is extracted from the recirculation circuit 17 upstream of the heating device 19. This extracted gas has a temperature close to ambient temperature and is advantageously introduced into shaft 1 in calcination mode, as in the illustrated kiln, through a top opening 20. This opening is closed in shaft 2, which is operating in preheating mode. To maintain the heat storage effect, cold gas must be injected at a slightly higher pressure at the top of shaft 1.

[0088] In the illustrated kiln, the heated cooling air is drawn at a height below the crossover channels 4 through a central collecting element 21 which communicates with an external extraction device 22 for removing the cooling air heated in contact with the decarbonated calcinate from the kiln. For the same purpose, each circular shaft may also be provided with an annular collector 23 which also communicates with the extraction device 22.

[0089] At least one heat exchanger supplied with the heated cooling air extracted from the calciner is advantageously arranged in the external recirculation circuit 17. In the calciner shown, the heated cooling air extracted by the extraction device 22 is supplied to the heat exchanger 24, where it exchanges heat with the cold gas leaving the treatment device 18. The air, which is at a temperature close to ambient temperature, is discharged into the atmosphere by an outlet 25, with energy recovery upstream of the heating device 19.

[0090] The illustrated calciner also advantageously comprises means 26 for injecting heated gas into the crossover channel 4. This gas is supplied from a mixing chamber 27 which is connected to the recirculation circuit 17 below the heating device 19 in order to collect a first portion of the recycled portion of the heated gaseous effluent, and which is also connected to a separator 28 arranged in the recirculation circuit 17 above the heating device 19 and able to transfer to the mixing chamber 27 a second portion of the recycled portion of the gaseous effluent not heated by the heating device. A gaseous mixture is thus obtained having a regulated temperature in the range 900-1100°C, which is higher than the temperature for recarbonation of the calcined ore but lower than the temperatures allowing the calcination of carbonate ores (advantageously in the range 1100-1500°C), and which can be injected into the crossover channel 4 by means of the connection 26 to compensate for the withdrawal of heated cooling air from the calciner.

[0091] In another embodiment, to supplement the withdrawal of heated cooling air from the calciner, the gaseous mixture having a temperature adjusted to the range of 900-1100°C that is injected into the crossover channel 4 is generated by a separate heating device that heats a second portion of the recycled portion of the CO2-based gaseous effluent that was not heated by the heating device 19 to the range of 900-1100°C and is injected directly into the crossover channel by connection 26. This embodiment is not shown in FIG.

[0092] In this illustrated calciner, the gaseous stream entering shaft 2 consists essentially solely of CO released during decarbonation in shaft 1, heated CO-based gas injected into shaft 1 at the top of calcination zone B by means 6, and heated CO-based gas injected into the crossover channel by means 26. Oxygen supplement for oxy-combustion is consumed primarily by oxy-combustion. This gaseous stream is not diluted with air, even though it may contain residual oxygen. Virtually no air is required for combustion, and cooling air is bled from the calciner. As a result, the gaseous effluent leaving the calciner has a high CO content. [Example]

[0093] The calciner in this example corresponds to the calciner shown in Figure 1 and is designed to produce 150 to 760 tonnes of lime per day. All gaseous flow rates mentioned are in Nm of dry gas of lime produced. 3 It is expressed as / t.

[0094] At the top of the shaft 1 operating in calcination mode, 270 to 1400 tpd (tons per day) of calcareous stone can be loaded through the inlet opening 5. At the same time, 300 to 500 Nm 3 / t of recycled gas is introduced through the top opening 20 at a temperature below 200°C to enhance the heat storage effect and to prevent the temperature at the exit of the kiln from becoming too high.

[0095] The means for injecting gas 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 the calcination. This temperature corresponds to the temperature of the mixture of the recycled cold gas at the top of the shaft and the hot gas injected at the top of the calcination zone. The obtained temperature is then well above 900°C, thereby obtaining a flow rate of 360-390 Nm 3 Decarbonation of the rock occurs with the release of 950-1400 Nm3 / t of CO2 in the calcination zone, which flows cocurrently with the calcined material. 3 / t of gaseous stream is formed.

[0096] 250~450Nm 3 1 / t of cooling air is introduced at the bottom of each shaft by a supply opening 10. After heat exchange with the calcined material, the heated cooling air is extracted from the kiln by means of collecting elements 11 and 13. To supplement this extraction, 0-600 Nm3 of cooling air having a temperature of 900-1000 °C is introduced. 3 / t of CO2-based gas is continuously introduced into the crossover channel 4 by injection means 30. This introduction makes it possible to avoid a drop in the temperature of the kiln.

[0097] After passing through the crossover channel 4, the gaseous stream is drawn towards the outlet opening 16 of the shaft 2, preheating the stone stored in the shaft 2. 3 / t of gaseous effluent leaves the calciner at a temperature of 150-200°C.

[0098] 1500-1800 Nm3 of gaseous emissions 3 A portion of the gaseous effluent is removed from the removal duct 13 by a separator 16 and then led to a recirculation circuit 17, while 300-500 Nm 3 The / t portion is discharged by the chimney 14. This removed gaseous portion has a temperature of 120-140°C before entering the treatment device 22 and a temperature of 30-50°C after treatment.

[0099] The separation element 34 separates the removed gaseous fraction into two parts: the first part is sent to the top of the calciner (250-500 Nm 3 / ton), the second portion is transferred to a heating device 19, such as a plasma torch, which heats the gaseous stream to a temperature of 1300-1500 °C.

[0100] In the embodiment of the calciner shown in Figure 1, 900 to 1200 Nm of this high-temperature gaseous mixture is 3 A portion of the / t is injected into the shaft 1 by the injection means 6 disclosed above, and 3 Another portion of the gaseous effluent is transferred to the mixing chamber 27, where it is mixed in a controlled manner with a lower temperature third portion of the gaseous effluent to obtain a controlled temperature of 900-1000°C. 3 / t is injected into the crossover channel 4 as disclosed above.

[0101] 300-500 Nm of gaseous emissions discharged by chimney 18 3 The / t portion has a CO2 content of more than 95% by volume, preferably 98% by volume, of dry gas.

[0102] It is to be understood that the invention is not limited to the described embodiments and that modifications can be applied without departing from the scope of the appended claims.

Claims

1. 1. A method for calcining carbonate ores in a parallel flow regenerative calciner having at least two shafts interconnected by a crossover channel, the method comprising, in standard operation: - loading carbonate ore at the top of each shaft; - preheating these loaded stones in a preheating zone; - calcining these preheated stones in a calcination zone to produce a decarbonated calcine; - cooling said calcinate with cooling air by heat exchange in a cooling zone to produce heated cooling air; - discharging the calcinate from the bottom of the shaft; - venting gaseous effluent from said calciner; - each shaft operates alternately in a calcination mode and a preheating mode, such that one shaft operates in the calcination mode for a predetermined time while at least another shaft operates in the preheating mode, and vice versa; - the calcination mode is - loading carbonate ore at the top of the shaft of the kiln; - calcining by increasing the temperature in the preheated carbonate ore, with the production of the decarbonated calcinate and the release of a gaseous stream flowing cocurrently with the calcinate; passing the gaseous stream through the crossover channel towards the at least one shaft operating in a preheat mode; - said preheating mode - preheating the charged carbonate ore by heat exchange with the gaseous stream coming from the crossover channel, the gaseous stream rising and flowing countercurrently through the charged carbonate ore; - discharging the gaseous stream as a gaseous effluent at the top of the at least one shaft in a preheat mode; the step of cooling includes supplying cooling air at the bottom of each of the shafts or only at the bottom of the shaft operating in the calcination mode; - recycling a portion of said gaseous effluent discharged from the top of said at least one shaft in preheating mode; - heating, outside the calciner, said recycled portion of the gaseous effluent by at least one device capable of heating gases; - injecting said heated portion of the recycled gaseous effluent into said shaft operating in calcination mode at a height situated at the top of said calcination zone, in order to obtain said temperature increase enabling the calcination of said carbonate ore; - withdrawing the heated cooling air from each shaft, the cooling air being supplied at a height located below the crossover channel, and the gaseous effluent leaving the kiln being CO ２ is enriched in

2. 2. The method of claim 1, further comprising, prior to the step of heating with the device capable of heating gas, performing at least one heat exchange between the heated cooling air extracted outside the calciner furnace and the recycled portion of the gaseous effluent.

3. 3. The method of claim 1 or 2, further comprising introducing into the crossover channel a gaseous mixture of a first portion of the recycled portion of gaseous effluent heated outside the calciner by the device capable of heating gases to obtain a controlled temperature that is lower than the temperature that allows the calcination of the carbonate ore and higher than its recarbonation temperature, and a second portion of the portion that has not been heated by the device.

4. 4. The method of claim 1, wherein a portion of the recycled portion of unheated gaseous effluent is injected at the top of each calcining shaft.

5. 5. The method according to any one of claims 1 to 4, wherein the heated portion of the recycled gaseous effluent injected into the shaft operating in calcination mode at a height located at the top of the calcination zone has a temperature comprised between 1100°C and 1500°C, said temperature comprised between 1100°C and 1500°C enabling calcination of the carbonate ore.

6. 5. The method of claim 1, wherein the heated portion of the recycled gaseous effluent injected into the shaft operating in calcination mode at a height located at the top of the calcination zone has a temperature below 1100°C, and oxygen is supplemented before and / or in the calcination zone, and the temperature increase enabling calcination of the carbonate ore is provided by oxy-combustion in the presence of the heated portion of the recycled gaseous effluent supplemented with oxygen.

7. A parallel-flow regenerative calciner comprising at least two shafts (1, 2) interconnected by a crossover channel (4), - each shaft, in its working or non-working position, - at least one inlet opening (5) at the top of the shaft for loading carbonate ore; at least one outlet opening (11) at the bottom of the shaft for discharging the decarbonated calcinate; -CO ２ an extraction duct (13) for discharging the base gaseous effluent from the top of said shaft; - a cooling air supply (8) at the bottom of the shaft for cooling the decarbonated calcinate that is discharged, The kiln further comprises an inversion system (15) configured to alternately drive each shaft between the operating position and the non-operating position to place the shaft in a calcination operating state and a preheating operating state, wherein one shaft (1) is in a calcination operating state for a predetermined time while at least another shaft (2) is in a preheating operating state, and vice versa, under the control of the inversion system (15); The shaft (1) operating in calcination comprises, successively from top to bottom, a preheating zone (A), a calcination zone (B), and a cooling zone (C), and the interconnecting crossover channel (4) is located at the bottom of the calcination zone (B); each shaft comprises means (6) for injecting heated gas into the shaft (1) operating for calcination at the top of the calcination zone (B), and means (21, 23) for removing the cooling air heated in contact with the calcined material from the calciner at a height lower than the crossover channel (4); The calciner further comprises an external recirculation circuit (17), the external recirculation circuit (17) a separator (16) for removing a portion of said gaseous effluent from said removal duct (13); a heating device (19) capable of heating gas, connected to said separator (16) and configured to heat said portion of the gaseous effluent; - said means (6) for injecting heated gas into said shaft (1) during calcination operation, connected to said heating device (19) and injecting said heated part to provide said gaseous effluent at a temperature above the calcination temperature of said ore charge; A parallel flow regenerative calcination furnace comprising:

8. 8. A parallel-flow regenerative kiln according to claim 7, characterized in that the means for removing heated cooling air from the kiln at the bottom of each shaft, at a height lower than the crossover channels (4), comprise a central collecting element (21) communicating with an external extraction device (22).

9. 9. A parallel-flow regenerative calcination furnace according to claim 7 or 8, characterized in that each shaft has a circular cross section and comprises a peripheral channel (3) at the bottom of the calcination zone (B), the cross-over channel (4) interconnecting the peripheral channels (3) of the shafts for passing gases from one shaft to another, and the means for removing heated cooling air from the calcination furnace comprise an annular collector (23) at a height lower than the peripheral and cross-over channels and communicating with an external withdrawal device (22).

10. 9. A parallel-flow regenerative kiln according to claim 7 or 8, characterized in that each shaft has a rectangular cross section, the side of one shaft faces the side of another shaft, the cross-over channels directly interconnect the shafts between the opposing sides, and the means for removing heated cooling air from the kiln comprise at least one collector on at least some sides of each shaft at a height below the cross-over channels, which collector communicates with an external extraction device.

11. 11. The parallel-flow regenerative calcination furnace 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, induction heating device, radiant panel, microwave oven or solar heating device.

12. Each shaft is heated ２ 12. A parallel-flow regenerative kiln according to any one of claims 7 to 11, comprising a top opening (20) for introducing a portion of the removed portion of the base gaseous effluent.

13. 13. The parallel-flow regenerative calciner according to claim 7, wherein at least one heat exchanger (24) is arranged in the external recirculation circuit (17), to which heated cooling air extracted from the calciner is supplied.

14. connected to the recirculation circuit (17) below the heating device for collecting a heated first portion of the recirculated portion of the heated gaseous effluent; CO not heated by the heating device ２ a mixing chamber (27) connected to a separator (28) arranged in the recirculation circuit above said heating device so as to be able to transfer a second portion of the recirculated portion of the base gaseous effluent to the mixing chamber; The configuration is for obtaining a gaseous mixture having a controlled temperature lower than that allowing the calcination of the carbonate ore, 14. The parallel-flow regenerative kiln according to any one of claims 7 to 13, wherein the mixing chamber is connected (26) to the crossover channel for injecting the gaseous mixture into the crossover channel, or is connected to means for injecting heated gas (6) for injecting the gaseous mixture when the shaft is in preheat mode.

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