A limestone fluidized calcination method and fluidized calcination furnace based on carbon cascade circulation

Abstract

The application discloses a limestone fluidization calcination method and fluidization calcination furnace based on carbon stepwise circulation, wherein hot air with high temperature and high CO2 content after high-temperature decomposition of limestone is selectively returned to the atmosphere of different stages of initial decomposition of limestone in a stepwise circulation mode, so that the content of effective calcium oxide in the product is increased while the limestone pyrolysis efficiency is improved, the concentration of CO2 in the exhaust gas is increased, and the heat of the initial pyrolysis is assisted, which creates favorable conditions for the capture and recovery of CO2, significantly reduces carbon emission and energy consumption, and the method and system have the advantages of short process, easy control, low investment cost, significant economic benefits and the like, and provide a new way for resource utilization of waste fine limestone.

Description

TECHNICAL FIELD

[0001] The present application relates to lime production technology, in particular to a limestone fluidized calcination method and fluidized calcination furnace based on carbon cascade circulation, and belongs to the technical field of lime production. BACKGROUND

[0002] Limestone is an important industrial raw material, which is widely used in metallurgy, building materials and other industries. It is a non-renewable resource. The existing limestone reserves in China can only maintain 30-40 years of development and utilization, and it is a scarce resource. Limestone is mainly used in high-temperature calcination process to convert CaCO3 into CaO products through thermal decomposition, which is directly applied in steel, building materials, medicine and other fields. However, a large amount of waste slag with particle size below 10mm is generated in the process of mining, crushing and processing of limestone. Since the existing limestone calcination kiln (mainly double-hearth kiln and rotary kiln) cannot utilize this part of fine particle materials, it leads to serious waste of resources. At the same time, the composition elements of limestone are Ca, C and O. The emission of 1mol of CO2 is generated when 1mol of CaCO3 is calcined, which is a huge amount of carbon emission and does not conform to the national low-carbon and low-energy consumption industrial policy.

[0003] For further resource utilization of limestone powder, some researchers have proposed a fluidized calcination scheme. For example, Chinese patent document CN107226627A discloses a kind of active powder lime two-stage suspension calcination device, which realizes the calcination treatment of limestone fine powder (fineness R0.08 sieve residue 5-25%) through a series of multi-stage suspension preheater, first-stage suspension calcination furnace, first-stage cyclone separator, second-stage suspension calcination furnace, second-stage cyclone separator, multi-stage suspension cooler and fluidized cooler. However, this scheme only realizes the pyrolysis of limestone powder, and the product quality is relatively poor. In addition, the production process is long, the equipment is complex, the production cost is high, the production efficiency is low, and it is difficult to realize the preparation of high-activity calcium oxide content and the enrichment and recovery of high-concentration carbon dioxide in a single furnace. SUMMARY

[0004] In view of the problems of long process flow, high equipment investment cost, large carbon emission and poor product quality in the existing limestone fluidized calcination process in the prior art, the present application provides a limestone fluidized calcination method and fluidized calcination furnace based on carbon cascade circulation. The hot air with high temperature and high CO2 content after high-temperature decomposition of limestone is selectively returned to the atmosphere of different stages of initial decomposition of limestone in a cascade circulation manner, thereby improving the pyrolysis efficiency of limestone and the content of effective calcium oxide in the product. At the same time, through the circulation of hot air, the concentration of CO2 in the exhaust gas is increased, and the heat of the initial pyrolysis is also increased, which creates favorable conditions for the capture and recovery of CO2 and helps to reduce the total carbon emission.

[0005] To achieve the above technical purposes, the technical solutions adopted by the present application are as follows:

[0006] According to the first embodiment of the present application, a limestone fluidized calcination method based on carbon cascade circulation is provided, which comprises the following steps:

[0007] 1) According to the flow direction of the material, limestone ore powder is added from the lower inlet of the fluidized furnace and moves upward under the action of the fluidizing gas for thermal decomposition treatment, and the solid product obtained after thermal decomposition is discharged from the upper discharge port of the fluidized furnace.

[0008] 2) According to the flow direction of the gas stream, the fluidizing gas enters from the lower gas inlet of the fluidized furnace and drives the limestone ore powder to move upward for thermal decomposition treatment, and then carries the gaseous product obtained after thermal decomposition out of the upper gas outlet of the fluidized furnace.

[0009] 3) During the fluidized thermal decomposition treatment of the limestone ore powder, according to the atmosphere characteristics of the fluidized furnace cavity in the vertical direction, part of the hot air located in the upper part of the fluidized furnace cavity is selectively circulated to the lower part of the fluidized furnace cavity, thereby realizing effective thermal decomposition of the limestone ore powder and enrichment and recovery of carbon dioxide.

[0010] As a preferred, the particle size of the limestone ore powder is 0.1-1mm, preferably 0.2-0.8mm, more preferably 0.3-0.5mm.

[0011] As a preferred, the fluidizing gas is air and / or nitrogen. Preferably, the flow rate of the fluidizing gas is 0.2-3m / s, preferably 0.5-2m / s.

[0012] As a preferred, the temperature for thermal decomposition treatment of the limestone ore powder is 650-1100℃, preferably 700-1000℃, more preferably 750-950℃. The thermal decomposition treatment time is 20-90min, preferably 30-80min, more preferably 45-70min.

[0013] As a preferred, step 3) is specifically: according to the content of carbon dioxide in the atmosphere of the fluidized furnace cavity, the fluidized furnace cavity is divided into multiple levels of furnace zones in series from top to bottom. The content of carbon dioxide in the atmosphere of the multiple levels of furnace zones gradually decreases from top to bottom. Part of the hot air in the upper part of the fluidized furnace cavity is circulated to the lower part of the fluidized furnace cavity.

[0014] Preferably, the fluidized bed furnace cavity is divided into a primary furnace zone, a secondary furnace zone, a tertiary furnace zone, and a quaternary furnace zone from top to bottom. Specifically, some of the hot air from the upper part of the primary furnace zone is circulated to the lower part of the secondary furnace zone, some of the hot air from the upper part of the secondary furnace zone is circulated to the lower part of the tertiary furnace zone, and some of the hot air from the upper part of the tertiary furnace zone is circulated to the lower part of the quaternary furnace zone.

[0015] Preferably, the carbon dioxide content in the primary furnace zone is higher than 80%, preferably 82-90%. The carbon dioxide content in the secondary furnace zone is 60-80%, preferably 65-75%. The carbon dioxide content in the tertiary furnace zone is 40-60%, preferably 45-55%. The carbon dioxide content in the quaternary furnace zone is less than 40%, preferably less than 35%.

[0016] Preferably, the amount of hot air circulating in the upper part of the primary furnace zone accounts for 40-80% of its total hot air volume, more preferably 50-70%. The amount of hot air circulating in the upper part of the secondary furnace zone accounts for 30-70% of its total hot air volume, more preferably 40-60%. The amount of hot air circulating in the upper part of the tertiary furnace zone accounts for 20-60% of its total hot air volume, more preferably 30-50%.

[0017] Preferably, step 3) specifically involves: dividing the fluidized bed furnace cavity into multiple temperature zones connected in series from top to bottom, based on the temperature of the atmosphere inside the fluidized bed furnace cavity. A portion of the hot air from the upper temperature zone inside the fluidized bed furnace cavity is then circulated to the lower temperature zone inside the fluidized bed furnace cavity.

[0018] Preferably, the fluidized bed furnace cavity is divided into four temperature zones from top to bottom: a primary temperature zone, a secondary temperature zone, a tertiary temperature zone, and a quaternary temperature zone. Specifically, a portion of the hot air from the upper part of the primary temperature zone is circulated to the lower part of the tertiary temperature zone, a portion of the hot air from the upper part of the secondary temperature zone is circulated to the lower part of the quaternary temperature zone, a portion of the hot air from the upper part of the tertiary temperature zone is circulated to the lower part of the primary temperature zone, and a portion of the hot air from the upper part of the quaternary temperature zone is circulated to the lower part of the secondary temperature zone.

[0019] Preferably, the temperature of the first-level temperature zone is 600-800℃, more preferably 650-750℃; the temperature of the second-level temperature zone is 800-1000℃, more preferably 850-950℃; the temperature of the third-level temperature zone is 550-750℃, more preferably 600-700℃; and the temperature of the fourth-level temperature zone is 100-500℃, more preferably 200-400℃.

[0020] Preferably, the amount of hot air circulating in the upper part of the first-stage temperature zone accounts for 40-80% of the total hot air volume, more preferably 50-70%. The amount of hot air circulating in the upper part of the second-stage furnace temperature zone accounts for 30-70% of the total hot air volume, more preferably 40-60%. The amount of hot air circulating in the upper part of the third-stage temperature zone accounts for 20-60% of the total hot air volume, more preferably 30-50%. The amount of hot air circulating in the upper part of the fourth-stage temperature zone accounts for 10-50% of the total hot air volume, more preferably 20-40%.

[0021] According to a second embodiment of the present invention, a limestone fluidized bed calcining furnace or a limestone fluidized bed calcining furnace for use in the method described in the first embodiment is provided. The limestone fluidized bed calcining furnace includes a furnace body and a furnace chamber. A feed inlet and a fluidized air inlet are provided at the lower part of the furnace body, and a discharge inlet and a fluidized exhaust outlet are provided at the upper part of the furnace body. The furnace chamber is divided into multiple series-connected chamber zones from top to bottom. Circulating air ducts are led out from the chamber zones located in the upper middle part of the furnace chamber and connected to the chamber zones located in the lower middle part of the furnace chamber. A heating device is also provided on the furnace body corresponding to the middle chamber zone.

[0022] Preferably, the furnace comprises four stages connected in series from top to bottom: a primary stage, a secondary stage, a tertiary stage, and a quaternary stage, each equipped with a carbon dioxide concentration detector. The upper part of the primary stage is connected to the lower part of the secondary stage via a first circulating air duct, the upper part of the secondary stage is connected to the lower part of the tertiary stage via a second circulating air duct, and the upper part of the tertiary stage is connected to the lower part of the quaternary stage via a third circulating air duct. Each of the first, second, and third circulating air ducts is independently equipped with a flow regulating valve and a circulating fan.

[0023] Preferably, the furnace comprises four stages connected in series from top to bottom: a primary stage, a secondary stage, a tertiary stage, and a quaternary stage, with a temperature sensor installed in each stage. The upper part of the primary stage is connected to the lower part of the tertiary stage via a first circulating air duct; the upper part of the secondary stage is connected to the lower part of the quaternary stage via a second circulating air duct; the upper part of the tertiary stage is connected to the lower part of the primary stage via a third circulating air duct; and the upper part of the quaternary stage is connected to the lower part of the secondary stage via a fourth circulating air duct. Each of the first, second, third, and fourth circulating air ducts is independently equipped with a flow regulating valve and a circulating fan.

[0024] Preferably, the furnace chamber is a gradually expanding cavity that is narrower at the top and wider at the bottom.

[0025] Preferably, the fluidized exhaust port is also connected to the carbon dioxide collector via an exhaust pipe.

[0026] Preferably, a screen is provided at the air inlet end of the circulating air duct. Preferably, the screen mesh has a pore size of 0.01-10 μm, more preferably 0.1-5 μm.

[0027] In existing technologies, limestone calcination pyrolysis is an endothermic decomposition reaction process under high-temperature conditions. In conventional calcination processes, both fuel combustion and limestone decomposition occur within the same kiln. The kiln gases include carbon dioxide, nitrogen, a small amount of oxygen, and a certain amount of dust. The concentration of carbon dioxide within the kiln has a significant impact on the limestone decomposition process; generally, the higher the carbon dioxide concentration, the slower the decomposition rate, which in turn reduces the decomposition efficiency. In existing fluidized bed calcination processes for limestone, although some of the exhaust high-temperature flue gas is returned to the bottom of the furnace, this is merely for utilizing the heat of the flue gas. The primary purpose is to use this high-temperature flue gas for preheating the limestone and improving waste heat utilization efficiency. However, this process overlooks the fact that the exhaust high-temperature flue gas contains a high concentration of CO2. If the flue gas circulation volume is low, the waste heat utilization efficiency is low. If the flue gas circulation volume is large, directly introducing it into the furnace along with the fluidizing gas will inhibit the decomposition efficiency of limestone from the initial stage, thus prolonging the complete decomposition time and increasing the likelihood of overburning, affecting product quality. Furthermore, if the calcination fuel for the limestone is a solid fuel, such as pulverized coal or coal lumps, the produced lime will contain impurities, which will also affect product quality.

[0028] In this invention, in view of the shortcomings of existing limestone production and processing, it is proposed to take waste fine-grained limestone as the research object and adopt a fluidized high-temperature calcination method more suitable for fine-grained materials. At the same time, taking advantage of the characteristic of CaCO3 high-temperature decomposition reaction emitting a large amount of CO2 gas, according to the atmosphere characteristics of the fluidized furnace cavity in the vertical direction, a portion of the hot air located in the upper part of the fluidized furnace cavity is selectively circulated to the lower part of the fluidized furnace cavity. First, limestone ground to a certain particle size is fed into the fluidized bed furnace tube. Fluidized gas (such as air and / or nitrogen) enters the system from the bottom of the furnace tube, where CaCO3 decomposes at high temperature to produce CaO and CO2. Second, when the decomposition reaction proceeds to a certain extent, the gas is selectively guided back to the middle and lower parts of the furnace tube at certain locations in the middle and upper parts. This part of the gas has a higher temperature, which has a preheating and supplementary heating effect on the material in the furnace tube, thereby improving the decomposition reaction efficiency and reducing energy consumption. As the limestone decomposition reaction continues, the emitted CO2 gas is continuously introduced into the fluidized bed system, and the CO2 gas concentration in the furnace tube continuously increases. Finally, when the CO2 concentration at the top of the furnace tube increases to 80% or more, the decomposition rate of limestone will be significantly reduced, and the high-concentration CO2 gas can be extracted and stored as a product. This method utilizes the characteristics of fine-grained limestone that can be calcined using fluidized bed roasting, the need for fluidized bed roasting, the ability to use emitted CO2 gas as a fluidizing medium, and the ability to use high-concentration CO2 gas as a product. By intercepting gas at different locations in the fluidized bed furnace tube as a fluidizing medium and gas product, CO2 gas is recycled, producing qualified quicklime and high-concentration CO2 products. This effectively reduces carbon emissions and energy consumption, and is in line with the national low-carbon and low-energy consumption industrial policy.

[0029] In this invention, limestone calcination is a high-temperature endothermic decomposition reaction process. Within the fluidized bed furnace, limestone added from the bottom of the furnace undergoes preheating, preliminary pyrolysis, and rapid, high-volume pyrolysis. The heat absorption during pyrolysis varies at different stages. This invention selectively circulates a portion of the hot air from the upper part of the fluidized bed furnace cavity to the lower part, thus matching the differences in heat absorption at different pyrolysis stages. This achieves efficient and rational utilization of waste heat while ensuring temperature stability at each pyrolysis stage, guaranteeing pyrolysis efficiency, and further improving carbon dioxide enrichment.

[0030] In this invention, the limestone calcination reaction is a process of recrystallization of the rhombic lattice of limestone into a cubic lattice. The resulting crystal structure is related to the rate of formation and growth of the new phase nuclei. When the former is greater than the latter, fine-grained crystals with a high number of active CaO molecules and high surface energy are obtained; conversely, coarse-grained crystals with low surface energy and a low number of active CaO molecules are obtained. Therefore, in the vertical direction of the furnace tube, since the decomposition rate of limestone varies in different sections, areas with a faster limestone pyrolysis rate generally require more circulating hot air from the upper part of the furnace due to the greater heat absorption. This not only replenishes the large amount of heat absorbed by the high-speed decomposition of limestone, maintaining temperature stability during pyrolysis in that area, but also supplements some carbon dioxide, slightly increasing the carbon dioxide concentration in the atmosphere and preventing excessively rapid limestone pyrolysis. In other words, stable temperature and atmosphere control helps to ensure that the rate of formation of new phase nuclei during limestone decomposition exceeds their growth rate, thereby increasing the number of active calcium oxide molecules and significantly improving the overall product quality. In areas with lower limestone pyrolysis rates (generally located below areas with higher limestone pyrolysis rates), the pyrolysis rate and degree are both lower, resulting in less heat absorption. Therefore, only a small amount of circulating hot air needs to be added. This helps to ensure that the limestone particles in this area are in a relatively uniform state when entering the next pyrolysis zone, which helps them maintain a rapid pyrolysis state in the next pyrolysis zone, thereby improving production efficiency.

[0031] In this invention, since CO2 separation proceeds slowly from the surface to the interior of the limestone, the larger the limestone particle size, the more difficult the calcination and the longer it takes. During the calcination of large-particle limestone, the gaseous product CO2 is released from inside the crystal lattice, thus requiring a higher temperature to obtain high CO2 pressure. However, excessively high calcination temperatures can cause the lime surface to "overburn," resulting in cracks due to shrinkage. Simultaneously, it can cause slagging with impurities such as SiO2 and Al2O3, leading to incomplete CO2 separation and the formation of semi-quicklime, resulting in low lime activity. Therefore, when limestone is calcined under high temperature conditions, it is advisable for the particle size of the limestone powder to be within the range of 0.1-1mm (preferably 0.2-0.8mm, more preferably 0.3-0.5mm). If the particle size is too fine, the pyrolysis rate will be too fast, and the flow rate and temperature control of the pyrolysis process will be difficult to control precisely, which will easily lead to the phenomenon of "overburning". Conversely, if the particle size is too coarse, the pyrolysis rate will be slow, and the heat will not have enough time to be transferred into the interior of the material particles, resulting in incomplete pyrolysis, which will easily lead to the phenomenon of "underburning".

[0032] Furthermore, at high temperatures, limestone decomposes into CaO upon heating. During this decomposition reaction, the formation of CO2 as a gaseous product causes CaO crystals to form a loose structure, retaining a polycrystalline structure. At this stage, the crystals are not fully developed and contain numerous defects, resulting in high reactivity of the lime. However, as the calcination temperature increases or the holding time is extended, the crystals gradually develop fully, promoting the conversion of active CaO into inactive CaO, thus reducing the lime's reactivity. Simultaneously, in a high-temperature environment, CaO can also react with other impurities, such as Fe2O3 and Al2O3, transforming into bound CaO, thereby reducing the content of active CaO. However, if the temperature is too low, CaCO3 decomposes incompletely. Therefore, when the limestone powder has a particle size in the range of 0.1-1 mm, it is treated at a temperature of 550-1000℃ (preferably 650-950℃, more preferably 700-900℃). The optimal processing time is 20-90 min (preferably 30-80 min, more preferably 45-70 min). Excessive or insufficient temperature, or excessive or insufficient processing time, will lead to a decrease in the quality of CaO products.

[0033] In this invention, the fluidizing gas is air and / or nitrogen. Given a specific limestone powder particle size and an ideal pyrolysis temperature, the flow rate of the fluidizing gas enables the limestone powder to move at an ideal velocity within the furnace tube. Preferably, the flow rate of the fluidizing gas is 0.2-3 m / s (preferably 0.5-2 m / s).

[0034] In this invention, to further improve the quality of limestone pyrolysis products and enhance carbon dioxide enrichment, the fluidized bed furnace cavity is divided into multiple series-connected furnace zones from top to bottom based on the carbon dioxide content in the atmosphere. Taking a four-stage furnace zone as an example: the fluidized bed furnace cavity is divided from top to bottom into a first-stage furnace zone (carbon dioxide content higher than 80%, preferably 82-90%), a second-stage furnace zone (carbon dioxide content 60-80%, preferably 65-75%), a third-stage furnace zone (carbon dioxide content 40-60%, preferably 45-55%), and a fourth-stage furnace zone (carbon dioxide content less than 40%, preferably less than 35%). The hot air circulation method is as follows: a portion of the hot air from the top of the first-stage furnace zone is circulated to the bottom of the second-stage furnace zone, a portion of the hot air from the top of the second-stage furnace zone is circulated to the bottom of the third-stage furnace zone, and a portion of the hot air from the top of the third-stage furnace zone is circulated to the bottom of the fourth-stage furnace zone. In other words, the hot air circulation is a top-down, step-by-step circulation. The advantage of this step-by-step circulation is that, since the difference in carbon dioxide concentration between adjacent furnace zones is relatively low, circulating a relatively large amount of hot air from the upper furnace zone to the lower furnace zone has little impact on the atmosphere in the lower furnace zone (mainly the increase in carbon dioxide content). (This impact is even smaller when some hot air from the lower furnace zone itself is circulated to the next lower furnace zone). Therefore, its inhibitory effect on the pyrolysis rate of limestone in the lower furnace zone is relatively small, and it actually helps to prevent limestone decomposition in the lower furnace zone. The rate of reaction is further accelerated (the decomposition reaction of CaCO3 occurs along the CaO-CaCO3 interface. Due to the low solubility of CaO in the old phase, a supersaturated state is formed, causing the new CaO phase to precipitate. However, as the reaction proceeds, the thickness of the limestone layer (CaO layer) gradually increases, and the low thermal conductivity of CaO makes it difficult for heat to penetrate into the limestone). Furthermore, the relatively large amount of hot air circulation can provide more supplementary heating to the lower furnace zone to compensate for the heat absorbed by the limestone pyrolysis in the lower furnace zone, thereby maintaining the temperature and relative position stability of the lower furnace zone, ensuring the efficient and stable operation of the system. It can also further improve the enrichment efficiency of carbon dioxide in the furnace and increase the concentration of carbon dioxide in the hot air discharged from the upper exhaust port of the furnace (facilitating the direct recovery and utilization of carbon dioxide, thereby reducing carbon emissions). It should also be noted that for the area where limestone pyrolysis occurs, removing some of the carbon dioxide-containing hot air can reduce the inhibitory effect of the increased carbon dioxide concentration on the decomposition reaction in that area.

[0035] It should be noted that the amount of hot air circulating in each furnace zone is mainly determined by the pyrolysis efficiency of limestone and the amount of heat absorbed in the next furnace zone. Generally, the fourth furnace zone mainly serves as a preheating area for newly fed limestone. In this area, limestone hardly undergoes pyrolysis. Therefore, the amount of hot air circulating into the fourth furnace zone is mainly considered to ensure that the limestone is preheated to the target preheating temperature before entering the third furnace zone. The third furnace zone mainly serves as a preheating and decomposition area (i.e., preliminary pyrolysis) for preheated limestone. In this area, limestone undergoes a certain degree of pyrolysis, but it is not intense and relatively absorbs heat. The amount of hot air circulating in this area is relatively small, so it is mainly used to replenish the heat absorbed by the partially pyrolyzed limestone, thus ensuring that the limestone reaches the target degree of preheating before entering the secondary furnace zone. The secondary furnace zone, as a deep and rapid pyrolysis zone for limestone, absorbs a large amount of heat. Therefore, the amount of hot air circulating in this zone needs to ensure the heat absorbed by the limestone during efficient pyrolysis while avoiding over-burning of the lime. The quaternary furnace zone mainly serves as a heat preservation zone for the material after efficient pyrolysis. Maintaining a certain heat preservation time helps ensure complete decomposition of the limestone. It should be noted that if the heat preservation time is too short, the central part of the limestone will not decompose completely, resulting in "under-burning" and low product activity. If the heat preservation time is too long, CaO crystals will fully develop, and active CaO will transform into inactive CaO, resulting in low product activity as well. Therefore, an appropriate heat preservation time must be selected during the calcination process.

[0036] In this invention, the fluidized bed furnace cavity can be divided into multiple temperature zones connected in series from top to bottom, based on the temperature of the atmosphere inside the fluidized bed furnace. Taking a four-level temperature zone as an example: the fluidized bed furnace cavity is divided from top to bottom into a first-level temperature zone (temperature 600-800℃, preferably 650-750℃), a second-level temperature zone (temperature 800-1000℃, preferably 850-950℃), a third-level temperature zone (temperature 550-750℃, preferably 600-700℃), and a fourth-level temperature zone (temperature 100-500℃, preferably 200-400℃). The hot air circulation method is as follows: a portion of the hot air from the upper part of the first-level temperature zone is circulated to the lower part of the third-level temperature zone; a portion of the hot air from the upper part of the second-level temperature zone is circulated to the lower part of the fourth-level temperature zone; a portion of the hot air from the upper part of the third-level temperature zone is circulated to the lower part of the first-level temperature zone; and a portion of the hot air from the upper part of the fourth-level temperature zone is circulated to the lower part of the second-level temperature zone. In the first-level temperature zone, the limestone, after undergoing efficient deep pyrolysis in the second-level temperature zone, is kept at a constant temperature. The heat contained in the hot air further pyrolyzes the core of the limestone powder particles, thereby promoting complete pyrolysis of the limestone. Since most of the limestone (i.e., the outer layer of the core) has been converted into highly active calcium oxide, to avoid "overburning" this calcium oxide, it is necessary not only to control the holding time in the first-level temperature zone but also to control the temperature of this zone (lower than the second-level temperature zone, slightly higher than the third-level temperature zone). This ensures that the pyrolysis requirements of the limestone at the core are met without causing "overburning" of the surface calcium oxide, thus improving the quality of the final product. Furthermore, in the atmosphere of the first-level temperature zone, the carbon dioxide concentration is relatively high and the atmospheric heat content is relatively large. Direct exhaust is not conducive to the further enrichment and recovery of carbon dioxide, nor is it conducive to the recycling of heat. Therefore, part of the hot air in the first-level temperature zone is circulated to the third-level temperature zone for further preheating of the preheated limestone and supplementary heating for preliminary pyrolysis, as well as for the recycling and enrichment of the contained carbon dioxide. In the third-level temperature zone, the limestone mainly undergoes deep preheating and preliminary pyrolysis. The high-temperature hot air from the first-level temperature zone can play a promoting role. Although it contains a high concentration of carbon dioxide and will slightly increase the concentration of carbon dioxide in the atmosphere of the third-level temperature zone, the tolerance range for carbon dioxide concentration in preliminary pyrolysis is relatively lenient. The slight increase in carbon dioxide concentration has a very weak impact on meeting the goal of preliminary pyrolysis.In the secondary temperature zone, limestone undergoes efficient deep pyrolysis, which is highly sensitive to temperature. Excessive temperature can cause the surface limestone to over-pyrolyze too quickly, leading to "overburning," while the core limestone remains unpyrolyzed. Conversely, insufficient heat transfer from the surface to the core can hinder the pyrolysis of the core limestone. Furthermore, the efficient pyrolysis of limestone in this zone releases a large amount of carbon dioxide. Excessive carbon dioxide inhibits the pyrolysis rate, requiring the limestone to remain in this zone for an extended period to meet pyrolysis requirements, again potentially causing "overburning" of the surface limestone. Therefore, by circulating some of the hot air from the secondary temperature zone to the quaternary temperature zone to preheat the newly added limestone, and since the limestone in the quaternary zone primarily absorbs heat for heating, even a high carbon dioxide content in the circulating hot air will not negatively impact the preheating target. In fact, the recirculation of carbon dioxide helps enrich the carbon dioxide, increasing the concentration in the flue gas and reducing the difficulty of subsequent carbon dioxide recovery.

[0037] It should be noted that since a portion of the hot air from the first-level temperature zone is circulated to the third-level temperature zone, the concentration of carbon dioxide in the third-level temperature zone is increased to some extent. Although this increase in carbon dioxide concentration has a small impact on the initial pyrolysis of limestone in the third-level temperature zone, it will gradually accumulate as this portion of hot air is continuously circulated and enters the second-level temperature zone. This may lead to a gradual increase in the carbon dioxide concentration in the initial atmosphere (i.e., the hot air from the third-level temperature zone) in the second-level temperature zone, thereby affecting the efficient and deep pyrolysis of limestone in the second-level temperature zone. Therefore, a portion of the hot air from the third-level temperature zone is directly circulated to the above temperature zones to reduce the total amount of carbon dioxide entering the second-level temperature zone. At the same time, a portion of the hot air from the fourth-level temperature zone is directly circulated to the second-level temperature zone. The hot air circulating in the fourth-level temperature zone dilutes the carbon dioxide concentration in the second-level temperature zone, thereby ensuring the stability of the carbon dioxide concentration in the initial atmosphere of the second-level temperature zone, that is, ensuring the stability of the operating conditions in the second-level temperature zone. In other words, by dividing the temperature zones into different zones and circulating hot air according to the operating characteristics of each zone, this invention improves and ensures the stability of the operating conditions in each zone, thereby improving product quality. At the same time, it also achieves the reflux enrichment of carbon dioxide and the recycling of heat.

[0038] In this invention, limestone ground to a certain particle size is fed into a fluidized bed furnace tube. Fluidized gas (such as air or nitrogen) enters the system from the bottom of the furnace tube. CaCO3 decomposes at high temperature to generate CaO and CO2. Secondly, when the decomposition reaction proceeds to a certain extent, based on the atmospheric characteristics of the fluidized bed furnace cavity in the vertical direction, a portion of the hot air located in the upper part of the fluidized bed furnace cavity is selectively circulated to the lower part of the fluidized bed furnace cavity to achieve effective thermal decomposition of limestone powder and enrichment and recovery of carbon dioxide. The limestone decomposition reaction continues, and the emitted CO2 gas is continuously circulated into the fluidized bed system, and the CO2 gas concentration in the furnace tube continuously increases. Finally, when the CO2 concentration at a certain position at the top of the furnace tube increases to 80% or more, the high-concentration CO2 gas is exported and stored as a product. This method utilizes the characteristics of fine-grained limestone that can be calcined using fluidized bed roasting, the need for fluidized bed roasting, the ability to recycle emitted CO2 gas as a fluidizing medium, and the ability to use high-concentration CO2 gas as a product. By intercepting gas at different locations in the fluidized bed furnace tube as a fluidizing medium and gas product, CO2 gas is recycled, and highly active quicklime and high-concentration CO2 products are prepared. This effectively reduces carbon emissions and energy consumption, and is in line with the national low-carbon and low-energy consumption industrial policy.

[0039] Furthermore, the fluidized bed furnace tube was improved from a traditional cylindrical shape to a trapezoidal tube, wider at the bottom and narrower at the top. Simultaneously, the furnace tube was divided into several sections based on CO2 concentration or temperature. Depending on the actual operating conditions, the hot air containing CO2 from the upper and middle sections was selectively redirected back into the next section of the furnace tube, creating a continuous cycle. This not only preheats the limestone material at the bottom and improves product quality, but also allows for further CO2 enrichment through the fusion of the high-concentration CO2 at the top and bottom. Combined with the increasingly narrow shape of the furnace tube and the decreasing space at the top, it is easier to increase the CO2 content of the upper gas, quickly obtaining a high-purity CO2 product.

[0040] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0041] 1. This invention uses a fluidized bed high-temperature calcination method to realize the resource utilization of waste fine-grained limestone. Based on the characteristics of limestone fluidized bed pyrolysis, the atmosphere in the fluidized bed furnace is selectively circulated internally, which can improve the quality of lime products and the stability of system operation. At the same time, it can also realize the cyclic enrichment of carbon dioxide, significantly reducing carbon emissions and energy consumption.

[0042] 2. The process and system of this invention are short, easy to control, low in investment cost, and have significant economic benefits, providing a new way for the resource utilization of waste fine-grained limestone. Attached Figure Description

[0043] Figure 1This is a schematic diagram of the limestone fluidized bed calcination process when the present invention is divided into multiple furnace zones.

[0044] Figure 2 This is a schematic diagram of the limestone fluidized bed calcination process when the present invention is divided into multiple temperature zones.

[0045] Figure 3 This is a simplified structural diagram of the limestone fluidized bed calcining furnace with multiple furnace zones according to the present invention.

[0046] Figure 4 This is a simplified structural diagram of the limestone fluidized bed calcining furnace with multiple temperature zones according to the present invention.

[0047] Figure 5 This is a simplified structural diagram of the limestone fluidized bed calcining furnace of the present invention when it has a furnace chamber that expands gradually from top to bottom.

[0048] Reference numerals in the attached drawings: 1: Furnace body; 101: Feed port; 102: Fluidized air inlet; 103: Discharge port; 104: Fluidized exhaust port; 2: Furnace chamber; 201: Carbon dioxide concentration detector; 202: Temperature detector; 3: Heating device; 4: Carbon dioxide collector; F1: First circulating air duct; F2: Second circulating air duct; F3: Third circulating air duct; F4: Fourth circulating air duct. Detailed Implementation

[0049] The technical solution of the present invention will be illustrated below with examples. The scope of protection sought by the present invention includes, but is not limited to, the following embodiments.

[0050] A limestone fluidized bed calcining furnace includes a furnace body 1 and a furnace chamber 2. A feed inlet 101 and a fluidized bed air inlet 102 are provided at the lower part of the furnace body 1, and a discharge inlet 103 and a fluidized bed exhaust outlet 104 are provided at the upper part of the furnace body 1. The furnace chamber 2 is divided into multiple series-connected chamber zones from top to bottom. Circulating air ducts are led out from the upper chamber zone of the furnace chamber 2 and connected to the lower chamber zone of the furnace chamber 2. A heating device 3 is also provided on the furnace body 1 corresponding to the middle chamber zone of the furnace chamber 2.

[0051] Preferably, the furnace 2 includes a primary furnace zone, a secondary furnace zone, a tertiary furnace zone, and a quaternary furnace zone connected in series from top to bottom, and a carbon dioxide concentration detector 201 is installed in each furnace zone. The upper part of the primary furnace zone is connected to the lower part of the secondary furnace zone through a first circulating air duct F1, the upper part of the secondary furnace zone is connected to the lower part of the tertiary furnace zone through a second circulating air duct F2, and the upper part of the tertiary furnace zone is connected to the lower part of the quaternary furnace zone through a third circulating air duct F3. A flow regulating valve and a circulating fan are independently installed on the first circulating air duct F1, the second circulating air duct F2, and the third circulating air duct F3.

[0052] Preferably, the furnace 2 includes a primary furnace zone, a secondary furnace zone, a tertiary furnace zone, and a quaternary furnace zone connected in series from top to bottom, and a temperature sensor 202 is installed in each furnace zone. The upper part of the primary furnace zone is connected to the lower part of the tertiary furnace zone through a first circulating air duct F1; the upper part of the secondary furnace zone is connected to the lower part of the quaternary furnace zone through a second circulating air duct F2; the upper part of the tertiary furnace zone is connected to the lower part of the primary furnace zone through a third circulating air duct F3; and the upper part of the quaternary furnace zone is connected to the lower part of the secondary furnace zone through a fourth circulating air duct F4. A flow regulating valve and a circulating fan are independently installed on each of the first circulating air duct F1, second circulating air duct F2, third circulating air duct F3, and fourth circulating air duct F4.

[0053] Preferably, the furnace chamber 2 is a gradually expanding chamber that is narrower at the top and wider at the bottom.

[0054] Preferably, the fluidized exhaust port 104 is also connected to the carbon dioxide collector 4 via an exhaust pipe.

[0055] Preferably, a screen is provided at the air inlet end of the circulating air duct. Preferably, the screen mesh has a pore size of 0.01-10 μm, more preferably 0.1-5 μm.

[0056] Example 1

[0057] like Figures 3-5 As shown, a limestone fluidized bed calcining furnace includes a furnace body 1 and a furnace chamber 2. A feed inlet 101 and a fluidized bed air inlet 102 are provided at the lower part of the furnace body 1, and a discharge inlet 103 and a fluidized bed exhaust outlet 104 are provided at the upper part of the furnace body 1. The furnace chamber 2 is divided into multiple series-connected chamber zones from top to bottom. Circulating air ducts are led out from the chamber zones located in the upper part of the furnace chamber 2 and connected to the chamber zones located in the lower part of the furnace chamber 2. A heating device 3 is also provided on the furnace body 1 corresponding to the middle chamber zone of the furnace chamber 2.

[0058] Example 2

[0059] The embodiment 1 is repeated, except that the furnace 2 includes a primary furnace zone, a secondary furnace zone, a tertiary furnace zone, and a quaternary furnace zone connected in series from top to bottom, and a carbon dioxide concentration detector 201 is installed in each furnace zone. The upper part of the primary furnace zone is connected to the lower part of the secondary furnace zone through a first circulating air duct F1, the upper part of the secondary furnace zone is connected to the lower part of the tertiary furnace zone through a second circulating air duct F2, and the upper part of the tertiary furnace zone is connected to the lower part of the quaternary furnace zone through a third circulating air duct F3. A flow regulating valve and a circulating fan are independently installed on the first circulating air duct F1, the second circulating air duct F2, and the third circulating air duct F3.

[0060] Example 3

[0061] Repeat Example 2, except that the furnace chamber 2 is a gradually expanding chamber that is narrower at the top and wider at the bottom.

[0062] Example 4

[0063] Example 3 is repeated, except that the fluidized exhaust port 104 is also connected to the carbon dioxide collector 4 through an exhaust pipe.

[0064] Example 5

[0065] Example 4 is repeated, except that a screen is installed at the air inlet of the circulating air duct. The screen has a pore size of 1 μm.

[0066] Example 6

[0067] Repeat Example 5, except that the sieve aperture is 3μm.

[0068] Example 7

[0069] The embodiment 1 is repeated, except that the furnace 2 includes a primary furnace zone, a secondary furnace zone, a tertiary furnace zone, and a quaternary furnace zone connected in series from top to bottom, and a temperature sensor 202 is installed in each furnace zone. The upper part of the primary furnace zone is connected to the lower part of the tertiary furnace zone through a first circulating air duct F1, the upper part of the secondary furnace zone is connected to the lower part of the quaternary furnace zone through a second circulating air duct F2, the upper part of the tertiary furnace zone is connected to the lower part of the primary furnace zone through a third circulating air duct F3, and the upper part of the quaternary furnace zone is connected to the lower part of the secondary furnace zone through a fourth circulating air duct F4. A flow regulating valve and a circulating fan are independently installed on each of the first circulating air duct F1, second circulating air duct F2, third circulating air duct F3, and fourth circulating air duct F4.

[0070] Example 8

[0071] Repeat Example 7, except that the furnace chamber 2 is a gradually expanding chamber that is narrower at the top and wider at the bottom.

[0072] Example 9

[0073] Example 8 is repeated, except that the fluidized exhaust port 104 is also connected to the carbon dioxide collector 4 through an exhaust pipe.

[0074] Example 10

[0075] Example 9 is repeated, except that a screen is installed at the air inlet of the circulating air duct. The screen has a mesh size of 2 μm.

[0076] Example 11

[0077] Repeat Example 10, except that the sieve aperture is 4μm.

[0078] Example 12

[0079] The method for fluidized bed calcination of limestone using the limestone fluidized bed calcination furnace described in Example 6:

[0080] 1) According to the direction of the material, 20 kg of limestone powder (average particle size of about 0.6 mm) is added from the lower feed port of the fluidized bed furnace and moves from bottom to top under the action of fluidizing gas to carry out thermal decomposition treatment. The solid product obtained after thermal decomposition is discharged from the upper discharge port of the fluidized bed furnace.

[0081] 2) According to the direction of airflow, the fluidizing gas (air with a flow rate of about 0.8 m / s) enters from the lower air inlet of the fluidizing furnace and carries the limestone powder from bottom to top for thermal decomposition treatment. Then, it carries the gaseous products obtained after thermal decomposition and is discharged from the upper exhaust port of the fluidizing furnace.

[0082] 3) During the fluidized bed thermal decomposition of limestone powder, the fluidized bed furnace is divided into four zones from top to bottom based on the carbon dioxide content in the atmosphere: a primary zone (region with carbon dioxide content higher than 80%), a secondary zone (region with carbon dioxide content between 60-80%), a tertiary zone (region with carbon dioxide content between 40-60%), and a quaternary zone (region with carbon dioxide content less than 40%). Approximately 60% of the hot air from the upper part of the primary zone is circulated to the lower part of the secondary zone; approximately 50% of the hot air from the upper part of the secondary zone is circulated to the lower part of the tertiary zone; and approximately 40% of the hot air from the upper part of the tertiary zone is circulated to the lower part of the quaternary zone.

[0083] After testing, the effective calcium oxide content in the lime (CaO) prepared by the method of this embodiment is about 88.2%, and the carbon dioxide content in the flue gas discharged from the upper exhaust port of the fluidized bed furnace is about 83.6%.

[0084] Example 13

[0085] The method for fluidized bed calcination of limestone using the limestone fluidized bed calcination furnace described in Example 11:

[0086] 1) According to the direction of the material, 25kg of limestone powder (average particle size of about 0.6mm) is added from the lower feed port of the fluidized bed furnace and moves from bottom to top under the action of fluidizing gas to carry out thermal decomposition treatment. The solid product obtained after thermal decomposition is discharged from the upper discharge port of the fluidized bed furnace.

[0087] 2) According to the direction of airflow, the fluidizing gas (air with a flow rate of about 1.0 m / s) enters from the lower air inlet of the fluidizing furnace and carries the limestone powder from bottom to top for thermal decomposition treatment. Then, it carries the gaseous products obtained after thermal decomposition and is discharged from the upper exhaust port of the fluidizing furnace.

[0088] 3) During the fluidized bed thermal decomposition of limestone powder, the fluidized bed furnace is divided into four temperature zones from top to bottom based on the temperature of the atmosphere inside the furnace: a primary temperature zone (approximately 700℃), a secondary temperature zone (approximately 950℃), a tertiary temperature zone (approximately 650℃), and a quaternary temperature zone (approximately 500℃). Specifically, 55% of the hot air volume from the upper part of the primary temperature zone is circulated to the lower part of the tertiary temperature zone; 45% of the hot air volume from the upper part of the secondary temperature zone is circulated to the lower part of the quaternary temperature zone; 35% of the hot air volume from the upper part of the tertiary temperature zone is circulated to the lower part of the primary temperature zone; and 25% of the hot air volume from the upper part of the quaternary temperature zone is circulated to the lower part of the secondary temperature zone.

[0089] After testing, the effective calcium oxide content in the lime (CaO) prepared by the method of this embodiment was 89.5%, and the carbon dioxide content in the flue gas discharged from the upper exhaust port of the fluidized bed furnace was 85.8%.

[0090] Comparative Example 1

[0091] 1) According to the direction of the material, 20 kg of limestone powder (average particle size of about 0.6 mm) is added from the lower feed port of the fluidized bed furnace and moves from bottom to top under the action of fluidizing gas to carry out thermal decomposition treatment. The solid product obtained after thermal decomposition is discharged from the upper discharge port of the fluidized bed furnace.

[0092] 2) According to the direction of airflow, the fluidizing gas (air with a flow rate of about 0.8 m / s) enters from the lower air inlet of the fluidizing furnace and carries the limestone powder from bottom to top for thermal decomposition treatment. Then, it carries the gaseous products obtained after thermal decomposition and is discharged from the upper exhaust port of the fluidizing furnace.

[0093] 3) During the fluidized thermal decomposition process of limestone powder, 40% of the flue gas discharged from the upper exhaust port of the fluidized furnace will be recycled to the lower air inlet of the fluidized furnace to serve as fluidizing gas.

[0094] After testing, the effective calcium oxide content in the lime (CaO) prepared by this comparative method was 72.3%, and the carbon dioxide content in the flue gas discharged from the upper exhaust port of the fluidized bed furnace was 70.2%.

[0095] Comparative Example 2

[0096] 1) According to the direction of the material, 25kg of limestone powder (average particle size of about 0.6mm) is added from the lower feed port of the fluidized bed furnace and moves from bottom to top under the action of fluidizing gas to carry out thermal decomposition treatment. The solid product obtained after thermal decomposition is discharged from the upper discharge port of the fluidized bed furnace.

[0097] 2) According to the direction of airflow, the fluidizing gas (air with a flow rate of about 1.0 m / s) enters from the lower air inlet of the fluidizing furnace and carries the limestone powder from bottom to top for thermal decomposition treatment. Then, it carries the gaseous products obtained after thermal decomposition and is discharged from the upper exhaust port of the fluidizing furnace.

[0098] 3) During the fluidized thermal decomposition process of limestone powder, 55% of the flue gas discharged from the upper exhaust port of the fluidized furnace will be recycled to the lower air inlet of the fluidized furnace to serve as fluidizing gas.

[0099] After testing, the effective calcium oxide content in the lime (CaO) prepared by this comparative method was 74.1%, and the carbon dioxide content in the flue gas discharged from the upper exhaust port of the fluidized bed furnace was 73.7%.

Claims

1. A method for fluidized calcination of limestone based on carbon cascade cycle, characterized by: The method comprises the following steps: 1) according to the flow direction of the material, the limestone ore powder is added from the lower inlet of the fluidized furnace and moves upward under the action of the fluidizing gas to perform thermal decomposition treatment, and the solid product obtained after thermal decomposition is discharged from the upper discharge port of the fluidized furnace; 2) according to the flow direction of the gas flow, the fluidizing gas enters from the lower gas inlet of the fluidized furnace and drives the limestone ore powder to move upward to perform thermal decomposition treatment, and then carries the gaseous product obtained after thermal decomposition to be discharged from the upper gas outlet of the fluidized furnace; 3) during the fluidized thermal decomposition treatment of the limestone ore powder, according to the content of carbon dioxide in the atmosphere in the inner cavity of the fluidized furnace, the inner cavity of the fluidized furnace is divided into a first furnace zone, a second furnace zone, a third furnace zone and a fourth furnace zone from top to bottom; wherein part of the hot air in the upper part of the first furnace zone is circulated to the lower part of the second furnace zone, part of the hot air in the upper part of the second furnace zone is circulated to the lower part of the third furnace zone, and part of the hot air in the upper part of the third furnace zone is circulated to the lower part of the fourth furnace zone; thereby realizing effective thermal decomposition of the limestone ore powder and enrichment and recovery of carbon dioxide; wherein: the carbon dioxide content in the first furnace zone is higher than 80%; the carbon dioxide content in the second furnace zone is 60-80%; the carbon dioxide content in the third furnace zone is 40-60%; the carbon dioxide content in the fourth furnace zone is less than 40%; or, According to the temperature of the atmosphere in the inner cavity of the fluidized furnace, the inner cavity of the fluidized furnace is divided into a first temperature zone, a second temperature zone, a third temperature zone and a fourth temperature zone from top to bottom; wherein part of the hot air in the upper part of the first temperature zone is circulated to the lower part of the third temperature zone, part of the hot air in the upper part of the second temperature zone is circulated to the lower part of the fourth temperature zone, part of the hot air in the upper part of the third temperature zone is circulated to the lower part of the first temperature zone, and part of the hot air in the upper part of the fourth temperature zone is circulated to the lower part of the second temperature zone; wherein: the temperature of the first temperature zone is 600-800℃, the temperature of the second temperature zone is 800-1000℃, the temperature of the third temperature zone is 550-750℃, and the temperature of the fourth temperature zone is 100-500℃.

2. The method of claim 1, wherein: The particle size of the limestone ore powder is 0.1-1mm; and / or The fluidizing gas is air and / or nitrogen; and / or The temperature for thermal decomposition treatment of the limestone ore powder is 650-1100℃; the thermal decomposition treatment time is 20-90min.

3. The method of claim 2, wherein: The particle size of the limestone ore powder is 0.2-0.8mm; and / or The flow rate of the fluidizing gas is 0.2-3m / s; and / or The temperature for thermal decomposition treatment of the limestone ore powder is 700-1000℃; the thermal decomposition treatment time is 30-80min.

4. The method of claim 3, wherein: The particle size of the limestone ore powder is 0.3-0.5mm; and / or The flow rate of the fluidizing gas is 0.5-2m / s; and / or The temperature for thermal decomposition treatment of the limestone ore powder is 750-950℃; the thermal decomposition treatment time is 45-70min.

5. The method of claim 1, wherein: The carbon dioxide content in the first furnace zone is 82-90%; the carbon dioxide content in the second furnace zone is 65-75%; the carbon dioxide content in the third furnace zone is 45-55%; and the carbon dioxide content in the fourth furnace zone is less than 35%.

6. The method of claim 1, wherein: The hot air amount of the upper part of the first furnace zone participating in the circulation accounts for 40-80% of the total hot air amount; the hot air amount of the upper part of the second furnace zone participating in the circulation accounts for 40-60% of the total hot air amount; and the hot air amount of the upper part of the third furnace zone participating in the circulation accounts for 30-50% of the total hot air amount.

7. The method of claim 6, wherein: The hot air amount of the upper part of the first furnace zone participating in the circulation accounts for 50-70% of the total hot air amount; the hot air amount of the upper part of the second furnace zone participating in the circulation accounts for 40-60% of the total hot air amount; and the hot air amount of the upper part of the third furnace zone participating in the circulation accounts for 30-50% of the total hot air amount.

8. The method of claim 1, wherein: The temperature of the first temperature zone is 650-750 DEG C, the temperature of the second temperature zone is 850-950 DEG C, the temperature of the third temperature zone is 600-700 DEG C, and the temperature of the fourth temperature zone is 200-400 DEG C.

9. The method of claim 1, wherein: The hot air amount of the upper part of the first temperature zone participating in the circulation accounts for 40-80% of the total hot air amount; the hot air amount of the upper part of the second temperature zone participating in the circulation accounts for 30-70% of the total hot air amount; the hot air amount of the upper part of the third temperature zone participating in the circulation accounts for 20-60% of the total hot air amount; and the hot air amount of the upper part of the fourth temperature zone participating in the circulation accounts for 10-50% of the total hot air amount.

10. The method of claim 9, wherein: The hot air amount of the upper part of the first temperature zone participating in the circulation accounts for 50-70% of the total hot air amount; the hot air amount of the upper part of the second temperature zone participating in the circulation accounts for 40-60% of the total hot air amount; the hot air amount of the upper part of the third temperature zone participating in the circulation accounts for 30-50% of the total hot air amount; and the hot air amount of the upper part of the fourth temperature zone participating in the circulation accounts for 20-40% of the total hot air amount.

11. A limestone fluidized calciner for use in the method of any one of claims 1-10, characterized by: The limestone fluidized calcining furnace comprises a furnace body (1) and a furnace chamber (2); a feeding port (101) and a fluidization air inlet (102) are arranged at the lower part of the furnace body (1), and a discharging port (103) and a fluidization air outlet (104) are arranged at the upper part of the furnace body (1); the furnace chamber (2) is divided into multiple series-connected chamber zones from top to bottom, and a circulating air pipe is led out from each chamber zone at the upper part of the furnace chamber (2) and is connected with the chamber zone at the lower part of the furnace chamber (2); a heating device (3) is further arranged on the furnace body (1) corresponding to the chamber zone at the middle part of the furnace chamber (2); The furnace chamber (2) comprises a first chamber zone, a second chamber zone, a third chamber zone and a fourth chamber zone which are sequentially connected in series from top to bottom, and a carbon dioxide concentration detector (201) is arranged in each chamber zone; the upper part of the first chamber zone is connected with the lower part of the second chamber zone through a first circulating air pipe (F1), the upper part of the second chamber zone is connected with the lower part of the third chamber zone through a second circulating air pipe (F2), and the upper part of the third chamber zone is connected with the lower part of the fourth chamber zone through a third circulating air pipe (F3); a flow regulating valve and a circulating air fan are independently arranged on the first circulating air pipe (F1), the second circulating air pipe (F2) and the third circulating air pipe (F3); or, The hearth (2) comprises a first hearth area, a second hearth area, a third hearth area and a fourth hearth area connected in series from top to bottom, and a temperature detector (202) is arranged in each hearth area; the upper part of the first hearth area is connected with the lower part of the third hearth area through a first circulating air pipe (F1), the upper part of the second hearth area is connected with the lower part of the fourth hearth area through a second circulating air pipe (F2), the upper part of the third hearth area is connected with the lower part of the first hearth area through a third circulating air pipe (F3), and the upper part of the fourth hearth area is connected with the lower part of the second hearth area through a fourth circulating air pipe (F4); a flow regulating valve and a circulating fan are independently arranged on the first circulating air pipe (F1), the second circulating air pipe (F2), the third circulating air pipe (F3) and the fourth circulating air pipe (F4).

12. The limestone fluidized calciner of claim 11, wherein: The hearth (2) is a gradually expanding hearth cavity with a narrow top and a wide bottom; the fluidized exhaust port (104) is further connected with a carbon dioxide collector (4) through an exhaust pipe; a screen is arranged at the air inlet end of the circulating air pipe.

13. The limestone fluidized calciner of claim 12, wherein: The screen hole diameter of the screen is 0.01-10 μm.

14. The limestone fluidized calciner of claim 13, characterized by: The screen hole diameter of the screen is 0.1-5 μm.

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