Method and system for preparing active calcium oxide from high-temperature overburned calcium oxide

Abstract

The application discloses a method and system for preparing active calcium oxide from high-temperature overburned calcium oxide. After cooling, the high-temperature overburned calcium oxide is reacted with atomized water or steam to generate calcium hydroxide. The obtained gas-solid mixture is separated by gas-solid separation and deep dedusting, and the combined calcium hydroxide material is sent into a suspension state decomposition device to complete calcination and decomposition under low-temperature conditions to generate high-activity calcium oxide. After gas-solid separation, the decomposition product is sent into a multi-stage cyclone cooling device to exchange heat with reverse-flow cooling air under a suspension flow state, and high-activity calcium oxide is obtained after cooling. The application completely destructs the dense structure of the overburned calcium oxide from the chemical level through the digestion reaction, effectively avoids the secondary sintering of the new-born crystal grains by using the low-temperature decomposition in the suspension state, and the product has high activity and stable performance. Meanwhile, the digestion reaction is driven by the sensible heat of the material, the waste heat of the system is recycled in stages, the production energy consumption is significantly reduced, and the application is suitable for industrial large-scale popularization and application.

Description

Technical Field

[0001] This application relates to the field of inorganic non-metallic material processing technology, specifically to a method and system for preparing active calcium oxide from high-temperature overheated calcium oxide. Background Technology

[0002] Calcium oxide (quicklime), as an important basic inorganic chemical raw material, is widely used in metallurgy, building materials, environmental protection, and chemical industries. Among them, activated calcium oxide, due to its fine grains, high porosity, and large specific surface area, exhibits significantly superior reactivity compared to ordinary calcium oxide, leading to increasing demand in high-end metallurgical desulfurization, fine chemical synthesis, and the preparation of new building materials. Therefore, obtaining high-quality activated calcium oxide is a technical issue of ongoing concern in this field.

[0003] Currently, industrially produced calcium oxide is mainly obtained by calcining limestone at high temperatures in rotary kilns or vertical kilns. However, in actual production, due to problems such as excessively high calcination temperatures, excessively long residence time of materials in the kiln, and uneven temperature distribution within the kiln, "overburning" often occurs, resulting in high-temperature overburned calcium oxide with coarse grains and a dense structure. This overburned calcium oxide has a contracted and closed crystal structure, a sharp decrease in specific surface area and porosity, and a significant reduction in hydration reactivity, making it unsuitable for high-value-added applications. It is typically discarded as waste or downgraded for use. This not only causes a serious waste of limestone resources but also imposes an additional burden of solid waste treatment on enterprises.

[0004] For the upgrading and reactivation of overburned calcium oxide, existing technologies mainly fall into two categories: physical modification and high-temperature recalcination. However, both face significant technical bottlenecks. Firstly, physical modification processes use high-intensity ball mills and roller mills to pulverize dense overburned calcium oxide blocks into extremely fine powder, increasing its specific surface area. However, the core reason for the deactivation of overburned calcium oxide is its dense internal crystal sintering and closed pore structure. Ultrafine grinding can only change the macroscopic particle size of the material and cannot repair its dense internal crystal structure and closed pore system, resulting in extremely limited activity enhancement. Furthermore, it increases grinding energy consumption, making it economically unfeasible. Secondly, the high-temperature recalcination process involves mixing overburned calcium oxide with limestone raw materials and then re-feeding it to a rotary kiln or vertical kiln for secondary high-temperature calcination. The core flaw of this process lies in the fact that overburned calcium oxide has already undergone the thermal decomposition of calcium carbonate. Further calcination at temperatures above 1000℃ not only fails to reconstruct and activate the crystal structure but also exacerbates the sintering and growth of calcium oxide grains and the densification of the structure, leading to a further decrease in material activity. Furthermore, this process suffers from low utilization of waste heat from both the material and the reaction, resulting in high energy consumption. In summary, existing technologies for upgrading and modifying overburned calcium oxide cannot simultaneously solve the problems of poor regeneration efficiency, high energy consumption, low waste heat utilization, unstable product performance, and difficulty in large-scale industrial application, severely restricting the high-value resource utilization of overburned calcium oxide. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and system for preparing active calcium oxide from high-temperature overburned calcium oxide.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This application provides a method for preparing active calcium oxide from high-temperature overheated calcium oxide, comprising the following steps: S1. After cooling the overheated calcium oxide to a preset temperature, it undergoes a digestion reaction with atomized water or steam to generate a gas-solid mixture of calcium hydroxide; S2. Perform gas-solid separation on the gas-solid mixture obtained in step S1 to obtain a first solid material and dust-containing exhaust gas. Then, perform deep dust removal on the dust-containing exhaust gas to collect and obtain a second solid material. Combine the first solid material and the second solid material. S3. The solid material combined in step S2 is fed into a suspension decomposition device and calcined and decomposed under low temperature conditions to obtain a gas-solid mixture containing highly active calcium oxide. S4. Perform gas-solid separation on the gas-solid mixture containing highly active calcium oxide obtained in step S3. Combine the separated calcium oxide material with the calcium oxide powder collected by deep dust removal and send it into a multi-stage cyclone cooling device to exchange heat with the counter-flowing cooling air in a suspended flow state. After cooling, the highly active calcium oxide product is obtained.

[0007] Optionally, in step S1, the feeding temperature of the high-temperature overburned calcium oxide is 800℃~1200℃, and the preset temperature after cooling is 550~700℃; the temperature of the digestion reaction is controlled at 200℃~500℃.

[0008] Optionally, in step S1, the amount of atomized water or steam introduced is 1.0 to 1.5 times the theoretical water requirement for the complete hydration of the high-temperature overburned calcium oxide.

[0009] Optionally, in step S3, the suspended decomposition device is a suspended calcining furnace or a fluidized bed reactor; the low temperature condition is 500℃~800℃, and the residence time of the material in the suspended decomposition device is 5s~60s.

[0010] Optionally, a heat recovery step may also be included: A portion of the digestion exhaust gas discharged after deep dust removal in step S2 is used to cool the high-temperature overburned calcium oxide in step S1 in order to recover its sensible heat. Part of the decomposition tail gas discharged after gas-solid separation in step S4 is introduced into the suspension decomposition device in step S3 as an auxiliary heat source to participate in the calcination decomposition reaction.

[0011] Optionally, in step S4, the multi-stage cyclone cooling device includes at least two cyclone tubes connected in series, and the discharge temperature of the highly active calcium oxide product after cooling is not higher than 100°C.

[0012] A system for implementing the above method includes: The primary cooling device is used to cool the overheated calcium oxide at high temperature to a preset temperature; A digestion device is used to react cooled calcium oxide with atomized water or steam to produce a gas-solid mixture of calcium hydroxide. The first gas-solid separation device and the first dust collection device are used for gas-solid separation and deep dust removal of the calcium hydroxide gas-solid mixture; The suspension decomposition device has its inlet connected to the discharge port of the first gas-solid separation device and the dust discharge port of the first dust collection device. It is used to calcine and decompose calcium hydroxide in a suspension state at low temperature to generate a highly active calcium oxide gas-solid mixture. The second gas-solid separation device and the second dust collection device are used to perform gas-solid separation and deep dust removal on the highly active calcium oxide gas-solid mixture. The multi-stage cyclone cooling device has its inlet connected to the discharge port of the second gas-solid separation device and the dust discharge port of the second dust collection device, and is used to perform suspension heat exchange cooling on calcium oxide material through counter-flowing cooling air.

[0013] Optionally, the digestion device is any one of a suspension digester, a stirred digester, or a spray digester.

[0014] Optionally, the air outlet of the first dust collection device is connected to the hot air inlet of the primary cooling device via a pipe to utilize the waste heat from the digestion exhaust gas to cool the high-temperature overburned calcium oxide; the air outlets of the second dust collection device and the primary cooling device are connected to the hot air inlet of the suspended decomposition device via pipes to recover waste heat for auxiliary decomposition reaction.

[0015] Optionally, the multi-stage cyclone cooling device consists of two or more cyclone cooling devices connected in series, with a material connecting pipe and an airflow connecting pipe between adjacent two-stage cyclone cooling devices to achieve countercurrent contact heat exchange between cooling air and calcium oxide material.

[0016] Compared with the prior art, this application has the following beneficial effects: This invention proposes a method and system for preparing active calcium oxide from high-temperature overburned calcium oxide. The sensible heat of the overburned calcium oxide is directly used to drive the digestion reaction, eliminating the need for an additional heat source. The digestion reaction causes the calcium oxide to hydrate and expand, and its crystal lattice to reorganize into calcium hydroxide. This chemically deconstructs the dense structure of the overburned calcium oxide, laying the foundation for subsequent low-temperature decomposition to generate highly active calcium oxide. The subsequent decomposition of calcium hydroxide is completed in a suspended state at a low temperature of 500℃–800℃, resulting in high mass and heat transfer efficiency and rapid decomposition. The newly formed calcium oxide grains are reconstructed at low temperatures and immediately detached from the high-temperature zone, effectively preventing secondary sintering and growth of the grains. This yields a product with fine grains, well-developed pores, and high activity. Simultaneously, the waste heat from the digestion and decomposition exhaust gases is recovered for material cooling and auxiliary decomposition reactions. A multi-stage cyclone cooling device achieves efficient countercurrent heat exchange between the finished product and air. The cooled air can be reused after heating, resulting in high system thermal energy utilization and significantly reducing production energy consumption. The entire process is simple, with high equipment integration, and the product exhibits stable batch-to-batch activity, making it suitable for large-scale continuous industrial production. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a system for preparing active calcium oxide from high-temperature overheated calcium oxide, as provided in this application.

[0018] Icons: 1-Rotary kiln; 2-Primary cooling device; 3-Digestion device; 4-First gas-solid separation device; 5-First dust collection device; 6-Suspended decomposition device; 7-Second gas-solid separation device; 8-Second dust collection device; 9-First-stage cooling device; 10-Second-stage cooling device; 11-Third-stage cooling device. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Furthermore, in this invention, an element referred to as fixed to or disposed on another element may be directly disposed on the other element, or there may be an intermediate element. When an element is considered to be connected to another element, it may be directly connected to the other element, or there may be an intermediate element present simultaneously. The terms vertical, horizontal, left, right, and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0021] See Figure 1 This application provides a method for preparing active calcium oxide from high-temperature overburned calcium oxide, comprising the following steps: S1. After cooling the overheated calcium oxide to a preset temperature, it undergoes a digestion reaction with atomized water or steam to generate a gas-solid mixture of calcium hydroxide.

[0022] Specifically: the high-temperature overburned calcium oxide produced by calcination in the rotary kiln is sent to the primary cooling device for cooling; the primary cooling device can use an air-cooled heat exchanger or an indirect water-cooled heat exchanger to quickly cool the high-temperature material to the preset temperature; the cooled calcium oxide then enters the digestion device, where it undergoes a vigorous digestion reaction with atomized water or steam to generate a calcium hydroxide gas-solid mixture; the digestion device is equipped with an atomized water or steam injection device to ensure that the hydration medium is highly dispersed and in full contact with the high-temperature calcium oxide.

[0023] Furthermore, the core technical significance of this step lies in the fact that the dense lattice structure inside the overburned calcium oxide expands and breaks due to the violent hydration reaction with water, and the crystal phase of calcium oxide is reorganized and transformed into loose calcium hydroxide. This chemical reconstruction process completely deconstructs the dense structure of the overburned calcium oxide at the chemical level, which is the core basis for obtaining highly active calcium oxide under low temperature conditions. It fundamentally solves the technical bottleneck that physical grinding processes cannot repair the internal pore structure.

[0024] S2. Perform gas-solid separation on the gas-solid mixture obtained in step S1 to obtain a first solid material and dust-laden exhaust gas. Then, perform deep dust removal on the dust-laden exhaust gas to collect and obtain a second solid material. Combine the first solid material and the second solid material.

[0025] Specifically: the calcium hydroxide gas-solid mixture obtained in step S1 is fed into a first gas-solid separation device for gas-solid separation; the first gas-solid separation device is preferably a cyclone separator, which can separate most of the solid calcium hydroxide particles from the gas flow to obtain the first solid phase material; the separated dust-laden exhaust gas is then sent to a first dust collection device for deep dust removal; the first dust collection device is used to efficiently capture the fine calcium hydroxide powder entrained in the exhaust gas to obtain the second solid phase material; while ensuring that the exhaust gas meets emission standards, the material recovery rate is maximized; subsequently, the first solid phase material obtained from the first gas-solid separation device and the second solid phase material captured by the first dust collection device are combined and sent to the downstream process.

[0026] S3. The solid material combined in step S2 is fed into a suspension decomposition device and calcined and decomposed under low temperature conditions to obtain a gas-solid mixture containing highly active calcium oxide.

[0027] Specifically: the calcium hydroxide solid material after step S2 is fed into a suspension decomposition device, where it is calcined and decomposed at low temperature to obtain a gas-solid mixture containing highly active calcium oxide; under suspension flow conditions, the calcium hydroxide particles are in full contact with the high-temperature gas, the gas-solid two-phase mass and heat transfer efficiency is extremely high, and the decomposition reaction can be completed in a very short time.

[0028] The innovative technical point of this step lies in the fact that the decomposition temperature of calcium hydroxide is much lower than that of calcium carbonate. This application controls the decomposition temperature within a low-temperature range and utilizes the efficient heat transfer of the suspended state to ensure that the material residence time is extremely short. Under low-temperature and short-time conditions, the newly formed calcium oxide grains have just completed the topological transformation from the calcium hydroxide lattice and are rapidly removed from the high-temperature reaction zone, without sufficient time for grain sintering and growth. Therefore, this step can simultaneously achieve the two goals of "complete decomposition" and "activity retention" under low-temperature conditions, obtaining a highly active calcium oxide product with fine grains, well-developed pores, and a large specific surface area. This completely avoids the problem of secondary sintering of the product and a decrease in activity caused by prolonged high-temperature recalcination processes in traditional high-temperature recalcination processes.

[0029] S4. Perform gas-solid separation on the gas-solid mixture containing highly active calcium oxide obtained in step S3. Combine the separated calcium oxide material with the calcium oxide powder collected by deep dust removal and send it into a multi-stage cyclone cooling device to exchange heat with the counter-flowing cooling air in a suspended flow state. After cooling, the highly active calcium oxide product is obtained.

[0030] Specifically: the gas-solid mixture obtained in step S3 is fed into a second gas-solid separation device for gas-solid separation; the second gas-solid separation device is preferably a cyclone separator to achieve rapid separation of high-temperature calcium oxide material from decomposition tail gas; the separated calcium oxide material is combined with the calcium oxide powder collected by the second dust collection device and sent together into a multi-stage cyclone cooling device; in the multi-stage cyclone cooling device, the cooling air and the calcium oxide material flow in opposite directions, and the two complete efficient heat exchange in a suspended flow state; this counter-current suspension cooling method has high heat exchange intensity and fast cooling speed, which can quickly terminate the potential thermal growth of calcium oxide grains; after heat exchange and cooling, a high-activity calcium oxide product is collected.

[0031] In a preferred embodiment, in step S1, the feeding temperature of the high-temperature overburned calcium oxide is 800℃~1200℃, and the preset temperature after cooling is 550~700℃; the temperature of the digestion reaction is controlled at 200℃~500℃.

[0032] In this embodiment, the feed temperature of the high-temperature overburned calcium oxide is typically 800℃~1200℃, such as 800℃, 900℃, 1000℃, 1100℃, 1200℃, etc., which are typical but not limiting temperatures. The large amount of sensible heat carried by the high-temperature overburned calcium oxide is an important energy source for the subsequent digestion reaction. Utilizing its own sensible heat to directly drive the digestion reaction, the entire hydration process does not require additional external heat sources, greatly reducing system energy consumption. After cooling by the primary cooling device, the preset temperature of the calcium oxide is 550~700℃, for example, 550℃. 600℃, 650℃, 700℃, etc.; this temperature range can ensure that the material has sufficient enthalpy when entering the digestion device to maintain the temperature required for the digestion reaction, and can also avoid the safety hazards caused by excessively high temperature leading to a large amount of instantaneous vaporization of the hydration medium; the temperature of the digestion reaction is controlled between 200℃ and 500℃, for example, 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, 500℃, etc.; within the above temperature range, the digestion reaction can proceed rapidly and fully, and the crystal structure of overburned calcium oxide can be completely expanded and deconstructed.

[0033] In a preferred embodiment, in step S1, the amount of atomized water or steam introduced is 1.0 to 1.5 times the theoretical water requirement for the complete hydration of the high-temperature overburned calcium oxide.

[0034] In this embodiment, to ensure that the overburned calcium oxide can undergo a full and complete hydration reaction, and to avoid incomplete digestion and failure to decompose some dense crystal lattices due to insufficient water, or increased energy consumption for subsequent evaporation and dehydration due to excessive water, the amount of atomized water or steam introduced is preferably 1.0 to 1.5 times the theoretical water required for complete hydration of high-temperature overburned calcium oxide. The determination of this dosage range takes into account the characteristics of the overburned calcium oxide itself, such as its dense crystal lattice and low reactivity. An appropriate excess of hydration medium can ensure that water molecules are in full contact with the interior of the calcium oxide particles and complete deep hydration, so that the dense structure can be completely expanded and decomposed, laying a solid material foundation for the subsequent low-temperature decomposition to generate highly active calcium oxide.

[0035] In a preferred embodiment, in step S3, the suspended decomposition device is a suspended calcining furnace or a fluidized bed reactor; the low temperature condition is 500℃~800℃, and the residence time of the material in the suspended decomposition device is 5s~60s.

[0036] In this embodiment, the suspension decomposition device can specifically be a suspension calcination furnace or a fluidized bed reactor. Both of these devices can enable solid materials to be in a suspended fluidized state in the gas flow, achieving efficient contact between the gas and solid phases. The mass and heat transfer efficiency is far superior to that of traditional packed or rotary equipment. The low temperature condition is 500℃~800℃, for example, typical but not limiting temperatures such as 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, and 800℃. The residence time of the material in the suspension decomposition device is controlled within 5s. 60s, for example, can be 5s, 10s, 20s, 30s, 45s, 60s, etc.; this residence time is much shorter than the hour-level calcination time of traditional rotary kilns or vertical kilns; its technical significance is that: the decomposition reaction of calcium hydroxide is itself an endothermic reaction, and under the condition of extremely high heat transfer efficiency in suspension, the decomposition reaction can be completed rapidly within a few seconds to tens of seconds; strictly controlling the residence time within this range can effectively avoid the abnormal growth and sintering of newly formed calcium oxide grains in a high-temperature environment while ensuring the decomposition rate, thus ensuring the high activity of the product.

[0037] As a preferred embodiment, a heat recovery step is also included: A portion of the digestion exhaust gas discharged after deep dust removal in step S2 is used in step S1 to cool the high-temperature overburned calcium oxide in order to recover its sensible heat.

[0038] Part of the decomposition tail gas discharged after gas-solid separation in step S4 is introduced into the suspension decomposition device in step S3 as an auxiliary heat source to participate in the calcination decomposition reaction.

[0039] In this embodiment, the step involves the cascade utilization of exhaust gas digestion and decomposition: Regarding the waste heat recovery from the digester exhaust gas: Although the digester exhaust gas discharged after deep dust removal in step S2 has been purified, it still carries a considerable amount of waste heat. Part of this digester exhaust gas is sent to the primary cooling device in step S1 to conduct counter-current gas-solid heat exchange with high-temperature overburned calcium oxide to recover the sensible heat of the high-temperature material. On the one hand, the digester exhaust gas acts as a cooling medium, replacing or supplementing part of the cold air or cooling water, reducing the consumption of cooling medium. On the other hand, while the high-temperature material is cooled, the digester exhaust gas itself is also heated, and the heated air can be further used for other heat-requiring links in the system. The remaining part of the digester exhaust gas can be used for waste heat power generation, realizing the further utilization of excess heat energy.

[0040] Regarding the waste heat recovery of decomposition tail gas: Part of the decomposition tail gas discharged after gas-solid separation in step S4 is introduced into the suspension decomposition device in step S3 as an auxiliary heat source to participate in the calcination decomposition reaction of calcium hydroxide; the decomposition tail gas has a high temperature, and direct reuse can effectively supplement the heat required for the decomposition reaction and reduce the consumption of external fuel or electricity; the excess decomposition tail gas can also be used for waste heat power generation; this closed-loop design of energy recovery enables the waste heat generated in each link of the system to be effectively utilized, significantly improving the thermal energy utilization efficiency of the entire process and greatly reducing production energy consumption.

[0041] In a preferred embodiment, in step S4, the multi-stage cyclone cooling device includes at least two stages of cyclone cylinders connected in series, and the discharge temperature of the highly active calcium oxide product after cooling is not higher than 100°C.

[0042] In this embodiment, the multi-stage cyclone cooling device includes at least two cyclone tubes connected in series. This multi-stage series arrangement significantly extends the contact path between the gas and solid phases, resulting in more thorough heat exchange. Cooling air enters from the end cyclone tube and flows forward stage by stage. High-temperature calcium oxide material enters from the first-stage cyclone tube and flows backward stage by stage. The two materials form counter-current contact within each cyclone tube, maintaining a relatively uniform temperature difference throughout the process. This significantly improves heat exchange efficiency compared to single-stage or co-current cooling. The discharge temperature of the high-activity calcium oxide product after heat exchange cooling is no higher than 100°C. Maintaining the finished product temperature below 100°C facilitates subsequent storage, packaging, and transportation, preventing damage to downstream conveying equipment and packaging materials from high-temperature materials. Furthermore, rapid cooling quickly terminates the potential thermal growth process of calcium oxide crystals at high temperatures, stably preserving the product's high-activity state. The heated air after heat exchange can be recycled for other heat-requiring processes within the system, further reducing overall energy consumption.

[0043] A system for implementing the above method includes: The primary cooling device is used to cool the overheated calcium oxide at high temperature to a preset temperature.

[0044] A digestion device is used to react cooled calcium oxide with atomized water or steam to produce a gas-solid mixture of calcium hydroxide.

[0045] The first gas-solid separation device and the first dust collection device are used to perform gas-solid separation and deep dust removal on the calcium hydroxide gas-solid mixture.

[0046] The suspension decomposition device has its inlet connected to the discharge port of the first gas-solid separation device and the dust discharge port of the first dust collection device. It is used to calcine and decompose calcium hydroxide in a suspended state at low temperature to generate a highly active calcium oxide gas-solid mixture.

[0047] The second gas-solid separation device and the second dust collection device are used to perform gas-solid separation and deep dust removal on the highly active calcium oxide gas-solid mixture.

[0048] The multi-stage cyclone cooling device has its inlet connected to the discharge port of the second gas-solid separation device and the dust discharge port of the second dust collection device, and is used to perform suspension heat exchange cooling on calcium oxide material through counter-flowing cooling air.

[0049] Specifically, the system mainly includes: a primary cooling device, a digestion device, a first gas-solid separation device, a first dust collection device, a suspended decomposition device, a second gas-solid separation device, a second dust collection device, and a multi-stage cyclone cooling device.

[0050] The primary cooling device has its feed inlet connected to the discharge end of the rotary kiln via a high-temperature resistant pipe. It is used to receive the high-temperature overburned calcium oxide generated by the rotary kiln and cool it to a preset temperature. The primary cooling device can use an air-cooled heat exchanger or an indirect water-cooled heat exchanger. The recovered sensible heat can be used for other heat-requiring links in the system, thereby improving the overall thermal energy utilization efficiency.

[0051] The digestion device has its inlet connected to the discharge port of the primary cooling device. It is used to allow the cooled calcium oxide to undergo a digestion reaction with atomized water or steam to generate a calcium hydroxide gas-solid mixture. The digestion device is equipped with an atomized water or steam injection device to ensure that the hydration medium is evenly dispersed and fully contacts and reacts with the calcium oxide material.

[0052] The first gas-solid separation device and the first dust collection device are used to perform gas-solid separation and deep dust removal on the calcium hydroxide gas-solid mixture obtained after the digestion reaction. The air inlet of the first gas-solid separation device is connected to the air outlet of the digestion device, and most of the separated calcium hydroxide material is discharged from its discharge port. The air inlet of the first dust collection device is connected to the air outlet of the first gas-solid separation device, and performs deep dust removal treatment on the dust-containing tail gas. The collected calcium hydroxide powder is discharged from its dust discharge port.

[0053] The suspension decomposition device has its inlet connected to the discharge port of the first gas-solid separation device and the dust discharge port of the first dust collection device, so that the combined calcium hydroxide material is centrally fed into it; the suspension decomposition device is equipped with a temperature control system and a material residence time control device, which are used to calcine and decompose calcium hydroxide in a suspension state at low temperature to generate a highly active calcium oxide gas-solid mixture; the suspension decomposition device can be equipped with an auxiliary heat source supply system to supplement the heat required during startup or fluctuations in operating conditions.

[0054] The second gas-solid separation device and the second dust collection device are used to perform gas-solid separation and deep dust removal on the highly active calcium oxide gas-solid mixture obtained after calcination and decomposition. The air inlet of the second gas-solid separation device is connected to the air outlet of the suspended decomposition device, and the separated calcium oxide material is discharged from its discharge port. The air inlet of the second dust collection device is connected to the air outlet of the second gas-solid separation device to further recover fine calcium oxide powder and improve product yield.

[0055] A multi-stage cyclone cooling device connects its inlet to the outlet of the second gas-solid separation device and the dust outlet of the second dust collection device, allowing high-temperature calcium oxide material to be centrally fed into the cooling system. The multi-stage cyclone cooling device is used to cool the calcium oxide material through suspension heat exchange via counter-flowing cooling air. Figure 1 As shown, the multi-stage cyclone cooling device consists of a primary cooling device 9, a secondary cooling device 10, and a tertiary cooling device 11 connected in series to achieve rapid cooling of materials.

[0056] In a preferred embodiment, the digestion device is any one of a suspension digester, a stirred digester, or a spray digester.

[0057] In this embodiment, the digestion device can be any one of a suspension digester, a stirred digester, or a spray digester; the specific selection can be flexibly determined according to the actual production scale, material characteristics, and process layout requirements; the suspension digester enables calcium oxide powder to react with water or steam in a suspended state, with a large gas-solid contact area, uniform reaction, and high efficiency, making it suitable for large-scale continuous production; the stirred digester enhances solid-liquid mixing through a mechanical stirring device, making it suitable for processing materials with coarse particles or those prone to agglomeration, and preventing localized clumping of materials during digestion; the spray digester sprays water or steam in an atomized form onto the surface of the calcium oxide material, resulting in highly dispersed hydration media, a large contact area, fast digestion speed, and a relatively simple equipment structure.

[0058] In a preferred embodiment, the air outlet of the first dust collection device is connected to the hot air inlet of the primary cooling device via a pipe to utilize the waste heat from the digestion exhaust gas to cool the high-temperature overburned calcium oxide; the air outlets of the second dust collection device and the primary cooling device are connected to the hot air inlet of the suspended decomposition device via pipes to recover waste heat for auxiliary decomposition reaction.

[0059] In this embodiment, the outlet of the first dust collection device is connected to the hot air inlet of the primary cooling device via a pipe to utilize the waste heat of the digestion exhaust gas to cool the high-temperature overburned calcium oxide. Specifically, although the digestion exhaust gas discharged after deep dust removal in step S2 has been purified, it still carries considerable waste heat. This waste heat is introduced into the primary cooling device to conduct counter-current gas-solid heat exchange with the high-temperature overburned calcium oxide. On the one hand, the digestion exhaust gas acts as a cooling medium, replacing or supplementing part of the cold air and reducing the consumption of the cooling medium. On the other hand, while the high-temperature material is cooled, the digestion exhaust gas itself is also heated. The outlets of the second dust collection device and the primary cooling device are connected to the hot air inlet of the suspended decomposition device via pipes to recover waste heat for auxiliary decomposition reaction. The hot air obtained from the heat exchange in the primary cooling device and part of the decomposition exhaust gas discharged from the second dust collection device are fed into the suspended decomposition device as an auxiliary heat source to directly participate in the low-temperature calcination decomposition reaction of calcium hydroxide, realizing closed-loop utilization of heat.

[0060] In a preferred embodiment, the multi-stage cyclone cooling device consists of two or more cyclone cooling devices connected in series, with a material connecting pipe and an airflow connecting pipe provided between adjacent two-stage cyclone cooling devices to achieve countercurrent contact heat exchange between cooling air and calcium oxide material.

[0061] In this embodiment, the multi-stage cyclone cooling device consists of two or more cyclone cooling devices connected in series; such as Figure 1 As shown, an exemplary configuration of a primary cooling device 9, a secondary cooling device 10, and a tertiary cooling device 11 connected in series is illustrated. Material connecting pipes and airflow connecting pipes are provided between adjacent cyclone cooling devices. The specific operating method is as follows: cooling air enters from the cold air inlet at the bottom of the terminal cyclone and flows forward stage by stage; high-temperature calcium oxide material enters from the primary cyclone and flows backward stage by stage. The two form counter-current contact within each cyclone stage and complete efficient gas-solid heat exchange in a suspended flow state. The material connecting pipe is used to transport the calcium oxide material separated from the previous cyclone stage to the inlet of the next cyclone stage. The airflow connecting pipe is used to introduce the heated air discharged from the next cyclone stage into the previous cyclone stage. This multi-stage counter-current suspension cooling method, compared to single-stage cooling or co-current cooling, results in a more uniform distribution of the heat exchange temperature difference throughout the process, more efficient utilization of the heat exchange driving force, and the ability to achieve rapid cooling of the material from high temperature to near ambient temperature with a smaller amount of cooling air.

[0062] The technical solution of this application will be described in detail below with reference to practical applications: In the following embodiments of this application, all raw materials used are commercially available products or prepared by conventional methods; overburned calcium oxide is derived from waste or downgraded products generated during the calcination of limestone in industrial rotary kilns or vertical kilns due to excessively high local temperatures and excessively long residence times. Its typical characteristics are coarse grains, dense structure, small specific surface area, and low hydration reactivity.

[0063] Example 1 This embodiment provides a method for preparing active calcium oxide from high-temperature overheated calcium oxide, specifically including the following steps: Step S1: The high-temperature overburned calcium oxide, with a feed temperature of 1200℃ generated by calcination in the rotary kiln, is sent to the primary cooling device through a high-temperature resistant pipe. The primary cooling device uses an air-cooled heat exchanger to rapidly cool the high-temperature overburned calcium oxide. After cooling, the temperature of the calcium oxide material drops to 550℃, and then it is sent to the digestion device. The digestion device is a suspension digester with a steam injection device inside. Atomized steam is introduced into the digestion device, and the steam flow rate is 1.5 times the theoretical water required for the complete hydration of the overburned calcium oxide. At a temperature of 200℃, the overburned calcium oxide undergoes a violent digestion reaction with the steam to generate a gas-solid mixture of calcium hydroxide. The dense lattice structure inside the overburned calcium oxide expands and breaks due to the hydration reaction, and the calcium oxide crystal phase recombines and transforms into loose calcium hydroxide.

[0064] Step S2: The calcium hydroxide gas-solid mixture obtained in step S1 is fed into the first gas-solid separation device; the first gas-solid separation device is a cyclone separator, which separates the first solid material and the dust-containing exhaust gas; the dust-containing exhaust gas is fed into the first dust collection device, which is a bag dust collector, to perform deep dust removal on the dust-containing exhaust gas and collect the second solid material; the first solid material and the second solid material are combined and sent to the downstream process.

[0065] Step S3: The calcium hydroxide solid material combined in step S2 is fed into a suspension decomposition device; the suspension decomposition device is a suspension calcination furnace; under the low temperature condition of 800℃, the material completes calcination decomposition in a suspended flow state with a residence time of 5s; calcium hydroxide is rapidly decomposed into calcium oxide and water vapor, resulting in a gas-solid mixture containing highly active calcium oxide; due to the low decomposition temperature and short residence time, the newly formed calcium oxide grains do not have time to sinter and grow, resulting in fine grains and well-developed pores in the product.

[0066] Step S4: The gas-solid mixture obtained in step S3 is fed into the second gas-solid separation device; the second gas-solid separation device is a cyclone separator, which realizes the rapid separation of calcium oxide material and decomposition tail gas; the separated calcium oxide material is combined with the calcium oxide powder collected by the second dust collection device and sent into the multi-stage cyclone cooling device; the second dust collection device is an electrostatic precipitator; the multi-stage cyclone cooling device consists of two cyclone tubes connected in series; the cooling air enters from the bottom of the end cyclone tube and comes into contact with the calcium oxide material in the opposite direction, and heat exchange occurs in the suspended flow state; after heat exchange and cooling, the high-activity calcium oxide product is collected, and the discharge temperature is 100℃.

[0067] Testing revealed that the highly active calcium oxide product prepared in this embodiment has fine grains, a large specific surface area, and high porosity, exhibiting significantly better reactivity than overburned calcium oxide raw materials.

[0068] Example 2 This embodiment provides a method for preparing active calcium oxide from high-temperature overheated calcium oxide, specifically including the following steps: Step S1: The high-temperature overburned calcium oxide, with a feed temperature of 800℃, generated by calcination in the rotary kiln, is sent to the primary cooling device through a high-temperature resistant pipe. The primary cooling device uses an indirect water-cooled heat exchanger to rapidly cool the high-temperature overburned calcium oxide. After cooling, the temperature of the calcium oxide material drops to 700℃, and then it is sent to the digestion device. The digestion device is a stirred digester with an internal atomized water spraying device. Atomized water is introduced into the digestion device, and the amount of atomized water introduced is 1.0 times the theoretical water required for the complete hydration of overburned calcium oxide. At a temperature of 500℃, the overburned calcium oxide and the atomized water undergo a violent digestion reaction to generate a gas-solid mixture of calcium hydroxide.

[0069] Step S2: The calcium hydroxide gas-solid mixture obtained in step S1 is fed into the first gas-solid separation device; the first gas-solid separation device is a cyclone separator, which separates the first solid material and the dust-containing exhaust gas; the dust-containing exhaust gas is fed into the first dust collection device, which is a cyclone dust collector, to perform deep dust removal on the dust-containing exhaust gas and collect the second solid material; the first solid material and the second solid material are combined and sent to the downstream process.

[0070] This embodiment also includes a heat recovery step: the digestion exhaust gas discharged from the first dust collection device is divided into two paths; one path is sent to the primary cooling device in step S1 to perform countercurrent gas-solid heat exchange with high-temperature overburned calcium oxide in order to recover the sensible heat of the high-temperature material; the other path is used for waste heat power generation.

[0071] Step S3: The calcium hydroxide solid material combined in step S2 is fed into a suspension decomposition device; the suspension decomposition device is a fluidized bed reactor; under the low temperature condition of 500℃, the material completes calcination decomposition in a suspended fluid state with a residence time of 60s; calcium hydroxide decomposes into calcium oxide and water vapor, resulting in a gas-solid mixture containing highly active calcium oxide.

[0072] The heat recovery method of the decomposition tail gas in this embodiment is as follows: part of the decomposition tail gas discharged by the second dust collection device in step S4 is introduced into the suspended decomposition device in step S3 as an auxiliary heat source to participate in the calcination decomposition reaction of calcium hydroxide and supplement the heat required to maintain the decomposition temperature; the excess decomposition tail gas is used for waste heat power generation.

[0073] Step S4: The gas-solid mixture obtained in step S3 is fed into the second gas-solid separation device; the second gas-solid separation device is a cyclone separator, which realizes the rapid separation of calcium oxide material and decomposition tail gas; the separated calcium oxide material is combined with the calcium oxide powder collected by the second dust collection device and sent into the multi-stage cyclone cooling device; the second dust collection device is a bag dust collector; the multi-stage cyclone cooling device consists of three cyclone tubes connected in series, with material connecting pipes and airflow connecting pipes between adjacent two stages; cooling air enters from the bottom of the third-stage cyclone tube and flows forward stage by stage; calcium oxide material enters from the first-stage cyclone tube and flows backward stage by stage, and the two form a counter-current suspended flow heat exchange in each stage of the cyclone tube; after heat exchange and cooling, the high-activity calcium oxide product is collected, and the discharge temperature is 80℃.

[0074] Testing revealed that the highly active calcium oxide product prepared in this embodiment has fine grains, well-developed pores, and significantly better reactivity than overburned calcium oxide raw material.

[0075] Example 3 This embodiment provides a method for preparing active calcium oxide from high-temperature overheated calcium oxide, specifically including the following steps: Step S1: The high-temperature overburned calcium oxide, with a feed temperature of 1000℃, generated by calcination in the rotary kiln, is sent to the primary cooling device through a high-temperature resistant pipe. The primary cooling device uses an air-cooled heat exchanger to rapidly cool the high-temperature overburned calcium oxide. After cooling, the temperature of the calcium oxide material drops to 650℃, and then it is sent to the digestion device. The digestion device is a spray-type digester with an internal atomized water spray device. Atomized water is introduced into the digestion device, and the amount of atomized water introduced is 1.2 times the theoretical water required for the complete hydration of overburned calcium oxide. Under the temperature condition of 350℃, the overburned calcium oxide and the atomized water undergo a violent digestion reaction to generate a gas-solid mixture of calcium hydroxide.

[0076] Step S2: The calcium hydroxide gas-solid mixture obtained in step S1 is fed into the first gas-solid separation device; the first gas-solid separation device is a cyclone separator, which separates the first solid material and the dust-containing exhaust gas; the dust-containing exhaust gas is fed into the first dust collection device, which is an electrostatic precipitator, to perform deep dust removal on the dust-containing exhaust gas and collect the second solid material; the first solid material and the second solid material are combined and sent to the downstream process.

[0077] Step S3: The calcium hydroxide solid material combined in step S2 is fed into a suspension decomposition device; the suspension decomposition device is a suspension calcination furnace; under the low temperature condition of 650℃, the material completes calcination decomposition in a suspension flow state, with a residence time of 30s; calcium hydroxide decomposes into calcium oxide and water vapor, obtaining a gas-solid mixture containing highly active calcium oxide.

[0078] Step S4: The gas-solid mixture obtained in step S3 is fed into the second gas-solid separation device; the second gas-solid separation device is a cyclone separator, which realizes the rapid separation of calcium oxide material and decomposition tail gas; the separated calcium oxide material is combined with the calcium oxide powder collected by the second dust collection device and sent into the multi-stage cyclone cooling device; the second dust collection device is a cyclone dust collector; the multi-stage cyclone cooling device consists of three cyclone tubes connected in series; the cooling air enters from the bottom of the end cyclone tube and comes into contact with the calcium oxide material in the opposite direction, and heat exchange occurs in the suspended flow state; after heat exchange and cooling, the high-activity calcium oxide product is collected, and the discharge temperature is 60℃.

[0079] Testing revealed that the highly active calcium oxide product prepared in this embodiment has a large specific surface area, high porosity, and significantly better reactivity than overburned calcium oxide raw material.

[0080] Comparative Example 1 This comparative example uses the same physical modification process as Example 1 to treat overburned calcium oxide. The specific operation is as follows: the overburned calcium oxide at a temperature of 1200℃ is naturally cooled to room temperature, and then fed into a ball mill for ultrafine grinding until the average particle size is comparable to the product obtained in Example 1.

[0081] Testing revealed that the internal structure of the milled product obtained in this comparative example remained dense, the pore structure was not effectively repaired, and the specific surface area and porosity were far lower than those of the product obtained in Example 1. The effect of improving the hydration reaction activity was extremely limited. Furthermore, the ball milling process consumed a large amount of electrical energy, resulting in poor economic efficiency.

[0082] Comparative Example 2 This comparative example uses the same high-temperature recalcination process as Example 2 to treat overburned calcium oxide. The specific operation is as follows: the overburned calcium oxide and limestone raw material are mixed at a mass ratio of 1:1 and then fed into a rotary kiln for secondary calcination at a high temperature of 1200℃ for 2 hours, followed by natural cooling to room temperature.

[0083] Testing revealed that the calcium oxide grains in the product obtained in this comparative example underwent further sintering and growth, resulting in increased structural density. The specific surface area and porosity were not only not improved, but were actually lower than those of the overburned calcium oxide raw material, leading to a further decrease in activity. At the same time, the secondary high-temperature calcination consumed a large amount of fuel, and the waste heat of the material was not recovered and utilized, resulting in production energy consumption far exceeding that of Example 2.

[0084] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0085] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing active calcium oxide from high-temperature overburned calcium oxide, characterized in that, Includes the following steps: S1. After cooling the overheated calcium oxide to a preset temperature, it undergoes a digestion reaction with atomized water or steam to generate a gas-solid mixture of calcium hydroxide; S2. Perform gas-solid separation on the gas-solid mixture obtained in step S1 to obtain a first solid material and dust-containing exhaust gas. Then, perform deep dust removal on the dust-containing exhaust gas to collect and obtain a second solid material. Combine the first solid material and the second solid material. S3. The solid material combined in step S2 is fed into a suspension decomposition device and calcined and decomposed under low temperature conditions to obtain a gas-solid mixture containing highly active calcium oxide. S4. Perform gas-solid separation on the gas-solid mixture containing highly active calcium oxide obtained in step S3. Combine the separated calcium oxide material with the calcium oxide powder collected by deep dust removal and send it into a multi-stage cyclone cooling device to exchange heat with the counter-flowing cooling air in a suspended flow state. After cooling, the highly active calcium oxide product is obtained.

2. The method according to claim 1, characterized in that, In step S1, the feeding temperature of the high-temperature overburned calcium oxide is 800℃~1200℃, and the preset temperature after cooling is 550~700℃; the temperature of the digestion reaction is controlled at 200℃~500℃.

3. The method according to claim 1 or 2, characterized in that, In step S1, the amount of atomized water or steam introduced is 1.0 to 1.5 times the theoretical water required for the complete hydration of the high-temperature overburned calcium oxide.

4. The method according to claim 1, characterized in that, In step S3, the suspended decomposition device is a suspended calcining furnace or a fluidized bed reactor; the low temperature condition is 500℃~800℃, and the residence time of the material in the suspended decomposition device is 5s~60s.

5. The method according to claim 1, characterized in that, It also includes a heat recovery step: A portion of the digestion exhaust gas discharged after deep dust removal in step S2 is used to cool the high-temperature overburned calcium oxide in step S1 in order to recover its sensible heat. Part of the decomposition tail gas discharged after gas-solid separation in step S4 is introduced into the suspension decomposition device in step S3 as an auxiliary heat source to participate in the calcination decomposition reaction.

6. The method according to claim 1, characterized in that, In step S4, the multi-stage cyclone cooling device includes at least two cyclone tubes connected in series, and the discharge temperature of the highly active calcium oxide product after cooling is not higher than 100°C.

7. A system for implementing the method according to any one of claims 1 to 6, characterized in that, include: The primary cooling device is used to cool the overheated calcium oxide at high temperature to a preset temperature; A digestion device is used to react cooled calcium oxide with atomized water or steam to produce a gas-solid mixture of calcium hydroxide. The first gas-solid separation device and the first dust collection device are used for gas-solid separation and deep dust removal of the calcium hydroxide gas-solid mixture; The suspension decomposition device has its inlet connected to the discharge port of the first gas-solid separation device and the dust discharge port of the first dust collection device. It is used to calcine and decompose calcium hydroxide in a suspension state at low temperature to generate a highly active calcium oxide gas-solid mixture. The second gas-solid separation device and the second dust collection device are used to perform gas-solid separation and deep dust removal on the highly active calcium oxide gas-solid mixture. The multi-stage cyclone cooling device has its inlet connected to the discharge port of the second gas-solid separation device and the dust discharge port of the second dust collection device, and is used to perform suspension heat exchange cooling on calcium oxide material through counter-flowing cooling air.

8. The system according to claim 7, characterized in that, The digestion device is any one of a suspension digester, a stirred digester, or a spray digester.

9. The system according to claim 7, characterized in that, The air outlet of the first dust collection device is connected to the hot air inlet of the primary cooling device through a pipe to utilize the waste heat from the digestion exhaust gas to cool the high-temperature overburned calcium oxide; the air outlets of the second dust collection device and the primary cooling device are connected to the hot air inlet of the suspended decomposition device through pipes to recover waste heat for auxiliary decomposition reaction.

10. The system according to claim 7, characterized in that, The multi-stage cyclone cooling device consists of two or more cyclone cooling devices connected in series. A material communication pipe and an airflow communication pipe are provided between adjacent two-stage cyclone cooling devices to achieve countercurrent contact heat exchange between cooling air and calcium oxide material.

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