A two-stage calcination and carbon dioxide recovery system and process for magnesite

Abstract

The application discloses a magnesite two-stage calcination and carbon dioxide recovery system and process, relates to the technical field of efficient utilization of magnesite, and aims to solve the problem of how to realize efficient and low-consumption calcination of high-quality magnesia and efficient recovery of carbon dioxide in a same process system. A rotary kiln is arranged in a rotary kiln combustion chamber, and the combustion chamber is used for heating the outer wall of the rotary kiln by gaseous fuel; the outlet end of the rotary kiln is communicated with a gas-solid separation chamber; magnesite powder is decomposed in the rotary kiln to generate carbon dioxide gas, which is led out by an induced draft fan through the gas-solid separation chamber, and micro-negative pressure in the kiln is maintained. High-temperature dust-containing carbon dioxide enters a downstream A1 carbon dioxide cyclone gas-solid separator for gas-solid separation. After heat exchange, cooling and dust removal, the high-temperature gas is transported to a carbon dioxide liquefaction and solidification treatment system; the solid material outlet of the gas-solid separation chamber is connected to the feeding port of a suspension decomposition furnace through a high-temperature airtight conveying device, and a decomposition furnace main combustion chamber is arranged at the bottom of the suspension decomposition furnace.

Description

Technical Field

[0001] This invention relates to the technical field of efficient utilization of magnesite, specifically a two-stage calcination system and process for magnesite and synergistic carbon dioxide recovery. Background Technology

[0002] Magnesium oxide is an important inorganic chemical product, widely used as a core raw material for refractory materials to manufacture the linings of high-temperature industrial kilns. It also has important applications in environmental protection, agriculture, and building materials, such as soil improvement, animal feed additives, and magnesium cementing materials.

[0003] Currently, magnesium oxide is mainly prepared by calcining magnesite. Traditional methods often employ single calcination equipment, such as an externally combusted rotary kiln (e.g., reference document 1: CN106082715B) or a fluidized bed pyrolysis furnace (e.g., reference document 2: CN110526597B). D1 discloses a method for preparing lightly calcined magnesium oxide using an externally combusted rotary kiln. By controlling parameters such as the wind speed of the primary and secondary air, calcination temperature, and time, the hydration activity and loss on ignition of lightly calcined magnesium oxide are improved. However, this method still has the following problems: the rotary kiln combustion chamber needs to maintain an extremely high temperature (1200℃-1300℃), which easily leads to severe wear of the kiln's refractory material and a short equipment lifespan during long-term operation; carbon dioxide is not effectively recovered and is directly emitted into the atmosphere, causing resource waste and environmental pollution; heat loss and energy consumption are also increased. D2 proposes a fluidized bed pyrolysis method for preparing lightly calcined magnesium oxide, utilizing a high-temperature carbon dioxide gas flow to achieve rapid pyrolysis, and then reforming the carbon dioxide produced by pyrolysis with methane to produce methanol, achieving preliminary utilization of carbon resources. First, large-scale electrically heated fluidized beds are extremely rare in industrial applications. Their heating efficiency, temperature uniformity, and long-term operational stability are difficult to match the continuous and high-capacity requirements of industrial applications, and cannot meet the actual application needs of large-scale industrial production lines. Moreover, the cost of electric heating is high. Carbon dioxide recovery depends on subsequent chemical conversion, and the market demand for methanol is limited.

[0004] Therefore, there is an urgent need in this field for an integrated system and process that can efficiently calcine magnesite to produce high-quality magnesium oxide and achieve efficient carbon dioxide recovery and resource utilization. Summary of the Invention

[0005] To address the aforementioned problems, namely the issues raised in the background technology, this invention proposes a two-stage calcination and carbon dioxide co-recovery system and process for magnesite, comprising a raw material preheating cyclone, the discharge end of which is connected to a rotary kiln maintaining a slight negative pressure, the rotary kiln being installed in the combustion chamber of the rotary kiln, and the combustion chamber of the rotary kiln being heated by gaseous fuel to heat the outer wall of the rotary kiln.

[0006] The rotary kiln's outlet is connected to a gas-solid separation chamber. The gas outlet of the gas-solid separation chamber is subjected to negative pressure by an induced draft fan, which transports dust-laden high-temperature carbon dioxide to the A1 carbon dioxide cyclone separator. The high-temperature gas captured by the A1 carbon dioxide cyclone separator is cooled and dust-removed by a heat exchange mechanism before being transported to the carbon dioxide liquefaction and solidification treatment system. The solid material outlet of the gas-solid separation chamber is connected to the feed inlet of the suspension decomposition furnace via a high-temperature sealed conveying device. The main combustion chamber of the decomposition furnace is installed at the bottom of the suspension decomposition furnace, and the top of the suspension decomposition furnace is connected to the C3 cyclone separator via a gooseneck pipe. The solid material outlet of the C3 cyclone separator is connected to the feed end of the multi-stage cooling mechanism, and the discharge end of the multi-stage cooling mechanism is connected to the clinker finished product warehouse.

[0007] A further provision of the present invention is that a pressure sensor is installed inside the rotary kiln to collect the pressure difference between the inside of the rotary kiln and the external atmospheric pressure in real time. The pressure sensor signal is transmitted to an external PLC system. The PLC system outputs a command according to the pressure difference and changes the rotation speed by adjusting the frequency of the inverter of the induced draft fan so that the rotary kiln maintains a slightly negative pressure state.

[0008] A further configuration of the present invention is as follows: the heat exchange mechanism includes an A2 heat exchanger, the gas inlet of the A2 heat exchanger is connected to the gas outlet of the A1 carbon dioxide cyclone separator, the cold air inlet of the A2 heat exchanger is connected to a blower, the hot air outlet of the A2 heat exchanger is connected to the air inlet of the rotary kiln combustion chamber, the gas outlet of the A2 heat exchanger is connected to a dust collection bag, the gas outlet of the dust collection bag is connected to an induced draft fan, the outlet end of the induced draft fan is sequentially connected to a water-cooled cooling device and a booster fan, and the outlet end of the booster fan transports the cooled and dust-removed carbon dioxide to the carbon dioxide liquefaction and solidification treatment system.

[0009] A further configuration of the present invention is as follows: the multi-stage cooling mechanism includes a C3 cyclone outlet, an L1 cyclone cooler, an L2 cyclone cooler, and an L3 cyclone cooler connected in sequence; the high-temperature clinker collected by the C3 cyclone is conveyed to the inlet pipe of the L1 cyclone cooler by a high-temperature feeder for the first stage of gas-solid heat exchange cooling; the material cooled by the L1 cyclone cooler is conveyed to the inlet pipe of the L2 cyclone cooler by a medium-temperature feeder for the second stage of gas-solid heat exchange cooling; the material cooled by the L2 cyclone cooler is conveyed to the inlet pipe of the L3 cyclone cooler by a low-temperature feeder for the third stage of gas-solid heat exchange cooling; the cooled clinker separated and collected by the L3 cyclone cooler is sent to the finished product warehouse through downstream conveying equipment.

[0010] A further feature of the present invention is that it also includes a high-temperature gas recovery circuit, wherein the rotary kiln combustion chamber is provided with a gas outlet and is connected to the suspension decomposition furnace through a high-temperature pipeline, and the high-temperature gas is used as an auxiliary heat source for the decomposition furnace.

[0011] In the medium-temperature heat exchange circuit, the gas outlet of the C3 cyclone is connected to a multi-tube cooler. The multi-tube cooler is divided into a hot air channel and a combustion air channel that are not interconnected by heat exchange elements. The hot air channel is connected to the gas outlet of the C3 cyclone and the gas inlet of the raw material preheating cyclone to preheat the raw material. One end of the combustion air channel is provided with a cold air inlet, and the other end is provided with a preheated air outlet. The preheated air outlet is connected to the gas inlet of the rotary kiln combustion chamber through a pipeline.

[0012] In the heat exchange circuit of the main combustion chamber of the decomposition furnace, the low-temperature gas discharged from the gas outlet of the L1 cyclone cooler is led to the main combustion chamber of the decomposition furnace through a pipeline.

[0013] A further provision of the present invention is that the gaseous fuel is fuel gas or natural gas.

[0014] A further configuration of the present invention includes a feeding mechanism, an iron removal mechanism, and a drying and dispersing machine connected in sequence. The feeding mechanism includes a feeding hopper and a belt scale located below its outlet for feeding and metering materials. The iron removal mechanism is located downstream of the belt scale for removing metal impurities from the materials. The drying and dispersing machine is located downstream of the iron removal mechanism for drying and dispersing the materials. The raw material preheating cyclone includes a C1 cyclone and a C2 cyclone. The outlet of the drying and dispersing machine is connected to the inlet of the C1 cyclone via a pipe, and the outlet of the C1 cyclone is connected to the inlet of the C2 cyclone. The outlet of the C2 cyclone is connected to the feed end of the rotary kiln for feeding the preheated materials into the kiln for subsequent processing.

[0015] A further embodiment of the present invention is that the carbon dioxide liquefaction and solidification treatment system includes: at least one pretreatment unit for filtering and / or adsorbing and purifying carbon dioxide gas; a compression and condensation unit consisting of one or more compressors and condensers for liquefying carbon dioxide gas; and an optional distillation unit for further purifying liquid carbon dioxide, or a solidification unit for converting liquid carbon dioxide into solid dry ice.

[0016] A process for a two-stage calcination and carbon dioxide co-recovery system for magnesite includes the following steps:

[0017] S1. Magnesite raw material is preheated by raw material preheating cyclone and then conveyed to a rotary kiln that dynamically maintains a slight negative pressure.

[0018] S2. Under the indirect radiant heat of 950-1000℃ provided by the rotary kiln combustion chamber, the temperature inside the rotary kiln is maintained at 650-700℃ for a pre-decomposition, generating partially decomposed intermediate products and gas with a carbon dioxide concentration ≥75 vol%.

[0019] S3. The high-temperature gas generated by the pre-decomposition enters the gas-solid separation chamber from the rotary kiln outlet for preliminary separation. The separated dust-laden gas is transported to the A1 carbon dioxide cyclone separator by an induced draft fan for efficient collection. The resulting high-temperature gas enters the heat exchange mechanism.

[0020] S4. The high-temperature gas flows sequentially through the A2 heat exchanger to recover waste heat, through the dust collection bag to remove dust, and through the water cooling device to cool down. Then, it is transported by the booster fan to the carbon dioxide liquefaction and solidification treatment system for resource recovery.

[0021] S5. The intermediate product separated from the gas-solid separation chamber is sent to the suspension decomposition furnace via a high-temperature sealed conveying device. At the same time, gaseous fuel is introduced through the gaseous fuel nozzle set in the main combustion chamber of the decomposition furnace to form a high-temperature flame. The high-temperature gas generated in the rotary kiln combustion chamber is introduced into the main combustion chamber of the decomposition furnace as an auxiliary heat source and gas source. The intermediate product comes into direct contact with the high-temperature flame and undergoes an instantaneous fluidized calcination reaction, completing the final decomposition at 1100-1200℃.

[0022] S6. The material calcined in the suspension decomposition furnace rises with the airflow to the gooseneck tube and enters the C3 cyclone separator for gas-solid separation. The separated medium-temperature gas is introduced to the raw material preheating cyclone separator as a heat source to preheat the raw material.

[0023] The solid high-temperature magnesium oxide clinker separated by the S7 and C3 cyclones enters a multi-stage cooling mechanism, including multi-stage gas-solid heat exchange cooling through the L1 cyclone cooler, L2 cyclone cooler and L3 cyclone cooler in sequence. The finally cooled clinker is transported to the finished product warehouse.

[0024] The beneficial technical effects of this invention are as follows:

[0025] 1. It solves the equipment wear and tear problem caused by high-temperature calcination in a single rotary kiln. By dividing the calcination process into two stages, namely the pre-decomposition in the rotary kiln (650~700℃) and the final decomposition in the suspension decomposition furnace (1100~1200℃), the temperature load of the rotary kiln section is significantly reduced, and the service life of the equipment is extended.

[0026] 2. It achieves efficient recovery and resource utilization of carbon dioxide. By setting up units such as gas-solid separation, high-temperature gas purification, and liquefaction and solidification, the carbon dioxide generated during calcination is captured and liquefied, which can be used to prepare food-grade carbon dioxide or dry ice, with a high degree of resource utilization.

[0027] 3. Improve system energy efficiency and carbon dioxide recovery rate through micro-negative pressure control. Dynamic micro-negative pressure control is adopted in the rotary kiln to avoid gas leakage or air intrusion. This not only protects the stability of the atmosphere in the kiln, but also improves the carbon dioxide capture efficiency, making up for the problem of decreased recovery rate caused by carbon dioxide dispersion in two-stage calcination.

[0028] 4. It achieves cascade utilization of thermal energy, with high system energy efficiency. Through multi-stage gas recovery loops, the waste heat at each stage is used for preheating raw materials and combustion chambers, significantly reducing external energy consumption.

[0029] 5. The process has a high degree of integration and is suitable for continuous industrial production. The system is compact and the units work together to ensure the product quality of light-burned magnesium oxide and realize the continuous recovery and utilization of carbon dioxide, which meets the requirements of green manufacturing and circular economy.

[0030] In summary, this invention overcomes the problems of poor economic efficiency and difficulty in industrialization caused by the reliance on electrical energy and complex chemical processes in existing technical solutions, and provides a brand-new solution based on mature equipment, reasonable energy utilization, and flexible and efficient CO2 recovery path. Attached Figure Description

[0031] Figure 1 A schematic diagram of the overall structure of the present invention is shown.

[0032] Figure 2 A schematic diagram of a carbon dioxide liquefaction and solidification treatment system is shown.

[0033] Figure reference numerals: 1. Raw material preheating cyclone separator; 2. Rotary kiln; 3. Rotary kiln combustion chamber; 4. Gas-solid separation chamber; 5. Induced draft fan; 6. A1 carbon dioxide cyclone separator; 7. Suspension decomposition furnace; 8. Decomposition furnace main combustion chamber; 9. C3 cyclone separator; 10. A2 heat exchanger; 11. Blower; 12. Dust collection bag; 13. Water cooling device; 14. Booster fan; 15. L1 cyclone cooler; 16. L2 cyclone cooler; 17. L3 cyclone cooler; 18. Multi-tube cooler. Detailed Implementation

[0034] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0035] This invention proposes a two-stage calcination and carbon dioxide co-recovery system for magnesite, including a raw material preheating cyclone 1. The discharge end of the raw material preheating cyclone 1 is connected to a rotary kiln 2 that maintains a slight negative pressure. The rotary kiln 2 is installed in a rotary kiln combustion chamber 3. The rotary kiln combustion chamber 3 heats the outer wall of the rotary kiln 2 with gaseous fuel, gas, or natural gas.

[0036] The outlet of the rotary kiln 2 is connected to the gas-solid separation chamber 4. The gas outlet of the gas-solid separation chamber 4 is subjected to negative pressure by an induced draft fan 5, which transports dust-laden high-temperature carbon dioxide to the A1 carbon dioxide cyclone separator 6. The high-temperature gas captured by the A1 carbon dioxide cyclone separator 6 is cooled and dust-removed by a heat exchange mechanism before being transported to the carbon dioxide liquefaction and solidification treatment system. The solid material outlet of the gas-solid separation chamber 4 is connected to the feed inlet of the suspension decomposition furnace 7 via a high-temperature sealed conveying device. The bottom of the suspension decomposition furnace 7 integrates the main combustion chamber 8 of the decomposition furnace. Because the material is suspended in the hot airflow, the contact area with the airflow is greatly increased, resulting in extremely fast heat transfer speed and high heat transfer efficiency. At the same time, the raw material powder and fuel are uniformly mixed in a suspended state, which can be rapidly decomposed, greatly improving production efficiency and thermal efficiency. The top of the suspension decomposition furnace 7 is connected to the C3 cyclone 9 via a gooseneck tube. The solid material outlet of the C3 cyclone 9 is connected to the feed end of the multi-stage cooling mechanism, and the discharge end of the multi-stage cooling mechanism is connected to the clinker finished product warehouse.

[0037] Gas inside rotary kiln 2 will not actively leak outwards, and external air will not actively enter the kiln, achieving "no spontaneous exchange of internal and external airflow." A pressure sensor is installed inside rotary kiln 2 to collect the pressure difference between the inside and outside atmospheric pressure in real time. The pressure sensor signal is transmitted to an external PLC system. The PLC system outputs instructions based on the pressure difference, adjusting the frequency of the induced draft fan 5 to change its rotational speed, thus maintaining a slightly negative pressure state in the rotary kiln. Specifically, the pressure sensor transmits the real-time pressure value to the PLC control system; the system compares the actual value with a set value range, calculates the deviation, and outputs instructions: if the real-time pressure is higher than the preset upper limit, the frequency of the induced draft fan is increased to increase the suction force, causing the pressure inside the kiln to drop. If the real-time pressure is lower than the preset lower limit, the frequency of the induced draft fan is decreased to reduce the suction force, causing the pressure inside the kiln to rise again.

[0038] The heat exchange mechanism includes an A2 heat exchanger 10. The gas inlet of the A2 heat exchanger 10 is connected to the gas outlet of the A1 carbon dioxide cyclone separator 6. The cold air inlet of the A2 heat exchanger 10 is connected to a blower 11. The hot air outlet of the A2 heat exchanger 10 is connected to the air inlet of the rotary kiln combustion chamber 3. The gas outlet of the A2 heat exchanger 10 is connected to a dust collection bag 12. The gas outlet of the dust collection bag 12 is connected to an induced draft fan 5. The outlet end of the induced draft fan 5 is sequentially connected to a water-cooled cooling device 13 and a booster fan 14. The outlet end of the booster fan 14 transports the cooled and dust-removed carbon dioxide to the carbon dioxide liquefaction and solidification treatment system.

[0039] The multi-stage cooling mechanism includes a C3 cyclone 9 discharge port, an L1 cyclone cooler 15, an L2 cyclone cooler 16, and an L3 cyclone cooler 17 connected in sequence. The high-temperature clinker collected by the C3 cyclone 9 is conveyed to the inlet pipe of the L1 cyclone cooler 15 by a high-temperature feeder for the first stage of gas-solid heat exchange cooling. The material cooled by the L1 cyclone cooler 15 is conveyed to the inlet pipe of the L2 cyclone cooler 16 by a medium-temperature feeder for the second stage of gas-solid heat exchange cooling. The material cooled by the L2 cyclone cooler 16 is conveyed to the inlet pipe of the L3 cyclone cooler 17 by a low-temperature feeder for the third stage of gas-solid heat exchange cooling. The cooled clinker separated and collected by the L3 cyclone cooler 17 is sent to the finished product warehouse through downstream conveying equipment.

[0040] It also includes a high-temperature gas recovery circuit. The rotary kiln combustion chamber 3 is equipped with a gas outlet and is connected to the suspension decomposition furnace 7 through a high-temperature pipeline, so that the high-temperature gas is used as an auxiliary heat source for the decomposition furnace.

[0041] In the medium-temperature heat exchange circuit, the gas outlet of the C3 cyclone 9 is connected to the multi-tube cooler 18. The multi-tube cooler 18 is divided into a hot air channel and a combustion air channel that are not interconnected by heat exchange elements. The hot air channel is connected to the gas outlet of the C3 cyclone 9 and the gas inlet of the raw material preheating cyclone 1 to preheat the raw material. One end of the combustion air channel is provided with a cold air inlet, and the other end is provided with a preheated air outlet. The preheated air outlet is connected to the gas inlet of the rotary kiln combustion chamber 3 through a pipe.

[0042] The medium-temperature gas discharged from the C3 cyclone 9 enters the hot air passage of the multi-tube cooler 18, where it undergoes indirect and efficient heat exchange with the cold air flowing through the combustion air passage. After passing through the hot air passage, the temperature of the medium-temperature gas drops significantly, and its residual heat is fully absorbed by the heat exchange elements. The cooled gas is then directed to the raw material preheating cyclone 1 as a preheating source for further utilization. Simultaneously, ambient-temperature combustion air supplied by the blower 11 enters the combustion air passage, where it is heated by the heat exchange elements and converted into high-temperature preheated air. This preheated air is then piped to the inlet of the rotary kiln combustion chamber 3 for use as combustion air. This process achieves efficient recovery of the gas temperature difference energy, significantly improving the overall thermal efficiency of the system and reducing external energy consumption during combustion.

[0043] The low-temperature gas discharged from the gas outlet of the L1 cyclone cooler 15 in the heat exchange circuit of the main combustion chamber of the decomposition furnace is led to the main combustion chamber 8 of the decomposition furnace through a pipeline.

[0044] It also includes a feeding mechanism, an iron removal mechanism, and a drying and dispersing machine connected in sequence. The feeding mechanism includes a feeding hopper and a belt scale located below its outlet for feeding and metering materials. The iron removal mechanism is located downstream of the belt scale for removing metal impurities from the materials. The drying and dispersing machine is located downstream of the iron removal mechanism for drying and dispersing the materials. The raw material preheating cyclone 1 includes a C1 cyclone and a C2 cyclone. The outlet of the drying and dispersing machine is connected to the inlet of the C1 cyclone through a pipe, and the outlet of the C1 cyclone is connected to the inlet of the C2 cyclone. The outlet of the C2 cyclone is connected to the feed end of the rotary kiln 2 for feeding the preheated materials into the kiln for subsequent processing.

[0045] The carbon dioxide liquefaction and solidification system includes: at least one pretreatment unit for filtering and / or adsorbing and purifying carbon dioxide gas; a compression and condensation unit consisting of one or more compressors and condensers for liquefying carbon dioxide gas; and an optional distillation unit for further purifying liquid carbon dioxide, or a solidification unit for converting liquid carbon dioxide into solid dry ice.

[0046] A two-stage calcination and carbon dioxide co-recovery process for magnesite includes the following steps: S1, the magnesite raw material is preheated by the raw material preheating cyclone 1 and then conveyed to the rotary kiln 2 which dynamically maintains a slight negative pressure.

[0047] S2. Under the indirect radiant heat of 950-1000℃ provided by the rotary kiln combustion chamber 3, the temperature inside the rotary kiln 2 is maintained at 650-700℃ for a pre-decomposition, generating partially decomposed intermediate products and gas with a carbon dioxide concentration ≥75 vol%.

[0048] S3. The high-temperature gas generated by the pre-decomposition enters the gas-solid separation chamber 4 from the outlet of the rotary kiln 2 for preliminary separation. The separated dust-laden gas is transported to the A1 carbon dioxide cyclone separator 6 by the induced draft fan 5 for efficient collection. The resulting high-temperature gas enters the heat exchange mechanism.

[0049] S4. The high-temperature gas flows sequentially through the A2 heat exchanger 10 to recover waste heat, the dust collection bag 12 to remove dust, and the water cooling device 13 to cool it. Then, it is transported by the booster fan 14 to the carbon dioxide liquefaction and solidification treatment system for resource recovery.

[0050] S5. The intermediate product separated from the gas-solid separation chamber 4 is sent to the suspension decomposition furnace 7 via a high-temperature sealed conveying device. At the same time, gaseous fuel is introduced through the gaseous fuel nozzle set in the main combustion chamber 8 of the decomposition furnace to form a high-temperature flame. The high-temperature gas generated in the rotary kiln combustion chamber 3 is introduced into the main combustion chamber 8 of the decomposition furnace as an auxiliary heat source and gas source. The intermediate product comes into direct contact with the high-temperature flame and undergoes an instantaneous fluidized calcination reaction, completing the final decomposition at 1100-1200℃.

[0051] S6, the material calcined in the suspension decomposition furnace 7 rises with the airflow to the gooseneck tube and enters the C3 cyclone 9 for gas-solid separation. The separated medium-temperature gas is led to the raw material preheating cyclone 1 as a heat source to preheat the raw material.

[0052] The solid high-temperature magnesium oxide clinker separated from S7 and C3 cyclone 9 enters a multi-stage cooling mechanism, including multi-stage gas-solid heat exchange cooling through L1 cyclone cooler 15, L2 cyclone cooler 16 and L3 cyclone cooler 17 in sequence, and finally the cooled clinker is transported to the finished product warehouse.

[0053] While the detailed connection methods between the various equipment in the two-stage calcination process of magnesite are well-known in the art, they are briefly described below for completeness. First, the raw magnesite, after preliminary crushing, screening, and drying / dispersing, is fed into the raw material preheating cyclone 1. In this preheater, the raw material undergoes thorough heat exchange with the cooling gas from the hot air passage of the multi-tube cooler 18, whose initial heat source is the medium-temperature gas discharged from the C3 cyclone 9, and is preheated to 300-350°C. This process not only significantly increases the raw material's furnace inlet temperature and reduces energy consumption in subsequent calcination processes, but also facilitates the pre-decomposition reaction of magnesite in the rotary kiln 2. After preheating, the heat exchange gas is treated by a dust collector bag and then discharged after exhaust gas purification.

[0054] The preheated magnesite enters a rotary kiln 2, which is placed inside a rotary kiln combustion chamber 3. In the combustion chamber 3, the introduced gaseous fuel burns with high-temperature air, generating high-temperature gas that heats the rotary kiln 2, causing the magnesite inside to decompose. The high-temperature gas produced by the reaction, along with the unreacted magnesite particles, enters a gas-solid separation chamber 4. After gas-solid separation is completed in the separation chamber 4, the high-temperature gas sequentially passes through an A1 carbon dioxide cyclone separator 6 for collection, an A2 heat exchanger 10 for preliminary heat exchange and cooling, a dust collection bag 12 for dust removal, and then a water-cooled cooling device 13 for deep cooling. Finally, it is transported by a booster fan 14 to a carbon dioxide liquefaction and solidification treatment system for purification and liquefaction solidification processing.

[0055] The solid intermediate products are rapidly fed from the gas-solid separation chamber 4 into the suspension decomposition furnace 7 via a high-temperature sealed conveyor. The design of the suspension decomposition furnace 7 ensures direct contact between the intermediate products and the high-temperature flame. This design promotes instantaneous fluidized bed calcination, allowing magnesite to complete its final decomposition in a very short time, generating high-temperature magnesia clinker. The high-temperature gas generated during decomposition, mixed with the magnesia clinker, is guided by a gooseneck tube into the C3 cyclone separator 9 for further gas-solid separation. The separated medium-temperature gas enters the multi-tube cooler 18, recovering waste heat for preheating combustion air and raw materials. After treatment by a dust collector bag, it is finally discharged through the exhaust system in compliance with standards.

[0056] Finally, the high-temperature magnesia clinker, sequentially cooled by gas-solid heat exchange in L1 cyclone cooler 15 and L2 cyclone cooler 16, not only experiences an effective temperature reduction but also ensures clinker quality through the fine processing of each stage of separators. The cooled clinker is then stored in L3 cyclone cooler 17 and subsequently transported to the finished product warehouse according to production needs, awaiting further processing or application. The design and operation of the entire system fully embodies the efficient and environmentally friendly concept of two-stage calcination of magnesite and synergistic recovery of carbon dioxide.

[0057] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0058] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, such that a process, article, or apparatus / device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to those processes, articles, or apparatus / devices.

[0059] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A two-stage calcination and carbon dioxide co-recovery system for magnesite, comprising a raw material preheating cyclone (1), characterized in that: The discharge end of the raw material preheating cyclone (1) is connected to the rotary kiln (2) which maintains a slight negative pressure. The rotary kiln (2) is installed in the rotary kiln combustion chamber (3), and the rotary kiln combustion chamber (3) heats the outer wall of the rotary kiln with gaseous fuel. The outlet of the rotary kiln (2) is connected to the gas-solid separation chamber (4). The gas outlet of the gas-solid separation chamber (4) forms a negative pressure through the induced draft fan (5) to transport the dust-laden high-temperature carbon dioxide to the A1 carbon dioxide cyclone separator (6). The high-temperature gas after gas-solid separation in the A1 carbon dioxide cyclone separator (6) is cooled and dust-removed by the heat exchange mechanism and then transported to the carbon dioxide liquefaction and solidification treatment system. The solid material outlet of the gas-solid separation chamber (4) is connected to the feed port of the suspension decomposition furnace (7) through a high-temperature sealed conveying device. The main combustion chamber (8) of the decomposition furnace is installed at the bottom of the suspension decomposition furnace (7). The top of the suspension decomposition furnace (7) is connected to the C3 cyclone (9) through a gooseneck pipe. The solid material outlet of the C3 cyclone (9) is connected to the feed end of the multi-stage cooling mechanism. The discharge end of the multi-stage cooling mechanism is connected to the finished product conveying equipment and transported to the clinker finished product warehouse. The heat exchange mechanism includes an A2 heat exchanger (10), the gas inlet of the A2 heat exchanger (10) is connected to the gas outlet of the A1 carbon dioxide cyclone separator (6), the cold air inlet of the A2 heat exchanger (10) is connected to a blower (11), the hot air outlet of the A2 heat exchanger (10) is connected to the air inlet of the rotary kiln combustion chamber (3), the gas outlet of the A2 heat exchanger (10) is connected to a dust collection bag (12), the gas outlet of the dust collection bag (12) is connected to an induced draft fan (5), the outlet end of the induced draft fan (5) is connected in sequence to a water-cooled cooling device (13) and a booster fan (14), the outlet end of the booster fan (14) transports the cooled and dust-removed carbon dioxide to the carbon dioxide liquefaction and solidification treatment system; The carbon dioxide liquefaction and solidification system includes: at least one pretreatment unit for filtering and / or adsorbing and purifying carbon dioxide gas; a compression and condensation unit consisting of one or more compressors and condensers for liquefying carbon dioxide gas; and an optional distillation unit for further purifying liquid carbon dioxide, or a solidification unit for converting liquid carbon dioxide into solid dry ice.

2. The magnesite two-stage calcination and carbon dioxide co-recovery system according to claim 1, characterized in that: The rotary kiln (2) is equipped with a pressure sensor for real-time acquisition of the pressure difference between the inside and outside atmospheric pressure. The pressure sensor signal is transmitted to an external PLC system. The PLC system outputs instructions based on the pressure difference and adjusts the frequency of the induced draft fan (5) to change the rotation speed so that the rotary kiln maintains a slightly negative pressure state.

3. The magnesite two-stage calcination and carbon dioxide co-recovery system according to claim 1, characterized in that: The multi-stage cooling mechanism includes the discharge port of C3 cyclone (9), L1 cyclone cooler (15), L2 cyclone cooler (16) and L3 cyclone cooler (17) connected in sequence; the high-temperature clinker collected by C3 cyclone (9) is conveyed to the inlet pipe of L1 cyclone cooler (15) by a high-temperature feeder for the first stage of gas-solid heat exchange cooling, and the material cooled by L1 cyclone cooler (15) is conveyed to the inlet pipe of L2 cyclone cooler (16) by a medium-temperature feeder for the second stage of gas-solid heat exchange cooling; The material cooled by the L2 cyclone cooler (16) is conveyed by the low temperature feeder to the inlet pipe of the L3 cyclone cooler (17) for the third stage of gas-solid heat exchange cooling; the cooled clinker collected by the L3 cyclone cooler (17) is sent to the finished product warehouse through the downstream conveying equipment.

4. The magnesite two-stage calcination and carbon dioxide co-recovery system according to claim 3, characterized in that: It also includes a high-temperature gas recovery circuit. The rotary kiln combustion chamber (3) is equipped with a gas outlet and is connected to the suspension decomposition furnace (7) through a high-temperature pipeline, so that the high-temperature gas is used as an auxiliary heat source for the decomposition furnace. In the medium-temperature heat exchange circuit, the gas outlet of the C3 cyclone (9) is connected to the multi-tube cooler (18). The multi-tube cooler (18) is separated into a hot air channel and a combustion air channel that are not connected to each other by heat exchange elements. The hot air channel is connected to the gas outlet of the C3 cyclone (9) and the gas inlet of the raw material preheating cyclone (1) to preheat the raw material. One end of the combustion air channel is provided with a cold air inlet, and the other end is provided with a preheated air outlet. The preheated air outlet is connected to the gas inlet of the rotary kiln combustion chamber (3) through a pipe. The medium-low temperature gas discharged from the gas outlet of the L1 cyclone cooler (15) in the heat exchange circuit of the main combustion chamber of the decomposition furnace is led to the main combustion chamber (8) of the decomposition furnace through a pipeline.

5. The magnesite two-stage calcination and carbon dioxide co-recovery system according to claim 1, characterized in that: The gaseous fuel is either fuel gas or natural gas.

6. The magnesite two-stage calcination and carbon dioxide co-recovery system according to claim 1, characterized in that: The system includes a feeding mechanism, an iron removal mechanism, and a drying and dispersing machine connected in sequence. The feeding mechanism includes a feeding hopper and a belt scale located below its outlet for feeding and metering materials. The iron removal mechanism is located downstream of the belt scale for removing metal impurities from the materials. The drying and dispersing machine is located downstream of the iron removal mechanism for drying and dispersing the materials. The raw material preheating cyclone (1) includes a C1 cyclone and a C2 cyclone. The outlet of the drying and dispersing machine is connected to the inlet of the C1 cyclone through a pipe, and the outlet of the C1 cyclone is connected to the inlet of the C2 cyclone. The outlet of the C2 cyclone is connected to the feed end of the rotary kiln (2) for feeding the preheated materials into the kiln for subsequent processing.

7. A process using the magnesite two-stage calcination and carbon dioxide co-recovery system according to any one of claims 1-6, characterized in that: Includes the following steps: S1. Magnesite raw material is preheated by raw material preheating cyclone (1) and then transported to rotary kiln (2) which dynamically maintains a slight negative pressure. S2. Under the indirect radiant heat of 950-1000℃ provided by the rotary kiln combustion chamber (3), the temperature inside the rotary kiln (2) is maintained at 650-700℃ for a period of pre-decomposition, generating partially decomposed intermediate products and gas with a carbon dioxide concentration ≥75vol%. S3. The high-temperature gas generated by the pre-decomposition enters the gas-solid separation chamber (4) from the outlet of the rotary kiln (2) for preliminary separation. The separated dust-laden gas is transported to the A1 carbon dioxide cyclone separator (6) by the induced draft fan (5) for efficient collection. The obtained high-temperature gas enters the heat exchange mechanism. S4. The high-temperature gas flows sequentially through the A2 heat exchanger (10) to recover waste heat, through the dust collection bag (12) to remove dust, and through the water cooling device (13) to cool it. Then, it is transported by the booster fan (14) to the carbon dioxide liquefaction and solidification treatment system for resource recovery. S5. The intermediate product separated in the gas-solid separation chamber (4) is sent to the suspension decomposition furnace (7) through a high-temperature sealed conveying device. At the same time, gaseous fuel is introduced through the gaseous fuel nozzle set in the main combustion chamber (8) of the decomposition furnace to form a high-temperature flame. The high-temperature gas generated in the rotary kiln combustion chamber (3) is also introduced into the main combustion chamber (8) of the decomposition furnace as an auxiliary heat source and gas source. The intermediate product comes into direct contact with the high-temperature flame and undergoes an instantaneous fluidized calcination reaction, completing the final decomposition at 1100-1200℃.

8. The two-stage calcination and carbon dioxide co-recovery process for magnesite according to claim 7, characterized in that: It also includes the following steps: S6, Suspension decomposition furnace (7) The calcined material rises with the airflow to the gooseneck tube and enters the C3 cyclone (9) for gas-solid separation. The separated medium-temperature gas is led to the raw material preheating cyclone (1) as a heat source to preheat the raw material. The solid high-temperature magnesium oxide clinker separated by the S7 and C3 cyclone separators (9) enters a multi-stage cooling mechanism, including multi-stage gas-solid heat exchange cooling through the L1 cyclone cooler (15), L2 cyclone cooler (16) and L3 cyclone cooler (17) in sequence. The finally cooled clinker is transported to the finished product warehouse.

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