System and process for carrying out suspension roasting on carbonate and co-producing CO2 by using external combustion furnace

Abstract

The invention discloses a system and a process for suspension roasting of carbonate and co-production of CO2 by using an external combustion furnace. The system comprises a suspension preheating system, a suspension cooling system, an external combustion type roasting furnace, a CO2 catcher and a waste heat utilization system, according to the method, high-purity CO2 gas can be co-produced while carbonate is roasted, the external combustion type roasting system is adopted for indirectly heating circulating waste gas containing CO2 to provide heat for the suspension roasting system and the suspension preheating system, raw materials are fully preheated, and the decomposition rate of carbonate and the purity of products are guaranteed; cO2-containing waste gas generated by fuel combustion and carbonate decomposition is cyclically enriched in the production system, one part of high-concentration CO2 waste gas is collected and purified by the carbon capture system, and the other part of the high-concentration CO2 waste gas is returned to the roasting furnace to be reheated and recycled, so that zero emission of CO2 generated by carbonate decomposition is realized; the method is simple and convenient in production process, high in automation degree, convenient to operate and maintain, high in carbonate decomposition rate, high in product activity and stable in quality.

Description

Technical Field

[0001] The present invention relates to the technical field of non-metallic mineral processing, and in particular to a system and process for suspended roasting of carbonate and co-production of CO2 using an external combustion furnace. Background Art

[0002] Carbonates are formed by the interaction of metal cations with carbonate ([CO3] 2- ) are salts combined with minerals, which are diverse and widely distributed. The most common carbonate metal cations in industry include elements such as calcium, magnesium, iron, and zinc. They are typically calcined to produce the corresponding solid metal oxides, while also producing gaseous CO2. These metal oxides are widely used in the chemical industry, metallurgy, building materials, papermaking, and environmental protection. CO2, as a high-quality raw material with high application value, is widely used in oil extraction, artificial rainfall, food production, agricultural production, and other fields.

[0003] Currently, kilns commonly used for carbonate calcination include vertical kilns, rotary kilns, and suspension kilns. Vertical kilns are suitable for bulk materials with a particle size of 40mm to 300mm. The larger the particle size, the less stable the product quality, and they struggle to process small and powdered materials. Rotary kilns have a wider range of particle sizes, but single kilns require long preheating times, direct flame contact with the material can easily overburn, require extensive equipment space, and consume high energy. In sleeve-type rotary kilns, fuel is burned in the inner tube, with heat transfer from the tube wall indirectly heating the material within the outer tube. While this method avoids overburning and low CO2 concentrations in the flue gas, it also consumes a lot of energy, causes significant wear on the furnace material, and is difficult to maintain and expensive. Suspension kilns are suitable for powdered materials and have the advantages of short reaction time, high product activity, and large single-unit processing capacity. Studies have shown that the decomposition time of limestone with a particle size of 100μm at 950℃ is less than 1s. However, this process uses hot flue gas after fuel combustion as the heat source for direct contact heat exchange with the material in the furnace. The CO2 after carbonate decomposition is mixed with combustion flue gas and excess hot air, resulting in low CO2 concentration, difficulty and high cost in separation and purification, and direct emission causes carbon emissions and other problems.

[0004] Traditional carbonate suspension calcination usually places the burner in the kiln and uses the hot flue gas generated by fuel combustion as the heat source for direct heating and calcination. Considering the high-temperature flue gas denitrification measures, the flue gas contains not only a large amount of dust and low-concentration CO2, but also trace amounts of CO, SO2, and NO. x NH3 is typically discharged directly into the atmosphere after waste heat utilization and dust removal, resulting in resource waste and carbon emissions. Furthermore, using coal as a fuel can lead to the inclusion of coal ash or even unburned coal powder in the product, affecting product purity. While using natural gas as a fuel can improve product purity, it is costly. Therefore, capturing and purifying CO2 while ensuring high-purity products from carbonate decomposition has significant research value and application prospects. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a system and process for suspended roasting of carbonates in an external combustion furnace and co-production of CO2, thereby obtaining a high-purity product and achieving near-zero CO2 emissions.

[0006] The technical solution adopted in the present invention is: A system for suspended roasting of carbonate and co-production of CO2 using an external combustion furnace, comprising a suspension preheating system, a suspension cooling system, an external combustion roasting furnace, a CO2 collector and a waste heat utilization system; The suspension preheating system includes at least four stages of cyclone preheaters, the air outlet ducts of each stage of the cyclone preheater are connected in sequence from bottom to top, and the bottom discharge ports of each stage of the cyclone preheater are connected to the corresponding air outlet ducts from top to bottom according to the single and double stages; The suspension cooling system includes at least four stages of suspension coolers, the air inlet of the first stage suspension cooler is respectively connected to the air outlet of the high-temperature fan and the bottom discharge port of the last stage cyclone preheater, the air outlet of the first stage suspension cooler is connected to the air inlet of the external combustion roasting furnace, the air inlet of the last stage suspension cooler is connected to the ambient air, the air outlet duct of the last stage suspension cooler is connected to the air outlet ducts of the remaining stages of suspension coolers except the first stage suspension cooler in sequence from bottom to top; the bottom discharge ports of the suspension coolers at each stage are respectively connected to the corresponding air outlet ducts from top to bottom according to the single and double stages; The external combustion roasting furnace is provided with a material air flow outlet at the top, a material feed port at the upper constriction, an air inlet at the lower constriction, a combustion flue gas outlet at the upper part of the furnace body, a combustion air inlet at the lower part of the furnace body, and a material discharge port at the bottom; the material air flow outlet is connected to the air inlet of the last stage cyclone preheater, and the material feed port is connected to the material discharge port at the bottom of the penultimate stage cyclone preheater; The waste heat utilization system includes two heat exchangers, the air inlet of the first heat exchanger is connected to the air outlet duct of the first-stage cyclone preheater, and the air outlet of the first heat exchanger is connected to the air inlet of the high-temperature fan; the air inlet of the second heat exchanger is connected to the air outlet duct of the second-stage suspension cooler and the combustion flue gas outlet on the side of the external-fired roasting furnace; the air outlet of the second heat exchanger is connected to the purification dust collector; The air outlet at the upper end of the CO2 collector is connected to the purification dust collector, the air inlet is connected to the air outlet of the high-temperature fan, and the bottom is the CO2 product outlet.

[0007] Specifically, the external-fired roasting furnace is evenly equipped with several inner sleeves in the furnace body as airflow heating areas and CO2 inlet and outlet channels. The two ends of the inner sleeves are respectively connected to the upper and lower constrictions of the furnace body. The internal space of the furnace body outside the inner sleeves is the fuel combustion area. At least two groups of staggered burners are arranged in the vertical direction of the furnace body in the fuel combustion area.

[0008] More specifically, the burner fuel is hydrogen, coal or natural gas.

[0009] Specifically, the air outlet of the second-stage suspension cooler is also connected to the combustion air inlet of the external-fired roasting furnace.

[0010] Specifically, an exhaust fan and a chimney are provided at the rear side of the purification dust collector.

[0011] Specifically, the discharge ports of the cyclone preheaters at various levels of the suspension preheating system, the discharge ports of the suspension coolers at various levels of the suspension cooling system, and the material discharge port of the external combustion roasting furnace are all provided with heavy hammer flap lock air valves.

[0012] Specifically, the lower side of the discharge port of the last-stage suspension cooler is connected to the feed port of the chain scraper conveyor.

[0013] A process for suspended roasting of carbonates and co-production of CO2 using an external combustion furnace, comprising the following steps: S1: Keep the chain scraper conveyor, waste heat utilization system, and CO2 collector closed; turn on the high-temperature fan, purification dust collector, and exhaust fan; open the electric butterfly valve at the air inlet of the first-stage suspension cooler as an air supply valve; turn on the external combustion roasting furnace to bake the furnace, creating conditions for the normal operation of the entire suspension preheating system; S2: When the temperature of the suspension preheating system reaches 250℃, the feeding condition is met. At this time, the chain scraper conveyor and the waste heat utilization system are first turned on, and then a small amount of particle size D is added to the air outlet pipe of the second stage cyclone preheater. 80 Powdered carbonate raw materials with a diameter of less than 80 μm are burned in an externally fired roaster to heat the circulating enriched CO2-containing exhaust gas. The CO2 collector is kept closed while gradually increasing the feed rate until reaching the production capacity. S3: After reaching full production and normal operation, the CO2 collector is turned on, and the circulated and enriched CO2-containing waste gas is indirectly heated to 950℃~1100℃ in the inner casing of the external combustion roasting furnace as a heat source to provide heat for the decomposition reaction of carbonates. After the carbonates are roasted, metal oxides and high-concentration CO2 waste gas are obtained respectively; S4: High-temperature, high-concentration CO2 waste gas enters the suspension preheating system for countercurrent heat exchange with the carbonate raw material, preheating the carbonate raw material step by step from top to bottom to 850℃~1000℃. The medium- and low-temperature CO2 waste gas after heat exchange enters the first-stage suspension cooler through the high-temperature fan, exchanges heat with the high-temperature pure oxide collected by the last-stage cyclone preheater, and then returns to the external-fired roasting furnace for further heating. The high-concentration CO2 waste gas treated by the waste heat utilization system is regularly discharged to the CO2 collector for CO2 gas recovery. The treated CO2-free waste gas is treated in a purification dust collector and then discharged. S5: The metal oxides that have been preliminarily cooled by the first-stage suspension cooler enter the lower independent air supply suspension cooling system and are cooled step by step from top to bottom to below 100°C and discharged from the discharge port of the last-stage suspension cooler. They are transported to the storage tank via a chain scraper conveyor. The independently supplied ambient air mixes with the combustion flue gas from bottom to top, and is discharged as air after waste heat utilization and dust removal.

[0014] Due to the adoption of the above-mentioned technical solution, the present invention has the following advantages: The present invention can co-produce high-purity CO2 gas while roasting carbonates. An external-fired roasting furnace is used to indirectly heat the circulating exhaust gas containing CO2 to provide heat for the suspension roasting system and the suspension preheating system, which not only fully preheats the raw materials but also ensures the decomposition rate of the carbonate and the purity of the product. The CO2-containing exhaust gas generated by fuel combustion and carbonate decomposition is circulated and enriched in the production system. A part of the high-concentration CO2 exhaust gas is collected and purified by the carbon capture system, and the rest is returned to the external-fired roasting furnace for reheating and recycling, thereby achieving zero CO2 emissions from carbonate decomposition. The present invention has a simple production process, a high degree of automation, and convenient operation and maintenance, a high carbonate decomposition rate, high product activity, and stable quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the overall process of the present invention.

[0016] Figure 2 It is a structural schematic diagram of the external combustion roasting furnace of the present invention.

[0017] Figure 3 Figure 2 Cross-sectional view of AA in the figure.

[0018] Figure 4 Figure 2 Cross-sectional view of the BB.

[0019] In the figure: 1-first stage cyclone preheater, 2-second stage cyclone preheater, 3-third stage cyclone preheater, 4-fourth stage cyclone preheater, 5-fifth stage cyclone preheater, 6-external combustion type roasting furnace, 6a-burner, 6b-burner, 6c-inner casing, 61-air flow outlet with material, 62-feed port, 63-air inlet, 64-material discharge port, 65-combustion air inlet, 66-combustion flue gas outlet, 7-first stage suspension cooler, 8-second stage suspension cooler, 9-third stage suspension cooler, 10-fourth stage suspension cooler, 11-chain scraper conveyor, 12-first heat exchanger, 13-high temperature fan, 14- CO2 collector, 15-second heat exchanger, 16-purification dust collector, 17-exhaust fan, 18-chimney, 19-weight hammer flap lock air valve, 20-electric butterfly valve, 21-manual plug valve. DETAILED DESCRIPTION

[0020] The present invention will be further explained below with reference to the accompanying drawings and embodiments, which should not be used to limit the scope of protection of the present invention. The purpose of disclosing the present invention is to protect all technical improvements within the scope of the present invention.

[0021] Combined with attachment Figure 1-4 The system shown utilizes an external combustion furnace for suspended roasting of carbonate and co-production of CO2, comprising a suspension preheating system, a suspension cooling system, an external combustion roasting furnace 6, a CO2 collector 14 and a waste heat utilization system.

[0022] The suspension preheating system includes a five-stage cyclone preheater, the outlet duct of the fifth-stage cyclone preheater 5 is connected to the air inlet of the fourth-stage cyclone preheater 4, the outlet duct of the fourth-stage cyclone preheater 4 is connected to the air inlet of the third-stage cyclone preheater 3, the outlet duct of the third-stage cyclone preheater 3 is connected to the air inlet of the second-stage cyclone preheater 2, and the outlet duct of the second-stage cyclone preheater 2 is connected to the air inlet of the first-stage cyclone preheater 1; the bottom discharge port of the first-stage cyclone preheater 1 is connected to the outlet duct of the third-stage cyclone preheater 3, the bottom discharge port of the second-stage cyclone preheater 2 is connected to the outlet duct of the fourth-stage cyclone preheater 4, and the bottom discharge port of the third-stage cyclone preheater 3 is connected to the outlet duct of the fifth-stage cyclone preheater 5.

[0023] The suspension cooling system includes a four-stage suspension cooler. The air inlet of the first-stage suspension cooler 7 is respectively connected to the air outlet of the high-temperature fan 13 and the bottom discharge port of the fifth-stage cyclone preheater 5. The air outlet of the first-stage suspension cooler 7 is connected to the air inlet 63 of the external-fired roasting furnace 6. The air inlet of the fourth-stage suspension cooler is connected to the ambient air. The air outlet duct of the fourth-stage suspension cooler is connected to the air inlet of the third-stage suspension cooler 9. The air outlet duct of the third-stage suspension cooler 9 is connected to the air inlet of the second-stage suspension cooler 8; the bottom discharge port of the first-stage suspension cooler 7 is connected to the air outlet duct of the third-stage suspension cooler 9, the bottom discharge port of the second-stage suspension cooler 8 is connected to the air outlet duct of the fourth-stage suspension cooler, the bottom discharge port of the third-stage suspension cooler 9 is connected to the ambient air inlet duct, and the lower side of the discharge port of the fourth-stage suspension cooler is connected to the feed port of the chain scraper conveyor 11.

[0024] The discharge ports of the cyclone preheaters at each level of the suspension preheating system, the discharge ports of the suspension coolers at each level of the suspension cooling system, and the material discharge port 64 of the external combustion roasting furnace 6 are all provided with a heavy hammer flap lock air valve 19.

[0025] The external combustion type roasting furnace 6 is provided with a plurality of inner sleeves 6c of silicon carbide ceramics uniformly in the furnace body as the air flow heating zone and the CO2 inlet and outlet channel. The two ends of the inner sleeve 6c are respectively connected with the upper and lower contractions of the furnace body. The internal space of the furnace body outside the inner sleeve 6c is the fuel combustion zone. In the fuel combustion zone, at least two groups of staggered burners 6a and 6b are provided in the vertical direction of the furnace body. The burner fuel is hydrogen, coal or natural gas. The top of the external combustion type roasting furnace 6 is provided with a material air flow outlet 61, and the upper contraction is provided with a There is a feed port 62, an air inlet 63 is provided on the lower constriction, a combustion flue gas outlet 66 is provided on the upper part of the furnace body, a combustion air inlet 65 is provided on the lower part of the furnace body, and a material discharge port 64 is provided at the bottom; the material-carrying air flow outlet 61 is connected to the air inlet of the fifth-stage cyclone preheater 5, the feed port 62 is connected to the bottom discharge port of the fourth-stage cyclone preheater 4, the combustion air inlet 65 is connected to the air outlet duct of the second-stage suspension cooler 8, and a part of the air outlet of the second-stage suspension cooler 8 is used as the combustion air of the external-fired roasting furnace 6.

[0026] The waste heat utilization system includes two heat exchangers. The air inlet of the first heat exchanger 12 is connected to the air outlet duct of the first-stage cyclone preheater 1, and the air outlet of the first heat exchanger 12 is connected to the air inlet of the high-temperature fan 13. The high-temperature fan 13 provides power for the suspension preheating system and the exhaust gas circulation of the external-fired roasting furnace 6; the air inlet of the second heat exchanger 15 is connected to the air outlet duct of the second-stage suspension cooler 8 and the combustion flue gas outlet 66 on the side of the external-fired roasting furnace 6; the air outlet of the second heat exchanger 15 is connected to the purification dust collector 16; an exhaust fan 17 and a chimney 18 are provided on the rear side of the purification dust collector 16, and the exhaust fan 17 provides power for the suspension cooling system.

[0027] The air outlet at the upper end of the CO2 collector 14 is connected to the purification dust collector 16, the air inlet is connected to the air outlet of the high-temperature fan 13, and the bottom is the CO2 product outlet.

[0028] A process for suspended roasting of carbonates and co-production of CO2 using an external combustion furnace, comprising the following steps: S1: Keep the chain scraper conveyor 11, waste heat utilization system, and CO2 collector 14 closed; turn on the high-temperature fan 13, purification dust collector 16, and exhaust fan 17, open the electric butterfly valve 20 at the air inlet of the first-stage suspension cooler 7 as an air supply valve, and turn on the external combustion roasting furnace 6 to bake the furnace, creating conditions for the normal operation of the entire suspension preheating system.

[0029] S2: When the temperature of the suspension preheating system reaches 250℃, the feeding condition is met. At this time, the chain scraper conveyor 11 and the waste heat utilization system are first turned on, and then a small amount of particle size D is added to the air outlet pipe of the second stage cyclone preheater 2. 80The powdered carbonate raw material with a particle size of less than 80 μm is burned in the external combustion roaster 6 to heat the circulating enriched CO2-containing exhaust gas, and the CO2 collector 14 is kept closed while gradually increasing the feed amount until the production is reached.

[0030] S3: After reaching full production and operating normally, the CO2 collector 14 is turned on, and the circulated and enriched CO2-containing waste gas is indirectly heated to 950°C~1100°C in the inner sleeve of the external combustion roasting furnace 6 as a heat source to provide heat for the decomposition reaction of the carbonate. After the carbonate is roasted, metal oxides and high-concentration CO2 waste gas are obtained respectively.

[0031] S4: High-temperature and high-concentration CO2 waste gas enters the suspension preheating system for countercurrent heat exchange with the carbonate raw material, and preheats the carbonate raw material from top to bottom step by step to 850℃~1000℃. The specific process is as follows: a part of the raw material fed into the outlet pipe of the second-stage cyclone preheater 2 enters the outlet pipe of the first-stage cyclone preheater 1 with the air flow, and enters the outlet pipe of the third-stage cyclone preheater 3 after gas-solid separation; the other part of the raw material is separated by gas and solid in the second-stage cyclone preheater 2 and enters the outlet pipe of the fourth-stage cyclone preheater 4; the raw material entering the third-stage cyclone preheater 3 enters the outlet pipe of the fifth-stage cyclone preheater 5 after gas-solid separation, and enters the outlet pipe of the fourth-stage cyclone preheater 4. The raw materials from the cyclone preheater 4 enter the external-fired roasting furnace 6 for further decomposition after gas-solid separation, and the raw materials entering the fifth-stage cyclone preheater 5 complete decomposition and enter the first-stage suspension cooler 7 for preliminary cooling after gas-solid separation; the medium and low-temperature CO2 exhaust gas after heat exchange enters the first-stage suspension cooler 7 through the high-temperature fan 13, exchanges heat with the high-temperature pure oxide collected by the fifth-stage cyclone preheater 5 to increase the temperature, and then returns to the external-fired roasting furnace 6 for further heating and temperature increase; the high-concentration CO2 exhaust gas treated by the waste heat utilization system is regularly discharged into the CO2 collector 14 for CO2 gas recovery, and the treated CO2-free exhaust gas is discharged after treatment in the purification dust collector 16.

[0032] S5: The metal oxides preliminarily cooled by the first-stage suspension cooler 7 enter the third-stage suspension cooler 9 for cooling, and then enter the fourth-stage suspension cooler after gas-solid separation in the second-stage suspension cooler 8. The air outlet duct is cooled to below 100°C by ambient cold air, and is discharged from the discharge port of the fourth-stage suspension cooler and transported to the storage tank via the chain scraper conveyor 11. The independently supplied ambient air mixes with the combustion flue gas from bottom to top, and is discharged as air after waste heat utilization and dust removal.

[0033] The present invention is attached Figure 1 The electric butterfly valve 20 and the manual plug-in valve 21 are existing technologies set by the system according to actual conditions, so they are not described in detail.

[0034] The embodiments selected herein for the purpose of disclosing the invention are presently considered suitable, but it should be understood that the invention is intended to include all variations and modifications of the embodiments that fall within the scope of the concept and invention.

Claims

1. A system for suspended roasting of carbonates and co-production of CO2 using an external combustion furnace, characterized by: It includes suspension preheating system, suspension cooling system, external combustion roaster, CO2 collector and waste heat utilization system; The suspension preheating system includes at least four stages of cyclone preheaters, the air outlet ducts of each stage of the cyclone preheater are connected in sequence from bottom to top, and the bottom discharge ports of each stage of the cyclone preheater are connected to the corresponding air outlet ducts from top to bottom according to the single and double stages; The suspension cooling system includes at least four stages of suspension coolers, the air inlet of the first stage suspension cooler is respectively connected to the air outlet of the high-temperature fan and the bottom discharge port of the last stage cyclone preheater, the air outlet of the first stage suspension cooler is connected to the air inlet of the external combustion roasting furnace, the air inlet of the last stage suspension cooler is connected to the ambient air, the air outlet duct of the last stage suspension cooler is connected to the air outlet ducts of the remaining stages of suspension coolers except the first stage suspension cooler in sequence from bottom to top; the bottom discharge ports of the suspension coolers at each stage are respectively connected to the corresponding air outlet ducts from top to bottom according to the single and double stages; The external combustion roasting furnace is provided with a material air flow outlet at the top, a material feed port at the upper constriction, an air inlet at the lower constriction, a combustion flue gas outlet at the upper part of the furnace body, a combustion air inlet at the lower part of the furnace body, and a material discharge port at the bottom; the material air flow outlet is connected to the air inlet of the last stage cyclone preheater, and the material feed port is connected to the material discharge port at the bottom of the penultimate stage cyclone preheater; The waste heat utilization system includes two heat exchangers, the air inlet of the first heat exchanger is connected to the air outlet duct of the first-stage cyclone preheater, and the air outlet of the first heat exchanger is connected to the air inlet of the high-temperature fan; the air inlet of the second heat exchanger is connected to the air outlet duct of the second-stage suspension cooler and the combustion flue gas outlet on the side of the external-fired roasting furnace; the air outlet of the second heat exchanger is connected to the purification dust collector; The air outlet at the upper end of the CO2 collector is connected to the purification dust collector, the air inlet is connected to the air outlet of the high-temperature fan, and the bottom is the CO2 product outlet.

2. The system for suspended roasting of carbonate and co-production of CO2 using an external combustion furnace according to claim 1, characterized in that: The external-fired roasting furnace is evenly equipped with several inner sleeves in the furnace body as airflow heating areas and CO2 inlet and outlet channels. The two ends of the inner sleeves are respectively connected to the upper and lower contractions of the furnace body. The internal space of the furnace body outside the inner sleeves is the fuel combustion area. At least two groups of staggered burners are arranged in the vertical direction of the furnace body in the fuel combustion area.

3. The system for suspended roasting of carbonate and co-production of CO2 using an external combustion furnace according to claim 2, characterized in that: The burner fuel is hydrogen, coal or natural gas.

4. The system for suspended roasting of carbonate and co-production of CO2 using an external combustion furnace according to claim 1, characterized in that: The air outlet of the second-stage suspension cooler is also connected to the combustion-supporting air inlet of the external-fired roasting furnace.

5. The system for suspended roasting of carbonate and co-production of CO2 using an external combustion furnace according to claim 1, characterized in that: An exhaust fan and a chimney are arranged on the rear side of the purification dust collector.

6. The system for suspended roasting of carbonate and co-production of CO2 using an external combustion furnace according to claim 1, characterized in that: The discharge ports of the cyclone preheaters at various levels of the suspension preheating system, the discharge ports of the suspension coolers at various levels of the suspension cooling system, and the material discharge port of the external combustion roasting furnace are all provided with heavy hammer flap lock air valves.

7. The system for suspended roasting of carbonate and co-production of CO2 using an external combustion furnace according to claim 1, characterized in that: The lower side of the discharge port of the last-stage suspension cooler is connected to the feed port of the chain scraper conveyor.

8. A process for a system for suspended roasting of carbonate and co-production of CO2 using an external combustion furnace as claimed in any one of claims 1 to 7, characterized in that: The specific steps are: S1: Keep the chain scraper conveyor, waste heat utilization system, and CO2 collector closed; turn on the high-temperature fan, purification dust collector, and exhaust fan; open the electric butterfly valve at the air inlet of the first-stage suspension cooler as an air supply valve; turn on the external combustion roasting furnace to bake the furnace, creating conditions for the normal operation of the entire suspension preheating system; S2: When the temperature of the suspension preheating system reaches 250℃, the feeding condition is met. At this time, the chain scraper conveyor and the waste heat utilization system are first turned on, and then a small amount of particle size D is added to the air outlet pipe of the second stage cyclone preheater. 80 Powdered carbonate raw materials with a diameter of less than 80 μm are burned in an externally fired roaster to heat the circulating enriched CO2-containing exhaust gas. The CO2 collector is kept closed while gradually increasing the feed rate until reaching the production capacity. S3: After reaching full production and normal operation, the CO2 collector is turned on, and the circulated and enriched CO2-containing waste gas is indirectly heated to 950℃~1100℃ in the inner casing of the external combustion roasting furnace as a heat source to provide heat for the decomposition reaction of carbonates. After the carbonates are roasted, metal oxides and high-concentration CO2 waste gas are obtained respectively; S4: High-temperature, high-concentration CO2 waste gas enters the suspension preheating system for countercurrent heat exchange with the carbonate raw material, preheating the carbonate raw material step by step from top to bottom to 850℃~1000℃. The medium- and low-temperature CO2 waste gas after heat exchange enters the first-stage suspension cooler through the high-temperature fan, exchanges heat with the high-temperature pure oxide collected by the last-stage cyclone preheater, and then returns to the external-fired roasting furnace for further heating. The high-concentration CO2 waste gas treated by the waste heat utilization system is regularly discharged to the CO2 collector for CO2 gas recovery. The treated CO2-free waste gas is treated in a purification dust collector and then discharged. S5: The metal oxides that have been preliminarily cooled by the first-stage suspension cooler enter the lower independent air supply suspension cooling system and are cooled step by step from top to bottom to below 100°C and discharged from the discharge port of the last-stage suspension cooler. They are transported to the storage tank via a chain scraper conveyor. The independently supplied ambient air mixes with the combustion flue gas from bottom to top, and is discharged as air after waste heat utilization and dust removal.

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