System for producing low-carbon cement using vertical externally-heated decomposition furnace

Abstract

This invention discloses a system for producing low-carbon cement using a vertical external thermal decomposition furnace, comprising a preheating mechanism, a decomposition furnace, a clinker calcination mechanism, and a carbon capture mechanism. The preheating mechanism includes a preheater with a first inlet for cement raw meal, a first outlet for preheated raw meal, and a second inlet for high-temperature heat exchange flue gas. The decomposition furnace has an internal decomposition zone and an external heating zone that are physically isolated from each other, with the external heating zone surrounding the internal decomposition zone. The top of the decomposition furnace has a third inlet connected to the internal decomposition zone, a second outlet connected to the internal decomposition zone, and a third outlet connected to the external heating zone. The clinker calcination mechanism includes a rotary kiln and a grate cooler. The rotary kiln is connected to the internal decomposition zone of the vertical external thermal decomposition furnace, and the grate cooler is connected to the rotary kiln. The carbon capture mechanism is connected to the decomposition furnace. The system for producing low-carbon cement using a vertical external thermal decomposition furnace provided by this invention has the advantages of balancing decomposition efficiency and carbon dioxide concentration.

Description

Technical Field

[0001] This invention relates to the field of low-carbon cement technology, and in particular to a system for producing low-carbon cement using a vertical external pyrolysis furnace. Background Technology

[0002] The cement industry is one of the major sources of global carbon emissions, primarily from limestone decomposition and fuel combustion. Current mainstream dry-process cement production tightly couples raw material decomposition and fuel combustion within a precalciner, resulting in a high degree of mixing between CO2 emitted during the process and the flue gas produced by combustion. This leads to low CO2 concentrations (typically below 30%) and complex composition in the flue gas. This necessitates the processing of massive amounts of mixed gas for subsequent carbon capture, utilization, and storage (CCUS), presenting challenges such as high energy consumption, large equipment size, and high costs.

[0003] Current designs for precalciner furnaces, such as cyclone and jet-type furnaces, are all internally heated reactors, which cannot solve the fundamental problem of CO2 dilution. While externally heated rotary kilns can achieve gas-solid separation, they suffer from problems such as large equipment size, large footprint, and relatively low heat transfer efficiency. Summary of the Invention

[0004] This invention is based on the inventor's discoveries and understanding of the following facts and problems: Obtaining high concentration of CO2 while ensuring high decomposition rate The present invention aims to at least partially solve one of the technical problems in the related art.

[0005] Therefore, embodiments of the present invention propose a system for producing low-carbon cement using a vertical external thermal decomposition furnace, comprising a preheating mechanism, a decomposition furnace, a clinker calcination mechanism, and a carbon capture mechanism. The preheating mechanism includes a preheater having a first inlet for introducing cement raw meal, a first outlet for discharging preheated raw meal, and a second inlet for introducing high-temperature heat exchange flue gas. The decomposition furnace has an internal decomposition zone and an external heating zone that are physically isolated from each other. The external heating zone surrounds the internal decomposition zone. The top of the decomposition furnace is provided with a third inlet and a second outlet connected to the internal decomposition zone, and a third outlet connected to the external heating zone. The bottom of the decomposition furnace is provided with an external heating zone connected to the internal decomposition zone. The clinker calcination mechanism includes a fourth inlet and a tertiary air inlet connected to the heating zone, a fifth inlet and a fourth outlet connected to the internal decomposition zone; the clinker calcination mechanism includes a rotary kiln and a grate cooler, the rotary kiln is connected to the internal decomposition zone of the vertical external pyrolysis furnace, the grate cooler is connected to the rotary kiln, and the carbon capture mechanism is connected to the decomposition furnace; the first outlet is connected to the third inlet, the third outlet is connected to the second inlet, the second outlet is connected to the carbon capture mechanism through a first pipeline, a first branch is provided on the first pipeline, and the first branch is connected to the fifth inlet; the grate cooler is connected to the tertiary air inlet.

[0006] The present invention offers advantages and technical benefits by balancing decomposition efficiency and carbon dioxide concentration. This application achieves a balance between efficient decomposition and high-concentration carbon capture by controlling the temperature, atmosphere, and material residence time during the pre-decomposition stage and optimizing the internal CO2 circulation. External heating for pre-decomposition and the use of carbon dioxide tail gas as a circulating fluidizing medium reduce carbon capture costs.

[0007] In some embodiments, the rotary kiln is connected to the fourth outlet via a sixth inlet 3c, the discharge end of the rotary kiln is connected to the feed inlet of the grate cooler, the fifth outlet 3d of the grate cooler discharges sintered cement clinker, and the sixth outlet 3e is connected to the tertiary air inlet.

[0008] In some embodiments, a CO2 replenishment interface is provided on the first branch, which is used to replenish external CO2 to the internal decomposition zone.

[0009] In some embodiments, the first pipeline is further provided with a cooling device, a dehydration device and a dust removal device in sequence. The cooling device, the dehydration device and the dust removal device are all located upstream of the first branch and between the second outlet and the first branch.

[0010] An embodiment of the present invention provides a method for producing low-carbon cement using a vertical external pyrolysis furnace, comprising the following steps: Preheating involves feeding cement raw materials into a preheater for counter-current heat exchange with high-temperature hot air, preheating them to 750-850℃ to obtain preheated raw materials. Pre-decomposition involves continuously feeding preheated raw materials into the internal decomposition zone from the top of the decomposition furnace. The external heating zone indirectly heats the preheated raw materials in the internal heating zone through the furnace wall from an external heat source, causing the calcium carbonate in the preheated raw materials to decompose, resulting in semi-cooked material that is discharged from the bottom of the decomposition furnace. The CO2 generated during decomposition is discharged from the top of the decomposition furnace.

[0011] Clinker calcination involves feeding the resulting semi-clinker into a rotary kiln, where it is sintered into clinker at 1450-1550℃, and then cooled to produce sintered cement clinker. Carbon capture and recycling involves extracting the CO2 tail gas generated in the decomposition zone during the pre-decomposition step, cooling, dehydrating, and removing dust, and then sending it to the carbon capture unit to obtain a high-purity CO2 product.

[0012] In some embodiments, the decomposition temperature in the internal decomposition zone during the pre-decomposition step is 850-950°C.

[0013] In some embodiments, a portion of the CO2 tail gas generated in the internal decomposition zone is pressurized and temperature-controlled before being returned to the bottom of the decomposition furnace as a circulating fluidizing gas to serve as the fluidizing medium for the raw materials in the decomposition furnace.

[0014] In some embodiments, the mass ratio of the CO2 circulating fluidized gas to the raw material processing volume is between 1:2 and 3:1.

[0015] In some embodiments, the high-temperature gas flow after cooling the clinker is fed into the bottom of the external heating zone of the decomposition furnace to assist fuel combustion in the heating zone.

[0016] In some embodiments, the high-temperature gas after combustion in the external heating zone of the decomposition furnace is extracted and sent to the preheater for countercurrent heat exchange with the cement raw materials.

[0017] This application offers the following advantages: The connection between the rotary kiln, decomposition furnace, and grate cooler, along with the connection between the high-temperature airflow from the grate cooler and the decomposition furnace, enables continuous transport of semi-clinker and clinker, reducing heat loss, recovering waste heat from clinker cooling to assist fuel combustion, lowering system energy consumption, and improving combustion efficiency. The CO2 replenishment interface rapidly replaces the air in the internal decomposition zone during system startup to establish a pure CO2 atmosphere, supplementing insufficient circulating gas during operation and maintaining stable raw material fluidization. Pre-treatment of the CO2 tail gas prevents impurities and high temperatures from adversely affecting subsequent circulation and carbon capture equipment, ensuring the cleanliness of the circulating fluidized gas and the purity of the carbon capture product. The phased preheating, pre-decomposition, clinker calcination, and carbon capture and circulation processes enable continuous cement production, ensuring the quality and efficiency of cement clinker production, achieving effective capture, and meeting the needs of low-carbon production. The pre-decomposition step controls the temperature in the internal decomposition zone at 850-950℃, ensuring sufficient decomposition of calcium carbonate, increasing the decomposition rate, reducing the rotary kiln load, and preventing side reactions and raw material crusting blockage. Part of the exhaust gas is pressurized and temperature-controlled before being returned as a fluidizing medium, achieving internal CO2 circulation and reducing the introduction of external media and system heat load. The mass ratio is controlled between 1:2 and 3:1, balancing raw material fluidization, calcium carbonate decomposition efficiency, and CO2 concentration enrichment. The high-temperature gas flow after cooling the clinker is sent to the bottom of the external heating zone of the decomposition furnace for auxiliary fuel combustion, achieving cascade recovery of clinker cooling waste heat. The high-temperature gas extracted from the external heating zone of the decomposition furnace is sent to the preheater for countercurrent heat exchange with cement raw materials, achieving efficient recovery of combustion waste heat and improving the overall thermal efficiency of the system. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a system for producing low-carbon cement using a vertical external pyrolysis furnace, according to an embodiment of the present invention.

[0019] Figure 2 This is a schematic flowchart of a method for producing low-carbon cement using a vertical external pyrolysis furnace according to an embodiment of the present invention.

[0020] Reference numerals: 1, preheater; 1a, first inlet; 1b, first outlet; 1c, second inlet; 2. Decomposition furnace; 2a. Third inlet, 2b. Second outlet, 2c. Fifth inlet, 2d. Fourth outlet, 2e. Fourth inlet, 2f. Tertiary air inlet, 2g. Third outlet, 2h. Supplementary interface; 3. Clinker calcination mechanism; 4. Carbon capture mechanism; 3a. Rotary kiln; 3b. Grate cooler; 3c. Sixth inlet; 3d. Fifth outlet; 3e. Sixth outlet. Detailed Implementation

[0021] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0022] An embodiment of the present invention proposes a system for producing low-carbon cement using a vertical external thermal decomposition furnace 2, comprising a preheating mechanism, a decomposition furnace 2, a clinker calcination mechanism, and a carbon capture mechanism 4. The preheating mechanism includes a preheater 1, which has a first inlet 1a for introducing cement raw meal, a first outlet 1b for discharging preheated raw meal, and a second inlet 1c for introducing high-temperature heat exchange flue gas. The decomposition furnace 2 has an internal decomposition zone and an external heating zone that are physically isolated from each other, with the external heating zone surrounding the internal decomposition zone. The top of the decomposition furnace 2 is provided with a third inlet 2a and a second outlet 2b connected to the internal decomposition zone, and a third outlet 2g connected to the external heating zone. The bottom of the decomposition furnace 2 is provided with an outlet connected to the external heating zone. The hot zone is connected to the fourth inlet 2e and the tertiary air inlet 2f, and the fifth inlet 2c and the fourth outlet 2d are connected to the internal decomposition zone; the clinker calcination mechanism includes a rotary kiln 3a and a grate cooler 3b. The rotary kiln 3a is connected to the internal decomposition zone of the vertical external pyrolysis furnace 2, the grate cooler 3b is connected to the rotary kiln 3a, and the carbon capture mechanism 4 is connected to the decomposition furnace 2; the first outlet 1b is connected to the third inlet 2a, the third outlet 2g is connected to the second inlet 1c, the second outlet 2b is connected to the carbon capture mechanism 4 through a first pipeline, a first branch is set on the first pipeline, and the first branch is connected to the fifth inlet 2c; the grate cooler 3b is connected to the tertiary air inlet 2f.

[0023] The system is designed with physically isolated decomposition furnace 2, where the external heating zone surrounds the internal decomposition zone. This separates the heating process of fuel combustion from the carbon production process of raw meal decomposition, preventing inert gases such as nitrogen in the combustion flue gas from diluting the carbon dioxide produced by raw meal decomposition, increasing the carbon dioxide concentration, and reducing the energy consumption and cost of carbon capture. The first inlet 1a of the preheater 1 is used for feeding cement raw meal, and the first outlet 1b is connected to the third inlet 2a of the decomposition furnace 2 to send the preheated raw meal into the internal decomposition zone, reducing heat loss during transport. The second inlet 1c is connected to the third outlet 2g of the decomposition furnace 2 to recover heat from the high-temperature flue gas after combustion in the external heating zone. This counter-current heat exchange preheats the cement raw meal, reducing the heat load during the raw meal decomposition stage and improving overall heat utilization efficiency. These multiple interfaces enable precise zoned transport of raw meal, carbon dioxide, fuel, and tertiary air, ensuring the independence and stability of the processes in the internal decomposition zone and the external heating zone, and avoiding interference between different media. The decomposition furnace 2 is a vertically arranged cylindrical structure.

[0024] The rotary kiln 3a of the clinker calcination mechanism is connected to the fourth outlet 2d of the internal decomposition zone of the decomposition furnace 2, receiving the semi-clinker after decomposition, shortening the conveying path and reducing heat loss. The grate cooler 3b is connected to the rotary kiln 3a, and its air outlet is connected to the tertiary air inlet 2f of the decomposition furnace 2, sending the high-temperature tertiary air generated from cooling the clinker into the external heating zone to assist fuel combustion, realizing heat recovery during the clinker cooling process and reducing energy consumption. The carbon capture mechanism 4 is connected to the second outlet 2b of the decomposition furnace 2 through the first pipeline, directly collecting the high-concentration carbon dioxide generated in the internal decomposition zone. The first branch of the first pipeline is set to connect to the fifth inlet 2c, which can return some of the high-concentration carbon dioxide to the internal decomposition zone as a fluidizing medium for raw materials, replacing the traditional air to ensure the fluidization state of the raw materials in the internal decomposition zone, improving heat and mass transfer efficiency, and enriching carbon dioxide to avoid carbon dioxide dilution caused by air introduction. The carbon capture module receives pretreated high-concentration CO2 tail gas. Depending on actual production needs, the carbon capture module uses processes such as chemical absorption, physical adsorption, and membrane separation to purify the pretreated CO2 tail gas into high-purity CO2 products.

[0025] The advantages and technical effects brought about by the independent claims according to the embodiments of the present invention.

[0026] In some embodiments, rotary kiln 3a is connected to fourth outlet 2d via sixth inlet 3c, the discharge end of rotary kiln 3a is connected to feed inlet of grate cooler 3b, fifth outlet 3d of grate cooler 3b discharges sintered cement clinker, and sixth outlet 3e is connected to tertiary air inlet 2f.

[0027] Specifically, the rotary kiln 3a is connected to the fourth outlet 2d of the decomposition zone inside the decomposition furnace 2 through the sixth inlet 3c, so as to realize the transportation of the semi-clinker after decomposition from the decomposition furnace 2 to the rotary kiln 3a. This can reduce the heat loss of the semi-clinker, ensure that the semi-clinker maintains a relatively high temperature when it enters the rotary kiln 3a, reduce the fuel consumption of the rotary kiln 3a in the sintering stage, and improve the thermal efficiency of clinker firing. The discharge end of rotary kiln 3a is directly connected to the feed inlet of grate cooler 3b. The high-temperature clinker after sintering enters grate cooler 3b for cooling treatment, avoiding heat waste caused by the natural cooling of high-temperature clinker in the external environment, and realizing the process connection between clinker calcination and cooling. The fifth outlet 3d serves as the discharge channel for finished clinker, realizing the efficient discharge of cooled cement clinker. The sixth outlet 3e is connected to the tertiary air inlet 2f of the external heating zone of decomposition furnace 2, sending the high-temperature tertiary air recovered during the cooling of high-temperature clinker by grate cooler 3b into the external heating zone as combustion air to participate in the fuel combustion in the external heating zone, improving fuel combustion efficiency, reducing fuel consumption, and realizing the cascade recovery and efficient utilization of waste heat during clinker cooling to reduce energy consumption.

[0028] Rotary kiln 3a is a short-type rotary kiln 3a, adapted to the process characteristics of pre-decomposition of most raw materials in decomposition furnace 2. The short-type rotary kiln 3a only undertakes the core process of clinker sintering. Compared to traditional rotary kilns 3a, it reduces the equipment's footprint and cost, lowers heat loss and operating energy consumption, and is suitable for low-carbon cement production needs. A material control device can be installed at the sixth inlet 3c to adjust the feed rate of semi-clinker into the rotary kiln 3a, ensuring the feed amount matches the sintering capacity of the rotary kiln 3a. This avoids insufficient clinker sintering due to excessive feed or idling due to insufficient feed, guaranteeing the stability of the rotary kiln 3a sintering process and the quality of the clinker product. A temperature and flow regulation component can be installed on the connecting pipeline between the sixth outlet 3e and the tertiary air inlet 2f. Based on the combustion requirements of the external heating zone of decomposition furnace 2, the delivery temperature and flow rate of high-temperature tertiary air can be adjusted to ensure that fuel combustion in the external heating zone is always under optimal conditions, guaranteeing stable heating temperature in the internal decomposition zone of decomposition furnace 2.

[0029] In some embodiments, a CO2 replenishment interface 2h is provided on the first branch, which is used to replenish external CO2 to the internal decomposition zone.

[0030] Specifically, the CO2 replenishment interface 2h set on the first branch serves as the external CO2 supply channel for the internal decomposition zone. At the initial stage of system startup, external CO2 is introduced into the internal decomposition zone to quickly replace the air in the internal decomposition zone, avoiding the dilution of CO2 generated by the subsequent raw material decomposition by residual inert gases such as nitrogen in the air, and establishing a pure CO2 fluidized atmosphere. During normal system operation, if the CO2 volume of the circulating fluidized bed is insufficient due to factors such as raw material processing volume adjustment or pipeline loss, external CO2 can be replenished in time at the replenishment interface every 2 hours to maintain the total amount of CO2 fluidized medium stable, ensure that the raw material is in a good fluidized state, and avoid problems such as raw material crusting and blockage of the internal decomposition zone caused by insufficient fluidized gas volume.

[0031] A flow control valve can be installed at the CO2 replenishment interface 2h to adjust the external CO2 replenishment flow rate according to the system operating conditions, so as to match the replenishment volume with the actual needs of the system, avoid excessive CO2 replenishment, and prevent insufficient replenishment volume from affecting the stable operation of the system.

[0032] In some embodiments, a cooling device, a dehydration device, and a dust removal device are sequentially provided in the first pipeline. The cooling device, the dehydration device, and the dust removal device are all located upstream of the first branch and between the second outlet 2b and the first branch.

[0033] Specifically, the cooling device, dehydration device, and dust removal device are located upstream of the first branch line to pre-treat the high-temperature, humid, and dusty CO2 tail gas discharged from the internal decomposition zone. The cooling device can quickly reduce the temperature of the CO2 tail gas, preventing high-temperature gas from entering subsequent pipelines and the carbon capture mechanism 4, thus avoiding equipment damage, reducing gas volume, and improving the processing efficiency of subsequent carbon capture. The dehydration device removes water vapor from the tail gas, preventing water vapor from condensing and causing corrosion in the pipelines, and preventing water vapor from entering the carbon capture mechanism 4, affecting the performance of the capture medium and the purity of the CO2 product. The dust removal device removes solid impurities such as raw material dust entrained in the tail gas, preventing impurities from accumulating and clogging the pipelines and the first branch line, and preventing impurities from entering the carbon capture mechanism 4, thus reducing the capture effect. Located upstream of the first branch line, the purified and temperature-controlled clean CO2 gas re-enters the first branch line and circulates back to the internal decomposition zone, avoiding direct circulation of dusty and humid high-temperature gas that may interfere with the decomposition reaction and ensuring the cleanliness of the circulating fluidized gas.

[0034] It can recover high-temperature waste heat from CO2 exhaust gas while cooling it down, and use the recovered heat to preheat raw materials or assist fuel combustion in external heating zones, thereby realizing the secondary utilization of exhaust gas waste heat and improving the overall thermal efficiency of the system.

[0035] An embodiment of the present invention provides a method for producing low-carbon cement using a vertical external pyrolysis furnace 2, comprising the following steps: Preheating involves feeding cement raw materials into preheater 1 for countercurrent heat exchange with high-temperature hot gas, preheating them to 750-850℃ to obtain preheated raw materials. The temperature range of 750-850℃ provides a suitable temperature environment for the calcium carbonate decomposition reaction, reducing the external heating load in the pre-decomposition stage, and avoiding premature local decomposition or crusting of the raw materials due to excessively high temperatures. This ensures smooth raw material transportation and subsequent decomposition. Countercurrent heat exchange improves heat exchange efficiency, fully utilizes the waste heat of high-temperature flue gas, and reduces heat waste in the system.

[0036] In the pre-decomposition process, preheated raw materials are continuously fed into the internal decomposition zone from the top of decomposition furnace 2. An external heating zone indirectly heats the preheated raw materials in the internal heating zone through the furnace wall, causing the calcium carbonate in the preheated raw materials to decompose, resulting in semi-cooked material which is discharged from the bottom of decomposition furnace 2. The CO2 generated during decomposition is discharged from the top of decomposition furnace 2. The pre-decomposition step, by continuously feeding preheated raw materials from the top of decomposition furnace 2 into the internal decomposition zone, combined with indirect heating from the external heating zone, achieves physical isolation between the heating process and the raw material decomposition process. This avoids the dilution of CO2 generated by combustion flue gas. Continuous feeding adapts to the needs of continuous industrial production, and indirect heat exchange ensures a uniform and stable temperature in the internal decomposition zone, guaranteeing a complete decomposition reaction. The gas-solid separation discharge path, with semi-cooked material discharged from the bottom and CO2 discharged from the top, effectively separates the decomposition products, allowing CO2 to quickly collect and be discharged, reducing its residence loss within decomposition furnace 2.

[0037] In the clinker calcination process, the resulting semi-clinker is fed into rotary kiln 3a and sintered into clinker at 1450-1550℃. The sintered clinker is then cooled to produce the final cement clinker. The sintering temperature of 1450-1550℃ is the optimal range for cement clinker sintering, ensuring sufficient reaction of the semi-clinker to form qualified cement clinker. Since most of the calcium carbonate decomposes during the pre-decomposition stage, rotary kiln 3a only sinters the clinker, reducing its workload and fuel consumption. The cooling process rapidly lowers the high-temperature clinker to storage and transportation temperature and recovers the high-temperature waste heat from the clinker, improving the system's energy utilization rate.

[0038] The carbon capture and recycling (CCRI) process involves extracting the CO2 tail gas generated in the decomposition zone during the pre-decomposition step. After cooling, dehydration, and dust removal, the gas is sent to the carbon capture unit to obtain a high-purity CO2 product. In the CCRI step, the CO2 tail gas undergoes sequential pretreatment to remove impurities and excess heat, preventing impurities from affecting equipment operation and product purity. Cooling also reduces the gas volume. The pretreated CO2 is then sent to the carbon capture unit to obtain a high-purity CO2 product, achieving resource recovery and utilization of CO2, which aligns with low-carbon requirements.

[0039] In some embodiments, the decomposition temperature in the internal decomposition zone during the pre-decomposition step is 850-950°C.

[0040] Specifically, the decomposition temperature is controlled within the range of 850-950℃ to ensure rapid and complete decomposition of calcium carbonate. This stabilizes the decomposition rate of calcium carbonate in the raw materials, reducing the load on subsequent clinker calcination processes, decreasing fuel consumption and sintering time in the rotary kiln 3a, avoiding slow decomposition reaction rates and incomplete decomposition due to excessively low temperatures, and preventing side reactions and impurity gas generation caused by excessively high temperatures. This also avoids diluting the CO2 generated by decomposition with impurity gases, reducing the difficulty of carbon capture and treatment. The stable decomposition temperature ensures the uniformity of the semi-clinker quality.

[0041] In some embodiments, a portion of the CO2 tail gas generated in the internal decomposition zone is pressurized and temperature-controlled before being sent back to the bottom of the decomposition furnace 2 as a circulating fluidizing gas to serve as the fluidizing medium for the raw materials in the decomposition furnace 2.

[0042] Specifically, a portion of the CO2 tail gas generated in the internal decomposition zone is pressurized and temperature-controlled before being returned to the bottom of decomposition furnace 2 as a raw material fluidizing medium, replacing the traditional air fluidization method. This avoids inert gases such as nitrogen in the air from entering the internal decomposition zone and diluting the CO2, maintaining a high CO2 atmosphere in the internal decomposition zone, ensuring a high CO2 concentration in the exhaust gas, and reducing the energy consumption and cost of carbon capture. Pressurizing the circulating CO2 tail gas increases the fluidizing gas's power, ensuring a uniform and stable fluidization state of the raw material in the internal decomposition zone, preventing raw material deposition and crusting, improving heat and mass transfer efficiency, promoting the complete decomposition of calcium carbonate, and regulating the fluidizing gas to a suitable temperature to avoid lowering the internal decomposition zone temperature, slowing down the decomposition reaction, and preventing local overheating and side reactions caused by high-temperature fluidizing gas, thus maintaining a stable internal decomposition zone temperature. Utilizing the CO2 generated during the decomposition process itself as a fluidizing medium achieves internal CO2 recycling, reducing the introduction of external media, and forming a closed loop between material and gas flow in the pre-decomposition process. CO2 performs better as a heat carrier than air, and the circulating CO2 fluidized gas enhances heat transfer in the internal decomposition zone.

[0043] In some embodiments, the mass ratio of CO2 circulating fluidized gas to raw material processing volume is between 1:2 and 3:1.

[0044] Specifically, precisely controlling the mass ratio of CO2 circulating fluidizing gas to raw meal processing volume within the range of 1:2 to 3:1 is the optimal ratio that balances raw meal fluidization effect, calcium carbonate decomposition efficiency, and CO2 concentration enrichment. At this ratio, the fluidizing gas flow rate can provide sufficient fluidization power for the raw meal in the internal decomposition zone, enabling the raw meal to form a uniform and stable fluidization state within the decomposition zone. This allows the raw meal particles to fully contact the furnace wall, significantly improving heat and mass transfer efficiency, ensuring the sufficiency of the calcium carbonate decomposition reaction, and preventing insufficient fluidizing of raw meal, deposition and crusting, or even blockage of the internal decomposition zone pipelines due to insufficient fluidizing gas flow rate. It also prevents excessive fluidizing gas flow rate from causing the raw meal to have too short a residence time in the decomposition zone, resulting in insufficient calcium carbonate decomposition, reduced raw meal decomposition rate, and increased sintering load of the subsequent rotary kiln 3a. This mass ratio range allows for effective mixing of the circulating CO2 fluidizing gas and the CO2 produced from raw material decomposition. It prevents excessive fluidizing gas from diluting the CO2 produced during decomposition, and also avoids insufficient fluidizing gas from causing instability in the CO2 atmosphere within the decomposition zone. This maintains a high concentration of CO2 in the exhaust gas, ensuring efficient subsequent carbon capture. This ratio also reduces energy consumption for pressurizing and temperature regulating the CO2 fluidizing gas. This ratio range is adaptable to different raw material processing volumes and allows for simultaneous adjustment of the CO2 circulating fluidizing gas supply based on the actual raw material feed rate.

[0045] In some embodiments, the high-temperature gas flow after cooling the clinker is sent to the bottom of the external heating zone of the decomposition furnace 2 to assist fuel combustion in the heating zone.

[0046] Specifically, the high-temperature airflow after cooling the clinker is sent to the bottom of the external heating zone of the decomposition furnace 2 to assist in fuel combustion, achieving waste heat recovery and cascade utilization. The high-temperature airflow replaces the ambient temperature combustion air, increasing the initial temperature of the external heating zone, reducing the energy consumption required for preheating fuel combustion, improving combustion efficiency, and reducing fuel consumption, thereby reducing the overall energy consumption and carbon emissions of the system. The high-temperature airflow is sent from the bottom of the external heating zone, mixing evenly with the fuel to form a stable hot airflow from bottom to top. The heat is transferred more evenly to the internal decomposition zone through the furnace wall, ensuring stable temperature in the internal decomposition zone and avoiding local temperature fluctuations that affect the decomposition efficiency of calcium carbonate. Bottom air supply ensures more complete fuel combustion in the heating zone, reducing the generation of unburned materials and lowering pollutant emissions.

[0047] The clinker calcination step and the pre-decomposition step form a closed heat loop, converting the low-grade waste heat generated by clinker cooling into the heat source required for pre-decomposition, improving heat utilization, reducing the demand for external heat sources, and the introduction of high-temperature airflow optimizes the flow field distribution in the external heating zone, enhances the heat conduction effect of the furnace wall, and makes the raw material in the internal decomposition zone more evenly heated, thus improving the quality of semi-clinker.

[0048] In some embodiments, the high-temperature gas after combustion in the external heating zone of the decomposition furnace 2 is extracted and sent to the preheater 1 for countercurrent heat exchange with the cement raw materials.

[0049] Specifically, the high-temperature gas from combustion in the external heating zone of the decomposition furnace 2 is extracted and sent to the preheater 1 for countercurrent heat exchange with the cement raw materials. This achieves the cascade recovery and efficient utilization of the waste heat from combustion in the external heating zone, fully tapping the waste heat value of the high-temperature flue gas. It replaces the method of setting up an additional preheating heat source, significantly reducing energy consumption in the raw material preheating stage, forming a complete closed loop for heat utilization, and further improving overall thermal efficiency. The countercurrent heat exchange method allows the high-temperature flue gas and cement raw materials to form a reverse contact heat exchange state, maximizing the contact time between the gas and solid phases and improving the sufficiency of heat exchange. This allows for rapid preheating of the cement raw materials to a suitable temperature of 750-850℃, reducing the heating load for subsequent pre-decomposition stages. Simultaneously, the temperature of the high-temperature flue gas is significantly reduced after heat exchange, reducing direct heat loss and lowering the temperature of subsequent flue gas treatment processes. The design optimizes equipment load; the high-temperature gas extracted from the external heating zone is clean flue gas from fuel combustion, free from CO2 contamination from raw material decomposition. After being fed into preheater 1, it only performs heat exchange, without interfering with the raw material preheating process or diluting the high-concentration CO2 generated in subsequent decomposition, thus ensuring the efficiency of the carbon capture stage. Furthermore, this design creates a directional flow channel for the flue gas in the external heating zone. Extracting high-temperature gas optimizes the flue gas flow field in the external heating zone, ensuring sufficient ventilation for fuel combustion, allowing for more complete combustion and further improving heating efficiency. Simultaneously, the stable flue gas extraction rate maintains pressure balance in the external heating zone, preventing pressure fluctuations within the furnace from affecting heat transfer through the furnace wall to the internal decomposition zone, ensuring temperature stability in the internal decomposition zone, and thus allowing the raw material decomposition reaction to proceed continuously and efficiently, improving the stability of the entire production process.

[0050] Example 1: A method for producing low-carbon cement using a vertical external pyrolysis furnace 2; a system for producing low-carbon cement using a vertical external pyrolysis furnace 2. When the system is started, high-concentration CO2 gas is introduced into the system through the gas replenishment inlet to replace the air in the decomposition zone inside the decomposition furnace 2 until a CO2 cycle is established.

[0051] Preheating involves exchanging heat between 100t / h of cement raw meal and high-temperature hot air in a countercurrent manner within the raw meal preheater 1, preheating it to 800℃.

[0052] In the externally heated precalciner, preheated raw meal is continuously fed into the top of the vertical externally heated precalciner 2 and into the internal precalciner zone, where the precalcination temperature is controlled at 900℃. The precalcined semi-clinker is discharged from the bottom of the precalciner 2, achieving a 97% decomposition rate of calcium carbonate in the raw meal. The CO2 produced during decomposition is discharged from the top of the precalciner 2. The external heating zone indirectly heats the raw meal in the internal heating zone through an external heat source via the furnace wall, causing the calcium carbonate in the raw meal to decompose. The high-temperature gas after combustion is extracted from the top and sent to the raw meal preheater 1 for countercurrent heat exchange with the cement raw meal.

[0053] In the clinker calcination process, the decomposed semi-clinker is fed into a short rotary kiln 3a and sintered into clinker at 1500°C. The sintered cement clinker is then cooled to produce sintered cement clinker. The high-temperature gas flow after cooling the clinker is sent to the bottom of the external heating zone of the external pyrolysis furnace 2 to assist in fuel combustion in the heating zone.

[0054] Carbon capture and recycling involves extracting the high-concentration CO2 tail gas generated in the decomposition zone. After cooling, dehydration, and dust removal, the CO2 concentration in the tail gas is approximately 93%, which is then sent to the carbon capture mechanism to obtain a high-purity CO2 product. Among these processes, 150 t / h of CO2-rich tail gas is extracted, pressurized, and temperature-adjusted before being sent back to the bottom of the decomposition furnace 2 in step S2 as a circulating fluidizing gas, serving as the fluidizing medium for raw material decomposition.

[0055] In the decomposition furnace 2, the raw material mainly undergoes the decomposition reaction of calcium carbonate. However, other components in the raw material will also undergo other side reactions at the temperature to produce impurity gases, which will affect the CO2 concentration in the tail gas. In addition, there may be trace gas exchanges between the reaction system and the outside world, which will prevent the CO2 concentration from reaching 100%.

[0056] In Example 2, other conditions were the same as in Example 1. 50 t / h of CO2-rich tail gas was extracted from the CO2 circulation and sent back to the bottom of the decomposer 2 as a fluidizing medium for raw material decomposition. In the decomposer 2, the decomposition rate of calcium carbonate in the raw material reached 91%, and the CO2 concentration in the tail gas sent to the carbon capture device was approximately 88%.

[0057] A decrease in the flow rate of the fluidizing medium reduces the efficiency of mass and heat transfer, and decreases the decomposition rate; the proportion of impurity gases generated by decomposition in the raw material increases, and the CO2 concentration decreases.

[0058] In Example 3, other conditions were the same as in Example 1. 300 t / h of CO2-rich tail gas was extracted from the CO2 cycle and sent back to the bottom of the decomposer 2 as a fluidizing medium for raw material decomposition. In the decomposer 2, the decomposition rate of calcium carbonate in the raw material reached 95%, and the CO2 concentration in the tail gas sent to the carbon capture device was approximately 94%.

[0059] As the flow rate of the fluidizing medium increases, the residence time of the raw meal in the decomposition furnace 2 decreases, and the decomposition rate decreases; the proportion of impurity gases generated by the decomposition of the raw meal decreases, and the CO2 concentration increases slightly.

[0060] In Example 4, other conditions were the same as in Example 1, with the temperature in the decomposition zone inside the decomposition furnace 2 controlled at 860°C. In the decomposition furnace 2, the decomposition rate of calcium carbonate in the raw material reached 88%, and the CO2 concentration in the exhaust gas sent to the carbon capture device was approximately 95%.

[0061] The decomposition reaction of calcium carbonate in raw materials is an endothermic reaction, and the reaction conversion rate decreases as the decomposition temperature decreases; the side reactions of raw materials in decomposition furnace 2 are reduced, the amount of impurity gas is reduced, and the CO2 concentration is increased.

[0062] In Example 5, other conditions were the same as in Example 1, with the temperature in the decomposition zone inside the decomposition furnace 2 controlled at 940°C. In the decomposition furnace 2, the decomposition rate of calcium carbonate in the raw material reached 99%, and the CO2 concentration in the tail gas sent to the carbon capture device was approximately 90%.

[0063] The decomposition reaction of calcium carbonate in raw materials is an endothermic reaction, and the reaction conversion rate increases with the increase of decomposition temperature; the side reactions of raw materials in decomposition furnace 2 increase, the amount of impurity gas increases, and the CO2 concentration decreases.

[0064] Comparative Example 1: Other conditions were the same as in Example 1, except that the CO2-rich tail gas was not extracted and sent back to the bottom of the decomposition furnace 2 as circulating fluidizing gas, and there was no fluidizing medium. In the decomposition furnace 2, the decomposition rate of calcium carbonate in the raw material was less than 60%, and the CO2 concentration in the tail gas sent to the carbon capture mechanism reached 99.5%.

[0065] Comparative Example 2, with other conditions the same as in Example 1, did not extract CO2-rich tail gas as circulating fluidizing gas to be sent back to the bottom of decomposer 2. Instead, 150 t / h of hot air was sent to the bottom of decomposer 2 as a fluidizing medium via a blower. In decomposer 2, the decomposition rate of calcium carbonate in the raw material was approximately 97%, and the CO2 concentration in the tail gas sent to the carbon capture device was only 22%.

[0066] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0067] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0068] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0069] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0070] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0071] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A system for producing low-carbon cement using a vertical external pyrolysis furnace, characterized in that, include: The system includes a preheating mechanism, a decomposition furnace, a clinker calcination mechanism, and a carbon capture mechanism. The preheating mechanism includes a preheater with a first inlet 1a for introducing cement raw meal, a first outlet 1b for discharging preheated raw meal, and a second inlet 1c for introducing high-temperature heat exchange flue gas. The decomposition furnace has an internal decomposition zone and an external heating zone that are physically isolated from each other. The external heating zone surrounds the internal decomposition zone. The top of the decomposition furnace is provided with a third inlet 2a and a second outlet 2b that communicate with the internal decomposition zone, and a third outlet 2g that communicates with the external heating zone. The bottom of the decomposition furnace is provided with a fourth inlet 2e and a tertiary air inlet 2f that communicate with the external heating zone, and a fifth inlet 2c and a fourth outlet 2d that communicate with the internal decomposition zone. The clinker calcination mechanism includes a rotary kiln and a grate cooler. The rotary kiln is connected to the internal decomposition zone of the vertical external pyrolysis furnace, the grate cooler is connected to the rotary kiln, and the carbon capture mechanism is connected to the decomposition furnace. The first outlet is connected to the third inlet, the third outlet is connected to the second inlet, the second outlet is connected to the carbon capture mechanism through the first pipeline, the first branch is provided on the first pipeline, and the first branch is connected to the fifth inlet; the grate cooler is connected to the tertiary air inlet 2f.

2. The system for producing low-carbon cement using a vertical external pyrolysis furnace according to claim 1, characterized in that, The rotary kiln is connected to the fourth outlet through the sixth inlet 3c, the discharge end of the rotary kiln is connected to the feed inlet of the grate cooler, the fifth outlet 3d of the grate cooler discharges sintered cement clinker, and the sixth outlet 3e is connected to the tertiary air inlet.

3. The system for producing low-carbon cement using a vertical external pyrolysis furnace according to claim 1, characterized in that, The first branch is provided with a CO2 replenishment interface, which is used to replenish the internal decomposition zone with external CO2.

4. The system for producing low-carbon cement using a vertical external pyrolysis furnace according to claim 1, characterized in that, The first pipeline is also provided with a cooling device, a dehydration device and a dust removal device in sequence. The cooling device, the dehydration device and the dust removal device are all located upstream of the first branch and between the second outlet 2b and the first branch.

5. A method for producing low-carbon cement using a vertical external pyrolysis furnace, characterized in that, Includes the following steps: Preheating involves feeding cement raw materials into a preheater for counter-current heat exchange with high-temperature hot air, preheating them to 750-850℃ to obtain preheated raw materials. Pre-decomposition involves continuously feeding preheated raw materials into the internal decomposition zone from the top of the decomposition furnace. The external heating zone indirectly heats the preheated raw materials in the internal heating zone through the furnace wall from an external heat source, causing the calcium carbonate in the preheated raw materials to decompose, resulting in semi-cooked material that is discharged from the bottom of the decomposition furnace. The CO2 generated during decomposition is discharged from the top of the decomposition furnace. Clinker calcination involves feeding the resulting semi-clinker into a rotary kiln, where it is sintered into clinker at 1450-1550℃, and then cooled to produce sintered cement clinker. Carbon capture and recycling involves extracting the CO2 tail gas generated in the decomposition zone during the pre-decomposition step, cooling, dehydrating, and removing dust, and then sending it to the carbon capture unit to obtain a high-purity CO2 product.

6. The method for producing low-carbon cement using a vertical external pyrolysis furnace according to claim 5, characterized in that, The decomposition temperature in the internal decomposition zone during the pre-decomposition step is 850-950℃.

7. The method for producing low-carbon cement using a vertical external pyrolysis furnace according to claim 5, characterized in that, A portion of the CO2 tail gas generated in the internal decomposition zone is pressurized and temperature-controlled before being returned to the bottom of the decomposition furnace as a circulating fluidizing gas to serve as the fluidizing medium for the raw materials in the decomposition furnace.

8. The method for producing low-carbon cement using a vertical external pyrolysis furnace according to claim 7, characterized in that, The mass ratio of the CO2 circulating fluidized gas to the raw material processing volume is between 1:2 and 3:

1.

9. The method for producing low-carbon cement using a vertical external pyrolysis furnace according to claim 5, characterized in that, The high-temperature gas flow after cooling the clinker is sent to the bottom of the external heating zone of the decomposition furnace to assist fuel combustion in the heating zone.

10. The method for producing low-carbon cement using a vertical external pyrolysis furnace according to claim 5, characterized in that, The high-temperature gas from the combustion in the external heating zone of the decomposition furnace is extracted and sent to the preheater for countercurrent heat exchange with the cement raw materials.

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