System and method for producing high purity co2 by indirect heating of cement raw meal with low energy consumption

Abstract

The application discloses a system and method for preparing high-purity carbon dioxide by indirectly heating cement raw materials with low energy consumption, which comprises a preheating subsystem, a calcining subsystem, a cooling subsystem, a heat-exchange and decomposition subsystem, a waste heat recovery subsystem and a CO2 storage subsystem; the material inlet of the heat-exchange and decomposition subsystem is connected with the preheating subsystem, the material outlet is connected with the inlet of a flue chamber, the hot flue gas inlet is communicated with the tertiary air of a decomposition furnace, the hot flue gas outlet after fuel combustion is connected with the hot air inlet of the waste heat recovery subsystem, the waste flue gas outlet is connected with the upper part of the decomposition furnace, and the CO2 outlet is connected with the waste heat recovery subsystem; the heat-exchange and decomposition subsystem is provided with a superheated steam inlet for directly contacting and exchanging heat with the raw materials and a fuel inlet. The application is combined with the characteristics of CO2 emission of the cement industry, coupled with and cooperated with the cement clinker sintering system for optimization, the carbon capture energy consumption and operation cost are reduced, the economic benefits of carbon emission reduction of the cement plant are improved, and the captured CO2 concentration reaches more than 95%.

Description

Technical Field

[0001] This invention relates to a system and method for coupling cement and CO2 preparation, and more particularly to a system and method for indirectly heating cement raw materials to produce high-purity CO2 with low energy consumption. Background Technology

[0002] Carbon emission reduction in the cement industry has a significant impact on achieving carbon neutrality goals, urgently requiring the industry to drive green and low-carbon development through technological innovation. Among carbon emission reduction measures such as improving energy efficiency, replacing raw materials and fuels, low-carbon cement, and CCUS (Carbon Capture, Utilization, and Storage), CCUS has the greatest emission reduction potential. Currently, research on CCUS technology both domestically and internationally mainly focuses on industries such as power, coal, and chemicals, and CCUS technology is still in its early stages.

[0003] In traditional cement production processes, fuel and flue gas generated after combustion come into direct contact with materials. The kiln tail exhaust gas volume is large, the CO2 concentration is low, and the content of various impurities is high, resulting in low CO2 capture efficiency, complex systems, and high operating costs.

[0004] CO2 emissions from the cement industry can be divided into two parts: fuel combustion emissions and production process (carbonate decomposition) emissions, i.e., Qtotal = ∑(Qcombustion + Qprocess). The direct CO2 emissions from the cement industry are approximately (0.8–0.85) kg / kg·cl, with CO2 from carbonate decomposition during production accounting for over 60%. On the other hand, the biggest challenge in carbon reduction is how to lower carbon capture costs and how to effectively, fully utilize, and store subsequent CO2. Currently, carbon reduction technologies in the cement industry, such as oxy-fuel combustion and chemical absorption, suffer from system complexity and high investment and operating costs. Therefore, it is necessary to propose a carbon reduction system and method that can reduce the energy consumption and operating costs of carbon capture in cement plants, taking into account the characteristics of CO2 emissions from the cement industry and the current actual utilization of captured CO2. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a low-energy cement raw material indirect heating system for producing high-purity CO2 with high CO2 capture rate and low operating cost;

[0006] A second objective of this invention is to provide a method for preparing high-purity CO2 using the system described above.

[0007] Technical Solution: The low-energy cement raw material indirect heating system for producing high-purity carbon dioxide according to the present invention includes a preheating subsystem, a calcination subsystem, and a cooling subsystem. It also includes a heat exchange decomposition subsystem for heating part of the raw material to decompose carbonates and generate CO2, a waste heat recovery subsystem for recovering heat from the generated CO2, and a CO2 storage subsystem for storing the recovered CO2. The material inlet of the heat exchange decomposition subsystem is connected to the preheating subsystem, the material outlet is connected to the flue gas chamber, the hot flue gas inlet is connected to the tertiary air of the decomposition furnace, the hot flue gas outlet after fuel combustion of the heat exchange decomposition subsystem is connected to the hot air outlet of the waste heat recovery subsystem, the waste flue gas outlet for discharging the heat-exchanged flue gas is connected to the upper part of the decomposition furnace, and the CO2 outlet is connected to the waste heat recovery subsystem. The heat exchange decomposition subsystem is equipped with a superheated steam inlet for direct heat exchange with the raw material.

[0008] The material inlet of the third cyclone of the preheating subsystem is connected in parallel with the material inlet of the heat exchange decomposition subsystem and then connected to the material outlet of the second cyclone; the material outlet of the heat exchange decomposition subsystem and the material outlet of the waste heat recovery subsystem are connected in parallel to the smoke chamber located below the decomposition furnace.

[0009] The heat exchange decomposition subsystem includes two or more reaction blocks. Each reaction block includes an outer heat exchange tube, an inner reaction tube, and an insulation layer, with a superheated steam pipe at the bottom. The inner reaction tube contains an inner heat exchange tube.

[0010] The heat exchange inner tube is provided with a baffle at an angle of 20 to 30 degrees to the horizontal plane, and the baffle has a spiral structure in the vertical direction of the heat exchange inner tube.

[0011] The waste heat recovery subsystem includes a cyclone separator and an air preheater; the material outlet of the cyclone separator is connected in parallel to the material outlet of the heat exchange decomposition subsystem and the material outlet of the waste heat recovery subsystem and is connected to the smoke chamber; the CO2 storage subsystem includes a water-gas separator, a dust collector, a gas drying tower and a liquefaction storage device connected in sequence.

[0012] The above-described method for preparing high-purity carbon dioxide includes the following steps:

[0013] Cement raw materials are added to the preheating subsystem. After heat exchange is completed in the preheating subsystem, they enter the calcination subsystem and are calcined into cement clinker. After cooling, the material is sent to the finished product warehouse for storage.

[0014] Part of the material separated from the discharge port of the second cyclone separator comes into contact with superheated steam in a countercurrent heat exchanger within the heat exchanger decomposition subsystem. The hot flue gas from fuel combustion and the tertiary air from the decomposition furnace enter the heat exchanger decomposition subsystem and undergo non-contact countercurrent heat exchange with the raw materials. The waste flue gas, cooled by heat exchange, returns to the upper part of the decomposition furnace. The CO2 released from the decomposition of carbonates in the material enters the waste heat recovery subsystem for waste heat recovery. The CO2 undergoes gas-solid separation in the waste heat recovery subsystem and exchanges heat with ambient air. The heated air is then used as combustion air for fuel and connected in parallel to the hot flue gas in the heat exchanger decomposition subsystem. The CO2 after heat exchange enters the CO2 storage subsystem, where it is condensed, dust collected, dried, and stored. The material from the heat exchanger decomposition subsystem and the material recovered by the waste heat recovery subsystem together serve as part of the raw materials for cement production, entering the smoke chamber to generate cement clinker.

[0015] Of the heat material separated from the raw material after the secondary heat exchange, 2-12% enters the heat exchange decomposition subsystem.

[0016] The temperature of the hot flue gas entering the heat exchange decomposition subsystem is 1000-1050℃, the temperature of the hot flue gas leaving the heat exchange decomposition subsystem is 930-950℃, and the material decomposition temperature is 950-1000℃.

[0017] The material temperature entering the heat exchange decomposition subsystem is 480-500℃, the material residence time is 5-15 seconds, and the material and CO2 gas temperature leaving the heat exchange decomposition subsystem is 900-950℃.

[0018] The temperature of the superheated steam entering the heat exchange decomposition subsystem is 950–1000℃, and the water vapor content in the gas within the heat exchange decomposition subsystem is 10–15%.

[0019] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects:

[0020] (1) This invention separates a portion of the hot material or raw material entering the kiln from the n-1 stage cyclone separator of the preheater and adds it to a heat exchange decomposition subsystem for indirect heating and decomposition of carbonates, which can directly produce high-purity CO2 gas. This eliminates the need for a separate preheater, making full use of the existing preheater in the cement production system, which helps reduce the system's heat and electricity consumption. The system is relatively simple, with a high CO2 capture rate and low carbon capture cost.

[0021] (2) The present invention rationally designs the internal components of the reaction block of the heat exchange decomposition subsystem. The internal components increase the material flow path on the one hand and slow down the downward movement speed of the material on the other hand. The combined effect of the two greatly increases the residence time of the material in the reaction block. Under the action of the internal components, the material is more easily dispersed, avoiding material deviation, and effectively enhancing the heat exchange effect between the gas and solid phases.

[0022] (3) Since high-temperature CO2 is difficult to transport and has an impact on carbonate decomposition, superheated steam with appropriate content is used to carry the material upward. This invention adopts a combination device of static, indirect heating carbonate decomposition, and indirect countercurrent heat exchange cooling (heat recovery) between superheated steam and material. Due to the adoption of static equipment, the number of moving parts is reduced, the reliability of operation at high temperature is improved, and the air leakage is greatly reduced, so high-purity CO2 gas can be produced.

[0023] (4) This invention fully considers the heat source supply method, heating method and temperature control, carbonate source, material movement method and residence time control, gas-solid separation and CO2 extraction, etc. Through coupling and synergistic optimization with the cement clinker calcination system, this technology and equipment development has fast heat exchange speed and high efficiency, realizes stable operation of capture and clinker calcination system, and is expected to become an important competitive carbon capture and emission reduction technology in the cement industry. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the system structure of the present invention;

[0025] Figure 2 This is a schematic diagram of a single reaction block structure of the present invention;

[0026] Figure 3 This is a schematic diagram of the horizontal cross-section of the four reaction blocks of the system of the present invention;

[0027] Figure 4 This is a schematic diagram of the horizontal cross-section of the baffle in the system of the present invention;

[0028] Figure 5 Material adhesion tests of the raw materials of this invention at room temperature, 1000°C, and 1200°C;

[0029] Figure 6 Cold model tests of the system with baffles for this invention under windless and ventilated conditions;

[0030] Figure 7 This is a comparison chart of the dwell time of the system of the present invention in numerical simulation with and without baffles. Detailed Implementation

[0031] The present invention will now be described in further detail.

[0032] like Figure 1-4As shown, the components are: 0 raw material inlet, 1 first cyclone, 2 second cyclone, 3 third cyclone, 4 fourth cyclone, 5 fifth cyclone, 6 decomposition furnace, 7 rotary kiln, 8 grate cooler, 9 reactor material inlet, 10 flue gas inlet, 11 tertiary air inlet, 12 heat exchanger outer tube, 13 rotary feeder, 14 material outlet, 15 superheated steam inlet, 16 reaction inner tube, 17 insulation layer, 18 flue gas outlet, 19 CO2 gas outlet, 20 cyclone separator, 21 air preheater, 22 water-gas separator, 23 condensate outlet, 24 dust collector, 25 gas drying tower, 26 liquefaction storage device, 27 flue gas to decomposition furnace inlet, 28 heat exchanger inner tube, 29 superheated steam pipe, 30 reaction block, 101 flap valve, 102 baffle, 103 product granules, 104 product hopper, 105 baffle, 106 smoke chamber. This invention provides a low-energy cement raw material indirect heating system for producing high-purity carbon dioxide, including a preheating subsystem, a calcination subsystem, a cooling subsystem, a heat exchange decomposition subsystem, a waste heat recovery subsystem, and a CO2 storage subsystem.

[0033] The preheating subsystem, from top to bottom, includes a first cyclone 1, a second cyclone 2, a third cyclone 3, a fourth cyclone 4, and a fifth cyclone 5, achieving five-stage heat exchange. The gas inlet of the first cyclone 1 is connected to the gas outlet of the second cyclone 2 via a pipeline; the gas outlet of the third cyclone 3 is connected to the gas inlet of the second cyclone 2 via a pipeline, and the gas inlet of the third cyclone 3 is connected to the gas outlet of the fourth cyclone 4 via a pipeline. The calcination subsystem includes a decomposition furnace 6, a fifth cyclone 5, and a rotary kiln 7, achieving high-temperature calcination of the clinker. The gas outlet of the decomposition furnace 6 is connected to the gas inlet of the fifth cyclone 5 via a pipeline; the gas inlet of the decomposition furnace 6 is connected to the gas outlet of the fifth cyclone 5 via a pipeline; the material outlet of the fourth cyclone 4 is connected to the material inlet of the decomposition furnace 6; the gas outlet at the top of the decomposition furnace 6 is connected to the gas inlet of the fifth cyclone 5, and the gas outlet of the fifth cyclone 5 is connected to the gas inlet of the fourth cyclone 4. The cooling subsystem includes a grate cooler 8, which cools the clinker.

[0034] like Figure 2-4As shown, the heat exchange decomposition subsystem includes two or more reaction blocks 30. Each reaction block 30 is a vertical static device with multi-point material distribution, and its height is 50-65m. In this embodiment, the heat exchange decomposition subsystem includes four reaction blocks 30. Each reaction block 30 consists of, from the outside to the inside, an insulation layer 17, an outer heat exchange tube 12, an inner reaction tube 16, and an inner heat exchange tube 28, with their center points coinciding to form a sealed casing. That is, each inner reaction tube 16 has an independent heating system to maintain the temperature balance of the raw materials. The inner reaction tube 16 contains the inner heat exchange tube 28, and each outer part is equipped with an independent outer heat exchange tube 12 and an insulation layer 17 from the inside out. A superheated steam pipe 29 is installed at the bottom of each reaction block 30, separated from the others. Multiple burners are spaced apart on the outer heat exchange tube for introducing fuel and exhaust gas; an exhaust pipe is led out from the tertiary air outlet of the decomposition furnace, and an air inlet is also provided on the outer heat exchange tube for communication with this exhaust pipe. The end of the superheated steam pipe 29 entering the inner reaction tube 16 coincides with the center of the inner reaction tube 16. A baffle 102 with an angle of 20-30 degrees to the horizontal plane is installed on the outside of the inner heat exchange tube 28. The baffle 102 has a spiral structure in the longitudinal direction and is evenly arranged in the transverse direction, so that the material falls from one baffle to the next, thereby slowing down the falling speed and prolonging the residence time. The materials of the outer heat exchange tube, inner reaction tube 16, outer heat exchange tube 12, inner heat exchange tube 28, and baffle 102 are all RA330 alloy, with a Cr content of 27-30% and a Ni content of 47-50%. An inverted conical product hopper 104 is provided at the bottom of the reaction block 30. Hot flue gas from the tertiary air and fuel combustion is evenly distributed on the outer heat exchange tube 12, indirectly heating the material in the inner reaction tube 16 without direct contact. The gas outlet of the reaction block 30 is connected to the upper middle part of the decomposition furnace 6. The waste gas temperature of the heat exchange decomposition subsystem is relatively high. It is introduced from the upper part of the decomposition furnace and will not affect the combustion of coal. It is connected to the original cement main system to avoid adding additional emission points.

[0035] The material inlet of the third cyclone 3 of the preheating subsystem is connected in parallel to the material inlet of the heat exchange decomposition subsystem and then connected to the material outlet of the second cyclone 2. This means that a portion of the system material from the second cyclone 2 is separated and added to the inner reaction tube 16, where the carbonates decompose and release CO2 gas. Under the action of the bottom baffle 102 of the reaction block 30, the material and gas at the bottom of the inner reaction tube 16 are separated. The CO2 gas flows out from the top and connects to the gas inlet of the cyclone separator 20 of the waste heat recovery system; the material flows out from the bottom of the inner reaction tube 16 and connects in parallel with the material recovered by the waste heat recovery subsystem to the smoke chamber 106 located at the bottom of the decomposition furnace 6.

[0036] The waste heat recovery subsystem includes a cyclone separator 20 and an air preheater 21, enabling heat exchange between the high-temperature CO2 gas from the heat exchange decomposition subsystem and the preheated air to recover waste heat. The air outlet of the air preheater 21, after being heated, is connected in parallel to the gas inlet of the heat exchange outer pipe 12 via the hot flue gas duct. The CO2 storage subsystem includes a water-gas separator 22, a dust collector 24, a gas drying tower 25, and a liquefaction storage device 26. The CO2 gas outlet of the air preheater 21 is connected to the gas inlet of the water-gas separator 22, separating most of the condensate. The dust collector 24 is connected to both the water-gas separator 22 and the gas drying tower 25. The material outlet of the reaction inner pipe 16 is connected in parallel to the material outlet of the cyclone separator 20 via the smoke chamber 106. The gas outlet of the gas drying tower 25 is connected to the gas inlet of the liquefaction storage device 26.

[0037] Another aspect of this invention provides a method for preparing high-purity carbon dioxide using the above-described system, mainly comprising the following steps:

[0038] Cement raw materials are added to the preheating subsystem. After completing four stages of heat exchange in the preheating subsystem, they enter the calcination subsystem for calcination. The rotary kiln calcines the raw materials into cement clinker. After cooling, the materials are sent to the finished product warehouse for storage.

[0039] After the fuel is burned, it serves as an external heat source and enters the heat exchange decomposition subsystem together with the hot flue gas from the tertiary air. It flows from bottom to top along the outer and inner heat exchange tubes, and flows counter-currently to the material flow in the inner reaction tube. In other words, the gas flow in the internal and external heating systems is opposite to the gas and solid flow in the reaction subsystem. Heat is transferred to the material from the wall, and the waste flue gas after heat exchange and cooling is returned to the decomposition furnace.

[0040] The hot material exiting the second cyclone separator is fed into the heat exchanger inner tube of the heat exchange decomposition subsystem. The reaction block also functions as a heat exchanger. The hot material descends from the top of the inner tube, where it is heated by conduction and radiation from the hot flue gas through the wall, undergoing heat exchange. Internal baffles disperse the material, preventing material deviation and enhancing heat exchange. Superheated steam introduced at the bottom of the reaction block directly contacts the material particles, providing heat transfer to the hot flue gas supplied by the inner and outer heat exchange tubes, carrying the material upwards, dispersing it, and increasing its residence time. The carbonates in the material decompose and release CO2 gas. Under the action of the baffles at the bottom of the reaction block, the material and gas are separated, with the CO2 gas flowing out from the top of the inner tube. The high-purity CO2 gas and superheated steam from the carbonate decomposition are directly captured. The calcined product particles are collected in the product hopper, where the material acts as a seal against the gas, preventing water vapor and decomposed CO2 gas from escaping and causing air leakage. The material flows out of the product hopper and, together with the material recovered by the waste heat recovery subsystem, enters the smoke chamber 106 as part of the raw material for cement to generate cement clinker.

[0041] CO2 gas discharged from the top of the heat exchanger tubes, after partial material recovery in the separator, enters the air preheater. High-temperature flue gas exchanges heat with air to recover some waste heat, and after condensation to recover most of the moisture, dust is collected. A small amount of water vapor is recovered in the gas drying tower and then stored in the liquefaction unit. Ambient air, after heat exchange in the air preheater, is connected in parallel to the hot flue gas of the heat exchange decomposition subsystem as fuel. The material recovered by the separator is connected in parallel to the reaction outlet material and returned to the flue gas chamber.

[0042] Tables 1 and 2 show the experimental decomposition data of raw meal after calcination for 10 min under CO2 and N2 atmospheres, respectively. Analysis of the loss on ignition (LOI) results shows a significant decrease in LOI after calcination. Comparing the two calcination atmospheres, the apparent decomposition rate of the material at each temperature point was higher under pure N2 atmosphere, indicating a greater degree of carbonate decomposition in the cement raw meal. Therefore, high calcination temperature and low CO2 concentration help promote the decomposition of cement raw meal.

[0043] In summary, the carbon dioxide atmosphere increases the decomposition temperature of carbonates. When the calcination atmosphere is atmospheric pressure CO2, CaCO3 decomposes at temperatures exceeding 900℃ or higher. The high-temperature resistance of the heat exchanger inner tube material must be considered. Using superheated steam is beneficial for CO2 separation from the product exhaust gas, but the separation of water vapor and CO2 results in significant energy loss. Considering all factors, a superheated steam volume percentage of 10-15% in the high-temperature CO2 gas is recommended.

[0044] During the heating and decomposition of cement raw materials, harmful components such as alkali, chlorine, and sulfur continuously volatilize and condense. The inner wall of the heat exchanger tubes places high demands on the equipment material; it must be heat-resistant, corrosion-resistant, have good thermal conductivity, and be easy to form and weld. Although experimental calculations show that the thermal conductivity of 2520 heat-resistant steel at 850℃~950℃ is 31.22~38.48w / m·K, comparisons reveal that 2520 heat-resistant steel (06Cr25Ni20, GB / T20878-2007) has an operating temperature below 1000℃ and is not recommended as a material for heat exchanger inner tubes. Therefore, RA330 alloy was selected as the material for the heat exchanger inner tubes. RA330 alloy is a nickel-iron-chromium heat-resistant alloy; the addition of 1.25% silicon gives it excellent high-temperature strength. RA330 alloy has excellent resistance to high-temperature oxidation and media corrosion, maintaining good strength, carbonization resistance, and oxidation resistance even at temperatures up to 1200℃. Figure 5 For the raw material adhesion test, by Figure 5 It can be seen that at high temperatures, most of the raw material powder is easy to fall off, and the amount of raw material powder adhering is relatively small.

[0045] Figure 6 The test was a cold model test. The results show that the material dispersion is good under the combined action of gas and baffles.

[0046] from Figure 7 A comparative analysis of the residence time in the heat exchanger inner tube with and without baffles shows that without baffles, the minimum residence time is 0.46 s, the maximum residence time is 1.55 s, and the average is 0.685 s. With baffles, the minimum residence time is 0.629 s, the maximum residence time is 7.706 s, and the average is 2.777 s. The average residence time increases with the presence of baffles.

[0047] Example 2

[0048] Taking a 5000t / d clinker production line with a five-stage preheater as an example, when the material consumption is 1.6, 8000t / d of cement raw meal is added to the preheating subsystem. After completing four stages of heat exchange in the preheating subsystem, it enters the calcination subsystem for calcination. The calcination is carried out in a rotary kiln to become cement clinker. After cooling, the material is sent to the finished product warehouse for storage.

[0049] A total of 6850 Nm of energy comes from fuel combustion and tertiary air at 1050°C. 3 The hot flue gas, at a rate of / h, enters the heat exchange and decomposition subsystem, flowing along the outer wall of the heat exchange inner tube. After heat exchange and cooling, the waste flue gas at 950℃ returns to the upper and middle flue chamber of the decomposition furnace.

[0050] The second cyclone separator separates 185 t / d of hot material at 490℃, representing 2.3% of the system's raw material, which is added to the heat exchanger inner tube of the heat exchanger decomposition subsystem. The reaction block also functions as a heat exchanger. The material descends from the top of the heat exchanger inner tube, where it is heated by conduction and radiation from the hot flue gas, undergoing heat exchange. Internal baffles disperse the material, preventing material deviation and enhancing heat exchange. Superheated steam introduced at the bottom of the reaction block carries the material upwards, further dispersing it and increasing its residence time. The gas-solid heat exchange efficiency of the heat exchanger decomposition subsystem is 90%, reaching 930℃. The carbonates in the material decompose, releasing CO2 gas. At the bottom of the heat exchanger inner tube, the material and gas are separated; the CO2 gas flows out from the top of the inner tube, while the material flows out from the bottom. This material, along with material recovered by the waste heat recovery subsystem, is used as part of the cement raw material and enters the flue chamber to generate cement clinker.

[0051] The CO2 gas discharged from the top of the heat exchanger inner tube contains 10% superheated steam. After partial material recovery in the separator, it enters the air preheater. High-temperature flue gas exchanges heat with air to recover some waste heat. After condensation to recover most of the moisture, dust is collected, and a small amount of water vapor is recovered in the gas drying tower before being stored in the liquefaction unit. Ambient air is heated to 4200 Nm³ in the air preheater. 3 After reaching 360°C and operating at a constant temperature, the gas is connected in parallel to the hot flue gas of the heat exchange decomposition subsystem as a heat source. The material recovered by the separator is connected in parallel to the outlet material of the heat exchange inner tube and returned to the flue gas chamber.

[0052] When using this production line to capture 20,000 tons / year of CO2, the energy consumption of the unit CO2 capture system is 2.0 GJ / t.CO2, with virtually no operating costs. The gas-solid heat exchange efficiency is 90%, the carbonate decomposition rate is 98%, and the captured CO2 concentration reaches 98%. During CO2 capture, there is no impact on the quality of clinker.

[0053] Example 3

[0054] Taking a 5000t / d clinker production line with a five-stage preheater as an example, when the material consumption is 1.6, 8000t / d of cement raw meal is added to the preheating subsystem. After completing four stages of heat exchange in the preheating subsystem, it enters the calcination subsystem for calcination. The calcination is carried out in a rotary kiln to become cement clinker. After cooling, the material is sent to the finished product warehouse for storage.

[0055] 25000 Nm from fuel and tertiary wind at 1000℃ 3 The hot flue gas, at a temperature of 940°C, enters the heat exchange and decomposition subsystem, flowing along the outer wall of the heat exchange inner tube. After heat exchange and cooling, the waste flue gas returns to the decomposition furnace.

[0056] The second cyclone separator separates 560 t / d of hot material at 500℃, representing 5.7% of the system's raw material, which is added to the heat exchanger inner tube of the heat exchanger decomposition subsystem. The reaction block also functions as a heat exchanger. The material descends from the top of the heat exchanger inner tube, where it is heated by the conduction and radiation of the hot flue gas, undergoing heat exchange. Internal baffles disperse the material, preventing material deviation and enhancing heat exchange. Superheated steam is introduced at the bottom of the reaction block, carrying the material upwards, further dispersing it and increasing its residence time. The gas-solid heat exchange efficiency of the heat exchanger decomposition subsystem is 83%, reaching 920℃. The carbonates in the material decompose and release CO2 gas. At the bottom of the heat exchanger inner tube, the material and gas are separated; the CO2 gas flows out from the top of the inner tube, while the material flows out from the bottom. This material, along with material recovered by the waste heat recovery subsystem, serves as part of the cement raw material and enters the flue chamber 106 to generate cement clinker.

[0057] The CO2 gas discharged from the top of the heat exchanger inner tube contains 12% superheated steam. After partial material recovery in the separator, it enters the air preheater. High-temperature flue gas exchanges heat with air to recover some waste heat. After condensation to recover most of the moisture, dust is collected, and a small amount of water vapor is recovered in the gas drying tower before entering the liquefaction unit for storage. Ambient air is heated to 11820 Nm³ in the air preheater. 3 After reaching 320℃ and operating at a constant temperature, the gas is connected in parallel to the hot flue gas of the heat exchange decomposition subsystem as a heat source. The material recovered by the separator is connected in parallel to the material outlet of the heat exchange inner tube and returned to the flue gas chamber.

[0058] When using this production line to capture 50,000 tons / year of CO2, the energy consumption of the unit CO2 capture system is less than 2.5 GJ / t.CO2, with virtually no operating costs. The gas-solid heat exchange efficiency is 88%, the carbonate decomposition rate is 98%, and the captured CO2 concentration reaches 95%.

[0059] Example 4

[0060] Taking a 5000t / d clinker production line with a five-stage preheater as an example, when the material consumption is 1.6, 8000t / d of cement raw meal is added to the preheating subsystem. After completing four stages of heat exchange in the preheating subsystem, it enters the calcination subsystem for calcination. The calcination is carried out in a rotary kiln to become cement clinker. After cooling, the material is sent to the finished product warehouse for storage.

[0061] 38600 Nm from fuel and tertiary wind at 1020℃ 3 The hot flue gas, at a rate of / h, enters the heat exchange and decomposition subsystem, flowing along the outer wall of the heat exchange inner tube. After heat exchange and cooling, the waste flue gas at 920℃ is returned to the decomposition furnace.

[0062] The second cyclone separator separates 2240 t / d of hot material at 500℃, representing 10% of the system's raw material, which is added to the heat exchanger inner tube of the heat exchanger decomposition subsystem. The reaction block also functions as a heat exchanger. The material descends from the top of the heat exchanger inner tube, where it is heated by conduction and radiation from the hot flue gas, undergoing heat exchange. Internal baffles disperse the material, preventing material deviation and enhancing heat exchange. Superheated steam introduced at the bottom of the reaction block carries the material upwards, further dispersing it and increasing its residence time. The gas-solid heat exchange efficiency of the heat exchanger decomposition subsystem is 80%. At 900℃, the carbonates in the material decompose, releasing CO2 gas. At the bottom of the heat exchanger inner tube, the material and gas are separated; the CO2 gas flows out from the top of the inner tube, while the material flows out from the bottom. This material, along with material recovered by the waste heat recovery subsystem, serves as part of the cement raw material and enters flue chamber 106 to generate cement clinker.

[0063] The CO2 gas discharged from the top of the heat exchanger inner tube contains 10% superheated steam. After partial material recovery in the separator, it enters the air preheater. High-temperature flue gas exchanges heat with air to recover some waste heat. After condensation to recover most of the moisture, dust is collected, and a small amount of water vapor is recovered in the gas drying tower before entering the liquefaction unit for storage. Ambient air is heated to 24800 Nm³ in the air preheater. 3 After reaching 300℃ and operating at a constant temperature, the gas is connected in parallel to the hot flue gas of the heat exchange decomposition subsystem as a heat source. The material recovered by the separator is connected in parallel to the outlet material of the heat exchange inner tube and returned to the flue gas chamber.

[0064] When using this production line to capture 200,000 tons / year of CO2, the energy consumption of the unit CO2 capture system is less than 2.5 GJ / t.CO2, with virtually no operating costs. The gas-solid heat exchange efficiency is 85%, the carbonate decomposition rate is 95%, and the captured CO2 concentration reaches 95%, which has no impact on the quality of clinker.

[0065] Table 1 shows the decomposition of the raw material of the present invention under a CO2 atmosphere; Table 2 shows the decomposition of the raw material of the present invention under a N2 atmosphere.

[0066] Table 1. Decomposition of raw meal under CO2 atmosphere

[0067] Calcination temperature LOI (wt%) Apparent decomposition rate (%) raw materials 36.15 / 850℃ 26.78 35.43 900℃ 25.02 41.07 950℃ 9.48 81.50

[0068] Table 2. Decomposition of raw materials under N2 atmosphere

[0069] Sample Name LOI (wt%) Apparent decomposition rate (%) raw materials 36.15 / 850 °C - 10 min - N2 17.84 61.65 <![CDATA[900℃-10min-N2]]> 0.97 98.27 <![CDATA[950℃-10min-N2]]> 0.65 98.85

Claims

1. A system for indirectly heating cement raw materials to produce high-purity carbon dioxide with low energy consumption, comprising a preheating subsystem, a calcination subsystem, and a cooling subsystem, characterized in that, It also includes a heat exchange decomposition subsystem for heating part of the raw material to decompose carbonates and generate CO2, a waste heat recovery subsystem for recovering heat from the generated CO2, and a CO2 storage subsystem for storing the CO2 after heat recovery; the material inlet of the heat exchange decomposition subsystem is connected to the preheating subsystem, the material outlet is connected to the inlet of the flue gas chamber (106), the hot flue gas inlet is connected to the tertiary air of the decomposition furnace (6), the hot flue gas outlet after fuel combustion of the heat exchange decomposition subsystem is connected to the hot air outlet of the waste heat recovery subsystem, the waste flue gas outlet for discharging the flue gas after heat exchange is connected to the upper part of the decomposition furnace (6), and the CO2 outlet is connected to the waste heat recovery subsystem; the heat exchange decomposition subsystem is provided with a superheated steam inlet for direct heat exchange with the raw material and a fuel inlet for introducing fuel. The material inlet of the third cyclone (3) of the preheating subsystem is connected in parallel with the material inlet of the heat exchange decomposition subsystem to the material outlet of the second cyclone (2); the material outlet of the heat exchange decomposition subsystem and the material outlet of the waste heat recovery subsystem are connected in parallel to the smoke chamber (106) below the decomposition furnace (6); the heat exchange decomposition subsystem includes two or more reaction blocks (30), and the reaction block (30) includes, from the inside to the outside, a heat exchange inner tube (28), a reaction inner tube (16), a heat exchange outer tube (12) and an insulation layer (17); the superheated steam port is located at the bottom of the reaction inner tube (16) for connecting the superheated steam pipe (29); both the heat exchange outer tube (12) and the heat exchange inner tube (28) are provided with hot flue gas inlets; the heat exchange inner tube (28) is provided with several baffles (102) with an angle of 20°~30° to the horizontal plane on the outside, and the several baffles (102) are spirally arranged vertically in the heat exchange inner tube (28); The waste heat recovery subsystem includes a cyclone separator (20) and an air preheater (21); the material outlet of the cyclone separator (20), the material outlet of the heat exchange decomposition subsystem and the material outlet of the waste heat recovery subsystem are connected in parallel to the smoke chamber (106) located below the decomposition furnace; the CO2 storage subsystem includes a water-gas separator (22), a dust collector (24), a gas drying tower (25) and a liquefaction storage device (26) connected in sequence.

2. A method for preparing high-purity carbon dioxide using the system described in claim 1, characterized in that, Includes the following steps: Cement raw materials are added to the preheating subsystem. After heat exchange is completed in the preheating subsystem, they enter the calcination subsystem and are calcined into cement clinker. After cooling, the material is sent to the finished product warehouse for storage. Part of the material separated from the outlet of the second cyclone (2) comes into contact with superheated steam in the heat exchange decomposition subsystem for countercurrent heat exchange. The hot flue gas after fuel combustion and the tertiary air of the decomposition furnace enter the heat exchange decomposition subsystem and conduct non-contact countercurrent heat exchange with the raw materials. The waste flue gas after heat exchange and cooling returns to the upper part of the decomposition furnace. The CO2 released by the decomposition of carbonates in the material enters the waste heat recovery subsystem to recover waste heat. After gas-solid separation in the waste heat recovery subsystem, CO2 exchanges heat with ambient air. The hot air after heat exchange is used as the combustion air for fuel and connected in parallel to the hot flue gas of the heat exchange decomposition subsystem. The CO2 after heat exchange enters the CO2 storage subsystem and is stored after condensation, dust collection and drying. The material from the heat exchange decomposition subsystem and the material recovered by the waste heat recovery subsystem are used as part of the raw materials for cement and enter the smoke chamber (106) to generate cement clinker.

3. The method for preparing high-purity carbon dioxide according to claim 2, characterized in that, After the secondary heat exchange, 2-12% of the raw material mass is separated and enters the heat exchange decomposition subsystem.

4. The method for preparing high-purity carbon dioxide according to claim 2, characterized in that, The temperature of the hot flue gas entering the heat exchange decomposition subsystem is 1000-1050℃, the temperature of the hot flue gas leaving the heat exchange decomposition subsystem is 930-950℃, and the material decomposition temperature is 950-1000℃.

5. The method for preparing high-purity carbon dioxide according to claim 2, characterized in that, The material temperature entering the heat exchange decomposition subsystem is 480~500℃, the material residence time is 5~15 seconds, and the material and CO2 gas temperature leaving the heat exchange decomposition subsystem is 900-950℃.

6. The method for preparing high-purity carbon dioxide according to claim 2, characterized in that, The temperature of the superheated steam entering the heat exchange decomposition subsystem is 950~1000℃, and the water vapor content in the gas in the heat exchange decomposition subsystem is 10~15%.

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