System and method for low-energy carbon capture and purification of flue from full-system oxy-fuel combustion cement kiln

Abstract

A system and method for low-energy carbon capture and purification of flue from a full-system oxy-fuel combustion cement kiln. The system comprises a oxy-fuel combustion cement clinker production system and a carbon capture and purification system, wherein an air outlet at the top end of a preheater (4) is connected to the first two cooling-medium inlets of a cooler (1) and to the carbon capture and purification system; the carbon capture and purification system comprises a precooler (12), a steam-water separator (13), a first booster fan (14), a vacuum pressure swing adsorption system (15), a second booster fan (16), a flue deep purification system (17), a refrigerator (18) and a rectification system (19); the volume fraction of CO2 in gases recovered by the vacuum pressure swing adsorption system (15) is 85%-97%; a recovery gas outlet of the vacuum pressure swing adsorption system (15) is sequentially connected to the second booster fan (16), the flue deep purification system (17), the refrigerator (18) and the rectification system (19); and a gas outlet of the rectification system (19) is connected to an inlet of the vacuum pressure swing adsorption system (15). Stable operations of a full-system oxy-fuel combustion system are achieved, and the overall CO2 recovery rate of the carbon capture and purification system is also improved, enabling the carbon capture CO2 recovery rate to be greater than or equal to 95%.

Description

A system and method for low-energy carbon capture and purification of flue gas from a fully oxygen-fired cement kiln. Technical Field

[0001] This invention relates to the field of flue gas carbon capture technology, and in particular to a system and method for low-energy carbon capture and purification of flue gas from a fully oxygen-fired cement kiln. Background Technology

[0002] Oxygen-based combustion, based on existing industrial kiln systems, replaces combustion air with high-purity oxygen. Simultaneously, flue gas recirculation regulates the flow rate and heat transfer characteristics of the entire kiln system, enriching all CO2 from fuel combustion and raw material decomposition. This achieves CO2 concentrations exceeding 80% by volume in the flue gas, enabling permanent CO2 sequestration or resource utilization at a relatively low cost, thus achieving large-scale industrial CO2 enrichment and emission reduction. Existing analyses indicate that compared to other carbon capture methods, oxygen-based combustion technology offers advantages in investment cost, operating cost, CO2 emission reduction cost, scalability, and compatibility with existing technologies.

[0003] Oxygen-fired combustion technology is a research hotspot in the international cement industry's carbon emission reduction field. Compared with traditional air combustion, oxygen-fired combustion technology can increase the CO2 concentration in the flue gas exiting the kiln tail preheater to over 80%. However, relying solely on oxygen-fired combustion to increase the CO2 concentration in the flue gas significantly increases the overall energy consumption and cost per unit of CO2 production. Further purification and enrichment of CO2 can be achieved through other technologies. After desulfurization and denitrification pretreatment, the flue gas exiting the oxygen-fired combustion system is mainly composed of carbon dioxide and nitrogen. Therefore, the separation of the pre-purified flue gas primarily involves the separation of carbon dioxide and nitrogen. Currently, CO2 purification methods mainly include cryogenic separation, pressure swing adsorption, and membrane separation. From the perspective of economics and investment scale, cryogenic separation technology is more suitable for higher concentrations of CO2 (>90%) and is suitable as a final purification step to prepare high-purity CO2 products. Membrane separation technology is highly dependent on membrane fabrication technology, and the membrane itself may have problems such as easy clogging, easy damage, and short service life. This technology is still in the development stage. Pressure swing adsorption separation technology has simple equipment, mature technology, and is suitable for medium-to-high concentration CO2 purification processes (50% to 80%). It has lower costs and energy consumption, and this technology has obvious advantages in the field of flue gas separation.

[0004] Chinese Patent Publication No. CN 115867515 A discloses a system and method for producing cement clinker through oxy-fuel combustion. This patent uses CO2 circulating flue gas discharged from the top of the preheater as a cooling medium, which is then introduced into the cooler and, after heat exchange, serves as the quaternary air passage at the bottom of the preheater. However, the relatively low-temperature CO2 circulating flue gas still carries acidic vapors such as water vapor, sulfur, chlorine, and fluorine. Directly introducing these vapors into the cooler can easily cause acid condensation, which, over time, will corrode the internal metal connectors, seals, anchors, and ventilation pipes of the cooler, weakening the sealing function and shortening the lifespan of the device.

[0005] Furthermore, Chinese Patent Publication No. CN115164592A discloses a system and method for enriching CO2 through secondary oxy-fuel combustion in a decomposition furnace. It proposes using oxy-fuel combustion combined with flue gas recirculation technology to achieve CO2 enrichment in the raw material decomposition stage. However, during cement clinker preparation, 5-10% of the raw material still needs decomposition during the calcination stage, and a large amount of CO2 generated by pulverized coal combustion at the kiln head remains unenriched. Chinese Patent Publication No. CN115745438A discloses a system and method for coupling oxy-fuel combustion with low-energy carbon purification in a cement kiln. It proposes using pressure swing adsorption (PSA) to further purify the CO2 in the oxy-fuel combustion outlet flue gas to 90%-95%. However, this method does not consider the problem that the exhaust gas from the top of the PSA tower still contains a large amount of low-concentration CO2 that is not recovered, resulting in a decrease in the overall CO2 recovery rate of the system. Chinese Patent Publication No. CN112608049A discloses a low-energy carbon enrichment cement production system and method with circulating preheating. This method realizes the CO2 enrichment process of the entire cement kiln system. However, the system does not have a special design for the clinker cooler, which may lead to cross-flow between cooling sections, affecting the CO2 enrichment concentration and the overall CO2 recovery rate of the system. Summary of the Invention

[0006] The purpose of this invention is to provide a system and method for low-energy carbon capture and purification of flue gas from a fully oxy-fueled cement kiln. This invention solves the problems of direct emission of tail gas from the process of existing oxy-fueled cement kiln systems, CO2 escape during capture and purification leading to a decrease in the system's CO2 recovery rate, and acid condensation caused by the direct introduction of low-temperature CO2 circulating flue gas into the oxy-fueled system, which significantly increases the overall energy consumption and production cost per unit of CO2 production. This invention has the advantages of low energy consumption and high carbon dioxide recovery rate.

[0007] The present invention is implemented as follows: a system for low-energy carbon capture and purification of flue gas from a fully oxy-fueled cement kiln, comprising an oxy-fueled cement clinker production system and a carbon capture and purification system.

[0008] The all-oxygen combustion cement clinker production system includes a preheater, a decomposition furnace, a kiln tail flue, a rotary kiln, and a cooler connected in sequence. The air outlet at the top of the preheater is connected to the first two cooling medium inlets of the cooler and the carbon capture and purification system. The air outlet at the top of the preheater discharges CO2 circulating flue gas with a dry basis CO2 concentration of 75-85%.

[0009] The carbon capture and purification system includes a precooler, a gas-liquid separator, a first booster fan, a vacuum pressure swing adsorption (VSA) system, a second booster fan, a deep flue gas purification system, a chiller, and a distillation system. The precooler, gas-liquid separator, first booster fan, and VSA system are connected in sequence. The exhaust outlet of the VSA system is connected to the waste gas treatment system. The CO2 volume fraction in the gas recovered by the VSA system is 85-97%. The recovered gas outlet of the VSA system is connected in sequence to the second booster fan, the deep flue gas purification system, the chiller, and the distillation system. The deep flue gas purification system includes a denitrification bed, a drying bed, and an adsorption bed connected in sequence. The distillation system includes a distillation column, a reboiler, and a liquefied product storage tank. The purified gas outlet of the chiller is connected to the inlet of the distillation column. The gas outlet of the distillation column is connected to the cooling gas inlet of the chiller through multi-stage pressure reduction. The cooling gas outlet of the chiller is connected to the inlet of the VSA system. The liquid outlet of the distillation column is connected in sequence to the reboiler and the liquefied product storage tank.

[0010] In the above technical solution, preferably, a flue gas pretreatment system is installed on the pipeline of the air outlet at the top of the preheater. The flue gas pretreatment system includes a dust removal and denitrification device, a wet desulfurization device, and a flue gas washing system arranged in sequence. The flue gas washing system includes a water storage tank, a water washing pump, and a flue gas washing tower. The outlet of the wet desulfurization device is connected to the air inlet of the flue gas washing tower. The water storage tank is connected to the water inlet of the flue gas washing tower through the water washing pump. The water outlet of the flue gas washing tower is connected to the inlet of the water washing pump. The air outlet of the flue gas washing tower is connected to a circulating flue gas pipeline and a carbon capture and purification system. The circulating flue gas pipeline is connected to the inlets of the first two cooling media of the cooler.

[0011] In the above technical solution, a more preferred embodiment is that a flue gas preheater is installed on the circulating flue gas duct to preheat the circulating flue gas to above the dew point temperature, the circulating flue gas duct is made of corrosion-resistant stainless steel, and an insulation layer is installed on the outside of the duct.

[0012] In the above technical solution, preferably, the cooler is divided into three sections from the clinker inlet to the outlet, namely the first section, the second section, and the third section; the outlet of the top cyclone separator of the preheater is connected to the inlet of the first section and the inlet of the second section; the inlet of the first section is supplied with a mixture of high-concentration O2 and CO2 circulating flue gas; the secondary and tertiary air intakes of the cooler are located in the first section and are connected to the rotary kiln and the decomposition furnace, respectively; the inlet of the second section is supplied with only CO2 circulating flue gas; the tertiary air intake is located in the second section and is connected to the inlet of the last stage cyclone separator of the preheater; a central roller crusher is installed between the second and third sections of the cooler, and steam generated from indirect drying of fuel is supplied to the air chamber below the central roller crusher.

[0013] In the above technical solution, a further preferred embodiment is that a first resistance baffle is provided between the first section and the second section of the cooler to reduce the leakage of O2 / CO2 mixture from the first section into the second section of the cooler; a second resistance baffle is provided between the second section and the third section of the cooler; the height of the bottom of the first and second resistance baffles and the gap between them and the corresponding cooler bed are ≤300mm, and the first and second resistance baffles are rotating and movable baffles.

[0014] In the above technical solution, a high-concentration oxygen inlet is further preferably provided on the channel at the first air inlet of the cooler.

[0015] In the above technical solution, preferably, the decomposition furnace is provided with a tertiary air inlet, a raw material feeding point and a fuel feeding point. The tertiary air inlet is located in the middle and lower part of the decomposition furnace. At least one raw material feeding point and one fuel feeding point are arranged between the tertiary air inlet and the bottom narrowing of the decomposition furnace, and the raw material feeding point is located above the fuel feeding point.

[0016] A method for low-energy carbon capture and purification of flue gas from an oxygen-fired cement kiln includes the following steps:

[0017] Raw materials are fed into an oxygen-fired preheater, where they exchange heat with flue gas and undergo gas-solid separation, preheating the raw materials to their decomposition temperature.

[0018] The preheated raw meal enters the oxy-fuel combustion decomposition furnace, where the heat released by the fuel combustion is used to decompose the raw meal in the furnace to obtain calcined raw meal; the calcined raw meal enters the rotary kiln for calcination to obtain hot clinker; the hot clinker is cooled in a cooler to obtain cement clinker.

[0019] The CO2 circulating flue gas generated from fuel combustion and raw material decomposition enters the preheater, and the low-temperature flue gas after heat exchange is discharged through the outlet of the cyclone separator at the top of the preheater.

[0020] The CO2 circulating flue gas discharged from the outlet of the cyclone separator at the top of the preheater is divided into two paths. One path enters the all-oxygen combustion cement clinker production system as a cooling medium and enters the cooler. The other path enters the carbon capture and purification system.

[0021] The CO2 circulating flue gas entering the carbon capture and purification system is pre-cooled to 0-10℃, and free water is separated from the gas. It then enters the vacuum pressure swing adsorption (VSA) system to concentrate and recover CO2, with the CO2 concentration exiting the VSA system ranging from 85-97%. The concentrated and recovered CO2-rich gas is pressurized and then enters the flue gas deep purification system, undergoing denitrification, drying, and adsorption for deep purification. The purified flue gas is then cooled to -15 to -35℃ by a chiller before being introduced into a distillation column. The distillation column removes light component impurities such as H2, CH4, CO, O2, and N2, as well as non-condensable gases, from the top of the column. After multi-stage pressure reduction, the gas is used as cooling gas for the chiller, recovering heat before entering the VSA system. The CO2 concentration in the exhaust gas from the VSA system is controlled to be ≤20%. Liquids are stored in liquefied product storage tanks, with CO2 purity ≥99.5% in the liquid products.

[0022] In the above technical solution, preferably, the CO2 circulating flue gas discharged from the outlet of the cyclone separator at the top of the preheater is first subjected to dust removal and denitrification to control the particulate matter in the flue gas to ≤5mg / Nm³. 3 NOx ≤ 50 mg / Nm 3 The SO2 in the flue gas is then controlled to ≤5mg / Nm³ after desulfurization. 3 The flue gas is then washed with water to reduce its temperature to ≤40℃, its water content to ≤10%, and its CO2 wet basis concentration to ≥80%. After that, it is divided into two streams and enters the all-oxygen combustion cement clinker production system and the carbon capture and purification system.

[0023] In the above technical solution, preferably, the CO2 circulating flue gas entering the all-oxygen combustion cement clinker production system is preheated to ≥60℃.

[0024] In the above technical solution, preferably, the O2 / CO2 mixed gas exiting the first stage of the cooler is used as secondary air and tertiary air respectively. The secondary air is introduced into the rotary kiln, the tertiary air is introduced into the decomposition furnace, and the CO2 circulating flue gas exiting the second stage of the cooler is introduced into the bottom of the preheater as quaternary air.

[0025] In the above technical solution, it is further preferred that the O2 concentration in the secondary and tertiary air is 30% to 70%; and the CO2 dry basis concentration in the tertiary air is 75% to 85% and the O2 concentration is less than 5%.

[0026] In the above technical solution, preferably, the CO2 dry basis concentration of the CO2 circulating flue gas discharged from the outlet of the cyclone separator at the top of the preheater is 75-85%, the temperature range is 300-400℃, and the water content is 20%-25%.

[0027] The advantages and positive effects of this invention are:

[0028] 1. In this invention, the CO2 circulating flue gas entering the carbon capture and purification system is pre-cooled, dehydrated, and compressed to meet the feed gas conditions of the vacuum pressure swing adsorption (VPSA) process. The vacuum pressure swing adsorption system purifies the CO2 gas by sequentially going through a series of steps including adsorption, pressure drop equalization, vacuuming, reflux rinsing, pressure rise equalization, and final rise cycle. The volume fraction of CO2 in the obtained gas is 85-97%.

[0029] 2. This invention pressurizes the CO2 flue gas concentrated by the vacuum pressure swing adsorption system to the pressure required for the distillation process. After three deep impurity removal processes, it is liquefied at low temperature and enters the distillation system. A liquid product with a CO2 concentration of ≥99.5% is obtained at the bottom of the distillation column. The exhaust gas at the top of the distillation column is depressurized and then heat-recovered again. It is then mixed with the feed gas of the vacuum pressure swing adsorption system in the column to complete the pressure swing adsorption concentration process. The CO2 concentration in the exhaust gas of the vacuum pressure swing adsorption system is controlled to be ≤20%, thereby improving the CO2 recovery rate of the carbon capture and purification system and keeping the CO2 recovery rate of the carbon capture and purification system above 95%.

[0030] 3. This invention aims to improve the CO2 enrichment concentration in the oxy-fuel combustion of cement kilns. It takes special consideration into account the air supply method and sealing form of the oxy-fuel combustion cooler, controls the temperature of the flue gas entering the cooler, and avoids the problem of acid condensation caused by directly introducing low-temperature CO2 circulating flue gas into the cooler. At the same time, by arranging rotating baffles to increase the flue gas flow resistance between the sections of the cooler, it avoids O2 leakage between the first and second sections of the cooler without affecting the movement of the material bed grate. The steam generated by the drying system is introduced into the lower air chamber of the central roller crusher as a cooling medium to form a steam curtain. This allows the gas environment in the cooling zones before and after the roller crusher to be relatively independent at a lower cost, and avoids air leakage between the roller gaps that would cause air to enter the system and affect the CO2 enrichment concentration of the system. Attached Figure Description

[0031] Figure 1 is a schematic diagram of the system for low-energy carbon capture and purification of all-oxygen combustion cement kiln flue gas provided in Embodiment 1 of the present invention.

[0032] In the diagram: A - High concentration of oxygen; B - CO2 circulating flue gas; C - Air; D - Steam; g2 - Secondary air; g3 - Tertiary air; g4 - Quaternary air; g5 - Air exiting the third stage of the cooler; F - Fuel; R - Raw materials; K - Cement clinker;

[0033] 1-Cooler; 101-First stage of cooler; 102-Second stage of cooler; 103-Third stage of cooler; 104-Central roller crusher; 1041-First resistance baffle; 1042-Second resistance baffle; 1a-First stage material bed of cooler; 1b-Second stage material bed of cooler; 1c-Third stage material bed of cooler;

[0034] 2-Rotary kiln; 3-Decomposition furnace; 4-Preheater; 5-Kiln tail flue; 6-Dust removal and denitrification device; 7-Wet desulfurization device; 8-Tail exhaust fan; 9-Circulating fan; 10-Flue gas preheater; 11-Flue gas washing system; 1101-Water storage tank; 1102-Washing pump; 1103-Flue gas washing tower; 12-Precooler; 13-Steam-water separator; 14-First booster fan; 15-Vacuum pressure swing adsorption system; 16-Second booster fan; 17-Deep flue gas purification system; 1701-Denitrification bed; 1702-Drying bed; 1703-Adsorption bed; 18-Refrigeration unit; 19-Distillation system; 1901-Distillation column; 1902-Reboiler; 1903-Liquefied product storage tank; 20-Multi-stage pressure reduction; 21-Carbon circulating fan;

[0035] The dashed line with an arrow indicates the airflow direction; the solid line with an arrow indicates the material flow direction. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] In the description of this invention, it should be understood that the terms "upper", "lower", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not 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 limiting this invention.

[0038] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0039] Example 1

[0040] Please refer to Figure 1. An embodiment of the present invention provides a system for low-energy carbon capture and purification of flue gas from a fully oxy-fueled cement kiln, including an oxy-fueled cement clinker production system and a carbon capture and purification system.

[0041] The all-oxygen combustion cement clinker production system includes a preheater 4, a decomposition furnace 3, a kiln tail flue chamber 5, a rotary kiln 2, and a cooler 1 connected in sequence.

[0042] The preheater has 4 to 7 stages. The air inlet of the bottom cyclone separator of the preheater 4 is connected to the air outlet of the decomposition furnace 3. The air outlet of the top cyclone separator of the preheater 4 discharges CO2 circulating flue gas B with a dry basis CO2 concentration of 75-85%. The connecting duct between the top cyclone separator of the preheater 4 and the second-stage cyclone separator is equipped with a raw material inlet. The outlet of the penultimate cyclone separator of the preheater 4 is connected to the decomposition furnace 3. The outlet of the bottom cyclone separator of the preheater 4 is connected to the kiln tail flue chamber 5.

[0043] Cement raw meal R is fed into the preheater 4 through the raw meal inlet. The raw meal R is preheated sequentially from top to bottom within the preheater until it enters the penultimate cyclone separator, and then flows into the decomposition furnace 3 via a discharge chute. To control the temperature distribution within the first decomposition furnace 3, multiple raw meal chutes can be set according to the number of pulverized coal injection points; this can be configured by those skilled in the art based on actual needs. The hot raw meal decomposes in the decomposition furnace, then undergoes gas-solid separation in the bottom cyclone separator of the preheater 4, before entering the rotary kiln 2 for calcination and the cooler 1 for cooling, ultimately producing cement clinker K.

[0044] The top outlet of the preheater 4 is connected to the first two cooling medium inlets of the cooler 1 and the carbon capture and purification system, respectively. The top outlet of the preheater 4 discharges CO2 circulating flue gas with a dry basis CO2 concentration of 75-85%.

[0045] Specifically, the oxygen generation system provides ≥90% high-concentration oxygen A, and the all-oxygen combustion decomposition furnace is a low-NOx type decomposition furnace, controlling the NOx at the furnace outlet to ≤500mg / Nm³ through gradient combustion and self-denitrification. 3 (@10% O2); The outlet of the all-oxygen combustion preheater produces CO2 circulating flue gas, with the following volume fractions: CO2 75%–85%, H2O 15%–20%, O2 4%–6%, SO2 0.1%–0.12%, and dust content ≤100g / Nm³. 3 The temperature range is 250–400℃.

[0046] The carbon capture and purification system includes a precooler 12, a gas-liquid separator 13, a first booster fan 14, a vacuum pressure swing adsorption (VSA) system 15, a second booster fan 16, a deep flue gas purification system 17, a chiller 18, and a distillation system 19. The precooler 12, gas-liquid separator 13, first booster fan 14, and VSA system 15 are connected sequentially. The exhaust outlet of the VSA system 15 is connected to the waste gas treatment system. The CO2 volume fraction in the gas recovered by the VSA system 15 is 85-97%. The recovered gas outlet of the VSA system 15 is sequentially connected to the second booster fan 16 and the deep flue gas purification system 17. 7. Refrigeration unit 18, distillation system 19, and flue gas deep purification system 17 include a denitrification bed 1701, a drying bed 1702, and an adsorption bed 1703 connected in sequence. The distillation system 19 includes a distillation column 1901, a reboiler 1902, and a liquefied product storage tank 1903. The purified gas outlet of the refrigeration unit 18 is connected to the inlet of the distillation column 1901. The gas outlet of the distillation column 1901 is connected to the cooling gas inlet of the refrigeration unit 18 through a multi-stage pressure reducing device 20. The cooling gas outlet of the refrigeration unit 18 is connected to the inlet of the vacuum pressure swing adsorption system 15. The liquid outlet of the distillation column 1901 is connected in sequence to the reboiler 1902 and the liquefied product storage tank 1903.

[0047] The CO2 circulating flue gas B from the flue gas washing system 11 enters the precooler 12 to be cooled to 0-10°C, and then passes through the steam-water separator 13 to remove moisture, making the water content ≤1.5%. After primary compression to 0.2-0.4 MPa, it enters the vacuum pressure swing adsorption system 15. CO2 in the flue gas, as a heavy component, enters the vacuum pressure swing adsorption system 15 and is adsorbed by the adsorbent, preferably silica gel. Unadsorbed light components such as N2 and O2 flow out from the top of the adsorption tower. Depending on the CO2 concentration in the feed gas, the vacuum pressure swing adsorption system 15 consists of multiple towers connected in series, achieving a CO2 concentration range of 85-97% at the outlet of the vacuum pressure swing adsorption system 15. Taking single-stage vacuum pressure swing adsorption (PSA) as an example, the adsorption-regeneration process of the adsorption tower follows the following procedure: The feed gas CO2, meeting the adsorption pressure, is preferentially adsorbed and retained in the adsorption bed as a strong adsorption component, achieving CO2 enrichment within the adsorption bed; pressure energy is recovered through a pressure equalization process, and light component gases such as O2 and N2 are sequentially released into the tower undergoing regeneration to reduce the pressure within the adsorption bed; after the forward release is complete, the light components are mostly discharged from the tower, and then CO2 gas in the adsorption bed is released in the reverse adsorption direction through vacuuming, regenerating the adsorbent, and the CO2 gas enters the buffer tank; after the reverse release is complete, the light component gas discharged from the tower undergoing adsorption steps is used to flush the bed in the reverse adsorption direction, carrying away the adsorbent and residual CO2 in the dead zone of the bed; after the flushing step, the exhaust gas from the pressure equalization process of the adsorption tower, which has completed adsorption, is used to sequentially perform pressure equalization and final pressure increase steps on the adsorption bed, and then the next adsorption cycle begins.

[0048] The heavy component product gas from the vacuum pressure swing adsorption system 15 is pressurized to 2.0-3.0 MPa through a two-stage compression process. The pressurized gas enters from the bottom of the denitrification bed 1701 and passes through the pre-set adsorbent inside the bed. The concentrations of hydrocarbons such as NOx, C6H6, C3-C7, and CH3X in the flue gas are controlled to be in the ppm level, with NOx ≤ 2 ppm and TOC ≤ 40 ppm. The flue gas then enters the drying bed 1702 from the top of the denitrification bed 1701. After passing through the pre-set adsorbent, impurities such as H2O and HF are removed from the flue gas, reducing the saturated water content to ≤30ppmv and HF to 0ppmvF. The gas phase exits from the top of the drying bed 1702 and enters the adsorption bed 1703. After treatment with the pre-set adsorbent, solid particulate matter, Hg, and NH3 are removed, reducing Hg to ≤0.00015ppmv, metal particles to 0ppmv, TOC to 0ppm(v / v), and NH3 to ≤10ppmv. The purified flue gas is then discharged from the top of the bed. The regeneration temperature of the three beds is 100–250℃.

[0049] The purified flue gas is cooled to -15 to -35°C by the refrigeration unit 18 before being introduced into the distillation column 1901. By adjusting the reflux ratio, light component impurities such as H2, CH4, CO, O2, and N2 and non-condensable gases in the flue gas are discharged from the top of the distillation column 1901. The liquid is stored in the liquefied product storage tank 1903. The CO2 purity in the liquid product is ≥99.5%.

[0050] The exhaust gas from the top of distillation column 1901 still contains 50-80% CO2. To improve the CO2 recovery rate of the carbon capture and purification system, the exhaust gas from the top of distillation column 1901 is subjected to multi-stage pressure reduction of 20 MPa to 0.2-0.3 MPa, so that the exhaust pressure drops to the pressure of the feed gas in the vacuum pressure swing adsorption system 15. After achieving pressure balance, the gas exchanges heat with the refrigeration unit 18 to recover the cooling capacity before entering the vacuum pressure swing adsorption system 15. It mixes with the feed gas entering the vacuum pressure swing adsorption system 15 and enters the adsorption column. The vacuum pressure swing adsorption system 15 recovers CO2 from the exhaust gas from the top of distillation column 1901, and controls the CO2 concentration in the exhaust gas of the vacuum pressure swing adsorption system 15 to ≤20%, so that the CO2 recovery rate of the carbon capture and purification system is maintained above 95%.

[0051] In a preferred embodiment, a flue gas pretreatment system is installed on the pipe at the top outlet of the preheater 4. The flue gas pretreatment system includes a dust removal and denitrification device 6, a wet desulfurization device 7, and a flue gas washing system 11 arranged in sequence. The flue gas washing system 11 includes a water storage tank 1101, a water washing pump 1102, and a flue gas washing tower 1103. The outlet of the wet desulfurization device 7 is connected to the air inlet of the flue gas washing tower 1103. The water storage tank 1101 is connected to the water inlet of the flue gas washing tower 1103 through the water washing pump 1102. The water outlet of the flue gas washing tower 1103 is connected to the inlet of the water washing pump 1102. The air outlet of the flue gas washing tower 1103 is connected to a circulating flue gas pipeline and a carbon capture and purification system. The circulating flue gas pipeline is connected to the first two cooling medium inlets of the cooler 1.

[0052] The dust removal and denitrification device 6 includes a bag filter or candle filter unit and an SCR reaction zone. The candle filter unit consists of a high-temperature ceramic / metal fiber filter element, a pulse-jet cleaning system, and a conical ash hopper equipped with a double-layer pneumatic ash discharge valve. The SCR reaction zone utilizes a honeycomb catalyst module, which can be VW / Ti, V-Mo / Ti, or a composite catalyst containing Fe, Ce, Mn, Bi, and Cu active elements. The CO2 circulating flue gas B, after passing through the bag filter or candle filter unit in the dust removal and denitrification device 6, controls the particulate matter in the flue gas to ≤5 mg / Nm³. 3 SCR was used to remove NOx from CO2 circulating flue gas, controlling the NOx concentration in the CO2 circulating flue gas to ≤50mg / Nm³. 3 The gas then undergoes a sulfur-fixing reaction with the desulfurizing agent slurry in the wet desulfurization unit 7. The desulfurizing agent can be an active component containing CaCO3 or Ca(OH)2, controlling the SO2 in the CO2 circulating flue gas to ≤5 mg / Nm³. 3 Meanwhile, the wet desulfurization unit 7 can reduce the flue gas temperature to ≤60℃. As the temperature decreases, water vapor in the flue gas condenses to remove liquid water, reducing the water content in the flue gas to ≤20%. To meet the water content requirements of the carbon capture and purification system, the CO2 circulating flue gas enters the flue gas washing system 11 via the tail exhaust fan 8 for further cooling and water removal. The flue gas temperature is reduced to ≤40℃, the water content in the flue gas is reduced to ≤10%, and the CO2 wet basis concentration is ≥80%.

[0053] In a preferred embodiment, a flue gas preheater 10 is installed on the circulating flue gas duct to preheat the circulating flue gas to above the dew point temperature. The circulating flue gas duct is made of corrosion-resistant stainless steel and has an insulation layer on the outside.

[0054] The remaining CO2 circulating flue gas B that does not enter the carbon capture and purification system is introduced into the cooler 1 via the circulating fan 9 as a clinker cooling medium. In order to avoid the flue gas cooling and condensation during long-distance circulating pipeline transportation, the water vapor in the flue gas needs to be converted to an unsaturated state. The dew point temperature of the CO2 circulating flue gas is determined by the Antoine equation (lgP=8.07131-1730.63 / (T+233.426), where P is the saturated vapor pressure, mmHg). The flue gas is reheated to ≥60°C by the flue gas reheater before being introduced into the cooler 1. During the process, the flue gas is always maintained above the dew point temperature. At the same time, the pipeline is made of corrosion-resistant stainless steel and an insulation layer is installed on the outside to ensure that the flue gas temperature is always maintained above the dew point temperature to the greatest extent and to avoid condensation and corrosion of the pipeline and equipment.

[0055] In a preferred embodiment, the combustion-supporting gas used in the all-oxygen combustion cement clinker production system enters the rotary kiln 2 and the decomposition furnace 3 respectively through the cooler 1. The cooler 1 is divided into three sections from the clinker inlet to the outlet (the process of cooling the clinker): the first section 101, the second section 102, and the third section 103. The outlet of the cyclone separator at the top of the preheater 4 is connected to the inlet of the first section 101 and the inlet of the second section 102. A mixture of high-concentration O2 and CO2 circulating flue gas B is introduced into the air inlet. The secondary and tertiary air inlets of the cooler are located in the first section of the cooler and are connected to the rotary kiln 2 and the decomposition furnace 3, respectively. The air inlet of the second section 102 of the cooler only introduces CO2 circulating flue gas B. The tertiary air inlet is located in the second section 102 of the cooler and is connected to the inlet of the last stage cyclone of the preheater. A central roller crusher 104 is installed between the second and third sections of the cooler. Steam D generated from indirect drying of fuel is introduced into the air chamber at the bottom of the central roller crusher 104.

[0056] The high-concentration oxygen (O2) and CO2 circulating flue gas B from the oxygen generation system are mixed and enter the first stage 101 of the cooler. After heat exchange with the clinker, they are used as secondary air (g2) and tertiary air (g3) and enter the decomposition furnace 3 and rotary kiln 2, respectively. The air inlet of the second stage 102 of the cooler only allows CO2 circulating flue gas B to enter. After heat exchange with the clinker, it is used as tertiary air (g4) and enters the final stage cyclone separator of the preheater. This reduces the raw material decomposition temperature under high CO2 partial pressure in the decomposition furnace and prevents scale buildup and blockage in the final stage cyclone separator due to increased raw material decomposition temperature and delayed fuel combustion. The cooling air of the third stage 103 of the cooler is divided into two streams. The first stream, located at the front of the third stage (the air chamber under the central roller crusher), introduces steam (D) generated for drying fuel moisture into the cooling air chamber under the central roller crusher 104. The second stream, located at the rear of the third stage, introduces air (C). This system can block direct airflow between the CO2 circulating flue gas (B) in the second stage of the cooler and the air used in the latter part of the third stage of the cooler, further controlling air leakage between the second and third stages of the cooler and minimizing the impact on clinker cooling efficiency, thus ensuring clinker quality. Part of the steam exiting the first stage of the third stage of the cooler mixes with the tertiary air through the gap of the central roller crusher and enters the preheater. The remaining steam mixes with the air exiting the latter part of the third stage of the cooler and is directly discharged from the system as low-grade heat.

[0057] Compared to conventional clinker calcination systems, the secondary and tertiary air consumption is 0.8–1.0 Nm³. 3 / kg.cl, the air volume required for secondary and tertiary air in the all-oxygen combustion system is significantly reduced to 0.4-0.6 Nm³. 3 / kg.cl, the remaining CO2 circulating flue gas will cause the cooling machine's heat recovery efficiency to decrease when discharged. Therefore, the remaining CO2 circulating flue gas B, which is used as the clinker cooling medium, is introduced into the preheater 4. This not only improves the cooling machine's thermal efficiency but also prevents this part of the flue gas from directly entering the furnace, which would cause the CO2 partial pressure in the decomposition furnace to rise and increase the carbonate decomposition temperature. On the other hand, it also avoids the problem of scale buildup and blockage in the lowest stage cyclone of the preheater 4 caused by the increase in the decomposition furnace outlet temperature.

[0058] In a preferred embodiment, a first resistance baffle 1041 is provided between the first section 101 and the second section 102 of the cooler to reduce the leakage of O2 / CO2 mixture from the first section 101 into the second section of the cooler; a second resistance baffle 1042 and a central roller crusher 104 are provided between the second section 102 and the third section 103 of the cooler. Steam D generated from indirect drying fuel is introduced into the air chamber at the bottom of the central roller crusher as a cooling medium to form an air curtain to further block the leakage; the height of the bottom of the first resistance baffle 1041 and the second resistance baffle 1042 and the gap between them and the corresponding cooler bed are ≤300mm, and the first resistance baffle 1041 and the second resistance baffle 1042 are rotating and movable baffles.

[0059] To further reduce the problem of cross-flow caused by differences in induced draft pressure between different sections of the cooler, a first resistance baffle 1041 is installed between the first section 101 and the second section 102 of the cooler to reduce cross-flow of O2 / CO2 mixture from the first section 101 into the second section. This prevents O2 from being incompletely combusted in the cement kiln and directly entering the carbon dioxide purification system via the quaternary air introduced into the preheater, thus increasing the load on the oxygen production system and the power consumption of the carbon dioxide purification system. A second resistance baffle 1042 is installed between the second section 102 and the third section 103 of the cooler. Based on the use of steam D as a cooling medium to block cross-flow in the lower air chamber of the central roller crusher 104, this further prevents cross-flow between CO2 circulating flue gas B cooling medium and air C cooling medium. This reduces the impact of air entering the second section of the cooler through the gap of the central roller crusher on the CO2 enrichment concentration and the CO2 escape caused by CO2 circulating flue gas entering the third section of the cooler, thus affecting the CO2 recovery rate. The height of the bottom of the first resistance baffle 1041 and the second resistance baffle 1042 is ≤300mm from the corresponding material bed of the cooler. The first resistance baffle 1041 and the second resistance baffle 1042 are rotating and movable baffles. When large lumps or balls of clinker enter the cooler and the material layer comes into contact with the baffle, hindering the reciprocating movement of the grate, they can rotate flexibly to avoid abnormal operation of the cooler.

[0060] In a preferred embodiment, a high-concentration oxygen inlet is provided on the channel at the air inlet of the first section 101 of the cooler.

[0061] The existing cooler requires a cooling air volume of 1.8–2.0 Nm³ for cooling clinker. 3 / kg.cl is required to achieve the desired clinker cooling effect. The O2 and CO2 circulating flue gas entering the all-oxygen combustion system cooler can provide 0.4~0.6Nm³. 3 The cooling air volume is / kg.cl, and the remaining cooling media are provided by water vapor generated from indirect fuel drying and conventional air C. The cooling air chamber that introduces water vapor is placed in the lower part of the central roller crush between the O2 / CO2 circulating flue gas chamber and the conventional air cooling air chamber, so as to prevent the CO2 circulating flue gas from escaping to the outside during the heat exchange with the hot raw material.

[0062] In a preferred embodiment, the decomposition furnace 3 is provided with a tertiary air inlet, a raw material feeding point and a fuel feeding point. The tertiary air inlet is located in the lower middle part of the decomposition furnace 3. At least one raw material feeding point and one fuel feeding point are arranged between the tertiary air inlet and the bottom narrowing of the decomposition furnace, and the raw material feeding point is located above the fuel feeding point.

[0063] In this embodiment, a tertiary air regulating valve is installed on the pipe between the tertiary air intake of the cooler 1 and the tertiary air inlet of the decomposition furnace 3 to regulate the tertiary air volume entering the decomposition furnace 3. A quaternary air regulating valve is installed on the pipe between the quaternary air intake of the cooler 1 and the bottom air inlet of the preheater 4 to distribute the quaternary air volume to the preheater, thereby achieving adjustable air volume.

[0064] A method for low-energy carbon capture and purification of flue gas from a cement kiln with full oxygen combustion, comprising the following steps:

[0065] Raw material R is fed into the oxygen-fired preheater 4. The raw material exchanges heat with the flue gas and undergoes gas-solid separation in the preheater, preheating the raw material to the decomposition temperature.

[0066] The preheated raw meal enters the oxy-fuel combustion decomposition furnace 3. The heat released by the fuel combustion provides heat for the raw meal in the decomposition furnace 3 to undergo carbonate decomposition reaction, releasing CO2 and obtaining calcined raw meal. The calcined raw meal enters the rotary kiln 2 and is calcined in the temperature range of 1100-1450℃ to synthesize mineral phases, obtaining hot clinker. The hot clinker is cooled in the cooler 1 to obtain cement clinker K.

[0067] The CO2 circulating flue gas generated from fuel combustion and raw material decomposition enters the preheater 4, and the low-temperature flue gas after heat exchange is discharged through the air outlet of the cyclone separator at the top of the preheater 4.

[0068] The CO2 circulating flue gas B discharged from the outlet of the cyclone separator at the top of the preheater 4 is divided into two paths. One path enters the all-oxygen combustion cement clinker production system as a cooling medium and enters the cooler. The other path enters the carbon capture and purification system.

[0069] The CO2 circulating flue gas B entering the carbon capture and purification system is pre-cooled to 0-10℃, and free water is separated from the gas. It then enters the vacuum pressure swing adsorption (VSA) system 15 to concentrate and recover CO2, with the CO2 concentration exiting the VSA system 15 ranging from 85% to 97%. The concentrated and recovered CO2-rich gas is pressurized and then enters the flue gas deep purification system 17, where it undergoes denitrification, drying, and adsorption for deep purification. The purified flue gas is then cooled to -15 to -35℃ by a chiller 18 before being introduced into the fine purification system. Distillation column 1901: Light component impurities and non-condensable gases such as H2, CH4, CO, O2, and N2 in the flue gas are discharged from the top of distillation column 1901. After passing through multi-stage pressure reduction 20, they are used as cooling gas for the refrigeration unit. After heat exchange and recovery of cold energy, they enter the vacuum pressure swing adsorption system 15 through carbon circulation fan 21. The CO2 concentration in the exhaust gas of the vacuum pressure swing adsorption system 15 is controlled to be ≤20%. The liquid is stored in the liquefied product storage tank 1903, and the CO2 purity in the liquid product is ≥99.5%.

[0070] In a preferred embodiment, the CO2 circulating flue gas B discharged from the outlet of the cyclone separator at the top of the preheater 4 is first subjected to dust removal and denitrification to control the particulate matter in the flue gas to ≤5mg / Nm³. 3 NOx ≤ 50 mg / Nm 3 The SO2 in the flue gas is then controlled to ≤5mg / Nm³ after desulfurization. 3 The flue gas is then washed with water to reduce its temperature to ≤40℃, its water content to ≤10%, and its CO2 wet basis concentration to ≥80%. After that, it is divided into two streams and enters the all-oxygen combustion cement clinker production system and the carbon capture and purification system.

[0071] As a preferred embodiment, the CO2 circulating flue gas B entering the all-oxygen combustion cement clinker production system is preheated to ≥60°C.

[0072] In a preferred embodiment, the O2 / CO2 mixture exiting the first stage 101 of the cooler is used as secondary air g2 and tertiary air g3, respectively. Secondary air g2 is introduced into the rotary kiln 2, and tertiary air g3 is introduced into the decomposition furnace 3. The CO2 circulating flue gas B exiting the second stage 102 of the cooler is introduced into the bottom of the preheater as quaternary air g4. The CO2 circulating flue gas being introduced into the preheater as quaternary air g4 can serve as a means of controlling the raw material decomposition temperature under high CO2 partial pressure in the decomposition furnace and preventing the problem of scale buildup and blockage in the last stage cyclone of the preheater due to the increased raw material decomposition temperature and delayed fuel combustion.

[0073] The O2 concentration in the secondary air g2 and the tertiary air g3 is 30% to 70%; the CO2 dry basis concentration in the quaternary air g4 is 75% to 85%, and the O2 concentration is less than 5%.

[0074] The CO2 circulating flue gas B discharged from the outlet of the cyclone separator at the top of the preheater has a dry basis CO2 concentration of 75-85%, a temperature range of 300-400℃, and a water content of 20%-25%.

[0075] The flue gas generated in the oxy-fuel combustion system flows in the opposite direction to the material flow. Under the oxy-fuel combustion environment, the CO2 circulating flue gas generated by fuel combustion and raw material decomposition serves as the main cooling medium for the cooler. The combustion-supporting gas used in the oxy-fuel combustion system is high-concentration oxygen A. The oxygen production system produces oxygen with a concentration ≥90%. Except for a small amount of O2 introduced as primary air into the burners of the oxy-fuel combustion decomposition furnace 3 and the rotary kiln 2, the remaining O2 is introduced into the oxy-fuel combustion system from the cooler's air chamber. After exchanging heat with the hot clinker in the cooler, it is used as secondary air g2 and tertiary air g3, respectively, and then enters the rotary kiln 2 and the oxy-fuel combustion decomposition furnace 3 from the cooler 1.

[0076] The CO2 circulating flue gas B exiting the all-oxygen combustion preheater is discharged through the outlet of the cyclone separator at the top of the preheater. After being pretreated by the flue gas pretreatment system, the CO2 circulating flue gas B is divided into two paths. One path is used as a cooling medium and enters the cooler; the remaining CO2 circulating flue gas B enters the carbon capture and purification system.

[0077] The CO2 circulating flue gas B, which enters the cooler as a cooling medium, enters the first stage 101 of the cooler in combination with high-concentration O2; the second stage enters the second stage 102 of the cooler as clinker cooling gas.

[0078] The CO2 circulating flue gas B entering the carbon capture and purification system is pre-cooled and dehydrated to meet the process feed gas inlet conditions of the vacuum pressure swing adsorption system. The vacuum pressure swing adsorption system purifies the CO2 gas by sequentially going through adsorption, pressure drop equalization, vacuuming, reflux rinsing, pressure rise equalization, and final rise cycle steps. The volume fraction of CO2 in the obtained gas is 85-97%.

[0079] The concentrated CO2 flue gas is pressurized to the pressure required for the distillation process. After three deep impurity removal processes, it is liquefied at low temperature and enters the distillation system. The liquid product with a CO2 concentration of ≥99.5% obtained at the bottom of the distillation column 1901 enters the liquefied product storage tank 1903. The exhaust gas at the top of the distillation column is depressurized and then exchanged with the refrigeration unit to recover the cold energy. It is then mixed with the feed gas of the vacuum pressure swing adsorption system in the column to complete the pressure swing adsorption concentration process, thereby improving the CO2 recovery rate of the carbon capture and purification system.

[0080] Light component gases produced during the concentration process in a vacuum pressure swing adsorption system are discharged after volatile organic compounds are removed by the waste gas treatment system.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A system for low-energy carbon capture and purification of flue gas from a fully oxy-fueled cement kiln, comprising an oxy-fueled cement clinker production system and a carbon capture and purification system; the oxy-fueled cement clinker production system comprising a preheater, a decomposition furnace, a kiln tail flue, a rotary kiln, and a cooler connected in sequence, characterized in that: The top air outlet of the preheater is connected to the first two cooling medium inlets of the cooler and the carbon capture and purification system, respectively. The top air outlet of the preheater discharges CO2 circulating flue gas with a dry basis CO2 concentration of 75-85%. The carbon capture and purification system includes a precooler, a gas-liquid separator, a first booster fan, a vacuum pressure swing adsorption (VSA) system, a second booster fan, a deep flue gas purification system, a chiller, and a distillation system. The precooler, gas-liquid separator, first booster fan, and VSA system are connected in sequence. The exhaust outlet of the VSA system is connected to the waste gas treatment system. The CO2 volume fraction in the gas recovered by the VSA system is 85-97%. The recovered gas outlet of the VSA system is connected in sequence to the second booster fan, the deep flue gas purification system, the chiller, and the distillation system. The deep flue gas purification system includes a denitrification bed, a drying bed, and an adsorption bed connected in sequence. The distillation system includes a distillation column, a reboiler, and a liquefied product storage tank. The purified gas outlet of the chiller is connected to the inlet of the distillation column. The gas outlet of the distillation column is connected to the cooling gas inlet of the chiller through multi-stage pressure reduction. The cooling gas outlet of the chiller is connected to the inlet of the VSA system. The liquid outlet of the distillation column is connected in sequence to the reboiler and the liquefied product storage tank.

2. The system for low-energy carbon capture and purification of all-oxygen combustion cement kiln flue gas according to claim 1, characterized in that: A flue gas pretreatment system is installed on the pipeline at the top outlet of the preheater. The flue gas pretreatment system includes a dust removal and denitrification device, a wet desulfurization device, and a flue gas washing system installed in sequence. The flue gas washing system includes a water storage tank, a washing pump, and a flue gas washing tower. The outlet of the wet desulfurization device is connected to the inlet of the flue gas washing tower. The water storage tank is connected to the inlet of the flue gas washing tower through the washing pump. The outlet of the flue gas washing tower is connected to the inlet of the washing pump. The outlet of the flue gas washing tower is connected to the circulating flue gas pipeline and the carbon capture and purification system. The circulating flue gas pipeline is connected to the inlets of the first two cooling media of the cooler.

3. The system for low-energy carbon capture and purification of all-oxygen combustion cement kiln flue gas according to claim 2, characterized in that: A flue gas preheater is installed on the circulating flue gas duct to preheat the circulating flue gas to above the dew point temperature. The circulating flue gas duct is made of corrosion-resistant stainless steel and has an insulation layer on the outside.

4. The system for low-energy carbon capture and purification of all-oxygen combustion cement kiln flue gas according to claim 1, characterized in that: The cooler is divided into three sections from the clinker inlet to the outlet: the first section, the second section, and the third section. The outlet of the cyclone separator at the top of the preheater is connected to the inlet of the first and second sections of the cooler. The inlet of the first section is supplied with a mixture of high-concentration O2 and CO2 circulating flue gas. The secondary and tertiary air intakes of the cooler are located in the first section and are connected to the rotary kiln and the decomposition furnace, respectively. The inlet of the second section is supplied with only CO2 circulating flue gas, and the tertiary air intake is located in the second section and is connected to the inlet of the last stage cyclone separator of the preheater. A central roller crusher is installed between the second and third sections of the cooler, and steam generated from indirect drying of fuel is introduced into the air chamber below the central roller crusher.

5. The system for low-energy carbon capture and purification of all-oxygen combustion cement kiln flue gas according to claim 4, characterized in that: A first resistance baffle is installed between the first and second sections of the cooler to reduce the leakage of O2 / CO2 mixture from the first section into the second section; a second resistance baffle is installed between the second and third sections of the cooler; the height of the bottom of the first and second resistance baffles and the gap between them and the corresponding cooler bed are ≤300mm, and the first and second resistance baffles are rotating baffles.

6. The system for low-energy carbon capture and purification of all-oxygen combustion cement kiln flue gas according to claim 4, characterized in that: A high-concentration oxygen inlet is installed on the channel at the first air inlet of the cooler.

7. The system for low-energy carbon capture and purification of all-oxygen combustion cement kiln flue gas according to claim 1, characterized in that: The decomposition furnace is equipped with a tertiary air inlet, a raw material feeding point, and a fuel feeding point. The tertiary air inlet is located in the lower middle part of the decomposition furnace. At least one raw material feeding point and one fuel feeding point are arranged between the tertiary air inlet and the bottom narrowing of the decomposition furnace, and the raw material feeding point is located above the fuel feeding point.

8. A method for low-energy carbon capture and purification of flue gas from a fully oxy-fueled cement kiln, based on the system implementation of low-energy carbon capture and purification of flue gas from a fully oxy-fueled cement kiln as described in any one of claims 1-7, characterized in that... Includes the following steps: Raw materials are fed into an oxygen-fired preheater, where they exchange heat with flue gas and undergo gas-solid separation, preheating the raw materials to their decomposition temperature. The preheated raw meal enters the oxy-fuel combustion decomposition furnace, where the heat released by the fuel combustion is used to decompose the raw meal in the furnace to obtain calcined raw meal; the calcined raw meal enters the rotary kiln for calcination to obtain hot clinker; the hot clinker is cooled in a cooler to obtain cement clinker. The CO2 circulating flue gas generated from fuel combustion and raw material decomposition enters the preheater, and the low-temperature flue gas after heat exchange is discharged through the outlet of the cyclone separator at the top of the preheater. The CO2 circulating flue gas discharged from the outlet of the cyclone separator at the top of the preheater is divided into two paths. One path enters the all-oxygen combustion cement clinker production system as a cooling medium and enters the cooler. The other path enters the carbon capture and purification system. The CO2 circulating flue gas entering the carbon capture and purification system is pre-cooled to 0-10℃, and free water is separated from the gas. It then enters the vacuum pressure swing adsorption (VSA) system to concentrate and recover CO2, with the CO2 concentration exiting the VSA system ranging from 85-97%. The concentrated and recovered CO2-rich gas is pressurized and then enters the flue gas deep purification system, undergoing denitrification, drying, and adsorption for deep purification. The purified flue gas is then cooled to -15 to -35℃ by a chiller before being introduced into a distillation column. The distillation column removes light component impurities such as H2, CH4, CO, O2, and N2, as well as non-condensable gases, from the top of the column. After multi-stage pressure reduction, the gas is used as cooling gas for the chiller, recovering heat before entering the VSA system. The CO2 concentration in the exhaust gas from the VSA system is controlled to be ≤20%. Liquids are stored in liquefied product storage tanks, with CO2 purity ≥99.5% in the liquid products.

9. The method for low-energy carbon capture and purification of flue gas from a fully oxygen-fired cement kiln according to claim 8, characterized in that: The CO2 circulating flue gas discharged from the outlet of the cyclone separator at the top of the preheater first undergoes dust removal and denitrification to control the particulate matter in the flue gas to ≤5mg / Nm³. 3 NOx ≤ 50 mg / Nm 3 The SO2 in the flue gas is then controlled to ≤5mg / Nm³ after desulfurization. 3 The flue gas is then washed with water to reduce its temperature to ≤40℃, its water content to ≤10%, and its CO2 wet basis concentration to ≥80%. After that, it is divided into two streams and enters the all-oxygen combustion cement clinker production system and the carbon capture and purification system.

10. The method for low-energy carbon capture and purification of flue gas from a fully oxygen-fired cement kiln according to claim 8, characterized in that: The CO2 circulating flue gas entering the all-oxygen combustion cement clinker production system is first preheated to ≥60℃.

11. The method for low-energy carbon capture and purification of flue gas from a fully oxygen-fired cement kiln according to claim 8, characterized in that: The O2 / CO2 mixture exiting the first stage of the cooler is used as secondary air and tertiary air, respectively. The secondary air is fed into the rotary kiln, and the tertiary air is fed into the decomposition furnace. The CO2 circulating flue gas exiting the second stage of the cooler is used as quaternary air and fed into the bottom of the preheater.

12. The method for low-energy carbon capture and purification of flue gas from a fully oxygen-fired cement kiln according to claim 11, characterized in that: The O2 concentration in the secondary and tertiary air is 30%–70%; the CO2 dry basis concentration in the quaternary air is 75%–85%, and the O2 concentration is less than 5%.

13. The method for low-energy carbon capture and purification of flue gas from a fully oxygen-fired cement kiln according to claim 8, characterized in that: The CO2 circulating flue gas discharged from the outlet of the cyclone separator at the top of the preheater has a dry basis CO2 concentration of 75-85%, a temperature range of 300-400℃, and a water content of 20%-25%.

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