Full-system oxy-fuel combustion coupled carbon capture system and method based on high-concentration carbon dioxide

Abstract

Disclosed in the present invention are a full-system oxy-fuel combustion coupled carbon capture system and method based on high-concentration carbon dioxide. The system comprises an oxy-fuel combustion cement clinker production system and a carbon capture and purification system. Flue gas protective sealing devices are provided at two ends of a rotary kiln, the flue gas protective sealing devices are each provided with a protective airbag, and high-concentration CO2 circulating flue gas having a dry basis CO2 concentration greater than or equal to 85% is exhausted from an air outlet in the top end of a preheater, and enters the protective airbags and the carbon capture and purification system. The carbon capture and purification system comprises a precooler, a water separation tank, a first booster fan, a flue gas deep purification system, a first liquefaction cold box, a first gas-liquid separator, a second liquefaction cold box, a second gas-liquid separator, a rectification system, a pressure swing adsorption recovery system, a buffer tank, a second booster fan, and a third liquefaction cold box. The present invention achieves stable operation of the oxy-fuel combustion system, and improves the overall CO2 recovery rate of the carbon capture and purification system, achieving a system CO2 recovery rate of at least 95%.

Description

A system and method for full-system oxy-fuel combustion coupled with high-concentration carbon dioxide and carbon capture Technical Field

[0001] This invention relates to the field of flue gas carbon capture technology, and in particular to a whole-system oxy-fuel combustion coupled carbon capture system and method based on high-concentration carbon dioxide. Background Technology

[0002] Oxygen-fired combustion, based on existing industrial kiln systems, replaces combustion air with high-purity oxygen, thereby achieving large-scale industrial CO2 enrichment and emission reduction at a relatively low cost. The resulting CO2 flue gas, after capture and purification, can be used for storage or resource utilization. Existing analyses show that, compared with other carbon capture methods, oxygen-fired combustion technology has advantages in terms of investment cost, operating cost, CO2 emission reduction cost, large-scale feasibility, and compatibility with existing technologies.

[0003] Compared to traditional air combustion, oxy-fuel combustion technology in the cement industry can significantly increase the CO2 concentration in the flue gas exiting the kiln tail preheater, which helps reduce the overall energy consumption and cost per unit of CO2 production. After desulfurization and denitrification pretreatment, the flue gas exiting the oxy-fuel 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 membrane separation, pressure swing adsorption (PSA), and cryogenic liquefaction separation technology. Membrane separation technology is highly dependent on membrane fabrication technology, and the membrane itself may suffer from problems such as easy clogging, easy damage, and short service life; this technology is still under development. PSA separation technology has simple equipment and mature technology, but it is only suitable for medium-to-high concentration CO2 purification processes (50%–80%) and not suitable for producing high-purity CO2. This technology has significant advantages in the field of flue gas separation. Low-temperature liquefaction separation technology relies on the boiling point differences of different components to separate mixtures. After liquefaction, the mixture is easy to store and transport. From the perspective of economy and investment scale, low-temperature liquefaction separation technology is more suitable for higher concentrations of CO2 (dry basis concentration ≥85%) and is suitable as a technical means for capturing and purifying carbon dioxide to prepare high-purity CO2 products.

[0004] The length of rotary kilns used in cement clinker calcination systems is generally over 50m. Existing rotary kilns generally use fish-scale sealing devices at both ends, but they face the following problems when operating at high temperatures: (1) The rotary kiln will experience radial sway due to the superposition of thermal stress under high-temperature conditions; (2) Due to the tilted placement of the kiln body, the rotary kiln tends to slide down under its own weight, resulting in a large axial thermal expansion during high-temperature operation; (3) During operation, the rotary kiln rotates axially dynamically, and the gap between the dynamic and static seals can reach more than 10mm under actual conditions, leading to an air leakage rate exceeding the design value. In the whole system of oxy-fuel combustion, the air leakage at the dynamic and static connection of the rotary kiln will have a significant impact on the CO2 enrichment concentration of the circulating flue gas in the system. The sealing method and structure at both ends of the rotary kiln should be the focus of attention for air leakage control in the whole system of oxy-fuel combustion. Chinese patent publication CN 115654914A proposes a cement production method utilizing alternative fuel oxy-fuel combustion coupled with carbon capture. This patent introduces CO2 circulating flue gas, after dust collection, regenerative combustion, waste heat power generation, desulfurization, condensation, and reheating to 35-45℃, into kiln head and kiln tail sealing equipment. However, the relatively low-temperature CO2 circulating flue gas still carries acidic vapors such as water vapor, sulfur, chlorine, and fluorine. During its introduction into the sealing equipment, acid condensation is easily generated. Over prolonged use, this can corrode the internal metal connectors, seals, anchors, and ventilation pipes of the sealing structure, weakening the sealing function and shortening the equipment's lifespan.

[0005] The CO2 concentration in the flue gas from oxy-fuel combustion in cement kilns determines the cost of CO2 capture and purification. In practical cases already in operation in the cement industry, oxy-fuel combustion technology can increase the dry basis CO2 concentration of the flue gas at the kiln tail preheater outlet to over 80%, and a post-capture process using pressure swing adsorption coupled with cryogenic distillation has achieved a capture energy consumption of ≤1.6 GJ / t.CO2 per unit of CO2. However, in reality, the existing technical route has not yet achieved optimal energy consumption. Chinese Patent Publication No. CN115745438A discloses a system and method for low-energy carbon purification coupled with oxy-fuel combustion in cement kilns. It proposes to purify the flue gas with a CO2 concentration ≥80% at the outlet of the oxy-fuel combustion system to 90%–95% using pressure swing adsorption, and then obtain a product with a CO2 concentration ≥99.5% through cryogenic distillation. In this process, the oxygen supply concentration (80%–90%) of the oxy-fuel combustion system is relatively low, and the control of system air leakage is neglected. The introduction of external air not only reduces the CO2 enrichment concentration but also leads to a decrease in the thermal efficiency of the oxy-fuel combustion system. Meanwhile, the introduction of impurity gases is a fundamental issue affecting the process flow, equipment scale, and investment cost of the post-capture and purification system. Therefore, developing a cement kiln oxy-fuel combustion coupled with carbon capture and purification flue gas technology with low operating costs and high CO2 recovery rate is a more practical and feasible method for carbon emission reduction in the cement industry. However, the following problems still exist:

[0006] (1) The main air leakage points such as the cooler, rotary kiln dynamic and static connection, and fuel pneumatic conveying of the all-oxygen combustion system were not effectively controlled, causing air to enter the system and reduce the CO2 enrichment concentration. Also, the direct introduction of low-temperature CO2 circulating flue gas into the all-oxygen combustion system easily produces acid condensation.

[0007] (2) Existing carbon capture and purification technologies have not yet achieved optimal energy consumption, and it is necessary to develop capture and purification processes for high-concentration CO2 flue gas (dry basis concentration ≥85%).

[0008] (3) Existing carbon capture and purification processes (pressure swing adsorption, low temperature distillation technology) will generate a large amount of CO2-containing flue gas, which will reduce the CO2 recovery rate of the system.

[0009] (4) The degree of synergistic optimization of technologies such as low-temperature distillation and pressure swing adsorption is insufficient, which limits the overall system performance.

[0010] Carbon dioxide, as a valuable resource, is widely used in many fields such as chemistry, food, machinery processing, and oil extraction. The capture, purification, and utilization of CO2 from cement kiln flue gas requires a balance between technology, cost, and profitability. Ensuring low production costs, high recovery rates in the capture and purification system, and high purity and stable product quality is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0011] To address the problems in existing oxy-fuel combustion coupled with carbon capture and purification technologies for cement kilns, such as low CO2 enrichment concentration during oxy-fuel combustion, CO2 escape during capture and purification leading to decreased CO2 recovery rate, and acid condensation caused by directly introducing low-temperature CO2 circulating flue gas into the oxy-fuel combustion system, which significantly increases the overall energy consumption and cost per unit of CO2 production, this invention proposes a whole-system oxy-fuel combustion coupled with carbon capture system and method based on high-concentration carbon dioxide. This optimizes both the whole-system oxy-fuel combustion process and the CO2 capture and purification system process, achieving reduced flue gas emissions, increased CO2 enrichment concentration and recovery rate, and simultaneously reducing the cost per unit of CO2 while achieving "net zero" CO2 emissions from the cement production system.

[0012] The present invention is implemented as follows: a full-system oxy-fuel combustion coupled carbon capture system based on high-concentration carbon dioxide, comprising an oxy-fuel combustion cement clinker production system and a carbon capture and purification system; the oxy-fuel combustion cement clinker production system comprises a preheater, a decomposition furnace, a kiln tail flue, a rotary kiln, and a cooler connected in sequence.

[0013] The rotary kiln is equipped with flue gas protection sealing devices at both ends. The flue gas protection sealing devices have protective airbags. A first sealing element is set between the outside of the protective airbag and the outside air, and a second sealing element is set between the inside of the protective airbag and the rotary kiln. High-concentration CO2 circulating flue gas with a dry basis CO2 concentration ≥85% is discharged from the air outlet at the top of the preheater and enters the carbon capture and purification system and the protective airbag.

[0014] The carbon capture and purification system includes a precooler, a water separator, a first booster fan, a deep flue gas purification system, a first liquefaction cold box, a first gas-liquid separator, a second liquefaction cold box, a second gas-liquid separator, a distillation system, a pressure swing adsorption recovery system, a buffer tank, a second booster fan, and a third liquefaction cold box. The precooler, water separator, first booster fan, deep flue gas purification system, first liquefaction cold box, first gas-liquid separator, second liquefaction cold box, and second gas-liquid separator are connected sequentially. The deep flue gas purification system includes a denitrification bed, a drying bed, and an adsorption bed connected sequentially. Various impurities in the denitrification bed, drying bed, and adsorption bed... The gas outlet is connected to the waste gas treatment system. The distillation system includes a distillation column, a reboiler, and a liquefied product storage tank. The liquid outlets of the first and second gas-liquid separators are both connected to the inlet of the distillation column. The gas outlets of the second gas-liquid separator and the distillation column are both connected to the inlet of the pressure swing adsorption recovery system. The liquid outlet of the distillation column is connected in sequence to the reboiler and the liquefied product storage tank. The recovered gas outlet of the pressure swing adsorption recovery system is connected in sequence to the buffer tank, the second booster fan, and the third liquefaction cold box. The outlet of the third liquefaction cold box is connected to the inlet of the distillation column. The exhaust outlet of the pressure swing adsorption recovery system is connected to the waste gas treatment system.

[0015] In the above technical solution, preferably, the precooler is used to cool the flue gas to ≤10℃, the first and second booster fans are both used to compress and boost the flue gas to ≥25 bar, the flue gas deep purification system is used to deeply remove impurities from the flue gas, the first liquefaction cold box is used to cool the flue gas to ≤-15℃, the second liquefaction cold box is used to cool the flue gas to ≤-25℃, the third liquefaction cold box is used to cool the flue gas to ≤-25℃, the first gas-liquid separator and the second gas-liquid separator are used to separate condensed liquid and residual gas, the distillation column is used to discharge light component impurities such as hydrogen, methane, carbon monoxide, oxygen, and nitrogen and non-condensable gases from the flue gas, so that the purity of liquid CO2 is ≥99.5%, and the pressure swing adsorption recovery system is used to concentrate and recover CO2, so that the CO2 recovery rate of the carbon capture and purification system is ≥95%.

[0016] In the above technical solution, preferably, a dust removal and denitrification device, a wet desulfurization device, and a flue gas washing system are sequentially installed on the pipeline of the air outlet at the top of the preheater. 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 the circulating flue gas pipeline that transports the high-concentration CO2 circulating flue gas discharged from the air outlet at the top of the preheater back to the all-oxygen combustion cement clinker production system, and the carbon capture and purification system. A flue gas reheater is installed on the circulating flue gas pipeline.

[0017] In the above technical solution, it is further preferred that the circulating flue gas duct is made of corrosion-resistant stainless steel and an insulation layer is provided on the outside of the duct.

[0018] In the above technical solution, preferably, the protective airbag has radial labyrinth baffles and axial labyrinth baffles. The radial labyrinth baffles form a spiral labyrinth channel along the kiln body axis, and the axial labyrinth baffles form a spiral labyrinth channel along the kiln body radially. The spiral labyrinth channels along the kiln body axis and radially cooperate to form a tortuous labyrinth sealing structure. Reverse sealing plates are provided on the airflow passage of the tortuous labyrinth sealing structure, and multiple CO2 protective gas inlet pipes are distributed circumferentially on the protective airbag.

[0019] In the above technical solution, preferably, the cooler is divided into three sections from the clinker inlet to the outlet: the first section, the second section, and the third section. High-concentration CO2 circulating flue gas with a dry basis CO2 concentration ≥85% discharged from the top outlet of the preheater also enters the cooling medium inlets of the first two sections of the cooler. The first section of the cooler is introduced 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 second section of the cooler only introduces 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. The third section of the cooler is further divided into two sections: the air chamber below the centrally located roller crusher in the first section is introduced with steam generated from indirect drying of fuel, and conventional air is introduced in the second section.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] In the above technical solution, preferably, the high-concentration CO2 circulating flue gas with a dry basis CO2 concentration ≥85% discharged from the top outlet of the preheater also enters the fuel pneumatic conveying pipeline. The fuel pneumatic conveying pipeline is equipped with a fuel conveying fan and a fuel storage silo, with the fuel conveying fan located upstream of the fuel storage silo.

[0024] A low-energy carbon capture method based on high-concentration carbon dioxide includes the following steps:

[0025] Raw meal is fed into a preheater, where it exchanges heat with flue gas and undergoes gas-solid separation to preheat the raw meal to its decomposition temperature. The preheated raw meal is then fed into a decomposition furnace. In the oxy-fuel combustion environment of the decomposition furnace, the large amount of heat released by fuel combustion is used to decompose the raw meal, resulting in hot raw meal. The hot raw meal enters a rotary kiln, where it is calcined in the oxy-fuel combustion environment to produce clinker. The clinker is then cooled in a cooler to obtain cement clinker.

[0026] The fuel produces a large amount of flue gas which enters the decomposition furnace. After mixing with the flue gas in the decomposition furnace, it enters the preheater. The low-temperature flue gas after heat exchange is discharged through the outlet of the cyclone separator at the top of the preheater.

[0027] 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 ≥85% and a temperature range of 250~400℃. It is divided into two paths: one path enters the all-oxygen combustion cement clinker production system, and the other path enters the carbon capture and purification system.

[0028] The CO2 circulating flue gas entering the all-oxygen combustion cement clinker production system is sent as the rotary kiln sealing protection gas into the flue gas protection sealing devices at both ends of the rotary kiln.

[0029] The CO2 circulating flue gas entering the carbon capture and purification system is sequentially cooled to ≤10℃ by a precooler, free water is separated by a water separator, and pressurized by a first booster fan. The flue gas then enters the deep purification system, where it undergoes denitrification, drying, and adsorption for deep purification. The purified flue gas undergoes two liquefaction and gas-liquid separation processes. The first liquefaction process cools the gas to ≤-15℃, and the second liquefaction process cools it to ≤-25℃. The separated gas enters the pressure swing adsorption recovery system, while the liquid from both gas-liquid separations enters a distillation column. The distillation column discharges light component impurities and non-condensable gases such as hydrogen, methane, carbon monoxide, oxygen, and nitrogen from the top of the column into the pressure swing adsorption (PSA) recovery system. The PSA system concentrates and recovers CO2, achieving a CO2 recovery rate of ≥95% in the carbon capture and purification system. The concentrated and recovered CO2-rich gas is pressurized and liquefied, then cooled to ≤-25℃ before entering the distillation column. The liquid in the distillation column is then passed through a reboiler into a liquefied product storage tank for storage, with a CO2 purity of ≥99.5% in the liquefied product.

[0030] 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 the water content to ≤10%, and then split into two streams to enter the all-oxygen combustion cement clinker production system and the carbon capture and purification system.

[0031] In the above technical solution, a further preferred embodiment is that the CO2 circulating flue gas entering the all-oxygen combustion cement clinker production system is preheated to ≥60℃.

[0032] In the above technical solution, a further preferred embodiment is that the CO2 circulating flue gas entering the all-oxygen combustion cement clinker production system is also combined with high-concentration O2 to enter the first stage of the cooler, and enters the second stage of the cooler as clinker cooling gas;

[0033] 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 final stage cyclone of the preheater.

[0034] 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 ≥85% and the O2 concentration is less than 5%.

[0035] In the above technical solution, preferably, the CO2 circulating flue gas entering the all-oxygen combustion cement clinker production system is also used as fuel conveying air to power the fuel gas to the decomposer and rotary kiln.

[0036] In the above technical solution, preferably, the CO2 concentration in the gas discharged from the second gas-liquid separation is ≥70%, and the CO2 concentration in the liquid discharged from the first gas-liquid and second gas-liquid separations is ≥99%.

[0037] The CO2 concentration in the exhaust gas from the distillation column is ≥50%;

[0038] The exhaust gas in the pressure swing adsorption recovery system has a CO2 concentration ≤20%, N2 concentration ≥60%, and O2 concentration ≥15%, and the CO2 concentration in the flue gas after pressure swing adsorption concentration recovery is ≥95%.

[0039] The advantages and positive effects of this invention are:

[0040] 1. This invention fully considers the problem of reduced CO2 enrichment concentration in exhaust gas caused by the introduction of external air into the entire oxy-fuel combustion system. It proposes a device structure and method that utilizes CO2 circulating flue gas as the sealing and protective gas for the rotary kiln, effectively controlling the main air leakage points of the entire oxy-fuel combustion system. This provides the carbon capture and purification system with high-concentration flue gas containing ≥85% dry CO2. The reduction in flue gas treatment volume can effectively reduce the equipment size and system footprint of the capture and purification system. At the same time, it considers that directly introducing low-temperature CO2 circulating flue gas into the oxy-fuel combustion system can easily lead to acid condensation.

[0041] 2. This patent proposes a low-energy carbon capture process based on high-concentration CO2, employing a two-step liquefaction + cryogenic distillation + pressure swing adsorption (PSA) recovery carbon capture technology. Detailed analysis and calculations show that although the cryogenic oxygen production method increases unit energy consumption compared to PSA oxygen production, the reduced CO2 concentration in the flue gas makes the increase in unit CO2 capture cost more significant. Compared to existing PSA coupled with cryogenic distillation technology, the carbon capture process provided by this patent further reduces unit CO2 production energy consumption by more than 15%, making the technological advantages of all-oxygen combustion in cement kilns even more pronounced.

[0042] 3. This invention fully considers the problem of CO2 escape from the exhaust gas of the carbon capture and purification system. It proposes a carbon capture and purification process that is both adaptable and economical for capturing and purifying high-concentration CO2 flue gas (dry basis CO2 concentration ≥ 85%). Existing all-oxygen combustion coupled carbon capture technology routes do not focus on CO2 recovery rate as a key indicator. This invention achieves CO2 recovery and capture from exhaust gas through pressure swing adsorption and low-temperature distillation by optimizing the process flow, thereby improving the overall CO2 recovery rate of the carbon capture and purification system to ≥ 95%.

[0043] 4. This invention aims to improve the CO2 enrichment concentration of oxy-fuel combustion in cement kilns. It takes special consideration into account the air supply method and sealing form of the oxy-fuel combustion cooler. By arranging rotating baffles to increase the flow resistance of flue gas 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 makes the gas environment in the cooling zones before and after the roller crusher relatively independent at a lower cost, avoiding air leakage between the roller gaps that would affect the CO2 enrichment concentration of the system. Attached Figure Description

[0044] Figure 1 is a flowchart of the whole-system oxygen-fuel combustion coupled carbon capture system based on high-concentration carbon dioxide provided in Embodiment 1 of the present invention;

[0045] Figure 2 is a flowchart of the whole-system oxygen-fuel combustion coupled carbon capture system based on high-concentration carbon dioxide provided in Embodiment 2 of the present invention;

[0046] Figure 3 is a schematic diagram of the kiln tail flue gas protection and sealing device provided in Embodiments 1 and 2 of the present invention;

[0047] Figure 4 is a schematic diagram of the kiln head flue gas protection sealing device provided in Embodiments 1 and 2 of the present invention.

[0048] In the diagram: A - High concentration oxygen; B - CO2 circulating flue gas; C - Steam; D - Air; g2 - Secondary air; g3 - Tertiary air; g4 - Quaternary air; g5 - Air exiting the third stage of the cooler; F - Fuel; R - Raw meal; K - Cement clinker; 1 - Cooler; 101 - First stage of cooler; 102 - Second stage of cooler; 103 - Third stage of cooler; 104 - Central roller crusher; 105 - Kiln hood; 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; 2-Rotary kiln; 201-Kiln head flue gas protection sealing device; 202-Kiln tail flue gas protection sealing device; 203-Kiln head burner; 204-Radial labyrinth baffle; 205-Axial labyrinth baffle; 206-CO2 protective gas inlet pipe; 207-Reverse sealing plate; 208-Composite sealing plate; 3-Decomposition furnace; 301-Decomposition furnace burner; 4-Preheater; 5-Kiln tail flue gas chamber; 6-Dust removal and denitrification device; 7-First tail exhaust fan; 8-Wet desulfurization device; 9-Circulating fan; 901-Fuel conveying fan; 902-CO2 protective gas conveying fan; 10-Flue gas reheater; 11-Fuel storage bin; 12-Second tail exhaust fan; 13- Flue gas scrubbing system; 1301-Water storage tank; 1302-Scrubbing pump; 1303-Flue gas scrubbing tower; 14-Induced draft fan; 15-Precooler; 16-Water separator; 17-First booster fan; 18-Deep flue gas purification system; 1801-Denitrification bed; 1802-Drying bed; 1803-Adsorption bed; 19-First liquefaction cold box; 20-First gas-liquid separator; 21-Second liquefaction cold box; 22-Second gas-liquid separator; 23-Distillation system; 2301-Distillation column; 2302-Reboiler; 2303-Liquefied product storage tank; 24-Pressure swing adsorption recovery system; 25-Buffer tank; 26-Second booster fan; 27-Third liquefaction cold box; Dashed arrows indicate airflow direction; solid arrows indicate material flow direction. Detailed Implementation

[0049] 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.

[0050] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "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 limitations on this invention.

[0051] 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.

[0052] Example 1

[0053] Please refer to Figure 1. An embodiment of the present invention provides a full-system oxy-fuel combustion coupled carbon capture system based on high-concentration carbon dioxide. The system consists of an oxy-fuel combustion cement clinker production system and a carbon capture and purification system.

[0054] 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.

[0055] The preheater 4 has 4 to 7 stages. The air inlet of the bottom cyclone separator of the preheater 4 is connected to the air outlet pipe of the decomposition furnace 3. The air outlet of the top cyclone separator of the preheater 4 discharges high-concentration CO2 flue gas with a dry basis CO2 concentration ≥85% and a flue gas temperature of 250-400℃. 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. The outlet of the bottom cyclone separator of the preheater 4 is connected to the kiln tail flue chamber 5. A kiln head burner 203 is installed on the rotary kiln 2. A decomposition furnace burner 301 is installed on the decomposition furnace.

[0056] 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.

[0057] Rotary kiln 2 is equipped with flue gas protection sealing devices at both ends. These devices have protective airbags, with a first seal between the outer side of the airbag and the outside air, and a second seal between the inner side of the airbag and the rotary kiln 2. The kiln head flue gas protection sealing device 201 is located outside the connection between the kiln door hood 105 and the rotary kiln 2, while the kiln tail flue gas protection sealing device 202 is located outside the connection between the kiln tail smoke chamber 5 and the rotary kiln 2. High-concentration CO2 circulating flue gas B with a dry basis CO2 concentration ≥85% is discharged from the preheater top outlet and enters the carbon capture and purification system and the protective airbags.

[0058] The carbon capture and purification system includes a precooler 15, a water separator 16, a first booster fan 17, a deep flue gas purification system 18, a first liquefaction cold box 19, a first gas-liquid separator 20, a second liquefaction cold box 21, a second gas-liquid separator 22, a distillation system 23, a pressure swing adsorption recovery system 24, a buffer tank 25, a second booster fan 26, and a third liquefaction cold box 27. The precooler 15, water separator 16, first booster fan 17, deep flue gas purification system 18, first liquefaction cold box 19, first gas-liquid separator 20, second liquefaction cold box 21, and second gas-liquid separator 22 are connected sequentially. The deep flue gas purification system 18 includes a denitrification bed 1801, a drying bed 1802, and an adsorption bed 1803 connected sequentially. Each impurity gas outlet is connected to the waste gas treatment system. The distillation system 23 includes a distillation column 2301, a reboiler 2302, and a liquefied product storage tank 2303. The liquid outlets of the first gas-liquid separator 20 and the second gas-liquid separator 22 are both connected to the inlet of the distillation column 2301. The gas outlets of the second gas-liquid separator 22 and the distillation column 2301 are both connected to the inlet of the pressure swing adsorption recovery system 24. The liquid outlet of the distillation column 2301 is connected in sequence to the reboiler 2302 and the liquefied product storage tank 2303. The recovery gas outlet of the pressure swing adsorption recovery system 24 is connected in sequence to the buffer tank 25, the second booster fan 26, and the third liquefied cold box 27. The outlet of the third liquefied cold box 27 is connected to the inlet of the distillation column 2301. The exhaust outlet of the pressure swing adsorption recovery system 24 is connected to the waste gas treatment system.

[0059] The precooler 15 is used to cool the flue gas to ≤10℃; the first booster fan 17 and the second booster fan 26 are both used to compress and boost the flue gas to ≥25 bar; the flue gas deep purification system 18 is used to deeply remove impurities from the flue gas; the first liquefaction cold box 19 is used to cool the flue gas to ≤-15℃; the second liquefaction cold box 21 is used to cool the flue gas to ≤-25℃; the third liquefaction cold box 27 is used to cool the flue gas to ≤-25℃; the first gas-liquid separator 20 and the second gas-liquid separator 22 are used to separate condensed liquid from residual gas; the distillation column is used to discharge light component impurities such as hydrogen, methane, carbon monoxide, oxygen, and nitrogen, as well as non-condensable gases from the flue gas, so that the purity of liquid CO2 is ≥99.5%; and the pressure swing adsorption recovery system 24 is used to concentrate and recover CO2, so that the CO2 recovery rate of the carbon capture and purification system is ≥95%.

[0060] High-concentration CO2 circulating flue gas B is first introduced into the precooler 15 via induced draft fan 14 for further cooling to ≤10℃, and then enters the water separator 16 to separate saturated water from the raw gas, reducing the saturated water content in the flue gas to below 0.5%. The flue gas exits from the top of the water separator 16 and enters the first booster fan 17, where it is compressed to the pressure conditions required for flue gas liquefaction. The flue gas exiting the first booster fan 17 enters the flue gas deep purification system 18, where it first enters from the bottom of the denitrification bed 1801. The adsorbent packed in the denitrification bed 1801 removes NOx from the flue gas, reducing NOx to ≤2mg / Nm³. 3 The flue gas exiting from the top of the denitrification bed 1801 enters the drying bed 1802, reducing the water content in the flue gas to <100ppm, further removing saturated water. It then exits from the top of the drying bed 1802 and enters the adsorption bed 1803, where pre-arranged adsorbents further remove residual solid particles, mercury, ammonia, and TOC from the feed gas flowing through it. The deep flue gas purification system 18 can reduce impurities such as solid particles, HF, NOx, H2O, NH3, C3-C7, and CH3X in the feed gas to the ppm level. After the adsorption process is complete, the denitrification bed 1801, drying bed 1802, and adsorption bed 1803 undergo depressurization and heating to release impurities, completing the regeneration process. The impurity gas enters the waste gas treatment system, and the denitrification bed 1801, drying bed 1802, and adsorption bed 1803 enter the next working cycle.

[0061] The flue gas purified by the deep flue gas purification system 18 meets the liquefaction conditions and enters the first liquefaction cold box 19. The first liquefaction cold box 19 cools the flue gas to ≤-15℃ and then enters the first gas-liquid separator 20. Part of the condensed liquid and the residual gas are separated in the first gas-liquid separator 20. The residual gas leaves from the top of the first gas-liquid separator 20 and enters the second liquefaction cold box 21. The residual gas is further cooled to ≤-25℃ in the second liquefaction cold box 21 and then enters the second gas-liquid separator 22, where it is separated. The separated lean flue gas enters the pressure swing adsorption recovery system 24. The condensed liquid after separation by the first gas-liquid separator 20 and the second gas-liquid separator 22 both enter the distillation column 2301. By controlling the reflux ratio, light component impurities such as hydrogen, methane, carbon monoxide, oxygen, and nitrogen, as well as non-condensable gases, are discharged from the top of the distillation column. The liquid is then stored in the liquefied product storage tank 2303 via the reboiler 2302. The CO2 purity in the liquefied product is ≥99.5%.

[0062] In this embodiment, the CO2 concentration in the residual gas of the first gas-liquid separator 20 and the second gas-liquid separator 22 is ≥70%, and the CO2 concentration in the condensate of the first and second gas-liquid separators is ≥99%. The carbon-rich liquid phase enters the distillation column 2301, and the reflux ratio in the column is controlled by the reboiler 2302 at the bottom of the column. 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 2301. In this embodiment, the CO2 concentration in the exhaust gas from the top of the distillation column 2301 is ≥50%. The liquid is then stored in the liquefied product storage tank 2303 to ensure that the CO2 purity in the liquid product is ≥99.5%.

[0063] To further improve the capture and recovery efficiency of CO2 in non-condensable gases, the non-condensable gases discharged from the top of the distillation column 2301 and the carbon-lean flue gas from the first gas-liquid separator 20 and the second gas-liquid separator 22 all enter the pressure swing adsorption recovery system 24. After the H2O and CO2 in the mixed gas are adsorbed by the adsorbent in the adsorption column, they enter the buffer tank 25. A small amount of unadsorbed CO2, N2 and O2 flow out from the top of the adsorption column, thus completing the concentration and recovery of CO2 in the non-condensable gases, making the CO2 recovery rate of the carbon capture and purification system ≥95%. The adsorption-regeneration process of the adsorption tower follows the procedure as follows: the pressure inside the adsorption tower is reduced through a pressure equalization process, and impurity components are gradually desorbed. After the pressure reduction is completed, the remaining O2 and N2 in the adsorption tower are released in the forward release sequence along the adsorption direction. After the forward release is completed, the CO2 gas in the adsorption tower is released in the reverse adsorption direction by means of vacuuming, etc., and the adsorbent is regenerated. The CO2 gas enters the buffer tank 25. After the reverse release is completed, the adsorption tower and other adsorption towers that need to be depressurized undergo pressure equalization and final pressure increase steps, and then the next adsorption is carried out.

[0064] In this embodiment, the exhaust gas concentration in the pressure swing adsorption recovery system 24 is ≤20%, N2 concentration is ≥60%, O2 concentration is ≥15%, and the CO2 concentration in the gas concentrated by the adsorption tower is ≥95%.

[0065] After being purified and concentrated, the gas passes through a buffer tank 25 for pressure stabilization before entering the second booster fan 26. The CO2-rich gas is then pressurized to ≥25 bar and enters the third liquefaction cold box 27. In the third liquefaction cold box 27, it is cooled to ≤-25℃ before entering the distillation column 2301. This ensures the concentrated gas meets the temperature and pressure parameters required by the distillation system, achieving CO2 concentration and recovery. A liquid product with CO2 purity ≥99.5% is obtained.

[0066] In a preferred embodiment, a dust removal and denitrification device 6, a wet desulfurization device 8, and a flue gas washing system 13 are sequentially installed on the pipeline at the top outlet of the preheater 4. The flue gas washing system 13 includes a water storage tank 1301, a water washing pump 1302, and a flue gas washing tower 1303. The outlet of the wet desulfurization device 8 is connected to the air inlet of the flue gas washing tower 1303. The water storage tank 1301 is connected to the water inlet of the flue gas washing tower 1303 through the water washing pump 1302. The water outlet of the flue gas washing tower 1303 is connected to the inlet of the water washing pump 1302. The air outlet of the flue gas washing tower 1303 is connected to the circulating flue gas pipeline that transports the high-concentration CO2 circulating flue gas B discharged from the top outlet of the preheater 4 back to the all-oxygen combustion cement clinker production system, and the carbon capture and purification system. A flue gas reheater 10 is installed on the circulating flue gas pipeline.

[0067] The CO2 circulating flue gas B is discharged from the outlet of the top cyclone separator of preheater 4. The CO2 circulating flue gas passes through the dust removal and denitrification device 6 to control the particulate matter in the CO2 circulating flue gas to ≤5mg / Nm³. 3 NOx ≤ 50 mg / Nm 3 SCR technology is preferably used to remove NOx from the CO2 circulating flue gas, and VW / Ti or V-Mo / Ti or composite catalysts containing Fe, Ce, Mn, Bi and Cu active elements are selected. After dust removal and denitrification, the CO2 circulating flue gas enters the wet desulfurization unit 8 via the first exhaust fan 7, where it comes into counter-current contact with the desulfurization agent slurry to undergo a sulfur fixation reaction. The desulfurization agent is preferably an active component containing CaCO3 or Ca(OH)2, controlling the SO2 in the CO2 circulating flue gas to ≤5 mg / Nm³. 3Simultaneously, trace impurities such as HCl and HF are removed. The flue gas exiting the wet desulfurization unit 8 then enters the flue gas scrubbing tower via the second tail exhaust fan 12. The flue gas in the scrubbing tower flows from the bottom to the top, directly counter-currently contacting the circulating process water in the scrubbing pump, reducing the flue gas temperature to ≤40℃. This cooling causes the saturated water in the flue gas to condense, controlling the water content in the flue gas to ≤10%. It is then sent to the circulating flue gas pipeline and carbon capture and purification system. A portion of the CO2 circulating flue gas B exiting the flue gas scrubbing system 13 is circulated to the all-oxygen combustion cement clinker production system via the circulating fan 9. To prevent the CO2 circulating flue gas from cooling and condensing during long-distance transportation, the directly cooled flue gas is reheated to ≥60℃ via the flue gas reheater 10, controlling the flue gas temperature to always remain above the dew point temperature of water vapor and acid vapor.

[0068] A portion of the CO2 circulating flue gas B after flue gas treatment enters the circulating flue gas channel and is used for rotary kiln sealing protection gas, fuel conveying air, and clinker cooling air, respectively, to prevent the flue gas from condensing and generating strong acidic substances that corrode the metal connectors, fasteners, pipelines and equipment passing through during the air supply process. The other portion of the CO2 circulating flue gas B enters the carbon capture and purification system.

[0069] The circulating flue gas duct is made of corrosion-resistant stainless steel, and an insulation layer is installed on the outside of the duct. The use of corrosion-resistant stainless steel and the installation of an external insulation layer in the circulating flue gas duct are designed to ensure that the flue gas temperature is always maintained above the dew point temperature, thus preventing condensation and corrosion of the duct and equipment.

[0070] In a preferred embodiment, the protective airbag has a radial labyrinth baffle 204 and an axial labyrinth baffle 205. The radial labyrinth baffle 204 forms a spiral labyrinth channel along the kiln body axis, and the axial labyrinth baffle 205 forms a spiral labyrinth channel along the kiln body radially. The spiral labyrinth channels along the kiln body axis and radially cooperate to form a tortuous labyrinth sealing structure. A reverse sealing plate 207 is provided on the airflow passage of the tortuous labyrinth sealing structure, and multiple CO2 protective gas inlet pipes 206 are distributed circumferentially on the protective airbag.

[0071] During the operation of the all-oxygen combustion system, the feed inlet and discharge outlet of the rotary kiln are under negative pressure. The gaps connecting the kiln end face with the kiln head hood and the kiln tail flue gas chamber make it easy for ambient air to leak in, affecting the CO2 flue gas enrichment concentration in the system. To ensure that the CO2 enrichment concentration and capture cost are not affected by system air leakage, this embodiment adds a protective gas seal structure with CO2 protective gasbags at both ends of the rotary kiln at the location of maximum system air leakage. A tortuous labyrinth seal structure is formed between the sealing sleeve and the shell using radial labyrinth baffles 204 and axial labyrinth baffles 205. The radial labyrinth baffles 204 form a spiral labyrinth channel along the kiln body axis, forcing the gas to move centrifugally and increasing the local resistance between the gas and the sealing wall. The axial labyrinth baffles 205 form a spiral labyrinth channel along the kiln body radially, prolonging the gas residence time. The reverse sealing plate 207 is used to generate reverse airflow disturbance and reduce gas kinetic energy. In this embodiment, the first sealing element is a composite sealing plate 208 used to seal the protective gasbag, which has temperature compensation and wear resistance characteristics. Meanwhile, multiple CO2 protective gas inlet pipes 206 are distributed circumferentially on the protective airbag. CO2 circulating flue gas B with a temperature ≥60℃ is introduced into the CO2 protective gas inlet pipes 206. The high-speed airflow with positive pressure can counteract the negative pressure environment inside the flue gas protective sealing device, isolate the air and prevent the air from entering the connection gap with the kiln door cover along the tortuous labyrinth, so as to achieve the purpose of not decreasing the CO2 enrichment concentration.

[0072] The kiln tail seal also adopts a similar structure and airtight form as the kiln head seal, and uses CO2 circulating flue gas as protective gas.

[0073] In a preferred embodiment, the cooler 1 is divided into three sections from the clinker inlet to the outlet (the process of cooling clinker): the first section 101, the second section 102, and the third section 103. The high-concentration CO2 circulating flue gas with a dry basis CO2 concentration ≥85% discharged from the top outlet of the preheater 4 also enters the cooling medium inlets of the first two sections of the cooler. The first section 101 of the cooler is introduced with a mixture of high-concentration O2 and CO2 circulating flue gas B. The secondary air intake and tertiary air intake of the cooler 1 are located in the first section 101 of the cooler and are connected to the rotary kiln 2 and the decomposition furnace 3, respectively. The second section 102 of the cooler is only introduced with CO2 circulating flue gas B. The tertiary air intake is located in the second section 102 of the cooler and is connected to the inlet of the last stage cyclone separator of the preheater 4.

[0074] A high-concentration oxygen inlet A is installed on the channel at the air inlet of the first section 101 of the cooler, and an oxygen concentration regulating valve is installed upstream of the high-concentration oxygen inlet of this channel to regulate the O2 concentration in the O2 / CO2 mixture entering the first section of the cooler.

[0075] The outlet of the circulating flue gas duct is connected to the inlet of the first section 101 of the cooler and the inlet of the second section 102 of the cooler; the inlet of the first section 101 of the cooler is supplied with O2 / CO2 mixed gas, which is composed of high-concentration O2 produced by the oxygen production system and CO2 circulating flue gas B produced by the all-oxygen combustion cement clinker production system; the inlet of the second section 102 of the cooler is supplied with only CO2 circulating flue gas B.

[0076] This is a means of controlling the temperature of raw material decomposition under high CO2 partial pressure in the decomposition furnace, and a means of controlling the temperature of the decomposition furnace outlet to avoid the problem of scale buildup and blockage in the last stage cyclone of the preheater due to the increase in raw material decomposition temperature and the delayed combustion of alternative fuels.

[0077] The O2 / CO2 mixture exiting the first stage of the cooler is used as secondary air g2 and tertiary air g3. Both secondary air g2 and tertiary air g3 are O2 / CO2 mixtures after heat exchange with clinker, recovering and utilizing the heat from the first stage cooler outlet. These gases then enter the rotary kiln 2 and the decomposition furnace 3 respectively, providing a combustion environment. The secondary air intake of the cooler is connected to the rotary kiln inlet, and the tertiary air intake of the cooler is connected to the tertiary air inlet of the decomposition furnace via a pipeline. By adjusting the CO2 circulating flue gas volume, the oxygen concentration in the O2 / CO2 mixture is controlled within a reasonable range that allows for controllable combustion temperatures, preventing excessively high oxygen concentrations from entering the kiln and causing fuel deflagration, resulting in localized high temperatures and potential process safety issues. The CO2 circulating flue gas from the second stage of the cooler absorbs heat from the high-temperature clinker and enters the preheater 4 as tertiary air g4. The tertiary air intake of the cooler is connected to the inlet of the final stage cyclone separator via a pipeline. Compared to conventional air-fired systems, the total air volume of secondary and tertiary air in an oxy-fuel combustion cement clinker production system is significantly reduced. This results in insufficient utilization of the waste heat recovered in the second stage of the cooler, leading to a decrease in the cooler's heat recovery efficiency. The tertiary air g4 transfers the heat from the CO2 circulating flue gas to the raw meal through the kiln tail preheater, thereby reducing the heat consumption of the oxy-fuel combustion cement clinker production system. The temperature range of the O2 / CO2 mixture entering the rotary kiln as secondary air g2 is 900–1200℃, the temperature range of the O2 / CO2 mixture entering the decomposer as tertiary air g3 is 800–1100℃, and the temperature of the CO2 circulating flue gas entering the preheater as tertiary air g4 is ≥500℃.

[0078] In this embodiment, an oxygen generation system using existing cryogenic distillation technology produces high-concentration oxygen, generally achieving an oxygen concentration ≥96%, an argon concentration ≤3%, and an N2 concentration ≤1%. The exhaust gas from the oxygen generation system is used for the regeneration of the adsorption tower in the flue gas deep purification system 18 and the pressure swing adsorption recovery system 24.

[0079] As a preferred embodiment, to further reduce the problem of air leakage caused by the difference 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 the leakage of O2 / CO2 mixture from the first section into the second section 102 of the cooler. This prevents O2 from not being fully combusted in the cement kiln and being directly introduced into the carbon capture and purification system by the quaternary air into the preheater 4, thus increasing the load on the oxygen production system and the power consumption of the carbon capture and purification system. A second resistance baffle 1042 and a central roller crusher 104 are installed between the second section 102 and the third section 103 of the cooler. The second resistance baffle 1042 can prevent air from entering the second section of the cooler through the gap of the central roller crusher and affecting the CO2 enrichment concentration. Indirect drying fuel is introduced into the air chamber below the central roller crusher. The generated steam C, acting as a cooling medium, forms an air curtain that further blocks cross-flow. Because there are gaps between the rollers of the centrally located roller crusher, to avoid affecting the gas composition and clinker cooling effect of different cooling media in different cooling zones during continuous cooling, steam C generated from indirect drying fuel / alternative fuel is introduced between the second section 102 and the third section 103 of the cooler as a cooling medium. This further blocks direct cross-flow between the CO2 circulating flue gas B cooling medium in the second section of the cooler and the air D cooling medium in the third section. This reduces the impact of air D entering the second section of the cooler through the gaps in the centrally located roller crusher on the CO2 enrichment concentration and prevents CO2 escape caused by the CO2 circulating flue gas entering the third section of the cooler. This avoids reducing the CO2 concentration in the second-section cooling medium due to cross-flow and improves the CO2 enrichment effect.

[0080] In this embodiment, the cooling air of the third section 103 of the cooler is divided into two streams. The first stream is located at the front of the third section of the cooler (the air chamber under the central roller crusher), through which steam C generated for drying fuel moisture is introduced. The second stream is located at the rear of the third section of the cooler, through which air D is introduced. This prevents direct cross-flow between the CO2 circulating flue gas B of the second section of the cooler and the air D used in the rear of the third section of the cooler, further controlling air leakage between the second and third sections of the cooler and minimizing the impact on the clinker cooling effect, thus ensuring clinker quality. Part of the steam C exiting the front of the third section of the cooler mixes with the quaternary air through the gap of the central roller crusher and enters the preheater 4. The remaining steam C mixes with the air D exiting the rear of the third section of the cooler and is directly discharged from the system as low-grade heat.

[0081] In this embodiment, 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. 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 resistance baffle, hindering the reciprocating movement of the grate, they can rotate flexibly back and forth along the material flow direction with the force of the cooler grate, thus avoiding abnormal operation of the cooler.

[0082] 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. 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.

[0083] 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. A quaternary air regulating valve is installed on the pipe between the quaternary air intake of the cooler and the bottom air inlet of the preheater 4 to distribute the quaternary air volume to the preheater 4, thereby achieving adjustable air volume.

[0084] In a preferred embodiment, the high-concentration CO2 circulating flue gas with a dry basis CO2 concentration ≥85% discharged from the top outlet of the preheater 4 also enters the fuel pneumatic conveying pipeline. The fuel pneumatic conveying pipeline is equipped with a fuel conveying fan 901 and a fuel storage silo 11. The fuel required by the decomposition furnace and the rotary kiln is placed in the fuel storage silo 11. The fuel conveying fan is located upstream of the fuel storage silo 11 and sends the required fuel into the decomposition furnace 3 and the rotary kiln 2.

[0085] By using CO2 circulating flue gas B as the sealing and protective gas for the rotary kiln and as the gas for fuel pneumatic conveying, the system air leakage is effectively controlled, enabling the all-oxygen combustion system to provide the carbon capture and purification system with high-concentration flue gas of dry basis CO2 ≥ 85%.

[0086] CO2 circulating flue gas B is divided into four paths entering the entire oxy-fuel combustion cement clinker production system. One path serves as the conveying air in the fuel pneumatic conveying pipeline, connecting to the burners of the rotary kiln and decomposer via fuel conveying fan 901. The second path serves as the rotary kiln sealing and protection gas, connecting to the flue gas protection and sealing devices at both ends of the rotary kiln via CO2 protection gas conveying fan 902, controlling air leakage at both ends of the rotary kiln. The main function of these two circulating air paths is to reduce the introduction of outside air, utilizing high-concentration CO2 circulating flue gas to achieve fuel pneumatic conveying and protective gas sealing, which helps to improve the CO2 enrichment concentration in the oxy-fuel combustion system. The third path serves as clinker cooling gas, connecting to the air inlet of the first stage of the cooler. By adjusting the total air volume of the first stage of the cooler, the oxygen concentration and temperature in the secondary and tertiary air are controlled within a reasonable range. The fourth path serves as clinker cooling gas, connecting to the air inlet of the second stage of the cooler. By adjusting the total air volume of the second stage of the cooler, the air volume required for clinker cooling is ensured, improving the heat recovery efficiency of the cooler.

[0087] The O2 / CO2 mixture exiting the first stage of the cooler is used as secondary air g2 and tertiary air g3. Secondary air g2 is introduced into the rotary kiln 2 through the secondary air inlet, and tertiary air g3 is introduced into the decomposition furnace 3 through the tertiary air inlet. The amount of CO2 circulating flue gas introduced into the furnace is adjusted by the tertiary air regulating valve, forming a fuel combustion zone above the tertiary air inlet. The CO2 circulating flue gas exiting the second stage of the cooler is used as quaternary air g4 and introduced into the preheater 4. The air volume is adjusted by the quaternary air regulating valve, which can be used as a means of controlling the raw material decomposition temperature under high CO2 partial pressure in the decomposition furnace. If all the quaternary air composed of CO2 circulating flue gas enters the furnace, it will cause the CO2 partial pressure in the flue gas in the decomposition furnace to increase, causing the raw material decomposition temperature to rise to 950℃ or even above 1000℃. At the same time, it can also be used as a means of controlling the outlet temperature of the decomposition furnace, avoiding 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. The steam C exiting the first section of the third stage of the cooler is mixed with the air D exiting the second section of the third stage of the cooler and discharged directly as low-grade heat from the system.

[0088] A low-energy carbon capture method based on high-concentration carbon dioxide includes the following steps:

[0089] Raw meal R is fed into preheater 4, where it exchanges heat with flue gas and undergoes gas-solid separation to preheat it to the decomposition temperature. The preheated raw meal is then fed into decomposition furnace 3. In the oxygen-rich combustion environment of the decomposition furnace, the large amount of heat released by the fuel combustion is used to decompose the raw meal in the decomposition furnace, resulting in hot raw meal. The hot raw meal enters rotary kiln 2, where it is calcined in the oxygen-rich combustion environment to produce clinker. The clinker is then cooled in cooler 1 to obtain cement clinker K.

[0090] The fuel generates a large amount of flue gas which enters the decomposition furnace 3. After mixing with the flue gas in the decomposition furnace, the flue gas enters the preheater 4. After heat exchange, the low-temperature flue gas is discharged through the outlet of the cyclone separator at the top of the preheater.

[0091] 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, and the other path enters the carbon capture and purification system.

[0092] The CO2 circulating flue gas B entering the all-oxygen combustion cement clinker production system is divided into four paths. The first and second paths serve as protective gases to prevent the system from entering conventional air. The first path, acting as a pneumatic conveying air for fuel, pneumatically conveys fuel to the decomposer 3 and rotary kiln 2, connecting the kiln head burner 203 and the decomposer burner 301, respectively. The second path, acting as a sealing gas for the rotary kiln, is sent to the flue gas protection sealing devices at both ends of the rotary kiln, connecting the kiln head flue gas protection sealing device 201 and the kiln tail flue gas protection sealing device 201 on both sides of the rotary kiln 2. The sealing device 202 provides sealing gas to control air leakage at the dynamic and static sections on both sides of the rotary kiln; the third path is connected to the air inlet of the first section 101 of the cooler, and enters the first section of the cooler with high-concentration O2, and a mixture of high-concentration O2 and CO2 circulating flue gas B is introduced. By controlling the total amount of mixed gas introduced, the material in the material bed 1a of the first section of the cooler is fully cooled; the fourth path is connected to the air inlet of the second section 102 of the cooler, and only CO2 circulating flue gas B is introduced as the clinker cooling gas entering the second section of the cooler.

[0093] The CO2 circulating flue gas B entering the carbon capture and purification system is sequentially cooled to ≤10℃ by precooler 15, separated into free water by water separator 16, and pressurized by first booster fan 17. The flue gas then enters the flue gas deep purification system 18, where it undergoes denitrification, drying, and adsorption for deep purification. The purified flue gas undergoes two liquefaction and gas-liquid separation processes. The first liquefaction process cools the gas to ≤-15℃, and the second liquefaction process cools it to ≤-25℃. The separated gas enters the pressure swing adsorption recovery system 24, while the liquid from both gas-liquid separations enters the distillation column 2301. 01 Light components such as hydrogen, methane, carbon monoxide, oxygen, and nitrogen, as well as non-condensable gases, are discharged from the top of the distillation column 2301 and enter the pressure swing adsorption recovery system 24. The pressure swing adsorption recovery system 24 concentrates and recovers CO2, making the CO2 recovery rate of the carbon capture and purification system ≥95%. The concentrated and recovered CO2-rich gas is pressurized and liquefied, and after being cooled to ≤-25℃, it enters the distillation column 2301. The liquid in the distillation column 2301 enters the liquefied product storage tank 2303 through the reboiler 2302 for storage. The CO2 purity in the liquefied product is ≥99.5%.

[0094] Specifically, in the first stage 101 of the cooler, the O2 concentration in the O2 / CO2 mixture is controlled within the range of 30% to 70%. The O2 / CO2 mixture is used as secondary air g2 and tertiary air g3, which enter the rotary kiln 2 and the decomposition furnace 3 respectively. The tertiary air volume is distributed through the tertiary air regulating valve, so that the temperature range of secondary air g2 entering the rotary kiln 2 is 900 to 1200℃, and the temperature range of tertiary air g3 entering the decomposition furnace 3 is 800 to 1100℃. The cooling medium in the second stage 102 of the cooler is provided only by CO2 circulating flue gas B, which cools the clinker conveyed to the second stage material bed 1b of the cooler by the grate. The flue gas that recovers the enthalpy of the clinker enters the preheater 4 as tertiary air g4. The CO2 concentration in the tertiary air is higher than 85%, and the O2 concentration is lower than 5%. The cooling medium in the third stage 103 of the cooler is provided by steam C and air D, which is used to cool the clinker located on the third stage material bed 1c of the cooler.

[0095] To ensure a suitable gas environment after heat exchange between the cooling medium and clinker in each section of the cooler, a first resistance baffle 1041 is installed between the first section 101 and the second section 102 of the cooler. This baffle reduces cross-flow between the O2 / CO2 mixture and the CO2 circulating flue gas, preventing O2 from directly entering the carbon dioxide purification system via the quaternary air, thus avoiding increased load on the oxygen production system and higher power consumption in 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 to prevent cross-flow between the CO2 circulating flue gas and air, which would affect the CO2 enrichment concentration in the all-oxygen combustion system. Simultaneously, the lower air chamber of the central roller crusher 104 utilizes steam C generated from indirect fuel drying to cool the clinker, further reducing cross-flow.

[0096] In this embodiment, the third section 103 of the cooler is divided into two parts. The front cooling air chamber is located below the central roller crusher 104 and is filled with steam C generated from indirect drying of fuel. The rear air inlet is filled with conventional air D. The steam after heat exchange is mixed with the air D exiting the rear section of the third section of the cooler and is directly discharged from the system as low-grade heat.

[0097] In a preferred embodiment, the CO2 circulating flue gas B discharged from the outlet of the cyclone separator at the top of preheater 4 has a CO2 dry basis concentration ≥85% and a temperature range of 250–400℃. The CO2 circulating flue gas 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 the water content to ≤10%, and then split into two streams to enter the all-oxygen combustion cement clinker production system and the carbon capture and purification system.

[0098] The CO2 circulating flue gas entering the all-oxygen combustion cement clinker production system is preheated to ≥60℃ to ensure that the flue gas temperature is always maintained above the dew point temperature to avoid condensation and corrosion of pipelines and equipment.

[0099] In a preferred embodiment, the O2 / CO2 mixture exiting the first stage of the cooler is used as secondary air g2 and tertiary air, respectively. Secondary air g2 is fed into the rotary kiln 2, and tertiary air g3 is fed into the decomposition furnace 3. The CO2 circulating flue gas exiting the second stage of the cooler is used as quaternary air g4 and fed into the final stage cyclone separator of the preheater. The CO2 circulating flue gas being fed as quaternary air g4 into the preheater 4 can serve as a control measure to reduce the raw material decomposition temperature under high CO2 partial pressure in the decomposition furnace and to prevent scale buildup and blockage in the final stage cyclone separator of the preheater due to increased raw material decomposition temperature and delayed fuel combustion.

[0100] The O2 concentration in the secondary air g2 and tertiary air g3 is 30% to 70%; the CO2 dry basis concentration in the quaternary air g4 is ≥85% and the O2 concentration is less than 5%.

[0101] As a preferred embodiment, the CO2 circulating flue gas B entering the all-oxygen combustion cement clinker production system also serves as fuel conveying air to the decomposer 3 and rotary kiln 2, further effectively controlling system air leakage.

[0102] In a preferred embodiment, the CO2 concentration in the gas discharged from the second gas-liquid separation is ≥70%, and the CO2 concentration in the condensate discharged from the first and second gas-liquid separations is ≥99%.

[0103] The CO2 concentration in the exhaust gas from the distillation column 2301 is ≥50%;

[0104] The exhaust gas in the pressure swing adsorption recovery system 24 has a CO2 concentration ≤20%, N2 concentration ≥60%, and O2 concentration ≥15%, and the CO2 concentration in the flue gas after pressure swing adsorption concentration recovery is ≥95%.

[0105] For existing oxy-fuel combustion coupled carbon capture technology in cement kilns, the dry basis CO2 concentration in the flue gas at the outlet of preheater 4 ranges from 75% to 85%, which is considered medium to high concentration CO2. Considering the technical characteristics and applicable CO2 concentration ranges of technologies such as pressure swing adsorption (PSA) and cryogenic distillation, the existing technology first uses PSA to increase the CO2 concentration in the oxy-fuel combustion flue gas to 90-95%, and then uses mature and reliable cryogenic distillation technology to obtain a CO2 product with a CO2 concentration ≥99.5%, achieving a CO2 recovery rate ≥80%, and a comprehensive power consumption per unit CO2 in the carbon capture system ≤250 kWh / t.CO2.

[0106] This invention determines the CO2 recovery rate of the carbon capture and purification system based on the airflow test and gas composition analyzer installed on the flue gas pipeline of the induced draft fan 14 and the exhaust flue gas pipeline of the pressure swing adsorption recovery system 24. Taking a 2700t / d clinker production line as an example, the flue gas volume entering the carbon capture and purification system is 122548 Nm³. 3 / h, CO2 concentration is 77.07% (corresponding to 90% dry basis CO2 concentration), and the exhaust gas volume of the pressure swing adsorption recovery system is 6348 Nm³. 3 The CO2 concentration was 21.3% per hour. Based on the monitoring values, the CO2 recovery rate of the carbon capture and purification system was calculated to be 98.6%, and the comprehensive power consumption per unit of CO2 in the carbon capture system was ≤210 kWh / t.CO2.

[0107] Example 2

[0108] As shown in Figure 2, unlike in Example 1, when the fuel / alternative fuel drying system is not working, steam cannot be supplied to the front air chamber of the third stage of the cooler. The third stage of the cooler is cooled by air D as the cooling medium, which causes a small amount of air to enter the all-oxygen combustion through the central roller crusher, reducing the dry basis concentration of CO2 flue gas entering the carbon capture and purification system to 85%.

[0109] The CO2 recovery rate of the carbon capture and purification system was determined based on the airflow test and gas composition analyzer used in the flue gas pipeline of the induced draft fan 14 and the exhaust flue gas pipeline of the pressure swing adsorption recovery system 24. Taking a 2700t / d clinker production line as an example, the flue gas flow rate into the carbon capture and purification system is 145200 Nm³. 3 The CO2 concentration is 72.25% per hour (corresponding to a dry basis CO2 concentration of 85%). As the only exhaust gas from the carbon capture and purification system, the exhaust gas volume of the pressure swing adsorption recovery system is 7820 Nm³. 3 The CO2 concentration was 25.3% per hour. Based on the monitoring values, the CO2 recovery rate of the carbon capture and purification system was calculated to be 98.1%.

[0110] 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 fully oxy-fuel combustion coupled carbon capture system based on high-concentration carbon dioxide, comprising an oxy-fuel combustion cement clinker production system and a carbon capture and purification system; the oxy-fuel combustion 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 rotary kiln is equipped with flue gas protection sealing devices at both ends. The flue gas protection sealing devices have protective airbags. A first sealing element is set between the outside of the protective airbag and the outside air, and a second sealing element is set between the inside of the protective airbag and the rotary kiln. High-concentration CO2 circulating flue gas with a dry basis CO2 concentration ≥85% is discharged from the air outlet at the top of the preheater and enters the carbon capture and purification system and the protective airbag. The carbon capture and purification system includes a precooler, a water separator, a first booster fan, a deep flue gas purification system, a first liquefaction cold box, a first gas-liquid separator, a second liquefaction cold box, a second gas-liquid separator, a distillation system, a pressure swing adsorption recovery system, a buffer tank, a second booster fan, and a third liquefaction cold box. The precooler, water separator, first booster fan, deep flue gas purification system, first liquefaction cold box, first gas-liquid separator, second liquefaction cold box, and second gas-liquid separator are connected sequentially. The deep flue gas purification system includes a denitrification bed, a drying bed, and an adsorption bed connected sequentially. Various impurities in the denitrification bed, drying bed, and adsorption bed... The gas outlet is connected to the waste gas treatment system. The distillation system includes a distillation column, a reboiler, and a liquefied product storage tank. The liquid outlets of the first and second gas-liquid separators are both connected to the inlet of the distillation column. The gas outlets of the second gas-liquid separator and the distillation column are both connected to the inlet of the pressure swing adsorption recovery system. The liquid outlet of the distillation column is connected in sequence to the reboiler and the liquefied product storage tank. The recovered gas outlet of the pressure swing adsorption recovery system is connected in sequence to the buffer tank, the second booster fan, and the third liquefaction cold box. The outlet of the third liquefaction cold box is connected to the inlet of the distillation column. The exhaust outlet of the pressure swing adsorption recovery system is connected to the waste gas treatment system.

2. The whole-system oxy-fuel combustion coupled carbon capture system based on high-concentration carbon dioxide according to claim 1, characterized in that: The precooler is used to cool the flue gas to ≤10℃. The first and second booster fans are both used to compress and boost the flue gas to ≥25 bar. The deep flue gas purification system is used to deeply remove impurities from the flue gas. The first liquefaction cold box is used to cool the flue gas to ≤-15℃, the second liquefaction cold box is used to cool the flue gas to ≤-25℃, and the third liquefaction cold box is used to cool the flue gas to ≤-25℃. The first and second gas-liquid separators are used to separate condensed liquid from residual gas. The distillation column is used to discharge light component impurities such as hydrogen, methane, carbon monoxide, oxygen, and nitrogen, as well as non-condensable gases from the flue gas, so that the purity of liquid CO2 is ≥99.5%. The pressure swing adsorption recovery system is used to concentrate and recover CO2, so that the CO2 recovery rate of the carbon capture and purification system is ≥95%.

3. The whole-system oxy-fuel combustion coupled carbon capture system based on high-concentration carbon dioxide according to claim 1, characterized in that: A dust removal and denitrification device, a wet desulfurization device, and a flue gas washing system are sequentially installed on the pipeline at the top outlet of the preheater. 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 that transports the high-concentration CO2 circulating flue gas discharged from the top outlet of the preheater back to the all-oxygen combustion cement clinker production system, and the carbon capture and purification system. A flue gas reheater is installed on the circulating flue gas pipeline.

4. The whole-system oxy-fuel combustion coupled carbon capture system based on high-concentration carbon dioxide according to claim 3, characterized in that: The circulating flue gas duct is made of corrosion-resistant stainless steel and has an insulation layer on the outside.

5. The whole-system oxy-fuel combustion coupled carbon capture system based on high-concentration carbon dioxide according to claim 1, characterized in that: The protective airbag contains radial labyrinth baffles and axial labyrinth baffles. The radial labyrinth baffles form a spiral labyrinth channel along the kiln body axis, and the axial labyrinth baffles form a spiral labyrinth channel along the kiln body radially. The spiral labyrinth channels along the kiln body axis and radially cooperate to form a tortuous labyrinth sealing structure. Reverse sealing plates are set on the airflow passage of the tortuous labyrinth sealing structure, and multiple CO2 protective gas inlet pipes are distributed circumferentially on the protective airbag.

6. The whole-system oxy-fuel combustion coupled carbon capture system based on high-concentration carbon dioxide 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. High-concentration CO2 circulating flue gas with a dry basis CO2 concentration ≥85% is discharged from the top outlet of the preheater and also enters the cooling medium inlets of the first two sections of the cooler. The first section of the cooler 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 second section of the cooler is supplied only with 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. The third section of the cooler is further divided into two sections: the air chamber below the centrally located roller crusher in the first section supplies steam generated from indirect drying of the fuel, while the second section supplies conventional air.

7. The whole-system oxy-fuel combustion coupled carbon capture system based on high-concentration carbon dioxide according to claim 6, 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.

8. The whole-system oxy-fuel combustion coupled carbon capture system based on high-concentration carbon dioxide according to claim 6, characterized in that: A high-concentration oxygen inlet is installed on the channel at the first air inlet of the cooler.

9. The whole-system oxy-fuel combustion coupled carbon capture system based on high-concentration carbon dioxide 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.

10. The whole-system oxy-fuel combustion coupled carbon capture system based on high-concentration carbon dioxide according to claim 1, characterized in that: The high-concentration CO2 circulating flue gas with a dry basis CO2 concentration of ≥85% discharged from the top outlet of the preheater also enters the fuel pneumatic conveying pipeline. The fuel pneumatic conveying pipeline is equipped with a fuel conveying fan and a fuel storage silo, with the fuel conveying fan located upstream of the fuel storage silo.

11. A whole-system oxy-fuel combustion coupled carbon capture method based on high-concentration carbon dioxide, implemented based on the whole-system oxy-fuel combustion coupled carbon capture system based on any one of claims 1-10, characterized in that, Includes the following steps: Raw meal is fed into a preheater, where it exchanges heat with flue gas and undergoes gas-solid separation to preheat it to the decomposition temperature. The preheated raw meal is then fed into a decomposition furnace. In the oxy-fuel combustion environment of the decomposition furnace, the large amount of heat released by fuel combustion is used to decompose the raw meal, resulting in hot raw meal. The hot raw meal enters a rotary kiln, where it is calcined in the oxy-fuel combustion environment to produce clinker. The clinker is then cooled in a cooler to obtain cement clinker. The fuel produces a large amount of flue gas which enters the decomposition furnace. After mixing with the flue gas in the decomposition furnace, it enters the preheater. 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 has a dry basis CO2 concentration of ≥85% and a temperature range of 250~400℃. It is divided into two paths: one path enters the all-oxygen combustion cement clinker production system, and the other path enters the carbon capture and purification system. The CO2 circulating flue gas entering the all-oxygen combustion cement clinker production system is sent as the rotary kiln sealing protection gas into the flue gas protection sealing devices at both ends of the rotary kiln. The CO2 circulating flue gas entering the carbon capture and purification system is sequentially cooled to ≤10℃ by a precooler, free water is separated by a water separator, and pressurized by a first booster fan. Then, the flue gas enters the deep purification system, where it undergoes denitrification, drying, and adsorption to complete deep purification. The purified flue gas undergoes two liquefaction and gas-liquid separation processes. The first liquefaction process cools the flue gas to ≤-15℃, and the second liquefaction process cools it to ≤-25℃. The separated gas enters the pressure swing adsorption recovery system. The liquid from both gas-liquid separation processes enters a distillation column. The distillation column discharges light component impurities such as hydrogen, methane, carbon monoxide, oxygen, and nitrogen, as well as non-condensable gases, from the top of the distillation column into the pressure swing adsorption recovery system. The pressure swing adsorption recovery system concentrates and recovers CO2, achieving a CO2 recovery rate of ≥95% in the carbon capture and purification system. The concentrated and recovered CO2-rich gas is then pressurized and liquefied, and after being cooled to ≤-25℃, it enters the distillation column. The liquid in the distillation column is passed through a reboiler and then enters a liquefied product storage tank for storage. The CO2 purity in the liquefied product is ≥99.5%.

12. The low-energy carbon capture method based on high-concentration carbon dioxide according to claim 11, 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 the water content to ≤10%, and then split into two streams to enter the all-oxygen combustion cement clinker production system and the carbon capture and purification system.

13. The low-energy carbon capture method based on high-concentration carbon dioxide according to claim 11, characterized in that: The CO2 circulating flue gas entering the all-oxygen combustion cement clinker production system is first preheated to ≥60℃.

14. The low-energy carbon capture method based on high-concentration carbon dioxide according to claim 11, characterized in that: The CO2 circulating flue gas entering the all-oxygen combustion cement clinker production system also enters the first stage of the cooler along with high-concentration O2, and enters the second stage of the cooler as clinker cooling gas; 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 final stage cyclone of the preheater.

15. The low-energy carbon capture method based on high-concentration carbon dioxide according to claim 14, 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 ≥85%, and the O2 concentration is less than 5%.

16. The low-energy carbon capture method based on high-concentration carbon dioxide according to claim 11, characterized in that: The CO2 circulating flue gas entering the all-oxygen combustion cement clinker production system also serves as fuel conveying air, which pneumatically transports the fuel to the decomposer and rotary kiln.

17. The low-energy carbon capture method based on high-concentration carbon dioxide according to claim 11, characterized in that: The CO2 concentration in the gas discharged from the second gas-liquid separation is ≥70%, and the CO2 concentration in the liquid discharged from the first and second gas-liquid separations is ≥99%. The CO2 concentration in the exhaust gas from the distillation column is ≥50%; The exhaust gas in the pressure swing adsorption recovery system has a CO2 concentration ≤20%, N2 concentration ≥60%, and O2 concentration ≥15%, and the CO2 concentration in the flue gas after pressure swing adsorption concentration recovery is ≥95%.

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