Cement kiln system for oxy-fuel combustion coupled with flue gas circulation enrichment and carbon dioxide capture

Abstract

The present invention belongs to the field of efficient carbon emission reduction and carbon cycle utilization, and discloses a cement kiln system for oxy-fuel combustion coupled with flue gas circulation enrichment and carbon dioxide capture. The grate cooler in this system adopts a three-section grate plate, with a partition inside to form three-section cavities. The first and second section cavities are provided with mixed gas inlets to pass the mixed gas of oxygen-rich gas and recycled flue gas, and the third section cavity is provided with an air inlet; the oxygen supply system is connected to relevant pipelines to provide oxygen-rich gas for the cement kiln; the decomposition furnace includes a main decomposition furnace and a pre-decomposition furnace, with a special structure and a specific position; the flue gas circulation system includes various components, and the flow direction of the flue gas is controlled according to the carbon dioxide concentration. The present invention avoids the cross-wind of the secondary and tertiary air and hot air, enables the oxygen-rich gas concentration of the secondary and tertiary air to be independently controlled, increases the carbon dioxide concentration in the cement kiln through flue gas circulation, reduces the capture difficulty and cost, and at the same time can precisely control the flow rate and temperature of the oxygen-rich gas and recycled flue gas in the kiln, and is applicable to the efficient and continuous production of cement clinker.

Description

Technical Field

[0001] The present invention belongs to the field of efficient carbon emission reduction and carbon cycle utilization, and particularly relates to a cement kiln system for oxy-fuel combustion coupled with flue gas circulation enrichment and carbon dioxide capture. Background Art

[0002] As one of the industries with relatively high carbon dioxide emissions, the cement industry is actively taking measures for low-carbon emission reduction. The coupling of oxy-fuel combustion, flue gas circulation enrichment, and carbon dioxide capture technology in cement kilns is an emission reduction path with broad development prospects. Compared with air combustion, oxy-fuel combustion can significantly reduce the participation of nitrogen, thereby increasing the concentration of carbon dioxide in the flue gas at the kiln tail. After coupling flue gas circulation, carbon dioxide continuously circulates and enriches in the cement kiln system, and its concentration gradually increases to 80%. The high-concentration carbon dioxide is recovered by the capture device at the kiln tail, which can improve the efficiency of carbon dioxide capture and reduce the capture cost, thus achieving efficient and low-cost carbon dioxide emission reduction.

[0003] Currently, the use of oxy-fuel combustion technology in the cement industry is only limited to primary air oxygen enrichment, and there is no industrial application example for secondary and tertiary air oxygen enrichment. However, secondary and tertiary air oxygen enrichment has advantages such as improving combustion efficiency, improving clinker quality, and reducing coal consumption. Therefore, it is very necessary for secondary and tertiary air oxygen enrichment. At the same time, the coupling of secondary and tertiary air oxygen enrichment with recycled flue gas entering the cement kiln system through the high-temperature clinker cooling zone of the grate cooler is a very innovative solution. Unfortunately, there is an imbalance in the air draft of the fans in the grate cooler, resulting in easy mixing and cross-flow between the secondary and tertiary air generated by heat exchange in the high-temperature section and the hot air from heat exchange in the medium- and low-temperature sections. This allows the hot air containing nitrogen to enter the cement kiln system through the secondary and tertiary air ducts, affecting the oxy-fuel combustion condition and reducing the circulating enrichment concentration of carbon dioxide in the kiln. It is also difficult to achieve differential control of the oxygen-rich gas concentration and flue gas circulation volume in the preset secondary and tertiary air ducts. Therefore, improving the structure of the grate cooler has become the key to implementing this technology. Summary of the Invention

[0004] The purpose of the present invention is to provide a cement kiln system for oxy-fuel combustion coupled with flue gas circulation enrichment and carbon dioxide capture, which is used to solve the technical problems existing in the prior art, such as easy mixing and cross-flow between the secondary and tertiary air and the hot air from heat exchange in the medium- and low-temperature sections, making it difficult to complete the oxygen enrichment transformation of different concentrations of secondary and tertiary air, and the low concentration of carbon dioxide in the kiln being difficult to capture.

[0005] The cement kiln system for oxy-fuel combustion coupled with flue gas circulation enrichment and carbon dioxide capture includes an oxygen supply system, a grate cooler (3), a rotary kiln (4), a decomposition furnace, a preheater (7), a flue gas circulation system, and a carbon dioxide capture system; the grate cooler (3) adopts a three-section clinker conveying grate plate, and a partition plate (306) is provided in the grate cooler (3) to separate the upper part of the space where the three-section grate plates are located to form a corresponding first-stage cavity, a second-stage cavity, and a third-stage cavity. A mixed gas inlet is provided below both the first-stage cavity and the second-stage cavity, and a mixed gas composed of oxygen-rich gas and kiln-tail recycled flue gas is input through the mixed gas pipeline (304). An air inlet (305) for inputting conventional air is provided in the third-stage cavity. The first-stage cavity is connected to the kiln head of the rotary kiln (4) through a secondary air channel (307), and the second-stage cavity is connected to the tertiary air duct (24) through an air extraction chamber (23). The oxygen supply system is connected to the burner primary air pipeline (25), the mixed gas pipelines (304) on the first-stage cavity and the second-stage cavity respectively through pipelines. The burner primary air pipeline (25) is located at the kiln head position of the rotary kiln (4). The tertiary air duct (24) is connected to the decomposition furnace, the decomposition furnace is connected to the preheater (7) through a pipeline, the preheater (7) is connected to the flue gas circulation system through a pipeline, the flue gas circulation system is connected to the air mixing chamber (9), the two mixed gas pipelines (304) on the grate cooler (3), and the carbon dioxide capture system respectively through pipelines, and the air mixing chamber (9) is connected to the decomposition furnace.

[0006] Preferably, the mixed gas pipeline (304) has a double-channel sleeve structure, including an outer pipeline (3041) and an inner pipeline (3402). The outer pipeline (3041) is connected to the flue gas circulation system for circulating kiln-tail recycled flue gas, and the inner pipeline (3402) is connected to the oxygen supply system for circulating oxygen-rich gas. A spiral guiding structure (3043) is provided in the inner pipeline (3402).

[0007] Preferably, the oxygen supply system includes an oxygen production device (1) and an oxygen splitting device (2). The oxygen production device (1) is connected to the oxygen splitting device (2) through a pipeline. The oxygen splitting device (2) is connected to the burner primary air pipeline (25) and the inner pipelines (3402) of the two mixed gas pipelines (304) respectively through three oxygen supply pipelines; the oxygen-rich splitting device splits oxygen and mixes it with air to form three different concentrations of oxygen-rich gas, which respectively enter the primary air system, the secondary air system, and the tertiary air system.

[0008] Preferably, the decomposition furnace includes a main decomposition furnace (6) and a pre-decomposition furnace (5). The pre-decomposition furnace (5) is externally mounted on the main decomposition furnace (6). The tertiary air duct (24) communicates with the pre-decomposition furnace (5) and receives the tertiary air containing oxygen-rich gas and recycled flue gas from the air extraction chamber (23). The pre-decomposition furnace (5) includes a primary combustion zone (503), a reburning zone (504), and a coke chamber (505). The primary combustion zone (503) is arranged as an inclined box structure. The upper end of the primary combustion zone (503) is provided with an alternative fuel and mixed gas inlet (501), and the lower end communicates with the reburning zone (504). One end of the reburning zone (504) is provided with a tertiary air inlet (502), and the other end is provided with a gas outlet (508). The bottom of the reburning zone (504) communicates with the coke chamber (505), and the bottom of the coke chamber (505) is an inclined box structure.

[0009] Preferably, the pre-decomposition furnace (5) is specifically arranged above the first conical part of the main decomposition furnace (6). The gas outlet (508) is arranged at an eccentric position on the central axis of the decomposition furnace and is located above the first conical part of the main decomposition furnace (6). The oxygen-rich tertiary air carries the pyrolysis gas and part of the small-particle coke and is sent into the furnace body in the tangential direction of the main decomposition furnace (6) to form a spiral gas flow in the furnace body.

[0010] Preferably, the flue gas circulation system includes a flue gas detection control valve (8), a first fan (14), a second fan (15), a mixing air chamber (9), a fourth flue gas flow regulating valve (21), a kiln tail chimney (22), and a third fan (16). The flue gas detection control valve (8) is provided with one air inlet and two air outlets. The air inlet is connected to the preheater (7) through a pipeline, and the two air outlets are respectively connected to the first fan (14) and the second fan (15) through pipelines. The second fan (15) is connected to the inlet of the kiln tail chimney (22) through a pipeline. The outlet of the kiln tail chimney (22) is connected to the fourth fan (17) through a pipeline. The outlet of the fourth fan (17) is connected to a kiln tail flue gas circulation pipeline provided with branches. The two branches of the kiln tail flue gas circulation pipeline are respectively communicated with the outer pipelines (3041) of two mixed gas pipelines (304), and the two branches are respectively provided with a first flue gas flow regulating valve (18) and a second flue gas flow regulating valve (19).

[0011] Preferably, the first flue gas flow regulating valve (18) is located on the pipeline for delivering the kiln tail recycled flue gas to the first-stage cavity, and is used to control the total gas flow of the secondary air; the second flue gas flow regulating valve (19) is located on the pipeline for delivering the kiln tail recycled flue gas to the second-stage cavity, and the third flue gas flow regulating valve (20) is located on the pipeline for the first blower (14) to deliver the recycled flue gas to the air mixing chamber (9). The second flue gas flow regulating valve (19) and the third flue gas flow regulating valve (20) are jointly used to control the total gas flow of the tertiary air mixture in the cement kiln system; the fourth flue gas flow regulating valve (21) is located on the pipeline for the extraction chamber (23) to deliver the tertiary air to the air mixing chamber (9). The fourth flue gas flow regulating valve (21) and the third flue gas flow regulating valve (20) cooperate to jointly control the temperature in the air mixing chamber (9) and the gas flow of the recycled flue gas entering the air mixing chamber (9).

[0012] Preferably, the cement kiln system further includes a boiler (10). One outlet of the flue gas detection control valve (8) is connected to the boiler (10) through a pipeline. The outlet of the boiler (10) is respectively connected to the second blower (15) and the carbon dioxide capture system; the carbon dioxide capture system includes a primary cyclone dust collector (11), a capture device (12) and a carbon dioxide storage tank (13). The outlet of the boiler (10) communicates with the primary cyclone dust collector (11) and is sequentially communicated with the capture device (12) and the carbon dioxide storage tank (13) through pipelines.

[0013] The present invention has the following advantages: on the one hand, the present invention realizes the separation of the spaces where the grate plates in each section of the grate cooler are located at the top exhaust part, forming multiple sections of cavities, avoiding the problem of mixing and cross-flow between the secondary and tertiary air generated by heat exchange in the high-temperature section of the grate cooler and the hot air generated by heat exchange in the medium- and low-temperature sections due to unbalanced air draft of the blower, and ensuring different concentrations of oxygen-enriched secondary and tertiary air. On the other hand, a flue gas circulation system is added, increasing the carbon dioxide concentration in the cement kiln system and reducing the difficulty and cost of carbon dioxide capture. At the same time, the configured mixed gas pipeline can enhance the mixing effect of the oxygen-enriched gas and the direct-current flue gas and its heat exchange efficiency by forming a swirl of the oxygen-enriched gas.

[0014] The decomposition furnace structure adopted by the present invention is combined with the tertiary air system, so that the oxygen-enriched tertiary air carries the pyrolysis gas and part of the small-particle coke, and is sent into the furnace body through the tangential direction of the main decomposition furnace (i.e., the circumferential tangent of the furnace body cross-section here), forming a spiral gas flow in the furnace body, fully stirring and mixing the alternative fuel, pulverized coal and materials, realizing the rapid and uniform distribution of the solid phase and gas phase, and strengthening the combustion effect. Since all the tertiary air formed by the oxygen-enriched gas first passes through the pre-decomposition furnace, on the one hand, the present invention makes the gas volume supplied to the pre-decomposition furnace large, and on the other hand, because the combustion-supporting gas is the oxygen-enriched gas, the alternative fuel can be quickly preheated or pre-burned, thereby increasing the disposal amount of the alternative fuel in the pre-decomposition furnace.

[0015] In the present invention, the flow direction and flow rate of the recycled flue gas are controlled by a fan and a flue gas detection control valve. The fan provides the traction for the flue gas to enter the circulation system, and the flue gas detection control valve controls whether the flue gas enters the circulation enrichment system or the carbon dioxide capture system according to the carbon dioxide concentration in the flue gas. The present invention also realizes the control of the temperature in the system and the control of the flow rate of the tertiary air by setting a flue gas flow regulating valve, so as to meet the gas volume requirements of the secondary air and the tertiary air in actual production and ensure the stable operation of the whole system. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic flow chart of a cement kiln system for oxy-fuel combustion coupled with flue gas circulation enrichment and carbon dioxide capture according to the present invention. The dotted arrows in the figure represent the conveying lines of the oxygen-rich gas, and the solid arrows are the conveying lines of the general flue gas.

[0017] Figure 2 is Figure 1 a schematic structural diagram of the grate cooler in the structure shown.

[0018] Figure 3 is Figure 2 a schematic structural diagram of the mixed gas pipeline in the structure shown.

[0019] Figure 4 is Figure 3 a schematic structural diagram of the spiral guiding structure in the structure shown.

[0020] Figure 5 is Figure 1 a schematic structural diagram of the precalciner in the structure shown.

[0021] The reference numerals in the accompanying drawings of the specification include: 1. oxygen generation device; 2. oxygen shunt device; 3. grate cooler; 301. first-stage grate plate; 302. second-stage grate plate; 303. third-stage grate plate; 304. mixed gas pipeline; 3041. external pipeline; 3402. internal pipeline; 3043. spiral flow guiding structure; 305. air inlet; 306. partition plate; 307. secondary air channel; 308. tertiary air channel; 309. roll crusher; 4. rotary kiln; 5. precalciner; 501. alternative fuel and mixed gas inlet; 502. tertiary air inlet; 503. primary combustion zone; 504. reburning zone; 505. coke chamber; 506. mobile slag pusher; 507. air cannon; 508. gas outlet; 509. coke outlet; 510. pressure sensor; 6. main precalciner; 7. preheater; 8. flue gas detection control valve; 9. air mixing chamber; 10. boiler; 11. primary cyclone dust collector; 12. trapping device; 13. carbon dioxide storage tank; 14. fan one; 15. fan two; 16. fan three; 17. fan four; 18. flue gas flow regulating valve one; 19. flue gas flow regulating valve two; 20. flue gas flow regulating valve three; 21. flue gas flow regulating valve four; 22. kiln tail chimney; 23. air extraction chamber; 24. tertiary air duct; 25. burner primary air pipeline. Detailed implementation manners

[0022] The following further elaborates on the specific implementation manners of the present invention by describing the embodiments with reference to the accompanying drawings, so as to help those skilled in the art have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention.

[0023] As Figures 1 to 5As shown in the figure, the present invention provides a cement kiln system for oxy-fuel combustion coupled with flue gas circulation enrichment and carbon dioxide capture, which includes an oxygen supply system, a grate cooler 3, a rotary kiln 4, a decomposition furnace, a preheater 7, a flue gas circulation system, and a carbon dioxide capture system; the grate cooler 3 adopts a three-stage clinker conveying grate plate, and a partition plate 306 is provided in the grate cooler 3 to separate the upper part of the space where the three-stage grate plates are located to form a corresponding first-stage cavity, a second-stage cavity, and a third-stage cavity. A mixed gas inlet is provided below both the first-stage cavity and the second-stage cavity, and the mixed gas inlet inputs a mixed gas composed of oxygen-rich gas and kiln tail recycle flue gas through a mixed gas pipeline 304. An air inlet 305 for inputting conventional air is provided in the third-stage cavity. The first-stage cavity is connected to the kiln head of the rotary kiln 4 through a secondary air channel 307. The second-stage cavity is connected to a tertiary air pipe 24 through an exhaust chamber 23. The oxygen supply system is connected to a burner primary air pipeline 25, the mixed gas pipelines 304 on the first-stage cavity and the second-stage cavity respectively through pipelines. The burner primary air pipeline 25 is located at the kiln head position of the rotary kiln 4. The tertiary air pipe 24 is connected to the decomposition furnace. The decomposition furnace is connected to the preheater 7 through a pipeline. The preheater 7 is connected to the flue gas circulation system through a pipeline. The flue gas circulation system is connected to a mixing chamber 9, the two mixed gas pipelines 304 on the grate cooler 3, and the carbon dioxide capture system respectively through pipelines. The mixing chamber 9 is connected to the decomposition furnace.

[0024] The mixed gas pipeline 304 has a sleeve double-channel structure, including an outer pipeline 3041 and an inner pipeline 3402. The outer pipeline 3041 is connected to the flue gas circulation system for circulating kiln tail recycle flue gas, and the inner pipeline 3402 is connected to the oxygen supply system for circulating oxygen-rich gas. A spiral flow guiding structure 3043 is provided in the inner pipeline 3402. The spiral flow guiding structure 3043 provides a swirling path for the oxygen-rich gas, thereby enhancing the mixing effect of the oxygen-rich gas and the direct-flow flue gas and its heat exchange efficiency.

[0025] The oxygen supply system includes an oxygen generation device 1 and an oxygen shunt device 2. The oxygen generation device 1 is connected to the oxygen shunt device 2 through a pipeline. The oxygen shunt device 2 is connected to the inside of the primary air duct 25 of the burner and the inner ducts 3402 of two mixed gas ducts 304 through three oxygen supply pipelines respectively. The oxygen-rich shunt device shunts oxygen and mixes it with air to form three oxygen-rich gases with different concentrations, which enter the primary air system, secondary air system, and tertiary air system respectively. The formed oxygen concentration range of the primary air is 25%-40%, the oxygen concentration range of the secondary air is 25%-35%, and the oxygen concentration range of the tertiary air is 30%-40%. The air excess coefficient at the kiln head is controlled to be 1.1-1.3, and the air excess coefficient at the kiln tail is set to be 1.1-1.2. Such a setting can minimize the flue gas heat loss caused by the gas volume input into the system while ensuring sufficient oxygen supply for fuel combustion and the gas velocity requirement of the decomposition furnace, and can also control the outlet oxygen concentration to reduce the impact of oxygen-rich combustion on pollutant emissions.

[0026] The clinker enters the grate cooler 3 from the kiln head and is conveyed by the three-stage clinker conveying grate plates. First, it passes through the first-stage grate plate 301 and exchanges heat with the mixed gas composed of oxygen-rich gas and kiln tail recycled flue gas. After heat exchange, the mixed gas in the first-stage cavity enters the rotary kiln 4 as secondary air; subsequently, the clinker is crushed by the roller crusher 309 and then falls onto the second-stage grate plate 302. After exchanging heat with the mixed gas (including oxygen-rich gas and kiln tail recycled flue gas) input into this space, the mixed gas in the second-stage cavity is output through the tertiary air duct 308 and enters the tertiary air pipe 24 through the exhaust chamber 23; the clinker is crushed by the roller crusher 309 again and then enters the third-stage grate plate 303. The clinker entering the third-stage cavity is medium- and low-temperature clinker, and is heat-exchanged with conventional air. The hot air after heat exchange enters the waste heat power generation system. In the structure of this grate cooler 3, the upper spaces of each stage of grate plates are isolated from each other. Cooperating with the air draft of the kiln head fan, it can ensure that the secondary air, tertiary air, and the medium- and low-temperature hot air are completely independent of each other, preventing air leakage. Finally, the temperature of the clinker at the tail outlet of the grate cooler 3 is about 100°C.

[0027] The decomposition furnace includes a main decomposition furnace 6 and a pre-decomposition furnace 5. The pre-decomposition furnace 5 is externally mounted on the main decomposition furnace 6. The tertiary air duct 24 communicates with the pre-decomposition furnace 5 and receives the tertiary air containing oxygen-rich gas and recycled flue gas from the air extraction chamber 23, so that the alternative fuel can be fully preheated and burned inside, thereby reducing the combustion pressure in the decomposition furnace. The pre-decomposition furnace 5 includes a primary combustion zone 503, a reburning zone 504 and a coke chamber 505. The primary combustion zone 503 is arranged as an inclined box structure. The upper end of the primary combustion zone 503 is provided with an alternative fuel and mixed gas inlet 501, and the lower end communicates with the reburning zone 504. One end of the reburning zone 504 is provided with a tertiary air inlet 502 and the other end is provided with a gas outlet 508. The bottom of the reburning zone 504 communicates with the coke chamber 505. The bottom of the coke chamber 505 is an inclined box structure. The inclination angle of the box of the primary combustion zone 503 is between 20° and 30°, and the inclination angle of the box of the coke chamber 505 is between 10° and 15°. One end of the coke chamber 505 is provided with a mobile slag pusher 506 and the other end is provided with a coke outlet 509. The bottom of the coke chamber 505 is provided with a pressure sensor 510 and an air cannon 507.

[0028] The pre-decomposition furnace 5 is specifically arranged above the first conical part of the main decomposition furnace 6. The gas outlet 508 is arranged at an eccentric position on the axis of the decomposition furnace and is 2 m above the first conical part of the main decomposition furnace 6. The purpose of such arrangement is to enable the oxygen-rich tertiary air to carry pyrolysis gas and some small particle coke, and send them into the furnace body through the tangential direction of the main decomposition furnace 6 (i.e., the circumferential tangent of the furnace body cross-section here), forming a spiral gas flow in the main decomposition furnace 6, fully stirring and mixing the alternative fuel, pulverized coal and materials, realizing the rapid and uniform distribution of solid and gas phases, and strengthening the combustion effect.

[0029] The flue gas circulation system inputs a mixed gas composed of recycled flue gas and a certain amount of tertiary air to the pre-decomposition furnace 5 through a pipeline. The mixed gas and the alternative fuel first enter the primary combustion zone 503 through the alternative fuel and mixed gas inlet 501. In the primary combustion zone 503, the alternative fuel is preheated and preliminarily burned; then the alternative fuel falls into the reburning zone 504. The front end of the reburning zone 504 is connected to the tertiary air duct 24, and the alternative fuel is fully burned by the hotter tertiary air. The gas outlet 508 at the rear end of the reburning zone 504 communicates with the main decomposition furnace 6 to provide the high-temperature mixed gas provided after the alternative fuel burns. The unburned coke and the fully preheated alternative fuel in the reburning zone 504 fall into the coke chamber 505. When the unburned alternative fuel accumulates at the bottom and the bottom pressure reaches the set value, the air cannon 507 is turned on, and the mobile slag pusher 506 is also started synchronously. The two work together to push the coke and some unburned alternative fuel into the decomposition furnace.

[0030] The main precalciner 6 is provided with a total of four coal injection pipes, two of which are located in the cone area of the main precalciner 6, and two are located 3 m above the cone of the main precalciner 6. The coke outlet 509 of the pre-calciner 5 is arranged above the coal injection pipe in the cone area of the precalciner. The mobile slag pusher 506 spreads coke or unburned alternative fuel into the furnace of the precalciner, which can fall to the spatial position where the pulverized coal burns violently, ensuring that the coke can be mixed with the pulverized coal and burned sufficiently as soon as it enters the precalciner. The innovation of the above structure lies in that all the tertiary air formed by the oxygen-rich gas first passes through the pre-calciner 5. On the one hand, this increases the amount of gas supplied to the pre-calciner 5. On the other hand, since the combustion support uses oxygen-rich gas, it can quickly preheat the alternative fuel or cause the alternative fuel to pre-burn, thereby increasing the disposal amount of the alternative fuel in the pre-calciner 5.

[0031] The flue gas circulation system includes a flue gas detection control valve 8, a first fan 14, a second fan 15, a mixing chamber 9, a kiln tail chimney 22 and a third fan 16. The flue gas detection control valve 8 is provided with an air inlet and two air outlets. The air inlet is connected to the preheater 7 through a pipeline, and the two air outlets are respectively connected to the first fan 14 and the second fan 15 through pipelines. The second fan 15 is connected to the inlet of the kiln tail chimney 22 through a pipeline. The outlet of the kiln tail chimney 22 is connected to the fourth fan 17 through a pipeline. The outlet of the fourth fan 17 is connected with a kiln tail flue gas circulation pipeline provided with branch pipes. The two branch pipes of the kiln tail flue gas circulation pipeline are respectively connected to the outer pipelines 3041 of two mixed gas pipelines 304, and the two branch pipes are respectively provided with a first flue gas flow regulating valve 18 and a second flue gas flow regulating valve 19.

[0032] The cement kiln system for oxygen-enriched combustion coupling flue gas circulation enrichment and carbon dioxide capture further includes a boiler 10. One air outlet of the flue gas detection control valve 8 is connected to the boiler 10 through a pipeline. The outlet of the boiler 10 is respectively connected to the second fan 15 and the carbon dioxide capture system. The carbon dioxide capture system includes a primary cyclone dust collector 11, a capture device 12 and a carbon dioxide storage tank 13. The outlet of the boiler 10 is connected to the primary cyclone dust collector 11 and is sequentially connected to the capture device 12 and the carbon dioxide storage tank 13 through pipelines.

[0033] In the flue gas circulation system, when the carbon dioxide concentration in the flue gas is lower than 80%, the first fan 14 and the second fan 15 are started to draw air, thereby opening the flue gas circulation channel. The first fan 14 is started to make the flue gas enter the mixing chamber 9 through the pipeline. The second fan 15 makes the flue gas enter the kiln tail chimney 22 after coming out of the boiler 10. The air drawing volume of the second fan 15 should ensure the gas volume stability of the whole circulation system. Taking a cement clinker production line with a daily output of 5000 tons as an example, the minimum air drawing volume of the second fan is 150000 Nm 3 / h. When the carbon dioxide concentration exceeds 80%, Fan 14 and Fan 15 stop working, and the draft is started through Fan 16 to open the channel of the carbon dioxide capture system. The flue gas comes out of the boiler 10, passes through the primary cyclone dust collector, and then enters the capture device 12. Note that the dust content at the outlet of the primary cyclone dust collector is controlled to be less than 1 g / m3, and the carbon dioxide captured by the capture device 12 is stored in the carbon dioxide storage tank 13. Fan 17 is arranged on the pipeline after the kiln tail chimney 22 to provide traction for the kiln tail recycled flue gas to enter the grate cooler 3. Among the above fans, Fan 14, Fan 15, and Fan 16 are all high-temperature fans with a maximum temperature resistance of 450 - 500 °C, while Fan 17 is a normal-temperature fan.

[0034] Four flue gas flow regulating valves are provided in the system to ensure precise control of the gas flow rate and temperature during the production process and meet the requirements of efficient and continuous cement clinker production. The first flue gas flow regulating valve 18 is located on the pipeline for transporting the kiln tail recycled flue gas to the first section of the cavity. The first section of the cavity sends secondary air to the kiln head of the rotary kiln 4 through the secondary air system. Therefore, the first flue gas flow regulating valve 18 is used to control the total gas flow rate of the secondary air. There are two aspects to the control factors of the secondary air: First, ensure that the gas volume of the oxygen-rich gas and the kiln tail mixed flue gas meets the continuous production requirements of the cement clinker production line. Taking a cement clinker production line with a daily output of 5000 tons as an example, it is necessary to maintain the total gas flow rate of the secondary air at 70000 Nm 3 / h, while maintaining the oxygen-rich gas concentration in the secondary air within the range of 25% - 35%; Second, ensure that the temperature of the secondary air after heat exchange with the clinker is not lower than 1200 °C, and the first section of the clinker is cooled to below 1200 °C.

[0035] The second flue gas flow regulating valve 19 is located on the pipeline for transporting the kiln tail recycled flue gas to the second section of the cavity. The third flue gas flow regulating valve 20 is located on the pipeline where Fan 14 transports the recycled flue gas to the mixing chamber 9. The second flue gas flow regulating valve 19 and the third flue gas flow regulating valve 20 are jointly used to control the total gas flow rate of the tertiary air mixture in the cement kiln system. Among them, the second flue gas flow regulating valve 19 can control the gas flow rate of the tertiary air, and the third flue gas flow regulating valve 20 controls the gas flow rate of the recycled flue gas mixed with the tertiary air. Taking a cement clinker production line with a daily output of 5000 tons as an example, the second flue gas flow regulating valve 19 and the third flue gas flow regulating valve 20 cooperate to maintain the total gas flow rate of the tertiary air mixture at 100000 Nm 3 / h. The control factors of the second flue gas flow regulating valve 19 also include maintaining the temperature of the tertiary air not lower than 1050 °C, ensuring that the clinker in the second section of the cavity is cooled to below 1050 °C, and at the same time ensuring that the oxygen-rich gas content in the tertiary air is between 30% - 40%.

[0036] The fourth flue gas flow regulating valve 21 is located on the pipeline through which the tertiary air is conveyed from the air extraction chamber 23 to the air mixing chamber 9. After a part of the tertiary air is mixed with the recycled flue gas in the air mixing chamber 9, the mixed gas is sent into the precalciner 5. The fourth flue gas flow regulating valve 21 is used to control the gas flow rate of the tertiary air in the air extraction chamber 23 entering the air mixing chamber 9. At the same time, the fourth flue gas flow regulating valve 21 and the third flue gas flow regulating valve 20 cooperate to jointly control the temperature in the air mixing chamber 9 and the gas flow rate of the recycled flue gas entering the air mixing chamber 9. The relevant control factors include: first, keeping the temperature in the air mixing chamber 9 between 550 - 850 °C; second, ensuring that the gas flow rate of the recycled flue gas entering the air mixing chamber 9 is not less than one-third of the total gas flow rate of the tertiary air, so as to ensure the stable operation of the initial combustion zone 503 in the external precalciner 5.

[0037] The present invention has been described exemplarily above in conjunction with the accompanying drawings. Obviously, the specific implementation of the present invention is not limited by the above-mentioned manner. As long as various non-substantive improvements are made by adopting the inventive concept and technical solution of the present invention, or the inventive concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A cement kiln system for oxy-fuel combustion coupled with flue gas circulation enrichment and carbon dioxide capture, characterized in that: It includes an oxygen supply system, a grate cooler (3), a rotary kiln (4), a decomposition furnace, a preheater (7), a flue gas circulation system and a carbon dioxide capture system; the grate cooler (3) adopts a three-stage clinker conveying grate plate, and a partition plate (306) is arranged in the grate cooler (3) to separate the upper part of the space where the three-stage grate plates are located to form a corresponding first-stage cavity, a second-stage cavity and a third-stage cavity. A mixed gas inlet is provided below both the first-stage cavity and the second-stage cavity. The mixed gas inlet inputs a mixed gas composed of oxygen-enriched gas and kiln tail recycled flue gas through a mixed gas pipeline (304), and an air inlet (305) for inputting conventional air is provided in the third-stage cavity. The first-stage cavity is connected to the kiln head of the rotary kiln (4) through a secondary air channel (307), the second-stage cavity is connected to a tertiary air duct (24) through an air extraction chamber (23), the oxygen supply system is connected to a burner primary air pipeline (25), and the mixed gas pipelines (304) on the first-stage cavity and the second-stage cavity through pipelines. The burner primary air pipeline (25) is located at the kiln head position of the rotary kiln (4). The tertiary air duct (24) is connected to the decomposition furnace, the decomposition furnace is connected to the preheater (7) through a pipeline, the preheater (7) is connected to the flue gas circulation system through a pipeline, the flue gas circulation system is connected to a mixing chamber (9), the two mixed gas pipelines (304) on the grate cooler (3) and the carbon dioxide capture system through pipelines, and the mixing chamber (9) is connected to the decomposition furnace; The decomposition furnace includes a main decomposition furnace (6) and a pre-decomposition furnace (5). The pre-decomposition furnace (5) is externally hung on the main decomposition furnace (6). The tertiary air duct (24) is connected to the pre-decomposition furnace (5) and receives the tertiary air containing oxygen-enriched gas and recycled flue gas from the air extraction chamber (23). The pre-decomposition furnace (5) includes an initial combustion zone (503), a reburning zone (504) and a coke chamber (505). The initial combustion zone (503) is arranged as an inclined box structure. An alternative fuel and mixed gas inlet (501) is provided at the upper end of the initial combustion zone (503), and the lower end is connected to the reburning zone (504). A tertiary air inlet (502) is provided at one end of the reburning zone (504), and a gas outlet (508) is provided at the other end. The bottom of the reburning zone (504) is connected to the coke chamber (505), and the bottom of the coke chamber (505) is an inclined box structure; The pre-decomposition furnace (5) is specifically arranged above the first cone part of the main decomposition furnace (6). The gas outlet (508) is arranged at an eccentric position on the axis of the decomposition furnace and is located above the first cone part of the main decomposition furnace (6); the oxygen-enriched tertiary air carries pyrolysis gas and part of small particle coke and is sent into the furnace body through the tangential direction of the main decomposition furnace (6) to form a spiral gas flow in the furnace body.

2. The cement kiln system for oxy-fuel combustion coupled with flue gas circulation enrichment and carbon dioxide capture according to claim 1, characterized in that: The mixed gas pipeline (304) has a sleeve double-channel structure, including an outer pipeline (3041) and an inner pipeline (3402). The outer pipeline (3041) is connected to the flue gas circulation system for circulating the kiln tail recycled flue gas, and the inner pipeline (3402) is connected to the oxygen supply system for circulating the oxygen-rich gas. A spiral guiding structure (3043) is provided in the inner pipeline (3402).

3. The cement kiln system for oxy-fuel combustion coupled with flue gas circulation enrichment and carbon dioxide capture according to claim 1, characterized in that: The oxygen supply system includes an oxygen generation device (1) and an oxygen shunt device (2). The oxygen generation device (1) is connected to the oxygen shunt device (2) through a pipeline. The oxygen shunt device (2) is connected to the primary air pipeline (25) of the burner and the inner pipelines (3402) of two mixed gas pipelines (304) through three oxygen supply pipelines respectively; the oxygen-rich shunt device shunts oxygen and mixes it with air to form three different concentrations of oxygen-rich gas, which enter the primary air system, secondary air system and tertiary air system respectively.

4. The cement kiln system for oxy-fuel combustion coupled with flue gas circulation enrichment and carbon dioxide capture according to claim 1, wherein: The flue gas circulation system includes a flue gas detection control valve (8), a first fan (14), a second fan (15), a mixing chamber (9), a fourth flue gas flow regulating valve (21), a kiln tail chimney (22) and a third fan (16). The flue gas detection control valve (8) has one air inlet and two air outlets. The air inlet is connected to the preheater (7) through a pipeline, and the two air outlets are connected to the first fan (14) and the second fan (15) through pipelines respectively. The second fan (15) is connected to the inlet of the kiln tail chimney (22) through a pipeline. The outlet of the kiln tail chimney (22) is connected to a fourth fan (17) through a pipeline. The outlet of the fourth fan (17) is connected to a kiln tail flue gas circulation pipeline with branches. The two branches of the kiln tail flue gas circulation pipeline are respectively connected to the outer pipelines (3041) of two mixed gas pipelines (304), and a first flue gas flow regulating valve (18) and a second flue gas flow regulating valve (19) are respectively provided on the two branches.

5. The cement kiln system for oxygen-enriched combustion coupled with flue gas circulation enrichment and carbon dioxide capture according to claim 4, wherein: The first flue gas flow regulating valve (18) is located on the pipeline for transporting the kiln tail recycled flue gas to the first-stage cavity, and is used to control the total gas flow of the secondary air; the second flue gas flow regulating valve (19) is located on the pipeline for transporting the kiln tail recycled flue gas to the second-stage cavity. The third flue gas flow regulating valve (20) is located on the pipeline for the first fan (14) to transport the recycled flue gas to the mixing chamber (9). The second flue gas flow regulating valve (19) and the third flue gas flow regulating valve (20) are jointly used to control the total gas flow of the tertiary air mixture in the cement kiln system. The fourth flue gas flow regulating valve (21) is located on the pipeline for the extraction chamber (23) to transport the tertiary air to the mixing chamber (9). The fourth flue gas flow regulating valve (21) and the third flue gas flow regulating valve (20) cooperate to jointly control the temperature in the mixing chamber (9) and the gas flow of the recycled flue gas entering the mixing chamber (9).

6. The cement kiln system for oxy-fuel combustion coupled with flue gas circulation enrichment and carbon dioxide capture according to claim 5, characterized in that: It further includes a boiler (10). One outlet of the flue gas detection control valve (8) is connected to the boiler (10) through a pipeline. The outlet of the boiler (10) is respectively connected to the second blower (15) and the carbon dioxide capture system. The carbon dioxide capture system includes a primary cyclone dust collector (11), a capture device (12) and a carbon dioxide storage tank (13). The outlet of the boiler (10) communicates with the primary cyclone dust collector (11) and is sequentially communicated with the capture device (12) and the carbon dioxide storage tank (13) through pipelines.

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