Low-no x full-system oxy-fuel combustion-based calciner control method, and cement clinker preparation method and system

Abstract

Disclosed are a low-NOX full-system oxy-fuel combustion-based calciner control method, and cement clinker preparation method and system, wherein kiln exhaust gas and suspension gas are introduced at a bottom of a calciner, the suspension gas is flue gas discharged from a gas outlet at a top end of a preheater and subjected to heat exchange via a middle cooling zone of a grate cooler, and the suspension gas has an O2 concentration lower than 5%, a CO2 concentration higher than 70%, and a temperature of 500 to 900 °C; tertiary gas is introduced into the calciner above the suspension gas, wherein the tertiary gas is a mixed gas consisting of industrial oxygen and the flue gas discharged from the gas outlet at the top end of the preheater, the mixed gas being subjected to heat exchange via a head cooling zone of the grate cooler, and the mixed gas has an O2 concentration greater than 30%; a reduction zone with an excess oxygen coefficient of less than 0.5 is formed in the calciner between a suspension gas inlet and a tertiary gas inlet, and the reduction zone has an average temperature of 800 to 1200 °C, thereby achieving in-situ reduction of NOX in the kiln exhaust gas and suspension of material below the tertiary gas inlet; and a burnout zone is formed above the tertiary gas inlet.

Description

Based on low NO X Methods for controlling a fully oxygen-fired decomposer, methods and systems for preparing cement clinker. Technical Field

[0001] This invention relates to the field of flue gas carbon capture technology, and in particular to a method based on low NO X Methods for controlling a decomposer with full oxygen combustion throughout the system, and methods and systems for preparing cement clinker. Background Technology

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

[0003] Oxygen-based combustion technology is a research hotspot in the international cement industry's carbon emission reduction field. However, compared with traditional air combustion, it presents challenges such as difficulty in controlling the combustion flame under high O2 concentrations and the generation of NO at high temperatures. X Issues such as increased oxygen concentration. With increased oxygen concentration, the highest flame temperature in the firing zone will rise rapidly; the combustion temperature under full oxygen conditions can reach over 2500℃. The thermal NO in the rotary kiln... X This will increase exponentially, raising the load on the flue gas denitrification system of the production line.

[0004] Chinese patent publication CN112500001A discloses a low-energy carbon-enriched cement production system and a method for producing cement clinker, proposing to partition the kiln head cooler, use the circulating flue gas in the medium-temperature section as lifter air, and recover the heat of the clinker exiting the kiln for use in the preheater system. Chinese patent publication CN115867515A discloses a system and method for producing cement clinker using oxy-fuel combustion, proposing to control the rotary kiln wall temperature using the lifter air from the grate cooler. While the above patents disclose the lifter air process for oxy-fuel combustion, they do not address the NO₂ in the flue gas during oxy-fuel combustion. X Emissions reduction is a key issue. Chinese Patent Publication No. CN108167860A discloses a gradient combustion self-denitrification process for a calcination system. It proposes creating a gradient combustion environment within the decomposition furnace, consisting of an extremely oxygen-deficient zone, an oxygen-deficient combustion zone, and an oxygen-rich burnout zone. This environment reduces NO from the rotary kiln using an oxygen-deficient reducing atmosphere. XHowever, this process is suitable for air combustion conditions. Under full oxygen combustion conditions, the amount of flue gas exiting the rotary kiln is greatly reduced. This can lead to the problem that the oxygen-deficient zone cannot properly support the raw materials due to the low air volume exiting the kiln, resulting in the collapse of the material at the bottom of the furnace. Summary of the Invention

[0005] This invention aims to solve the problem of NO in the flue gas exiting the kiln during the cement clinker firing process under oxy-fuel combustion conditions. X To address the challenges of high NO concentration and difficult denitrification, a method based on low NO concentration was proposed. X The method and system for controlling a decomposer with full oxy-fuel combustion, and for preparing cement clinker, involves moving the tertiary air position of the decomposer upwards and introducing the lift air from the grate cooler into the furnace bottom. Fuel is injected into the mixture of the kiln exhaust gas and the lift air, thereby creating an oxygen-deficient combustion environment in the lower part of the decomposer. In this oxygen-deficient combustion environment, the fuel gasifies to produce reducing gases, forming a reduction zone, thus achieving the reduction of NO in the kiln exhaust gas. X Self-removal. At the same time, due to the reduction of kiln air volume under full oxygen conditions and the upward shift of tertiary air, the single kiln flue gas is insufficient to lift the material in the reduction zone. By introducing part of the lifting air from the grate cooler into the reduction zone at the bottom of the furnace and regulating the air volume in the reduction zone, the problem of raw material collapse caused by insufficient air volume at the bottom of the furnace can be prevented.

[0006] This invention is implemented as follows: a method based on low NO X The control method for a precalciner system with full oxygen combustion includes the following steps:

[0007] The bottom of the decomposition furnace is vented with kiln exhaust gas and lifting air. The lifting air comes from the exhaust gas discharged from the top of the preheater and has been cooled by heat exchange in the middle cooling zone of the grate cooler. The O2 concentration in the lifting air is less than 5%, the CO2 concentration is greater than 70%, and the temperature is 500-900℃.

[0008] The decomposition furnace is supplied with tertiary air above the lifting air. The tertiary air comes from the mixture of industrial oxygen and flue gas discharged from the top outlet of the preheater and heat exchanged in the cooling zone of the grate cooler head. The O2 concentration in the mixture is greater than 30%.

[0009] Fuel and raw materials are fed into the decomposition furnace between the catalytic air inlet and the tertiary air inlet, with an oxygen coefficient of less than 0.5, forming a reduction zone. This reduction zone maintains an average temperature of 800–1200℃, effectively reducing NO in the flue gas exiting the kiln. X Self-removal and lifting of materials below the tertiary air inlet; raw materials are introduced above the tertiary air inlet to form a combustion zone.

[0010] In the above technical solution, preferably, the flue gas at the top outlet of the decomposition furnace first rises and then falls, and the lifting air is introduced into the falling pipe to adjust the outlet temperature of the decomposition furnace.

[0011] In the above technical solution, preferably, the lifting air swirls into the decomposition furnace, and along the lifting air flow direction, the lifting air first contacts the raw material and then contacts the fuel.

[0012] In the above technical solution, preferably, the wind speed at the bottom of the decomposition furnace is maintained between 30 and 50 m / s.

[0013] In the above technical solution, preferably, the O2 concentration in the industrial oxygen is greater than 80%.

[0014] A method for preparing cement clinker using a low-NOx, fully oxygen-based combustion system includes the following steps:

[0015] Raw materials are fed into a preheater, where they exchange heat with flue gas and undergo gas-solid separation, preheating the raw materials to their decomposition temperature.

[0016] The preheated raw material is fed into the decomposition furnace; a decomposition reaction occurs in the decomposition furnace to obtain hot raw material; and a large amount of flue gas is generated and enters the preheater. After heat exchange, the low-temperature flue gas is discharged through the cyclone outlet at the top of the preheater.

[0017] Hot raw materials enter a rotary kiln and are calcined to produce clinker; the clinker is cooled in a grate cooler to obtain cement clinker;

[0018] The low-temperature flue gas discharged from the cyclone outlet at the top of the preheater is partially recycled flue gas and enters the head cooling zone and the middle cooling zone of the grate cooler respectively.

[0019] The cooling medium in the head cooling zone of the grate cooler is a mixture of industrial oxygen and circulating flue gas, the cooling medium in the middle cooling zone is circulating flue gas, and the cooling medium in the tail cooling zone is air.

[0020] The high-temperature gas exiting the head cooling zone 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 circulating flue gas exiting the middle cooling zone is fed into the decomposition furnace as lifting air.

[0021] The decomposition furnace is controlled using the aforementioned decomposition furnace control method.

[0022] In the above technical solution, preferably, there is no cross-flow between the head cooling zone, middle cooling zone, and tail cooling zone of the grate cooler.

[0023] In the above technical solution, preferably, the CO2 concentration in the low-temperature flue gas discharged from the top cyclone outlet is greater than 70%.

[0024] A low NO X A system for preparing cement clinker through full-system oxy-fuel combustion, used to achieve the above-mentioned low-NOx method for preparing cement clinker through full-system oxy-fuel combustion, includes a preheater, a decomposer, a kiln tail flue, a rotary kiln, and a grate cooler connected in sequence.

[0025] The grate cooler is divided into three zones from the clinker inlet to the outlet: a head cooling zone, a middle cooling zone, and a tail cooling zone. The air outlet of the cyclone separator at the top of the preheater is connected to the air inlet of the head cooling zone and the air inlet of the middle cooling zone, respectively. An industrial oxygen inlet is provided at the air inlet of the head cooling zone. Its characteristic is that:

[0026] The decomposition furnace is equipped with a tertiary air inlet, a lifting air inlet, a raw material feeding point, and a fuel feeding point. The lifting air inlet is located below the tertiary air inlet. The secondary air intake of the cooling zone at the head of the grate cooler is connected to the rotary kiln, and the tertiary air intake is connected to the tertiary air inlet of the decomposition furnace via a pipe. The lifting air intake of the middle cooling zone is connected to the lifting air inlet of the decomposition furnace via a pipe. At least two raw material feeding points are provided, with at least one raw material feeding point located between the lifting air inlet and the tertiary air inlet, and at least one raw material feeding point located above the tertiary air inlet. The height of the lifting air inlet is below the raw material feeding point below the tertiary air inlet. The fuel feeding point is located between the lifting air inlet and the tertiary air inlet, so that the fuel is sprayed into the mixture of the kiln exhaust gas and the lifting air. A reduction zone is formed inside the decomposition furnace between the lifting air inlet and the tertiary air inlet, and a combustion zone is formed above the tertiary air inlet.

[0027] In the above technical solution, preferably, the air outlet of the cyclone at the top of the preheater is connected to a high-temperature fan, and the outlet of the high-temperature fan is divided into two paths, one of which is connected to the carbon capture system, and the other is connected to the air inlet of the cooling zone at the head of the grate cooler and the air inlet of the cooling zone in the middle.

[0028] In the above technical solution, preferably, the top outlet of the decomposition furnace is provided with an upward-downward pipe, and the air intake of the central cooling zone is also connected to the downward pipe through a pipe.

[0029] In the above technical solution, a further preferred embodiment is that a first circulating air regulating valve is installed on the pipe between the lifting air intake and the downward pipe in the cooling zone of the grate cooler, and a second circulating air regulating valve is installed on the pipe between the lifting air intake and the lifting air inlet of the decomposition furnace.

[0030] In the above technical solution, preferably, a tertiary air regulating valve is installed on the pipeline between the tertiary air intake of the cooling zone at the head of the grate cooler and the tertiary air inlet of the decomposition furnace.

[0031] In the above technical solution, preferably, a material distribution valve is installed on the feeding pipe at the raw material feeding point of the decomposition furnace to adjust the material distribution ratio at each raw material feeding point so that the average temperature in the reduction zone of the decomposition furnace is 800-1200℃.

[0032] In the above technical solution, preferably, the decomposition furnace has a first narrowing at the tertiary air inlet and a second narrowing at the lifting air inlet.

[0033] In the above technical solution, preferably, the head cooling zone and the middle cooling zone of the grate cooler are located in the first section of the grate cooler, and the tail cooling zone is located in the second section of the grate cooler. An intermediate roller crusher is provided between the first section and the second section of the grate cooler to reduce air leakage between the two sections. A partition wall is provided in the middle of the first section of the grate cooler to reduce air leakage between the head cooling zone and the middle cooling zone.

[0034] The advantages and positive effects of this invention are:

[0035] (1) This invention moves the tertiary air inlet of the decomposition furnace upward and introduces the lifting air from the grate cooler into the bottom of the decomposition furnace, so that the fuel is sprayed into the mixture of the kiln exhaust gas and the lifting air, thereby creating an oxygen-deficient combustion environment in the lower part of the decomposition furnace. The fuel is gasified in the oxygen-deficient combustion environment to produce reducing gas, forming a reduction zone, thereby achieving the reduction of NO in the kiln exhaust gas. X Self-removal; at the same time, due to the reduction of kiln air volume under full oxygen conditions and the upward shift of the tertiary air inlet position, the single kiln flue gas is insufficient to lift the material in the reduction zone. By introducing part of the lifting air from the grate cooler into the furnace bottom reduction zone and regulating the air volume in the reduction zone, the problem of raw material collapse caused by insufficient air volume at the furnace bottom can be avoided.

[0036] (2) This invention achieves the reduction of NO in the flue gas exiting the kiln under full oxygen combustion conditions. X The self-removal mechanism can prevent raw material collapse caused by insufficient airflow at the furnace bottom, ensuring stable system operation. Attached Figure Description

[0037] Figure 1 shows the low NO content provided in Embodiment 2 of the present invention. X A schematic diagram of a system for producing cement clinker using oxy-fuel combustion throughout the entire system;

[0038] Figure 2 is a top view of the lifting air intake of the furnace provided by the dual air intake structure in Embodiment 2 of the present invention;

[0039] Figure 3 is a top view of the lifting air intake of the furnace provided in Embodiment 3 of the present invention.

[0040] In the diagram: A - Industrial oxygen; B - Circulating flue gas; C - Air; g2 - Secondary air; g3 - Tertiary air; g4 - Lifting air; g41 - First lifting air path; g42 - Second lifting air path; g5 - Air exiting the air cooling zone; F1 - Fuel entering the rotary kiln; F2 - Fuel entering the decomposition furnace; R - Raw meal; K - Cement clinker;

[0041] 1-Grate cooler; 101-First section of grate cooler; 102-Second section of grate cooler; 103-Intermediate roller crusher; 104-Partition wall; 1a-Head cooling zone; 1b-Middle cooling zone; 1c-Tail cooling zone;

[0042] 2-Rotary kiln; 3-Decomposition furnace; 301-Reduction zone; 302-Combustion zone; 303-Downflow pipe; 304-Burner; 305-Feeding box; 306-Lifting air inlet; 4-Preheater; 401-First-stage cyclone separator; 402-Second-stage cyclone separator; 403-Third-stage cyclone separator; 404-Fourth-stage cyclone separator; 405-Fifth-stage cyclone separator; 5-Kiln tail flue; 6-High-temperature fan; 903-Tertiary air regulating valve; 904-First-path circulating air regulating valve; 905-Second-path circulating air regulating valve; 906-Material distribution valve;

[0043] The dashed line with an arrow indicates the airflow direction; the solid line with an arrow indicates the material flow direction. Detailed Implementation

[0044] 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.

[0045] 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.

[0046] 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.

[0047] Example 1

[0048] Under full oxy-fuel combustion conditions, the O2 concentration in the secondary air entering the kiln is greater than 30%, and the flue gas volume exiting the kiln is less than 0.3 Nm³. 3 / kg. clinker, while the flue gas volume exiting the kiln under normal air combustion conditions is generally 0.4~0.45Nm. 3 / kg.clinker, therefore, the flue gas volume exiting the kiln is reduced by more than 25% compared to conventional air combustion conditions. With the increased O2 concentration in the secondary air entering the kiln and the increased combustion flame temperature, NOx in the rotary kiln will increase. If the NOx in the flue gas exiting the kiln can be reduced in the reduction zone of the decomposition furnace, NOx emissions will be reduced. Therefore, it is necessary to design a low-NOx decomposition furnace. However, for low-NOx decomposition furnaces, the raw meal entering the furnace is mainly supported by the flue gas moving upwards from the kiln tail smoke chamber into the furnace bottom. The decrease in the air volume of the kiln tail smoke chamber can easily lead to insufficient momentum for raw meal support, resulting in material collapse. Therefore, a supporting air stream g4 needs to be added at the bottom of the decomposition furnace. The supporting air stream g4 is located below the raw meal feeding point and can supplement the supporting function of the raw meal. When the O2 content in the supporting air stream g4 is less than 5%, after the supporting air stream g4 enters the reduction zone 301, it can still ensure that the oxygen coefficient of the reduction zone is less than 0.5, thus not reducing the denitrification effect of the reduction zone.

[0049] Specifically, based on low NO X The control method for a precalciner system with full oxygen combustion includes the following steps:

[0050] The bottom of the decomposition furnace 3 is introduced with kiln exhaust gas and lifting air g4. The lifting air g4 comes from the exhaust gas discharged from the top air outlet of the preheater 4 and has been cooled by heat exchange in the middle cooling zone of the grate cooler. The O2 concentration in the lifting air is less than 5%, the CO2 concentration is higher than 70%, and the temperature is 500-900℃.

[0051] The decomposition furnace is supplied with tertiary air g3 above the lifting air g4. The tertiary air g3 comes from the mixture of industrial oxygen A and flue gas discharged from the top outlet of the preheater and heat exchanged in the cooling zone 1a at the head of the grate cooler. The O2 concentration in the mixture is greater than 30%.

[0052] Fuel and raw materials are fed into the decomposition furnace between the lifting air inlet 306 and the tertiary air inlet, with an oxygen coefficient of less than 0.5, forming a reduction zone 301. This reduces the average temperature within the reduction zone to 800–1200℃, thereby controlling the NO in the flue gas exiting the kiln. X Self-removal and lifting of materials below the tertiary air inlet; raw materials are fed above the tertiary air inlet to form combustion zone 302.

[0053] In a preferred embodiment, the flue gas at the top outlet of the decomposition furnace 3 first rises and then falls, and the lifting air is introduced into the falling pipe 303 to adjust the outlet temperature of the decomposition furnace 3 and prevent the final stage cyclone of the preheater 4 from forming scale and clogging.

[0054] In a preferred embodiment, the lifting air g4 enters the decomposition furnace 3 in a swirling motion. Along the lifting air flow direction, the lifting air first contacts the raw material and then the fuel. On the one hand, the lifting air is relatively close to the raw material, which is beneficial for lifting the raw material; on the other hand, the temperature of the lifting air g4 is 500-900℃, which is lower than the temperature of the flue gas exiting the kiln (1000-1200℃). The lifting air is relatively far from the fuel, so it will not reduce the temperature of the fuel feeding area or the fuel gasification rate.

[0055] In a preferred embodiment, the bottom wind speed of the decomposition furnace 3 is maintained between 30 and 50 m / s to ensure that the material at the bottom of the decomposition furnace is supported.

[0056] In a preferred embodiment, the industrial oxygen A has an O2 concentration greater than 80% and originates from an oxygen generation system.

[0057] Example 2

[0058] Please refer to Figure 1. An embodiment of the present invention provides a low NO... X The system for preparing cement clinker by oxy-fuel combustion includes a preheater 4, a decomposition furnace 3, a kiln tail flue chamber 5, a rotary kiln 2, and a grate cooler 1 connected in sequence.

[0059] The preheater 4 can be a two- to seven-stage preheater; this embodiment uses a five-stage preheater as an example. The raw material R entering the preheater 4 is fed through the outlet duct of the second-stage cyclone separator for gas-solid heat exchange, and then enters the first-stage cyclone separator 401 under the influence of airflow. After gas-solid separation in the first-stage cyclone separator 401, the material is fed from the discharge pipe of the first-stage cyclone separator 401 into the outlet duct of the third-stage cyclone separator 403. Following this process, the material sequentially enters the second-stage cyclone separator 402, the third-stage cyclone separator 403, and the fourth-stage cyclone separator 404. The raw material after gas-solid separation in the fourth-stage cyclone separator 404 enters the decomposition furnace 3, where it undergoes decomposition. The decomposed hot raw material is carried by airflow into the fifth-stage cyclone separator 405, where, after gas-solid separation, it is fed into the kiln tail flue chamber 5 and then into the rotary kiln 2 for calcination to produce clinker. Finally, it is cooled by the grate cooler 1 to obtain cement clinker K.

[0060] The grate cooler 1 is divided into three zones from the clinker inlet to the outlet: a head cooling zone 1a, a middle cooling zone 1b, and a tail cooling zone 1c. The head cooling zone 1a and the middle cooling zone are located in the first section 101 of the grate cooler, and the tail cooling zone 1c is located in the second section 102. The outlet of the cyclone separator at the top of the preheater is connected to the inlet of the head cooling zone 1a and the inlet of the middle cooling zone, respectively. An industrial oxygen inlet is provided at the inlet of the head cooling zone 1a. Under full oxygen combustion conditions, the flue gas discharged from the outlet of the cyclone separator at the top of the preheater 4 is low-temperature flue gas with a CO2 concentration greater than 70%, referred to as CO2 circulating flue gas. The inlet of the head cooling zone 1a is supplied with a mixture of industrial oxygen A and CO2 circulating flue gas, i.e., an O2 / CO2 mixture. The inlet of the middle cooling zone 1b is supplied with only CO2 circulating flue gas, and the inlet of the tail cooling zone 1c is supplied with air C. The grate cooler consists of an O2 / CO2 mixed gas cooling zone, a circulating flue gas cooling zone, and an air cooling zone, from the clinker inlet to the outlet. The outlet of the cyclone at the top of the preheater 4 is connected to the inlet of the O2 / CO2 mixed gas cooling zone and the inlet of the circulating flue gas cooling zone. The inlet of the O2 / CO2 mixed gas cooling zone is supplied with a mixture of industrial oxygen A and CO2 circulating flue gas. The inlet of the circulating flue gas cooling zone is supplied with only CO2 circulating flue gas. The inlet of the air cooling zone is supplied with air C.

[0061] The decomposition furnace 3 is equipped with a tertiary air inlet, a lifting air inlet 306, a raw material feeding point, and a fuel feeding point. The lifting air inlet 306 is located below the tertiary air inlet. The secondary air intake of the O2 / CO2 mixed gas cooling zone of the grate cooler is connected to the air inlet of the rotary kiln. The tertiary air intake of the O2 / CO2 mixed gas cooling zone of the grate cooler is connected to the tertiary air inlet of the decomposition furnace through a pipeline. The high-temperature gas exiting the O2 / CO2 mixed gas cooling zone is used as secondary air g2 and tertiary air g3, respectively. The lifting air intake of the circulating flue gas cooling zone of the grate cooler is connected to the lifting air inlet 306 of the decomposition furnace through a pipeline. The CO2 circulating flue gas exiting the circulating flue gas cooling zone is used as lifting air g4. The decomposition furnace has at least two raw material feeding points, with at least one point located between the lifting air inlet 306 and the tertiary air inlet, and at least one point located above the tertiary air inlet. The height of the lifting air inlet is below the raw material feeding point below the tertiary air inlet, thus lifting the material below the tertiary air inlet and preventing material collapse. The fuel feeding point is located between the lifting air inlet 306 and the tertiary air inlet, allowing fuel to be sprayed into the mixture of the kiln exhaust gas and the lifting air. A reduction zone 301 is formed within the decomposition furnace between the lifting air inlet 306 and the tertiary air inlet, thereby reducing NO in the kiln exhaust gas. X Self-removal forms a combustion zone 302 above the tertiary air inlet.

[0062] The high-temperature gas exiting the O2 / CO2 mixed gas cooling zone is used as secondary air g2 and tertiary air g3, respectively. The secondary air intake of the grate cooler is connected to the rotary kiln inlet, and the tertiary air intake of the grate cooler is connected to the tertiary air inlet of the decomposition furnace through a pipeline. Both secondary air g2 and tertiary air are O2 / CO2 mixed gas after heat exchange, recovering and utilizing the heat from the O2 / CO2 mixed gas cooling zone outlet, and then entering the rotary kiln 2 and decomposition furnace 3 respectively to provide a combustion environment. The CO2 circulating flue gas exiting the circulating flue gas cooling zone is used as lift air. The lift air is the CO2 circulating flue gas after heat exchange, with a CO2 concentration higher than 70%, an O2 concentration lower than 5%, and a temperature higher than 500℃. The lift air is introduced into the lower part of the decomposition furnace, causing fuel to be sprayed into the mixture of kiln exit flue gas and lift air, thereby establishing an oxygen-deficient combustion environment in the lower part of the decomposition furnace. In the oxygen-deficient combustion environment, the fuel gasifies to produce reducing gas, forming a reduction zone 301, realizing the reduction of NO in the kiln exit flue gas. X Self-removal, while regulating the air volume of the reduction zone 301 to prevent raw material collapse caused by insufficient air volume at the furnace bottom.

[0063] As a preferred embodiment, as shown in Figure 2, in this embodiment, the lifting air enters the furnace in a dual-inlet configuration. The decomposition furnace 3 is equipped with two lifting air inlets 306, two material spreading boxes 305, and two burners 304. The two lifting air inlets are arranged symmetrically at the center, the two burners 304 are arranged axially symmetrically, and the two material spreading boxes are arranged axially symmetrically. As shown in Figure 2, the two streams of lifting air enter the decomposition furnace in swirling motions. Along the direction of the lifting air flow, each stream of lifting air first contacts its adjacent downstream raw material and then its adjacent downstream fuel. On the one hand, the lifting air is relatively close to the raw material, which is beneficial for lifting the raw material; on the other hand, the temperature of the lifting air is 500-900℃, which is lower than the temperature of the flue gas exiting the kiln (1000-1200℃). The lifting air is relatively far from the fuel, which will not reduce the temperature of the fuel feeding area or reduce the fuel gasification rate.

[0064] In a preferred embodiment, the top outlet of the decomposition furnace 3 is equipped with an upward-downward duct. The lifting air intake of the grate cooler's circulating flue gas cooling zone is also connected to the downward duct 303 via a duct. The lifting air intake of the grate cooler is connected to the lifting air inlet of the decomposition furnace and the downward duct via ducts respectively. The first lifting air g41 is introduced into the lower part of the decomposition furnace to achieve the removal of NO from the kiln exhaust gas. X Self-removal, while regulating the air volume of reduction zone 301 to prevent raw material collapse caused by insufficient air volume at the furnace bottom; the second lifting air g42 is introduced into the decomposition furnace outlet downflow pipe 303 to regulate the decomposition furnace outlet temperature and prevent the preheater final stage cyclone tube from forming scale and clogging.

[0065] As a preferred embodiment, the decomposition furnace has a first constriction at the tertiary air inlet and a second constriction at the lifting air inlet 306, which enhances gas-solid mixing and turbulence effects, prevents material settling and accumulation, and further ensures system stability.

[0066] In a preferred embodiment, a tertiary air regulating valve 903 is installed on the pipe between the tertiary air intake of the grate cooler and the tertiary air inlet of the decomposition furnace. A first-path circulating air regulating valve 904 is installed on the pipe between the lifting air intake of the grate cooler and the downflow pipe 303, and a second-path circulating air regulating valve 905 is installed on the pipe between the lifting air intake of the grate cooler and the lifting air inlet 306 of the decomposition furnace. These valves are used to distribute the airflow to the reduction zone 301 at the bottom of the decomposition furnace and the downflow pipe, thus achieving adjustable airflow. Both the first-path circulating air regulating valve 904 and the second-path circulating air regulating valve 905 are high-temperature gate valves.

[0067] In a preferred embodiment, a material distribution valve 906 is installed on the feed pipe at the raw material feeding point of the decomposition furnace to adjust the material distribution ratio at each raw material feeding point, so that the average temperature in the reduction zone of the decomposition furnace is 800-1200℃.

[0068] In a preferred embodiment, the flue gas discharged from the top outlet of the preheater 4 is low-temperature flue gas with a CO2 concentration greater than 70%. The outlet of the cyclone separator at the top of the preheater 4 is connected to a high-temperature fan 6. The outlet of the high-temperature fan 6 is divided into two paths: one path connects to a carbon capture system, and the other path, after circulating flue gas B, is divided into two branches connecting to a grate cooler. A flue gas circulation volume regulating valve, a bag filter, and a circulating fan can be sequentially installed on the pipeline containing circulating flue gas B. The flue gas circulation volume regulating valve is used to regulate the circulation volume of circulating flue gas B, and the bag filter is used to reduce the dust concentration in the circulating fan to 100 mg / m³. 3 The exhaust gas from the high-temperature fan 6 is divided into two parts. One part enters the next carbon capture process, and the other part can be circulated back to the grate cooler under the induced draft of the circulating fan and used as CO2 circulating flue gas.

[0069] Specifically, the outlet of the circulating fan is divided into two branches: one branch connects to the air inlet of the O2 / CO2 mixed gas cooling zone of the grate cooler, and the other branch connects to the air inlet of the circulating flue gas cooling zone of the grate cooler. An industrial oxygen inlet is installed on the branch connecting to the air inlet of the O2 / CO2 mixed gas cooling zone of the grate cooler, and an oxygen concentration regulating valve is installed upstream of the industrial oxygen inlet of this branch to allow industrial oxygen A and CO2 circulating flue gas to mix and enter the O2 / CO2 mixed gas cooling zone of the grate cooler.

[0070] The cooling medium in the grate cooler is divided into three stages: the first stage is an O2 / CO2 mixture, the second stage is CO2 circulating flue gas, and the third stage is air. By adding a CO2 circulating flue gas stage between the O2 / CO2 mixture and air, direct cross-flow between the O2 / CO2 mixture and air is blocked, reducing the decrease in CO2 concentration in the exhaust gas due to cross-flow and improving the CO2 enrichment effect. Simultaneously, the second-stage CO2 circulating flue gas acts as a lifting air, serving as a heat exchange medium to transfer heat from the high-temperature clinker to the raw meal. The CO2 circulating flue gas absorbs heat from the high-temperature clinker and transfers this heat to the raw meal through the preheater at the kiln tail, thereby reducing the heat consumption of the cement production system.

[0071] In a preferred embodiment, the grate cooler is divided into two sections: the O2 / CO2 mixed gas cooling zone and the circulating flue gas cooling zone are located in the first section of the grate cooler, and the air cooling zone is located in the second section of the grate cooler. An intermediate roller crusher is provided between the first and second sections of the grate cooler to reduce air leakage between the two sections. A partition wall 104 is provided in the middle of the first section of the grate cooler to reduce air leakage between the O2 / CO2 mixed gas cooling zone and the circulating flue gas cooling zone. The partition wall is located between the tertiary air intake and the lifting air intake.

[0072] In summary, the oxygen for combustion in the decomposition furnace 3 mainly comes from the tertiary air. To achieve the desired NO₂ levels in the flue gas exiting the kiln... X To remove NO, the lifting air from the grate cooler is introduced into the furnace bottom. Fuel is injected into the mixture of the kiln exhaust gas and the lifting air, thus creating an oxygen-deficient combustion environment in the lower part of the decomposition furnace. Under this oxygen-deficient combustion environment, the fuel gasifies to produce reducing gases, forming a reduction zone 301, thereby achieving the removal of NO from the kiln exhaust gas. X Self-removal. At the same time, under full oxygen conditions, the kiln outlet air volume is reduced and the tertiary air moves upward. The single kiln outlet flue gas is insufficient to lift the material in the reduction zone. By introducing part of the lifting air from the grate cooler into the furnace bottom reduction zone and regulating the air volume in the reduction zone, the problem of raw material collapse caused by insufficient air volume at the furnace bottom can be prevented.

[0073] Example 3

[0074] As shown in Figure 3, unlike Example 2, the lifting air in this example is a single-inlet type. The decomposition furnace 3 is equipped with a lifting air inlet 306, a feeding box 305, and two burners 304, with the two burners arranged axially symmetrically. As shown in Figure 3, the raw material feeding box in the reduction zone is located between the lifting air inlet and the burners. The lifting air enters the decomposition furnace in a swirling flow. Looking along the lifting air flow direction, the lifting air first contacts the raw material and then contacts the fuel. On the one hand, the lifting air is relatively close to the raw material, which is beneficial for lifting the raw material; on the other hand, the temperature of the lifting air is 500-900℃, which is lower than the temperature of the flue gas in the exhaust chamber (1000-1200℃). The lifting air is relatively far from the fuel, so it will not reduce the temperature of the fuel feeding area or reduce the fuel gasification rate.

[0075] Example 4

[0076] A method for preparing cement clinker using a low-NOx, fully oxygen-based combustion system includes the following steps:

[0077] Raw materials are fed into a preheater, where they exchange heat with flue gas and undergo gas-solid separation, preheating the raw materials to their decomposition temperature.

[0078] The preheated raw materials enter the decomposition furnace through the raw material feeding point located between the lifting air inlet 306 and the tertiary air inlet, and the raw material feeding point located above the tertiary air inlet. The decomposition reaction occurs in the decomposition furnace to obtain hot raw materials. A large amount of flue gas is generated and enters the preheater. After heat exchange, the low-temperature flue gas is discharged through the outlet of the top cyclone of the preheater. The CO2 concentration in the low-temperature flue gas discharged from the outlet of the top cyclone of the preheater is greater than 70%.

[0079] Hot raw materials enter rotary kiln 2 and are calcined in the rotary kiln to produce clinker; the clinker is cooled in a grate cooler to obtain cement clinker.

[0080] The low-temperature flue gas enters the high-temperature fan 6, and then splits into two paths. One path enters the carbon capture system, while the other path reduces the dust concentration in the flue gas to 100 mg / m³ through dust collection. 3 The gas then enters the circulating fan, and then splits into two branches, which, as circulating flue gas (clinker cooling gas), enter the O2 / CO2 mixed gas cooling zone and the circulating flue gas cooling zone of the grate cooler, respectively.

[0081] The cooling medium in the O2 / CO2 mixed gas cooling zone is a mixture of industrial oxygen A and CO2 circulating flue gas, i.e., O2 / CO2 mixed gas. The cooling medium in the circulating flue gas cooling zone is CO2 circulating flue gas. The cooling medium in the air cooling zone is air. There is no cross-flow between the O2 / CO2 mixed gas cooling zone, the circulating flue gas cooling zone, and the air cooling zone.

[0082] The high-temperature gas exiting the O2 / CO2 mixed gas cooling zone is used as secondary air g2 and tertiary air, respectively, to recover and utilize the heat at the outlet of the O2 / CO2 mixed gas cooling zone. Secondary air g2 is introduced into rotary kiln 2, and tertiary air is introduced into the decomposition furnace through the tertiary air inlet, forming a combustion zone 302 above the tertiary air inlet. The CO2 circulating flue gas exiting the grate cooler circulating flue gas cooling zone is used as lifting air, and part of it is introduced into the bottom of the decomposition furnace to maintain the wind speed at the second constriction between 30 and 50 m / s. At the same time, the fuel of the decomposition furnace is sprayed into the mixture of kiln exit flue gas and lifting air, forming a reduction zone 301 between the lifting air inlet 306 and the tertiary air inlet. The average temperature in the reduction zone is 800-1200℃, achieving the goal of reducing NO in the kiln exit flue gas. XThe system is self-removing and simultaneously lifts the material below the tertiary air inlet; a portion is introduced into the decomposition furnace outlet downpipe 303, avoiding the problem that the lifting air composed of CO2 circulating flue gas is all introduced into the furnace from the bottom of the decomposition furnace, which would increase the CO2 partial pressure in the flue gas inside the decomposition furnace and cause the raw material decomposition temperature to rise to 950℃ or even above 1000℃; at the same time, it regulates the decomposition furnace outlet temperature to prevent the decomposition furnace outlet temperature from being too high and causing the preheater's final stage cyclone to form scale and become blocked; the air g5 from the air cooling zone is directly discharged from the system.

[0083] 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 method based on low NO X The method for controlling a decomposer furnace with full oxygen combustion throughout the entire system is characterized by, Includes the following steps: The bottom of the decomposition furnace is vented with kiln exhaust gas and lifting air. The lifting air comes from the exhaust gas discharged from the top of the preheater and has been cooled by heat exchange in the middle cooling zone of the grate cooler. The O2 concentration in the lifting air is less than 5%, the CO2 concentration is greater than 70%, and the temperature is 500-900℃. The decomposition furnace is supplied with tertiary air above the lifting air. The tertiary air comes from the mixture of industrial oxygen and flue gas discharged from the top outlet of the preheater and heat exchanged in the cooling zone of the grate cooler head. The O2 concentration in the mixture is greater than 30%. In the decomposition furnace, between the lifting air inlet and the tertiary air inlet, the oxygen peroxide coefficient is less than 0.5, forming a reduction zone. This reduction zone maintains an average temperature of 800–1200℃, effectively reducing NO in the flue gas exiting the kiln. X It removes and lifts the material below the tertiary air inlet; above the tertiary air inlet, a combustion zone is formed.

2. The low NO-based method according to claim 1 X The method for controlling a decomposer furnace with full oxygen combustion throughout the entire system is characterized by: The flue gas at the top outlet of the decomposition furnace first rises and then falls, and the lifting air is introduced into the falling pipe to adjust the outlet temperature of the decomposition furnace.

3. The low NO-based method according to claim 1 X The method for controlling a decomposer furnace with full oxygen combustion throughout the entire system is characterized by: The lifting air swirls into the decomposition furnace, and along the lifting air flow direction, the lifting air first contacts the raw material and then contacts the fuel.

4. The low NO-based method according to claim 1 X The method for controlling a decomposer furnace with full oxygen combustion throughout the entire system is characterized by: The wind speed at the bottom of the decomposition furnace is maintained between 30 and 50 m / s.

5. The low NO-based method according to claim 1 X The method for controlling a decomposer furnace with full oxygen combustion throughout the entire system is characterized by: The industrial oxygen contains an O2 concentration greater than 80%.

6. A method for preparing cement clinker using a low-NOx, fully oxygen-based combustion system, characterized in that, Includes the following steps: Raw materials are fed into a preheater, where they exchange heat with flue gas and undergo gas-solid separation, preheating the raw materials to their decomposition temperature. The preheated raw material is fed into the decomposition furnace; A decomposition reaction occurs in the decomposition furnace to obtain hot raw materials; and a large amount of flue gas is generated and enters the preheater. After heat exchange, the low-temperature flue gas is discharged through the air outlet of the cyclone at the top of the preheater. Hot raw materials enter a rotary kiln and are calcined to produce clinker; the clinker is cooled in a grate cooler to obtain cement clinker; The low-temperature flue gas discharged from the cyclone outlet at the top of the preheater is partially recycled flue gas and enters the head cooling zone and the middle cooling zone of the grate cooler respectively. The cooling medium in the head cooling zone of the grate cooler is a mixture of industrial oxygen and circulating flue gas, the cooling medium in the middle cooling zone is circulating flue gas, and the cooling medium in the tail cooling zone is air. The high-temperature gas exiting the head cooling zone 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 circulating flue gas exiting the middle cooling zone is fed into the decomposition furnace as lifting air. The decomposition furnace is controlled by the control method described in any one of claims 1-5.

7. The method for preparing cement clinker using a low-NOx, fully oxygen-based combustion system according to claim 1, characterized in that: There is no cross-flow between the head cooling zone, middle cooling zone, and tail cooling zone of the grate cooler.

8. The method for preparing cement clinker using a low-NOx, fully oxygen-based combustion system according to claim 1, characterized in that: The CO2 concentration in the low-temperature flue gas discharged from the top cyclone outlet is greater than 70%.

9. A low NO X A system for preparing cement clinker through full-system oxy-fuel combustion, used to implement the method described in any one of claims 6 or 7, comprising a preheater, a decomposition furnace, a kiln tail flue, a rotary kiln, and a grate cooler connected in sequence; The grate cooler is divided into three zones from the clinker inlet to the outlet: a head cooling zone, a middle cooling zone, and a tail cooling zone. The air outlet of the cyclone separator at the top of the preheater is connected to the air inlet of the head cooling zone and the air inlet of the middle cooling zone, respectively. An industrial oxygen inlet is provided at the air inlet of the head cooling zone. Its characteristic is that: The decomposition furnace is equipped with a tertiary air inlet, a lifting air inlet, a raw material feeding point, and a fuel feeding point. The lifting air inlet is located below the tertiary air inlet. The secondary air intake of the cooling zone at the head of the grate cooler is connected to the rotary kiln, and the tertiary air intake is connected to the tertiary air inlet of the decomposition furnace via a pipe. The lifting air intake of the middle cooling zone is connected to the lifting air inlet of the decomposition furnace via a pipe. At least two raw material feeding points are provided, with at least one raw material feeding point located between the lifting air inlet and the tertiary air inlet, and at least one raw material feeding point located above the tertiary air inlet. The height of the lifting air inlet is below the raw material feeding point below the tertiary air inlet. The fuel feeding point is located between the lifting air inlet and the tertiary air inlet, so that the fuel is sprayed into the mixture of the kiln exhaust gas and the lifting air. A reduction zone is formed inside the decomposition furnace between the lifting air inlet and the tertiary air inlet, and a combustion zone is formed above the tertiary air inlet.

10. The low NO content according to claim 9 X A system for preparing cement clinker using oxy-fuel combustion throughout the entire system, characterized in that: The air outlet of the cyclone at the top of the preheater is connected to a high-temperature fan. The outlet of the high-temperature fan is divided into two paths: one path is connected to the carbon capture system, and the other path is connected to the air inlet of the cooling zone at the head of the grate cooler and the air inlet of the cooling zone in the middle.

11. The low NO content according to claim 9 X A system for preparing cement clinker using oxy-fuel combustion throughout the entire system, characterized in that: The top outlet of the decomposition furnace is equipped with an upward-downward pipe, and the air intake of the central cooling zone is also connected to the downward pipe through a pipe.

12. The low NO content according to claim 11 X A system for preparing cement clinker using oxy-fuel combustion throughout the entire system, characterized in that: A first circulating air regulating valve is installed on the pipe between the lifting air intake and the downward pipe in the cooling zone of the grate cooler, and a second circulating air regulating valve is installed on the pipe between the lifting air intake and the lifting air inlet of the decomposition furnace.

13. The low NO content according to claim 9 X A system for preparing cement clinker using oxy-fuel combustion throughout the entire system, characterized in that: A tertiary air regulating valve is installed on the pipe between the tertiary air intake of the cooling zone at the head of the grate cooler and the tertiary air inlet of the decomposition furnace.

14. The low NO content according to claim 9 X A system for preparing cement clinker using oxy-fuel combustion throughout the entire system, characterized in that: A material distribution valve is installed on the feed pipe at the raw material feeding point of the decomposition furnace to adjust the material distribution ratio at each raw material feeding point, so that the average temperature in the reduction zone of the decomposition furnace is 800-1200℃.

15. The low NO content according to claim 9 X A system for preparing cement clinker using oxy-fuel combustion throughout the entire system, characterized in that: The decomposition furnace has a first narrowing at the tertiary air inlet and a second narrowing at the lifting air inlet.

16. The low NO content according to claim 1 X A system for preparing cement clinker using oxy-fuel combustion throughout the entire system, characterized in that: The head cooling zone and middle cooling zone of the grate cooler are located in the first section of the grate cooler, and the tail cooling zone is located in the second section of the grate cooler. An intermediate roller crusher is provided between the first section and the second section of the grate cooler to reduce air leakage between the two sections. A partition wall is provided in the middle of the first section of the grate cooler to reduce air leakage between the head cooling zone and the middle cooling zone.

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