A self-denitration system and process for self-adjusting temperature and air coefficient in a decomposition furnace

Abstract

The present application relates to the technical field of cement kiln waste gas emission control, in particular to a self-denitrification system and process with self-adjustment of temperature and air coefficient in a decomposing furnace, which comprises: a rotary kiln and a flue; a denitrification furnace comprising a denitrification cone part and a denitrification cylinder part; a decomposing furnace comprising a lower decomposing cylinder and an upper decomposing cylinder, the inner diameter of the lower decomposing cylinder being larger than that of the denitrification cylinder part, and a decomposing cone part being arranged between the lower decomposing cylinder and the denitrification cylinder part; a necking structure being arranged between the lower decomposing cylinder and the upper decomposing cylinder; a tertiary air pipe comprising a lower branch pipe and an upper branch pipe; and a material distribution structure for conveying raw materials to the decomposing furnace and the denitrification furnace. The present application avoids skinning and uneven mixing of flue gas, forms a cyclone effect in the decomposing furnace, strengthens the mixing of combustion-supporting air and flue gas, accelerates the burnout of fuel to reduce heat consumption, realizes precise control of the distribution ratio, precisely adjusts the temperature field in the denitrification furnace and the decomposing furnace, and provides a stable high-temperature area for NOx reduction and fuel combustion.

Description

Technical Field

[0001] This invention relates to the field of cement kiln exhaust gas control technology, specifically to a self-denitrification system and process for self-regulating temperature and air coefficient inside the decomposition furnace. Background Technology

[0002] The precalciner is one of the core pieces of equipment in the cement clinker calcination system. Its role is to combust part of the fuel and decompose the raw meal, providing a high-decomposition-rate and stable supply of raw meal for calcination in the rotary kiln, which significantly impacts the stable production of the system. Generally, the ratio of coal used in the precalciner to that used in the rotary kiln is 60-65:35-40, and the ratio of flue gas volume at the rotary kiln outlet to that at the precalciner outlet (under standard conditions) is 27-34:100.

[0003] NOx emissions from cement kilns can be categorized into thermal NOx, fuel NOx, rapid NOx, and feedstock NOx. Thermal and fuel NOx typically account for over 95% of the total, making them key areas for NOx emission reduction. Thermal NOx is generated in rotary kilns due to the high calcination temperatures, and it is the primary form of NOx generated there; the NOx content generated in rotary kilns generally accounts for over 65% to 70% of the total system emissions. Fuel NOx is mainly generated in the decomposition furnace, formed by the reaction of nitrogen (N) in the fuel with oxygen during combustion.

[0004] Currently, the mainstream denitrification technologies both domestically and internationally include low-NOx decomposition furnaces with staged combustion design, SNCR (Selective Non-Catalytic Reduction) denitrification technology, and SCR (Selective Catalytic Reduction) denitrification technology. SNCR technology has the advantages of simple design and construction and low investment, but its denitrification efficiency is often less than 70%, and it is prone to ammonia slip. SCR technology has higher investment and operating costs, but its denitrification efficiency is high (up to 90%), ammonia consumption is low, and ammonia slip is less likely to occur.

[0005] Low-NOx decomposition furnaces generally adopt a fuel staged combustion and air staged combustion design. The main principle is to inject pulverized coal into the flue gas at the bottom of the decomposition furnace to create a strong reducing atmosphere, which reduces NOx to N2. At the same time, by supplying air in different zones through the three-stage air system, a low-oxygen reducing atmosphere is maintained in the main combustion zone to reduce the generation of fuel-type NOx.

[0006] There are two main designs for staged combustion of fuel. One is to use a conventional decomposition furnace design, in which the tertiary air duct is raised to the straight section of the decomposition furnace, and the decomposition furnace cone and part of the straight section are used as the reduction zone. This method makes full use of the large furnace size, and only the tertiary air duct needs to be raised by 4 to 6m to increase the denitrification space. However, due to the relatively low flue gas volume in the kiln, the cross-sectional wind velocity in the reduction zone is only 2 to 3m / s, resulting in poor flue gas mixing. It will be difficult to completely reduce low concentrations (700 to 1500ppm) of NOx. On the other hand, the low cross-sectional wind velocity will make it easier for particles to settle and accumulate on the inner wall of the furnace at high temperatures, thus producing a large amount of crust, which will affect the stable operation of the system. The second type of staged combustion of fuel uses a duct system, in which flue gas is drawn out of the flue chamber through a duct (the cross-sectional velocity is generally 15~18m / s) and then connected back to the decomposition furnace. The reduction reaction takes place entirely in the duct. This type solves the problem of flue gas mixing, but in order to ensure the residence time of the flue gas, the duct length is often 40~60m, which increases the system resistance by 500~600Pa, resulting in increased power consumption of the high-temperature fan. In addition, since the design connects back to the decomposition furnace body, it is impossible to avoid the formation of bends in the duct, which easily leads to scaling and affects the stable operation of the system.

[0007] Staged air combustion involves installing a branch pipe on the tertiary air duct. This branch pipe typically connects the middle to the upper part of the decomposition furnace. The excess air coefficient in the area from the main tertiary air duct to the branch pipe is generally controlled at around 0.9, mainly to reduce the formation of fuel-type NOx by maintaining a low-reducing atmosphere in the area. However, in actual production, the existing method of the tertiary air branch pipe entering the furnace is to face the straight section of the decomposition furnace directly. Due to the low velocity of the tertiary air and flue gas in the furnace, and the lack of swirling effect between gases, the mixing effect is poor. Furthermore, the fuel in this area is in a state of gradual burning of residual carbon, resulting in incomplete combustion of fuel in the furnace. This affects the stability and further improvement of the raw material decomposition rate in the kiln, ultimately making it difficult to calcine clinker in the rotary kiln, causing system fluctuations and increased heat consumption. At the same time, unburned fuel will continue to generate fuel-type NOx after entering the preheater. The temperature in the preheater is generally lower than the operating temperature range of the SNCR system (850~1000℃), thus causing NOx emissions to exceed the standard. A common problem in existing low-NOx decomposition furnaces is the difficulty in controlling the separation ratio of feed from the penultimate preheater to the decomposition furnace, making precise feed distribution impossible. This leads to uncontrollable temperature fields within the furnace, easily resulting in high-temperature zones that cause scaling and affect production, or the entire furnace remaining in a low-temperature zone of 820-860°C, causing slow pulverized coal combustion and incomplete combustion, thus impacting system heat consumption. Current decomposition furnace designs utilize a combination of the swirling effect created by tertiary air intake and the jetting effect of kiln gas to achieve spatially uniform mixing of flue gas, fuel, and raw materials. The core combustion zone temperature can reach 1100-1200°C. However, as the raw material heats up and carbonates decompose significantly, the flue gas temperature rapidly drops to 820-860°C, leading to a decrease in fuel combustion rate. Enlarging the furnace volume or increasing the amount of combustion air is necessary to achieve complete fuel combustion within the decomposition furnace. Therefore, feed distribution is a crucial technical measure to increase the furnace temperature, accelerate fuel combustion, and reduce system heat consumption. The existing material distribution problem is caused by the fact that after the material is collected by centrifugal force in the preheater, its distribution in the horizontal direction is relatively random, and the feed pipe is vertical at 90°. Therefore, the material is also randomly distributed on the horizontal cross section of the feed pipe, making it difficult for the material distribution valve to control the material distribution ratio.

[0008] For example, patent document CN210980793U discloses a "low-NOx decomposition furnace for a cement production line," characterized by raising the tertiary air duct to the straight section of the decomposition furnace and designing denitrification reduction zones in the conical section and a small portion of the straight section. This patent utilizes the decomposition furnace body, but because the flue gas volume inside the kiln is much lower than the flue gas volume at the decomposition furnace outlet, the cross-sectional wind velocity in the straight section of the decomposition furnace is too low. Dust easily settles onto the cone, causing scaling and affecting production stability. Simultaneously, the horizontal mixing effect of the flue gas is poor, affecting denitrification efficiency.

[0009] For example, patent document CN111750671A discloses "a decomposition furnace zoned combustion self-denitrification system and process," which features a kiln gas flue between the kiln tail flue and the decomposition furnace as a strong reduction zone for reducing NOx in the kiln gas, while the area below the tertiary air branch pipe serves as a weak reduction zone to control the NOx content in the furnace. Using a pipeline design for the strong reduction zone presents challenges: insufficient pipeline length results in a small reduction zone volume, hindering reduction effectiveness; excessive length leads to high resistance and increased system power consumption. Furthermore, the kiln gas pipeline entering the furnace will have bends, which can easily cause scaling and affect stable system operation.

[0010] In summary, the problems with existing technologies are as follows:

[0011] (1) When the fuel staged combustion uses the decomposition furnace cone and straight section as the forced denitrification zone, the flue gas mixing effect is poor, the denitrification efficiency is not high, and the dust is easy to settle and cause crusting. When the pipeline is used as the forced denitrification zone, a long pipeline is required to ensure the volume, which increases the system resistance and power consumption, and cannot avoid crusting caused by the bend in the pipe.

[0012] (2) In staged combustion of air, the way the tertiary air branch pipe enters the furnace is unreasonable, which affects the mixing effect of the tertiary air and the flue gas in the furnace, reduces the fuel burnout rate, increases coal consumption, and affects the NOx control of the system.

[0013] (3) The proportion of material distribution from the preheater to the decomposition furnace and the denitrification zone is difficult to control, which makes the temperature field in the decomposition furnace prone to fluctuation. If the temperature is too high, it will cause crusting and burn the refractory material. If the temperature is too low, it will affect the combustion rate and cause incomplete combustion, resulting in a large fluctuation in the decomposition rate of raw materials entering the kiln. The calcination regime of the rotary kiln cannot be stabilized.

[0014] Therefore, it is necessary to propose a more reasonable technical solution to solve the technical problems existing in the current technology. Summary of the Invention

[0015] To overcome at least one of the aforementioned defects, this invention proposes a self-regulating denitrification system and process for temperature and air coefficient in a decomposition furnace. This system enables controllable and adjustable temperature field and air coefficient within the decomposition furnace. On one hand, it ensures effective airflow mixing in the forced reduction zone, controls the temperature field in the forced reduction zone, improves self-denitrification efficiency, reduces scaling, and stabilizes operating conditions. On the other hand, it increases the pulverized coal combustion rate in the weak reduction control zone and the burnout zone, preventing incomplete combustion of pulverized coal that could lead to NOx generation in the preheater and excessive NOx emissions. Simultaneously, it stabilizes the decomposition rate of the material entering the kiln and the clinker calcination regime in the rotary kiln.

[0016] To achieve the above objectives, the self-denitrification system disclosed in this invention can adopt the following technical solution:

[0017] A self-regulating denitrification system for temperature and atmosphere within a decomposition furnace, comprising:

[0018] The rotary kiln and the flue gas chamber connected to the rotary kiln are used to guide the flue gas from the rotary kiln to the denitrification furnace.

[0019] The denitrification furnace includes a denitrification cone and a denitrification cylinder that are interconnected, and the denitrification cone is connected to the smoke chamber; the side wall of the denitrification cone is provided with a number of cone fuel addition structures and a number of cone material spreading structures, and the cone material spreading structures are set at a higher height than the cone fuel addition structures;

[0020] A decomposition furnace is located above a denitrification furnace and includes a lower decomposition cylinder and an upper decomposition cylinder that are connected to each other. The inner diameter of the lower decomposition cylinder is larger than the inner diameter of the denitrification cylinder. A decomposition cone is provided between the lower decomposition cylinder and the denitrification cylinder. A narrowing structure is provided between the lower decomposition cylinder and the upper decomposition cylinder. A cylinder fuel addition structure, a lower cylinder material spreading structure, and an upper cylinder material spreading structure are respectively provided on the side wall of the lower decomposition cylinder.

[0021] The tertiary air duct is used to supply air into the decomposition furnace. The tertiary air duct includes a lower branch pipe that connects to the lower decomposition cylinder and an upper branch pipe that connects to the constriction structure. The connection between the upper branch pipe and the constriction structure is lower than the minimum diameter position of the constriction structure.

[0022] The material distribution structure is used to supply raw materials to the system; the material distribution structure includes a cone-shaped material spreading structure, a lower part of the cylinder material spreading structure, and an upper part of the cylinder material spreading structure.

[0023] The aforementioned self-denitrification system, by adjusting the structure of the denitrification furnace and the decomposition furnace, and changing the addition position of fuel and raw materials, enables more complete combustion of fuel, improves the NOx treatment effect in flue gas, and avoids scale formation in the denitrification furnace and decomposition furnace. Therefore, the flue gas treatment effect of the entire system is improved, and the stability of system operation is also greatly enhanced.

[0024] Furthermore, in this invention, the inner diameter of the denitrification cylinder is smaller than the inner diameter of the lower decomposition cylinder. The specific limitation method is not unique, depending on the variations in the inner diameters of the denitrification cylinder and the lower decomposition cylinder. Here, we optimize the design and provide one feasible option: both the inner diameters of the denitrification cylinder and the lower decomposition cylinder are fixed, and the inner diameter of the denitrification cylinder is 0.6 to 0.75 times the inner diameter of the lower decomposition cylinder. Using this approach better enhances the horizontal mixing of the flue gas, increases the denitrification reaction rate, and simultaneously reduces system resistance.

[0025] Furthermore, in this invention, the direction of tertiary air entering the decomposition furnace is restricted by the lower branch pipe. One feasible option is to optimize this by having the lower branch pipe tangentially connect to the interior of the lower decomposition cylinder and supply swirling air into it. With this configuration, the airflow within the lower branch pipe can flow along the inner wall of the decomposition furnace, thus better forming a swirling flow. This mixing with the fuel gas enhances the combustion heat release effect, resulting in a higher degree and efficiency of raw material decomposition. The decomposition cone connects to the straight section of the denitrification furnace, forming a strong reduction zone. The lower branch pipe tangentially swirls in from the lower part of the lower decomposition cylinder, mixing with the vertically entering strong reducing gas, fuel, and raw material. This creates a simultaneous combustion of fuel and decomposition of raw material on the horizontal cross-section of the lower decomposition cylinder.

[0026] Furthermore, in this invention, the tertiary air also forms a swirling flow within the constriction structure to enhance the degree of raw material decomposition in the decomposition furnace and reduce NOx generation. Similarly, improving the coordination between the upper branch pipe and the constriction structure can alter the flowability of the tertiary air intake within the constriction structure. The specific coordination is not uniquely limited; optimization is performed here, and one feasible option is given: the upper branch pipe is tangentially connected to the interior of the constriction structure and used to supply swirling air into the constriction structure. The upper branch pipe is connected to the side of the lower part of the constriction structure, and the tertiary air enters the constriction structure tangentially and rotates, enhancing the mixing effect of flue gas on the horizontal cross-section inside the constriction structure and promoting fuel burnout. The upper branch pipe can distribute air by adjusting valves, maintaining the excess air coefficient of the lower decomposition cylinder at 0.85~0.95, so that the fuel in the lower decomposition cylinder is in a weakly reducing atmosphere during combustion, reducing the generation of NOx from the fuel.

[0027] Furthermore, the location of the fuel addition structure in this invention affects the combustion of the fuel. Here, optimization is proposed, and one feasible option is as follows: the conical fuel addition structure is located within the 10% to 25% height range of the denitrification cone and is evenly spaced along the circumference on the side wall of the denitrification cone. This approach allows for more uniform fuel addition, higher mixing with the flue gas, facilitating combustion heat release and flue gas treatment to reduce NOx. With this approach, excess fuel is fed into the denitrification cone, reducing the excess air coefficient of the denitrification cone and denitrification cylinder to below 0.6, forming a high concentration of volatile matter and CO, thus fully reducing NOx in the kiln tail flue gas.

[0028] Furthermore, the location of the spreading structure also affects the decomposition rate and degree of raw materials, and affects the crust formation. Here, optimization is carried out and one feasible option is given: the cone spreading structure is located in the height range of 50% to 67% of the denitrification cone.

[0029] Furthermore, the material spreading structure at the bottom of the cylinder in the decomposition furnace is also higher than the fuel adding structure. Here, we optimize the design and offer one feasible option: the height of the fuel adding structure is flush with the centerline of the lower branch pipe, and the material spreading structure at the bottom of the cylinder is 600-1000mm higher than the lower branch pipe. With this design, the fuel gas and flue gas are thoroughly mixed before combustion and heat release, resulting in more complete decomposition of the added raw materials.

[0030] Furthermore, in this invention, raw materials are added from the upper feeding structure, the lower feeding structure, and the denitrification cone feeding structure of the cylinder through a material distribution structure. The structure of the material distribution structure can be constructed in various forms and is not limited to a single one. Here, we optimize and give one feasible option: The material distribution structure includes a rectifier inclined tube and a feeding pipe connected together, and the rectifier inclined tube and the feeding pipe form an angle of 55°~65° with the horizontal plane; the rectifier inclined tube is also provided with an upper material distribution pipe connected to the upper feeding structure of the cylinder, and the feeding pipe is also provided with a middle material distribution pipe connected to the lower feeding structure of the cylinder and a lower material distribution pipe connected to the cone feeding structure; an upper material distribution valve is provided at the connection between the upper material distribution pipe and the rectifier inclined tube, and a lower material distribution valve is provided at the connection between the middle material distribution pipe and the feeding pipe; a flap control structure is provided on the rectifier inclined tube, the feeding pipe, the upper material distribution pipe, the middle material distribution pipe, and the lower material distribution pipe. When this scheme is adopted, the amount of raw material entering the upper distribution pipe is controlled by the upper distribution valve, and the amount of raw material entering the middle and lower distribution pipes is controlled by the lower distribution valve, thereby controlling the reduction effect of NOx in the internal flue gas and reducing NOx generation.

[0031] The above content discloses the structure of the denitrification system. This invention also discloses the denitrification process, which will now be described.

[0032] A self-regulating denitrification process for temperature and air coefficient within a decomposition furnace, employing the aforementioned disclosed self-denitrification system, includes:

[0033] Raw materials and 50% to 80% fuel are added to the rotary kiln flue gas entering the denitrification furnace, and the gas is burned in the denitrification cone to generate strong reducing flue gas. The strong reducing flue gas enters the denitrification cylinder and decomposition cone to reduce NOx, where NOx is reduced to N2.

[0034] Raw materials and 20% to 50% fuel are added to the flue gas entering the decomposition furnace. After mixing with the tertiary air sent in by the lower branch pipe, the mixture is combusted to release heat and generate weakly reducing flue gas.

[0035] The flue gas reaching the constriction structure mixes with the tertiary air introduced by the upper branch pipe and completely combusts the fuel. The flow velocity of the tertiary air introduced by the upper branch pipe into the constriction structure is 16m / s to 20m / s, and the excess air coefficient of the flue gas is 1.02 to 1.05.

[0036] Furthermore, the flow rate and temperature of the flue gas are also limited in the above process. Here, we optimize the process and provide some feasible options: the temperature of the rotary kiln flue gas entering the denitrification furnace is 1000℃~1200℃, and the excess air coefficient is 1.0~1.15; after adding raw materials and fuel to the denitrification furnace, the temperature of the flue gas in the denitrification furnace changes to 950℃~1050℃, the flow rate is 5m / s~7m / s, and the excess air coefficient is less than 0.6; after adding raw materials and fuel to the decomposition furnace, the temperature of the flue gas in the decomposition furnace changes to 900℃~950℃, and the excess air coefficient is 0.85~0.95.

[0037] Compared with the prior art, some of the beneficial effects of the technical solution disclosed in this invention include:

[0038] 1. This invention avoids the adverse effects on stable system operation caused by dust settling and scaling resulting from using the straight section of the decomposition furnace as the main body of denitrification in current mainstream designs, as well as by high system resistance and scaling in bends caused by using pipelines as the denitrification volume carrier. The dust in the denitrification furnace flows through in a fluidized state, avoiding the scaling caused by dust deposition and the uneven mixing of flue gas caused by an excessively large furnace cross-section, which would affect the denitrification efficiency.

[0039] 2. This invention creates a swirling effect at the lower end of the decomposition furnace by tangentially inserting the tertiary air branch pipe into the constricted area of ​​the decomposition furnace, thereby enhancing the mixing of combustion air and flue gas, accelerating fuel combustion, and reducing system heat consumption.

[0040] 3. This invention uses a rectifier inclined tube and flap control structure to control the spatial distribution and flow rate of the preheater feed, achieving precise control of the feed ratio and precise adjustment of the temperature field in the denitrification furnace and decomposition furnace, providing a stable high-temperature zone for NOx reduction and fuel combustion. Attached Figure Description

[0041] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a schematic diagram of the structure of the decomposition furnace and the denitrification furnace, as well as a schematic diagram of the flue gas flow direction.

[0043] Figure 2 A schematic diagram showing the locations of the fuel addition and spreading structures on the denitrification furnace.

[0044] Figure 3 This is a schematic diagram of the structure where the lower branch pipe connects to the decomposition furnace.

[0045] Figure 4 This is a schematic diagram of the upper branch pipe connecting constriction structure.

[0046] Figure 5 This is a schematic diagram of the material distribution structure from one perspective.

[0047] Figure 6 This is a schematic diagram of the material distribution structure from another perspective.

[0048] In the above attached figures, the meanings of each number are as follows:

[0049] 1. Denitrification furnace; 101. Denitrification cone; 102. Denitrification cylinder; 103. Cone fuel addition structure; 104. Cone material spreading structure; 2. Decomposition furnace; 201. Decomposition cone; 202. Lower decomposition cylinder; 203. Narrowing structure; 204. Upper decomposition cylinder; 205. Cylinder fuel addition structure; 206. Lower material spreading structure of cylinder; 207. Upper material spreading structure of cylinder; 3. Smoke chamber; 4. Tertiary air duct; 401. Upper branch pipe; 402. Lower branch pipe; 403. Branch pipe valve; 5. Rectifying inclined pipe; 6. Feed pipe; 7. Upper distribution pipe; 8. Middle distribution pipe; 9. Lower distribution pipe; 10. Upper distribution valve; 11. Lower distribution valve; 12. Flip control structure. Detailed Implementation

[0050] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments.

[0051] In view of the shortcomings of existing technologies, such as incomplete treatment of flue gas containing large amounts of NOx and the tendency for sedimentation and crusting, the following embodiments are optimized and adjusted to overcome the defects of existing technologies.

[0052] Example 1

[0053] like Figure 1 As shown, this embodiment provides a self-regulating denitrification system with self-adjusting temperature and atmosphere in the decomposition furnace 2, which aims to improve the reduction effect of NOx in flue gas, reduce the generation of NOx during combustion, and reduce the sedimentation and scaling phenomenon in the system.

[0054] like Figure 1 As shown, one of the structures of the self-denitrification system provided in this embodiment includes:

[0055] The rotary kiln and the flue gas chamber 3 connected to the rotary kiln are used to guide the flue gas from the rotary kiln to the denitrification furnace 1.

[0056] The flue gas in the rotary kiln contains a large amount of NOx, which needs to be reduced in the subsequent treatment process; the flue gas enters the flue gas chamber 3, and then enters the denitrification furnace 1 and the decomposition furnace 2 for further treatment.

[0057] As the self-denitrification system disclosed in this embodiment, its second structure includes:

[0058] The denitrification furnace 1, used for initial adjustment of temperature and excess air coefficient of rotary kiln flue gas, includes a denitrification cone 101 and a denitrification cylinder 102 that are interconnected, and the denitrification cone 101 is connected to the flue gas chamber 3; a number of cone fuel addition structures 103 and a number of cone material spreading structures 104 are provided on the side wall of the denitrification cone 101, and the cone material spreading structure 104 is set at a higher height than the cone fuel addition structure 103.

[0059] In this embodiment, the location of the fuel addition structure affects the combustion of the fuel. This embodiment optimizes the process by adopting one feasible option: the conical fuel addition structure 103 is located in the 10%~25% height range of the denitrification cone 101 and is evenly spaced along the circumference on the side wall of the denitrification cone 101. This design allows for more uniform fuel addition, higher mixing with the flue gas, and facilitates combustion heat release and flue gas treatment to reduce NOx. With this design, excess fuel is fed into the denitrification cone 101, reducing the excess air coefficient of the denitrification cone 101 and the denitrification cylinder 102 to below 0.6, forming a high concentration of volatile matter and CO, thus fully reducing NOx in the kiln tail flue gas.

[0060] Preferred, such as Figure 2 As shown, there are four conical fuel addition structures 103, which are evenly spaced on the circumference at the same height.

[0061] Preferably, the position of the material spreading structure also affects the decomposition rate and degree of raw materials, and thus the crust formation. This embodiment optimizes the process and adopts one feasible option: the cone-shaped material spreading structure 104 is located in the height range of 50% to 67% of the height of the denitrification cone 101. Furthermore, the number of cone-shaped material spreading structures 104 is generally one, but can be adjusted according to the number of preheaters in the series.

[0062] like Figure 1 As shown, the third structure of the self-denitrification system disclosed in this embodiment includes:

[0063] The decomposition furnace 2 for raw material decomposition is located above the denitrification furnace 1 and includes a lower decomposition cylinder 202 and an upper decomposition cylinder 204 connected to each other. The inner diameter of the lower decomposition cylinder 202 is larger than the inner diameter of the denitrification cylinder 102. A decomposition cone 201 is provided between the lower decomposition cylinder 202 and the denitrification cylinder 102. When the denitrification system is running, the excess air coefficient of the decomposition cone 201 is within 0.6. A constriction structure 203 is provided between the lower decomposition cylinder 202 and the upper decomposition cylinder 204. A cylinder fuel addition structure 205, a lower cylinder material spreading structure 206, and an upper cylinder material spreading structure 207 are respectively provided on the side wall of the lower decomposition cylinder 202.

[0064] Preferably, in this embodiment, the specific limitation method is not unique, depending on the changes in the inner diameter of the denitrification cylinder and the lower decomposition cylinder 202. This embodiment optimizes and adopts one feasible option: the inner diameters of both the denitrification cylinder and the lower decomposition cylinder 202 are fixed, and the inner diameter of the denitrification cylinder 102 is 0.6~0.75 times the inner diameter of the lower decomposition cylinder 202. Using this scheme can better enhance the horizontal mixing of flue gas, improve the denitrification reaction rate, and reduce system resistance.

[0065] Preferably, the material spreading structure 206 at the lower part of the cylinder on the decomposition furnace 2 is also higher than the fuel adding structure 205 of the cylinder, such as... Figure 1 As shown, this embodiment is optimized and adopts one of the feasible options: the height of the cylinder fuel adding structure 205 is flush with the center line of the lower branch pipe 402, and the lower part of the cylinder spreading structure 206 is 600~1000mm higher than the lower branch pipe 402.

[0066] like Figure 1 As shown, the fourth structure of the self-denitrification system disclosed in this embodiment includes:

[0067] The tertiary air duct 4 is used to supply air into the decomposition furnace 2. The tertiary air duct 4 includes a lower branch pipe 402 that connects to the lower decomposition cylinder and an upper branch pipe 401 that connects to the constriction structure 203. The connection between the upper branch pipe 401 and the constriction structure 203 is lower than the minimum diameter position of the constriction structure 203.

[0068] Preferably, in this embodiment, both the upper branch pipe 401 and the lower branch pipe 402 are provided with branch pipe valves 403.

[0069] In this embodiment, the direction of tertiary air entering the decomposition furnace 2 is restricted by the lower branch pipe 402, such as... Figure 3As shown, an optimization is performed here, employing one feasible option: the lower branch pipe 402 is tangentially connected to the interior of the lower decomposition cylinder and used to introduce swirling air into the lower decomposition cylinder. With this scheme, the airflow within the lower branch pipe 402 can flow along the inner wall of the decomposition furnace 2, thereby better forming a swirling flow. After mixing with the fuel gas, the combustion heat release effect of the fuel gas is improved, resulting in a higher degree of decomposition and decomposition efficiency of the raw materials. The decomposition cone 201 connects to the denitrification cylinder 102 and is a strong reduction zone. The lower branch pipe 402 enters tangentially from the lower part of the lower decomposition cylinder 202, mixing with the vertically entering strong reducing gas, fuel, and raw materials, creating a condition where fuel combustion and raw material decomposition occur simultaneously on the horizontal cross-section of the lower decomposition cylinder 202.

[0070] In this embodiment, the tertiary air also forms a swirling flow within the constriction structure 203 to improve the degree of raw material decomposition in the decomposition furnace 2 and reduce NOx generation. Similarly, improving the fit between the upper branch pipe 401 and the constriction structure can change the flowability of the tertiary air within the constriction structure 203. The specific fit is not uniquely limited, such as... Figure 4 As shown, an optimization is performed here, employing one feasible option: the upper branch pipe 401 is tangentially connected to the interior of the constriction structure 203 and used to supply swirling air into the constriction structure 203. The upper branch pipe 401 is connected to the lower side of the constriction structure 203, and the tertiary air enters the constriction structure 203 tangentially, enhancing the mixing effect of the flue gas on the horizontal cross-section inside the constriction structure 203 and promoting fuel burnout; the upper branch pipe 401 can distribute air through adjusting valves, maintaining the excess air coefficient of the lower decomposition cylinder 202 at 0.85~0.95, so that the fuel in the lower decomposition cylinder 202 is in a weakly reducing atmosphere during combustion, reducing the formation of NOx from the fuel.

[0071] like Figure 5 , Figure 6 As shown, the fifth structure of the self-denitrification system disclosed in this embodiment includes:

[0072] The material distribution structure is used to supply raw materials to the system; the material distribution structure includes a cone-shaped material spreading structure 104, a lower part of the cylinder material spreading structure 206, and an upper part of the cylinder material spreading structure 207.

[0073] In this embodiment, raw materials are added from the upper cylinder spreading structure 207, the lower cylinder spreading structure 206, and the denitrification cone 101 spreading structure via a material distribution structure. The material distribution structure can be constructed in various forms and is not limited to a single one. Here, optimization is performed, and one feasible option is adopted: the material distribution structure includes a connected rectifier inclined tube 5 and a feeding pipe 6, forming an angle of 55° to 65° with the horizontal plane; the rectifier inclined tube also... The system includes an upper distribution pipe 7 connected to the upper feeding structure 207 of the cylinder, and a middle distribution pipe 8 connected to the lower feeding structure 206 of the cylinder and a lower distribution pipe 9 connected to the conical feeding structure 104. An upper distribution valve 10 is installed at the connection between the upper distribution pipe 7 and the rectifier inclined pipe 5, and a lower distribution valve 11 is installed at the connection between the middle distribution pipe 8 and the feeding pipe 6. Each of the rectifier inclined pipe 5, feeding pipe 6, upper distribution pipe 7, middle distribution pipe 8, and lower distribution pipe 9 is equipped with a flap control structure 12. With this design, the amount of raw material entering the upper distribution pipe 7 is controlled by the upper distribution valve 10, and the amount of raw material entering the middle and lower distribution pipes 9 is controlled by the lower distribution valve 11. This allows for control of the NOx reduction treatment effect in the internal flue gas and reduction of NOx generation. Furthermore, the temperature of the flue gas can be controlled by adding raw material, thus improving the flue gas treatment efficiency and results. Meanwhile, the flap control structure 12 can directly control the opening or closing of the corresponding pipe section, thereby controlling the raw material addition process.

[0074] Preferably, in this embodiment, the rectifier inclined tube 5, the feeding tube 6 and the upper distribution tube 7 are connected at one point, and a flap control structure 12 is provided at the connection point; at the same time, the feeding tube 6, the middle distribution tube 8 and the lower distribution tube 9 are connected at one point, and a flap control structure 12 is provided at the connection point.

[0075] Preferably, in this embodiment, the flap control structure 12 adopts a flap valve.

[0076] Preferably, the material distribution structure is connected to the preheater and is used to receive the raw material discharged from the preheater. The raw material separated by the preheater is randomly distributed and integrated on the horizontal cross section so that it slides along the lower wall of the pipe. The rectifier inclined tube 5 and the feeding pipe 6 are square tubes. The valve plate of the flap valve makes the material flow slide downward in a flat square shape, so as to match the opening ratio of the material distribution valve with the material distribution ratio.

[0077] The self-denitrification system provided in this embodiment, by adjusting the structure of the denitrification furnace 1 and the decomposition furnace 2, and changing the addition position of fuel and raw materials, enables more complete combustion of fuel, improves the NOx treatment effect in flue gas, reduces NOx generation, and avoids scale formation inside the denitrification furnace 1 and the decomposition furnace 2, thus greatly improving the stability of system operation.

[0078] Example 2

[0079] The above embodiment 1 discloses the structure of the denitrification system. This embodiment also discloses the denitrification process, which will now be described.

[0080] A self-regulating denitrification process for temperature and air coefficient within a decomposition furnace 2, employing the self-denitrification system disclosed in Example 1 above, includes:

[0081] Raw materials and 50%~80% of kiln tail fuel are added to the rotary kiln flue gas entering the denitrification furnace 1, and the gas is burned in the denitrification cone 101 to generate strong reducing flue gas. The strong reducing flue gas enters the denitrification cylinder 102 and the decomposition cone 201 to reduce NOx, wherein NOx is reduced to N2.

[0082] Raw materials and 20% to 50% of kiln tail fuel are added to the flue gas entering the decomposition furnace 2. After mixing with the tertiary air sent in by the lower branch pipe 402, the mixture is burned to release heat and generate weakly reducing flue gas.

[0083] The flue gas reaching the constriction structure 203 mixes with the tertiary air introduced by the upper branch pipe 401 and completely combusts the fuel. The flow velocity of the tertiary air introduced by the upper branch pipe 401 into the constriction structure 203 is 16m / s to 20m / s, and the excess air coefficient of the flue gas is 1.02 to 1.05.

[0084] In the above denitrification process, there are also limitations on the flow rate and temperature of the flue gas. Here, optimization is carried out and feasible options are adopted: the temperature of the rotary kiln flue gas entering the denitrification furnace 1 is 1000℃~1200℃, and the excess air coefficient is 1.0~1.15; after adding raw materials and fuel to the denitrification furnace 1, the temperature of the flue gas in the denitrification furnace 1 changes to 950℃~1050℃, the flow rate is 5m / s~7m / s, and the excess air coefficient is less than 0.6; after adding raw materials and fuel to the decomposition furnace 2, the temperature of the flue gas in the decomposition furnace 2 changes to 900℃~950℃, and the excess air coefficient is 0.85~0.95, of which the excess air coefficient of the decomposition cone 201 is within 0.6.

[0085] The above are the embodiments listed in this example. However, this example is not limited to the optional embodiments described above. Those skilled in the art can arbitrarily combine the above methods to obtain other various embodiments. Anyone can derive other various forms of embodiments under the guidance of this example. The above specific embodiments should not be construed as limiting the scope of protection of this example. The scope of protection of this example should be defined in the claims.

Claims

1. A self-regulating denitrification system for self-adjusting temperature and air coefficient inside a decomposition furnace, characterized in that, include: The rotary kiln and the flue gas chamber (3) connected to the rotary kiln are used to guide the flue gas from the rotary kiln to the denitrification furnace (1). The denitrification furnace (1) includes a denitrification cone (101) and a denitrification cylinder (102) that are interconnected, and the denitrification cone (101) is connected to the smoke chamber (3); a number of cone fuel addition structures (103) and a number of cone material spreading structures (104) are provided on the side wall of the denitrification cone (101), and the cone material spreading structure (104) is set at a height higher than the cone fuel addition structure (103). A decomposition furnace (2) is located above a denitrification furnace (1) and includes a lower decomposition cylinder (202) and an upper decomposition cylinder (204) that are connected to each other. The inner diameter of the lower decomposition cylinder (202) is larger than the inner diameter of the denitrification cylinder (102). A decomposition cone (201) is provided between the lower decomposition cylinder (202) and the denitrification cylinder (102). A narrowing structure (203) is provided between the lower decomposition cylinder (202) and the upper decomposition cylinder (204). A cylinder fuel addition structure (205), a cylinder lower spreading structure (206), and a cylinder upper spreading structure (207) are respectively provided on the side wall of the lower decomposition cylinder (202). The tertiary air duct (4) is used to supply air to the decomposition furnace (2); the tertiary air duct (4) includes a lower branch pipe (402) that connects to the lower decomposition cylinder (202) and an upper branch pipe (401) that connects to the constriction structure (203), and the connection between the upper branch pipe (401) and the constriction structure (203) is lower than the minimum diameter position of the constriction structure (203); The material distribution structure is used to supply raw materials to the system; the material distribution structure includes a cone-shaped material distribution structure (104), a lower cylinder material distribution structure (206), and an upper cylinder material distribution structure (207).

2. The self-regulating denitrification system for temperature and air coefficient in the decomposition furnace according to claim 1, characterized in that: The inner diameter of the denitrification cylinder (102) is 0.6 to 0.75 times the inner diameter of the lower decomposition cylinder (202).

3. The self-regulating denitrification system for temperature and air coefficient in the decomposition furnace according to claim 1, characterized in that: The lower branch pipe (402) is tangentially connected to the interior of the lower decomposition cylinder (202) and is used to feed swirling air into the lower decomposition cylinder (202).

4. The self-regulating denitrification system for temperature and air coefficient in the decomposition furnace according to claim 1 or 3, characterized in that: The upper branch pipe (401) is tangentially connected to the inside of the constriction structure (203) and is used to feed swirling air into the constriction structure (203).

5. The self-regulating denitrification system for temperature and air coefficient in the decomposition furnace according to claim 1, characterized in that: The conical fuel addition structure (103) is located in the 10% to 25% height range of the denitrification cone (101) and is evenly spaced along the circumference on the side wall of the denitrification cone (101).

6. The self-regulating denitrification system for temperature and air coefficient in the decomposition furnace according to claim 1, characterized in that: The cone-shaped material spreading structure (104) is located in the height range of 50% to 67% of the height of the denitrification cone (101).

7. The self-regulating denitrification system for temperature and air coefficient in the decomposition furnace according to claim 1, characterized in that: The height of the cylinder fuel addition structure (205) is flush with the center line of the lower branch pipe (402), and the lower part of the cylinder spreading structure (206) is 600~1000mm higher than the lower branch pipe.

8. The self-regulating denitrification system for temperature and air coefficient in the decomposition furnace according to claim 1, characterized in that: The material distribution structure includes a rectifier inclined tube (5) and a feeding tube (6) connected together, with the rectifier inclined tube (5) and the feeding tube (6) forming an angle of 55°~65° with the horizontal plane; the rectifier inclined tube (5) is also provided with an upper material distribution tube (7) connected to the upper part of the cylinder spreading structure (207), and the feeding tube (6) is also provided with a middle material distribution tube (8) connected to the lower part of the cylinder spreading structure (206) and a lower material distribution tube (9) connected to the cone spreading structure (104); an upper material distribution valve (10) is provided at the connection between the upper material distribution tube (7) and the rectifier inclined tube (5), and a lower material distribution valve (11) is provided at the connection between the middle material distribution tube (8) and the feeding tube (6); a flap control structure (12) is provided on the rectifier inclined tube (5), the feeding tube (6), the upper material distribution tube (7), the middle material distribution tube (8) and the lower material distribution tube (9).

9. A self-regulating denitrification process for temperature and air coefficient in a decomposition furnace, employing the self-denitrification system according to any one of claims 1 to 8, characterized in that, include: Raw materials and 50%~80% of kiln tail fuel are added to the rotary kiln flue gas entering the denitrification furnace (1), and strong reducing flue gas is generated by combustion in the denitrification cone (101). The strong reducing flue gas enters the denitrification cylinder (102) and the decomposition cone (201) to reduce NOx, wherein NOx is reduced to N2. Raw materials and 20%~50% of kiln tail fuel are added to the flue gas entering the decomposition furnace (2), and after mixing with the tertiary air sent in by the lower branch pipe (402), the mixture is burned to release heat and generate weakly reducing flue gas. The flue gas reaching the constriction structure (203) mixes with the tertiary air introduced by the upper branch pipe (401) and completely burns the fuel. The flow velocity of the tertiary air introduced by the upper branch pipe (401) into the constriction structure (203) is 16m / s to 20m / s, and the excess air coefficient of the flue gas is 1.02 to 1.

05.

10. The self-regulating denitrification process for temperature and air coefficient in the decomposition furnace (2) according to claim 9, characterized in that: The temperature of the rotary kiln flue gas entering the denitrification furnace (1) is 1000℃~1200℃, and the excess air coefficient is 1.0~1.

15. After adding raw materials and fuel to the denitrification furnace (1), the temperature of the flue gas in the denitrification furnace (1) changes to 950℃~1050℃, the flow rate is 5m / s~7m / s, and the excess air coefficient is less than 0.

6. After adding raw materials and fuel to the decomposition furnace (2), the temperature of the flue gas in the decomposition furnace (2) changes to 900℃~950℃, and the excess air coefficient is 0.85~0.95, of which the excess air coefficient of the decomposition cone (201) is less than 0.6.

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