System and method for denitration of cement kiln flue gas

Abstract

The invention discloses a system and a method for denitration of cement kiln flue gas. The system comprises a rotary denitration device and a penetrating denitration device which are arranged on a flue between a rotary cement kiln and a decomposing furnace. The penetrating type denitration device is mainly used for removing nitrogen oxides (including a thermal type and a fuel type) generated by combustion of head coal in the rotary cement kiln; the rotary denitration device is used for further denitrating the flue gas generated in the rotary kiln, and meanwhile, the generation of tail coal fuel type nitric oxide is strongly inhibited, and the concentration of tail coal fuel type NOX is reduced.

Description

Technical Field

[0001] This invention relates to the technical field of flue gas treatment, and in particular to a system and method for denitrifying flue gas from cement kilns. Background Technology

[0002] The cement production industry is an important basic material industry in my country.

[0003] In the cement production process, the thermal decomposition reaction of cement raw materials and the mineralization reaction of cement clinker are completed only through the high temperatures (approximately >825℃ and >1450℃, respectively) obtained from the combustion of pulverized coal. During this process, nitrogen-containing substances in the pulverized coal produce nitrogen oxides (NOx) upon combustion. x (Fuel type); In addition, if the high temperature exceeds 1200℃ (such as under the mineralization reaction conditions of cement clinker), N2 in the combustion air will also be oxidized into NO. x (Thermal type). Therefore, the rotary kiln (equipment that completes the mineralization reaction of cement clinker) and the decomposition furnace (equipment that completes the decomposition of CaCO3 in cement raw meal into CaO) used in cement production will produce a large amount of NO-containing substances during the combustion process. x Flue gas containing air pollutants such as nitrogen oxides, sulfur dioxide, and particulate matter.

[0004] In 2013, the state issued and implemented the mandatory national standard GB4915-2013 "Emission Standard of Air Pollutants for Cement Industry", which stipulates that NO2 in air pollutants emitted from cement kilns and kiln tail waste heat utilization systems must meet certain requirements. x The emission limit is 320 mg / Nm³. 3 (Calculated based on a 10% baseline oxygen content). In the subsequent implementation process, local environmental protection departments in various provinces and cities further reduced NO based on local conditions. x The emission limits. In January 2024, five ministries, including the Ministry of Ecology and Environment, jointly issued the "Opinions on Promoting the Implementation of Ultra-Low Emissions in the Cement Industry" (hereinafter referred to as the "Opinions"), which gradually promoted the implementation of nitrogen oxide emission limits of ≤50mg / Nm³ for cement clinker production. 3 (Based on a 10% baseline oxygen content), the ammonia water usage for denitrification is ≤3.5 kg / ton of clinker (based on a 20% ammonia water concentration), and ammonia slip is ≤8 mg / Nm³. 3 Therefore, the flue gas generated during cement production must be treated to meet the above-mentioned standards before it can be released into the atmosphere.

[0005] To meet the requirements of various standards and guidelines, the cement production industry currently mainly uses two types of denitrification methods:

[0006] The first category is chemical denitrification technologies for kiln tail gas, represented by "Selective Non-Catalytic Reduction (SNCR)" and "Selective Catalytic Reduction (SCR)". SNCR typically uses ammonia as a reducing agent to chemically reduce nitrogen oxides in the flue gas. However, this technology cannot simultaneously meet the requirements of the aforementioned "Opinions" regarding "nitrogen oxide emission limits," "ammonia usage for denitrification," and "ammonia slip." While SCR can meet ultra-low emission regulations, its construction cost is approximately 20 million RMB, and it requires regular replacement of catalyst components, resulting in high operating and maintenance costs, increasing cement clinker production costs. Furthermore, discarded catalyst components pose a potential risk of secondary pollution.

[0007] The second category is denitrification technology represented by "staged combustion" of pulverized coal. This involves using reducing gases (mainly CO) generated during the oxygen-deficient combustion of pulverized coal in the decomposer to reduce nitrogen oxides produced during combustion into harmless nitrogen, thereby reducing the nitrogen oxide content in the flue gas emitted from the cement kiln system and achieving denitrification. However, this denitrification technology has low efficiency and is easily affected by the cement clinker production process. Even when used in conjunction with SNCR, it cannot reliably meet the nitrogen oxide emission limits specified in the aforementioned "Opinions." Summary of the Invention

[0008] The purpose of this invention is to address the technical deficiencies in the prior art. In the first aspect, it provides a system for denitrifying cement kiln flue gas, including a rotary denitrification device (01) and a penetrating denitrification device (02) that are interconnected and located in the rising flue (15).

[0009] The rotary denitrification device (01) includes a hollow, funnel-shaped cylinder (16). The cylinder wall of the cylinder (16) is equipped with a number of first nozzles (03-1) for spraying tailings and water vapor into the inner cavity of the cylinder (16). All first nozzles (03-1) are deflected to the same side at the same angle and are integrated nozzles that can spray coal powder and water vapor simultaneously and separately.

[0010] The penetrating denitrification device (02) includes a pipe body (17) and multiple second nozzles (04-1) installed on the side wall of the pipe body (17) for spraying tailings and water vapor into the inner cavity of the pipe body (17); the second nozzles (04-1) face the central axis of the pipe body (17) and are integrated nozzles that can spray coal powder and water vapor simultaneously and separately.

[0011] Preferably, the weight ratio of pulverized coal ejected from the second nozzle (04-1) and the first nozzle (03-1) is approximately (20%-30%): (70%-80%).

[0012] The rotary denitrification device (01) and the penetrating denitrification device (02) are installed on the rising flue (15) from bottom to top or from top to bottom; when installed from top to bottom, the upper part of the cylinder (16) of the rotary denitrification device (01) is connected to the cone part (13) of the decomposition furnace, and the lower part of the tube (17) of the penetrating denitrification device (02) is connected to the smoke chamber (14).

[0013] The cylinder (16) of the rotary denitrification device (01) and the tube (17) of the penetrating denitrification device (02) are coaxially arranged or not coaxially arranged;

[0014] Optionally, the first nozzle (03-1) and the second nozzle (04-1) are respectively arranged in the horizontal direction, or at an angle to the horizontal direction.

[0015] The angle at which the first nozzle (03-1) deflects to the same side is the angle between the nozzle axis and the tangent of the cylinder circumference at the nozzle position, and the angle does not exceed 75°.

[0016] The first nozzle (03-1) and the second nozzle (04-1) are formed by coaxially mounting the pulverized coal conveying pipe (311) and the steam conveying pipe (312), respectively, or the pulverized coal conveying pipe (311) and the steam conveying pipe (312) are each independently mounted in a main conveying pipe (31).

[0017] In a second aspect, the present invention provides a cement kiln production system, including a rotary kiln (11), a decomposition furnace (12), and an ascending flue (15) connecting the rotary kiln (11) and the decomposition furnace (12), characterized in that it further includes a flue gas denitrification device provided at the location of the ascending flue (15), the flue gas denitrification device being the above-mentioned system, and the decomposition furnace (12) is not provided with a tailings inlet (08).

[0018] Thirdly, the present invention provides a method for denitrifying cement kiln flue gas, wherein the above-mentioned system is used to denitrify cement kiln flue gas, specifically as follows:

[0019] The first nozzle of the rotary denitrification device introduces pulverized coal and water vapor into the cylinder, and generates a rotating airflow field in the cylinder. Under the high temperature and oxygen-deficient conditions provided by the secondary flue gas entering the rotary denitrification device, the fixed carbon in the pulverized coal and water vapor undergo a water-gas reaction to produce reducing gases (H2 and CO, etc.). At the same time, the volatiles in the pulverized coal undergo pyrolysis and gasification to produce reducing gases. The reducing gases together reduce the nitrogen oxides from the secondary flue gas and the fuel-type nitrogen oxides generated by the pulverized coal itself in the rotary denitrification device to nitrogen.

[0020] The second nozzle of the penetrating denitrification device introduces pulverized coal and water vapor into the tube. Under the high temperature and oxygen-deficient conditions provided by the flue gas entering the penetrating denitrification device, the fixed carbon in the pulverized coal and water vapor undergo a water-gas reaction to produce reducing gases (H2 and CO, etc.). At the same time, the volatiles in the pulverized coal undergo pyrolysis and gasification to produce reducing gases (CO, etc.), so as to reduce the nitrogen oxides from the flue gas and the fuel-type nitrogen oxides generated by the pulverized coal itself in the penetrating denitrification device into nitrogen.

[0021] The pulverized coal in the first and second nozzles both came from the tail coal conveying pipeline of the original cement production system.

[0022] Preferably, the mass of pulverized coal introduced into the pipe of the penetrating denitrification device by the second nozzle does not exceed 50% of the total mass of tailings.

[0023] Fourthly, the present invention provides a method for controlling the temperature of flue gas in a cement kiln. In the rotary denitrification device (01) and the penetrating denitrification device (02), the amount of water vapor is controlled to control the water-gas reaction (strong endothermic reaction) process, thereby controlling the temperature in the two denitrification devices to be within a set range, typically about 900℃ to 1200℃.

[0024] Fifthly, the present invention provides a method for denitrifying cement kiln flue gas, comprising the following operations: simultaneously introducing pulverized coal and steam into the flue at two positions above and below the rising flue (15) to denitrify the cement kiln flue gas;

[0025] The coal powder and water vapor introduced at one of the locations enter at high speed along the tangential off-center direction of the inner wall of the flue, forming a gas-solid two-phase rotating airflow field. The high-temperature flue gas entering this rotating airflow field provides high-temperature and oxygen-deficient conditions for the coal powder and water vapor, causing the fixed carbon in the coal powder and water vapor to undergo a water-gas reaction to produce reducing gases (H2 and CO, etc.). At the same time, the coal powder is also pyrolyzed and gasified to produce reducing gases (CO, etc.), so as to reduce the nitrogen oxides in the flue gas and the fuel-type nitrogen oxides produced by the coal powder itself into nitrogen.

[0026] The pulverized coal and water vapor introduced from another location enter radially along the flue, allowing the pulverized coal and water vapor to penetrate the flue gas flow field of the rising flue and reach the central region of the flue gas channel cross section. The flue gas provides high-temperature and oxygen-deficient conditions for the pulverized coal and water vapor, causing the fixed carbon in the pulverized coal and water vapor to undergo a water-gas reaction to produce reducing gases (H2 and CO, etc.). At the same time, the pulverized coal is also pyrolyzed and gasified to produce reducing gases, so as to reduce the nitrogen oxides in the flue gas and the fuel-type nitrogen oxides produced by the pulverized coal itself into nitrogen.

[0027] The flue gas is secondary air flue gas from the smoke chamber or rising flue gas after being introduced by pulverized coal and water vapor;

[0028] Preferably, the mass of pulverized coal in direct contact with the secondary flue gas does not exceed 50% of the total mass of tailings.

[0029] Sixthly, the present invention provides a cement production process, including a method for producing cement clinker using a rotary kiln, a method for thermally decomposing calcium carbonate in cement raw meal using a decomposition furnace, and the above-mentioned method for denitrifying cement kiln flue gas, wherein the fuel for thermally decomposing calcium carbonate in cement raw meal in the decomposition furnace is entirely derived from the denitrified rising flue gas obtained by the above-mentioned method.

[0030] Preferably, the rising flue gas after denitrification enters the decomposition furnace, mixes with tertiary air, and is re-burned to decompose calcium carbonate.

[0031] This invention adds two different types of denitrification devices to the existing flue between the rotary kiln and the decomposition furnace: ① a rotary denitrification device; ② a through-type denitrification device. This invention significantly improves flue gas denitrification efficiency by simply modifying the equipment structure of the existing cement clinker production line. It is ingeniously conceived, has low implementation costs, and is readily accepted for application and promotion.

[0032] The method of this invention uses the aforementioned system to denitrify the flue gas from the cement clinker production process. Based on a thorough consideration of the cement clinker production process conditions and equipment, a unique denitrification process (including a denitrification method and device) is designed. This denitrification process takes into account the cement clinker production process related to denitrification, achieving close integration with the cement clinker production process and fully utilizing the material composition and heat transfer during cement production. Furthermore, this denitrification process essentially does not alter the original cement clinker production process and does not interfere with it. It can also be used in conjunction with SNCR denitrification technology. Using the system and / or method of this invention to denitrify the flue gas from the cement clinker production process fully meets the aforementioned requirements for NOx emissions during cement clinker production as outlined in the "Opinions". Attached Figure Description

[0033] Figure 1 The diagram shows the structure of an existing cement clinker production system.

[0034] Figure 2 The diagram shown is a structural schematic of the system of the present invention.

[0035] Figure 3 The diagram shown is a cross-sectional view of the rotary denitrification device along line AA in the system of the present invention.

[0036] Figure 4 The diagram shown is a cross-sectional view of the penetration-type denitrification device along BB in the system of the present invention.

[0037] Figure 5The diagram shows the arrangement of a rotary denitrification device according to another embodiment of the system of the present invention.

[0038] Figure 6 The diagram shows the arrangement of a rotary denitrification device according to another embodiment of the system of the present invention.

[0039] Figure 7 The diagram shown is a structural schematic of the first nozzle in another embodiment of the system of the present invention.

[0040] Figure 8 The diagram shown is a structural schematic of the second nozzle in another embodiment of the system of the present invention.

[0041] Figures 9A-9C The diagram shows the structure of the first or second nozzle in several embodiments of the system of the present invention.

[0042] Figures 10A-10B The diagram shows structural schematics of pulverized coal nozzles and steam nozzles in several embodiments of the system of the present invention.

[0043] In the picture:

[0044] 01: Rotary denitrification device; 02: Penetration denitrification device; 03-1: First nozzle; 03-2: First pulverized coal nozzle; 03-3: First steam nozzle; 04-1: Second nozzle; 04-2: Second pulverized coal nozzle; 04-3: Second steam nozzle; 05: Temperature detection device; 06: Secondary air; 07: Tertiary air inlet; 08: Tailings inlet; 09: Fourth-stage cylinder feed pipe; 10: Fifth-stage cylinder feed pipe; 11: Rotary kiln; 12: Decomposition furnace; 13: Decomposition furnace cone; 14: Smoke chamber; 15: Rising flue; 16: Cylinder body; 17: Pipe body; 31: Main conveying pipe; 311: Pulverized coal conveying pipe; 312: Steam conveying pipe. Detailed Implementation

[0045] like Figure 1 As shown, the existing cement clinker production process is as follows:

[0046] The high temperature (1450℃~1600℃) generated by the combustion of lead coal in a cement rotary kiln completes the mineralization reaction of the materials inside the kiln, generating four main minerals: C3S, C2S, C3A, and C4AF, i.e., clinker. The high-temperature secondary flue gas (containing thermal and fuel NO2) produced during the lead coal combustion process... X Through the rotary kiln 11, following the direction indicated by the secondary air arrow 06, it passes from bottom to top through the smoke chamber 14, the rising flue 15 at the kiln tail, and the decomposition furnace cone 13, before entering the decomposition furnace 12.

[0047] Tailings pulverized coal along the tailings inlet 08 ( Figure 1(In the direction indicated by the middle arrow) enters the decomposition furnace 12, while the high-temperature air (tertiary air) required for tail coal combustion enters through the tertiary air inlet 07. Figure 1 The air (in the direction indicated by the middle arrow) also enters the decomposition furnace 12. The tertiary air comes from the high-temperature air generated during the cooling of cement clinker, with a typical temperature of around 950℃. Cement raw meal enters the decomposition furnace 12 through the four-stage feed pipe 09. The high temperature (approximately 850℃~1000℃) generated by the combustion of tailings completes the chemical reaction in the raw meal within the decomposition furnace 12, where calcium carbonate decomposes into calcium oxide.

[0048] All reactants and high-temperature flue gas generated during the combustion of tailings in decomposition furnace 12 (containing NO) X The gas, mainly fuel-type, along with secondary air from the rising flue 15, enters the fifth-stage cylinder (not shown in the figure) through the gooseneck pipe from the upper outlet of the decomposer 12 for gas-solid separation. The solid powder (hot raw material) separated from the fifth-stage cylinder enters the rotary kiln along the fifth-stage cylinder feed pipe 10. When it reaches the calcination zone in the rotary kiln, it completes the mineralization reaction under the high temperature (1450℃~1600℃) generated by the combustion of the first coal, producing clinker.

[0049] The "staged combustion" denitrification technology mentioned in the background technology usually involves introducing a portion of tailings at position 13 of the decomposition furnace cone. Since this is an oxygen-deficient environment, the fixed carbon and volatiles in the tailings generate reducing gases such as CO under the oxygen-deficient high-temperature environment, which in turn reduces nitrogen oxides in the secondary air flue gas from the rising flue 15 into nitrogen.

[0050] However, since the secondary flue gas velocity is as high as 20 to 30 meters per second, the nitrogen oxides entering the decomposition furnace cone 13 do not have enough time to undergo a reduction reaction. In addition, the presence of raw materials in the decomposition furnace cone 13 can also interfere with the reduction reaction process. Therefore, the denitrification efficiency of this technology is low, and even when used in combination with SNCR, it cannot simultaneously meet the requirements of all indicators in the aforementioned "Opinions".

[0051] Based on the existing cement clinker production process and considering the shortcomings of the denitrification technologies commonly used in the industry, this invention proposes a novel denitrification system and method for cement kiln flue gas.

[0052] The following specific embodiments illustrate the content of the present invention in more detail and further elaborate the present invention, but these embodiments are by no means intended to limit the present invention.

[0053] As mentioned earlier, in the production of cement clinker, the temperature of the flue gas entering the rising flue duct 15 is approximately 1000℃~1100℃, and the oxygen content by volume is usually ≤3.5%, which is a high-temperature, oxygen-deficient condition. The concentration of nitrogen oxides can even reach as high as 1000mg / Nm³. 3The above is an explanation of the invention's originality. This invention proposes a modification to existing flue systems by adding a denitrification device to the original rising flue. For example, see [link to relevant documentation]. Figure 2 As shown, at least a rotary denitrification device 01 is added, or a rotary denitrification device 01 and a through-type denitrification device 02 connected in sequence are added simultaneously, while the tailings inlet 08 originally located on the decomposition furnace 12 is removed (see...). Figure 1 Instead of the denitrification furnace 12 or the denitrification furnace cone 13, the tailings are fed into the denitrification device of this invention (the method of feeding tailings into the denitrification device will be described later), thus forming the denitrification system for cement kiln flue gas of this invention.

[0054] like Figure 2 and Figure 3 As shown, the rotary denitrification device 01 includes a hollow, funnel-shaped cylinder 16. A temperature detection device 05 is located inside the cylinder 16 in an easily accessible position, typically near the top surface of the cylinder 16. Multiple first nozzles 03-1 are mounted on the cylinder wall to spray pulverized coal and water vapor. These first nozzles 03-1 are evenly distributed on the inner wall of the cylinder 16, with their outlets facing and extending into the inner cavity of the cylinder. All first nozzles 03-1 are deflected to the same side at the same angle (e.g., not exceeding 75°), which is the angle between the nozzle axis and the tangent to the cylinder circumference at the nozzle's location, allowing them to enter the cylinder 16 along the approximate tangential direction (see enlarged partial structure). Figure 3 (As shown), this allows the pulverized coal and water vapor ejected from the first nozzle 03-1 to form a swirling flow along the inner wall of the cylinder 16 when injected into the inner cavity of the cylinder 16 through the first nozzle 03-1. The first nozzle 03-1 can be arranged horizontally (see...). Figure 9A It can also be at an angle to the horizontal direction. For example, if it is necessary to prolong the time the flue gas stays in the cylinder 16, the first nozzle 03-1 can be inserted in a downward direction. See [link to relevant documentation]. Figure 9B Conversely, if it is necessary to shorten the time the flue gas spends inside the cylinder 16, the first nozzle 03-1 can be inserted in an upward direction, see [reference]. Figure 9C .

[0055] In this invention, the first nozzle 03-1 is optimally designed as an integrated nozzle capable of simultaneously and separately injecting pulverized coal and steam, for example, formed by a pulverized coal conveying pipe 311 and a steam conveying pipe 312 fitted together, see [reference]. Figure 10A The assembly can be a combination of an outer / inner coal pulverized coal conveying pipe 311 and an inner / outer steam conveying pipe 312, with the two pipes coaxially mounted; or as follows: Figure 10B The two conveying pipes shown are each independently fitted into a main conveying pipe 31. Here, the steam conveying pipe 312 can be connected to an independent steam generator or to the waste steam pipeline of the original kiln tail waste heat power generation in the cement kiln system to reuse the waste steam; the pulverized coal conveying pipe 311 inputs the tail coal.

[0056] The first nozzle 03-1 can also be an independently configured first pulverized coal nozzle 03-2 and a first steam nozzle 03-3 (e.g., ...). Figure 7 As shown), pulverized coal nozzles and steam nozzles can be arranged alternately on the same horizontal plane (not shown in the figure), or they can be paired vertically and arranged alternately in the horizontal direction (see Figure 1). Figure 7 The first steam nozzle 03-3 can be connected to an independent steam generator or to the waste steam pipeline of the existing kiln tail waste heat power generation system to reuse the waste steam; the first pulverized coal nozzle 03-2 is used to input tail coal.

[0057] The specific arrangement of the first nozzle 03-1 of the present invention is not limited to... Figure 3 The method can be two nozzles or four nozzles arranged approximately tangentially to the cylinder 16 at 90-degree intervals to introduce pulverized coal and water vapor into the cylinder 16 and generate a rotating airflow therein.

[0058] The approximate tangent direction mentioned here refers to a sectional view taken along a horizontal direction (e.g., ...). Figure 3 ,along Figure 2 The first nozzle 03-1, when positioned in any direction within the tangential direction of the cylinder 16 (or understood as the range of deflection angles between the nozzle axis and the tangent), can cause pulverized coal and steam to form a swirling flow when they enter the cylinder 16 through the first nozzle 03-1. For example, this range could be a range in which the nozzle deviates from the tangential direction by no more than 75 degrees.

[0059] In the aforementioned rotary denitrification device, a mixture of pulverized coal and steam enters the cylinder at high speed through nozzles along the tangential off-center direction of the inner wall of the rotary denitrification device, forming a gas-solid two-phase rotating fluidized bed. Within this rotating flow field, the residence time of pulverized coal and steam is prolonged, and the mixing of pulverized coal and steam is more thorough in the edge region of the rising flue gas flow field. Simultaneously, under the oxygen-deficient, high-temperature environment inside the rotary denitrification device cylinder, the following physicochemical reactions occur: ① The volatiles in the pulverized coal undergo pyrolysis and gasification to produce reducing gases such as CO, which in turn remove NO from the secondary flue gas. X ① It is reduced to harmless nitrogen gas; ② Water vapor reacts with fixed carbon in pulverized coal to produce H2 (strong reducing agent) gas and CO gas, which in turn reduces NO in the secondary flue gas. X ③ During the pyrolysis and gasification process of pulverized coal, most of the volatile nitrogen and some coke nitrogen in the pulverized coal are released into the gas phase, and under a strong reducing atmosphere, most of them are converted into harmless nitrogen gas; that is to say, most of the fuel-type NO produced during the pyrolysis and gasification process of pulverized coal is converted into harmless nitrogen gas. XIt is also reduced to harmless nitrogen by reducing gases such as H2 and CO. Based on these reactions, the rotary denitrification unit can not only effectively remove nitrogen oxides from secondary flue gas and strongly inhibit and remove fuel-type nitrogen oxides generated by pulverized coal itself, but also significantly improve the combustion characteristics of pulverized coal, which helps to make the subsequent aerobic combustion process faster and more stable, thereby reducing the requirements of the production system on the quality of pulverized coal and reducing the production cost of cement clinker.

[0060] As an optimized implementation, the present invention also provides a penetration-type denitrification device 02, such as... Figure 2 and Figure 4 As shown, the penetrating denitrification device 02 includes the original rising flue (see...). Figure 1 The second nozzle 04-1 is installed on the pipe body 17 and the side wall of the pipe body 17. The second nozzle 04-1 is an integrated nozzle that can simultaneously inject pulverized coal and water vapor. Its structure is exactly the same as that of the first nozzle 03-1, and will not be described again here.

[0061] The second nozzle 04-1 can also be an independently configured second pulverized coal nozzle 04-2 and second steam nozzle 04-3 (e.g.) Figure 8 As shown), pulverized coal nozzles and steam nozzles can be arranged alternately on the same horizontal plane (not shown in the figure), or they can be paired vertically and arranged alternately in the horizontal direction (see Figure 1). Figure 8 The second steam nozzle 04-3 can be connected to an independent steam generator or to the waste steam pipeline of the existing kiln tail waste heat power generation system in the cement kiln system to reuse the waste steam.

[0062] The second nozzle 04-1 can be positioned horizontally or at an angle to the horizontal (for example, if it is necessary to prolong the time the flue gas spends in the pipe 17, the second nozzle 04-1 can be inserted in a downward tilting direction; conversely, if it is necessary to shorten the time the flue gas spends in the pipe 17, the second nozzle 04-1 can be inserted in an upward tilting direction; see reference). Figures 9A-9C (The setting method of the first nozzle in the middle).

[0063] The second nozzle 04-1 has the same structure and form as the first nozzle 03-1, and different forms can be used alone or in combination.

[0064] In the aforementioned penetrating denitrification device, a mixture of pulverized coal and water vapor, entering at high speed radially inward through nozzles along the pipe (flue gas channel), penetrates the flue gas flow field of the rising flue and reaches the central region of the flue gas channel cross-section. Mixtures of pulverized coal and water vapor entering from different radial directions collide in the central region of the flue gas channel, forming intense turbulence and mixing with the flue gas. Simultaneously, under the oxygen-deficient, high-temperature environment inside the pipe of the aforementioned penetrating denitrification device, the following three main physicochemical reactions occur: ① The volatiles in the pulverized coal undergo pyrolysis and gasification to produce reducing gases such as CO, which in turn remove NO from the flue gas. X ① It is reduced to harmless nitrogen gas; ② Water vapor reacts with fixed carbon in pulverized coal to produce H2 (a strong reducing gas) and CO gas, which in turn reduces NO in the flue gas. X ③ During the pyrolysis and gasification process of pulverized coal, most of the volatile nitrogen and some coke nitrogen in the pulverized coal are released into the gas phase, and under a strong reducing atmosphere, most of them are converted into harmless nitrogen gas; that is to say, most of the fuel-type NO produced during the pyrolysis and gasification process of pulverized coal is converted into harmless nitrogen gas. X It is also reduced to harmless nitrogen by reducing gases such as H2 and CO. Based on these reactions, the through-type denitrification device can not only effectively remove nitrogen oxides from the secondary flue gas and strongly inhibit and remove fuel-type nitrogen oxides generated by pulverized coal itself, but also consume the high oxygen levels in the secondary flue gas when the cement clinker process is in an abnormal state. This improves the adaptability of the denitrification system to process fluctuations in the clinker production system and ensures the denitrification efficiency of the system.

[0065] In this invention system, the rotary denitrification device 01 and the through-type denitrification device 02 are preferably arranged in combination. When arranged in combination, their relative positions in the secondary air / flue gas flow direction can be interchanged. For example, the through-type denitrification device 02 and the rotary denitrification device 01 can be arranged from bottom to top along the secondary air / flue gas flow direction, or as... Figure 2 The rotary denitrification device 01 and the through-type denitrification device 02 in the example are arranged from bottom to top along the flow direction of the secondary air flue gas.

[0066] One implementation method involves using only a rotary denitrification device 01 without a through-type denitrification device 02. Compared to a through-type denitrification device, the residence time of pulverized coal and water vapor in the rotary denitrification device is longer. Therefore, even with a large amount of pulverized coal, the three reactions mentioned above can be largely completed. Compared to a through-type denitrification device, the rotary denitrification device can achieve the production of fuel-type NO from a large amount of pulverized coal. X The removal.

[0067] In this invention, the geometric shape of the inner wall of the cylinder 16 of the rotary denitrification device 01 and the tube 17 of the penetrating denitrification device 02 can be cylindrical, elliptical, square, polygonal, or a combination of these shapes. When it is square or polygonal, the deflection angle of the first nozzle 03-1 is the angle between the nozzle axis and the inner wall of the cylinder.

[0068] In this invention, such as Figure 5 , Figure 6 As shown, the cylinder 16 of the rotary denitrification device 01 and the tube 17 of the penetrating denitrification device 02 can be coaxially or non-coaxially; both can be coaxially or non-coaxially with the flue and smoke chamber.

[0069] With the above setup, the tailings that were originally fed into the decomposition furnace are no longer fed into the decomposition furnace. Instead, they are injected into the rotary denitrification device 01 and the penetrating denitrification device 02 by the first nozzle 03-1 and the second nozzle 04-1, respectively. The amount of pulverized coal injected into the penetrating denitrification device 02 by the second nozzle 04-1 accounts for 0-50% of the total tailings ("0" means no penetrating denitrification device is installed), and the remaining tailings are injected into the rotary denitrification device 01 by the first nozzle 03-1. Preferably, the amount of pulverized coal injected by the second nozzle 04-1 accounts for 20-30% of the total tailings, and the amount of pulverized coal injected by the first nozzle 03-1 accounts for 70-80% of the total tailings.

[0070] The denitrification system and denitrification method of the present invention will be further described below with reference to specific embodiments.

[0071] In this embodiment, the penetrating denitrification device 02 and the rotary denitrification device 01 are arranged from bottom to top along the direction of the secondary air flue gas (i.e., the flow direction). Specifically, the rotary denitrification device 01 is located at the upper part of the original flue (closer to the decomposition furnace than the penetrating denitrification device 02), and the top surface of the cylinder 16 is the top surface of the rotary denitrification device 01, communicating with the cone portion 13 of the decomposition furnace; the bottom surface of the cylinder 16 is connected to the top of the penetrating denitrification device 02. The penetrating denitrification device 02 is located at the lower part of the original flue (closer to the smoke chamber than the rotary denitrification device 01), and the top surface of the pipe 17 is connected to the bottom surface of the rotary denitrification device 01; the bottom surface of the pipe 17 is connected to the top of the smoke chamber 14.

[0072] When using the system of this embodiment for denitrification, the specific steps include:

[0073] (1) Secondary flue gas 06 with a temperature of approximately 1050℃ (O2 concentration approximately <3.5%) enters the penetrating denitrification device 02 through the smoke chamber 14. It then enters the mixture of tailings coal powder and water vapor (approximately 30% of the total tailings coal powder) within the penetrating denitrification device 02 through four second nozzles 04-1. The penetrating flue gas flow reaches the central region of the flue gas channel cross-section and collides with the central region of the flue gas channel radially, forming strong turbulence and mixing with the flue gas. Figure 2 and Figure 4 As shown. Simultaneously, under the oxygen-deficient, high-temperature environment inside the penetrating denitrification unit 02, the following three main physicochemical reactions occur: ① The volatiles in the pulverized coal undergo pyrolysis and gasification to produce reducing gases such as CO, which in turn reduce the NO in the flue gas 06. X ① It is reduced to harmless nitrogen gas; ② Water vapor reacts with fixed carbon in pulverized coal to produce H2 and CO gas, which in turn reduces NO in the flue gas. X ③ During the pyrolysis and gasification process of pulverized coal, most of the volatile nitrogen and some of the coke nitrogen in the pulverized coal are released into the gas phase, and under a strong reducing atmosphere, most of them are converted into harmless nitrogen. Furthermore, all the final products of the above reactions enter the rotary denitrification unit 01 through a connected common flue.

[0074] The main chemical reactions occurring in the 02 permeation-type denitrification unit are as follows:

[0075] C + O₂ → CO₂ + Q (exothermic reaction)

[0076] 2C + O₂ → 2CO + Q (exothermic reaction)

[0077] C + H₂O(g) → CO + H₂ - Q (Water-gas reaction, endothermic reaction)

[0078] 2CO + 2NO → N₂ + 2CO₂ (Denitrification reaction)

[0079] 2H₂ + 2NO → N₂ + 2H₂O (Denitrification reaction).

[0080] (2) Flue gas from the penetrating denitrification device 02 (temperature approximately 900℃~1200℃, O2 concentration approximately <1.5%) enters the rotary denitrification device 01. It then enters the rotary denitrification device 01 through two first nozzles 03-1. The mixture of tailings coal powder and water vapor (of which tailings coal powder accounts for approximately 70% of the total tailings coal powder) forms a gas-solid two-phase rotating fluidized bed, such as... Figure 2 and Figure 3As shown. Within this rotating flow field, the residence time of pulverized coal and water vapor is prolonged, and the mixing of pulverized coal and water vapor in the rising flue gas edge region is more thorough; simultaneously, under the oxygen-deficient high-temperature environment inside the rotary denitrification device 01, the following physicochemical reactions occur simultaneously: ① The volatiles in the pulverized coal undergo pyrolysis and gasification to produce reducing gases such as CO, which in turn remove NO from the flue gas inside device 01. X ① It is reduced to harmless nitrogen gas; ② Water vapor reacts with fixed carbon in pulverized coal to produce water gas, generating H2 gas and CO gas, which in turn removes NO from the flue gas in device 01. X ③ During the pyrolysis and gasification process of pulverized coal, most of the volatile nitrogen and some coke nitrogen in the pulverized coal are released into the gas phase, and under a strong reducing atmosphere, most of them are converted into harmless nitrogen gas; that is to say, most of the fuel-type NO produced by the pulverized coal, which accounts for about 70% of the total amount of tail coal pulverized coal, during the pyrolysis and gasification process is converted into harmless nitrogen gas. X The nitrogen gas is reduced to harmless nitrogen by reducing gases such as H2 and CO. Furthermore, all the final products of the above reactions enter the decomposition furnace 12 through the connected common flue and the decomposition furnace cone 13.

[0081] The main chemical reactions occurring in the rotary denitrification unit 01 are as follows:

[0082] 2C + O₂ → 2CO + Q (exothermic reaction)

[0083] C + H₂O(G) → CO + H₂ - Q (Water-gas reaction, endothermic reaction)

[0084] 2CO + 2NO → N₂ + 2CO₂ (Denitrification reaction)

[0085] 2H₂ + 2NO → N₂ + 2H₂O (Denitrification reaction).

[0086] (3) The rising flue gas from the rotary denitrification unit 01 (the temperature of which is usually controlled within the range of 900℃ to 1200℃) enters the decomposition furnace 12. The rising flue gas contains H2 gas, CO gas, CO2 gas, N2 gas, coke, semi-coke, ash, and a small amount of unreacted coal powder, etc. After encountering tertiary air in the decomposition furnace 12, it is re-burned to complete the decomposition of calcium carbonate.

[0087] Taking a clinker production line with a designed output of 5,000 tons / day as an example, if the denitrification system and method of this embodiment are fully adopted, the NO at the decomposition furnace outlet will be reduced. X The concentration level, without the use of any other denitrification technologies, is approximately 150 mg / Nm³. 3 The following NO levels are significantly lower than those of other denitrification technologies. X Content level (in most cases ≥400mg / Nm) 3 Typically 400 mg / Nm3 ~600mg / Nm 3 NO here X At the specified NO content level, when using SNCR denitrification technology in combination, while meeting the NO content requirement... X Emissions <50mg / Nm 3 Under the given conditions, the theoretical dosage of SNCR denitrification ammonia water (20% concentration) is approximately <1 kg / ton of clinker.

[0088] Using the denitrification system and method of this invention, under temperature conditions of around 1000℃, compared to CO gas of the same concentration, H2 is more effective at reducing NO. X The reduction efficiency of CO to NO is X The efficiency is 3 to 4 times higher; therefore, a steam nozzle is added to the nozzle of the system of the present invention, so that the steam sprayed from the nozzle can establish a water-gas chemical reaction system with the fixed carbon in the coal powder. The reaction products of the reaction system not only increase the concentration of CO gas, but more importantly, they also significantly increase the concentration of H2 gas, thereby improving the denitrification efficiency of the system.

[0089] Furthermore, in both the rotary denitrification device and the through-type denitrification device described above, the physicochemical processes such as pyrolysis and gasification of pulverized coal volatiles, water-gas reaction, and denitrification reaction all require additional heat to continue. In this invention, the continuous, stable, and sufficient heat carried by the secondary flue gas, generated by the complete combustion of coal at the rotary kiln head, is cleverly utilized as the heat source for the aforementioned physicochemical reactions, thereby fully ensuring their progress.

[0090] Furthermore, by adjusting the amount of water vapor injected into the rotary denitrification device and the through-type denitrification device, the reaction intensity of the water-gas reaction in the above devices can be controlled, thereby ensuring that the temperature inside the rotary denitrification device and the through-type denitrification device is always within a reasonable range.

[0091] Furthermore, if other denitrification technologies have already been adopted in the existing clinker production system, or if the nitrogen content of the pulverized coal is low, causing the existing system to have low NO content, X When overall emission levels are low, rotary or through-type denitrification units can be added separately to achieve the most cost-effective NO reduction. X Denitrification methods that comply with emission standards.

[0092] Furthermore, the spatial order of the rotary denitrification device and the penetrating denitrification device can be changed according to the spatial conditions of the original clinker production equipment, and the denitrification effect after the exchange is not significantly different from that before the exchange.

[0093] In addition to generating reducing H2 and CO gases, the water vapor injected into the system and method of this invention plays an important role in regulating the temperature within the system to a reasonable range. By adjusting the amount of water vapor ejected from the first nozzle of the rotary denitrification device 01 and the second nozzle of the penetrating denitrification device 02, the temperature within the rotary denitrification device 01 and the penetrating denitrification device 02 can be regulated. The principle is as follows: In the chemical reactions occurring within the rotary denitrification unit 01 and the through-type denitrification unit 02, the water-gas reaction C + H₂O(G) → CO + H₂ is a strongly endothermic reaction. By adjusting the amount (or molar equivalent) of steam, the probability of the water-gas reaction is adjusted, ensuring that the temperature within the rotary denitrification unit 01 and the through-type denitrification unit 02 is within a reasonable range. This temperature allows the coal powder to form tiny coke or semi-coke particles after gasification, which can then be carried by the flue gas into the decomposition furnace for re-combustion. This avoids the situation where excessively high local temperatures within the system (mainly in the rotary denitrification unit 01) cause the coal powder ash to melt, forming a crust or clump that adheres to the inner wall of the equipment, affecting its normal operation. Specifically, when the amount of steam is increased, the probability of the water-gas reaction increases, more heat is consumed by the endothermic reaction, and the temperature inside the rotary denitrification unit 01 and the through-type denitrification unit 02 decreases; conversely, the temperature increases. This temperature range needs to be set according to the ash melting temperature of the pulverized coal used, and is usually about 900℃~1200℃.

[0094] This invention cleverly incorporates a denitrification device at the location of the existing flue, where there is less cement material, thus minimizing interference with the denitrification reaction and resulting in better denitrification performance. When used in conjunction with SNCR denitrification technology, the denitrification system and method of this invention can meet the ultra-low emission environmental protection requirements for the cement production industry outlined in the aforementioned "Opinions."

[0095] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered as part of the present invention.

Claims

1. A system for denitrifying cement kiln flue gas, characterized in that, It includes a rotary denitrification device (01) and a penetrating denitrification device (02) that are interconnected and located in the rising flue (15); The rotary denitrification device (01) includes a hollow, funnel-shaped cylinder (16). The cylinder wall of the cylinder (16) is equipped with a number of first nozzles (03-1) for spraying tailings and water vapor into the inner cavity of the cylinder (16). All first nozzles (03-1) are deflected to the same side at the same angle and are integrated nozzles that can spray coal powder and water vapor simultaneously and separately. The penetrating denitrification device (02) includes a pipe body (17) and multiple second nozzles (04-1) installed on the side wall of the pipe body (17) for spraying tailings and water vapor into the inner cavity of the pipe body (17); the second nozzles (04-1) face the central axis of the pipe body (17) and are integrated nozzles that can spray coal powder and water vapor simultaneously and separately. Preferably, the weight ratio of pulverized coal ejected from the second nozzle (04-1) and the first nozzle (03-1) is approximately (20%-30%): (70%-80%).

2. The system according to claim 1, characterized in that, The rotary denitrification device (01) and the penetrating denitrification device (02) are installed on the rising flue (15) from bottom to top or from top to bottom; when installed from top to bottom, the upper part of the cylinder (16) of the rotary denitrification device (01) is connected to the cone part (13) of the decomposition furnace, and the lower part of the tube (17) of the penetrating denitrification device (02) is connected to the smoke chamber (14).

3. The system according to claim 1, characterized in that, The cylinder (16) of the rotary denitrification device (01) and the tube (17) of the penetrating denitrification device (02) are coaxially arranged or not coaxially arranged; Optionally, the first nozzle (03-1) and the second nozzle (04-1) are respectively arranged in the horizontal direction, or at an angle to the horizontal direction.

4. The system according to claim 1, characterized in that, The angle at which the first nozzle (03-1) deflects to the same side is the angle between the nozzle axis and the tangent of the cylinder circumference at the nozzle position, and the angle does not exceed 75°.

5. The system according to any one of claims 1-4, characterized in that, The first nozzle (03-1) and the second nozzle (04-1) are formed by coaxially mounting the pulverized coal conveying pipe (311) and the steam conveying pipe (312), respectively, or the pulverized coal conveying pipe (311) and the steam conveying pipe (312) are each independently mounted in a main conveying pipe (31).

6. A cement kiln production system, comprising a rotary kiln (11), a decomposition furnace (12), and an ascending flue (15) connecting the rotary kiln (11) and the decomposition furnace (12), characterized in that, It also includes a flue gas denitrification device located at the rising flue (15), the flue gas denitrification device being the system described in any one of claims 1-5, and the decomposition furnace (12) is not provided with a tail coal inlet (08).

7. A method for denitrifying cement kiln flue gas, characterized in that, The denitrification of cement kiln flue gas using the system described in any one of claims 1-5 is specifically as follows: The first nozzle of the rotary denitrification device introduces pulverized coal and water vapor into the cylinder, and generates a rotating airflow field in the cylinder. Under the high temperature and oxygen-deficient conditions provided by the secondary flue gas entering the rotary denitrification device, the fixed carbon in the pulverized coal and water vapor undergo a water-gas reaction to produce reducing gases (H2 and CO, etc.). At the same time, the volatiles in the pulverized coal undergo pyrolysis and gasification to produce reducing gases. The reducing gases together reduce the nitrogen oxides from the secondary flue gas and the fuel-type nitrogen oxides generated by the pulverized coal itself in the rotary denitrification device to nitrogen. The second nozzle of the penetrating denitrification device introduces pulverized coal and water vapor into the tube. Under the high temperature and oxygen-deficient conditions provided by the flue gas entering the penetrating denitrification device, the fixed carbon in the pulverized coal and water vapor undergo a water-gas reaction to produce reducing gases (H2 and CO, etc.). At the same time, the volatiles in the pulverized coal undergo pyrolysis and gasification to produce reducing gases (CO, etc.), so as to reduce the nitrogen oxides from the flue gas and the fuel-type nitrogen oxides generated by the pulverized coal itself in the penetrating denitrification device into nitrogen. The pulverized coal in the first and second nozzles both came from the tail coal conveying pipeline of the original cement production system. Preferably, the mass of pulverized coal introduced into the pipe of the penetrating denitrification device by the second nozzle does not exceed 50% of the total mass of tailings.

8. A method for controlling the temperature of flue gas in a cement kiln, characterized in that, In the rotary denitrification device (01) and the through-type denitrification device (02), the water-gas reaction (strong endothermic reaction) process is controlled by controlling the amount of water vapor, thereby controlling the temperature in the two denitrification devices to be within a set range, typically about 900℃ to 1200℃.

9. A method for denitrifying cement kiln flue gas, characterized in that, The following operations are included: simultaneously introducing pulverized coal and steam into the flue at two positions above and below the rising flue (15) to denitrify the cement kiln flue gas; The coal powder and water vapor introduced at one of the locations enter at high speed along the tangential off-center direction of the inner wall of the flue, forming a gas-solid two-phase rotating airflow field. The high-temperature flue gas entering this rotating airflow field provides high-temperature and oxygen-deficient conditions for the coal powder and water vapor, causing the fixed carbon in the coal powder and water vapor to undergo a water-gas reaction to produce reducing gases (H2 and CO, etc.). At the same time, the coal powder is also pyrolyzed and gasified to produce reducing gases (CO, etc.), so as to reduce the nitrogen oxides in the flue gas and the fuel-type nitrogen oxides produced by the coal powder itself into nitrogen. The pulverized coal and water vapor introduced from another location enter radially along the flue, allowing the pulverized coal and water vapor to penetrate the flue gas flow field of the rising flue and reach the central region of the flue gas channel cross section. The flue gas provides high-temperature and oxygen-deficient conditions for the pulverized coal and water vapor, causing the fixed carbon in the pulverized coal and water vapor to undergo a water-gas reaction to produce reducing gases (H2 and CO, etc.). At the same time, the pulverized coal is also pyrolyzed and gasified to produce reducing gases, so as to reduce the nitrogen oxides in the flue gas and the fuel-type nitrogen oxides produced by the pulverized coal itself into nitrogen. The flue gas is secondary air flue gas from the smoke chamber or rising flue gas after being introduced by pulverized coal and water vapor; Preferably, the mass of pulverized coal in direct contact with the secondary flue gas does not exceed 50% of the total mass of tailings.

10. A cement production process, comprising a method for producing cement clinker using a rotary kiln and a method for thermally decomposing calcium carbonate in cement raw meal using a decomposition furnace, characterized in that, It also includes the method described in any one of claims 7-9, wherein the fuel for the thermal decomposition of calcium carbonate in cement raw materials in the decomposition furnace is entirely derived from the denitrified flue gas obtained by the method described in claim 7 or 9; Preferably, the rising flue gas after denitrification enters the decomposition furnace, mixes with tertiary air, and is re-burned to decompose calcium carbonate.

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