A system and method for reducing nitrogen oxide emissions from a cement kiln

Abstract

The application discloses a system and method for reducing nitrogen oxide emission of a cement kiln. The system comprises, in sequence along the flue gas flow direction, a rotary kiln, a decomposing furnace, a six-stage cyclone preheater, an SCR denitration reactor, a waste heat boiler and a high-temperature fan. The SCR denitration reactor integrates a zigzag flue gas passage composed of multiple stages of baffles, and is provided with a dust removal filter, a quenching heat exchanger, a nitrogen oxide concentration detection device, an ammonia injection grid device and an SCR catalyst layer along the passage. The application recovers heat in multiple stages for deep heat recovery and preliminary cooling, combines efficient dust removal and precise quenching technology, processes the flue gas to a low dust concentration and an optimal reaction temperature, dynamically adjusts ammonia injection based on real-time infrared detection data, realizes accurate mixing of ammonia and nitrogen and efficient catalytic reduction, and has high system integration, a denitration efficiency of more than 90%, low ammonia escape, and is especially suitable for ultra-low emission treatment of cement kiln flue gas with high dust and complex components.

Description

Technical Field

[0001] This invention relates to the field of environmental protection technology in cement production, specifically to a system and method for reducing nitrogen oxide emissions from cement kilns. Background Technology

[0002] Cement production is a vital basic industry of the national economy, but its production process, especially the high-temperature calcination stage in rotary kilns, generates large amounts of nitrogen oxides (NOx), one of the major air pollutants. With increasingly stringent environmental protection requirements, effectively controlling NOx emissions from cement kilns has become an urgent problem for the industry. Selective catalytic reduction (SCR) technology is currently one of the most widely used and efficient flue gas denitrification technologies. Its principle is to inject a reducing agent (such as ammonia) into the flue gas under the action of a catalyst, reducing NOx to harmless nitrogen and water. However, directly applying SCR technology to cement kiln exhaust gas treatment faces many challenges: high dust concentration: the dust concentration in cement kiln exhaust gas is extremely high, reaching up to 80 g / Nm³. 3 The above points highlight several issues: High dust levels can clog, wear down, and poison SCR catalysts, severely shortening their lifespan and significantly increasing operating costs. Complex flue gas composition: Alkali metals, heavy metals, and other substances in the flue gas can poison and deactivate the catalyst. Temperature window limitations: Common SCR catalysts have their optimal reaction temperature range. However, the flue gas temperature at the outlet of the cement kiln preheater fluctuates significantly, potentially exceeding this range, leading to decreased denitrification efficiency or increased ammonia slip. Existing cement kiln denitrification technologies, such as low-NOx burners and staged combustion, while able to reduce the original NOx concentration to some extent, struggle to meet the latest ultra-low emission standards (e.g., below 50 mg / Nm³). 3 While conventional "high-temperature, high-dust" SCR (Self-Determination Catalyst) setups can utilize the existing temperature of the flue gas, they offer insufficient protection for the catalyst and suffer from poor system reliability. Therefore, developing a system and method that adapts to the characteristics of cement kiln flue gas, effectively protects the catalyst, and achieves stable and efficient denitrification is crucial. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a system and method for reducing nitrogen oxide emissions from cement kilns that has a reasonable system layout, can efficiently remove dust, accurately control temperature, and achieve precise mixing and reaction of ammonia and nitrogen.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a system for reducing nitrogen oxide emissions from cement kilns, comprising a rotary kiln, a decomposer, a preheater, an SCR denitrification reactor, a waste heat boiler, and a high-temperature fan arranged sequentially along the flue gas flow direction. The preheater employs a six-stage cyclone preheater. Compared to a traditional five-stage preheater, adding an extra stage further reduces the flue gas temperature at the preheater outlet, achieving a gradient reduction in flue gas temperature and more efficient heat recovery, providing a relatively stable flue gas condition closer to the optimal reaction temperature for subsequent SCR denitrification. The SCR denitrification reactor includes a vertical shell with a tortuous flue gas channel composed of multi-stage baffles. Within this channel, arranged sequentially along the flue gas flow direction, are a dust filter for deep filtration of dust in the flue gas, reducing its concentration to a level that the SCR catalyst can tolerate long-term (e.g., below 50 mg / Nm³). 3 The quench heat exchanger is used to rapidly and precisely cool the flue gas after dust removal to the optimal temperature (around 300°C) required for the denitrification reaction. An ammonia injection grid device is installed at the bottom of the shell to inject ammonia into the purified and cooled flue gas. A nitrogen oxide concentration detection device is installed above the ammonia injection grid device to monitor the NOx concentration in the flue gas in real time, providing data support for precise ammonia injection. An SCR catalyst layer is located at the bottom of the shell, where the final denitrification reduction reaction takes place.

[0005] Furthermore, the tortuous flue gas passage is achieved through the following baffle structure: First baffle: inclinedly positioned at the top of the shell, its high end connects to one side wall of the shell to form an inclined first flue, which communicates with the flue gas inlet on the shell. This design utilizes the initial change in airflow direction to achieve preliminary settling of coarse dust particles. Second baffle: vertically positioned below the low end of the first baffle, forming a second vertical flue between it and the opposite side wall of the shell. Third baffle: inclinedly positioned below the second vertical flue, used to receive the settled dust and guide the flue gas direction. Fourth baffle: vertically positioned at the high end of the third baffle, forming a fourth vertical flue between it and the other side wall of the shell. The quench heat exchanger is then located within this vertical flue, facilitating uniform heat exchange.

[0006] Furthermore, the nitrogen oxide concentration detection device is an online gas analyzer located below the third partition. It includes multiple infrared emitters and receivers positioned opposite each other on both sides of the housing. The infrared emitters and receivers are sealed within a first protective cover and a second protective cover, respectively. Light-transmitting holes are opened on the side walls of the housing, and light-transmitting plates are installed. This design effectively reduces interference from high-dust environments on optical measurements, enabling online, accurate, and real-time measurement of NOx concentration.

[0007] Furthermore, the quench heat exchanger includes horizontally arranged upper and lower positioning plates, forming a sealed cooling chamber between them, and connected to a coolant circulation pipeline. Multiple heat exchange tubes for supplying flue gas vertically penetrate the cooling chamber. The flue gas flows inside the tubes, while the coolant flows outside the tubes within the chamber, achieving efficient heat exchange through the tube walls and realizing precise cooling of the flue gas.

[0008] Furthermore, the dust filter is disposed within a third vertical flue formed by the second, third, and fourth partitions. It comprises a filter block with several vertical air inlet channels at its bottom and several vertical air outlet channels at its top, with the inlet and outlet channels staggered. Flue gas must pass through the sidewalls with micropores between adjacent channels to flow, thereby achieving forced filtration and deep dust removal.

[0009] Furthermore, a purge pipe is installed on the inner wall of the air outlet channel, with the jet nozzles on the side wall of the purge pipe directly facing the filter micropores. A pump connected to the air pipe performs periodic purges, cleaning the dust clogging the micropores and maintaining the filter's long-term stable operating efficiency.

[0010] Furthermore, the ammonia injection grid device includes a horizontal fixed plate with a conical exhaust pipe installed in its center. A gas collection hood is installed above the exhaust pipe, and a multi-ringed ammonia injection main pipe is located at the top of the gas collection hood. First ammonia nozzles and second ammonia nozzles are evenly distributed at the bottom of the main pipe and on the inner wall of the gas collection hood, respectively. This three-dimensional ammonia injection design, combined with the guiding effect of the conical exhaust pipe, ensures that ammonia and flue gas are fully and uniformly mixed before entering the catalyst layer, avoiding localized excess or deficiency of ammonia, thereby improving denitrification efficiency and reducing ammonia escape.

[0011] On the other hand, the present invention provides a method for reducing nitrogen oxide emissions from cement kilns using the above-described system, comprising the following steps: S1: The flue gas from the rotary kiln tail is introduced into the six-stage cyclone preheater for multi-stage heat exchange. The flue gas temperature is reduced to below 320°C through gradient heat exchange, and the heat is recovered in stages. S2: The cooled flue gas enters the tortuous flue gas channel composed of multi-stage baffles through the flue gas inlet of the SCR denitrification reactor. In the inclined first flue, the initial separation of coarse dust particles is achieved by changing the airflow direction and gravity settling. S3: The flue gas is guided through the staggered inlet and outlet channels of the dust collector filter, forcing the flue gas to penetrate the filter micropores for deep dust removal, reducing the dust concentration from the initial 80 mg / Nm³. 3 The above decreased to below 50 mg / Nm 3 Meanwhile, high-pressure gas is periodically sprayed through the purge pipe integrated in the air outlet channel to clean the filter micropores in reverse, preventing clogging and maintaining filtration efficiency. S4: The flue gas after deep dust removal enters the fourth vertical flue, and through the heat exchange tubes set vertically in the rapid cooling heat exchanger, it undergoes efficient heat exchange with the circulating coolant in the cooling chamber, so as to precisely control the flue gas temperature at the optimal temperature window of denitrification reaction of about 300℃. S5: An online gas analyzer is used to monitor the concentration of nitrogen oxides in the flue gas after dust removal and cooling in real time. Through the relatively set infrared transmitter and receiver, and with the help of a protective cover and light-transmitting plate structure to reduce dust interference, the online accurate measurement of nitrogen oxide concentration is achieved. S6: Based on the nitrogen oxide concentration data detected in real time in step S5, ammonia gas is injected into the flue gas through the first and second ammonia gas nozzles arranged in a three-dimensional manner in the ammonia injection grid device, and the ammonia gas and flue gas are mixed and evenly distributed in a multi-stage manner by using the gas collection hood and the conical exhaust pipe structure, and the ammonia-nitrogen molar ratio is controlled between 0.8 and 1.0. S7: The uniformly mixed flue gas undergoes a catalytic reduction reaction through the SCR catalyst layer, converting nitrogen oxides into nitrogen and water. The denitrified flue gas then enters the waste heat boiler to recover heat before being discharged by a high-temperature fan.

[0012] Furthermore, in step S6, the amount of ammonia injected is dynamically adjusted based on the real-time nitrogen oxide concentration data detected by the online gas analyzer. The control system calculates the required ammonia volume in real time and adjusts the flow valve on the supply pipe to achieve on-demand ammonia injection, controlling the ammonia-nitrogen molar ratio within the optimal range of 0.85-0.95. This ensures a denitrification efficiency higher than 90% while keeping the ammonia slip concentration below 3 mg / Nm³. 3 .

[0013] Furthermore, in step S5, the online gas analyzer synchronously monitors the changes in dust concentration in the flue gas. When an abnormal increase in dust concentration is detected that exceeds the set threshold, the early warning system is automatically triggered to indicate that the filter is clogged or damaged, and the abnormal time and concentration data are recorded to guide maintenance personnel to conduct targeted inspections and maintenance of the dust filter.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention, through a combined dust removal design of "preliminary settling and deep filtration", especially the unique cross-channel dust removal filter, can effectively reduce the dust concentration to the long-term operating range allowed by the SCR catalyst, greatly extending the catalyst life and reducing operating costs.

[0015] 2. By employing a rapid cooling heat exchanger, this invention can quickly and accurately adjust the flue gas temperature to the optimal activity window of the catalyst, overcoming the problem of flue gas temperature fluctuations and ensuring stable high denitrification efficiency.

[0016] 3. This invention uses high-precision and high-reliability infrared beam detection technology to monitor NOx concentration in real time and dynamically adjust the ammonia injection amount accordingly. Combined with a three-dimensional ammonia injection grid design, it achieves precise matching and uniform mixing of ammonia and nitrogen, significantly improving denitrification efficiency and effectively controlling ammonia escape.

[0017] 4. This invention integrates functions such as dust removal, cooling, detection, ammonia injection, and reaction into a single SCR reactor shell. Through multi-stage baffles, a compact tortuous flow field is formed, resulting in a compact structure and reasonable pressure drop. It is particularly suitable for the renovation and construction of existing cement production lines. Attached Figure Description

[0018] To more clearly illustrate the technical solution of the present invention, the drawings used in the implementation examples will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0019] Figure 1 This is a schematic diagram of the overall process flow of the system in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the internal structure of the SCR denitrification reactor in Embodiment 1 of the present invention; Figure 3 As in Embodiment 1 of the present invention Figure 2 A magnified schematic diagram of the structure at position I. Figure 4 As in Embodiment 1 of the present invention Figure 2 A magnified schematic diagram of the structure at position II in the middle; Figure 5 This is a three-dimensional structural diagram of the dust removal filter according to Embodiment 1 of the present invention; Figure 6 As in Embodiment 1 of the present invention Figure 5 A magnified schematic diagram of the structure at position III in the middle; Figure 7 This is a schematic diagram of the internal structure of the dust filter in Embodiment 1 of the present invention; Figure 8 This is a schematic diagram of the internal structure of the ammonia injection grid device according to Embodiment 1 of the present invention; Figure 9 This is a schematic diagram of the bottom structure of the ammonia injection grid device according to Embodiment 1 of the present invention; Figure 10 This is a three-dimensional structural diagram of the quench heat exchanger according to Embodiment 1 of the present invention; Figure 11 This is a comparison diagram of the implementation effects of Embodiment 1 of the present invention.

[0020] In the diagram: 1-Rotary kiln; 2-Decomposition furnace; 3-Preheater; 4-SCR denitrification reactor; 5-Waste heat boiler; 6-High temperature fan; 41-Shell; 42-Dust filter; 43-Quick cooler heat exchanger; 44-Ammonia injection grid device; 45-Nitrogen oxide concentration detection device; 46-SCR catalyst layer; 400-Flue gas inlet; 401-First flue; 402-Second vertical flue; 403-Third vertical flue; 404-Fourth vertical flue; 411-First baffle; 412-Second baffle; 413-Third baffle; 414-Fourth baffle; 415-Fifth baffle; 421-Filter block; 422-Air inlet channel; 423 - Exhaust channel; 424- Filter micropores; 425- Purge pipe; 426- Jet nozzle; 427- Air pipe; 430- Cooling chamber; 431- Upper positioning plate; 432- Lower positioning plate; 433- Coolant circulation pipeline; 434- Heat exchanger pipe; 441- Fixing plate; 442- Conical exhaust pipe; 443- Gas collection hood; 444- Support pipe; 445- Ammonia injection main pipe; 446- Connecting pipe; 447- First ammonia nozzle; 448- Second ammonia nozzle; 449- Air pipe; 451- Infrared transmitter; 452- Infrared receiver; 453- First protective cover; 454- Second protective cover; 455- Light-transmitting plate; 456- Cold air nozzle. Detailed Implementation

[0021] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings.

[0022] Example 1: Please see Figures 1-10 A system for reducing nitrogen oxide emissions from cement kilns includes a rotary kiln 1, a decomposition furnace 2, a preheater 3, an SCR denitrification reactor 4, a waste heat boiler 5, and a high-temperature fan 6 arranged sequentially along the flue gas flow direction. The preheater 3 is a six-stage cyclone preheater. The SCR denitrification reactor 4 includes a vertical shell 41, inside which is a tortuous flue gas channel composed of multi-stage baffles. Inside the flue gas channel, along the flue gas flow direction, are arranged a dust filter 42 for filtering dust in the flue gas and a quench heat exchanger 43 for cooling the flue gas to the temperature required for the denitrification reaction. At the bottom of the shell is an ammonia injection grid device 44 for injecting ammonia into the purified flue gas. Above the ammonia injection grid device 44 is a nitrogen oxide concentration detection device 45. An SCR catalyst layer 46 is arranged inside the lower end of the shell 41.

[0023] Specifically, rotary kiln 1 is located below decomposition furnace 2. A kiln tail flue is located at the kiln tail of rotary kiln 1, and the top of the kiln tail flue is connected to the bottom of decomposition furnace 2. A grate cooler is located at the kiln head of rotary kiln 1. The decomposition furnace and the grate cooler are connected via a tertiary air duct to introduce hot air for cooling cement clinker into decomposition furnace 2, thereby decomposing the cement raw materials in decomposition furnace 2 and providing oxygen for the re-combustion of unburned pulverized coal and carbon monoxide. Preheaters are located on both sides above the decomposition furnace. Each preheater includes four primary cyclone preheaters (C11A, C12A, C11B, C12B), two secondary cyclone preheaters (C2A, C2B), and two tertiary cyclone preheaters (C3A, C3B) connected sequentially from top to bottom. The system includes two four-stage cyclone preheaters (C4A, C4B), two five-stage cyclone preheaters (C5A, C5B), and two six-stage cyclone preheaters (C6A, C6B). The exhaust port of one of the first-stage cyclone preheaters (C11A, C12A) is located at the top and connected to the inlet of the SCR denitrification reactor 4 via a gas pipeline. The inlet on the side wall of the first-stage cyclone preheater (C11A, C12A) is connected to the outlet at the top of the second-stage cyclone preheater (C2A) via a pipeline. The inlet on the side wall of the second-stage cyclone preheater (C2A) is connected to the outlet at the top of the third-stage cyclone preheater (C3A) via a pipeline. The inlet on the side wall of the third-stage cyclone preheater (C3A) is connected to the fourth-stage cyclone preheater (C4A) via a pipeline. The air outlet at the top of C4A is connected to the air inlet on the side wall of the fourth-stage cyclone preheater (C4A), which is connected to the air outlet at the top of the fifth-stage cyclone preheater (C5A) via a pipe. The air inlet on the side wall of the fifth-stage cyclone preheater (C5A) is connected to the air outlet at the top of the sixth-stage cyclone preheater (C6A) via a pipe. The air inlet on the side wall of the sixth-stage cyclone preheater (C6A) is connected to the air outlet at the top of the decomposition furnace 2 via a pipe. The exhaust ports of the first-stage cyclone preheaters (C11B, C12B) on the other side are located at the top and connected to the air inlet of the SCR denitrification reactor 4 via a gas pipe. The air inlets on the side walls of the first-stage cyclone preheaters (C11B, C12B) are connected to the air outlet at the top of the second-stage cyclone preheater (C2B) via a pipe. Next, the air inlet on the side wall of the secondary cyclone preheater (C2B) is connected to the air outlet at the top of the tertiary cyclone preheater (C3B) via a pipe. The air inlet on the side wall of the tertiary cyclone preheater (C3B) is connected to the air outlet at the top of the quaternary cyclone preheater (C4B) via a pipe. The air inlet on the side wall of the quaternary cyclone preheater (C4B) is connected to the air outlet at the top of the quinary cyclone preheater (C5B) via a pipe. The air inlet on the side wall of the quinary cyclone preheater (C5B) is connected to the air outlet at the top of the septum cyclone preheater (C6B) via a pipe. The air inlet on the side wall of the septum cyclone preheater (C6B) is connected to the air outlet at the top of the decomposition furnace 2 via a pipe. The septum cyclone preheater can further reduce the flue gas outlet temperature and reduce heat loss.The outlet temperature of the sixth-stage preheater can be reduced to below 320℃, which is 40℃ lower than that of the fifth-stage preheater. This can save a large amount of standard coal and reduce carbon emissions every year.

[0024] Specifically, please see Figure 2 A first partition 411 is inclinedly disposed at the top of the housing 41, which is supported and fixed by a frame. Its high end is fixedly connected to one side wall of the housing 41 to form an inclined first flue 401, which communicates with the flue gas inlet 400 disposed on the housing 41. A second partition 412 is vertically fixedly disposed below the low end of the first partition 411, forming a second vertical flue 402 between it and the opposite side wall of the housing 41. A third partition 413 is inclinedly fixedly disposed below the second vertical flue 402 to receive settled dust and guide the flue gas to a different direction. A fourth partition 414 is vertically disposed at the high end of the third partition 413, forming a fourth vertical flue 404 between it and the other side wall of the housing 41. A quench heat exchanger 43 is disposed in the fourth vertical flue 404 to further cool the flue gas and prevent unstable flue gas temperature from affecting the subsequent denitrification reaction.

[0025] Specifically, please refer to Figure 2 , 34. The nitrogen oxide concentration detection device 45 is an online gas analyzer located below the third partition 413. It includes multiple infrared emitting ends 451 and multiple infrared receiving ends 452 arranged horizontally on both sides of the housing 41. The multiple infrared emitting ends 451 are provided with a first protective cover 453 fixedly connected to the housing 41, and the multiple infrared receiving ends 452 are provided with a second protective cover 454 fixedly connected to the housing 41. Each infrared emitting end 451 is fixedly connected to the first protective cover 453, and each infrared receiving end 452 is fixedly connected to the second protective cover 454. Two light-transmitting holes for infrared rays are provided on the two side walls of the housing 41, and a light-transmitting plate 455 is fixedly provided on each light-transmitting hole. Due to the significant temperature difference between the inside and outside of the light-transmitting plate 455, water mist can easily form on its surface, affecting its light transmittance. Therefore, circulating cold air inlets should be installed at the top of both the first protective cover 453 and the second protective cover 454, and circulating cold air outlets should be installed at the bottom, connected to air outlet connectors. These outlet connectors are connected to cold air circulation pipes to allow cold air to circulate and cool. Clean, low-temperature nitrogen is supplied by connecting the outer end of each circulating cold air inlet to a cold air supply pipe, which is connected to the air outlet of the air cooler unit. The inner end of each circulating cold air inlet is connected to a cold air nozzle 456, which is installed at an angle with its nozzle facing the light-transmitting plate. 455. By connecting the circulating cold air outlet to the cold air exhaust pipe, cold air is supplied to the inside of the first protective cover 453 and the second protective cover 454 to first defog the light-transmitting plate 455, preventing fogging of the light-transmitting plate 455 from affecting the light penetration effect of the online gas analyzer. In addition, a fifth partition 415 parallel to the third partition 413 is provided below it. The fifth partition 415 is fixedly connected to the front and rear side walls of the housing 41 and the side wall of the housing 41 on the same side as the infrared receiver 452, so that the flue gas can flow obliquely between the third partition 413 and the fifth partition 415, increasing the uniformity of the flue gas flow and increasing the accuracy of detection.

[0026] In the above embodiments, the infrared gas analyzer is based on the non-dispersive infrared (NDIR) principle. When infrared light of a specific wavelength passes through flue gas, NOx molecules absorb the infrared light of that specific wavelength, and the absorption intensity is proportional to the NOx concentration. By measuring the intensity change of the absorbed infrared light, the NOx concentration can be calculated. The nitrogen oxide concentration detection device 45 is an online gas analyzer based on the non-dispersive infrared (NDIR) principle. It includes an infrared emitter 451 and an infrared receiver 452, which are precisely aligned on mounting bases on both sides of the housing 41 to form a single-optical-path measurement system. The infrared emitter 451 integrates a precision infrared light source and a beam-cutting modulation system to generate modulated infrared light of a specific wavelength. The core of the infrared receiver 452 is a narrow-band optical interference filter and an infrared detector. The filter only allows infrared light of the characteristic absorption band of nitrogen oxide molecules to pass through and blocks light of other interfering wavelengths. When infrared light passes through the gas to be measured in the flue, NOx molecules selectively absorb the light energy at their characteristic wavelengths, resulting in attenuation of the light intensity reaching the receiver. The infrared detector converts the light signal into an electrical signal. The system's built-in microprocessor, based on Lambert-Beer Law, calculates the attenuation of light intensity at a specific wavelength to accurately determine the volume concentration of nitrogen oxides in the flue gas. To cope with the high dust conditions in cement kilns, both the transmitter and receiver are equipped with high-temperature resistant, high-transmittance sapphire light-transmitting plates 455 to ensure long-term stability and accuracy of the measurement. The system controller (such as a PLC or DCS) receives feedback on the flue gas concentration, indicating an increase or decrease in the ammonia injection amount, and converts this into a control signal to adjust the opening of the flow control valve on the ammonia injection header 445, achieving precise and dynamic control of the ammonia injection amount.

[0027] Specifically, please refer to Figure 2 , 10 The rapid cooling heat exchanger 43 includes an upper positioning plate 431 and a lower positioning plate 432 horizontally arranged in the fourth vertical flue 404, forming a closed cooling chamber 430 between them. The cooling chamber 430 is connected to a coolant circulation pipe 433. Multiple flue gases are supplied vertically through the cooling chamber 430 via heat exchange tubes 434. Both ends of the heat exchange tubes 434 are sealed and connected to air holes opened on the upper positioning plate 431 and the lower positioning plate 432, respectively, so that the flue gas in the fourth vertical flue 404 enters the heat exchange tubes 434 through the air holes and exchanges heat with the coolant in the cooling chamber 430, so that the gas is maintained within a suitable range.

[0028] Specifically, please refer to Figure 2The dust filter 42 is disposed within the third vertical flue 403 formed by the second partition 412, the third partition 413, and the fourth partition 414. The dust filter 42 includes a filter block 421. The bottom of the filter block 421 is provided with several vertical air inlet channels 422, and the top is provided with several vertical air outlet channels 423. The air inlet channels 422 and the air outlet channels 423 are staggered with each other. The side wall between two adjacent air inlet channels 422 and air outlet channels 423 is provided with A filter micropore 424 is provided. During the upward process, the gas enters the intake channel 422 and then passes horizontally through the filter micropore 424. After the dust is filtered through the filter micropore 424, the gas exits through the exhaust channel 423 and continues upward. The dust in the intake channel 422 falls back onto the third partition 413. A maintenance port is provided on the side wall of the housing 41 above the third partition 413, and an inspection door is provided in the maintenance port. The dust accumulated on the third partition 413 can be cleaned by opening the inspection door.

[0029] Specifically, please refer to Figure 5 , 6 7. A rectangular groove is provided on the inner wall of the air outlet channel 423. A vertically placed purge pipe 425 is embedded in the groove. The purge pipe 425 has a rectangular cross-section and is fixedly embedded in the purge pipe 425. An air jet head 426 is provided on the outer wall of the purge pipe 425. The air jet head 426 is horizontally opposite to the filter micropores 424. The purge pipe 425 is connected to the air pump through the air pipe 427. The solenoid valve on the air pipe 427 controls the blowing of high-pressure gas into the filter micropores 424 to periodically unclog the filter micropores 424.

[0030] Specifically, please refer to Figure 2 , 8 9. The ammonia injection grid device 44 includes a fixing plate 441, which is horizontally set on the inner wall of the housing 41. A mounting hole is provided in the middle of the fixing plate 441, and a conical exhaust pipe 442 is vertically arranged in the mounting hole. A gas collection hood 443 is arranged above the exhaust pipe 442, and the upper part of the exhaust pipe 442 extends into the gas collection hood 443. The gas collection hood 443 is connected and fixed to the inner wall of the housing 41 by a support pipe 444. Multiple annular ammonia injection headers 445 are concentrically arranged at the top of the gas collection hood 443, and the ammonia injection headers 445 are connected to each other by a connecting pipe 446. Multiple first ammonia nozzles 4... 47 are evenly distributed at the bottom of the ammonia injection main pipe 445. Multiple second ammonia nozzles 448 are evenly arranged on the inner side wall of the gas collection hood 443. The second ammonia nozzles 448 are connected to the ammonia injection main pipe 445 through gas pipes 449. The ammonia injection main pipe 445 is connected to the liquid supply pipe 440. The liquid supply pipe 440 is sleeved inside the support pipe 444. One end passes through the side wall of the gas collection hood 443 and is connected to the ammonia injection main pipe 445. The other end passes through the side wall of the shell 41 and is connected to the ammonia storage tank outside the shell 41. The supply of ammonia is controlled by installing a flow meter and a flow valve on the liquid supply pipe 440.

[0031] Based on the above-mentioned system for reducing nitrogen oxide emissions from cement kilns, the present invention also discloses a method for reducing nitrogen oxide emissions from cement kilns, comprising the following steps: S1: The flue gas from the tail of rotary kiln 1 is introduced into a six-stage cyclone preheater for multi-stage heat exchange. The flue gas temperature is reduced to below 320℃ through gradient heat exchange, and the heat is recovered and utilized in stages. S2: The cooled flue gas enters the tortuous flue gas channel composed of multi-stage baffles through the flue gas inlet of the SCR denitrification reactor. In the inclined first flue, the initial separation of coarse dust particles is achieved by changing the airflow direction and gravity settling. S3: Guide the flue gas through the staggered inlet and outlet channels of the dust collector filter, forcing the flue gas to penetrate the filter micropores for deep dust removal, reducing the dust concentration from the initial 80mg / Nm³. 3 The above decreased to below 50 mg / Nm 3 Meanwhile, high-pressure gas is periodically sprayed through the purge pipe integrated in the air outlet channel to clean the filter micropores in reverse, preventing clogging and maintaining filtration efficiency. S4: The flue gas after deep dust removal enters the fourth vertical flue, and through the heat exchange tubes set vertically in the rapid cooling heat exchanger, it undergoes efficient heat exchange with the circulating coolant in the cooling chamber, so as to precisely control the flue gas temperature at the optimal temperature window of denitrification reaction of about 300℃. S5: An online gas analyzer is used to monitor the concentration of nitrogen oxides in the flue gas after dust removal and cooling in real time. Through the relatively set infrared transmitter and receiver, and with the help of a protective cover and light-transmitting plate structure to reduce dust interference, the online accurate measurement of nitrogen oxide concentration is achieved. S6: Based on the nitrogen oxide concentration data detected in real time in step S5, ammonia gas is injected into the flue gas through the first and second ammonia gas nozzles arranged in a three-dimensional manner in the ammonia injection grid device, and the ammonia gas and flue gas are mixed and evenly distributed in a multi-stage manner by using the gas collection hood and the conical exhaust pipe structure, and the ammonia-nitrogen molar ratio is controlled between 0.8 and 1.0. S7: The uniformly mixed flue gas undergoes a catalytic reduction reaction through the SCR catalyst layer, converting nitrogen oxides into nitrogen and water. The denitrified flue gas then enters the waste heat boiler to recover heat before being discharged by a high-temperature fan.

[0032] In step S6, the amount of ammonia injected is dynamically adjusted based on the real-time nitrogen oxide concentration data detected by the online gas analyzer. The control system calculates the required ammonia volume in real time and adjusts the flow valve on the supply pipe to achieve on-demand ammonia injection, controlling the ammonia-nitrogen molar ratio within the optimal range of 0.85-0.95. This ensures a denitrification efficiency higher than 90% while keeping the ammonia slip concentration below 3 mg / Nm³. 3 .

[0033] In step S5, the online gas analyzer synchronously monitors the changes in dust concentration in the flue gas. When the dust concentration is detected to rise abnormally and exceed the set threshold, the early warning system is automatically triggered to indicate that the filter is clogged or damaged, and the abnormal time and concentration data are recorded to guide maintenance personnel to conduct targeted inspections and maintenance of the dust filter.

[0034] The system of this invention, along the flue gas flow direction, sequentially includes a rotary kiln 1, a decomposition furnace 2, a six-stage cyclone preheater 3, an SCR denitrification reactor 4, a waste heat boiler 5, and a high-temperature blower 6. After completing the task of preheating the raw materials, the temperature of the kiln tail flue gas drops to below approximately 320°C and is drawn out from the outlet of the preheater 3, entering the SCR denitrification reactor 4. The flue gas enters the shell 41 from the inlet 400. It first impacts the inclined first baffle 411, forming an inclined first flue 401. This first change in airflow direction causes some coarse dust to initially settle under gravity. The flue gas then deflects into the second vertical flue 402 and flows downwards.

[0035] Furthermore, the flue gas of the present invention then enters a third vertical flue 403 formed by a second partition 412, a third partition 413, and a fourth partition 414, where a dust filter 42 is installed. Figure 4 and Figure 5 As shown, flue gas enters the filter block 421 through multiple inlet channels 422 at the bottom. Because the outlet channel 423 at the top is misaligned with the inlet channels 422, the flue gas cannot rise directly and must penetrate the sidewall covered with filter micropores 424. Dust is trapped within the inlet channels 422, and the purified flue gas enters the outlet channel 423 and flows upward. A purge pipe 425 embedded in the inner wall of the outlet channel 423 periodically sprays high-pressure gas to purge the filter micropores 424 in the reverse direction, shaking the accumulated dust into the bottom ash hopper, achieving self-cleaning. The purge pipe 425 is a closed pipe at the bottom, and its upper end is connected to an air pump outside the housing 41 via a gas pipe. A solenoid valve should be installed on the gas pipe to control the air pump's supply of high-pressure gas.

[0036] In this embodiment of the invention, the temperature of the flue gas after deep dust removal is still relatively high, requiring cooling. After being guided and diverted by the third baffle 413, the flue gas enters the fourth vertical flue 404. Figure 2 and Figure 10As shown, the quench heat exchanger 43 is installed here. Flue gas enters the vertical heat exchange tube 434, and the coolant circulates in the cooling chamber 430 formed by the upper positioning plate 431 and the lower positioning plate 432. The cooling chamber 430 is provided with a circulating liquid inlet and a circulating liquid outlet on its side wall. The circulating liquid inlet is connected to the circulating liquid storage tank through a pipe and a pump to supply circulating coolant, and the circulating liquid outlet is connected to the circulating liquid storage tank to return the circulating coolant, realizing the recycling of the circulating coolant. The flue gas undergoes efficient heat exchange with the heat exchange tube 434 through the tube wall, and the flue gas temperature is precisely controlled at about 300°C.

[0037] In this embodiment of the invention, the cooled flue gas continues to flow downwards, and its NOx concentration needs to be detected before it enters the ammonia injection area. For example... Figure 2 and Figure 3 As shown, the nitrogen oxide concentration detection device 45 is installed below the third partition 413. Its online gas analyzer emits infrared light of a specific wavelength through the flue via an infrared emitter 451 and an infrared receiver 452 positioned opposite each other. NOx gas absorbs the light of that specific wavelength, and the NOx concentration can be calculated by measuring the degree of light intensity attenuation. The laser is sealed within a first protective cover 453 and a second protective cover 454, and a light-transmitting plate 455 protects the optical window from dust contamination, ensuring the accuracy and reliability of the measurement.

[0038] During the implementation of this invention, after detecting the NOx concentration signal, the control system calculates the required ammonia injection amount. The ammonia injection grid device 44 then begins operation. Ammonia gas is delivered through the ammonia injection header 445 and ejected from the first ammonia nozzle 447 at the bottom and the second ammonia nozzle 448 on the side, respectively, where it is initially mixed with the downward-flowing flue gas within the gas collection hood 443. The mixed gas flow then passes through the conical exhaust pipe 442 for rectification and diffusion, achieving an extremely uniform distribution of ammonia gas in the flue gas.

[0039] Finally, the uniformly mixed gas enters the bottom SCR catalyst layer 46. An inspection port with a maintenance door is provided on the side wall of the shell 41 corresponding to the catalyst layer 46. Opening the maintenance door facilitates catalyst replacement every three years. The flue gas undergoes a reduction reaction on the catalyst surface, converting NOx into N. The purified flue gas then enters the waste heat boiler 5 to recover some heat, and is finally drawn to the chimney by the high-temperature fan 6 for emission.

[0040] The method described in this invention achieves efficient and stable denitrification of high-dust and high-temperature flue gas from cement kilns through the synergistic effect of the aforementioned systems, with the final emission concentration stably controlled at 50 mg / Nm³. 3 The following meet ultra-low emission requirements and offer significant environmental and economic benefits. See also Figure 11Compared to traditional SNCR technology, this invention achieves a qualitative leap in denitrification efficiency, improving it from failing to meet standards to achieving stable ultra-low emission levels, completely solving the fundamental problem that SNCR technology cannot meet the latest environmental standards. Compared to conventional high-temperature, high-dust SCR technology, this invention solves the catalyst lifespan problem. Through a "preliminary settling and deep filtration" dust removal system, it greatly reduces the scouring and poisoning effects of dust on the catalyst, extending the catalyst lifespan by more than double and significantly reducing the industry's highest maintenance costs. Precise control of flue gas temperature is achieved through a quench heat exchanger, ensuring the catalyst always operates within its optimal activity window. Precise matching and uniform mixing of ammonia and nitrogen are achieved through a three-dimensional ammonia injection grid and real-time concentration feedback, thereby achieving higher denitrification efficiency while keeping ammonia escape at extremely low levels.

[0041] This invention achieves significant and synergistic progress in denitrification efficiency, stability, operating costs, and long-term reliability through the synergistic effect of technologies such as a six-stage preheater, integrated dust removal, precise rapid cooling, and intelligent ammonia injection. It provides the best technical path for the cement industry to achieve economical and reliable ultra-low emissions.

[0042] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope of the invention is indicated by the claims.

[0043] It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention.

Claims

1. A system for reducing nitrogen oxide emissions from cement kilns, comprising a rotary kiln (1), a decomposition furnace (2), a preheater (3), an SCR denitrification reactor (4), a waste heat boiler (5), and a high-temperature fan (6) arranged sequentially along the flue gas flow direction, characterized in that: The preheater (3) is a six-stage cyclone preheater; the SCR denitrification reactor (4) includes a vertical shell (41), and the shell (41) is provided with a tortuous flue gas channel composed of multi-stage baffles. The flue gas channel is provided with a dust filter (42) for filtering dust in the flue gas and a quench heat exchanger (43) for cooling the flue gas to the temperature required for the denitrification reaction in sequence along the flue gas flow direction. The bottom of the shell (41) is provided with an ammonia injection grid device (44) for injecting ammonia into the purified flue gas. A nitrogen oxide concentration detection device (45) is provided above the ammonia injection grid device (44). An SCR catalyst layer (46) is provided at the lower end of the shell (41). A first partition (411) is inclinedly disposed at the top of the shell (41), and its high end is connected to one side wall of the shell (41) to form an inclined first flue (401), which communicates with the flue inlet (400) provided on the shell (41); a second partition (412) is vertically disposed below the low end of the first partition (411), and forms a second vertical flue (402) between it and the opposite side wall of the shell (41); a third partition (413) is inclinedly disposed below the second vertical flue (402) for receiving settled dust and guiding flue gas to a different direction; a fourth partition (414) is vertically disposed at the high end of the third partition (413), and forms a fourth vertical flue (404) between it and the other side wall of the shell (41); wherein, the quench heat exchanger (43) is disposed in the fourth vertical flue (404); The nitrogen oxide concentration detection device (45) is an online gas analyzer located below the third partition (413). It includes multiple infrared emitting ends (451) and multiple infrared receiving ends (452) arranged opposite to each other on both sides of the housing (41). The multiple infrared emitting ends (451) are provided with a first protective cover (453) fixedly connected to the housing (41), and the multiple infrared receiving ends (452) are provided with a second protective cover (454) fixedly connected to the housing (41). Each infrared emitting end (451) is fixedly connected to the first protective cover (453), and each infrared receiving end (452) is fixedly connected to the second protective cover (454). Two light-transmitting holes for passing infrared rays are provided on the two side walls of the housing (41), and a light-transmitting plate (455) is provided on each light-transmitting hole. The rapid cooling heat exchanger (43) includes an upper positioning plate (431) and a lower positioning plate (432) horizontally arranged in the fourth vertical flue (404), forming a closed cooling cavity (430) between them. The cooling cavity (430) is connected to a coolant circulation pipeline (433). Multiple flue gas supplies pass vertically through the cooling cavity (430) via heat exchange tubes (434), and both ends of the heat exchange tubes (434) are connected to air holes opened on the upper positioning plate (431) and the lower positioning plate (432) respectively. The dust filter (42) is disposed in the third vertical flue (403) formed by the second partition (412), the third partition (413) and the fourth partition (414). The dust filter (42) includes a filter block (421). The filter block (421) has several vertical air inlet channels (422) at the bottom and several vertical air outlet channels (423) at the top. Each air inlet channel (422) and air outlet channel (423) is staggered. Filter micropores (424) are provided on the side wall between two adjacent air inlet channels (422) and air outlet channels (423). A purge pipe (425) is provided on the inner wall of the air outlet channel (423), and a jet head (426) is provided on the side wall of the purge pipe (425). The jet head (426) is arranged opposite to the filter micropores (424). The purge pipe (425) is connected to the air pump through an air pipe (427). The ammonia spraying grid device (44) includes: a fixing plate (441) horizontally disposed on the inner wall of the housing (41), a mounting hole provided in the middle of the fixing plate (441), a conical exhaust pipe (442) vertically disposed in the mounting hole, a gas collecting hood (443) disposed above the exhaust pipe (442), the upper end of the exhaust pipe extending into the interior of the gas collecting hood (443), the gas collecting hood (443) being connected and fixed to the inner wall of the housing (41) by a support pipe (444), and the gas collecting hood (443) being... Multiple annular ammonia injection main pipes (445) are concentrically arranged at the top of the hood (443). The ammonia injection main pipes (445) are connected to each other by connecting pipes (446). Multiple first ammonia nozzles (447) are evenly distributed at the bottom of the ammonia injection main pipes (445). Multiple second ammonia nozzles (448) are evenly arranged on the inner side wall of the gas collection hood (443). The second ammonia nozzles (448) are connected to the ammonia injection main pipes (445) through gas pipes. The ammonia injection main pipes (445) are connected to the liquid supply pipe.

2. A method for reducing nitrogen oxide emissions from cement kilns using the system as described in claim 1, characterized in that, Includes the following steps: S1: The flue gas from the tail of the rotary kiln (1) is introduced into a six-stage cyclone preheater for multi-stage heat exchange. The flue gas temperature is reduced to below 320℃ through gradient heat exchange, and the heat is recovered in stages. S2: The cooled flue gas enters the tortuous flue gas channel composed of multi-stage baffles through the flue gas inlet of the SCR denitrification reactor (4), and the initial separation of coarse dust particles is achieved in the first flue (401) set at an inclination by changing the airflow direction and gravity settling. S3: The flue gas is guided through the staggered air inlet channel (422) and air outlet channel (423) of the dust filter (42), forcing the flue gas to penetrate the filter micropores (424) for deep dust removal, reducing the dust concentration from the initial 80g / Nm 3 The above decreased to below 50 mg / Nm 3 Meanwhile, high-pressure gas is periodically sprayed through the purge pipe (425) integrated in the air outlet channel (423) to clean the filter micropores (424) in reverse, preventing blockage and maintaining filtration efficiency. S4: The flue gas after deep dust removal enters the fourth vertical flue (404), and through the heat exchange tube (434) set vertically in the rapid cooling heat exchanger (43), it exchanges heat efficiently with the circulating coolant in the cooling chamber (430), and the flue gas temperature is precisely controlled at the optimal temperature window of denitrification reaction of about 300℃. S5: An online gas analyzer is used to monitor the concentration of nitrogen oxides in the flue gas after dust removal and cooling in real time. The concentration of nitrogen oxides is accurately measured online by using an infrared transmitter (451) and an infrared receiver (452) that are set up in opposite directions, and by using a protective cover and a light-transmitting plate (455) to reduce dust interference. S6: Based on the nitrogen oxide concentration data detected in real time in step S5, ammonia gas is injected into the flue gas through the first ammonia gas nozzle (447) and the second ammonia gas nozzle (448) arranged in three dimensions in the ammonia injection grid device (44), and the multi-stage mixing and uniform distribution of ammonia gas and flue gas are achieved by using the structure of the gas collection hood (443) and the conical exhaust pipe (442), and the ammonia-nitrogen molar ratio is controlled between 0.8 and 1.0; S7: The uniformly mixed flue gas passes through the SCR catalyst layer (46) for catalytic reduction reaction, converting nitrogen oxides into nitrogen and water. The denitrified flue gas enters the waste heat boiler (5) to recover heat and is then discharged by the high-temperature fan (6). In step S6, the amount of ammonia injected is dynamically adjusted based on the real-time nitrogen oxide concentration data detected by the online gas analyzer. The control system calculates the required ammonia volume in real time and adjusts the flow valve on the supply pipe to achieve on-demand ammonia injection, controlling the ammonia-nitrogen molar ratio within the optimal range of 0.85-0.

95. This ensures a denitrification efficiency higher than 90% while keeping the ammonia slip concentration below 3 mg / Nm³. 3 ; In step S5, the online gas analyzer synchronously monitors the change in dust concentration in the flue gas. When the dust concentration is detected to rise abnormally and exceed the set threshold, the early warning system is automatically triggered to indicate that the dust filter (42) is blocked or damaged, and the abnormal time and concentration data are recorded to guide maintenance personnel to conduct targeted inspections and maintenance of the dust filter (42).

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