Carbon and ammonia combined denitration method for cement kiln
By setting up reduction denitrification furnaces and decomposition furnaces in the cement production process, and combining carbon-based staged combustion and dual-layer dual-stage selective non-catalytic reduction denitrification technology, the problem of nitrogen oxide emissions in cement production has been solved, achieving ultra-low emissions and stable operation.
Patent Information
- Application Number
- CN202511669688.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-14
- Publication Date
- 2026-01-16
AI Technical Summary
During cement production, the direct emission of nitrogen oxides (NOx) from rotary kilns causes serious environmental pollution. Existing technologies are unable to effectively remove them and there is also the problem of ammonia escape.
A reduction denitrification furnace is installed at the bottom of the decomposition furnace. It adopts carbon-based staged combustion, double-layer double selective non-catalytic reduction denitrification technology and carbon-ammonia combined deep denitrification synergistic control technology. Through the synergistic effect of the reduction denitrification furnace and the decomposition furnace, it achieves efficient reduction of nitrogen oxides and reduces the amount of ammonia water used.
It achieves ultra-low nitrogen oxide emissions, reduces ammonia water usage and lowers the risk of ammonia escape, and ensures the stable operation of the denitrification system.
Smart Images
Figure CN121338522A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of cement production technology, and specifically to a method for combined carbon and ammonia denitrification in cement kilns. Background Technology
[0002] As global attention to environmental protection continues to rise, the cement industry, as a major contributor to carbon and pollutant emissions in the industrial sector, faces extremely severe environmental challenges.
[0003] In simple terms, the cement firing process involves calcining cement raw materials (a mixture of limestone, clay, iron powder, etc. in a specific ratio) at high temperatures, causing a series of physical and chemical reactions that ultimately form hydraulic clinker minerals. This process mainly takes place in a system consisting of a rotary kiln and a decomposition furnace.
[0004] Nitrogen oxides (mainly nitric oxide NO and nitrogen dioxide NO2, collectively known as NOx) generated during cement production are a very important environmental pollutant with multifaceted harms. They not only damage the environment and ecosystems but also directly threaten human health and even affect economic development.
[0005] In the cement production process, nitrogen oxides (NOx) are mainly generated from the high-temperature combustion process, with rotary kilns being the largest source. If the flue gas generated by the rotary kiln is directly emitted, the large amount of nitrogen oxides in the flue gas will cause serious air pollution. Therefore, there is an urgent need for a method to denitrify the nitrogen oxides in the flue gas generated by the rotary kiln in order to reduce environmental pollution. Summary of the Invention
[0006] To address the aforementioned shortcomings of existing technologies, this invention provides a combined carbon and ammonia denitrification method for cement kilns, which removes nitrogen oxides from the flue gas generated by rotary kilns, thereby reducing environmental pollution.
[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:
[0008] A combined carbon-ammonia denitrification method for cement kilns includes a reduction denitrification furnace installed at the bottom of a decomposition furnace, with the lower part of the decomposition furnace connected to the reduction denitrification furnace. The combined carbon-ammonia denitrification method for cement kilns comprises a denitrification method within the reduction denitrification furnace and a denitrification method within the decomposition furnace.
[0009] The denitrification method in the reduction denitrification furnace is as follows: a first proportion of pulverized coal is injected into the reduction denitrification furnace, and all the flue gas from the rotary kiln is introduced into the reduction denitrification furnace. The pulverized coal in the reduction denitrification furnace is pyrolyzed and gasified in an oxygen-deficient environment to produce reducing gas. The nitrogen oxides in the flue gas from the rotary kiln react with the reducing gas produced by the pyrolysis and gasification of the pulverized coal in the reduction denitrification furnace, so that the nitrogen oxides are reduced to nitrogen and then transported upward with the flue gas into the decomposition furnace.
[0010] The denitrification method in the decomposition furnace is as follows: a second proportion of pulverized coal is injected into the decomposition furnace, and tertiary air is introduced at the lower part of the decomposition furnace. Simultaneously, raw material is conveyed into the decomposition furnace from the lower part, and the raw material inlet on the decomposition furnace is located at the tertiary air inlet. The tertiary air introduced into the decomposition furnace provides oxygen. The raw material in the decomposition furnace undergoes pre-decomposition under the action of oxygen and pulverized coal. Nitrogen oxides generated from pulverized coal combustion in the decomposition furnace are reduced using a double-layer, double-stage selective non-catalytic reduction denitrification method.
[0011] Preferably, in the denitrification method within the reduction denitrification furnace:
[0012] A pre-combustion zone and a reduction zone are arranged vertically in the reduction denitrification furnace, with the pre-combustion zone located below the reduction zone. Pulverized coal is injected into the pre-combustion zone of the reduction denitrification furnace, and all the flue gas from the rotary kiln is sent into the reduction zone of the reduction denitrification furnace. The pulverized coal undergoes pyrolysis and gasification in the pre-combustion zone to produce reducing gas. The reducing gas moves upward into the reduction zone and reacts with the nitrogen oxides in the flue gas from the rotary kiln, thereby reducing the nitrogen oxides in the flue gas to nitrogen.
[0013] Preferably, in the denitrification method within the reduction denitrification furnace:
[0014] The flue gas from the rotary kiln is fed into the reduction zone from the upper part, causing the flue gas to move downwards within the reduction zone. The downward-moving flue gas moves in the opposite direction to the reducing gas moving from the pre-combustion zone to the reduction zone. After reaching the reduction zone, the reducing gas comes into contact with the flue gas, and the speed of the reducing gas is greater than the speed of the downward-moving flue gas. This allows the flue gas to move synchronously upwards in the reduction zone under the impetus of the reducing gas.
[0015] Preferably, in the denitrification method within the reduction denitrification furnace:
[0016] The initial contact point between the reducing gas and the flue gas is located at the junction of the reduction zone and the pre-combustion zone, and the upward movement speed of the reducing gas is twice the downward movement speed of the flue gas.
[0017] Preferably, in the denitrification method within the reduction denitrification furnace:
[0018] The reduction zone has a slender structure, and the time for the reducing gas to enter the reduction zone is t1, the time for the reducing gas to leave the reduction zone is t2, and t2-t1>3s.
[0019] Preferably, in the denitrification method within the reduction denitrification furnace:
[0020] 80% of the pulverized coal is injected into the reduction denitrification furnace, and the temperature inside the reduction denitrification furnace is 850-950℃.
[0021] Preferably, in the denitrification furnace denitrification method:
[0022] 20% of the pulverized coal is injected into the decomposition furnace, and oxygen-enriched air is introduced at the connection between the decomposition furnace and the reduction denitrification furnace, wherein the oxygen concentration in the oxygen-enriched air is 28%.
[0023] Preferably, in the denitrification furnace denitrification method:
[0024] The dual-layer, dual-stage selective non-catalytic reduction denitrification method is as follows: a fan-shaped atomizing spray gun is used to spray ammonia water in the upper layer of the decomposition furnace to fully cover the flue gas; a swirl spray gun is used to spray ammonia water in the lower layer of the decomposition furnace to enhance local turbulent mixing; and a dual-stage ammonia injection is formed between the upper and lower ammonia water, with a time interval of 0.5 seconds between the two stages of ammonia injection.
[0025] Preferably, in the denitrification furnace denitrification method:
[0026] The sprayed ammonia droplets have a diameter of 50-100 μm.
[0027] Preferably, in the denitrification furnace denitrification method:
[0028] The concentration of nitrogen oxides in the flue gas at the outlet of the decomposition furnace is detected. When the concentration of nitrogen oxides at the outlet of the decomposition furnace is greater than the standard value, the injection volume of ammonia water from the fan-shaped atomizing spray gun and the swirl spray gun is increased. When the concentration of nitrogen oxides at the outlet of the decomposition furnace is less than the standard value, the injection volume of ammonia water from the fan-shaped atomizing spray gun and the swirl spray gun is decreased.
[0029] Compared with the prior art, the present invention has the following advantages:
[0030] 1. This invention incorporates a reduction denitrification furnace at the bottom of the decomposition furnace. The denitrification process of the flue gas transported from the rotary kiln is primarily concentrated in this furnace, allowing the nitrogen oxide concentration at the furnace outlet to approach or reach zero. Simultaneously, a dual-layer, dual-stage selective non-catalytic reduction denitrification method is employed in the decomposition furnace to reduce the less difficult-to-denitrify nitrogen oxides generated later in the process. This achieves the goal of reducing nitrogen oxide emission concentrations to ultra-low levels while minimizing ammonia usage and ensuring ammonia escape does not exceed limits. Therefore, by dispersing the denitrification process between the reduction denitrification furnace and the decomposition furnace, this solution effectively treats nitrogen oxides, achieving ultra-low emission concentrations. Furthermore, ammonia is only used to treat low-concentration nitrogen oxides within the decomposition furnace, reducing both ammonia usage and ammonia escape.
[0031] 2. This invention studies carbon-based staged combustion technology in reduction denitrification furnaces, double-layer double-stage SNCR high-efficiency denitrification technology, and carbon-ammonia combined deep denitrification synergistic control technology to achieve ultra-low NOx emissions from cement kilns without the use of catalysts and ensure the stable operation of the denitrification system.
[0032] 3. This scheme studies carbon-based staged combustion technology in a reduction denitrification furnace, designs a multi-stage nested structure for the furnace, and includes a pre-combustion zone where fuel undergoes initial pyrolysis and gasification, providing sufficient high-concentration reducing agent (mainly CO) for subsequent reduction reactions. A multi-stage diameter reduction and guide plate combination design is employed to enhance flue gas turbulent mixing, extend the residence time of reducing gas to 3 seconds, and precisely control the temperature range to 850-950℃, creating a "fuel-rich, strong reducing, low-oxygen" denitrification reaction environment. A CFD-DPM coupled flow field simulation model is developed to analyze the multiphase flow patterns of pulverized coal particles, reducing gas, and flue gas. By optimizing the furnace cone angle, swirl intensity, and secondary air introduction method, a composite flow field of "central recirculation zone + outer ring spiral flow" is formed, achieving efficient mass transfer reaction of CO and NOx, bringing the NOx concentration at the furnace outlet close to zero. Simultaneously, a correlation model between pulverized coal particle size and reactivity is established, and high-volatile coal types are screened to improve CO generation efficiency.
[0033] 4. This scheme studies a dual-layer, dual-stage SNCR high-efficiency denitrification technology. The upper layer uses a fan-shaped atomizing spray gun to achieve full coverage of the flue gas cross-section, while the lower layer uses a swirl-type spray gun to enhance local turbulent mixing. The two-stage ammonia injection interval is 0.5 seconds to match the flue gas residence time. Discrete phase simulation (DPM) is used to optimize the nozzle arrangement density and atomization angle, controlling the ammonia droplet size within the range of 50-100μm and increasing the coverage rate to over 98%. An intelligent ammonia injection control system is developed. By monitoring parameters such as nitrogen oxide concentration, flue gas temperature, and flow rate in real time, an adaptive fuzzy control algorithm is used to dynamically adjust the ammonia injection rate. When the nitrogen oxide concentration increases, the system automatically increases the ammonia injection rate; conversely, it decreases the ammonia injection rate, ensuring denitrification efficiency while minimizing ammonia usage and reducing the risk of ammonia escape.
[0034] 5. This scheme studies the synergistic control technology of carbon-ammonia combined deep denitrification, establishes a thermodynamic balance model of the decomposition furnace and the reduction denitrification furnace, and stabilizes the oxygen content at the outlet of the reduction denitrification furnace in the range of 1.5%-2.5% through the linkage adjustment of tertiary air volume, pulverized coal fineness and feed rate. This suppresses NOx generation from later fuel combustion and avoids chemical incomplete combustion losses caused by excessive CO. A "gradient oxygen supplementation" process is designed to supplement a small amount of oxygen-enriched air (O2 concentration 28%) in the cone section of the decomposition furnace to achieve directional oxidation of residual CO and efficient combustion of supplementary pulverized coal. A synergistic optimization model of "front-end carbon reduction + back-end ammonia assistance" is established, which automatically activates the emergency enhancement mode of the SNCR system when NOx fluctuates at the outlet of the reduction denitrification furnace to ensure the denitrification efficiency of the entire system. Attached Figure Description
[0035] Appendix Figure 1 This is a schematic diagram of the decomposition furnace and reduction denitrification furnace in the cement kiln carbon-ammonia combined denitrification method of the present invention.
[0036] Figure labels: Decomposition furnace 1, Reduction and denitrification furnace 2. Detailed Implementation
[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.
[0038] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.
[0039] Furthermore, in describing representative embodiments, the specification may have presented methods and / or processes as a specific sequence of steps. However, the method or process should not be limited to the specific order of steps described herein, to the extent that it does not depend on such a specific order. As will be understood by those skilled in the art, other sequences of steps are also possible. Therefore, the specific order of steps set forth in the specification should not be construed as a limitation on the embodiments. Moreover, the method and / or process should not be limited to the steps performed in the written order; those skilled in the art will readily understand that these orders can be varied and still remain within the spirit and scope of the embodiments of this application.
[0040] Nitrogen oxides (mainly nitric oxide (NO) and nitrogen dioxide (NO2), collectively known as NOx) generated during cement production are a very important environmental pollutant with multifaceted harms. They not only damage the environment and ecosystems but also directly threaten human health and even hinder economic development. In the cement production process, the generation of nitrogen oxides (NOx) primarily originates from the high-temperature combustion process, with rotary kilns being the largest source.
[0041] To reduce the concentration of nitrogen oxides in flue gas emitted during cement production, this specific embodiment provides a combined carbon and ammonia denitrification method for cement kilns, as shown in the attached figure. Figure 1 As shown, this method involves setting a reduction denitrification furnace 2 at the bottom of the decomposition furnace 1, with the bottom of the decomposition furnace 1 connected to the reduction denitrification furnace 2. This method mainly includes a denitrification method in the reduction denitrification furnace and a denitrification method in the decomposition furnace.
[0042] Specifically, the decomposition furnace is mainly used to pre-decompose the raw meal powder. Inside the furnace, the raw meal powder (mainly composed of calcium carbonate, CaCO3) is mixed with injected pulverized coal in a suspended state. The combustion of the pulverized coal generates a high temperature of 850-900°C, and the raw meal powder rapidly absorbs heat, undergoing the following chemical reaction:
[0043] CaCO3 → CaO + CO2
[0044] This process is called "calcium carbonate decomposition".
[0045] In traditional processes, this extremely heat-intensive decomposition process mainly takes place in a rotary kiln. Now, approximately 60% of the fuel and 90-95% of the decomposition work have been transferred to the decomposition furnace. This allows the rotary kiln to handle only a small portion of the decomposition work and the final sintering, significantly increasing kiln speed and output.
[0046] Specifically, the reduction denitrification furnace is the core reaction site of the entire denitrification process. Its main functions can be summarized as follows:
[0047] Provide a suitable reaction environment: Maintain a specific temperature window inside the reduction denitrification furnace (usually 800℃-1100℃), which is the optimal range for the efficient reduction reaction between the amino reducing agent and nitrogen oxides (NOx).
[0048] Ensuring sufficient mixing and reaction time: The design of the denitrification furnace (such as size, shape, and airflow organization) ensures that the flue gas carrying ammonia (or ammonia precursors) has enough time and space to undergo turbulent mixing with carbon powder (or carbon-containing fuel), thereby completing the complex chemical reaction.
[0049] Achieving efficient NOx reduction: Inside the reduction denitrification furnace, NOx in the flue gas (mainly nitric oxide NO and nitrogen dioxide NO2) is reduced into harmless nitrogen (N2) and water (H2O).
[0050] In this specific embodiment, the denitrification method in the reduction denitrification furnace is as follows: a first proportion of pulverized coal is injected into the reduction denitrification furnace. In this specific embodiment, 80% of the pulverized coal is injected into the reduction denitrification furnace to create a fuel-rich state within the furnace. Simultaneously, all the flue gas from the rotary kiln enters the reduction denitrification furnace, and the temperature inside the furnace is 850-950℃. The pulverized coal in the furnace undergoes pyrolysis and gasification in an oxygen-deficient environment to produce reducing gas. The nitrogen oxides in the flue gas from the rotary kiln react with the reducing gas produced by the pyrolysis and gasification of the pulverized coal in the furnace, reducing the nitrogen oxides to nitrogen gas, which is then transported upwards with the flue gas into the decomposition furnace.
[0051] Specifically, in the reduction denitrification furnace, pulverized coal is injected into the furnace with little or no air introduced, creating a fuel-rich environment where the pulverized coal burns under oxygen-deficient conditions. This inhibits NOx formation and produces a large amount of incomplete combustion products, such as CO, H2, and CxHy, forming a reduction zone within the furnace. The flue gas from the rotary kiln contains a large amount of nitrogen oxides (NOx) produced in the high-temperature kiln, and this gas first passes through this reduction zone. The reducing gases (such as CO) react chemically with the NOx, reducing it to harmless nitrogen (N2), thus achieving in-situ denitrification within the furnace.
[0052] Specifically, a pre-combustion zone and a reduction zone are arranged vertically in the reduction denitrification furnace, with the pre-combustion zone located below the reduction zone. Pulverized coal is injected into the pre-combustion zone, while all flue gas from the rotary kiln is fed into the reduction zone. In the pre-combustion zone, the pulverized coal undergoes pyrolysis and gasification, producing reducing gases. These reducing gases move upwards into the reduction zone and react with nitrogen oxides in the flue gas from the rotary kiln, reducing the nitrogen oxides to nitrogen. The pre-combustion zone is the combustion area for the pulverized coal, where it burns and produces a large amount of reducing gases. These gases continuously move from the pre-combustion zone to the reduction zone. In the reduction zone, the flue gas from the rotary kiln reacts with the reducing gases, and the NOx in the flue gas undergoes a chemical reaction to produce harmless nitrogen (N2).
[0053] Specifically, the flue gas from the rotary kiln is input into the reduction zone from the upper part, causing the flue gas to move downwards within the reduction zone. The downward-moving flue gas moves in the opposite direction to the reducing gas moving from the pre-combustion zone to the reduction zone. After reaching the reduction zone, the reducing gas comes into contact with the flue gas, and the speed of the reducing gas is greater than the speed of the downward-moving flue gas. This allows the flue gas to move synchronously upwards in the reduction zone under the impetus of the reducing gas.
[0054] For example, the initial contact point between the reducing gas and the flue gas is located at the junction of the reduction zone and the pre-combustion zone, and the upward movement speed of the reducing gas is twice the downward movement speed of the flue gas.
[0055] In this way, the flue gas from the rotary kiln is input into the reduction zone from the upper part. The flue gas moves from top to bottom in the reduction zone, and the two make initial contact at the junction of the reduction zone and the pre-combustion zone. Since the reducing gas moves upward at twice the speed of the flue gas moving downward, it drives the flue gas to move upward synchronously. During the upward movement, the reducing gas and the flue gas mix and react fully. At the same time, since the flue gas has a certain downward velocity, it can move into the interior of the reducing gas, making the reducing gas uniformly filled with flue gas. This greatly increases the contact area between the flue gas and the reducing gas, allowing them to fully contact and reduce the nitrogen oxides in the flue gas.
[0056] Specifically, the reduction zone is designed with a long and narrow structure, and the time for the reducing gas to enter the reduction zone is t1, and the time for the reducing gas to leave the reduction zone is t2, with t2-t1>3s. This allows the reducing gas to have sufficient residence time in the reduction zone, thus enabling it to react with the nitrogen oxides in the flue gas and ensuring the reduction effect of nitrogen oxides in the flue gas.
[0057] The denitrification method in the decomposition furnace is as follows: a second proportion of pulverized coal is injected into the decomposition furnace. In this specific embodiment, 20% of the pulverized coal is injected into the decomposition furnace, and tertiary air is introduced at the lower position of the decomposition furnace. At the same time, raw material is transported into the decomposition furnace from the lower position. The input port for raw material on the decomposition furnace is located at the input port for tertiary air on the decomposition furnace. The tertiary air introduced into the decomposition furnace provides oxygen. The raw material in the decomposition furnace undergoes pre-decomposition under the action of oxygen and pulverized coal. The nitrogen oxides generated by the combustion of pulverized coal in the decomposition furnace are reduced by a double-layer double-stage selective non-catalytic reduction denitrification method.
[0058] Because the raw materials (mainly calcium carbonate, CaCO3) in the decomposition furnace need to undergo vigorous decomposition at a high temperature of approximately 850-900°C, the reaction formula is as follows:
[0059] CaCO3 → CaO + CO2 - Heat
[0060] This reaction is endothermic and requires a large amount of heat to react.
[0061] Therefore, pulverized coal needs to be injected and burned in the decomposition furnace. The combustion of the pulverized coal rapidly releases a huge amount of heat, providing energy for the decomposition reaction. This allows the raw materials to achieve a decomposition rate of over 90%-95% before entering the rotary kiln.
[0062] Tertiary air refers to the large amount of high-temperature flue gas produced during the combustion of pulverized coal in a rotary kiln. Simultaneously, a dedicated "cooler" at the kiln head cools the high-temperature clinker exiting the kiln. The cold air blown into the cooler is heated into high-temperature hot air while cooling the clinker. This hot air (usually from the cooler) is extracted from the kiln head through a dedicated duct and transported to the precalciner. Because it is neither the primary air from the kiln head burner nor the secondary air from the cooler, it is called "tertiary air."
[0063] Tertiary air is characterized by its high temperature, typically between 800°C and 950°C, and its high oxygen content (approximately 21%). Tertiary air is the "lifeline" for the normal operation of the precalciner, its core function being to provide the necessary oxygen for the combustion of pulverized coal within the precalciner.
[0064] The main functions of the three winds include:
[0065] Combustion-supporting function: A large amount of pulverized coal (accounting for about 60% of the total pulverized coal in the entire system) needs to be injected into the decomposition furnace, and this pulverized coal requires oxygen to burn. Tertiary air is their main "air source".
[0066] Providing the reaction temperature: The pulverized coal burns in the tertiary air, releasing a large amount of heat, raising and maintaining the furnace temperature at around 850-900°C. This temperature is the optimal temperature required for the rapid decomposition of raw calcium carbonate (CaCO3).
[0067] The efficient denitrification reaction provides the necessary temperature window for the occurrence of a two-layer, two-stage selective non-catalytic reduction denitrification method.
[0068] Material conveying and suspension: The high-speed tertiary air entering at the bottom of the decomposition furnace forms a powerful swirling or jetting flow, which helps to: fully disperse and suspend the falling raw meal powder and coal powder in the furnace, greatly increasing the contact area between the gas and solid phases, resulting in extremely high heat transfer and mass transfer (chemical reaction) efficiency.
[0069] In this specific embodiment, the dual-layer, dual-stage selective non-catalytic reduction denitrification method is as follows: Ammonia water is sprayed using a fan-shaped atomizing spray gun in the upper layer of the decomposition furnace to fully cover the flue gas; ammonia water is sprayed using a swirling spray gun in the lower layer of the decomposition furnace to enhance local turbulent mixing. A dual-stage ammonia spray is formed between the upper and lower layers, with a time interval of 0.5 seconds between the two stages. The nozzle arrangement density and atomization angle are optimized using discrete phase simulation (DPM) to control the ammonia water droplet size within the range of 50-100 μm, increasing the coverage rate to over 98%.
[0070] The core principle of the double-layer, double-selective non-catalytic reduction denitrification method is to use ammonia as a reducing agent to reduce NOx (mainly NO, including some NO2) into harmless nitrogen (N2) and water (H2O) under specific conditions.
[0071] The main reaction equation is:
[0072] 4NH3 + 4NO + O2 → 4N2 + 6H2O
[0073] 4NH3 + 2NO2 + O2 → 3N2 + 6H2O
[0074] However, in practical applications, ammonia escape often occurs. The root cause of ammonia escape is that the injected ammonia gas (or ammonia derivative) fails to undergo a reduction reaction with the nitrogen oxides in the flue gas, resulting in excessive residues in the flue gas. Escaping ammonia (NH3) is an alkaline gas, while flue gas contains various acidic gases (mainly SO3 and HNO3). When these gases meet, a typical neutralization reaction occurs, producing the corresponding ammonium salts. The resulting ammonium sulfate / ammonium nitrate salts transform from the gas phase to the particulate phase through homogeneous nucleation and heterogeneous condensation mechanisms as the flue gas temperature decreases.
[0075] These newly generated particles, or coatings adhering to fly ash, are very small and constitute inhalable particulate matter (PM2.5). Therefore, it is necessary to reduce ammonia escape.
[0076] In this specific embodiment, to reduce ammonia escape, the concentration of nitrogen oxides (NOx) in the flue gas at the decomposition furnace outlet is monitored. When the NOx concentration at the decomposition furnace outlet exceeds the standard value, the injection volume of ammonia water from the fan-shaped atomizing spray gun and the swirl spray gun is increased; when the NOx concentration at the decomposition furnace outlet is below the standard value, the injection volume of ammonia water from the fan-shaped atomizing spray gun and the swirl spray gun is decreased. This ensures denitrification efficiency while minimizing ammonia water usage and reducing the risk of ammonia escape. Therefore, this solution, on the one hand, continuously monitors the NOx concentration to adjust the ammonia water dosage in real time, ensuring effective reduction of NOx while minimizing ammonia escape. On the other hand, the ammonia water in this solution is only used to reduce low-difficulty NOx generated in the later stages of denitrification in the decomposition furnace, resulting in a low concentration of NOx to be treated and simple processing, thereby reducing ammonia escape.
[0077] Specifically, oxygen-enriched air with an oxygen concentration of 28% is introduced at the connection point between the decomposition furnace and the reduction denitrification furnace. Introducing oxygen-enriched air enables the directional oxidation of residual CO and the efficient combustion of pulverized coal.
[0078] Compared with existing technologies, this invention features a reduction denitrification furnace located at the bottom of the decomposition furnace. This concentrates the denitrification process of the flue gas transported from the rotary kiln primarily within the reduction denitrification furnace, allowing the nitrogen oxide concentration in the flue gas at the furnace outlet to approach or reach zero. Simultaneously, a dual-layer, dual-stage selective non-catalytic reduction denitrification method is employed in the decomposition furnace to reduce the less difficult-to-denitrify nitrogen oxides generated later in the process. This achieves the goal of reducing nitrogen oxide emission concentrations to ultra-low levels while minimizing ammonia usage and ensuring ammonia escape does not exceed limits. Therefore, by dispersing the denitrification process between the reduction denitrification furnace and the decomposition furnace, this solution effectively treats nitrogen oxides, achieving ultra-low emission concentrations. Furthermore, ammonia is only used to treat low-concentration nitrogen oxides within the decomposition furnace, reducing both ammonia usage and ammonia escape. 2. This invention studies carbon-based staged combustion technology in a reduction denitrification furnace, dual-layer double-stage SNCR high-efficiency denitrification technology, and carbon-ammonia combined deep denitrification synergistic control technology to achieve ultra-low NOx emissions from cement kilns without the use of catalysts, ensuring the stable operation of the denitrification system. 3. This scheme studies carbon-based staged combustion technology in a reduction denitrification furnace, designs a multi-stage nested structure for the furnace, and sets up a pre-combustion zone where fuel undergoes preliminary pyrolysis and gasification, providing sufficient high-concentration reducing agent (mainly CO) for subsequent reduction reactions. A multi-stage diameter reduction and guide plate combination design is adopted to enhance flue gas turbulent mixing, extend the residence time of reducing gas to 3 seconds, and precisely control the temperature range to 850-950℃, constructing a "fuel-rich, strong reducing, low-oxygen" denitrification reaction environment. A CFD-DPM coupled flow field simulation model is developed to analyze the multiphase flow patterns of pulverized coal particles, reducing gas, and flue gas. By optimizing the cone angle, swirl intensity, and secondary air introduction method of the reduction denitrification furnace, a composite flow field of "central recirculation zone + outer ring spiral flow" is formed, achieving efficient mass transfer reaction of CO and NOx, and bringing the NOx concentration at the outlet of the reduction denitrification furnace close to zero. Simultaneously, a correlation model between pulverized coal particle size and reactivity is established, and high-volatile coal types are screened to improve CO generation efficiency. 4. This scheme studies the dual-layer, dual-stage SNCR high-efficiency denitrification technology. The upper layer uses a fan-shaped atomizing spray gun to achieve full coverage of the flue gas cross-section, while the lower layer uses a swirl-type spray gun to enhance local turbulent mixing. The two-stage ammonia injection interval is 0.5 seconds to match the flue gas residence time. Discrete phase simulation (DPM) is used to optimize the nozzle arrangement density and atomization angle, controlling the ammonia droplet size within the range of 50-100 μm, and increasing the coverage rate to over 98%. An intelligent ammonia injection control system was developed. By monitoring parameters such as nitrogen oxide concentration, flue gas temperature, and flow rate in real time, and using an adaptive fuzzy control algorithm, the ammonia injection rate is dynamically adjusted. When the nitrogen oxide concentration increases, the system automatically increases the ammonia injection rate; conversely, it decreases the ammonia injection rate. This ensures denitrification efficiency while minimizing ammonia water usage and reducing the risk of ammonia escape.5. This scheme studies the synergistic control technology of carbon-ammonia combined deep denitrification, establishes a thermodynamic balance model of the decomposition furnace and the reduction denitrification furnace, and stabilizes the oxygen content at the outlet of the reduction denitrification furnace in the range of 1.5%-2.5% through the linkage adjustment of tertiary air volume, pulverized coal fineness and feed rate. This suppresses NOx generation from later fuel combustion and avoids chemical incomplete combustion losses caused by excessive CO. A "gradient oxygen supplementation" process is designed to supplement a small amount of oxygen-enriched air (O2 concentration 28%) in the cone section of the decomposition furnace to achieve directional oxidation of residual CO and efficient combustion of supplementary pulverized coal. A synergistic optimization model of "front-end carbon reduction + back-end ammonia assistance" is established, which automatically activates the emergency enhancement mode of the SNCR system when NOx fluctuates at the outlet of the reduction denitrification furnace to ensure the denitrification efficiency of the entire system.
[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.
Claims
1. A method for combined denitration of carbon and ammonia in a cement kiln, characterized in that, The cement kiln carbon and ammonia combined denitration method comprises a reduction denitration furnace arranged at the lower part of a decomposition furnace, the lower part of the decomposition furnace being communicated with the reduction denitration furnace, and a reduction denitration furnace internal denitration method and a decomposition furnace internal denitration method. The reduction denitration furnace internal denitration method is that a first proportion of coal powder is sprayed into the reduction denitration furnace, and all the flue gas from the rotary kiln is sent into the reduction denitration furnace, the coal powder in the reduction denitration furnace is pyrolyzed and gasified to produce reducing gas under anoxic environment, and the nitrogen oxides in the flue gas from the rotary kiln react with the reducing gas produced by the pyrolysis and gasification of the coal powder in the reduction denitration furnace, so that the nitrogen oxides are reduced to nitrogen gas and then transported upward with the flue gas into the decomposition furnace. The decomposition furnace internal denitration method is that a second proportion of coal powder is sprayed into the decomposition furnace, and the tertiary air is input at the lower part of the decomposition furnace, while the raw meal is transported into the decomposition furnace from the lower part of the decomposition furnace, and the input port for inputting the raw meal on the decomposition furnace is located at the input port for inputting the tertiary air on the decomposition furnace, the tertiary air input into the decomposition furnace provides oxygen for the decomposition furnace, and the raw meal in the decomposition furnace is pre-decomposed under the action of oxygen and coal powder, and the nitrogen oxides produced by the combustion of the coal powder in the decomposition furnace are reduced by a double-layer double-time selective non-catalytic reduction denitration method.
2. The cement kiln carbon-ammonia combined denitration method according to claim 1, characterized in that, In the reduction denitration furnace internal denitration method, A pre-combustion zone and a reduction zone are arranged in the vertical direction in the reduction denitration furnace in sequence, and the pre-combustion zone is located at the lower side of the reduction zone, the coal powder is sprayed into the pre-combustion zone of the reduction denitration furnace, and all the flue gas from the rotary kiln is sent into the reduction zone of the reduction denitration furnace, the coal powder is pyrolyzed and gasified in the pre-combustion zone to produce reducing gas, and the reducing gas moves upward to the reduction zone to react with the nitrogen oxides in the flue gas from the rotary kiln, so that the nitrogen oxides in the flue gas are reduced to nitrogen gas.
3. The cement kiln carbon-ammonia combined denitration method according to claim 2, characterized in that, In the reduction denitration furnace internal denitration method, The flue gas from the rotary kiln is input into the reduction zone from the upper part of the reduction zone, so that the flue gas moves downward in the reduction zone, the flue gas moving downward is opposite to the moving direction of the reducing gas moving from the pre-combustion zone to the reduction zone, the reducing gas contacts the flue gas after moving to the reduction zone, and the moving speed of the reducing gas is greater than that of the flue gas moving downward, so that the flue gas can move synchronously with the reducing gas to the upper part of the reduction zone under the pushing of the reducing gas after contacting the reducing gas.
4. The cement kiln carbon-ammonia combined denitration method according to claim 3, characterized in that, In the reduction denitration furnace internal denitration method, The initial contact position of the reducing gas and the flue gas is located at the joint of the reduction zone and the pre-combustion zone, and the upward moving speed of the reducing gas is twice the downward moving speed of the flue gas.
5. The cement kiln carbon-ammonia combined denitration method according to claim 4, characterized in that, In the reduction denitration furnace internal denitration method, The reduction zone is in an elongated structure, the time for the reducing gas to enter the reduction zone is t1, the time for the reducing gas to leave the reduction zone is t2, and t2-t1>3s.
6. The cement kiln carbon-ammonia combined denitration method according to claim 5, characterized in that, In the reduction denitration furnace internal denitration method, 80% of the coal powder is sprayed into the reduction denitration furnace, and the temperature in the reduction denitration furnace is 850-950℃.
7. The cement kiln carbon-ammonia combined denitrification method according to claim 6, characterized in that, The decomposition furnace internal denitration method comprises the following steps: 20% of the pulverized coal is sprayed into the decomposition furnace, and oxygen-rich air is introduced at a position where the decomposition furnace is communicated with the reduction denitration furnace, and the oxygen concentration of the oxygen-rich air is 28%.
8. The cement kiln carbon-ammonia combined denitration method according to claim 7, characterized in that, The decomposition furnace internal denitration method comprises the following steps: The double-layer double-time selective non-catalytic reduction denitration method is as follows: the fan-shaped atomizing spray gun is used to spray ammonia water in the upper layer of the decomposition furnace to fully cover the flue gas, and the cyclone spray gun is used to spray ammonia water in the lower layer of the decomposition furnace to strengthen local turbulent mixing, and double-stage ammonia spraying is formed between the upper-layer ammonia water and the lower-layer ammonia water, and the time interval of the double-stage ammonia spraying is 0.5 seconds.
9. The cement kiln carbon-ammonia combined denitrification method according to claim 8, characterized in that, The decomposition furnace internal denitration method comprises the following steps: The sprayed ammonia water droplet particle size is 50-100 μm.
10. The cement kiln carbon-ammonia combined denitrification method according to claim 9, characterized in that, The decomposition furnace internal denitration method comprises the following steps: The nitrogen oxide concentration in the flue gas at the outlet of the decomposition furnace is detected, when the nitrogen oxide concentration at the outlet of the decomposition furnace is greater than the standard value, the spraying amount of the fan-shaped atomizing spray gun and the cyclone spray gun ammonia water is increased, and when the nitrogen oxide concentration at the outlet of the decomposition furnace is less than the standard value, the spraying amount of the fan-shaped atomizing spray gun and the cyclone spray gun ammonia water is reduced.