Method and system suitable for purifying high-ammonia low-nitrogen flue gas in cement industry

Abstract

The invention relates to the technical field of flue gas purification in the cement industry, and discloses a purification method and system suitable for high-ammonia low-nitrogen flue gas in the cement industry. The method comprises the following steps: monitoring the concentration of NH3 and NOX in the flue gas in real time, calculating the molar ratio of ammonia to nitrogen, automatically adding a ferric nitrate nitrogen increasing agent or ammonia water for adjustment when the ratio is unbalanced, and then carrying out heat exchange preheating and supplementary heating on the flue gas, and feeding the flue gas into a denitration reactor for synergistic removal. The system comprises an online monitoring control unit, an ammonia spraying system, a nitrogen increasing system, an online detector, a heat exchange system, a heating system and a denitration reactor. The problem of high-ammonia low-nitrogen flue gas treatment is solved, efficient synergistic removal of NOX and NH3 is achieved under the low-temperature condition of 180-280 DEG C, the denitration efficiency exceeds 90%, ammonia escape is lower than 5 mg / Nm < 3 >, and the method has the advantages of being low in energy consumption, high in adaptability, free of secondary pollution and the like.

Description

Technical Field

[0001] This invention relates to the field of industrial flue gas purification technology, and in particular to a purification method and system suitable for high-ammonia, low-nitrogen flue gas generated in cement industry production. Background Technology

[0002] In cement production, especially in clinker production lines using calcium carbide slag as raw material, the flue gas exhibits a significant high ammonia and low nitrogen composition due to the unique characteristics of the raw materials and processes. This phenomenon mainly stems from the ammonia produced during the hydrolysis of calcium carbide to produce acetylene, where impurities such as calcium nitride (Ca3N2) decompose upon contact with water. Ammonia is also continuously released during the raw material grinding and drying process and in the decomposition furnace. Furthermore, excessive ammonia injection in the upstream SNCR denitrification process further exacerbates the ammonia escape problem, resulting in peak ammonia concentrations in the flue gas reaching thousands of milligrams per cubic meter, while nitrogen oxide concentrations remain relatively low, creating a typical ammonia-nitrogen imbalance.

[0003] Following the Ministry of Ecology and Environment's issuance of the "Opinions on Promoting the Implementation of Ultra-Low Emissions in the Cement Industry" in January 2024, which set forth NOx requirements for cement enterprises... X Emission concentration not exceeding 50 mg / Nm 3 Ammonia escape concentration not exceeding 8 mg / Nm 3 The stringent standards pose a serious challenge to existing governance technologies.

[0004] Current methods for treating this type of flue gas include adsorption, condensation, oxidation, and membrane separation. However, these technologies generally suffer from limited removal efficiency, high operating costs, and a tendency to generate secondary pollution, particularly in their poor adaptability to flue gas conditions with high humidity (14%–35%) and low temperature (90–180℃). While traditional SCR technology offers high denitrification efficiency, it typically requires operation above 300℃ and cannot effectively address the problem of uncontrolled ammonia escape in high-ammonia environments. SNCR technology, although suitable for the high-temperature environment within the decomposition furnace, has limited denitrification efficiency and is prone to excessive ammonia injection.

[0005] Therefore, developing a purification technology that can adapt to the special working conditions of the cement industry and achieve synergistic and efficient removal of ammonia and nitrogen oxides has become the key to promoting the industry to achieve ultra-low emissions. Summary of the Invention

[0006] This invention aims to address the challenges posed by high-ammonia, low-nitrogen flue gas generated in cement production, particularly in carbide slag clinker production lines. Due to the severe imbalance in the ammonia-nitrogen ratio, low flue gas temperature, and high humidity, existing denitrification and deammoniation technologies struggle to achieve efficient and coordinated removal of pollutants. Furthermore, these technologies suffer from technical problems such as excessive ammonia escape, high operating costs, and poor adaptability.

[0007] To achieve the above objectives, the present invention provides the following technical solution: On the one hand, the present invention provides a purification method for high-ammonia, low-nitrogen flue gas in the cement industry, comprising the following steps: S1. Real-time monitoring of NH3 and NO in the flue gas exiting the decomposer using an online detector. X Concentration, and calculate the ammonia nitrogen molar ratio (NSR); S2. When NSR > 1.2, a nitrogen-enhancing agent is injected into the decomposition furnace through a nitrogen-enhancing system, and the nitrogen-enhancing agent decomposes into NO2 at high temperature; When NSR < 1.2, ammonia water is injected into the decomposition furnace through the ammonia injection system; When NSR=1.2, no operation is performed; S3. The flue gas after being treated in step S2 enters the heat exchange system after dust removal and desulfurization, and the heat exchange system preheats the flue gas; S4. The preheated flue gas enters the heating system, which further heats the flue gas; S5. The heated flue gas enters the denitrification reactor, where it passes through a catalyst bed to react with NH3 and NO in the flue gas. X Perform coordinated removal.

[0008] As an optional implementation, in step S2, the ammonia nitrogen molar ratio (NSR) is controlled within the range of 0.8 to 1.2.

[0009] As an optional implementation, in step S2, the nitrogen-increasing agent is a ferric nitrate solution with a concentration of 40% to 60%.

[0010] As an optional implementation, in step S4, the heating system heats the flue gas to 180°C to 280°C.

[0011] As an optional implementation, in step S5, the catalyst bed of the denitrification reactor comprises a multilayer vanadium-titanium catalyst.

[0012] On the other hand, the present invention also provides a purification system for high-ammonia, low-nitrogen flue gas in the cement industry using the above method, comprising: Control unit, ammonia injection system, nitrogen enrichment system, online monitoring instrument, heat exchange system, heating system, and denitrification reactor; The online detector is located at the outlet of the decomposition furnace and is connected to the control unit; The ammonia injection system and nitrogen enrichment system are connected to the decomposition furnace via spray guns and are controlled by the control unit; The inlet of the heat exchange system is connected to the outlet of the desulfurization equipment, and the outlet is connected to the inlet of the heating system. The outlet of the heating system is connected to the inlet of the denitrification reactor.

[0013] As an optional implementation, the control unit is configured to: The start and stop of the ammonia injection system or nitrogen enrichment system are controlled based on the NSR value measured by the online monitoring instrument.

[0014] As an alternative implementation, the nitrogen enrichment system includes a storage tank and a spray gun, wherein the storage tank contains a ferric nitrate solution.

[0015] As an optional implementation, the ammonia spraying system includes a storage tank and a spray gun, wherein the storage tank stores ammonia water.

[0016] As an optional implementation, the denitrification reactor includes multiple catalyst beds arranged from top to bottom, wherein the catalyst is a vanadium-titanium catalyst.

[0017] This invention achieves precise control of the ammonia-nitrogen molar ratio in flue gas by introducing a real-time monitoring and dynamic adjustment mechanism, thereby ensuring that the reactants are always in an optimal ratio. Furthermore, it innovatively uses ferric nitrate solution as a nitrogen-enhancing agent, which decomposes into NO2 at high temperatures in the decomposition furnace, effectively solving the compositional imbalance problem of high-ammonia, low-nitrogen flue gas. This design breaks through the limitation of traditional technologies that can only adjust in one direction. Simultaneously, the optimized denitrification reactor can achieve highly efficient catalytic reactions within a relatively low temperature range of 180℃ to 280℃, not only adapting to the characteristics of high dust, high alkali, and high humidity in cement flue gas, but also significantly reducing system energy consumption.

[0018] Practical verification has shown that this technology can maintain a denitrification efficiency of over 90% while controlling ammonia slip concentration to within 5 mg / Nm³. 3 Within the specified range, it fully meets the requirements of current ultra-low emission standards, and has a significant advantage in terms of operating costs compared to traditional methods, providing cement companies with an economical and feasible deep treatment solution. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0020] Figure 1 This is a schematic diagram of the purification system of the present invention; Figure 2 This is a logic control flowchart of the control unit of the present invention; Figure 3 The purification process of this invention involves NH3 and NO. X Schematic diagram of concentration change over time; In the diagram: 1. Control unit; 2. Ammonia injection system; 3. Nitrogen supply system; 4. Online monitoring instrument; 5. Heat exchange system; 6. Heating system; 7. Denitrification reactor; 8. Flue gas inlet; 9. Kiln tail induced draft fan outlet; 10. Decomposition furnace; 11. Dust removal equipment; 12. Desulfurization equipment. Detailed Implementation

[0021] This invention relates to the field of flue gas purification technology in the cement industry, and in particular to a complete purification method and system for the high-ammonia, low-nitrogen flue gas characteristics generated in carbide slag cement production lines. The following detailed description, in conjunction with the accompanying drawings, will illustrate two specific embodiments of the invention. Embodiment 1 mainly describes the implementation process of the purification method, while Embodiment 2 details the system configuration for implementing the method.

[0022] Example 1: Please see Figure 1 The schematic diagram of the purification system shown illustrates the specific implementation process of the purification method in this embodiment. First, an online detector 4 installed at the outlet of the decomposition furnace 10 monitors the concentrations of ammonia and nitrogen oxides in the flue gas in real time. This online detector 4 transmits the real-time data to the control unit 1. After receiving the concentration data, the control unit 1 calculates the ammonia-nitrogen molar ratio (NSR) according to a preset program. This value is the core parameter of the entire control logic.

[0023] like Figure 2 As shown, when the calculated NSR value is greater than 1.2, it indicates that the ammonia content in the flue gas is relatively high while the nitrogen oxide content is insufficient. At this time, the control unit 1 sends a command to the nitrogen enrichment system 3 to start the nitrogen enrichment agent injection program. The nitrogen enrichment system 3 stores a ferric nitrate solution with a concentration range of 40% to 60%. As a preferred embodiment, a ferric nitrate solution with a concentration of 40%, 50%, or 60% can be used. These concentrations of ferric nitrate solution achieve a good balance between storage stability and decomposition efficiency. The nitrogen enrichment system 3 atomizes the ferric nitrate solution and sprays it into the decomposition furnace 10 through eight spray guns arranged in a circumferential array. In the high-temperature environment of about 800°C in the furnace, the ferric nitrate rapidly decomposes to generate nitrogen dioxide and iron oxide. The nitrogen dioxide is added to the flue gas, effectively increasing the concentration of nitrogen oxides, while the iron oxide is carried into the rotary kiln by the airflow in the kiln along with the raw material powder, without causing secondary pollution.

[0024] When the monitored NSR value is less than 1.2, the situation is exactly the opposite, indicating that the nitrogen oxide content in the flue gas is relatively high and the ammonia is insufficient. At this time, the control unit 1 sends a command to the ammonia injection system 2. The ammonia injection system 2 stores ammonia water, which is injected into the decomposition furnace 10 through eight other spray guns. Under the action of high temperature, the ammonia water is rapidly vaporized to form ammonia gas, which is then added to the flue gas.

[0025] When the NSR value is exactly 1.2, the system maintains its current state and does not perform any adjustment operations.

[0026] This feedback control mechanism based on real-time monitoring ensures that the concentration of reactants in the flue gas is always within the optimal range, creating favorable conditions for subsequent deep purification.

[0027] After component adjustment, the flue gas then enters the dust removal equipment 11 to remove most of the particulate matter. Subsequently, the flue gas can enter the desulfurization equipment 12 for desulfurization treatment. The desulfurization equipment 12 preferably employs a wet desulfurization process, where the flue gas and desulfurization slurry (such as limestone slurry) come into countercurrent contact within the absorption tower. The sulfur dioxide contained in the slurry reacts chemically with the alkaline substances in the slurry and is effectively removed. This process also further washes away trace dust and some water-soluble substances in the flue gas. After desulfurization and purification, the flue gas temperature will decrease, typically to around 90°C. Then, this low-temperature purified flue gas enters the heat exchange system 5 through the flue gas inlet 8. The heat exchange system 5 can adopt a tubular heat exchanger structure, with its cold-side inlet receiving the low-temperature purified flue gas from the outlet of the desulfurization equipment 12, and its hot-side inlet receiving the high-temperature purified flue gas from the outlet of the denitrification reactor 7. Through heat exchange, the low-temperature purified flue gas is preheated to between 150°C and 170°C, while simultaneously recovering waste heat and reducing the total energy consumption of the system.

[0028] The preheated flue gas then enters heating system 6, which precisely supplements the heating of the flue gas, ultimately raising its temperature to the operating temperature range required for the eSCR reaction. Optionally, heating system 6 heats the flue gas to temperatures such as 190°C, 210°C, or 220°C, all within the preferred range of 180°C to 280°C. The heated flue gas then enters denitrification reactor 7, which contains four layers of vanadium-titanium catalyst arranged from top to bottom, preferably V2O5-WO3 / TiO2 series catalysts. Under the action of the catalyst, ammonia and nitrogen oxides in the flue gas undergo a synergistic reaction, with the two most critical chemical reactions as follows: 4NO + 4NH3 + O2 → 4N2 + 6H2O, this reaction is considered the main reaction in the standard SCR reaction; The reaction NO2 + NO + 2NH3 → 2N2 + 3H2O is known as the fast SCR reaction, which has a much higher reaction rate than the main reaction. This is the fundamental reason why supplementing the system with nitrogen dioxide through a nitrogen enrichment system can significantly improve the overall removal efficiency. These reactions completely transform pollutants into harmless substances.

[0029] To verify the effectiveness of the method in this embodiment, we conducted a purification test on the high-ammonia flue gas generated from the No. 1 kiln of a carbide slag clinker cement production line in a certain factory. The flue gas volume was 200,000 m³. 3 / Nm 3 .

[0030] Initially, the ammonia concentration at the inlet of denitrification reactor 7 is 650 mg / Nm³. 3 NO X Concentration of 500 mg / Nm 3 At this point, the NSR value is 1.3.

[0031] After the system starts, nitrogen-enhancing system 3 begins adding a 40% ferric nitrate solution. After continuous adjustment for 60–120 minutes, as… Figure 3 As shown, the ammonia concentration at the inlet of denitrification reactor 7 gradually decreased and stabilized at 500 mg / Nm³. 3 Around 900 mg / Nm³, the nitrogen oxide concentration rose to 900 mg / Nm³. 3 Around 1.2, the NSR value approaches the ideal range of 1.2.

[0032] After treatment by denitrification reactor 7, the outlet nitrogen oxide concentration decreased to 35 mg / Nm³. 3 Below, the ammonia concentration drops to 5 mg / Nm³. 3 The following denitrification efficiency exceeds 90%, and the ammonia removal efficiency exceeds 95%, fully meeting the requirements of the current ultra-low emission standards.

[0033] The purification method described in this embodiment achieves precise control of reactant concentrations in flue gas through real-time monitoring and dynamic adjustment. It innovatively uses ferric nitrate as a nitrogen-enhancing agent, and its efficiency is improved through a rapid SCR reaction pathway after decomposition. Combined with an optimized denitrification reactor, it achieves highly efficient synergistic removal of pollutants under low-temperature conditions. This method is particularly suitable for the high-ammonia, high-humidity, and low-temperature flue gas conditions of carbide slag cement production lines, significantly reducing operating energy consumption while ensuring ultra-low emissions, and has significant industrial application value.

[0034] Example 2: like Figure 1 As shown, this embodiment provides a purification system for high-ammonia and low-nitrogen flue gas in the cement industry, applicable to the method described in Embodiment 1 above. The system is composed of multiple functional units organically combined, and the units are connected by pipes and signal lines to form a complete automated purification system.

[0035] Control unit 1 is the brain of the entire system, employing an industrial-grade PLC controller and equipped with a data acquisition module and a control output module. This control unit 1 is connected to the online detector 4 via a signal cable to receive concentration monitoring data in real time. Simultaneously, this unit is also connected to the actuators of the ammonia injection system 2 and the nitrogen enhancement system 3 via control cables, issuing control commands according to a preset program. Control unit 1 is installed in a dustproof and waterproof control cabinet, positioned near the decomposition furnace 10 in an easily accessible location.

[0036] The ammonia injection system 2 includes an ammonia storage tank, a metering pump, a pressure regulating valve, and an injection gun assembly. The capacity of the ammonia storage tank is determined based on the scale of the production line, typically ranging from 10 to 50 m³. 3 It stores ammonia water with a concentration of 20%–25%. The metering pump uses frequency conversion control, which can accurately adjust the ammonia water delivery rate according to the control signal. Eight spray guns are evenly distributed around the decomposition furnace 10, and the insertion depth has been optimized through computational fluid dynamics simulation to ensure that the ammonia water and flue gas are fully mixed. The spray guns are made of high-temperature resistant stainless steel and have atomizing nozzles inside to ensure efficient vaporization of ammonia water.

[0037] The nitrogen enrichment system 3 is structurally similar to the ammonia injection system 2, but the material selection needs to consider the corrosiveness of ferric nitrate. This system includes a ferric nitrate solution storage tank, a corrosion-resistant metering pump, a pressure regulating valve made of a special material, and a spray gun assembly. The ferric nitrate solution storage tank can be made of fiberglass and stores ferric nitrate solutions with a concentration range of 40%–60%. There are also eight spray guns, arranged alternately with the spray guns of the ammonia injection system 2 around the decomposition furnace 10 to ensure uniform distribution of the nitrogen enrichment agent. The spray guns can be made of Hastelloy alloy, which can withstand the corrosion of ferric nitrate solution and high-temperature environments.

[0038] The online detector 4 employs laser absorption spectroscopy technology to accurately measure the concentrations of ammonia and nitrogen oxides in flue gas in real time. This detector is installed on the outlet flue of the decomposition furnace 10. The sampling probe features high-temperature filtration and insulation to ensure sample representativeness. The online detector 4 is connected to the control unit 1 via a signal cable, and the data transmission interval can be set from 1 to 10 seconds.

[0039] The heat exchange system 5 employs a shell-and-tube heat exchanger design, with the shell made of carbon steel and the heat exchange tubes made of corrosion-resistant stainless steel. The cold-side inlet connects to the outlet of the desulfurization equipment 12 via a flue, receiving raw flue gas at approximately 110°C. The hot-side inlet connects to the outlet of the denitrification reactor 7 via a flue, receiving clean flue gas at approximately 210°C. Through precisely designed heat exchange areas, the raw flue gas can be preheated to approximately 160°C while the clean flue gas is cooled to below 150°C, achieving highly efficient energy recovery.

[0040] Heating system 6 is located after heat exchange system 5 and uses either gas or electric heating. This system includes a heater body, a temperature sensor, and a control system. The temperature sensor monitors the flue gas temperature in real time and feeds feedback to the control system to adjust the heating power, ensuring the flue gas temperature is accurately controlled within the set range. The heater adopts a modular design, and its power can be configured according to actual needs, typically capable of heating flue gas from 160℃ to any set temperature between 180℃ and 280℃.

[0041] The denitrification reactor 7 is the core equipment of the entire purification process. It adopts a steel structure shell with an internal insulation layer thickness of 200-300mm. Four catalyst beds are arranged inside the denitrification reactor 7 from top to bottom. The catalyst is vanadium-titanium based, with TiO2 as the carrier and V2O5 and WO3 as the active components, exhibiting high low-temperature activity. It is within this denitrification reactor 7 that the key chemical reactions mentioned earlier occur, including the main reaction and the rapid SCR reaction, thereby efficiently converting nitric oxide, nitrogen dioxide, and ammonia into harmless nitrogen and water. A flue gas distributor can be installed at the top inlet of the denitrification reactor 7 to ensure uniform airflow through the catalyst bed. An ash hopper is installed at the bottom to periodically remove any accumulated dust.

[0042] The connections between the systems are as follows: the outlet of desulfurization equipment 12 is connected to the cold-side inlet of heat exchange system 5 via a flue; the cold-side outlet of heat exchange system 5 is connected to the inlet of heating system 6 via a flue; the outlet of heating system 6 is connected to the inlet of denitrification reactor 7 via a flue; the outlet of denitrification reactor 7 is connected to the hot-side inlet of heat exchange system 5 via a flue, and finally connected to the outlet 9 of the kiln tail induced draft fan and the chimney. Control unit 1 is connected to online detector 4, ammonia injection system 2, and nitrogen enrichment system 3 via signal cables, forming a complete monitoring and control network.

[0043] The system described in this embodiment achieves effective treatment of high-ammonia, low-nitrogen flue gas through the organic coordination of its various functional units. The system adopts a modular design for easy installation and maintenance; automated control reduces manual intervention; and waste heat recovery technology significantly reduces operating costs. Actual operating data shows that the system can control nitrogen oxide emission concentrations to 35 mg / Nm³. 3 The ammonia slip concentration is controlled below 5 mg / Nm³. 3 The following indicators are all superior to the national ultra-low emission standards, providing reliable technical equipment for flue gas treatment in the cement industry.

[0044] The above embodiments are merely preferred embodiments of the present invention. Any modifications, equivalent substitutions, and improvements made by those skilled in the art based on the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for purifying high-ammonia, low-nitrogen flue gas in the cement industry, characterized in that, Includes the following steps: S1. The NH3 and NO in the flue gas at the outlet of the decomposition furnace (10) are monitored in real time by an online detector (4). X Concentration, and calculate the ammonia nitrogen molar ratio (NSR); S2. When NSR > 1.2, a nitrogen-enhancing agent is injected into the decomposition furnace (10) through the nitrogen-enhancing system (3), and the nitrogen-enhancing agent decomposes into NO2 at high temperature; When NSR < 1.2, ammonia water is injected into the decomposition furnace (10) through the ammonia injection system (2); When NSR=1.2, no operation is performed; S3. After being treated in step S2, the flue gas enters the heat exchange system (5) after being desulfurized and dust removed. The heat exchange system (5) preheats the flue gas. S4. The preheated flue gas enters the heating system (6), which provides supplementary heating to the flue gas; S5. The heated flue gas enters the denitrification reactor (7), where it passes through the catalyst bed to react with NH3 and NO in the flue gas. X Perform coordinated removal.

2. The purification method for high-ammonia, low-nitrogen flue gas in the cement industry according to claim 1, characterized in that, In step S2, the ammonia nitrogen molar ratio (NSR) is controlled within the range of 0.8 to 1.

2.

3. The purification method for high-ammonia, low-nitrogen flue gas in the cement industry according to claim 1, characterized in that, In step S2, the nitrogen-increasing agent is a ferric nitrate solution with a concentration of 40% to 60%.

4. The purification method for high-ammonia, low-nitrogen flue gas in the cement industry according to claim 1, characterized in that, In step S4, the heating system (6) heats the flue gas to 180°C to 280°C.

5. The purification method for high-ammonia, low-nitrogen flue gas in the cement industry according to claim 1, characterized in that, In step S5, the catalyst bed of the denitrification reactor (7) includes a multilayer vanadium-titanium catalyst.

6. A purification system for high-ammonia, low-nitrogen flue gas in the cement industry, employing the method described in any one of claims 1 to 5, characterized in that, include: Control unit (1), ammonia injection system (2), nitrogen enhancement system (3), online detector (4), heat exchange system (5), heating system (6), and denitrification reactor (7); The online detector (4) is located at the outlet of the decomposition furnace (10) and is connected to the control unit (1); The ammonia injection system (2) and the nitrogen enrichment system (3) are connected to the decomposition furnace (10) via spray guns and are controlled by the control unit (1); The inlet of the heat exchange system (5) is connected to the outlet of the desulfurization equipment (12), and the outlet is connected to the inlet of the heating system (6); The outlet of the heating system (6) is connected to the inlet of the denitrification reactor (7).

7. The purification system for high-ammonia, low-nitrogen flue gas in the cement industry according to claim 6, characterized in that, The control unit (1) is configured to: The start and stop of the ammonia injection system (2) or the nitrogen enrichment system (3) are controlled based on the NSR value measured by the online detector (4).

8. The purification system for high-ammonia, low-nitrogen flue gas in the cement industry according to claim 6, characterized in that: The nitrogen enrichment system (3) includes a storage tank and a spray gun, wherein the storage tank contains a ferric nitrate solution.

9. The purification system for high-ammonia, low-nitrogen flue gas in the cement industry according to claim 6, characterized in that: The ammonia spraying system (2) includes a storage tank and a spray gun, wherein the storage tank stores ammonia water.

10. The purification system for high-ammonia, low-nitrogen flue gas in the cement industry according to claim 6, characterized in that: The denitrification reactor (7) includes a multi-layer catalyst bed arranged from top to bottom, and the catalyst is a vanadium-titanium catalyst.

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