A method for removing nitrogen oxides in the magnesium smelting industry

Abstract

The application provides a method for removing nitrogen oxides in a magnesium smelting industry, and belongs to the technical field of environmental protection, and comprises the following steps: a spraying layer is arranged in a uniform distribution state and in steps between a kiln head and a heat exchange chamber of an ore vertical preheater according to the outer diameter of the vertical preheater; a denitration reaction layer is arranged in a uniform distribution state and in steps according to the outer diameter of the vertical preheater at the front of a heat exchanger of the vertical preheater in the flow direction of flue gas, and at the lower end of the flow direction of flue gas of the spraying layer; a temperature probe, an oxygen content detection probe and a nitrogen oxide monitoring system are arranged in a flue provided with the spraying layer, and relevant data passing through the spraying layer are collected in real time; and the removal of nitrogen oxides is realized by spraying a denitration agent from the spraying layer according to the initial concentration of nitrogen oxides collected in real time passing through the spraying layer. The method creatively proposes a method for reducing the temperature of the agent to achieve an ideal temperature window of reduction and denitration, and fundamentally overthrows the problem that the selection of a denitration position in traditional SNCR technology is too dependent on the temperature area of flue gas.

Description

Technical Field

[0001] This invention relates to the field of environmental protection technology, and more particularly to a method for removing nitrogen oxides in the calcination section of a magnesium smelting industry. Background Technology

[0002] The raw materials and processes in the magnesium smelting and calcination section are similar to those in cement production, both generating NOx. The temperature inside the high-temperature rotary kiln in the calcination section exceeds 1300℃, leading to the generation of thermal NOx. x The amount produced is high, and the atmospheric emission concentration is usually around 500 mg / Nm³. 3 Around [amount missing]. The CO concentration in the high-temperature flue gas from the calcination section is high (sometimes reaching several thousand mg / Nm³). 3 Low levels of H2O and O2 significantly affect the efficiency of high-temperature flue gas denitrification due to atmospheric changes. The amendment to the "Emission Standard of Pollutants for Magnesium and Titanium Industry" (GB25468-2010) sets a special NOx emission limit of 100 mg / Nm³. 3 .

[0003] Selective non-catalytic reduction (SNCR), polymeric non-catalytic reduction (PNCR), and selective catalytic reduction (SCR) are currently the mainstream NOx removal technologies. SNCR and PNCR have a temperature window of 800-1100℃, and the reducing agent reacts with NO... x A minimum residence time of 2 seconds is required for the reaction. Currently, research and patents on SNCR and PNCR denitrification technologies for high-temperature kilns such as rotary kilns mainly focus on the cement kiln industry. Research content primarily involves adjusting denitrification agent formulations, optimizing reductant injection methods, and developing combined SNCR+PNCR denitrification systems. For example, patents 201910455195.1 "A Combined SNCR and PNCR Denitrification System and Flue Gas Denitrification Method for High-Temperature Kilns" (family 201920787881.4) and 202021749856.6 "An Ultra-Low Emission System for Nitrogen Oxides in Cement Kiln Exhaust Gas" both follow conventional settings, placing the reductant injection point at the outlet of the decomposition furnace to meet the reaction temperature requirements of traditional SNCR. Patent 202110191347.9, "A cement kiln device and an SNCR denitrification method", involves injecting the reducing agent into the 750-850℃ region, but it requires the use of a synergist containing a metal catalyst.

[0004] In the magnesium calcination section, the flue gas temperature near the rotary kiln head and preheater outlet is generally sufficient. However, due to the structure of high-temperature kilns such as rotary kilns, the height of the space between the kiln head and the preheater is typically only 0.5–3 m. This results in insufficient residence time for the flue gas before it enters the preheater, leading to a denitrification reaction time of only about 1–1.5 seconds. The low degree of mixing in the flue gas results in low denitrification efficiency. Furthermore, in actual engineering, limitations imposed by the location of the reducing agent injection and process conditions mean that the large volume of ore causing disturbance during its fall can affect the sufficient contact between the flue gas and the reagent. The denitrification efficiency of SNCR units located in this area is typically only around 40%.

[0005] While SCR denitrification technology is relatively mature in coal-fired power plants and glass kilns, the flue gas characteristics of high-temperature rotary kilns differ significantly from those in these environments. Some magnesium smelting enterprises have implemented SNCR+SCR denitrification projects in their calcination sections, which generally meet the special NOx emission limits. However, SCR systems require substantial investment and have high operating costs. Considering the costs of reagents (ammonia water), electricity, producer gas for heating, and low-temperature catalyst depletion, the operating cost per ton of magnesium increases by more than 1000 yuan.

[0006] In summary, the NOx emissions from clean production in the magnesium smelting industry... x Emission reduction faces technical challenges. It is difficult to achieve a significant improvement in denitrification efficiency by relying on traditional methods such as adjusting the denitrification agent formula, optimizing the injection method, or simply combining denitrification systems. Summary of the Invention

[0007] Based on the technical, engineering, and economic issues mentioned in the background section, this invention provides a method for removing nitrogen oxides in the calcination section of magnesium smelting. This invention fully considers the process of the rotary kiln in magnesium smelting and the high-temperature nitrogen oxide reduction and removal mechanism, and develops a double-layer superimposed denitrification method. By employing a double-layer injection system at appropriate points between the kiln head and the ore preheater, the optimal denitrification reaction temperature window is extended, achieving an innovative application of high-temperature reduction denitrification technology in a high-temperature rotary kiln.

[0008] The technical means employed in this invention are as follows:

[0009] A method for removing nitrogen oxides in the magnesium smelting industry includes the following steps:

[0010] Step 1: Fix the vertical preheater by setting the cap at the top of the vertical preheater, and install the vertical probe-type reagent transport spray composite device according to the flue gas flow direction. Between the kiln head and the heat exchange chamber of the ore vertical preheater, the spray layer is evenly distributed in steps according to the outer diameter of the probe-type reagent transport spray composite device.

[0011] Step 2: In the direction of flue gas flow at the front of the vertical preheater heat exchanger, the denitrification reaction layer is evenly distributed and stepwise arranged at the lower end of the spray layer flue gas flow along the outer diameter of the probe-type reagent transport spray composite device.

[0012] Step 3: Install temperature probes, oxygen content detection probes, and nitrogen oxide monitoring systems in the flue with the spray layer to collect real-time data on the temperature, oxygen content, and nitrogen oxide concentration of the flue gas passing through the spray layer.

[0013] Step 4: Based on the real-time collected initial concentration of nitrogen oxides passing through the spray layer, a denitrification agent is sprayed through the spray layer;

[0014] Step 5: When the flue gas temperature of the spray layer is higher than 1100℃ or the oxygen content of the flue gas is greater than 10.5%, the flue gas temperature is reduced to the suitable reaction temperature for non-catalytic reduction denitrification by liquid evaporation in the denitrification reaction layer. At the denitrification reaction layer, the oxygen content in the flue gas is reduced to the suitable reaction temperature for non-catalytic reduction denitrification based on the consumption of organic antioxidants.

[0015] Step 6: When the temperature of the flue gas in the spray layer is below 1100℃ or the oxygen content of the flue gas is less than 10.5%, proceed with step 4 to remove nitrogen oxides.

[0016] Furthermore, in step 1, the number of nozzles in the spray layer and the spray angle of the nozzles are set by introducing a constraint formula.

[0017] Furthermore, the number of nozzles in the spray layer is set based on the system's ammonia consumption, nitrogen oxide emissions, ammonia emissions, and compressed air, calculating the maximum number N of nozzles that meets the thermodynamic limits under operating conditions. max,热力学 :

[0018]

[0019] Where, ρ gas A1 represents the average density of the flue gas; v represents the cross-sectional area of ​​the flue. max Indicates the maximum allowable flow velocity in the flue; c p ΔT represents the specific heat capacity of flue gas. amax Indicates the maximum permissible temperature difference; η min h represents the lower limit of efficiency under the most unfavorable operating conditions. fg h represents the latent heat of water vaporization. fg =2260kJ / kg; Q pnozzle N represents the flow rate of a single nozzle; 冗余 Indicates the number of redundant nozzles.

[0020] Furthermore, the spray angle is set according to the spray type; the spray type includes: static liquid spray and solid spray.

[0021] Furthermore, when the spray type is static liquid spray, the liquid spray angle directly affects the water mist coverage area and residence time, thus affecting the cooling and reaction efficiency. Therefore, the static liquid spray angle θ1 is:

[0022] θ1=clip(k1×ln(v)+k2+k T ×ΔT extreme ,θ min ,θ max );

[0023] Where v represents the flue gas velocity; k1 represents the logarithmic correction coefficient for the velocity; k2 represents the baseline angle value; k T Indicates the temperature extreme value correction factor; ΔT extreme θ represents the difference between the extreme high / low temperature and the preset temperature. min Indicates the minimum allowable angle for the nozzle mechanism; θ max Indicates the maximum allowable angle of the nozzle mechanically;

[0024] When the injection type is solid injection, to ensure sufficient reaction, the residence time of the solid injection in the flue should be >0.3s. Therefore, the solid injection angle θ2 is:

[0025]

[0026] Where θ0 represents the calibration reference angle; v represents the flue gas velocity; v0 represents the reference velocity, v0 = 5 m / s; d 颗粒 The average diameter of the drug particles is represented by d0; d0 represents the reference particle diameter, d0 = 50 μm; D 烟道 Indicates the diameter or width of the flue; D0 represents the standard flue dimension, D0 = 2m; k v k represents the flow rate correction factor. d k represents the particle diameter correction factor. D This indicates the correction factor for the flue size.

[0027] Furthermore, the spray layer includes a liquid spray layer and a solid spray layer; the liquid spray layer and the solid spray layer are arranged alternately, and the distance between the liquid spray layer and the solid spray layer is 5cm-10cm.

[0028] Furthermore, the liquid spray layer continuously sprays water-soluble composite reagents through an injector; the water-soluble composite reagents contain organic antioxidants that remove active oxygen from the flue gas through an oxidation reaction, forming a low-temperature, low-oxygen zone with a temperature of 1000℃-1050℃ and an oxygen content of 8.5%-10.5% within 1-2 seconds.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] This invention is applied to the rotary kiln head of magnesium smelting, solving the problem that nitrogen oxide reduction and removal technology cannot be used due to excessively high flue gas temperature and short ideal temperature window time, and achieving good removal efficiency at low cost.

[0031] Meanwhile, the method of this invention solves the problem of poor performance of traditional reduction denitrification technology caused by a large amount of ore falling backward with flue gas. After the denitrification technology is implemented, the data fluctuation is small and the stability is greatly increased.

[0032] The spray volume of the spray layer and the amount of denitrifying agent added to the reaction layer can be adjusted to realize process changes under different nitrogen oxide emission modes in different seasons and loads. It can be adapted to the annual nitrogen oxide emission control of rotary kiln at low cost and effectively control extreme values ​​and large-area high emission periods.

[0033] In the production process, while ensuring the kiln head temperature, spraying can be used to appropriately reduce the kiln head temperature, remove the dust layer on the outer shell of the ore, improve calcination efficiency, eliminate ore caking, and thus promote the production process. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of the overall process of the present invention.

[0036] Figure 2 This is a schematic diagram of the process of the present invention.

[0037] Figure 3 This is a schematic diagram of the process of the spray layer of the stacked reaction system of the present invention.

[0038] Figure 4 This is a schematic diagram of the denitrification layer of the stacked reaction system of the present invention.

[0039] Among them, 1 is the vertical preheater; 2 is the heat exchange chamber; 3 is the rotary kiln; 4 is the probe spray pipe; 5 is the spray layer reactor system; 6 is the denitrification layer reactor system; 7 is the algorithm / control unit; 8 is the temperature / flow measurement probe; 5-1 is the cross-section of the vertical preheater flue; 5-2 is the liquid composite spray agent injection unit; 5-3 is the optional liquid composite spray agent injection unit; 6-1 is the cross-section of the vertical preheater flue; 6-2 is the liquid denitrification agent injection unit; 6-3 is the solid denitrification agent injection unit. Detailed Implementation

[0040] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0041] 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 the 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 a 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.

[0042] like Figure 1 As shown, the present invention provides a method for removing nitrogen oxides in the magnesium smelting industry, comprising the following steps:

[0043] Step 1: Fix the vertical preheater by setting the cap at the top of the vertical preheater, and install the vertical probe-type reagent transport spray composite device according to the flue gas flow direction. Between the kiln head and the heat exchange chamber of the ore vertical preheater, the spray layer is evenly distributed in steps according to the outer diameter of the probe-type reagent transport spray composite device.

[0044] Step 2: In the direction of flue gas flow at the front of the vertical preheater heat exchanger, the denitrification reaction layer is evenly distributed and stepwise arranged at the lower end of the spray layer flue gas flow along the outer diameter of the probe-type reagent transport spray composite device.

[0045] Step 3: Install temperature probes, oxygen content detection probes, and nitrogen oxide monitoring systems in the flue with the spray layer to collect real-time data on the temperature, oxygen content, and nitrogen oxide concentration of the flue gas passing through the spray layer.

[0046] Step 4: Based on the real-time collected initial concentration of nitrogen oxides passing through the spray layer, a denitrification agent is sprayed through the spray layer;

[0047] Step 5: When the flue gas temperature of the spray layer is higher than 1100℃ or the oxygen content of the flue gas is greater than 10.5%, the flue gas temperature is reduced to the suitable reaction temperature for non-catalytic reduction denitrification by liquid evaporation in the denitrification reaction layer. At the denitrification reaction layer, the oxygen content in the flue gas is reduced to the suitable reaction temperature for non-catalytic reduction denitrification based on the consumption of organic antioxidants.

[0048] Step 6: When the temperature of the flue gas in the spray layer is below 1100℃ or the oxygen content of the flue gas is less than 10.5%, proceed with step 4 to remove nitrogen oxides.

[0049] Preferably, in step 1, the number of nozzles in the spray layer and the spray angle of the nozzles are set by introducing a constraint formula. The number of nozzles in the spray layer is set based on the system's ammonia consumption, nitrogen oxide emissions, ammonia emissions, and compressed air, calculating the maximum number of nozzles N that meets the thermodynamic limits under operating conditions. max,热力学 :

[0050]

[0051] Where, ρ gas A1 represents the average density of the flue gas; v represents the cross-sectional area of ​​the flue. max Indicates the maximum allowable flow velocity in the flue; c p ΔT represents the specific heat capacity of flue gas. max Indicates the maximum permissible temperature difference; η min h represents the lower limit of efficiency under the most unfavorable operating conditions. fg h represents the latent heat of water vaporization. fg =2260kJ / kg; Q pnozzle N represents the flow rate of a single nozzle. 冗余 Indicates the number of redundant nozzles.

[0052] As a preferred approach, in order to further optimize the nozzle setup, the standard k-ε turbulence model of Reynolds average (RANS) can be used to perform CFD simulation on the spray system to analyze the temperature field, velocity field, and turbulence characteristics, check for the existence of backflow zones, uncovered areas, or local high-temperature zones, and optimize the number of nozzles and the spray angle scheme of the spray layer.

[0053] In this application, the spray angle is set according to the spray type; the spray type includes: static liquid spray and solid spray.

[0054] When the spray type is static liquid spray, the liquid spray angle directly affects the water mist coverage and residence time, thus affecting the cooling and reaction efficiency. Therefore, the static liquid spray angle θ1 is:

[0055] θ1=clip(k1×ln(v)+k2+k T ×ΔTextreme ,θ min ,θ max );

[0056] Where v represents the flue gas velocity; k1 represents the logarithmic correction coefficient for the velocity; k2 represents the baseline angle value; k T Indicates the temperature extreme value correction factor; ΔT extreme θ represents the difference between the extreme high / low temperature and the preset temperature. min Indicates the minimum allowable angle for the nozzle mechanism; θ max Indicates the maximum allowable angle of the nozzle mechanically;

[0057] When the injection type is solid injection, to ensure sufficient reaction, the residence time of the solid injection in the flue should be >0.3s. Therefore, the solid injection angle θ2 is:

[0058]

[0059] Where θ0 represents the calibration reference angle; v represents the flue gas velocity; v0 represents the reference velocity, v0 = 5 m / s; d 颗粒 The average diameter of the drug particles is represented by d0; d0 represents the reference particle diameter, d0 = 50 μm; D 烟道 Indicates the diameter or width of the flue; D0 represents the standard flue dimension, D0 = 2m; k v k represents the flow rate correction factor. d k represents the particle diameter correction factor. D This indicates the correction factor for flue dimensions.

[0060] As a preferred option, such as Figure 2-4 As shown, the spray layer includes a liquid spray layer and a solid spray layer; the liquid spray layer and the solid spray layer are staggered, and the stagger distance between the liquid spray layer and the solid spray layer is 5cm-10cm. On the flue between the rotary kiln head and the heat exchange chamber of the vertical preheater, as shown in the vertical preheater 1, a spray layer reactor system 5 is arranged at a distance of 80cm-120cm from the heat exchange chamber. A denitrification layer reactor system 6 is arranged 40cm-80cm above the spray layer reactor system 5. The specific layout of the spray layer reactor system 5 and the denitrification layer reactor system 6 is as follows: Figure 3 and Figure 4 To ensure full coverage of the flue gas flow section and the principle of sufficient contact between the reactants and the flue gas, the temperature / flow measurement probe 8 monitors the data, and the algorithm / control unit 7 calculates the flow rate of the composite spray agent according to the heat of evaporation to ensure that the flue gas temperature at the denitrification layer 6 is between 1000℃ and 1050℃. The spray layer reactor system 5, the denitrification layer reactor system 6, the algorithm / control unit 7, and the temperature / flow measurement probe 8 together constitute the stacked denitrification reaction system 4.

[0061] The liquid spray layer continuously sprays water-soluble composite reagents through an injector; the water-soluble composite reagents contain organic antioxidants that remove active oxygen from flue gas through an oxidation reaction, forming a low-temperature, low-oxygen zone with a temperature of 1000℃-1050℃ and an oxygen content of 8.5%-10.5% within 1-2 seconds.

[0062] Example 1

[0063] In a magnesium smelting enterprise in northern Shaanxi, NO x Initial emission concentration 550 mg / m³ 3 The kiln head temperature is 1220℃, and the effective reaction distance in the flue is 0.6 meters. In application, liquid spray agent is first sprayed onto the kiln head through a spray layer (the spray rate can be around 800L / h as a reference). After 1 hour of equilibrium, the oxygen content at the kiln head decreases (from 10.5% to below 9.5% as a reference), the humidity increases (from 3% to above 5.0% as a reference), and the kiln head temperature drops from 1220℃ to 1180℃. A low concentration of denitrification agent is then added in both solid and liquid forms (based on a solid feed rate of 20kg / h and a liquid feed rate of 2% urea as a reference), allowing for a certain equilibrium time (about half an hour). Under this process, NOx emissions are between 100-280mg / m³. 3 Fluctuations, with a mean of 240 mg / m³ 3 Furthermore, both the peak and average sulfur dioxide emissions have been significantly reduced (with a reduction rate of over 50% as a reference).

[0064] Example 2

[0065] At a magnesium smelting enterprise in northern Shaanxi, the initial NOx emission concentration was 500 mg / m³. 3 The kiln head temperature is 1200℃, the effective reaction distance in the flue is 2 meters, and the injection point temperature is 1160℃. In application, liquid spray agent is first sprayed onto the kiln head through the spray layer (the spray rate can be around 500L / h as a reference). After 0.5 hours of equilibrium, the oxygen content at the kiln head decreases (from 10.0% to 9.2% as a reference), the humidity increases (from 2.8% to 4.0% as a reference), and the kiln head temperature drops from 1200℃ to 1190℃. A low concentration of denitrification agent is then added in both solid and liquid forms (based on a solid feed rate of 20kg / h and a liquid feed rate of 1.5% urea as a reference), allowing a certain equilibrium time (half an hour as a reference). Under this process, NOx emissions are stabilized at 250mg / m³. 3 Furthermore, both the peak and average sulfur dioxide emissions have been significantly reduced (with a reduction rate of over 50% as a reference).

[0066] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0067] In the above embodiments of the present invention, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0068] In the several embodiments provided in this application, it should be understood that the disclosed technical content can be implemented in other ways. The device embodiments described above are merely illustrative; for example, the division of units can be a logical functional division, and in actual implementation, there may be other division methods. For instance, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the displayed or discussed mutual coupling, direct coupling, or communication connection may be through some interfaces; the indirect coupling or communication connection between units or modules may be electrical or other forms.

[0069] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0070] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0071] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks, or optical disks.

[0072] 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 them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for removing nitrogen oxides in the magnesium smelting industry, characterized in that, Includes the following steps: Step 1: Fix the vertical preheater by setting the cap at the top of the vertical preheater, and install the vertical probe-type reagent transport spray composite device according to the flue gas flow direction. Between the kiln head and the heat exchange chamber of the ore vertical preheater, the spray layer is evenly distributed in steps according to the outer diameter of the probe-type reagent transport spray composite device. Step 2: In the direction of flue gas flow at the front of the vertical preheater heat exchanger, the denitrification reaction layer is evenly distributed and stepwise arranged at the lower end of the spray layer flue gas flow along the outer diameter of the probe-type reagent transport spray composite device. Step 3: Install temperature probes, oxygen content detection probes, and nitrogen oxide monitoring systems in the flue with the spray layer to collect real-time data on the temperature, oxygen content, and nitrogen oxide concentration of the flue gas passing through the spray layer. Step 4: Based on the real-time collected initial concentration of nitrogen oxides passing through the spray layer, a denitrification agent is sprayed through the spray layer; Step 5: When the flue gas temperature of the spray layer is higher than 1100℃ or the oxygen content of the flue gas is greater than 10.5%, the flue gas temperature is reduced to the suitable reaction temperature for non-catalytic reduction denitrification by liquid evaporation in the denitrification reaction layer. At the denitrification reaction layer, the oxygen content in the flue gas is reduced to the suitable reaction temperature for non-catalytic reduction denitrification based on the consumption of organic antioxidants. Step 6: When the temperature of the flue gas in the spray layer is below 1100℃ or the oxygen content of the flue gas is less than 10.5%, proceed with step 4 to remove nitrogen oxides.

2. The method for removing nitrogen oxides in the magnesium smelting industry according to claim 1, characterized in that, In step 1, the number of nozzles in the spray layer and the spray angle of the nozzles are set by introducing a constraint formula.

3. The method for removing nitrogen oxides in the magnesium smelting industry according to claim 2, characterized in that, The number of nozzles in the spray layer is set based on the system's ammonia consumption, nitrogen oxide emissions, ammonia emissions, and compressed air, calculating the maximum number of nozzles N that meets the thermodynamic limits under operating conditions. max,热力学 N: Where, ρ gas A1 represents the average density of the flue gas; v represents the cross-sectional area of ​​the flue. max Indicates the maximum allowable flow velocity in the flue; c p ΔT represents the specific heat capacity of flue gas. max Indicates the maximum permissible temperature difference; η min h represents the lower limit of efficiency under the most unfavorable operating conditions. fg h represents the latent heat of water vaporization. fg =2260kJ / kg; Q pnozzle N represents the flow rate of a single nozzle; 冗余 Indicates the number of redundant nozzles.

4. The method for removing nitrogen oxides in the magnesium smelting industry according to claim 2, characterized in that, The spray angle is set according to the spray type; the spray type includes: static liquid spray and solid spray.

5. The method for removing nitrogen oxides in the magnesium smelting industry according to claim 4, characterized in that, When the spray type is static liquid spray, the liquid spray angle directly affects the water mist coverage and residence time, thus affecting the cooling and reaction efficiency. Therefore, the static liquid spray angle θ1 is: θ1=clip(k1×ln(v)+k2+k T ×ΔT extreme ,i min ,i max ); Where v represents the flue gas velocity; k1 represents the logarithmic correction coefficient for the velocity; k2 represents the baseline angle value; k T Indicates the temperature extreme value correction factor; ΔT extreme θ represents the difference between the extreme high / low temperature and the preset temperature. min Indicates the minimum allowable angle for the nozzle mechanism; θ max Indicates the maximum allowable angle of the nozzle mechanically; When the injection type is solid injection, to ensure sufficient reaction, the residence time of the solid injection in the flue should be >0.3s. Therefore, the solid injection angle θ2 is: Where θ0 represents the calibration reference angle; v represents the flue gas velocity; v0 represents the reference velocity, v0 = 5 m / s; d 颗粒 The average diameter of the drug particles is represented by d0; d0 represents the reference particle diameter, d0 = 50 μm; D 烟道 Indicates the diameter or width of the flue; D0 represents the standard flue dimension, D0 = 2m; k v k represents the flow rate correction factor. d k represents the particle diameter correction factor. D This indicates the correction factor for the flue size.

6. The method for removing nitrogen oxides in the magnesium smelting industry according to claim 1, characterized in that, The spray layer includes a liquid spray layer and a solid spray layer; the liquid spray layer and the solid spray layer are arranged alternately, and the distance between the liquid spray layer and the solid spray layer is 5cm-10cm.

7. The method for removing nitrogen oxides in the magnesium smelting industry according to claim 1, characterized in that, The liquid spray layer continuously sprays water-soluble composite reagents through an injector; the water-soluble composite reagents contain organic antioxidants that remove active oxygen from flue gas through an oxidation reaction, forming a low-temperature, low-oxygen zone with a temperature of 1000℃-1050℃ and an oxygen content of 8.5%-10.5% within 1-2 seconds.

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