Method for removing NOX in flue gas by utilizing desulfurization tail liquid of molten lead-zinc slag after iron extraction and dilution in cooperation with oxidizing agent

Abstract

The invention relates to the technical field of industrial flue gas purification, in particular to a method for removing NOX in flue gas through cooperation of iron-extracted and depleted molten lead-zinc slag desulfurization tail liquid and an oxidizing agent, and the method comprises the following steps that S1, iron-extracted and depleted molten lead-zinc slag is ground till the particle size is not larger than 0.075 mm, water is added according to the solid-to-liquid ratio of 1: 200 g / mL, and ore pulp is prepared; s2, flue gas containing SO2 is introduced into the ore pulp, and SO2 in the flue gas is removed; s3, raising the temperature of the desulfurization tail liquid from which SO2 is removed to 25-65 DEG C, adding an oxidizing agent, introducing NOX-containing flue gas, and removing NOX in the flue gas; according to the method, the nitric oxide can be effectively removed by utilizing the desulfurization tail liquid of the molten lead-zinc slag after iron extraction and dilution, so that the comprehensive utilization of resources is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial flue gas purification, and particularly relates to a method for removing NO in flue gas by using the desulfurization tail liquid of molten lead-zinc slag after iron extraction and impoverishment and a synergistic oxidant X Method Background Technique

[0002] Nitrogen oxides are a class of compounds composed of nitrogen and oxygen elements and are one of the main pollutants in the atmosphere. Fuel combustion in industrial kilns and the like will generate this gas, and nitrogen oxides will also be generated in many industrial processes. The emission of NO during the combustion process X results in photochemical smog, acid rain and damage to the ozone layer, causing serious damage to the ecological system and human health. Inhaling high concentrations of nitrogen oxides may cause symptoms such as respiratory irritation, coughing, and difficulty breathing. Long-term exposure to low concentrations of nitrogen oxides may also increase the risk of chronic respiratory diseases

[0003] At present, various denitrification processes have been reported. Among them, the selective catalytic reduction method (SCR) is a mature and efficient denitrification method. However, the flue gas composition is complex, some pollutants are prone to cause catalyst poisoning, and the investment and operation costs are high

[0004] Currently, molten lead-zinc furnace slag is mainly used in the field of building materials, but there is a risk of heavy metal leaching, causing serious pollution to soil and groundwater. From the perspective of chemical composition, the desulfurization tail liquid of molten lead-zinc slag after iron extraction and impoverishment contains alkaline earth metal oxides and metal ions that are beneficial to adsorb NO X and has the feasibility of being used as a desulfurization and denitrification adsorbent. Combining the removal of NO X with the treatment of molten lead-zinc furnace slag after iron extraction and impoverishment can effectively solve the corresponding environmental problems Summary of the Invention

[0005] The purpose of the present invention is to provide a method for removing NO in flue gas by using the desulfurization tail liquid of molten lead-zinc slag after iron extraction and impoverishment and a synergistic oxidant X Method. The present invention can effectively remove nitrogen oxides by using the desulfurization tail liquid of molten lead-zinc slag after iron extraction and impoverishment, and realize resource comprehensive utilization

[0006] To achieve the above technical purpose and reach the above technical effect, the present invention is realized through the following technical solutions

[0007] A method for removing NO in flue gas by using the desulfurization tail liquid of molten lead-zinc slag after iron extraction and impoverishment and a synergistic oxidant X Method, including the following steps

[0008] S1: Grind the molten lead-zinc slag after iron extraction and impoverishment to a particle size not greater than 0.075 mm, and prepare a pulp by adding water according to a solid-liquid ratio of 1:200 g / mL

[0009] S2: Pass SO2-containing flue gas into the pulp to remove SO2 in the flue gas.

[0010] S3: Heat the desulfurized tail liquid after removing SO2 to 25 - 65 °C. After adding an oxidant, pass in NO X -containing flue gas to remove NO X in the flue gas.

[0011] Furthermore, the molten lead-zinc slag after iron extraction and impoverishment is the lead-zinc molten slag obtained by electro-enhanced carbon immersion reduction for deep iron extraction and impoverishment of lead-zinc. The mass percentages of its various components are as follows: iron oxide 33.5% - 37.5%, manganese oxide 11.41% - 12.41%, silicon dioxide 17.25% - 21.25%, zinc oxide 4.21% - 5.21%, and the rest are inevitable impurities.

[0012] Furthermore, the concentration of NO X in the NO X -containing flue gas is 100 - 900 ppm; the NO X -containing smelting flue gas also contains oxygen, and the volume fraction of oxygen is 0 - 10%.

[0013] Furthermore, the flow rate of the NO X -containing flue gas passed in is 200 - 600 mL / min.

[0014] Advantages of the present invention:

[0015] Relying on the comprehensive utilization of waste lead-zinc slag and the efficient oxidation characteristics of NaClO2, the present invention shows a significant improvement in the co-removal of multiple pollutants; metal oxides such as Fe2O3 and MnO in the lead-zinc slag are not only used for SO2 adsorption in chemical reactions, but also prevent the release of sulfur dioxide by forming stable complex forms. In the denitrification stage, these metal components promote the Fenton-like reaction, enabling the efficient utilization of the reactive oxygen species OCl - and ClO· radicals generated by the decomposition of NaClO2, thereby enhancing the oxidation ability of NO and directly converting it into soluble NO2 and HNO3. The metal components in the solid waste are recycled, greatly improving the resource value, and at the same time reducing the environmental pressure caused by waste landfill.

[0016] In the present invention, NaClO2 exerts its efficacy through a multi-level oxidation mechanism. Under neutral conditions, ClO2 - ions can directly oxidize NO to generate NO3 - , and at the same time, affected by Fe 2+ / Fe 3+Regarding the influence of the catalytic cycle, ClO2- can generate a large number of free radical species. These strong oxidizing free radicals undergo a chain oxidation reaction with NO, ensuring the x efficient removal of NO. This enables the oxidation ability of NaClO2 to remain stable over a wide concentration range, and in the coexistence of oxygen, the rate of the free radical reaction under the synergistic effect is increased, thus ensuring an efficient pollutant removal effect.

[0017] In the present invention, controlling the addition of oxygen not only promotes the conversion of NO to a higher oxidation state but also improves the activity and lifespan of the catalyst by enhancing the redox cycle of metal ions. At the same time, the moderately reduced flow rate ensures the sufficiency of gas-liquid interface mass transfer, further enhancing the efficiency of NOx absorption and subsequent oxidation reactions.

[0018] Of course, it is not necessary for any product implementing the present invention to simultaneously achieve all the above-mentioned advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for describing the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0020] Figure 1 Removal rate diagram of NO for Example 1 X ;

[0021] Figure 2 Removal rate diagram of NO for Example 2 X ;

[0022] Figure 3 Removal rate diagram of NO for Example 3 X ;

[0023] Figure 4 Removal rate diagram of NO for Example 4 X ;

[0024] Figure 5 Diagram for comparing the denitrification performance of different metal ion systems in Example 5. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0026] The molten lead-zinc slag after iron extraction and dephosphorization used in the examples is the lead-zinc molten slag obtained by electro-enhanced carbon submerged reduction for deep iron extraction and dephosphorization of lead-zinc. The mass percentages of its components are as follows: iron oxide 33.5%-37.5%, manganese oxide 11.41%-12.41%, silicon dioxide 17.25%-21.25%, zinc oxide 4.21%-5.21%, and the rest are inevitable impurities (such as crystal water, etc.).

[0027] Example 1

[0028] A method for removing NO in flue gas by using the desulfurization tail liquid of molten lead-zinc slag after iron extraction and dephosphorization and a synergistic oxidant according to this example X comprises the following steps:

[0029] S1: Use a jaw crusher to crush the molten lead-zinc slag after iron extraction and dephosphorization, then screen it with a standard sieve, select the ore powder with a particle size less than or equal to 0.075 mm as the experimental raw material, and prepare a slurry by adding water to the molten lead-zinc slag powder after iron extraction and dephosphorization according to a solid-liquid ratio of 0.1:200 g / mL. After adjusting the slurry, put it into a three-necked flask;

[0030] S2: Put the three-necked flask into a magnetic stirring water bath, set the temperature to 45°C, and introduce the mixed flue gas into the slurry of molten lead-zinc slag after iron extraction and dephosphorization in the three-necked flask. The mixed flue gas contains O2, SO2, N2, the SO2 concentration is 2000 ppm, and desulfurization is carried out for 5 h.

[0031] S3: Use the desulfurization tail liquid collected in S2, add 0.5 g of NaClO2, then put the three-necked flask into a magnetic stirring water bath, set the temperature to 45°C, and introduce the mixed flue gas into the desulfurization tail liquid in the three-necked flask. The mixed flue gas contains O2, NO X , N2, the NO X concentration is 300 ppm. Taking the NO X concentration as a variable, adjust the NO X concentration to 100 ppm, 200 ppm, 500 ppm, 700 ppm, 900 ppm respectively, and N2 is the balance gas;

[0032] S4: React multiple portions of desulfurization tail liquid with the same composition and mass with the introduced different flue gases, set the gas flow rate to 200 mL / min, and take gas at 0, 30, 60, 90, and 120 minutes respectively. Each gas sampling time is 6 minutes. Measure the collected gas with a flue gas analyzer. Compared with the initial NO X concentration, calculate the removal efficiency of NOX by the desulfurization tail liquid of molten lead-zinc slag after iron extraction and dephosphorization through the change of NO X concentration. The calculation formula is as follows:

[0033] Removal efficiency

[0034] Where: C0——Initial NO X concentration; C t ——NO concentration at time t X concentration.

[0035] The calculation results are as Figure 1 shown. It can be seen from the figure that the desulfurized tail liquid can well absorb NO in the flue gas X , and the effect is best when NO X = 100 ppm.

[0036] Example 2

[0037] A method for removing NO in flue gas by using the desulfurized tail liquid of molten lead-zinc slag after iron extraction and impoverishment and a synergistic oxidant X comprises the following steps:

[0038] S1: Use a jaw crusher to crush the molten lead-zinc slag after iron extraction and impoverishment, then screen it with a standard sieve, select the ore powder with a particle size less than or equal to 0.075 mm as the experimental raw material, and prepare a pulp by adding water to the molten lead-zinc slag powder after iron extraction and impoverishment according to a solid-liquid ratio of 0.1:200 g / mL. After adjusting the pulp, put it into a three-neck flask;

[0039] S2: Put the three-neck flask into a magnetic stirring water bath, set the temperature to 45 °C, and pass the mixed flue gas into the molten lead-zinc slag pulp after iron extraction and impoverishment in the three-neck flask. The mixed flue gas contains O2, SO2, N2, the SO2 concentration is 2000 ppm, and desulfurization is carried out for 5 h.

[0040] S3: Use the desulfurized tail liquid collected in S2, add 0.5 g of NaClO2, then put the three-neck flask into a magnetic stirring water bath, set the temperature to 45 °C, and pass the mixed flue gas into the desulfurized tail liquid in the three-neck flask. The mixed flue gas contains O2, NO X , N2, the NO X concentration is 300 ppm. Take the O2 content as a variable, and adjust the O2 volume fraction content to 0%, 5%, 10%, 15%, 20% respectively, with N2 as the balance gas;

[0041] S4: React multiple portions of desulfurized tail liquid with the same composition and mass with the introduced different flue gases. Set the gas flow rate to 200 mL / min, and take gas at 0, 30, 60, 90, and 120 minutes respectively. Each gas collection time is 6 minutes. Measure the collected gas with a flue gas analyzer according to the method of Example 1, and calculate the removal rate of NO X . As Figure 2 shown. It can be seen from the figure that the pulp can well absorb NO in the flue gas X, the best effect is achieved when O2 = 10%.

[0042] Example 3

[0043] A method for removing NO in flue gas by using desulfurized tail liquid of molten lead-zinc slag after iron extraction and impoverishment and a synergistic oxidant according to this example X comprises the following steps:

[0044] S1: Use a jaw crusher to crush the molten lead-zinc slag after iron extraction and impoverishment, then screen it with a standard sieve, select the ore powder with a particle size less than or equal to 0.075 mm as the experimental raw material, and prepare a pulp by adding water to the molten lead-zinc slag powder after iron extraction and impoverishment according to a solid-liquid ratio of 0.1:200 g / mL. After adjusting the pulp, put it into a three-necked flask;

[0045] S2: Put the three-necked flask into a magnetic stirring water bath, set the temperature to 45 °C, and pass the mixed flue gas into the molten lead-zinc slag pulp after iron extraction and impoverishment in the three-necked flask. The mixed flue gas contains O2, SO2, and N2, the SO2 concentration is 2000 ppm, and desulfurization is carried out for 5 h.

[0046] S3: Use the desulfurized tail liquid collected in S2, add 0.5 g of NaClO2, then put the three-necked flask into a magnetic stirring water bath, set the temperature to 45 °C, and pass the mixed flue gas into the desulfurized tail liquid in the three-necked flask. The mixed flue gas contains O2, NO X , N2, and the NO X concentration is 300 ppm, and N2 is the balance gas; taking the temperature (T) as a variable, adjust the T of the desulfurized tail liquid to 25 °C, 35 °C, 45 °C, 55 °C, and 65 °C respectively;

[0047] S4: React multiple portions of desulfurized tail liquid with the same composition and mass with the introduced different flue gases, set the gas flow rate to 200 mL / min, conduct gas collection at 0, 30, 60, 90, and 120 minutes respectively, and the gas collection time for each time is 6 minutes. Measure the collected gas with a flue gas analyzer according to the method of Example 1, and calculate the removal rate of NO X , as Figure 3 shown. It can be seen from the figure that the pulp can well absorb NO in the flue gas X , and the best effect is achieved when T = 45 °C.

[0048] Example 4

[0049] A method for removing NO in flue gas by using desulfurized tail liquid of molten lead-zinc slag after iron extraction and impoverishment and a synergistic oxidant according to this example X comprises the following steps:

[0050] S1: Use a jaw crusher to crush the molten lead-zinc slag after iron extraction and impoverishment, then screen it with a standard sieve, and select the ore powder with a particle size less than or equal to 0.075 mm as the experimental raw material. Prepare the molten lead-zinc slag powder after iron extraction and impoverishment into a pulp by adding water according to a solid-liquid ratio of 0.1:200 g / mL, and put the pulp into a three-necked flask after pulp adjustment;

[0051] S2: Place the three-necked flask in a magnetic stirring water bath, set the temperature to 45 °C, and pass the mixed flue gas into the molten lead-zinc slag pulp after iron extraction and impoverishment in the three-necked flask. The mixed flue gas contains O2, SO2, and N2, and the SO2 concentration is 2000 ppm. Desulfurization is carried out for 5 h.

[0052] S3: Use the desulfurized tail liquid collected in S2, add 0.5 g of NaClO2, then place the three-necked flask in a magnetic stirring water bath, set the temperature to 45 °C, and pass the mixed flue gas into the desulfurized tail liquid in the three-necked flask. The mixed flue gas contains O2, NO X 、N2, the volume fraction of O2 is 10%, and NO X The concentration is 300 ppm, and N2 is the balance gas.

[0053] S4: React multiple portions of desulfurized tail liquid with the same composition and mass with flue gas at different gas flow rates. Take the gas flow rate (v) as a variable, adjust the gas flow rate (v) to 200 mL / min, 300 mL / min, 400 mL / min, 500 mL / min, 600 mL / min, and connect the gas at 0, 30, 60, 90, and 120 minutes. Each gas connection time is 6 minutes. Measure the collected gas with a flue gas analyzer according to the method of Example 1, and calculate the removal rate of NO X As shown in Figure 4 , the pulp can well absorb NO in the flue gas X . It can be seen from the figure that the effect is the best when v = 200 mL / min.

[0054] Example 5

[0055] The source of lead-zinc molten slag after iron extraction and impoverishment is the research content of the national key research and development project "Technology and Demonstration of Simultaneous Smelting of Lead and Zinc with Metal-based Solid Waste in Lead-Zinc Ore". In the project, through the addition of plasma-enhanced iron reduction technology in the traditional smelting furnace, the lead-zinc molten slag with deep iron extraction by electro-enhanced carbon immersion reduction of lead and zinc is obtained, and the iron component in the molten lead-zinc slag is recovered to obtain the iron-extracted and impoverished lead-zinc slag. According to BET analysis, compared with the molten lead-zinc slag before iron extraction and impoverishment, the specific surface area of the molten lead-zinc slag after iron extraction and impoverishment increases, the total pore volume increases, and the average pore diameter decreases; according to SEM analysis, the microstructure of the lead-zinc molten slag after iron extraction and impoverishment becomes more fragmented and the surface becomes rougher compared with that before iron extraction and impoverishment; according to XPS analysis, more Fe(III) sites are exposed in the lead-zinc molten slag after iron extraction and impoverishment compared with that before iron extraction and impoverishment. To sum up, the molten lead-zinc slag treated by iron extraction and impoverishment has greater activity in desulfurization and denitrification.

[0056] (1) In this example, the synergistic denitrification effect of the complex system of metal sulfates such as Fe 3+ , Mn 2+ , K + , Zn 2+ , Na + and sodium chlorite on NOx in simulated flue gas was first investigated. Two groups of controls were set in the experiment: the experimental group used a mixed absorbent solution of a single metal sulfate solution (2.5 mmol / L) and sodium chlorite (25 mmol / L), and the control group was an equal volume of pure sodium chlorite solution. The experimental conditions were: reaction temperature 45 °C, gas flow rate 200 mL / min, flue gas oxygen content 10%, and initial NO concentration 300 ppm. The comparison results of the denitrification performance of different metal ion systems are shown in Figure 5 .

[0057] According to Figure 5 's experimental data, under the condition of a reaction time of 180 minutes, when sodium chlorite was used in combination with Fe 3+ , Zn 2+ , K + , Mn 2+ and Na + ions, the denitrification efficiency of each system showed significant differences, specifically 92.3%, 82.37%, 85.43%, 81.33% and 77% respectively, and the denitrification efficiency of the blank control group was 78%. It can be seen that Fe 3+ , K + , Zn 2+ , Mn 2+ combined with NaClO2 had a higher removal rate of NO X . At the same time, the NO + removal rate of the Na X +NaClO2 group was similar to that of the group without added metal ions. It shows that Fe3+ , K + 、Zn 2+ , Mn 2+ The combined use of four metal ions and sodium chlorite solution can enhance the denitrification effect, among which Fe 3+ The promoting effect of K + Next is Zn 2+ With Mn 2+ The synergistic effect is relatively weak and the effects of the two are close.

[0058] (2) The reaction mechanism of NaClO2 denitrification of molten lead-zinc slag desulfurized slurry after iron extraction is shown in Table 1 and can be divided into two parts: (1) oxidation of NO; (2) absorption of NO2.

[0059] NO is mainly converted to ClO2 at the gas-liquid interface - Oxidized to NO2 (Formula 1), then converted to NO3 in the liquid phase - (Formula 2). A small amount of NO is directly oxidized to NO3 in the liquid phase - (Equation 3), the remaining NO is oxidized to NO2 by ClO2 in the liquid or gas phase (Equation 4).

[0060] In the oxidation reaction, ClO2 - In addition, the oxidation efficiency of NaClO2 in acidic environment is restricted by two factors: in an environment with low pH value, ClO2 - The oxidizability of NaClO2 will be improved; under acidic conditions, NaClO2 + Effects and metal ions, especially Fe 3+ Under the activation of , more ClO2 with stronger oxidizing ability is generated.

[0061] Fe 3+ The activation of NaClO2 is due to the Fe 3+ Will react with ClO2 - Rapid formation of FeClO2 2+ The complex then decomposes into Fe 2+ and ClO2, the divalent iron is quickly oxidized to trivalent iron, thus forming a cycle. - It is reduced to divalent chlorine and reacts with other ClO2 - Produces ClO2 and HOCl. Therefore, Fe 3+ The overall reaction process of the catalytic decomposition reaction of NaClO2 can be expressed as (Equation (5)).

[0062] During the absorption reaction, nitrogen dioxide (NO2) can be directly absorbed by the aqueous phase according to Equation (6). At the same time, a small amount of nitric oxide (NO) and nitrogen dioxide (NO2) will also undergo aqueous-phase oxidation and absorption reactions according to Equation (7). Further, the absorbed acid radicals will continue to be oxidized by chlorite (ClO2 - ) and chlorine dioxide (ClO2) in the solution according to Equations (8) and (9), and finally converted into nitrate ions (NO3 - ).

[0063]

[0064] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principle and practical application of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A method for removing NO from flue gas by using the desulfurization tail liquid of molten lead-zinc slag after iron extraction and impoverishment and a synergistic oxidant X , which is characterized in that It includes the following steps: S1: Grind the molten lead-zinc slag after iron extraction and dephosphorization to a particle size not greater than 0.075 mm, and prepare a pulp by adding water according to a solid-liquid ratio of 1:200 g / mL; S2: Pass SO2-containing flue gas into the pulp to remove SO2 in the flue gas; S3: Heat the desulfurized tail liquid after SO2 removal to 25 - 65 °C, add an oxidant, and then introduce the flue gas containing NO X for NO removal from the flue gas. X ​ 2. Method for removing NO in flue gas by using desulfurization tail liquid of molten lead-zinc slag after iron extraction and impoverishment and co-oxidant as claimed in claim 1 X , characterized in that: The molten lead-zinc slag after iron extraction and dephosphorization is the lead-zinc molten slag obtained by electro-enhanced carbon immersion reduction for deep iron extraction and dephosphorization of lead-zinc. The mass percentages of its components are as follows: iron oxide 33.5%-37.5%, manganese oxide 11.41%-12.41%, silicon dioxide 17.25%-21.25%, zinc oxide 4.21%-5.21%, and the rest are inevitable impurities.

3. Method for removing NO in flue gas by using desulfurization tail liquid of molten lead-zinc slag after iron extraction and impoverishment and co-oxidant as claimed in claim 1 X , characterized in that: The NO-containing X concentration of NO in the flue gas X is 100 - 900 ppm; the NO-containing X smelting flue gas also contains oxygen, and the volume fraction of oxygen is 0 - 10%.

4. Method for removing NO in flue gas by using desulfurization tail liquid of molten lead-zinc slag after iron extraction and impoverishment and co-oxidant as claimed in claim 1 X , characterized in that: The NO-containing X The inlet flow rate of the flue gas is 200 - 600 mL / min.

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