Double-layer pellet for realizing emission reduction of VOCs (volatile organic compounds) in metallurgical sludge ore blending sintering process as well as preparation method and application of double-layer pellet

Abstract

The invention discloses a double-layer pellet for realizing emission reduction of VOCs (Volatile Organic Compounds) in a metallurgical sludge ore blending sintering process as well as a preparation method and application of the double-layer pellet, and belongs to the technical field of metallurgical sludge treatment. The double-layer pellet comprises an inner-layer pellet and a pellet shell wrapping the outer layer of the inner-layer pellet. Wherein the raw materials of the inner-layer pellets comprise an oxidizing agent and metallurgical sludge which is pyrolyzed to generate VOCs, the VOCs discharging temperature interval of the metallurgical sludge used by the inner-layer pellets is 250-450 DEG C, the oxidizing agent is used for being decomposed at 240-450 DEG C to form oxygen, the raw materials of the pellet shells comprise at least one of acid-base neutralized sludge and OG coarse grains and modified iron oxide sludge particles, and the modified iron oxide sludge particles are used for being decomposed at 240-450 DEG C to form oxygen. The modified iron oxide sludge contains gamma-Fe2O3. In the ore blending and sintering process, VOCs generated by the internal pellets react with O2 to decompose the VOCs, the modified iron oxide sludge capable of catalyzing the oxidation reaction of the VOCs wraps the inner layer pellets, and meanwhile, the pelletizing performance of the modified iron oxide sludge is improved by using acid-base to neutralize the sludge or OG coarse grains.

Description

Technical Field

[0001] The present invention relates to the technical field of metallurgical sludge treatment, and more specifically, to a double-layer pellet for reducing VOCs emissions in a metallurgical sludge ore blending and sintering process, and a preparation method and application thereof. Background Art

[0002] A large amount of metallurgical solid waste is generated during the production process of the steel industry. Adding it to the sintering mixture for sintering and disposal is one of the main ways to treat metallurgical solid waste. However, direct sintering of metallurgical solid waste will cause the pollutant emissions in the resulting flue gas to exceed the standard. Taking the sludge solid waste generated by a domestic steel company as an example, it mainly includes iron oxide sludge, OG coarse particles, acid-base neutralization sludge, continuous casting sludge, biological sludge, calcium carbonate sludge, etc. The inventor's previous related research found that when the sludge solid waste of the above-mentioned steel plant is directly mixed with sintering raw materials for sintering, the biological sludge and continuous casting sludge will produce a large amount of volatile organic compounds (VOCs) during the ore blending and sintering process. VOCs are one of the main pollutants in the air. High concentrations of VOCs will not only cause atmospheric pollution, but also endanger human health. Therefore, effective treatment measures must be taken for the VOCs generated during the ore blending and sintering process of biological sludge and continuous casting sludge.

[0003] At present, there are two types of treatment methods for VOCs: recovery method and destruction method. Recovery methods mainly include condensation method, membrane separation method, absorption method and adsorption method; destruction method refers to the decomposition of VOCs into carbon dioxide and water by oxidation, which is a relatively common method for treating VOCs. For example, the Chinese patent application with publication number CN115105936A discloses a method and device for the coordinated purification of CO, VOCs, NOx and hydrogen halide in metallurgical flue gas. The application achieves the coordinated purification of CO, VOCs, NOx and hydrogen halide in the flue gas by heating the metallurgical flue gas twice. The application belongs to the destruction method.

[0004] For another example, the Chinese patent application with publication number CN 118491295 A discloses a high-concentration VOCs waste gas ultra-low emission treatment equipment and method, which solves the problem in the prior art that direct emission of VOCs waste gas with a concentration exceeding 1 / 4LEL causes serious environmental pollution. This application also belongs to the destructive method of treatment.

[0005] However, the above applications all belong to the flue gas treatment process after VOCs escape from solid waste. There are problems such as high energy consumption per unit of waste gas treatment, the need for professional flue gas treatment equipment, and high equipment investment costs. Summary of the invention

[0006] In view of the problem that a large amount of VOCs will be generated during the sintering process of sludge solid waste blending and ore blending in the prior art, causing pollution, and the energy consumption and cost of VOCs treatment are both high, the present invention provides a double-layer pellet for reducing VOCs emissions during the sintering process of metallurgical sludge blending and ore blending, and a preparation method and application thereof to achieve the double-layer pellet for reducing VOCs emissions during the sintering process of metallurgical sludge blending and ore blending. This solution uses different types of metallurgical sludge to prepare inner layer pellets and pellet shells respectively, adds an oxidant to the inner layer pellets, and controls the release window of the oxidant and the inner layer pellets to be roughly the same. At the same time, the pellet shell is made of multiple types of metallurgical sludge, which can not only catalyze and oxidize VOCs, but also ensure the stability of the pellet shell structure. Sintering the double-layer pellet blending and ore blending can reduce VOCs emissions from the source.

[0007] The first aspect of the present invention provides a double-layer pellet for reducing VOCs emissions in the process of metallurgical sludge ore blending and sintering, the double-layer pellet comprises an inner-layer pellet and a pellet shell wrapped around the outer layer of the inner-layer pellet; wherein the raw materials of the inner-layer pellet comprise an oxidant and metallurgical sludge, the temperature range of VOCs emitted by the metallurgical sludge used in the inner-layer pellet is 250 to 450°C, and the oxidant is used to decompose at 240 to 450°C to form oxygen; the raw materials of the pellet shell comprise at least one of acid-base neutralization sludge, OG coarse particles, and modified iron oxide sludge particles, and the modified iron oxide sludge contains γ-Fe2O3.

[0008] Based on the pyrolysis experiments on various metallurgical sludges such as iron oxide sludge, OG coarse particles, acid-base neutralization sludge, continuous casting sludge, biological sludge, and calcium carbonate sludge, the inventors found that the VOCs emissions of biological sludge and continuous casting sludge were relatively high during the pyrolysis process, which were 17.30 mg / g and 6.59 mg / g respectively, and the release temperature range of VOCs generated by sludge pyrolysis was 250-450°C. In the process of mixing various metallurgical sludges in a certain proportion and then sintering them with ore, taking the addition of steel plant sludge solid waste accounting for 1% of the sintering raw materials as an example, the VOCs emission concentration reached 143 mg / m 3 .

[0009] In view of the problem that metallurgical sludge is used for ore blending and sintering in the prior art and is prone to produce a large amount of VOCs, the inventor uses a variety of metallurgical sludges in a certain proportion to prepare double-layer pellets, mixes metallurgical sludge with a large amount of VOCs release and an oxidant to form an inner layer of pellets, and wraps the modified iron oxide mud on the outside of the inner layer of pellets as the outer shell of the pellets. By preparing double-layer pellets with the above structure, it is expected to achieve VOCs reduction in the sintering process of metallurgical sludge. The above double-layer pellets, which account for 1% of the mass proportion of the sintering raw materials, are added to the sintering raw materials in the form of external blending for sintering, and volatile organic compounds VOCs are tested online. The test found that the VOCs emission concentration was high, the VOCs emission reduction efficiency was not obvious, and the emission reduction requirements could not be met.

[0010] Through further exploration of the previous experimental results, the inventors found that the modified iron oxide mud used as the outer shell of the pellets in the above-mentioned double-layer pellets has poor ball-forming performance. Specifically, as the sintering temperature increases, the outer shell of the pellets cracks and falls off prematurely at high temperatures, so that the modified iron oxide mud cannot fully play the role of catalytic oxidation and decomposition of VOCs. Therefore, the modified iron oxide mud cannot be simply used as the raw material for the outer shell of the pellets, and the strength and stability of the raw materials for the outer shell of the pellets need to be fully considered. The inventors continued to try to improve the above-mentioned double-layer pellets. Through the combination of theory and practice, it was found that at least one of the acid-base neutralization sludge and OG coarse particles was added to the outer shell of the pellets. After drying, the two sludges can effectively realize the solid-phase connection of the raw materials of the outer shell of the pellets and adhere to the inner layer of the pellets to form a whole. At the same time, certain pores can be formed, which is beneficial to increase the porosity and strength of the pellets, so that VOCs can be fully diffused and oxidized after being discharged, and the outer shell of the pellets is prevented from cracking and falling off due to the impact of the inner layer of gas, thereby increasing the stability of the outer shell structure of the pellets.

[0011] The specific mechanism of action of the double-layer pellets prepared based on the above research process is as follows: During the sintering process, as the sintering material is heated to 250-450°C, the metallurgical sludge in the internal pellets will decompose to form a large amount of VOCs, so an oxidant that decomposes and produces O2 in this temperature range is selected. The outer shell of the pellets is stably present outside the inner layer of the pellets. Since the outer shell of the pellets contains γ-Fe2O3, the VOCs and O2 in the inner layer will contact the γ-Fe2O3 when diffusing to the outer shell of the pellets. Under the catalytic action of γ-Fe2O3, VOCs will react with O2 to form CO2 and H2O, thereby achieving the oxidative decomposition of VOCs. That is, the present invention cleverly uses metallurgical sludge solid waste to make a double-layer pellet structure, so that most of the VOCs generated during the sintering process of metallurgical sludge are oxidatively decomposed during the diffusion process. In the iron ore sintering process, ultra-low emissions of VOCs from sludge solid waste are achieved, which can effectively reduce the treatment cost of VOCs and simplify the treatment process compared to the prior art.

[0012] Furthermore, the oxidant is KMnO4. The temperature range of VOCs emitted by metallurgical sludge used in the inner pellets is 250-450°C, and KMnO4 decomposes to generate oxygen at 240-450°C. The release temperatures of the two are almost the same, so that VOCs can be oxidized by O2 at the beginning of release.

[0013] Furthermore, the oxygen agent decomposes to form oxygen, and the mass ratio of VOCs emitted by the inner pellets is 0.7 to 2, so that the oxygen formed by the decomposition of the oxidant can provide sufficient O2 for the catalytic oxidation of VOCs.

[0014] Furthermore, the metallurgical sludge used for the inner layer pellets includes biological sludge and / or continuous casting sludge. From the pyrolysis experiment of the above sludge, it can be seen that the VOCs release per unit mass of biological sludge and / or continuous casting sludge is relatively high. Selecting at least one of the two sludges as the raw material for the inner layer pellets can achieve a better VOCs emission reduction purpose.

[0015] Furthermore, the thickness of the pellet shell is 3-4 mm. By designing the thickness of the pellet shell to be 3-4 mm, VOCs can stay in the pellet shell for a longer time, allowing the modified iron oxide sludge particles to fully play a catalytic oxidation role, thereby improving the oxidation and decomposition efficiency of VOCs generated by the inner layer pellets.

[0016] Furthermore, the pellet shell also includes calcium carbonate sludge. The calcium carbonate sludge has a high content of CaCO3, which can act as a flux, so that the prepared double-layer pellets are fully combined with the sintering raw materials during the sintering process, ensuring that the quality of the sintered ore does not fluctuate greatly.

[0017] Furthermore, the raw materials for the pellet shell include modified iron oxide sludge, acid-base neutralization sludge, calcium carbonate sludge and OG coarse particles, and the mass ratio of the modified iron oxide sludge, acid-base neutralization sludge, calcium carbonate sludge and OG coarse particles after drying is 16-18:35-40:5-7:21-25. By optimizing the design of the types of raw materials for the pellet shell, the raw materials for the pellet shell include four metallurgical sludges, which can not only effectively ensure the overall structural strength of the obtained pellet shell, but also realize the coordinated treatment and disposal of more types of metallurgical sludges. Furthermore, the optimized design of the mass ratio of the four types of sludge in the pellet shell is mainly based on the annual output of various metallurgical sludges in the production of domestic steel enterprises. The advantage of this selection method is to further improve the coordinated treatment and disposal efficiency of various sludges by steel enterprises.

[0018] The second aspect of the present invention provides a method for preparing the above-mentioned double-layer pellets for achieving VOCs emission reduction in the metallurgical sludge ore blending and sintering process, comprising: making the inner layer pellet raw material into inner layer small balls; coating the raw material of the pellet shell on the outer surface of the inner layer small balls to produce double-layer pellets.

[0019] Furthermore, the method also includes the steps of drying and crushing the iron oxide sludge and heating it in an oxygen atmosphere to obtain modified iron oxide sludge particles.

[0020] Furthermore, the particle size of the modified iron oxide sludge particles is less than 0.074 mm.

[0021] A third aspect of the present invention provides the above double-layer pellets, or the use of the double-layer pellets prepared by the above preparation method in sintering materials.

[0022] Furthermore, the sintering material also includes sintering raw materials, wherein the mass ratio of the double-layer pellets to the sintering raw materials is 1 to 3:100.

[0023] Furthermore, the sintering raw materials include mixed ore, return ore, limestone, dolomite, quicklime, external dust and coke powder.

[0024] In summary, the technical solution provided by the present invention can have the following beneficial effects compared with the prior art:

[0025] (1) Compared with the direct mixing of sludge with ore for sintering, the present invention prepares double-layer pellets, utilizes the VOCs generated by the inner pellets to react with O2 during the sintering process to achieve the decomposition of VOCs, and wraps the modified iron oxide sludge that can catalyze the oxidation reaction of VOCs on the outside of the inner pellets to improve the timing of VOCs oxidation and decomposition. At the same time, the temperature of the oxidant to generate oxygen is close to the temperature range of VOCs released during the sintering of metallurgical sludge, so that VOCs have sufficient O2 to undergo corresponding oxidation reactions during the release process.

[0026] (2) The present invention further optimizes the design of the inner layer pellets, and uses two types of biological sludge and continuous casting sludge that generate high VOCs content by pyrolysis as raw materials for preparing the inner layer pellets, further improving the VOCs emission reduction efficiency. In addition, the oxidant is preferably KMnO4, and the temperature at which KMnO4 decomposes to generate oxygen is close to the temperature of the VOCs release peak during the sintering process of metallurgical sludge, so that VOCs have sufficient O2 to undergo corresponding oxidation reactions during the release process.

[0027] (3) According to the properties of the dust and mud in the steel plant, the present invention also uses acid-base neutralization sludge, calcium carbonate sludge, and OG coarse particles as the raw materials for the pellet shell. The raw materials for the pellet shell include modified iron oxide sludge, OG coarse particles, acid-base neutralization sludge, and calcium carbonate sludge. The acid-base neutralization sludge and OG coarse particles can improve the spheroidization of the modified iron oxide sludge, which is beneficial to improve the strength of the pellets and increase the porosity of the pellets, so that VOCs can fully diffuse and undergo oxidation reactions after being discharged. In addition, the CaCO3 component in the calcium carbonate sludge is equivalent to a flux, which allows the prepared double-layer pellets to be fully combined with the mixed ore, ensuring that the quality of the sintered ore does not fluctuate greatly due to the addition of sludge. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a process flow chart for preparing double-layer pellets in Example 1 of the present invention. DETAILED DESCRIPTION

[0029] In order to further understand the content of the present invention, the present invention is described in detail in conjunction with embodiments.

[0030] Example 1

[0031] This embodiment provides a method for preparing double-layer pellets for reducing VOCs emissions in the sintering process of metallurgical sludge. Figure 1 As shown, the steps are as follows:

[0032] (I) Raw material pretreatment

[0033] (1) Sludge pretreatment: biological sludge, continuous casting sludge, iron oxide sludge, acid-base neutralization sludge, calcium carbonate sludge and OG coarse particles are obtained from the steel plant, dried, and then crushed into particles smaller than 0.074 mm to obtain biological sludge particles, continuous casting sludge particles, iron oxide sludge particles, acid-base neutralization sludge particles, calcium carbonate sludge particles and OG coarse particles.

[0034] Based on 100 parts, the biological sludge particles used in this embodiment include the following components in mass parts: TFe: 15.41 parts, SiO2: 3.25 parts, CaO: 3.25 parts, MgO: 0.31 parts, Al2O3: 24.07 parts, and the rest are unavoidable impurities.

[0035] The continuous casting sludge particles include the following components in parts by mass: TFe: 22.04 parts, SiO2: 8.60 parts, CaO: 9.03 parts, MgO: 1.58 parts, Al2O3: 17.19 parts, MnO: 9.84 parts, and the rest are unavoidable impurities.

[0036] The iron oxide sludge includes the following components in parts by mass: TFe: 67.09 parts, SiO2: 0.87 parts, CaO: 0.54 parts, MgO: 0.11 parts, Al2O3: 0.73 parts; MnO: 0.82 parts, and the rest are unavoidable impurities.

[0037] The acid-base neutralization sludge includes the following components in parts by mass: TFe: 32.64 parts, SiO2: 5.57 parts, CaO: 6.82 parts, MgO: 12.73 parts, Al2O3: 15.39 parts; MnO: 0.90 parts, and the rest are unavoidable impurities.

[0038] The calcium carbonate sludge includes the following components in parts by mass: TFe: 10.09 parts, SiO2: 0.45 parts, CaO: 70.53 parts, MgO: 0.84 parts, Al2O3: 0.45 parts; MnO: 0.08 parts, and the rest are unavoidable impurities.

[0039] The OG coarse particles include the following components in parts by mass: TFe: 56.79 parts, SiO2: 3.40 parts, CaO: 7.68 parts, MgO: 3.25 parts, Al2O3: 0.97 parts; MnO: 0.69 parts, and the rest are unavoidable impurities.

[0040] (2) Iron oxide sludge modification treatment: The iron oxide sludge particles obtained by the above pretreatment are heated at 280°C for 8 hours under an oxygen atmosphere to fully oxidize the FeO in the iron oxide sludge particles to form γ-Fe2O3, thereby obtaining modified iron oxide sludge particles.

[0041] (II) Pelletizing

[0042] (1) Based on the total mass of the metallurgical sludge used in the inner and outer layers as 100 parts, 14 parts of biological sludge particles, 2 parts of continuous casting sludge particles and 2 parts of KMnO4 were mixed to prepare a mixture A, wherein the particle size of the KMnO4 used was less than 0.074 mm; 17 parts of modified iron oxide sludge, 38 parts of acid-base neutralization sludge, 6 parts of calcium carbonate sludge and 23 parts of OG coarse particles were mixed to prepare a mixture B;

[0043] (2) Mixture A is supplemented with water to 8±0.5wt.%, and then the inner layer of small balls is prepared by a disc pelletizer; mixture B is supplemented with water to 8±0.5wt.%, and then covered on the outer surface of the inner layer of small balls to prepare double-layer pellets, and the thickness of the outer shell of the pellets is 3mm±0.2m.

[0044] (III) Ore blending and sintering cup test

[0045] The sintering raw materials used include mixed ore, return ore, limestone, dolomite, quicklime, external dust, and coke powder. The specific components and proportions are shown in Table 2.

[0046] Table 2 Chemical composition of raw materials for sintering cup test, wt.%

[0047]

[0048]

[0049] (1) Mixing: Add 1% of the double-layer pellets by weight of the sintering raw materials to the sintering raw materials in the form of an external mixture and mix for 2 minutes; then add water and mix for 5 minutes, and control the moisture content of the mixture to 7.5±0.2% to obtain a mixed material;

[0050] (2) Before conducting the sintering cup test, 2 kg of sintered ore with a particle size of 10 to 16 mm was evenly added to the bottom of the sintering cup as a base material, and then the mixed material obtained in step (1) was poured into the sintering cup. The mixture was ignited for 1.5 min using liquefied gas at a temperature of 1100 ± 50 °C and a vacuum pressure of 7 kPa. The vacuum pressure was adjusted to 14 kPa for vacuum sintering. The vacuum volume of the sintering cup fan was 80 m 3 ·h -1 .

[0051] (IV) Testing VOCs emissions from sintering flue gas

[0052] During the exhaust process of the sintering machine, an oil-free vacuum pump is used to take out the sintering flue gas from the sampling port. The gas pipeline is connected in parallel to take gas. A portable non-methane total hydrocarbon tester and a filter device are connected to the end of the gas pipeline to perform online detection of volatile organic compounds (VOCs). The test results are detailed in Table 3.

[0053] (V) Testing the quality of sintered ore

[0054] The sintered ore yield and drum strength are tested according to national standards and metallurgical industry standards. The sintered ore yield is the mass percentage of the sintered ore with a particle size of +5mm in the total material after screening, %. The drum strength is an indicator to measure the strength of the finished sintered ore. In this study, 7.5kg of finished sintered ore with a particle size between 10-40mm was used for drum strength testing, and finally the particles with a particle size of >6.3mm were screened out. The drum strength is expressed as a mass percentage, %. The test results are shown in Table 3.

[0055] Comparative Example 1

[0056] This comparative example provides a method for preparing double-layer pellets for reducing VOCs emissions in the sintering process of metallurgical sludge ore blending. The difference between the method and Example 1 is that KMnO4 is not added to mixture A, mixture A and mixture B are directly mixed, and then added to the sintering raw materials in an external form, that is, KMnO4 is not added and pelletizing treatment is not performed, and other operations are basically the same; the test results are detailed in Table 3.

[0057] Comparative Example 2

[0058] This comparative example provides a method for preparing double-layer pellets for reducing VOCs emissions in the sintering process of metallurgical sludge. The difference between the method and Example 1 is that KMnO4 is not added to the mixture A, and other operations are basically the same. The test results are detailed in Table 3.

[0059] Comparative Example 3

[0060] This comparative example provides a method for preparing double-layer pellets for reducing VOCs emissions in the sintering process of metallurgical sludge. The difference between this method and Example 1 is that iron oxide sludge particles are used in mixture B instead of the modified iron oxide sludge particles in Example 1; other operations are basically the same; the test results are detailed in Table 3.

[0061] Comparative Example 4

[0062] This comparative example provides a method for preparing double-layer pellets for reducing VOCs emissions in the sintering process of metallurgical sludge. The difference between this method and Example 1 is that mixture A and mixture B are mixed to prepare single-layer pellets to replace the double-layer pellets in Example 1, and other operations are basically the same. The test results are detailed in Table 3.

[0063] Comparative Example 5

[0064] This comparative example provides a method for preparing double-layer pellets for reducing VOCs emissions in the sintering process of metallurgical sludge ore blending. The difference between this method and comparative example 1 is that double-layer pellets accounting for 2% of the mass proportion of the sintering raw materials are added to the sintering raw materials in the form of external blending, and the remaining operations are basically the same; the test results are detailed in Table 3.

[0065] Comparative Example 6

[0066] This comparative example provides a method for preparing double-layer pellets for reducing VOCs emissions in the sintering process of metallurgical sludge ore blending. The difference between this method and comparative example 1 is that double-layer pellets accounting for 3% of the mass proportion of the sintering raw materials are added to the sintering raw materials in the form of external blending, and the remaining operations are basically the same; the test results are detailed in Table 3.

[0067] Comparative Example 7

[0068] This embodiment provides a method for preparing double-layer pellets for reducing VOCs emissions in the metallurgical sludge ore blending and sintering process. The difference between this method and Example 1 is that the mixture B used only includes modified iron oxide sludge particles, and the number of modified iron oxide sludge particles is 84 parts; the remaining operations are basically the same, and the test results are detailed in Table 3.

[0069] Example 2

[0070] This embodiment provides a method for preparing double-layer pellets for reducing VOCs emissions in the sintering process of metallurgical sludge ore blending. The difference between this method and Example 1 is that double-layer pellets accounting for 2% of the mass proportion of the sintering raw materials are added to the sintering raw materials in the form of external blending, and the remaining operations are basically the same. The test results are detailed in Table 3.

[0071] Example 3

[0072] This embodiment provides a method for preparing double-layer pellets for reducing VOCs emissions in the sintering process of metallurgical sludge ore blending. The difference from Example 1 is that double-layer pellets accounting for 3% of the mass of the sintering raw materials are added to the sintering raw materials in the form of external blending, and the remaining operations are basically the same. The test results are detailed in Table 3.

[0073] Example 4

[0074] This embodiment provides a method for preparing double-layer pellets for reducing VOCs emissions in the sintering process of metallurgical sludge. The difference between this method and Example 1 is that in the mixture A, the amount of KMnO4 added is 1 part, that is, KMnO4 accounting for 1% of the mass of the metallurgical sludge is added in an external manner, and the rest of the operations are basically the same. The test results are detailed in Table 3.

[0075] Example 5

[0076] This embodiment provides a method for preparing double-layer pellets for reducing VOCs emissions in the sintering process of metallurgical sludge. The difference between this method and Example 1 is that in the mixture A, the amount of KMnO4 added is 3 parts, that is, KMnO4 accounting for 3% of the mass of the metallurgical sludge is added in an external manner, and the rest of the operations are basically the same. The test results are detailed in Table 3.

[0077] Example 6

[0078] The present embodiment provides a method for preparing double-layer pellets for reducing VOCs emissions in the process of metallurgical sludge ore blending and sintering. The difference between the method and Example 1 is that 13 parts of biological sludge particles, 5 parts of continuous casting sludge particles and 2 parts of KMnO4 are mixed to prepare a mixture A, 16 parts of modified iron oxide sludge particles, 40 parts of acid-base neutralization sludge particles, 5 parts of calcium carbonate sludge particles and 23 parts of OG coarse particles are mixed to prepare a mixture B, the thickness of the pellet shell in the preparation of the double-layer pellets is 4 mm, and the other operations are basically the same; the test results are detailed in Table 3.

[0079] Example 7

[0080] The present embodiment provides a method for preparing double-layer pellets for reducing VOCs emissions in the process of metallurgical sludge ore blending and sintering. The difference between the present embodiment and embodiment 1 is that: 15 parts of biological sludge particles and 2 parts of KMnO4 are mixed to prepare mixture A, 18 parts of modified iron oxide sludge, 35 parts of acid-base neutralization sludge particles, 7 parts of calcium carbonate sludge particles and 25 parts of OG coarse particles are mixed to prepare mixture B, and the thickness of the pellet shell in the prepared double-layer pellets is 3 mm; the remaining operations are basically the same; the test results are detailed in Table 3.

[0081] Example 8

[0082] This embodiment provides a method for preparing double-layer pellets for reducing VOCs emissions in the sintering process of metallurgical sludge. The difference between this method and Example 1 is that 17 parts of modified iron oxide sludge particles and 67 parts of acid-base neutralization sludge particles are mixed to prepare mixture B; the remaining operations are basically the same; the test results are detailed in Table 3.

[0083] Example 9

[0084] This embodiment provides a method for preparing double-layer pellets for reducing VOCs emissions in the sintering process of metallurgical sludge. The difference between this method and Example 1 is that 17 parts of modified iron oxide sludge particles and 67 parts of OG coarse particles are mixed to prepare mixture B; the remaining operations are basically the same; the test results are detailed in Table 3.

[0085] Table 3 VOCs emission during sludge sintering process in various embodiments and comparative examples

[0086]

[0087]

[0088] The sludge-to-ore ratio in the above table refers to the ratio of the mass of double-layer pellets or the mass of metallurgical sludge after direct mixing added to the sintering raw materials in the form of external mixing; the KMnO4 addition ratio refers to the ratio of KMnO4 added to the metallurgical sludge raw materials in the form of external mixing, which is the ratio of KMnO4 to the total mass of the inner and outer layer metallurgical sludge raw materials.

[0089] By analyzing the data in Table 3, we can know that:

[0090] (1) By comparing Example 1 with Comparative Example 1, Example 2 with Comparative Example 5, and Example 3 with Comparative Example 6, it can be seen that by making KMnO4, biological sludge and continuous casting sludge into inner layer pellets, and using modified iron oxide sludge as the outer shell of the pellets, double-layer pellets are prepared. When the addition amount of the double-layer pellets is 1% to 3% of the sintering raw materials, the VOCs emission reduction efficiency reaches more than 80%, and the emission reduction effect is significant.

[0091] (2) By comparing Example 1 with Comparative Example 2, it can be seen that when KMnO4 is not added to the inner layer pellets, the VOCs emission reduction efficiency is reduced from 80% to 40%, indicating that the addition of KMnO4 to the inner layer pellets has a significant effect on promoting VOCs emission reduction. KMnO4 decomposes into O2 within the temperature window of VOCs release, providing sufficient reaction conditions for the VOCs oxidation reaction.

[0092] (3) By comparing Example 1 with Comparative Example 3, it can be seen that when the iron oxide sludge is not modified, the VOCs emission reduction efficiency is reduced to 34%, indicating that the modified iron oxide sludge particles have a significant effect on promoting VOCs emission reduction and effectively catalyze and promote the occurrence of VOCs oxidation reaction.

[0093] (4) By comparing Example 1 with Comparative Example 4, it can be seen that the VOCs emission reduction efficiency of preparing single-layer pellets is reduced from 80% to 40% compared with preparing double-layer pellets. This indicates that when preparing double-layer pellets, sludge containing higher VOCs is placed inside the double-layer pellets. When the internal sludge decomposes to form VOCs, it will diffuse to the outer shell of the pellets and undergo an oxidation reaction under the catalytic action of the modified iron oxide sludge, thereby increasing the oxidation decomposition rate of VOCs.

[0094] (5) By comparing Example 1, Example 4, and Example 5, it can be seen that adding different proportions of KMnO4 has a greater impact on the VOCs emission reduction rate. When the KMnO4 addition ratio is 1%, 2%, and 3%, the VOCs emission reduction rate is 66%, 80%, and 75% respectively. By adding KMnO4, the oxygen-containing atmosphere during the sintering process is increased, and the oxidation reaction of VOCs is promoted. The optimal ratio of KMnO4 is 2%.

[0095] (6) By comparing Example 1 with Comparative Example 7, it can be seen that due to the poor ball-forming performance of the modified iron oxide mud, the outer shell of the double-layer pellets cracks at high temperatures, and the iron oxide mud cannot play a role in catalytic oxidation and decomposition of VOCs, and the VOCs emission reduction efficiency is only 18%. At the same time, the sintered ore yield and drum strength are slightly reduced.

[0096] (7) By comparing Examples 8 and 9 with Comparative Example 7, it can be seen that by adding acid-base neutralization sludge particles and OG coarse particles separately, the VOCs emission reduction efficiency is increased to 74% and 75%, respectively. At the same time, the yield rate and drum strength of the obtained sintered ore are slightly improved.

Claims

1. A double-layer pelletizing system for reducing VOCs emissions in the sintering process of metallurgical sludge, characterized in that: The double-layer pellets include an inner layer pellet and a pellet shell wrapped around the inner layer pellet; the raw materials of the inner layer pellets include an oxidant and metallurgical sludge, the temperature range of VOCs emitted by the metallurgical sludge used in the inner layer pellets is 250-450°C, and the oxidant is used to decompose at 240-450°C to form oxygen; the raw materials of the pellet shell include at least one of acid-base neutralization sludge, OG coarse particles, and modified iron oxide sludge particles, and the modified iron oxide sludge contains γ-Fe2O3.

2. The double-layer pelletizing method for reducing VOCs emission in the sintering process of metallurgical sludge ore blending according to claim 1 is characterized in that: The oxidant is selected as KMnO4; and / or the mass ratio of oxygen generated by decomposition of the oxygen agent to VOCs emitted by the inner pellets is 0.7 to 2; And / or the metallurgical sludge for inner pelletizing includes biological sludge and / or continuous casting sludge.

3. The double-layer pelletizing method for reducing VOCs emission in the sintering process of metallurgical sludge ore blending according to claim 1 or 2, characterized in that: The thickness of the pellet shell is 3-4 mm.

4. The double-layer pelletizing method for reducing VOCs emission in the sintering process of metallurgical sludge ore blending according to claim 3 is characterized in that: The pellet shell raw material also includes calcium carbonate sludge.

5. The double-layer pelletizing method for reducing VOCs emission in the sintering process of metallurgical sludge ore blending according to claim 3 is characterized in that: The pellet shell raw materials include modified iron oxide sludge, acid-base neutralization sludge, calcium carbonate sludge and OG coarse particles, and the mass ratio of the modified iron oxide sludge, acid-base neutralization sludge, calcium carbonate sludge and OG coarse particles after drying is 16-18:35-40:5-7:21-25.

6. A method for preparing double-layer pellets for reducing VOCs emissions in the sintering process of metallurgical sludge ore blending as claimed in any one of claims 1 to 5, characterized in that: include: The inner layer pellet raw materials are made into inner layer pellets; The raw materials of the pellet shell are coated on the outer surface of the inner layer of small balls to prepare double-layer pellets.

7. The method for preparing double-layer pellets for reducing VOCs emissions in the sintering process of metallurgical sludge ore blending according to claim 6, characterized in that: The method also includes drying, crushing, and heating the iron oxide sludge in an oxygen atmosphere to obtain modified iron oxide sludge particles; And / or the particle size of the modified iron oxide sludge particles is less than 0.074 mm.

8. Use of the double-layer pellets as claimed in any one of claims 1 to 5, or prepared by the method of claim 6 or 7, in sintering materials.

9. The use of double-layer pellets in sintering materials for reducing VOCs emissions in the sintering process of metallurgical sludge ore blending according to claim 8, characterized in that: The sintering material further comprises sintering raw materials, wherein the mass ratio of the double-layer pellets to the sintering raw materials is 1 to 3:

100.

10. The use of double-layer pellets in sintering materials for reducing VOCs emissions in the sintering process of metallurgical sludge ore blending according to claim 9, characterized in that: The sintering raw materials include mixed ore, return ore, limestone, dolomite, quicklime, external dust and coke powder.

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