Iron ore pellets with self-catalytic denitration function and methods of making and using the same

Abstract

The purpose of this invention is to address the problems existing in current NOx control technologies for flue gas in pellet production, and to provide an iron ore pellet with autocatalytic denitrification function, as well as its preparation and application methods. This method involves mixing magnetite concentrate, fine-grained biomass, and bentonite to form pellets I. Then, an organic binder and vanadium-titanium magnetite concentrate are added to allow pellet I to continue growing, resulting in pellet II. Oxidized pellets are then prepared from pellet II using a chain grate-rotary kiln process. The advantages of this method are: it constructs a novel structure containing fine-grained biomass particles internally and fine-grained vanadium-titanium magnetite concentrate adhering to its surface; it utilizes the carbon and hydrogen components generated from biomass pyrolysis as reducing agents and the coupled catalytic effect of iron, vanadium, and titanium to achieve economical, efficient, and clean autocatalytic denitrification in the pellet production process, solving problems such as low denitrification efficiency and ammonia escape in ammonia injection denitrification during pellet production.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgical pelletizing process technology, and specifically relates to an iron ore pellet with self-catalytic denitrification function and its preparation and use method. Background Technology

[0002] Currently, NOx control technologies for pelletizing flue gas are mainly divided into three aspects: source control, process control, and end-of-pipe treatment, with end-of-pipe treatment being the most widely used. Current flue gas denitrification technologies mainly include selective catalytic reduction (SCR), non-catalytic reduction (SNCR), and SCR / SNCR hybrid methods. However, pelletizing flue gas is large in volume and complex in composition, including O2, H2O(g), COx, NOx, SOx, and dust. Relying on a single end-of-pipe denitrification technology requires high NOx removal efficiency, making it difficult to achieve ultra-low emissions economically and efficiently. The chain grate-rotary kiln is a major iron ore pelletizing process in my country. Developing NOx control technologies for this process, considering its characteristics, is of great significance for achieving economical, efficient, and ultra-low NOx emissions from pelletizing flue gas. Chinese patent application (CN108404660 A) discloses an SCR denitrification method in the iron ore oxide pellet production process, and Chinese patent application (CN110904332 A) discloses an enhanced ammonia injection denitrification method based on the catalytic performance of iron ore pellet surfaces. Both utilize the characteristic that the temperature of the drying section in the chain grate-rotary kiln pellet production process meets the temperature requirements for catalytic denitrification, and achieve denitrification in the pellet production process by injecting NH3 in this area. However, due to the short airflow time through the material layer, the NH3 reduction denitrification efficiency is relatively low, and unreacted NH3 entering the flue gas poses a hazard of generating secondary pollutants. Therefore, developing an economical, efficient, and pollution-free NOx control technology for the pellet production process is of great significance for achieving ultra-low NOx emissions from pellet production flue gas. Summary of the Invention

[0003] The purpose of this invention is to address the problems existing in current NOx control technologies for flue gas in pellet production, and to provide an iron ore pellet with autocatalytic denitrification function, as well as its preparation and application methods. This method involves mixing magnetite concentrate, fine-grained biomass, and bentonite to form pellets I. Then, an organic binder and vanadium-titanium magnetite concentrate are added to allow pellet I to continue growing, resulting in pellet II. Oxidized pellets are then prepared from pellet II using a chain grate-rotary kiln process. The advantages of this method are: it constructs a novel structure containing fine-grained biomass particles internally and fine-grained vanadium-titanium magnetite concentrate adhering to its surface; it utilizes the carbon and hydrogen components generated from biomass pyrolysis as reducing agents and the coupled catalytic effect of iron, vanadium, and titanium to achieve economical, efficient, and clean autocatalytic denitrification in the pellet production process, solving problems such as low denitrification efficiency and ammonia escape in ammonia injection denitrification during pellet production.

[0004] To achieve the above technical objectives, the present invention provides an iron ore pellet with autocatalytic denitrification function, which is composed of the following components in mass percentage: 87.2-93.1% magnetite concentrate, 0.1-0.3% fine biomass, 0.6-1.0% bentonite, 0.005-0.01% organic binder, and 6-12% fine vanadium-titanium magnetite concentrate.

[0005] Furthermore, in the aforementioned iron ore pellets with autocatalytic denitrification function, the fine particulate biomass includes one or a mixture of several of the following: fruit kernels, fruit shells, and sugarcane bagasse.

[0006] Furthermore, in the aforementioned iron ore pellets with autocatalytic denitrification function, the fine biomass particle size composition is such that the mass percentage of particles smaller than 50 micrometers is not less than 60%, the mass percentage of particles larger than 100 micrometers is not more than 10%, and the moisture content is not more than 10%.

[0007] Furthermore, in the aforementioned iron ore pellets with autocatalytic denitrification function, the fine-grained vanadium-titanium magnetite concentrate contains a TiO2 content of not less than 3%, a V2O3 content of not less than 0.1%, a content smaller than 0.074 mm of ore of not less than 85%, and a specific surface area of ​​not less than 1700 cm². 2 / g.

[0008] Furthermore, in the aforementioned iron ore pellets with autocatalytic denitrification function, the organic binder includes one or a mixture of several of Peridur, sodium carboxymethyl cellulose, hydroxypropyl methylcellulose, and povidone.

[0009] Furthermore, in the aforementioned iron ore pellets with autocatalytic denitrification function, the magnetite concentrate specifications are: a particle size of less than 0.074 mm with a content of not less than 80%, and a specific surface area of ​​not less than 1500 cm². 2 / g.

[0010] This invention also provides a method for preparing iron ore pellets with autocatalytic denitrification function, comprising the following steps:

[0011] (1) Magnetite concentrate, fine biomass and bentonite are mixed according to mass percentage, and then pelletized to obtain pellet I.

[0012] (2) Organic binder and vanadium-titanium magnetite concentrate are mixed according to mass percentage and added to the surface of pellet I in a disc pelletizer to prepare pellet II, thus obtaining pellets with self-catalytic denitrification function.

[0013] This invention also provides a method for using iron ore pellets with self-catalytic denitrification function. The pellets with self-catalytic denitrification function are fed onto a chain grate machine, and drying, preheating, roasting and cooling are completed sequentially in the chain grate machine-rotary kiln-annular cooler system.

[0014] Furthermore, in the above-mentioned method of using iron ore pellets with autocatalytic denitrification function, the preheating temperature of the chain grate is 860-950℃ and the preheating time is 7-10 minutes; the maximum temperature of the rotary kiln is controlled at 1230-1270℃ and the high-temperature roasting time is 20-30 minutes.

[0015] Furthermore, in the above-mentioned method of using iron ore pellets with autocatalytic denitrification function, the thickness of the pellet layer in the chain grate is 150~210mm, and the speed of the chain grate is 3.5~4.0m / min.

[0016] Compared with the prior art, the beneficial effects of this invention are as follows:

[0017] (1) Using the method provided by the present invention, a certain proportion of fine biomass particles are added to the raw materials for pellet preparation. The particles are small in size, rough in surface, and have strong adhesion. They can act as a binder in the process of green pellet preparation, thereby reducing the amount of bentonite used. They can also decompose at high temperature, thereby increasing the total iron content of the final pellets.

[0018] (2) Using the method provided by the present invention, the prepared pellets have a novel structure containing fine biomass particles inside and fine vanadium-titanium magnetite concentrate adhering to the surface. During the drying process of the pellets, the volatiles in the fine biomass particles in the inner layer of the pellets are decomposed into highly reducing H2 and CO small molecule gases under the catalytic action of the iron ore particles, and then diffuse to the surface of the pellets; while the NOx in the hot gas passing through the pellet material layer will diffuse from the gas flow boundary layer to the surface of the pellets, and be catalytically reduced and degraded by H2 and CO under the action of the catalyst composed of iron, vanadium, titanium and other metals on the surface (CO+NOx → CO2+N2, H2+NOx → H2O+N2), thereby achieving efficient denitrification in the iron ore pellet production process;

[0019] (3) When the pellets prepared by the method provided by the present invention enter the preheating process from the drying process, the small amount of carbon particles remaining in the pellets due to the biomass pyrolysis will continue to undergo gasification reaction to generate CO, and a catalytic reduction reaction of NOx will occur on the surface of the pellets (CO+NOx → CO2+N2), further reducing the amount of NOx emissions in the preheating process.

[0020] (4) Using the method provided by the present invention, the added fine biomass particles act as a binder in the preparation of green pellets, act as a source of NOx reducing agent in the drying and preheating process, and leave fine pore channels after the pyrolysis and gasification reaction, which is beneficial to improving the reduction performance of the pellets and enhancing their smelting performance.

[0021] (5) The method provided by the present invention requires minimal adjustment to the production process, is easy to operate, and the added fine biomass is agricultural and forestry waste, resulting in low addition cost and great potential for industrial application.

[0022] (6) The method provided by this invention can achieve NO emission reduction in the pellet production process. X With emissions reduced by 25-55%, the investment and operating costs of end-of-pipe flue gas treatment equipment can be significantly reduced. Detailed Implementation

[0023] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0024] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The patent terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the invention.

[0025] Unless otherwise specified, the various reagents and raw materials used in this invention are commercially available products or products that can be prepared by known methods.

[0026] Example 1

[0027] The raw materials for pellet preparation are prepared according to the following mass percentages: 92% fine-grained magnetite concentrate, 0.1% micro-fine-grained corn stalks, 0.8% bentonite, 0.005% sodium carboxymethyl cellulose, and 7.095% micro-fine-grained vanadium-titanium magnetite concentrate. The fine-grained magnetite concentrate, micro-fine-grained corn stalks, and bentonite are mixed according to the above mass percentages and then prepared into pellet I in a pelletizing disc. Then, an organic binder and the vanadium-titanium magnetite concentrate are mixed according to the above mass percentages and added to the pelletizing disc, coating the outer layer of pellet I, thus preparing iron ore pellets with autocatalytic denitrification function. The iron ore pellets are then fed onto a chain grate machine with a layer thickness of 180 mm and a machine speed of 3.8 m / min, undergoing drying, preheating, roasting, and cooling processes sequentially. The preheating temperature of the chain grate machine is 860–950℃, and the preheating time is 7–10 min; the maximum temperature of the rotary kiln is controlled at 1230–1270℃, and the high-temperature roasting time is 20–30 min. The basic physicochemical properties of vanadium-titanium magnetite concentrate and fine-grained corn straw are shown in Tables 1 and 2. The NOx emission reduction ratio in the pellet production process is shown in Table 3. The quality indicators of preheated and roasted pellets are shown in Table 4, all of which meet the requirements of industrial production.

[0028] Example 2

[0029] The raw materials for pellet preparation are prepared according to the following mass percentages: 90.1% fine-grained magnetite concentrate, 0.15% micro-fine-grained corn stalks, 0.7% bentonite, 0.007% sodium carboxymethyl cellulose, and 9.043% micro-fine-grained vanadium-titanium magnetite concentrate. The fine-grained magnetite concentrate, micro-fine-grained corn stalks, and bentonite are mixed according to the above mass percentages and then prepared into pellet I in a pelletizing disc. Then, the organic binder and vanadium-titanium magnetite concentrate are mixed according to the above mass percentages and added to the pelletizing disc, coating the outer layer of pellet I, thus preparing iron ore pellets with autocatalytic denitrification function. The iron ore pellets are then fed onto a chain grate machine with a material layer thickness of 180 mm and a chain grate machine speed of 3.8 m / min, undergoing drying, preheating, roasting, and cooling processes sequentially. The preheating temperature of the chain grate machine is 860–950℃, and the preheating time is 7–10 min; the maximum temperature of the rotary kiln is controlled at 1230–1270℃, and the high-temperature roasting time is 20–30 min. The basic physicochemical properties of vanadium-titanium magnetite concentrate and fine-grained corn straw are shown in Tables 1 and 2. The NOx emission reduction ratio in the pellet production process is shown in Table 3. The quality indicators of preheated and roasted pellets are shown in Table 4, all of which meet the requirements of industrial production.

[0030] Example 3

[0031] The raw materials for pellet preparation are prepared according to the following mass percentages: 88.1% fine-grained magnetite concentrate, 0.2% micro-fine-grained corn stalks, 0.7% bentonite, 0.007% sodium carboxymethyl cellulose, and 10.993% micro-fine-grained vanadium-titanium magnetite concentrate. The fine-grained magnetite concentrate, micro-fine-grained corn stalks, and bentonite are mixed according to the above mass percentages and then prepared into pellet I in a pelletizing disc. Then, the organic binder and vanadium-titanium magnetite concentrate are mixed according to the above mass percentages and added to the pelletizing disc, coating the outer layer of pellet I, thus preparing iron ore pellets with autocatalytic denitrification function. The iron ore pellets are then fed onto a chain grate machine with a layer thickness of 180 mm and a machine speed of 3.8 m / min, undergoing drying, preheating, roasting, and cooling processes sequentially. The preheating temperature of the chain grate machine is 860–950℃, and the preheating time is 7–10 min; the maximum temperature of the rotary kiln is controlled at 1230–1270℃, and the high-temperature roasting time is 20–30 min. The basic physicochemical properties of vanadium-titanium magnetite concentrate and fine-grained corn straw are shown in Tables 1 and 2. The NOx emission reduction ratio in the pellet production process is shown in Table 3. The quality indicators of preheated and roasted pellets are shown in Table 4, all of which meet the requirements of industrial production.

[0032] Comparative Example 1

[0033] The raw materials for pellet preparation are prepared according to the following mass percentages: 88.1% fine-grained magnetite concentrate, 1.5% bentonite, 0.007% sodium carboxymethyl cellulose, and 10.393% ultrafine vanadium-titanium magnetite concentrate. The fine-grained magnetite concentrate and bentonite are mixed according to the above mass percentages and then used to prepare pellet I in a pelletizing disc. Then, sodium carboxymethyl cellulose and vanadium-titanium magnetite concentrate are mixed according to the above mass percentages and added to the pelletizing disc, coating pellet I, thus preparing iron ore pellets with autocatalytic denitrification function. The iron ore pellets are then fed onto a chain grate machine with a layer thickness of 180 mm and a machine speed of 3.8 m / min, undergoing drying, preheating, roasting, and cooling processes sequentially. The preheating temperature of the chain grate is 860–950℃, and the preheating time is 7–10 min; the maximum temperature of the rotary kiln is controlled at 1230–1270℃, and the high-temperature roasting time is 20–30 min. The basic physicochemical properties of vanadium-titanium magnetite concentrate are shown in Table 1, the NOx emission reduction ratio in the pellet production process is shown in Table 3, and the quality indicators of preheated and roasted pellets are shown in Table 4.

[0034] Comparative Example 2

[0035] The raw materials for pellet preparation were prepared according to the following mass percentages: 98.3% fine-grained magnetite concentrate, 1.5% bentonite, and 0.2% micro-fine-grained biomass. The fine-grained magnetite concentrate, bentonite, and micro-fine-grained corn stalks were then mixed according to the above mass percentages and prepared into iron ore pellets in a pelletizing pan. The iron ore pellets were fed onto a chain grate machine with a layer thickness of 180 mm and a machine speed of 3.8 m / min, undergoing drying, preheating, roasting, and cooling processes sequentially. The preheating temperature of the chain grate machine was 860–950℃, and the preheating time was 7–10 min; the maximum temperature of the rotary kiln was controlled at 1230–1270℃, and the high-temperature roasting time was 20–30 min. The basic physicochemical properties of the micro-fine-grained corn stalks are shown in Table 2, the NOx emission reduction ratio during pellet production is shown in Table 3, and the quality indicators of the preheated and roasted pellets are shown in Table 4.

[0036] Comparative Example 3

[0037] The raw materials for pellet preparation are prepared according to the following mass percentages: 88.1% fine-grained magnetite concentrate, 1.5% bentonite, 0.2% micro-fine-grained corn stalks, and 10.2% micro-fine-grained vanadium-titanium magnetite concentrate. The fine-grained magnetite concentrate and bentonite are mixed according to the above mass percentages and then prepared into pellet I in a pelletizing disc. Then, the vanadium-titanium magnetite concentrate is added to the pelletizing disc according to the above mass percentages, coating the outer layer of pellet I, thus preparing iron ore pellets with autocatalytic denitrification function. The iron ore pellets are fed onto a chain grate machine with a layer thickness of 180 mm and a machine speed of 3.8 m / min, undergoing drying, preheating, roasting, and cooling processes sequentially. The preheating temperature of the chain grate machine is 860–950℃, and the preheating time is 7–10 min; the maximum temperature of the rotary kiln is controlled at 1230–1270℃, and the high-temperature roasting time is 20–30 min. The basic physicochemical properties of vanadium-titanium magnetite concentrate and fine-grained corn straw are shown in Tables 1 and 2. The NOx emission reduction ratio in the pellet production process is shown in Table 3. The quality indicators of preheated pellets and roasted pellets are shown in Table 4.

[0038] Table 1. Mineralization characteristics of vanadium-titanium magnetite concentrate

[0039] TFe / % FeO / % <![CDATA[SiO2 / %]]> CaO / % MgO / % <![CDATA[Al2O3 / %]]> <![CDATA[TiO2 / %]]> <![CDATA[V2O3 / %]]> <0.074mm <![CDATA[Specific surface area / (cm 2 / g)]]> 55.16 29.60 3.95 0.21 3.87 3.40 9.97 0.60 95 2100

[0040] Table 2. Physicochemical properties of corn straw

[0041] >100μm 50-100μm <50μm Moisture / % 5 22 73 8.5

[0042] Table 3. NOx emission reduction ratios of different embodiments and comparative examples

[0043] plan NOx emission reduction percentage / % Example 1 37 Example 2 43 Example 3 49 Comparative Example 1 3 Comparative Example 2 17 Comparative Example 3 31

[0044] Table 4. Quality indicators of pellets prepared in different embodiments and comparative examples

[0045] plan Preheated ball compressive strength (N / P) Compressive strength of sintered spheres (N / P) Firing ball drum index (+6.3mm) / % Example 1 465 2750 93.07 Example 2 470 2837 94.35 Example 3 484 2815 93.88 Comparative Example 1 461 2733 92.87 Comparative Example 2 467 2745 93.16 Comparative Example 3 458 2761 93.38

Claims

1. Iron ore pellets having a self-catalytic denitration function, characterized in that, It is composed of the following components by mass percentage: 87.2-93.1% magnetite concentrate, 0.1-0.3% fine-grained biomass, 0.6-1.0% bentonite, 0.005-0.01% organic binder, and 6-12% fine-grained vanadium-titanium magnetite concentrate; Its preparation method includes the following steps: (1) Magnetite concentrate, fine biomass and bentonite are mixed according to mass percentage, and then pelletized to obtain pellet I. (2) Organic binder and vanadium-titanium magnetite concentrate are mixed according to mass percentage and added to the surface of pellet I in a disc pelletizer to prepare pellet II, thus obtaining pellets with self-catalytic denitrification function.

2. The iron ore pellets with self-catalytic denitration function according to claim 1, characterized in that, The fine particulate biomass includes one or a mixture of several of the following: fruit pits, fruit shells, and sugarcane bagasse.

3. The iron ore pellets with self-catalytic denitration function according to claim 1, characterized in that, The fine biomass particles have a particle size composition of not less than 60% by mass of particles smaller than 50 micrometers, not more than 10% by mass of particles larger than 100 micrometers, and a moisture content of not more than 10% by mass.

4. The iron ore pellets with self-catalytic denitration function according to claim 1, characterized in that, The micro-particle vanadium-titanium magnetite concentrate has TiO2 content of not less than 3%, V2O3 content of not less than 0.1%, particle size of less than 0.074 mm content of not less than 85%, and specific surface area of not less than 1700 cm 2 / g.

5. The iron ore pellets with self-catalytic denitration function according to claim 1, characterized in that, The organic binder includes one or a mixture of several of the following: perlido, sodium carboxymethyl cellulose, hydroxypropyl methylcellulose, and povidone.

6. The iron ore pellets with self-catalytic denitration function according to claim 1, characterized in that, The magnet concentrate has the following specifications: content of particle size less than 0.074 mm is not less than 80%, specific surface area is not less than 1500 cm 2 / g.

7. A method of producing iron ore pellets having a self-catalytic denitration function, characterized by, Includes the following steps: (1) Magnetite concentrate, fine biomass and bentonite are mixed according to mass percentage, and then pelletized to obtain pellet I. (2) Organic binder and vanadium-titanium magnetite concentrate are mixed according to mass percentage and added to the surface of pellet I in a disc pelletizer to prepare pellet II, thus obtaining pellets with self-catalytic denitrification function; The iron ore pellets are composed of the following components in mass percentage: 87.2-93.1% magnetite concentrate, 0.1-0.3% fine-grained biomass, 0.6-1.0% bentonite, 0.005-0.01% organic binder, and 6-12% fine-grained vanadium-titanium magnetite concentrate.

8. A method for using the iron ore pellets with self-catalytic denitration function, characterized in that the iron ore pellets with self-catalytic denitration function according to claim 1 are used. The pellets with self-catalytic denitrification function are fed onto the chain grate machine, and drying, preheating, calcination and cooling are completed sequentially in the chain grate machine-rotary kiln-annular cooler system.

9. The method of using iron ore pellets having a self-catalytic denitration function according to claim 8, characterized in that, The preheating temperature of the chain grate machine is 860-950℃, and the preheating time is 7-10 minutes; the maximum temperature of the rotary kiln is controlled at 1230-1270℃, and the high-temperature section firing time is 20-30 minutes.

10. The method of using iron ore pellets having a self-catalytic denitration function according to claim 8, characterized in that, The thickness of the pellet layer in the chain grate is 150~210mm, and the machine speed is 3.5~4.0m / min.