Iron ore dry-method powder preparation process

Abstract

The invention provides an iron ore dry-method pulverizing process, belongs to the technical field of mineral processing, and solves the problems of high energy consumption, complex process flow and high labor intensity of a wet-type ore grinding pulverizing process. 0-20mm raw iron ore obtained by crushing, screening and the like is fed into a V-shaped powder concentrator through a bucket elevator A for primary separation; coarse particles and small particles separated by the dynamic powder concentrator are mixed and then fed into a high-pressure roller mill through a bucket elevator B, rolled products are fed into a bucket elevator A to be mixed with raw ore for circular separation, and a closed-loop rolling-separation system is formed; fine fractions separated by the dynamic powder concentrator are collected by a cyclone dust collector; dust-containing gas is divided into two paths through a circulating fan, one path is circulated in a system, the other path is purified by a bag-type dust collector and then is discharged in an ultra-low manner, and fine materials collected by the two dust collectors are conveyed by an air cushion type conveyor and are fed into a final powder bin through a bucket elevator C, so that qualified dry-method powder products are obtained. The method has the advantages of simple process, energy conservation, environmental protection, stable operation and the like.

Description

Technical Field

[0001] This invention belongs to the field of mineral processing technology, specifically relating to a dry powdering process for iron ore. Background Technology

[0002] my country possesses abundant resources of complex and refractory iron oxide ores, characterized by their complex mineral composition, weak magnetic properties, and fine particle size, making it difficult to achieve ideal separation parameters using conventional high-intensity magnetic separation processes. However, if these ores undergo reduction-magnetic roasting pretreatment followed by magnetic separation and reverse flotation processes, better separation parameters can often be obtained.

[0003] In recent years, with the development of magnetized roasting technology, the method of fluidized bed roasting for complex and difficult-to-process iron oxide ores has been gradually applied. Before using fluidized bed roasting, the iron ore needs to be made into powder of qualified particle size.

[0004] Existing suspension magnetization roasting production lines use wet grinding to pulverize iron ore. The iron ore is rolled to -3mm using a high-pressure roller mill, then further ground using a wet ball mill to obtain a raw ore slurry with approximately 50% of the ore being -0.075mm. After filtration, drying, and dispersing, this slurry enters the suspension magnetization roasting furnace. In actual production, the slurry produced by wet grinding often exhibits high moisture content and uneven filter cake thickness during filtration. Drying the filter cake is energy-intensive and prone to agglomeration, requiring dispersing. Therefore, the wet grinding pulverization process combined with suspension magnetization roasting technology suffers from drawbacks such as high energy consumption, complex process flow, and high labor intensity. It is necessary to invent a dry ore pulverization process. Summary of the Invention

[0005] The purpose of this invention is to provide a dry grinding process for iron ore to solve the problems of high energy consumption, complex process flow, and high labor intensity in wet grinding processes.

[0006] The technical solution of this invention is: a dry iron ore powdering process, comprising the following steps: Step 1: After the large iron ore is crushed and screened, the 0-20mm iron ore undersize is sent to the raw ore bin for storage via a belt conveyor system. A belt conveyor is installed at the bottom of the raw ore bin to send the 0-20mm iron ore into the bucket elevator A. Step 2: Bucket elevator A lifts 0-20mm iron ore and sends it into V-type air classifier. After initial separation by V-type air classifier, the iron ore is separated into coarse and fine particles. The coarse particles fall to the bottom of V-type air classifier, while the fine particles are carried by airflow from the top of V-type air classifier to the next process. Step 3: The fine iron ore obtained in Step 2 is fed into the dynamic air classifier with the airflow. Under the separation action of the dynamic air classifier, it is separated into small iron ore particles and fine-grained iron ore. The small iron ore particles fall into the lower cone of the dynamic air classifier and, through the one-way airlock valve and chute, mix with the coarse iron ore particles obtained in Step 2 at the bottom of the V-type air classifier before entering the next process. The fine-grained iron ore particles are carried out from the upper outlet of the dynamic air classifier by the high-speed airflow before entering the next process. Step 4: Mix the coarse and fine iron ore particles obtained in Steps 2 and 3 and feed them from the bottom of the V-type classifier into the bucket elevator B via a chute. The bucket elevator B lifts the mixture and feeds it through a chute into the buffer bin in front of the high-pressure roller mill. Then, it is slowly fed into the high-pressure roller mill through a feeding device. The roller-pressed product discharged from the high-pressure roller mill is mixed with the 0-20mm iron ore raw ore from Step 1 and fed into the bucket elevator A. Repeat the operations of Steps 2 and 3 until a product that meets the particle size requirements is obtained. Step 5: The fine-grained iron ore obtained in Step 3 is sent from the top outlet of the dynamic classifier by high-speed airflow through the air duct into the cyclone dust collector. A cyclone is formed inside the cyclone dust collector. Under the action of centrifugal force, the ore particles gradually sink downward and fall into the air cushion conveyor through the bottom discharge valve. The dust-laden gas is discharged upward from the inner cylinder of the cyclone dust collector. Step Six: The dust-laden gas generated in Step Five enters the circulating fan through the duct. When it passes through the outlet of the circulating fan, it is divided into two paths. One path enters the feeding end of the V-type classifier through the duct and circulates in the circulating fan-V-type classifier-dynamic classifier-cyclone dust collector-circulating fan system. The other path is connected to the bag filter dust collector through the duct. After dust removal and purification to meet the ultra-low emission requirements, it is discharged from the external chimney. The powder product collected by the bag filter dust collector falls from the bottom funnel into the air cushion conveyor. Step 7: All the fine-grained iron ore collected by the cyclone dust collector and bag dust collector is transported by the air cushion conveyor to the bucket elevator C, which lifts it into the final powder silo for storage. This fine-grained iron ore is a qualified product produced by the dry powdering system that meets the particle size requirements.

[0007] As a further improvement of the present invention, in step one, an electromagnetic iron remover, a metal detector and a metal separator are installed on the belt conveyor from the raw ore bin to the bucket elevator A, and two permanent magnet iron removers are installed on the chute of the buffer bin before the high-pressure roller mill connected to the bucket elevator B, to remove iron blocks and metal blocks that may be mixed in the iron ore, so as to protect the safe operation of the high-pressure roller mill in step four.

[0008] As a further improvement of the present invention, the power for the fine-grained iron ore to flow with the airflow in the V-type classifier, dynamic classifier and cyclone dust collector is provided by the circulating fan, and the system wind speed is adjustable between 15-20m / s; the air volume discharged after dust collection by the bag filter is one-third of the total circulating air volume of the system, and at the same time, a makeup air pipe is set on the circulating air duct at the inlet end of the V-type classifier to adjust the system air volume and ensure the balance of the system air volume.

[0009] As a further improvement of the present invention, in order to avoid condensation of iron ore due to its high moisture content during the system separation process, which would cause it to adhere to the equipment surface and reduce the system's classification efficiency or even affect production, a hot blast stove is set up in the system to dry the iron ore material. When the moisture content of the iron ore is >4% or the air humidity is >85%, the hot blast stove starts to work and can heat the air to above 500°C. The hot air is introduced into the circulating air duct before the inlet of the V-type air classifier from the tail of the hot blast stove, mixes with the circulating air and enters the V-type air classifier, and dries the iron ore during the dispersion and separation process of the V-type air classifier and the dynamic air classifier. The energy medium used for combustion in the hot blast stove is blast furnace gas or coke oven gas.

[0010] As a further improvement of the present invention, in step one, the Protodyakonov hardness coefficient f of the iron ore should be ≤16, and the true density of the iron ore should be ≤4.0 t / m³. 3 The abrasiveness index should be <0.3g / t, and the grindability, i.e., the grinding work index, should be ≤13kWh / t.

[0011] As a further improvement of the present invention, in order to adapt to the high abrasiveness of iron ore and ensure the service life of system pipelines and equipment, considering the wind speed and ore particle size in various parts of the pulverizing system, wear-resistant steel plates or welded composite steel plates are used as wear-resistant layers in the parts that come into contact with iron ore inside the V-type classifier, dynamic classifier and chute, and wear-resistant ceramic sheets are used as wear-resistant layers on the inner walls of the cyclone dust collector and circulating air duct.

[0012] As a further improvement of the present invention, the qualified product particle size range is: +1mm content is 0%, +0.5mm content is <1%, -74μm content is 50±5%, and -38μm content is <30%. During production, the product particle size range can be adjusted by parameters such as the rotor speed of the dynamic classifier, the direction of the guide vanes, and the system wind speed.

[0013] As a further improvement of the present invention, in order to provide a basis for real-time monitoring of the particle size composition of the powdered product and adjusting the system process parameters, an online iron ore particle size detection device is installed at the unloading end of the air cushion conveyor.

[0014] The beneficial effects of this invention are as follows: 1. This invention solves the problems of complex product filtration, drying and dispersing processes and high energy consumption in traditional wet ball milling of iron ore, and can provide uniform and loose dry iron ore materials for subsequent suspension magnetization roasting production.

[0015] 2. During the iron ore rolling process, the high-pressure roller mill of this invention can achieve selective crushing due to the supporting effect of large iron ore particles, reducing the "over-crushing" phenomenon of fine iron ore particles. It can effectively control the content of -500mm micro-fine iron ore particles in the powder product, which is conducive to the smooth operation of suspension magnetization roasting production.

[0016] 3. This invention is based on the "layer crushing" principle of high-pressure roller mills. After iron ore is crushed by the high-pressure roller mill, not only is the ore effectively pulverized, but a large number of cracks are also generated inside the ore particles, mainly including intragranular cracks, intergranular cracks, and transgranular cracks. These cracks are widely present in each ore particle, improving the ore's permeability and regrindability. In suspension magnetized roasting production, it helps to improve the overflow and penetration of reducing gas, thereby increasing the reduction rate, shortening the reduction time, reducing energy consumption, and increasing production capacity. In the grinding and beneficiation of roasted products, it helps to shorten grinding time, reduce energy consumption, improve the degree of liberation between ore and gangue, and increase magnetic separation efficiency.

[0017] 4. The hot air produced by the hot air furnace of this invention enters the circulating air system before the V-type classifier, which can dry the iron ore during the dispersion and separation process, effectively reducing the moisture content of the iron ore and eliminating the phenomenon of ore powder adhering to equipment and pipelines due to condensation during the production process.

[0018] 5. The particle size range of the powder produced by this invention can be adjusted as needed by parameters such as the rotor speed of the dynamic classifier, the direction of the guide vanes, and the system air velocity. It is also equipped with an online particle size detection function, providing a basis for adjusting system process parameters.

[0019] 6. The entire dry powder making process system of this invention is designed with negative pressure and full sealing, and each dust-generating point is equipped with a dust removal device, so there is no dust overflow.

[0020] The main steps of this invention include conveying and storing 0-20mm iron ore, primary selection by a V-type classifier, secondary selection by a dynamic classifier, circulating grinding and separation of coarse iron ore by a high-pressure roller mill, cyclone dust collection of powdered products, dust removal and purification of dusty air, and conveying and storing the products.

[0021] Compared with traditional wet ball milling, the powder-making process of this invention can solve the problems of complex processes and high energy consumption in wet product filtration, drying, and dispersion. The supporting effect of large iron ore particles during the high-pressure roller mill pressing process can effectively reduce the "over-crushing" phenomenon of iron ore, which is conducive to the smooth production of suspension magnetization roasting. Based on the "laminated crushing" principle of the high-pressure roller mill, a large number of cracks will be generated inside the dry powder product, which is conducive to improving the subsequent roasting and grinding effect, saving energy and reducing consumption. It has the advantages of simple process, energy saving and environmental protection, and stable operation. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] Example 1 Step 1: After the large iron ore ore is crushed and screened, the 0-20mm iron ore undersize is sent to the raw ore bin for storage via a belt conveyor system. A belt conveyor is installed at the bottom of the raw ore bin to send the 0-20mm iron ore into the bucket elevator A. An electromagnetic iron remover, metal detector and metal separator are installed on the belt conveyor to remove any iron or metal pieces that may be mixed in with the 0-20mm iron ore, so as to protect the safe operation of the high-pressure roller mill in Step 4.

[0025] Step 2: Bucket elevator A lifts 0-20mm iron ore and feeds it into the V-type air classifier. As the 0-20mm iron ore falls from the feed port of the V-type air classifier, it is dispersed by the layer-by-layer impact of the dispersing plate. During this process, a high-speed airflow with a wind speed of 15-20m / s enters from one side of the V-type air classifier. Because the 0-2mm fine iron ore particles are less affected by gravity, they cannot continue to fall and are carried by the high-speed airflow through the separation channel into the dynamic air classifier. However, the 2-20mm coarse iron ore particles cannot be carried away by the airflow due to gravity and finally fall to the bottom of the V-type air classifier.

[0026] Step 3: The fine iron ore particles obtained in Step 2 enter the dynamic air classifier with the airflow. Each individual ore particle will be subjected to centrifugal force generated by the rotation of the dynamic air classifier rotor, suction force generated by the airflow, and its own gravity. Since the sum of the centrifugal force and gravity on the 0.5-2mm small iron ore particles is greater than the suction force generated by the airflow, they pass through the rotor and guide vanes and fall into the lower cone of the dynamic air classifier. Through the one-way airlock valve and chute, they mix with the 2-20mm coarse iron ore particles at the bottom of the V-type air classifier and enter the next process. At the same time, the 0-0.5mm fine iron ore particles, due to their smaller mass, are subjected to suction force generated by the airflow that is greater than the sum of the centrifugal force and gravity, and are thus carried out by the high-speed airflow from the upper outlet of the dynamic air classifier to enter the next process.

[0027] The particle size range of the powdered product can be adjusted by parameters such as rotor speed, guide vane direction, and airflow velocity.

[0028] Step 4: The coarse and fine iron ore particles obtained in Steps 2 and 3 are mixed and fed from the bottom of the V-type classifier into the bucket elevator B via a chute. The bucket elevator B lifts the mixture and feeds it through a chute into the buffer bin before the high-pressure roller mill. Then, it is slowly fed into the high-pressure roller mill through a feeding device. The roller-pressed product discharged from the high-pressure roller mill is mixed with the 0-20mm iron ore raw ore described in Step 1 and fed into the bucket elevator A. Steps 2 and 3 are repeated until a product that meets the particle size requirements is obtained.

[0029] Two permanent magnet chute separators are installed on the chute between the bucket elevator B and the buffer bin to remove iron lumps and metal blocks that may have been mixed into the iron ore during production, thus protecting the safe operation of the high-pressure roller mill in step four. The effective volume of the buffer bin is four times the system's capacity.

[0030] Step 5: The fine-grained iron ore obtained in Step 3 is sent from the top outlet of the dynamic classifier by high-speed airflow through the duct into the cyclone dust collector. A cyclone is formed inside the cyclone dust collector. Under the action of centrifugal force, the ore particles gradually sink downward and fall into the air cushion conveyor through the bottom discharge valve. The dust-laden gas is discharged upward from the inner cylinder of the cyclone dust collector.

[0031] Step Six: The dust-laden gas generated in Step Five enters the circulating fan through the duct. Upon exiting the circulating fan, it splits into two paths. One path enters the feed end of the V-type classifier and circulates within the "circulating fan - V-type classifier - dynamic classifier - cyclone dust collector - circulating fan" system. The other path connects to the bag filter. After dust removal and purification to meet ultra-low emission requirements, the gas is discharged from the exhaust chimney. The powdered product collected by the bag filter falls from the bottom funnel into the air cushion conveyor. The exhaust air volume after dust collection by the bag filter is one-third of the total circulating air volume of the system. Simultaneously, a makeup air pipe is installed on the circulating duct at the inlet end of the V-type classifier to regulate the system air volume and ensure system air volume balance.

[0032] Step 7: All the fine-grained iron ore collected by the cyclone dust collector and bag dust collector is transported by the air cushion conveyor to the bucket elevator C, which lifts it into the final powder silo for storage. This fine-grained iron ore is a qualified product produced by the dry powdering system that meets the particle size requirements.

[0033] The circulating fan provides power for the fine-grained iron ore to flow with the airflow in the V-type classifier, dynamic classifier and cyclone dust collector. The system wind speed is adjustable between 15-20m / s.

[0034] To prevent condensation from forming on the equipment surface due to the high moisture content of iron ore during the system's sorting process, which could reduce system classification efficiency and even affect production, a hot blast stove is installed to dry the iron ore. The hot blast stove starts operating when the iron ore moisture content is >4% or the air humidity is >85%, heating the air to over 500℃. This hot air is introduced from the tail end of the hot blast stove into the circulating air duct before the V-type air classifier inlet, mixing with the circulating air before entering the V-type air classifier. The iron ore is then dried during the dispersion and sorting process in the V-type air classifier and the dynamic air classifier. The energy medium used for combustion in the hot blast stove is blast furnace gas or coke oven gas.

[0035] To monitor the particle size distribution of the powdered product in real time and provide a basis for adjusting the system process parameters, an online iron ore particle size detection device was installed at the unloading end of the air cushion conveyor.

[0036] To adapt to the high abrasiveness of iron ore and ensure the service life of system pipelines and equipment, considering the wind speed and ore particle size in various parts of the pulverizing system, wear-resistant steel plates or welded composite steel plates are used as wear-resistant layers in the parts that come into contact with iron ore inside the V-type classifier, dynamic classifier, and sluice. Wear-resistant ceramic sheets are used as wear-resistant layers on the inner walls of the cyclone dust collector and circulating air duct.

[0037] The entire dry powder production process system is designed with negative pressure and is fully sealed. Each dust-generating point is equipped with a dust removal device, so there is no dust overflow.

[0038] Specifically, the Protodyakonov hardness coefficient f is 16, and the true density of the iron ore is 3.8 t / m³. 3 Iron ore with an abrasion index of 0.24 g / t and a grindability (grinding work index) of 12.45 kWh / t was dry-processed using this technology. The qualified product had the following particle sizes: +1 mm content 0%, +0.5 mm content 0.95%, -74 μm content 53.6%, and -38 μm content 28.5%.

Claims

1. A dry grinding process for iron ore, characterized in that: Includes the following steps: Step 1: After the large iron ore is crushed and screened, the 0-20mm iron ore undersize is sent to the raw ore bin for storage via a belt conveyor system. A belt conveyor is installed at the bottom of the raw ore bin to send the 0-20mm iron ore into the bucket elevator A. Step 2: Bucket elevator A lifts 0-20mm iron ore and sends it into V-type air classifier. After initial separation by V-type air classifier, the iron ore is separated into coarse and fine particles. The coarse particles fall to the bottom of V-type air classifier, while the fine particles are carried by airflow from the top of V-type air classifier to the next process. Step 3: The fine iron ore obtained in Step 2 is fed into the dynamic air classifier with the airflow. Under the separation action of the dynamic air classifier, it is separated into small iron ore particles and fine-grained iron ore. The small iron ore particles fall into the lower cone of the dynamic air classifier and, through the one-way airlock valve and chute, mix with the coarse iron ore particles obtained in Step 2 at the bottom of the V-type air classifier before entering the next process. The fine-grained iron ore particles are carried out from the upper outlet of the dynamic air classifier by the high-speed airflow before entering the next process. Step 4: Mix the coarse and fine iron ore particles obtained in Steps 2 and 3 and feed them from the bottom of the V-type classifier into the bucket elevator B via a chute. The bucket elevator B lifts the mixture and feeds it through a chute into the buffer bin in front of the high-pressure roller mill. Then, it is slowly fed into the high-pressure roller mill through a feeding device. The roller-pressed product discharged from the high-pressure roller mill is mixed with the 0-20mm iron ore raw ore from Step 1 and fed into the bucket elevator A. Repeat the operations of Steps 2 and 3 until a product that meets the particle size requirements is obtained. Step 5: The fine-grained iron ore obtained in Step 3 is sent from the top outlet of the dynamic classifier by high-speed airflow through the air duct into the cyclone dust collector. A cyclone is formed inside the cyclone dust collector. Under the action of centrifugal force, the ore particles gradually sink downward and fall into the air cushion conveyor through the bottom discharge valve. The dust-laden gas is discharged upward from the inner cylinder of the cyclone dust collector. Step Six: The dust-laden gas generated in Step Five enters the circulating fan through the duct. When it passes through the outlet of the circulating fan, it is divided into two paths. One path enters the feeding end of the V-type classifier through the duct and circulates in the circulating fan-V-type classifier-dynamic classifier-cyclone dust collector-circulating fan system. The other path is connected to the bag filter dust collector through the duct. After dust removal and purification to meet the ultra-low emission requirements, it is discharged from the external chimney. The powder product collected by the bag filter dust collector falls from the bottom funnel into the air cushion conveyor. Step 7: All the fine-grained iron ore collected by the cyclone dust collector and bag dust collector is transported by the air cushion conveyor to the bucket elevator C, which lifts it into the final powder silo for storage. This fine-grained iron ore is a qualified product produced by the dry powdering system that meets the particle size requirements.

2. The dry iron ore grinding process according to claim 1, characterized in that: In step one, an electromagnetic iron separator, a metal detector, and a metal separator are installed on the belt conveyor from the raw ore bin to the bucket elevator A. Two permanent magnet iron separators are installed on the chute of the buffer bin before the high-pressure roller mill connected to the bucket elevator B to remove iron blocks and metal blocks that may be mixed in with the iron ore.

3. The dry iron ore grinding process according to claim 1, characterized in that: The power for the fine-grained iron ore to flow with the airflow in the V-type classifier, dynamic classifier, and cyclone dust collector is provided by the circulating fan, and the system wind speed is adjustable between 15-20m / s. The air volume discharged after dust collection by the bag filter is one-third of the total circulating air volume of the system. At the same time, a makeup air pipe is installed on the circulating air duct at the inlet end of the V-type classifier to adjust the system air volume and ensure the balance of the system air volume.

4. The dry grinding process for iron ore according to claim 1, characterized in that: A hot blast stove is set up to dry iron ore. The hot blast stove starts working when the moisture content of the iron ore is >4% or the air humidity is >85%. It can heat the air to over 500°C. The hot air is introduced into the circulating air duct before the inlet of the V-type air classifier from the tail of the hot blast stove. It mixes with the circulating air and enters the V-type air classifier. The iron ore is dried during the dispersion and separation process of the V-type air classifier and the dynamic air classifier. The energy medium used for combustion in the hot blast stove is blast furnace gas or coke oven gas.

5. The dry grinding process for iron ore according to claim 1, characterized in that: In step one, the Protodyakonov hardness coefficient (f) of the iron ore should be ≤16, and the true density of the iron ore should be ≤4.0 t / m³. 3 The abrasiveness index should be <0.3g / t, and the grindability, i.e., the grinding work index, should be ≤13kWh / t.

6. The dry grinding process for iron ore according to claim 1, characterized in that: Wear-resistant steel plates or welded composite steel plates are used as wear-resistant layers in the parts of the V-type classifier, dynamic classifier and sluice that come into contact with iron ore, respectively. Wear-resistant ceramic sheets are used as wear-resistant layers on the inner walls of the cyclone dust collector and circulating air duct.

7. The dry grinding process for iron ore according to claim 1, characterized in that: In step seven, the qualified product particle size range is: +1mm content is 0%, +0.5mm content is <1%, -74μm content is 50±5%, and -38μm content is <30%. During production, the product particle size range can be adjusted by parameters such as the rotor speed of the dynamic classifier, the direction of the guide vanes, and the system wind speed.

8. The dry grinding process for iron ore according to claim 1, characterized in that: Install online iron ore particle size detection equipment at the unloading end of the air cushion conveyor.

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