Process for producing high-quality baked binder-free pellets by dry roller milling of mainstream hematite and limonite rich powder

Abstract

The invention discloses a process for producing high-quality baked binder-free pellets by dry-method roller milling of hematite and limonite rich powder, and belongs to the technical field of iron ore pellet production. Hematite and limonite rich powder with the crystal water content of 2.0%-10.0%, the proportion of particles smaller than 10 mm being larger than or equal to 90% and the physical water content being smaller than 12% is selected as a raw material, extrusion shearing modification is conducted through dry-method roller milling equipment, and the high-quality baked binder-free pellets are obtained; the temperature of a separation medium (flue gas) is controlled to be 450-650 DEG C, the proportion of the particle size of 0.074 mm after grinding is larger than 70%, the specific surface area is 3400-4400 cmg, and the balling index is 0.4-0.6; the preparation method comprises the following steps: preparing green pellets (falling times are greater than or equal to 5 times) through pelletizing equipment without adding a binder and a pelletizing additive, and carrying out gradient roasting through a belt type roasting machine or equivalent equipment to finally obtain high-quality binder-free pellets with compressive strength greater than or equal to 2500NP and an expansion index less than or equal to 15%.

Description

Technical Field

[0001] This invention relates to the field of iron ore pellet production technology, and in particular to a process for producing high-quality, calcined, binder-free pellets from mainstream hematite-rich powder using dry roller milling. Background Technology

[0002] Currently, pellet production faces two major bottlenecks: First, the supply of raw materials is limited. As a strategic mineral resource, iron ore in my country suffers from poor resource endowment and uneven regional distribution of iron concentrate supply and demand. In 2024, China produced approximately 300 million tons of iron concentrate domestically and imported approximately 125 million tons, while the actual output of pellets nationwide was only about 230 million tons. Moreover, the iron concentrate powder used in pellet production is controlled by foreign countries, making it difficult to meet the capacity expansion needs of large-scale pellet smelting. Second, the adaptability of raw materials is insufficient. About 70% of the globally exploitable smelting iron ore is hematite, which has a crystal water content of 2.5%-8% and high viscosity. Ordinary grinding methods cannot solve the problem of filtration and dehydration, resulting in high grinding costs and ineffective utilization.

[0003] From a technical equipment perspective, existing technologies generally employ vertical roller mills, which can increase the surface energy and specific surface area of ​​iron ore powder through extrusion and shearing. Furthermore, using high-temperature flue gas as an air classifier removes gravitational water and some crystal water, providing a technical foundation for the processing and utilization of hematite. Meanwhile, belt roasters, as large-scale pelletizing equipment, are highly adaptable to raw material quality and can meet the capacity requirements of high-proportion blast furnace pelletizing. However, current technologies have not yet achieved large-scale production of high-quality, binder-free pellets from rich hematite powder, still relying on binders such as bentonite. This not only consumes resources but also increases the slag ratio, fuel ratio, and carbon emissions in blast furnace smelting, raising smelting costs. Therefore, developing a high-quality pelletizing process that effectively utilizes rich hematite powder without binders is crucial to overcoming resource limitations in pelletizing production and promoting the low-carbon and green development of the steel industry. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a process for producing high-quality calcined binder-free pellets from mainstream hematite powder by dry roller milling.

[0005] To solve the above technical problems, the technical solution of the present invention is as follows: A process for producing high-quality, calcined, binder-free pellets from mainstream hematite powder using dry roller milling includes the following steps: The rich powder of hematite is continuously and stably fed into the dry vertical roller mill through a belt weighing scale. During the grinding process, the particle size distribution, specific surface area and sphericity index of the ground powder are monitored in real time, and the roller mill pressure and flue gas velocity parameters are dynamically adjusted according to the test results. The qualified ground powder is fed into the pelletizing equipment. No slag-forming binder or pelletizing additive is needed. By adjusting the pelletizing speed and water spray intensity, green pellets are prepared. The green pellets fall on the steel plate from a height of 500mm, and the number of drops is ≥7. A belt roaster is used for roasting. The position of the highest roasting temperature is adjusted in the opposite direction to the lowest bursting temperature of the green pellets, allowing sufficient time for the decomposition of the limonite crystal water and reducing the probability of bursting during pellet preheating and roasting. The roasting parameters are precisely set as follows: Base material thickness: 80±10mm; The temperature of the blower section is 330±20℃, the blower speed is controlled at 1.2-1.5m / s, and the blower time is 12-15min; Ventilation temperature in the exhaust section: 350±10℃, exhaust velocity controlled at 1.0-1.3m / s, and exhaust time 10-12min; Preheating furnace initial temperature: 400±10℃, preheating section heating rate: 5-8℃ / min, preheating time: 15-18min; Highest temperature in the roasting furnace: 1275±10℃, holding time: 20-25min; Calcination endpoint temperature: 580±20℃; After roasting, the pellets are sieved to remove broken pellets and powder smaller than 8mm, resulting in the finished binder-free pellets.

[0006] In a further preferred embodiment of the present invention, the content of crystal water in the rich red ochre powder is 2.5%-8%, satisfying the requirements of <10mm particle size ratio ≥90% and physical moisture content <12%.

[0007] A further preferred embodiment of the present invention includes: controlling the temperature T of the flue gas in the sorting and transporting medium to be 450℃≤T≤650℃, removing ≥15% of the water of crystallization and all the gravitational water from the hematite; controlling the proportion of -0.074mm particles in the ground powder to be >70% by adjusting the flue gas flow rate of the sorting, the specific surface area of ​​the ground powder to be ∈{3400cm2·g-1,4400cm2·g-1}, and the sphericity index to be ∈{0.4,0.6}.

[0008] In a further preferred embodiment of the present invention, the pelletizing equipment is a disc pelletizer with a disc inclination angle of 45°-50° and a disc rotation speed of 18-22 r / min. The water spraying adopts an atomized water spraying method, and the water spraying volume is 8%-10% of the mass of the ground powder.

[0009] In a further preferred embodiment of the present invention, the binder-free pellets produced have a compressive strength ≥2500 N·P⁻¹ and an expansion index ≤15%.

[0010] This invention utilizes the extrusion and shearing action of dry roller milling to enhance the surface activity of mineral powder. Combined with an optimized roasting regime, it promotes intergranular crystal bridge connection, eliminating the need for slag-forming binders such as bentonite and pelletizing additives. This avoids the consumption of binder resources and reduces the input of slag-forming components such as SiO2 and Al2O3 in blast furnace smelting, thereby lowering the slag ratio and fuel ratio per ton of iron. At the same time, unqualified pellets and dust can be recycled for grinding, achieving a comprehensive raw material utilization rate of ≥95%, further reducing raw material loss costs. Simultaneously, the grinding stage uses a high-temperature medium at 450-650℃ to remove ≥15% of crystal water and all physical moisture, with particle size control down to -0.074mm, simultaneously improving pelletizing and dehydration efficiency. The roasting stage employs a reverse adjustment of the high temperature point and a gradient heating and heat preservation design to specifically address the cracking problem caused by the decomposition of crystal water in hematite. Detailed Implementation

[0011] To make the content of this invention easier to understand, the invention will be further described in detail below based on specific embodiments. Example 1

[0012] This embodiment provides a process for producing high-quality, calcined, binder-free pellets from mainstream hematite powder using dry roller milling, including the following steps: The rich hematite powder is continuously and stably fed into the dry vertical roller mill using a belt weighing scale. The rich hematite powder has a crystal water content of 2.5%-8%, and meets the requirements of <10mm particle size ratio ≥90% and physical moisture content <12%. The dry vertical roller mill was started, and the separation and transport medium was set to high-temperature flue gas, with its temperature T controlled at 550℃. By adjusting the flow rate of the separation flue gas, the proportion of -0.074mm particles in the ground powder reached 75%. The indicators of the ground powder were monitored in real time during the grinding process, and the specific surface area of ​​the ground powder was finally controlled to be 3800cm²・g⁻¹, and the sphericity index was 0.5. The test showed that under the grinding conditions, the removal rate of crystal water in hematite was 20%, and the gravitational water was completely removed. The qualified ground powder is fed into a disc pelletizer with a disc inclination angle of 45° and a disc rotation speed of 20 r / min. Water is sprayed using an atomized water spray method, with a water volume of 9% of the mass of the ground powder. By adjusting the rotation speed and water spray intensity of the disc pelletizer, green pellets are prepared. The number of drops of the green pellets is tested. The drop height is 500 mm, and the green pellets fall on a steel plate. The number of drops is 8. A belt roaster is used for roasting. The position of the highest roasting temperature is adjusted in the opposite direction to the lowest bursting temperature of the green pellets, allowing sufficient time for the decomposition of the limonite crystal water and reducing the probability of bursting during pellet preheating and roasting. The roasting parameters are precisely set as follows: Base layer thickness: 85mm; The temperature of the blower section is 340℃, the blower speed is controlled at 1.4m / s, and the blower time is 14min; Ventilation temperature in the exhaust section: 360℃, ventilation speed controlled at 1.2m / s, ventilation time 11min; The initial temperature of the preheating furnace is 410℃, the heating rate of the preheating section is 7℃ / min, and the preheating time is 16min. Highest temperature in the roasting furnace: 1280℃, holding time: 22min; Firing endpoint temperature: 590℃; After calcination, the pellets were sieved to remove broken pellets and powder smaller than 8 mm, resulting in finished binder-free pellets. The finished pellets were then subjected to quality testing, and the results were as follows: compressive strength of 2600 N·P⁻¹ and expansion index of 15%.

[0013] The flue gas generated during the roasting process is introduced into the waste gas treatment system. After desulfurization, denitrification, and dust removal, monitoring results show that the particulate matter emission concentration is 8 mg / m³, the SO2 emission concentration is 30 mg / m³, and the NO emission concentration is... x The emission concentration is 45 mg / m³, which meets the ultra-low emission requirements of the steel industry.

[0014] In addition to the above embodiments, the present invention may have other implementation methods; all technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A process for producing high-quality, calcined, binder-free pellets from mainstream hematite powder using dry roller milling, characterized in that, Includes the following steps: The rich powder of hematite is continuously and stably fed into the dry vertical roller mill through a belt weighing scale. During the grinding process, the particle size distribution, specific surface area and sphericity index of the ground powder are monitored in real time, and the roller mill pressure and flue gas velocity parameters are dynamically adjusted according to the test results. The qualified ground powder is fed into the pelletizing equipment. No slag-forming binder or pelletizing additive is needed. By adjusting the pelletizing speed and water spray intensity, green pellets are prepared. The green pellets fall on the steel plate from a height of 500mm, and the number of drops is ≥7. A belt roaster is used for roasting. The position of the highest roasting temperature is adjusted in the opposite direction to the lowest bursting temperature of the green pellets, allowing sufficient time for the decomposition of the limonite crystal water and reducing the probability of bursting during pellet preheating and roasting. The roasting parameters are precisely set as follows: Base material thickness: 80±10mm; The temperature of the blower section is 330±20℃, the blower speed is controlled at 1.2-1.5m / s, and the blower time is 12-15min; Ventilation temperature in the exhaust section: 350±10℃, exhaust velocity controlled at 1.0-1.3m / s, and exhaust time 10-12min; Preheating furnace initial temperature: 400±10℃, preheating section heating rate: 5-8℃ / min, preheating time: 15-18min; Highest temperature in the roasting furnace: 1275±10℃, holding time: 20-25min; Calcination endpoint temperature: 580±20℃; After roasting, the pellets are sieved to remove broken pellets and powder smaller than 8mm, resulting in the finished binder-free pellets.

2. The process for producing high-quality, calcined, binder-free pellets from mainstream hematite powder using dry roller milling according to claim 1, characterized in that: The rich hematite powder has a crystal water content of 2.5%-8%, and meets the requirements of <10mm particle size ratio ≥90% and physical moisture content <12%.

3. The process for producing high-quality, calcined, binder-free pellets from mainstream hematite powder using dry roller milling according to claim 1, characterized in that: The temperature T of the flue gas used for sorting and transporting is controlled to be 450℃≤T≤650℃ to remove ≥15% of the water of crystallization and all the gravitational water from the hematite. The proportion of -0.074mm particles in the ground powder is controlled to be >70% by adjusting the flue gas flow rate. The specific surface area of ​​the ground powder is ∈{3400cm2·g-1,4400cm2·g-1}, and the sphericity index is ∈{0.4,0.6}.

4. The process for producing high-quality, calcined, binder-free pellets from mainstream hematite powder using dry roller milling according to claim 1, characterized in that: The pelletizing equipment is a disc pelletizer with a disc inclination angle of 45°-50° and a disc rotation speed of 18-22 r / min. The water spraying adopts an atomized water spraying method, and the water spraying volume is 8%-10% of the mass of the ground powder.

5. The process for producing high-quality, calcined, binder-free pellets from mainstream hematite powder using dry roller milling according to claim 1, characterized in that: The binder-free pellets produced have a compressive strength ≥2500 N·P⁻¹ and an expansion index ≤15%.