Pellet and preparation method thereof
By mixing limonite and specularite and then dynamically drying and roller-grinding with a hot medium to prepare fine ground powder, the problems of high porosity and strong water retention of limonite in pellet production are solved, the compressive strength and thermal stability of the pellets are improved, and the production cost is reduced.
Patent Information
- Application Number
- CN202510788540.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-13
- Publication Date
- 2025-09-12
AI Technical Summary
In the existing technology, when using limonite as raw material to produce pellets, there are problems such as high porosity, strong water retention, difficult sedimentation during wet grinding, poor thermal stability of green pellets, low burst temperature, poor consolidation of finished pellets, and low compressive strength.
Limonite and specularite are mixed in a certain proportion and then subjected to dynamic drying roller grinding with a hot medium to prepare fine ground powder, which is then mixed with other raw materials to form pellets. Pellets are prepared through a drying, roasting, soaking and cooling process to optimize particle size distribution and ballability.
The compressive resistance and thermal stability of the pellets are improved, the production cost is reduced, the diameter of the pellet raw materials is widened, and the ball forming property and thermal burst resistance are improved.
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of steel smelting, and in particular relates to a pellet and a preparation method thereof. Background Art
[0002] The entire pellet roasting process—drying, preheating, roasting, soaking, and cooling—is completed on a single piece of equipment. This features high single-unit production capacity, simple process flow, compact layout, lightweight equipment, and low energy consumption due to the recycling of hot exhaust gases. Throughout the roasting process, the pellets remain in a static layer, eliminating the generation of powder due to changes in pellet strength or relative motion during heating. As a result, the belt roasting process has been widely developed.
[0003] However, most domestic pellet production lines use more than 90% magnetite plus a small amount of other iron-containing raw materials to produce pellets. A small number of them will also use a small proportion of hematite. There is basically no production of pellets using a large proportion of limonite as raw material. Limonite raw material cost is low, but the main problems of using limonite for pellet roasting production are as follows:
[0004] 1) Limonite has high porosity and strong water holding capacity, making it difficult to settle and filter during wet grinding;
[0005] 2) When the ratio of hematite to limonite is high, the thermal stability of the green pellets is poor, the bursting temperature is low, and the crack rate of the pellets is high;
[0006] 3) Limonite contains a large amount of crystal water, which consumes a lot of heat in the drying and preheating stages, and the roasting temperature is high, resulting in high energy consumption in the process;
[0007] 4) The finished pellets have poor consolidation, low compressive strength and high powder content. Summary of the Invention
[0008] In view of the above problems existing in the prior art, the present invention provides a pellet and a preparation method thereof, which can obtain pellets with excellent performance using limonite as a raw material.
[0009] To achieve the above-mentioned purpose, the technical solution provided by the present invention is as follows:
[0010] In a first aspect, the present application provides a method for preparing pellets, comprising:
[0011] The limonite and specularite are mixed in a mass ratio of (6-8):3 and then subjected to dynamic drying and roller grinding with a hot medium to obtain fine ground powder;
[0012] The finely ground powder is humidified at a water mass ratio of 6% to 10% to obtain prefabricated iron ore powder;
[0013] Prefabricated iron ore powder, low-grade mixed ore, magnetite, sulfuric acid slag and highly dusted ash are mixed to obtain a mixture, and the mixture is pelletized and sieved to obtain green balls;
[0014] The green pellets are dried, roasted, homogenized and cooled in sequence to obtain finished pellets.
[0015] Optionally, the finely ground powder has a particle size of 200 mesh ≥ 80% and an average specific surface area ≥ 3000 cm 2 / g.
[0016] Optionally, the dynamic drying with heat medium includes: using hot air at 450-550° C. for blowing, and the heat treatment time is 28 s-3 min.
[0017] Optionally, the roller milling pressure is 6.8-9.0 MPa, and the roller milling processing time is 28 seconds to 3 minutes.
[0018] Optionally, the mixture comprises the following components in the following mass ratios: 15-25% prefabricated iron ore powder, 45-55% low-grade mixed ore, 10-20% magnetite, 5-15% sulfuric acid slag and 2-7% highly dusted ash.
[0019] Optionally, the green balls have a diameter of 8-16 cm and are dropped 5-8 times.
[0020] Optionally, the drying includes sequentially arranged forced air drying and exhaust air drying, the forced air drying temperature is ≥150°C, and the exhaust air drying temperature is 250-400°C.
[0021] Optionally, the green balls are dried and preheated before being roasted, the temperature of the preheating section is 400-1200°C, and the temperature of the roasting section is 1100-1300°C; the roasted green balls are treated in the soaking section and then enter the cooling section.
[0022] Optionally, the cooling section includes a first cooling section and a second cooling section which are arranged in sequence, the temperature of the first cooling section is 550-1100°C, and the temperature of the second cooling section is ≤550°C.
[0023] Optionally, the mass ratio of limonite to specularite is 7:3.
[0024] On the other hand, the present application also provides a pellet prepared according to the method described in the first aspect.
[0025] Compared with the prior art, this application has at least the following beneficial effects:
[0026] The present invention solves the problem that single specularite powder is difficult to form into pellets, and single limonite powder has strong hydrophilicity but is easy to deform; it breaks through the technical bottleneck of preparing pellets with a high ratio of limonite powder / specularite, greatly improves the addition ratio of specularite and limonite powder in pellet production, realizes the wide-caliber pellet raw materials, and reduces the raw material production cost of pellet ore.
[0027] By mixing limonite and specularite in a certain ratio, grinding them into powder under dynamic drying with a hot medium and then using them as raw materials for preparing pellets, the strength and thermal cracking resistance of the green balls are improved, and the influence of roasting high-burning-loss and high-crystallization-water iron ore powder on the pellet structure is reduced. No bentonite needs to be added during the preparation process; the finished pellets have excellent compressive properties.
[0028] The finely ground powder obtained by the present invention has a wide particle size distribution, which is conducive to achieving close packing of particles in the ball-making process and also helps to improve ball-forming properties. The static ball-forming property index is increased by more than 1 times. DETAILED DESCRIPTION
[0029] The present invention is described in further detail below:
[0030] Unless otherwise specified, the experimental methods used in the embodiments of the present invention are conventional methods.
[0031] The present application provides a method for preparing pellets, comprising:
[0032] The limonite and specularite are mixed in a mass ratio of (6-8):3 and then subjected to dynamic drying and roller grinding with a hot medium to obtain fine ground powder;
[0033] The finely ground powder is humidified to a moisture content of 6% to 10% by mass to obtain prefabricated iron ore powder;
[0034] Prefabricated iron ore powder, low-grade mixed ore, magnetite, sulfuric acid slag and highly dusted ash are mixed to obtain a mixture, and the mixture is pelletized and sieved to obtain green balls;
[0035] The green pellets are dried, roasted, homogenized and cooled in sequence to obtain finished pellets.
[0036] The pellets prepared by the method of the present invention have a compression index of ≥2000N / P, RI ≥80%, and RDI +3.15 ≥96%, RSI≤18%.
[0037] In certain embodiments of the present invention, the finely ground powder has a particle size of 200 mesh ≥ 80% and an average specific surface area ≥ 3000 cm 2 / g. The roller milling process improves the surface activity and surface energy of the finely ground powder.
[0038] In certain embodiments of the present invention, the dynamic drying with heat medium includes: using hot air at 450-550° C. for blowing, and the dynamic drying time of the heat medium is 28 seconds to 3 minutes.
[0039] Through the dynamic drying of the hot medium in the roller mill process, part of the crystal water can be removed, promoting 5%-30% of the limonite phase to be converted into hematite, reducing its thermal sensitivity and burning loss, and improving the roasting performance of the pellets.
[0040] In certain embodiments of the present invention, the mixture comprises the following components in the following mass ratios: 15-25% prefabricated iron ore fines, 45-55% low-grade mixed ore, 10-20% magnetite, 5-15% sulfate slag and 2-7% highly dusted ash.
[0041] In certain embodiments of the present invention, the green balls have a diameter of 8-16 cm, and the green balls are dropped 5-8 times.
[0042] In certain embodiments of the present invention, the drying comprises sequentially arranged forced air drying and exhaust air drying, the forced air drying temperature is ≥150°C, and the exhaust air drying temperature is 250-400°C.
[0043] In certain embodiments of the present invention, the green balls are dried, preheated, and then roasted. The temperature of the preheating section is 400-1200°C, and the temperature of the roasting section is 1100-1300°C. The roasted green balls are treated in the soaking section and then enter the cooling section.
[0044] In certain embodiments of the present invention, the cooling section comprises a first cooling section and a second cooling section which are sequentially arranged, the temperature of the first cooling section is 550-1100°C, and the temperature of the second cooling section is ≤550°C.
[0045] In certain embodiments of the present invention, the mass ratio of limonite to specularite is 7:3.
[0046] Taking advantage of the characteristics of specularite, which has high hardness, weak hydrophilicity and poor ball-forming property, and limonite, which has low hardness, strong hydrophilicity and good ball-forming property, mixed dry grinding under dynamic treatment of hot medium is carried out at a ratio of limonite: specularite = 7:3, which can form fine ground powder that is inlaid with each other and complements each other.
[0047] Example
[0048] A pellet, the preparation method of which is as follows:
[0049] Limonite and specularite were mixed in a mass ratio of 7:3 and then subjected to dynamic drying and roller grinding in a vertical roller mill using a hot medium to obtain fine ground powder; the fine ground powder had a particle size of 83% at -200 mesh and an average specific surface area of 3000 cm 2 / g;
[0050] The dynamic drying temperature of the hot medium is 500°C, the processing time is 40 s, the roller mill pressure is 7.2 MPa, and the roller mill processing time is 28 s, until part of the limonite phase is converted into hematite.
[0051] The finely ground powder is humidified to a moisture content of 8% by mass to obtain prefabricated iron ore powder;
[0052] A mixture, calculated by mass percentage, is prepared by mixing 22.2% prefabricated iron ore fines, 48.5% low-grade mixed ore, 18.2% magnetite, 7.1% sulfuric acid slag, and 4% highly dusted ash. The mixture is then pelletized and sieved to produce green balls. The green ball diameter is controlled to be 8-16 cm, and the balls fall between 5-8 times. The composition of the mixture is shown in Table 1. Other components are not listed, as they have little impact on pellet performance. In the following table, -200 indicates the percentage of material that falls through a 200-mesh sieve within a given component.
[0053] Table 1 Composition of components in the mixture
[0054] variety Moisture TFe FeO <![CDATA[SiO2]]> S P CaO Zn Cr <![CDATA[TiO2]]> -200 Low-grade mixed ore 11.3 60.80 7.50 5.15 0.340 0.090 0.40 0.030 0.020 0.740 65.0 sulfuric acid slag 17.0 61.00 4.42 6.32 1.000 0.040 1.90 0.090 0.003 0.056 80.0 magnetite 11.1 65.66 27.16 4.20 0.041 0.013 0.59 0.005 0.010 0.333 96.0 Blast furnace dust 0.0 50.00 3.77 5.50 0.335 0.065 6.86 0.021 0.003 0.177 60.0 Prefabricated iron ore powder 7.0 57.50 0.50 3.30 0.08 0.03 0.05 0.015 0.60 0.250 83.0
[0055] The green pellets are sequentially dried by forced air and exhausted air, preheated, calcined, soaked and cooled in two stages to obtain finished pellets. The obtained pellets have a compressive strength of 2400 N / P, RI of 81% and RDI of 1. +3.15 The temperature of each section is shown in Table 2.
[0056] Table 2 Temperature of each section
[0057] project Blast drying section Exhaust drying section Preheating section Roasting section Soaking section A cold period Second cooling section Temperature index / ℃ 280 360 1170 1260 1060 900 300
[0058] Comparative Example 1
[0059] The difference between this comparative example and the embodiment is that no dynamic drying of the heat medium is performed during the roller milling process.
[0060] The finely ground powder obtained in this comparative example has a moisture content of 10.0% and an average specific surface area of 2000 cm 2 / g. Because dynamic drying of the heat medium is not carried out during the roller milling process, the moisture content of the ground powder increases and the specific surface area decreases, which is not conducive to the control of the subsequent ball making and roasting steps.
[0061] The compressive strength of the pellets obtained in this comparative example is 1800 N / P, RI 76%, RDI +3.15 92.5%, RSI 19%.
[0062] Comparative Example 2
[0063] The difference between this comparative example and the embodiment is that limonite and specularite are mixed in a mass ratio of 5:5.
[0064] The proportion of limonite used in the grinding process was reduced, the proportion of specularite was increased, and the average specific surface area of the finely ground powder obtained was 1800 cm2 / g, and the ball formation index was reduced. The compressive strength of the pellets obtained in this comparative example was 2100 N / P, RI 70%, and RDI +3.15 94.5%, RSI 18%.
Claims
1. A method for preparing pellets, characterized in that: include: The limonite and specularite are mixed in a mass ratio of (6-8):3 and then subjected to dynamic drying and roller grinding with a hot medium to obtain fine ground powder; The finely ground powder is humidified to a moisture content of 6% to 10% by mass to obtain prefabricated iron ore powder; Prefabricated iron ore powder, low-grade mixed ore, magnetite, sulfuric acid slag and highly dusted ash are mixed to obtain a mixture, and the mixture is pelletized and sieved to obtain green balls; The green pellets are dried, roasted, homogenized and cooled in sequence to obtain finished pellets.
2. The method for preparing pellets according to claim 1, wherein: The finely ground powder-200 mesh ≥80%, average specific surface area ≥3000cm 2 / g.
3. The method for preparing pellets according to claim 1, characterized in that: The dynamic drying of the heat medium includes: using hot air at 450-550° C. for blowing, and the dynamic drying time of the heat medium is 28 seconds to 3 minutes.
4. The method for preparing pellets according to claim 1, wherein: The roller milling pressure is 6.8-9.0 MPa, and the roller milling processing time is 28 seconds to 3 minutes.
5. The method for preparing pellets according to claim 1, wherein: The mixture comprises the following components in the following mass ratios: 15-25% prefabricated iron ore powder, 45-55% low-grade mixed ore, 10-20% magnetite, 5-15% sulfuric acid slag and 2-7% highly dusted ash.
6. The method for preparing pellets according to claim 1, characterized in that: The diameter of the green balls is 8-16 cm, and the green balls fall between 5-8 times.
7. The method for preparing pellets according to claim 1, wherein: The drying includes sequentially arranged forced air drying and exhaust air drying, the forced air drying temperature is ≥150°C, and the exhaust air drying temperature is 250-400°C; the cooling section includes a first cooling section and a second cooling section arranged sequentially, the temperature of the first cooling section is 550-1100°C, and the temperature of the second cooling section is ≤550°C.
8. The method for preparing pellets according to claim 1, wherein: After the green balls are dried, they are preheated and then roasted. The temperature of the preheating section is 400-1200°C, and the temperature of the roasting section is 1100-1300°C. The roasted green balls are treated in the soaking section and then enter the cooling section.
9. The method for preparing pellets according to claim 1, wherein: The mass ratio of the limonite to the specularite is 7:
3.
10. A pellet prepared according to the method according to any one of claims 1 to 9.