Roasting method for improving strength of magnesian pellets

Abstract

The invention discloses a roasting method for improving the strength of magnesian pellets. According to the method, the burst temperature of the green pellets is detected, and then thermal control parameters are formulated according to the burst temperature of the green pellets as a reference; the air bellow pressure of the forced air drying section is controlled to be 3.0 + / -0.5 KPa, the air bellow temperature of the forced air drying section is controlled to be lower than the green pellet bursting temperature of 120 + / -20 DEG C, the outlet furnace cover temperature of the air draft drying section is controlled to be lower than the green pellet bursting temperature of 110 + / -20 DEG C, the furnace cover temperature of the preheating section is controlled to be 600 + / -20 DEG C, the terminal furnace cover temperature of the roasting section is controlled to be 1260 + / -10 DEG C, and the temperature of a 7 # air bellow is controlled to be 160 + / -20 DEG C. Under the condition that the gas fuel consumption is not increased, the compressive strength of the magnesian pellets produced by adopting the method disclosed by the invention is increased from about 2500N / ball to 3000N / ball or above; during the period, the intensity fluctuation is reduced, and the proportion of the part less than 1000N in the pellets is reduced from about 10% to about 3%; the proportion of the part, smaller than 2000 N, in the pellets is reduced from about 30% to within 15%, the power energy consumption index is excellent, and the method can be well applied to production of the magnesium pellets from the raw materials with the small particle size and high water content.

Description

Technical Field

[0001] The invention belongs to the technical field of pellet preparation, and in particular relates to a roasting method for improving the strength of magnesium pellets. Background Art

[0002] With the continuous advancement of blast furnace ironmaking technology, blast furnaces have higher and higher requirements for refined materials. Pellets have good smelting properties, such as: high iron grade, which is conducive to improving the comprehensive grade of blast furnace materials; uniform and regular shape, high strength, less powder, more in line with the requirements of airflow distribution in the blast furnace; low FeO content and a large number of micropores, reflecting good reducibility. At present, increasing the proportion of pellets has become a development trend of various blast furnaces, especially magnesium pellets with high MgO content.

[0003] In the production of pellets, lightly burned dolomite powder with high MgO content is added to produce magnesium pellets. Because the main component of this material, MgCO3, has a low melting point, it decomposes at a certain temperature to generate MgO and CO2 gas, which significantly reduces the bursting temperature of green balls. Green balls are prone to bursting during the roasting process, resulting in a decrease in the pellet yield and an increase in power energy consumption, which brings great difficulties to the control of pellet production. In addition, the strength of cracked pellets is low, which affects the strength of finished pellets. In addition, different varieties of iron raw materials have different moisture and ball-forming properties, resulting in different bursting temperatures during the drying process of green balls.

[0004] The belt roaster pellet production method is to transfer the finished green balls to a trolley through a belt conveyor for drying, preheating, roasting, equalizing and cooling. All processes from drying to cooling are carried out on the same equipment. The green balls are in a stationary state on the roaster. The roasting process uses gas fuel, which is mainly drawn from top to bottom through the process fan. When the airflow passes through the material layer, it preferentially passes through places with small resistance. Where the resistance is large, the airflow passes less, resulting in uneven strength of the roasted pellets. Usually, the strength is low at the bottom of the material layer and where the airflow passes less, affecting the comprehensive strength of the finished pellets.

[0005] The pellet production of a certain factory is due to the high moisture content of the iron raw materials used (9.8% to 10.9% after mixing with iron concentrate); the particle size is fine, and the main materials used (accounting for about 80%) -200 mesh particle size accounts for about 99%; the strength of the produced pellets fluctuates greatly, with an average compressive strength of about 2500N / ball, but of which less than 1000N / ball accounts for about 10%, and less than 2000N / ball accounts for about 30%. The low-strength pellets are prone to form powder when impacted or squeezed by materials, affecting the airflow, and thus affecting the use of the blast furnace.

[0006] In view of the above problems, the present invention aims to provide a roasting method for improving the strength of magnesia pellets, so as to improve the quality of the produced pellets and create good basic conditions for increasing the ball strength and reducing the burning of blast furnaces. Summary of the invention

[0007] The object of the present invention is to provide a roasting method for improving the strength of magnesia pellets.

[0008] The object of the present invention is achieved by a roasting method for improving the strength of magnesium pellets, which is achieved by the following steps: 1) The laboratory simulates the production site according to the mixed material ratio to make balls, and detects the bursting temperature of the green balls; 2) The green balls on the belt roaster have been running at a speed of 2.2±0.2m / min, and the pressure of the 1# and 2# bellows in the blast drying section is 3±0.5kPa; the temperature of the 1# and 2# bellows in the blast drying section is controlled at 280±20℃ for drying, and the temperature of the furnace hood outlet in the exhaust drying section is controlled at 290±20℃ for drying, the temperature of the 7# bellows of the belt roaster is controlled at 160±20℃, the temperature of the furnace hood inlet in the preheating section is controlled at 600±20℃, the roasting terminal temperature is controlled at 1260±20℃, and the temperature of the equalizing section is 1060±20℃, so as to obtain magnesium pellets; wherein, the drying stage adopts gradual heating drying, the temperature of the bellows in the blast drying section is 120±20℃ lower than the green ball bursting temperature, and the temperature of the furnace hood in the exhaust drying section is 110±20℃ lower than the green ball bursting temperature.

[0009] The magnesia pellets produced by the method of the present invention have no increase in fuel (coke oven gas) consumption, and the average compressive strength is increased from about 2500N / ball to more than 3000N / ball; during the period, the strength fluctuation is reduced, and the proportion of the part less than 1000N in the pellets is reduced from about 10% to about 3%; the proportion of the part less than 2000N in the pellets is reduced from about 30% to less than 15%. The method can be well applied to the production of magnesia pellets with raw materials of fine particle size and high moisture content, creating good basic conditions for increasing the use ratio of pellets in blast furnaces, and is beneficial to reducing the smelting cost of blast furnaces. DETAILED DESCRIPTION

[0010] The present invention is further described below with reference to the embodiments.

[0011] The present invention provides a roasting method for improving the strength of magnesium pellets, which is implemented by the following steps: 1) The laboratory simulates the production site according to the mixed material ratio to make balls, and detects the bursting temperature of the green balls; 2) The green balls on the belt roaster are running at a speed of 2.2±0.2m / min, and the pressure of 1# and 2# bellows in the blast drying section is 3±0.5kPa; the temperature of 1# and 2# bellows in the blast drying section is controlled at 280±20℃ for drying, and the temperature at the outlet of the furnace hood in the exhaust section is controlled at 290±20℃ for drying, the temperature of 7# bellows in the belt roaster is controlled at 160±20℃, the temperature at the inlet of the furnace hood in the preheating section is controlled at 600±20℃, the roasting terminal temperature is controlled at 1260±20℃, and the temperature in the equalizing section is 1060±20℃ to obtain magnesium pellets.

[0012] The drying stage adopts gradual temperature increase drying, the bellows temperature of the blast drying section is 120±20℃ lower than the bursting temperature of the green balls, and the furnace hood temperature of the exhaust drying section is 110±20℃ lower than the bursting temperature of the green balls.

[0013] The thickness of the green balls on the belt roaster is 410±20mm, and the thickness deviation on the north and south sides is less than 20mm.

[0014] In step 1), the mixture is composed of 95.8-96.2% iron ore concentrate, 1.5-1.8% bentonite, 1.5-1.7% light-burned dolomite powder and 0.8% dust ash by mass percentage, the moisture content of the mixture after mixing is 9.6-10.4%, and the particle size of the mixture is -200 mesh with a ratio of 94.61-97.98%; The iron concentrate consists of 75-85% of concentrate A, 5-12% of concentrate B, 5-8% of concentrate C and 0-5% of concentrate D in terms of mass percentage.

[0015] Example 1 The laboratory mixed the pre-mixed materials (A concentrate (80%) + B concentrate (12%) + C concentrate (8%)), and the comprehensive moisture content after mixing was 10.11%, and the particle size (-200 mesh) ratio was 97.30%; the mixture ratio was (iron concentrate (96%) + bentonite (1.6%) + light-burned dolomite powder (1.6%) + dust ash (0.8%)), and the moisture content of the mixture after mixing was 9.61%, and the particle size (-200 mesh) ratio was 95.61%; the bursting temperature of the green balls produced was tested to be 430℃.

[0016] The raw balls are dried, preheated, roasted, homogenized and cooled to obtain magnesium oxide pellets, wherein the roasting machine speed is 2.2m / min, the negative pressure of the air box in the blast drying section is 3.0±0.5KPa, the temperature of the air box in the blast drying section is controlled at 300±20℃, the furnace hood temperature at the outlet of the drying section is 310±20℃, the furnace hood temperature in the preheating section is 600±20℃, the furnace hood temperature at the end of the roasting section is controlled at 1260±10℃, and the temperature of the 7# wind box is controlled at 160±20℃.

[0017] After testing, the strength of the pellets prepared in this implementation is 3104~3474N / ball, the proportion of pellets with compressive strength less than 2000N / ball is between 4.56~18.17%; the proportion of pellets with compressive strength less than 1000N / ball is between 2.12~3.35%. The compressive strength meets the requirements of more than 2500N / ball, and the proportion of pellets with compressive strength less than 2000N / piece and less than 1000N meets the requirements (requirements: compressive strength ≥2500N / ball; proportion of pellets less than 2000N ≤30%; proportion of pellets less than 1000N ≤5%); process energy consumption is between 26.32~28.2kgce / t; coke gas consumption is between 28.42~30.21m3 / t, all of which are at a good level.

[0018] Example 2 The laboratory mixed the pre-mixed materials (A concentrate (75%) + B concentrate (12%) + C concentrate (8%) + D concentrate (5%)) with a total moisture content of 10.68% and a particle size (-200 mesh) ratio of 96.78%; the mixed material ratio was (iron concentrate (96.5%) + bentonite (1.6%) + light-burned dolomite powder (1.7%) + dust ash (0.8%)) with a total moisture content of 10.09% and a particle size (-200 mesh) ratio of 97.3% after mixing); the bursting temperature of the green balls produced was tested to be 400±20℃.

[0019] After drying, preheating, roasting, equalizing and cooling, the raw balls are obtained into magnesium oxide pellets. Among them, the negative pressure of the air drying section bellows is 3.0±0.3KPa, the temperature of the air drying section bellows is controlled at 280±20℃, the temperature of the furnace cover at the outlet of the drying section is 300±20℃, the temperature of the furnace cover at the preheating section is 600±20℃, the temperature of the furnace cover at the end of the roasting section is controlled at 1260±10℃, and the temperature of the 7# bellows is controlled at 160±20℃.

[0020] After testing: the strength of the pellets prepared in this embodiment is 2996-3385N / ball, the proportion of pellets with compressive strength less than 2000N / ball is between 4.74-18.87%; the proportion of pellets with compressive strength less than 1000N / ball is between 1.86-3.68%. The compressive strength is above 2500N / ball, and the proportion of pellets with compressive strength less than 2000N / piece and less than 1000N meets the requirements (requirements: compressive strength ≥ 2500N / ball; proportion of pellets less than 2000N ≤ 30%; proportion of pellets less than 1000N ≤ 5%); process energy consumption is between 26.72-29.62kgce / t; coke gas consumption is between 28.63-30.96m3 / t, all of which are at a good level.

[0021] Example 3 The laboratory prepared the pre-mixed materials (A concentrate (85%) + B concentrate (5%) + C concentrate (5%) + D concentrate (5%), with a total moisture content of 10.43% after mixing) and a particle size (-200 mesh) ratio of 97.84%; the mixture ratio was (iron concentrate (95.8%) + bentonite (1.5%) + light-burned dolomite powder (1.7%) + dust ash (1.0%)), with a total moisture content of 10.31% after mixing) and a particle size (-200 mesh) ratio of 96.67%; the bursting temperature of the green balls produced was tested to be 380±20℃.

[0022] After drying, preheating, roasting, equalizing and cooling, the raw balls are obtained into magnesium oxide pellets. Among them, the negative pressure of the air box in the blast drying section is 3.0±0.3KPa, the temperature of the air box in the blast drying section is controlled at 270±20℃, the temperature of the furnace cover at the outlet of the drying section is 280±20℃, the temperature of the furnace cover in the preheating section is 600±20℃, the temperature of the furnace cover at the end of the roasting section is controlled at 1260±10℃, and the temperature of the 7# wind box is controlled at 160±20℃.

[0023] After testing: the strength of the pellets prepared in this embodiment is 2854-3270N / ball, the proportion of pellets with compressive strength less than 2000N / ball is between 3.06-24.54%, and the proportion of pellets with compressive strength less than 1000N / ball is between 2.36-4.18%. The compressive strength is above 2500N / ball, and the proportion of pellets with compressive strength less than 2000N / ball and less than 1000N meets the requirements (requirements: compressive strength ≥ 2500N / ball; proportion of pellets less than 2000N ≤ 30%; proportion of pellets less than 1000N ≤ 5%); process energy consumption is between 27.44-30.62kgce / t; coke gas consumption is between 28.56-32.46m3 / t, all of which are at a good level.

[0024] The difference between Comparative Examples 1-3 and Example 1 lies in the different parameters of the forced air drying section, the exhaust air drying section and the roasting section.

[0025] Comparative Example 1 When the negative pressure of the bellows in the blast drying section is lower than 2.7KPa and the temperature of the bellows in the blast drying section is controlled to be lower than the bursting temperature of the green ball within 300±20℃, the furnace hood temperature at the outlet of the extraction section is lower than the bursting temperature of the green ball within 290±20℃, the furnace hood temperature in the preheating section is 600±20℃, the furnace hood temperature at the end of the roasting section is controlled to be 1260±10℃, and the temperature of the 7# bellows is controlled at 160±20℃.

[0026] After testing, the strength of the pellets prepared in this comparative example is between 2680 and 2865N / ball, the proportion of pellets with compressive strength less than 2000N / ball is between 17.04 and 29.53%; the proportion of pellets with compressive strength less than 1000N / ball is between 2.92 and 8.29%; the compressive strength meets the requirement of being above 2500N / ball, and the proportion of pellets with compressive strength less than 2000N / ball and less than 1000N / ball can both meet the requirements, but the energy consumption of the process is between 27.65 and 34.88kgce / t, which is on the high side; the power consumption is 30.48 to 40.68kwh / t, which is on the high side, and the proportion of red balls in the on-site pellets is high, indicating that the drying effect is slightly poor.

[0027] Comparative Example 2 When the negative pressure of the air box in the blast drying section is greater than 3.5KPa and the temperature of the air box in the blast drying section is controlled within 320±20℃, the temperature of the furnace hood at the outlet of the extraction section is controlled within 330±20℃, the temperature of the furnace hood in the preheating section is 600±20℃, the temperature of the furnace hood at the end of the roasting section is controlled at 1260±10℃, and the temperature of the 7# air box is controlled at 160±20℃.

[0028] After testing, the strength of the pellets prepared in this comparative example is between 2280 and 3025N / ball, the proportion of pellets with compressive strength less than 2000N / ball is between 25.46 and 44.44%; the proportion of pellets with compressive strength less than 1000N / ball is between 5.92 and 18.49%; the compressive strength meets the requirements of more than 2500N / ball, and the proportion of pellets with compressive strength less than 2000N / ball and less than 1000N / ball are both substandard. The energy consumption of the process is 29.65 to 35.82kgce / t, which is relatively high; the power consumption is 31.64 to 47.68kwh / t, which is relatively high, and the proportion of broken balls and cracked balls in the on-site pellets is high, indicating that the drying temperature is too high and there is bursting in the drying process of the raw balls.

[0029] Comparative Example 3 When the negative pressure of the wind box in the blast drying section is less than 2.7KPa and the temperature of the wind box in the blast drying section is controlled within 340±20℃, the temperature of the furnace hood at the outlet of the extraction section is controlled within 340±20℃, the temperature of the furnace hood in the preheating section is 600±20℃, the temperature of the furnace hood at the end of the roasting section is controlled at 1260±10℃, and the temperature of the 7# wind box is controlled at 160±20℃.

[0030] After testing, the strength of the pellets prepared in this comparative example is between 2160 and 3425N / ball, the proportion of pellets with compressive strength less than 2000N / ball is between 15.46 and 44.44%; the proportion of pellets with compressive strength less than 1000N / ball is between 6.92 and 28.69%; the average compressive strength meets the requirements of more than 2500N / ball, and the proportion of pellets with compressive strength less than 2000N / ball and less than 1000N / ball are both substandard. The energy consumption of the process is between 30.32 and 37.23kgce / t, which is on the high side; the power consumption is 29.64 to 47.74kwh / t, which is high, and the proportion of broken balls and cracked balls in the on-site pellets is high, indicating that the drying temperature is too high and there is serious bursting in the drying process of the raw balls.

[0031] The difference between Comparative Examples 4-6 and Example 2 lies in the different parameters of the drying section, the extraction section and the roasting section.

[0032] Comparative Example 4 When the negative pressure of the wind box in the blast drying section is lower than 2.7KPa and the temperature of the wind box in the blast drying section is controlled within 280±20℃, the temperature of the furnace hood at the outlet of the extraction section is controlled within 290±20℃, the temperature of the furnace hood in the preheating section is 600±20℃, the temperature of the furnace hood at the end of the roasting section is controlled at 1260±10℃, and the temperature of the 7# wind box is controlled at 160±20℃.

[0033] After testing, the strength of the pellets prepared in this comparative example is between 2630 and 2943 N / ball, the proportion of pellets with compressive strength less than 2000 N / ball is between 13.04 and 27.64%; the proportion of pellets with compressive strength less than 1000 N / ball is between 2.12 and 4.89%; the compressive strength meets the requirement of being above 2500 N / ball, and the proportion of pellets with compressive strength less than 2000 N / ball and less than 1000 N / ball can both meet the requirements, but the energy consumption of the process is between 29.82 and 35.42 kgce / t, which is on the high side; the power consumption is 30.13 to 43.46 kwh / t, which is on the high side, and the proportion of red balls in the on-site pellets is high, indicating that the drying effect is slightly poor.

[0034] Comparative Example 5 When the negative pressure of the air box in the blast drying section is greater than 3.3KPa and the temperature of the air box in the blast drying section is controlled within 300±20℃, the temperature of the furnace hood at the outlet of the extraction section is controlled within 310±20℃, the temperature of the furnace hood in the preheating section is 600±20℃, the temperature of the furnace hood at the end of the roasting section is controlled at 1260±10℃, and the temperature of the 7# air box is controlled at 160±20℃.

[0035] After testing, the strength of the pellets prepared in this comparative example is between 2568 and 2845 N / ball, the proportion of pellets with compressive strength less than 2000 N / ball is between 24.46 and 46.68%; the proportion of pellets with compressive strength less than 1000 N / ball is between 5.62 and 20.36%; the compressive strength meets the requirements of more than 2500 N / ball, and the proportion of pellets with compressive strength less than 2000 N / ball and less than 1000 N / ball are both substandard. The energy consumption of the process is between 30.48 and 34.48 kgce / t, which is on the high side; the power consumption is 31.94 to 48.60 kwh / t, which is high, and the proportion of broken balls and cracked balls in the on-site pellets is high, indicating that the drying temperature is too high and there is bursting in the drying process of the raw balls.

[0036] Comparative Example 6 When the negative pressure of the wind box in the blast drying section is less than 2.7KPa and the temperature of the wind box in the blast drying section is controlled within 320±20℃, the temperature of the furnace hood at the outlet of the extraction section is controlled within 330±20℃, the temperature of the furnace hood in the preheating section is 600±20℃, the temperature of the furnace hood at the end of the roasting section is controlled at 1260±10℃, and the temperature of the 7# wind box is controlled at 160±20℃.

[0037] After testing, the strength of the pellets prepared in this comparative example is between 1972 and 2756 N / ball, the proportion of pellets with compressive strength less than 2000 N / ball is between 21.46 and 46.74%; the proportion of pellets with compressive strength less than 1000 N / ball is between 6.86 and 31.56%; the compressive strength does not meet the requirement of more than 2500 N / ball, and the proportion of pellets with compressive strength less than 2000 N / ball and less than 1000 N / ball are both substandard. The energy consumption of the process is between 30.64 and 37.86 kgce / t, which is high; the electricity consumption is between 30.58 and 46.74 kwh / t, which is high, and the proportion of broken balls and cracked balls in the on-site pellets is high, indicating that the drying temperature is too high and there is bursting in the drying process of the green balls.

[0038] The difference between Comparative Examples 7-9 and Example 3 lies in the different parameters of the drying section, the extraction section and the roasting section.

[0039] Comparative Example 7 When the negative pressure of the wind box in the blast drying section is lower than 2.7KPa and the temperature of the wind box in the blast drying section is controlled within 280±20℃, the temperature of the furnace hood at the outlet of the extraction section is controlled within 290±20℃, the temperature of the furnace hood in the preheating section is 600±20℃, the temperature of the furnace hood at the end of the roasting section is controlled at 1260±10℃, and the temperature of the 7# wind box is controlled at 160±20℃.

[0040] After testing, the strength of the pellets prepared in this comparative example is between 2510 and 2920 N / ball, the proportion of pellets with compressive strength less than 2000 N / ball is between 15.37 and 29.61%; the proportion of pellets with compressive strength less than 1000 N / ball is between 2.36 and 4.97%; the compressive strength meets the requirement of being above 2500 N / ball, and the proportion of pellets with compressive strength less than 2000 N / ball and less than 1000 N / ball can both meet the requirements, but the energy consumption of the process is between 30.82 and 34.2 kgce / t, which is on the high side; the power consumption is 30.62 to 42.66 kwh / t, which is on the high side, and the proportion of red balls in the on-site pellets is high, indicating that the drying effect is slightly poor.

[0041] Comparative Example 8 When the negative pressure of the wind box in the blast drying section is greater than 3.3KPa and the temperature of the wind box in the blast drying section is controlled within 260±20℃, the temperature of the furnace hood at the outlet of the extraction section is controlled within 270±20℃, the temperature of the furnace hood in the preheating section is 600±20℃, the temperature of the furnace hood at the end of the roasting section is controlled at 1260±10℃, and the temperature of the 7# wind box is controlled at 160±20℃.

[0042] After testing, the strength of the pellets prepared in this comparative example is between 2260 and 2896 N / ball, the proportion of pellets with compressive strength less than 2000 N / ball is between 22.34 and 44.06%; the proportion of pellets with compressive strength less than 1000 N / ball is between 5.83 and 21.76%; the compressive strength does not meet the requirement of more than 2500 N / ball, and the proportion of pellets with compressive strength less than 2000 N / ball and less than 1000 N / ball are both substandard. The energy consumption of the process is between 29.88 and 34.46 kgce / t, which is on the high side; the power consumption is 32.04 to 46.60 kwh / t, which is on the high side, and the proportion of broken balls and cracked balls in the on-site pellets is high, indicating that the drying temperature is too high and there is bursting in the drying process of the raw balls.

[0043] Comparative Example 9 When the negative pressure of the wind box in the blast drying section is less than 2.7KPa and the temperature of the wind box in the blast drying section is controlled within 310±20℃, the temperature of the furnace hood at the outlet of the extraction section is controlled within 320±20℃, the temperature of the furnace hood in the preheating section is 600±20℃, the temperature of the furnace hood at the end of the roasting section is controlled at 1260±10℃, and the temperature of the 7# wind box is controlled at 160±20℃.

[0044] After testing, the strength of the pellets prepared in this comparative example is between 1952 and 2456 N / ball, the proportion of pellets with compressive strength less than 2000 N / ball is between 24.46 and 45.32%; the proportion of pellets with compressive strength less than 1000 N / ball is between 7.06 and 35.56%; the compressive strength does not meet the requirement of more than 2500 N / ball, and the proportion of pellets with compressive strength less than 2000 N / ball and less than 1000 N / ball are both substandard. The energy consumption of the process is between 30.64 and 36.72 kgce / t, which is high; the electricity consumption is between 30.43 and 45.52 kwh / t, which is high, and the proportion of broken balls and cracked balls in the on-site pellets is high, indicating that the drying temperature is too high and there is bursting in the drying process of the green balls.

[0045] A factory adopts the roasting process with the same mixed material ratio as Example 1 before 2024 as follows (Table 1): the pressure requirement of the air box in the blast drying section is ≥0.5Kpa, the air temperature of the blast drying section 1# and 2# is controlled at 300±20℃ for drying, the temperature of the furnace cover inlet of the exhaust section is controlled at 320±20℃ for drying, the temperature of the belt roaster 7# air box is controlled at 160±20℃, the temperature of the furnace cover inlet of the preheating section is controlled at 600±20℃, and the roasting end temperature is controlled at 1250±20℃. The produced magnesium pellets have cracks, resulting in large fluctuations in compressive strength, and the average compressive strength of the pellets is about 2500N / ball; the proportion of the pellets less than 2000N accounts for about 30%, and the proportion of the pellets less than 1000N accounts for about 10%, which affects the use effect of the blast furnace.

[0046] Table 1 Comparison of roasting process parameters before and after the roasting method improvement of a certain factory Note: M is the bursting temperature of green balls.

[0047] When a factory produces magnesia pellets with fine raw material particle size (-200 mesh ratio 96%~98%) and high pre-batch moisture (9.8%~10.9%), and adds lightly burned dolomite powder, the factory detects the green ball bursting temperature and then formulates thermal control parameters based on the green ball bursting temperature as a reference; the bellows pressure of the blast drying section is controlled at 3.0±0.3KPa, the bellows temperature of the blast drying section is controlled to be 120±20℃ lower than the green ball bursting temperature, the furnace hood temperature at the outlet of the exhaust drying section is controlled to be 110±20℃ lower than the green ball bursting temperature, the furnace hood temperature in the preheating section is 600±20℃, the furnace hood temperature at the end of the roasting section is controlled to be 1260±10℃, and the temperature of the 7# bellows is controlled at 160±20℃. The comprehensive compressive strength of the pellets produced without increasing the consumption of gas fuel (coke oven gas) increased, and the average compressive strength increased from about 2500N / ball to more than 3000N / ball; during the period, the strength fluctuation decreased, and the proportion of pellets with a strength less than 1000N decreased from about 10% to about 3%; the proportion of pellets with a strength less than 2000N decreased from about 30% to less than 20% (Table 2).

[0048] Table 2 Power energy consumption and quality of pellets before and after the roasting method of a certain factory was improved

Claims

1. A roasting method for improving the strength of magnesium pellets, characterized in that: To do this, follow these steps: 1) The laboratory simulates the production site according to the mixed material ratio to make balls, and detects the bursting temperature of the green balls; 2) The green balls are running at a speed of 2.2±0.2m / min on the belt roaster, and the pressure of the 1# and 2# wind boxes in the blast drying section is 3±0.5kPa; the temperature of the 1# and 2# wind boxes in the blast drying section is controlled at 280±20℃ for drying, and the outlet temperature of the furnace cover in the exhaust section is controlled at 290±20℃ for drying, the temperature of the 7# wind box of the belt roaster is controlled at 160±20℃, the inlet temperature of the furnace cover in the preheating section is controlled at 600±20℃, the end temperature of roasting is controlled at 1260±20℃, and the temperature of the soaking section is 1060±20℃, thus obtaining magnesium pellets; The drying stage adopts gradual temperature increase drying, the bellows temperature of the blast drying section is 120±20℃ lower than the bursting temperature of the green balls, and the furnace hood temperature of the exhaust drying section is 110±20℃ lower than the bursting temperature of the green balls.

2. The roasting method for improving the strength of magnesium pellets according to claim 1, characterized in that: The thickness of the green balls on the belt roaster is 410±20mm, and the thickness deviation on the north and south sides is less than 20mm.

3. The roasting method for improving the strength of magnesium pellets according to claim 1, characterized in that: In step 1), the mixture is composed of 95.8-96.2% iron ore concentrate, 1.5-1.8% bentonite, 1.5-1.7% light-burned dolomite powder and 0.8% dust ash by mass percentage, the moisture content of the mixture after mixing is 9.6-10.4%, and the particle size of the mixture is -200 mesh with a ratio of 94.61-97.98%; The iron concentrate consists of 75-85% of concentrate A, 5-12% of concentrate B, 5-8% of concentrate C and 0-5% of concentrate D in terms of mass percentage.

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