Method for comprehensively improving cold-state strength of alkaline pellets produced from Bayan Obo iron ore concentrate

Abstract

The invention discloses a method for comprehensively improving the cold-state strength of alkaline pellets produced from bayan obo iron ore concentrate. The method is characterized in that raw materials comprise, by weight, 70%-75% of bayan obo iron ore concentrate, 25%-30% of common magnetite concentrate, 2.4%-2.8% of externally-matched bentonite and 2.5%-3.0% of externally-matched limestone. The invention aims to solve the problem of low cold-state strength of alkaline pellets prepared from Bayan Obo iron ore concentrate with high proportion, high natural alkalinity, poor pelletizing property and high volatile components in a chain grate machine-rotary kiln-circular cooler. The invention discloses a production technology for improving the cold-state strength of the alkaline pellets by comprehensively applying a high-pressure roller grinding pretreatment technology, binder type optimization and other comprehensive technical measures on a chain grate machine, a rotary kiln and a circular cooler, and creates better raw material conditions for high-pellet-ratio smelting of the alkaline pellets in a blast furnace.

Description

Technical Field

[0001] The invention belongs to the technical field of ironmaking raw material pelletizing, and in particular relates to a method for comprehensively improving the cold strength of alkaline pellets produced by Bayan Obo iron ore concentrate. Background Art

[0002] Bayan Obo iron concentrate is the main ironmaking material of Baotou Steel. It has the characteristics of "high calcium and low silicon". The natural alkalinity of the iron concentrate is about 2.0. Based on the control of the reduction expansion rate of the pellet ore, the development of alkaline pellets can achieve a high proportion of Bayan Obo iron concentrate in Baotou Steel's pellet production. However, it contains relatively high impurity elements such as potassium, sodium, fluorine, and sulfur. During the oxidation roasting process, F and S volatilize at high temperatures, and the organic matter in the added composite binder volatilizes at high temperatures, resulting in more pores in the pellets and low cold strength. On the other hand, the Bayan Obo iron concentrate used in alkaline ball production has a low specific surface area, poor ball formation, and low density. It deteriorates the contact between iron mineral particles during preheating roasting, reduces the inter-crystallization between iron mineral particles, reduces the porosity of the roasted pellets, and thus reduces the cold strength of the finished balls. In order to further improve the cold strength of finished alkaline pellets, the present invention discloses a production technology for improving the cold strength of alkaline pellets by comprehensively applying a chain grate-rotary kiln-ring cooler high-pressure roller mill pretreatment technology and optimizing the types of binders. Summary of the invention

[0003] In response to the problem of low cold strength of alkaline pellets prepared by chain grate, rotary kiln and ring cooler using Bayan Obo iron concentrate with a high proportion of natural alkalinity but poor ball forming property and high volatile matter, comprehensive technical measures such as the comprehensive application of high-pressure roller mill pretreatment technology and optimization of binder types in chain grate, rotary kiln and ring cooler are disclosed to achieve a production technology that improves the cold strength of alkaline pellets, creating better raw material conditions for the application of alkaline pellets in blast furnaces for high ball ratio smelting.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The present invention discloses a method for comprehensively improving the cold strength of alkaline pellets produced by Bayan Obo iron concentrate. The comparative raw materials include, by weight percentage, 70% to 75% of Bayan Obo iron concentrate, 25% to 30% of ordinary magnetite concentrate, 3.1% to 3.4% of binder (external), and 2.5% to 3.0% of limestone (external). The example raw materials include, by weight percentage, 70% to 75% of Bayan Obo iron concentrate, 25% to 30% of ordinary magnetite concentrate, 2.4% to 2.8% of binder (external), and 2.5% to 3.0% of limestone (external).

[0006] Further: the chemical composition of the Bayan Obo iron concentrate includes, by weight percentage: TFe is 64.5-65.0%, FeO is 28.5-29.5%, MgO is 1.30-1.40%, CaO is 2.0%-2.3%, Al2O3≤0.20%, SiO2 is 0.90%-1.60%, S is 0.70-0.80%, F is 0.25%-0.30%, K2O≤0.10%, Na2O≤0.10%; the percentage of concentrate with a particle size of ≤0.074mm in the Bayan Obo iron concentrate is at least 90% of the total weight of the first iron concentrate;

[0007] Further: The chemical composition of the ordinary magnetite concentrate includes TFe of 67.0-67.50%, SiO2 of 1.80-2.50%, S of 0.20%-0.30%, F≤0.05%, K2O+Na2O≤0.09% in terms of weight percentage; the percentage of concentrate with a particle size of ≤0.074mm in the ordinary magnetite concentrate is at least 90% of the total weight of the ordinary magnetite concentrate.

[0008] Further: The chemical composition of the bentonite used in the embodiment includes SiO2 of 58.0% to 60.0% by weight, and Ig≤12.0%. The chemical composition of the binder used in the comparative example includes SiO2 of 54.0% to 56.0% by weight, and Ig≤14.0%.

[0009] Further: the chemical composition of the limestone includes CaO of 50.0% to 52.0%, SiO2 of 2.0% to 4.0%, MgO of 1.0% to 3.0%, and I g≤42.0%.

[0010] Further: According to weight percentage, the embodiment contains 73% Bayan Obo iron concentrate, 27% ordinary magnetite concentrate, 2.6% bentonite (external), and 2.8% limestone (external); the comparative example contains 73% Bayan Obo iron concentrate, 27% ordinary magnetite concentrate, 3.1% binder (external), and 2.9% limestone (external).

[0011] A production method for comprehensively improving the cold strength of alkaline pellets produced from Baiyunebo iron ore concentrate, comprising the following steps:

[0012] The embodiment firstly pre-processes the mixed iron material by high pressure roller mill, and controls the moisture of the roller mill feed material to be 7.0%-8.0%, so as to increase the specific surface area of ​​the mixed material with sulfuric acid slag by 300cm 2 ·g -1 The comparative example has no high pressure roller mill pretreatment.

[0013] Further: the green balls are evenly spread on the chain grate through the green ball distribution device and the screening device, the thickness of the green balls of the chain grate is 175mm~205mm, and the speed of the chain grate is 1.70m / min~1.75m / min.

[0014] Further: the green pellets are dried through the grate blast drying section and the exhaust drying section, the conditions of the blast drying section are: the temperature of the blast drying section bellows is controlled at 200°C to 250°C, the time is 3.43min to 3.53min. The conditions of the exhaust drying section are: the temperature of the exhaust drying section hood is controlled at 320°C to 360°C, the time is 6.86min to 7.05min.

[0015] Further: the dry ball is preheated by a chain grate preheating stage 1 and a preheating stage 2, and the preheating stage conditions are: the preheating stage hood temperature is controlled at 700±20°C for 3.43min to 3.53min. The preheating stage hood temperature is controlled at 1020°C to 1050°C for 10.29min to 10.58min.

[0016] Further: the quality control of the preheated ball: compressive strength 600N / P~800N / P.

[0017] Further: the preheated balls are roasted in a rotary kiln, and the conditions for the rotary kiln roasting are: the temperature of the kiln tail cover is controlled at 950°C to 1000°C, and the temperature of the kiln head cover is controlled at 1030°C to 1060°C.

[0018] Further: Quality control requirements for roasted balls: FeO content <5.0%, S content <0.30%, compressive strength ≥1500N / P.

[0019] Further: the calcined balls are cooled and recrystallized through a ring cooler, and the process conditions of the ring cooler are: the ring cooler speed is 0.90m / min~0.95m / min, the secondary air temperature is controlled at 980℃~1040℃, the second stage wind temperature of the ring cooling is 820±30℃, and the third stage wind temperature of the ring cooling is 430±40℃. After the calcined balls are cooled, fluorine-containing alkaline pellets with added sulfuric acid slag are finally obtained.

[0020] Furthermore: the quality indicators of the alkaline pellets are: TFe≥62.5%, FeO content<1.0%, S content<0.15%, MgO content≥1.0%, SiO2 content≤3.5%, F content≤0.20%, binary basicity is 1.05-1.20, and the compressive strength is increased from 2100N / P of the comparative example to more than 2300N / P.

[0021] Compared with the prior art, the beneficial technical effects of the present invention are:

[0022] The technical problem to be solved by the present invention is the low cold strength problem of alkaline pellets prepared by a chain grate, rotary kiln and ring cooler using Bayan Obo iron concentrate with a high proportion of natural alkalinity but poor ball forming property and high volatile matter. The present invention discloses a production technology for improving the cold strength of alkaline pellets by comprehensively applying high-pressure roller mill pretreatment technology and optimization of binder types in a chain grate, rotary kiln and ring cooler, thereby creating better raw material conditions for the application of alkaline pellets in blast furnaces for high ball ratio smelting. DETAILED DESCRIPTION

[0023] The specific embodiments of the present invention are further described below by way of examples, but the specific embodiments of the present invention are not limited to the following examples.

[0024] The chain grate machine-rotary kiln-ring cooler comprehensively improves the cold strength of alkaline pellets in the production of Bayan Obo iron ore. The raw material configuration, process parameters, pellet composition and related properties used in the comparative examples and embodiments are shown in Tables 1-3 respectively.

[0025] Table 1 Comparative Examples and Examples Raw Materials Ratios

[0026]

[0027] From Table 1, we can see that:

[0028] (1) Compared with the comparative example, during the implementation of the embodiment, the iron material was pre-treated by high pressure roller milling to increase the specific surface area of ​​the mixed iron material by 300 cm 2 ·g -1 about.

[0029] (2) Compared with the comparative example, during the implementation of the embodiment, on the basis of improving the ball-forming property of the raw material by high pressure roller mill, bentonite was used to replace the binder, and the ratio was reduced.

[0030] Table 2 Main process parameters of chain grate machine-rotary kiln-ring cooler for comparative example and embodiment

[0031]

[0032] From Table 2, we can see that:

[0033] Compared with the comparative example, the thermal parameters were stable during the implementation of the embodiment without obvious changes.

[0034] Table 3 Cold strength statistics of finished balls in various embodiments

[0035] Example No. Compressive strength, N / P Comparative Example 2098 Example 2390

[0036] From Table 3, we can see that:

[0037] Compared with the comparative example, the compressive strength of the pellets during the implementation of the present invention increased by 292N / P.

[0038] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for comprehensively improving the cold strength of alkaline pellets produced from Bayan Obo iron ore concentrate, characterized in that: The raw materials include, by weight percentage: 70% to 75% of Bayan Obo iron concentrate, 25% to 30% of common magnetite concentrate, 2.4% to 2.8% of external bentonite, and 2.5% to 3.0% of external limestone; The mixed iron material is pre-treated by high pressure roller mill, and the moisture content of the roller mill feed is controlled at 7.0%-8.0%; The green balls are evenly spread on the chain grate through the green ball distribution device and the screening device. The thickness of the green balls on the chain grate is 175mm-205mm, and the speed of the chain grate is 1.70m / min-1.75m / min. The green pellets are dried through the grate blast drying section and the exhaust drying section. The conditions of the blast drying section are as follows: the bellows temperature of the blast drying section is controlled at 200°C to 250°C for 3.43min to 3.53min. The conditions of the exhaust drying section are as follows: the hood temperature of the exhaust drying section is controlled at 320°C to 360°C for 6.86min to 7.05min. The dry ball is preheated by the chain grate preheating stage 1 and preheating stage 2. The preheating stage conditions are as follows: the preheating stage hood temperature is controlled at 700±20℃ for 3.43min~3.53min. The preheating stage hood temperature is controlled at 1020℃~1050℃ for 10.29min~10.58min. The preheated balls are roasted in a rotary kiln, wherein the roasting conditions of the rotary kiln are as follows: the temperature of the kiln tail hood is controlled at 950°C to 1000°C, and the temperature of the kiln head hood is controlled at 1030°C to 1060°C; The roasted balls are cooled and recrystallized by a ring cooler. The process conditions of the ring cooler are as follows: the ring cooler speed is 0.90m / min-0.95m / min, the secondary air temperature is controlled at 980℃-1040℃, the second stage wind temperature of the ring cooling is 820±30℃, and the third stage wind temperature of the ring cooling is 430±40℃. After the roasted balls are cooled, fluorine-containing alkaline pellets with added sulfuric acid slag are finally obtained.

2. The method for comprehensively improving the cold strength of alkaline pellets produced from Bayan Obo iron concentrate according to claim 1, characterized in that: The chemical composition of the Bayan Obo iron concentrate includes, by weight percentage: TFe is 64.5-65.0%, FeO is 28.5-29.5%, MgO is 1.30-1.40%, CaO is 2.0%-2.3%, Al2O3≤0.20%, SiO2 is 0.90%-1.60%, S is 0.70-0.80%, F is 0.25%-0.30%, K2O≤0.10%, and Na2O≤0.10%; the percentage of concentrate with a particle size of ≤0.074mm in the Bayan Obo iron concentrate is at least 90% of the total weight of the first iron concentrate.

3. The method for comprehensively improving the cold strength of alkaline pellets produced from Bayan Obo iron concentrate according to claim 1, characterized in that: The chemical composition of the ordinary magnetite concentrate includes TFe of 67.0-67.50%, SiO2 of 1.80-2.50%, S of 0.20%-0.30%, F≤0.05%, and K2O+Na2O≤0.09% by weight; the percentage of concentrate with a particle size of ≤0.074mm in the ordinary magnetite concentrate is at least 90% of the total weight of the ordinary magnetite concentrate.

4. The method for comprehensively improving the cold strength of alkaline pellets produced from Bayan Obo iron concentrate according to claim 1, characterized in that: The chemical composition of the bentonite includes SiO2 of 58.0% to 60.0% by weight, and Ig≤12.0%. The chemical composition of the binder used in the comparative example includes SiO2 of 54.0% to 56.0% by weight, and Ig≤14.0%.

5. The method for comprehensively improving the cold strength of alkaline pellets produced from Bayan Obo iron concentrate according to claim 1, characterized in that: The chemical composition of the limestone includes, by weight percentage, 50.0% to 52.0% CaO, 2.0% to 4.0% SiO2, 1.0% to 3.0% MgO, and Ig≤42.0%.

6. The method for comprehensively improving the cold strength of alkaline pellets produced from Bayan Obo iron concentrate according to claim 1, characterized in that: The raw materials include, by weight percentage: 73% Bayan Obo iron concentrate, 27% ordinary magnetite concentrate, 2.6% external bentonite, and 2.8% limestone.

7. The method for comprehensively improving the cold strength of alkaline pellets produced from Bayan Obo iron concentrate according to claim 6, characterized in that: The compressive strength is increased to over 2300N / P.

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