A method for improving the quality of basic pellets

Abstract

The invention discloses a method for improving the quality of alkaline pellets, which uses a vertical strong mixer to mix pipeline concentrate and quicklime, controls the water content to be about 7%, and digests the quicklime with the moisture of the pipeline concentrate, thereby eliminating the agglomeration phenomenon that occurs when the quicklime is digested and mixed with mineral powder, and preventing cracking during the roasting process of alkaline pellets; when producing high-alkalinity pellets, quicklime is partially substituted for limestone to prevent the problem that the limestone ratio is too high, resulting in too many pores inside the pellets, thereby causing the compressive strength to decrease, and ensures that the compressive strength of the high-alkalinity alkaline pellets is at a high level; and then mixed with dry concentrate and fine-grained limestone to make pellets, and the alkalinity is adjusted with fine-grained limestone to increase the porosity, so that the active lime is mixed more evenly, thereby improving the reducibility of the pellets, inhibiting the cracking of the pellets, improving the strength of the pellets and improving the quality, and reducing the carbon emission of the pellets. Compared with the use of ordinary alkaline pellets, it is more conducive to improving the permeability of the blast furnace and the utilization rate of coal gas.

Description

Technical Field

[0001] The invention belongs to the field of iron ore agglomeration, and particularly relates to a production process technology of alkaline pellets, and specifically to a method for improving the quality of alkaline pellets. Background Art

[0002] At present, the solvent used in the production process of alkaline pellets is quicklime or limestone. The use of quicklime has the problem of poor mixing effect with ore powder after digestion, and the agglomeration of quicklime is difficult to suppress, which leads to cracking during the roasting process of the pellets and low strength of the pellets. When limestone is used as a solvent, the carbon dioxide is released by the decomposition of limestone under heat, which increases the pores inside the pellets. When the alkalinity of the pellets is too high, the internal pores increase to a certain extent, and the strength of the pellets will be reduced, limiting the upper limit of the alkalinity of high-quality pellets. At the same time, the use of limestone as a solvent requires heat for the decomposition of limestone, which increases production energy consumption, and the decomposition of limestone releases carbon dioxide, which increases carbon emissions. Summary of the invention

[0003] In order to overcome the defects of the above-mentioned prior art, the present invention uses a vertical strong mixer to mix pipeline concentrate and quicklime, and in the mixing process, the quicklime is digested with the moisture of the pipeline concentrate, thereby eliminating the agglomeration phenomenon that occurs in the process of mixing the quicklime with the ore powder after digestion, and preventing the cracking problem that occurs in the alkaline pellet roasting process. At the same time, fine-grained limestone is used to adjust the alkalinity of the pellets and increase the porosity of the pellets. Ultimately, the purpose of increasing the strength of the pellets, improving the reducibility of the pellets, improving the quality of the alkaline pellets, and reducing the carbon emission of the alkaline pellets is achieved.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides a method for improving the quality of basic pellets, comprising the following steps:

[0005] ① Put quicklime and pipeline concentrate into a vertical intensive mixer at a mass ratio of 0.4-1.5:1 to mix and obtain mixture I;

[0006] ② Drying the concentrate;

[0007] ③ Mix the mixture I obtained in step ① with the concentrate and limestone after drying in step ② in a mass ratio of: 0.5-1.5% of mixture I, 98% of dried concentrate, and 0.5-1.5% of limestone, and then use a disc pelletizer to make balls, and the moisture content of the obtained green balls is 8-9%;

[0008] ④ Roast the green balls obtained in step ③ in a muffle furnace; preheating temperature 925-950°C, preheating time 15-20min, roasting temperature 1230-1250°C, roasting time 25-30min.

[0009] Pipeline concentrate refers to iron concentrate transported by pipeline. Any iron concentrate is transported by pipeline under high pressure after adding water. After the pipeline is pre-laid, the transportation cost is low. Step ① The pipeline concentrate has a moisture content of 10-15% and an alkalinity of 0.05-0.2; the quicklime has a CaO content of 85-90% and an alkalinity of 64-66. The mixture I obtained in step ① has a moisture content of 6-7% and an alkalinity of 19-40. Step ③ The limestone has a CaO mass content of 50-54%, a particle size of <0.1mm and a proportion greater than 95%. The pellets obtained in step ④ have an alkalinity of 0.5-0.9.

[0010] A basic pellet ore produced by the above method.

[0011] Compared with the prior art, the present invention has the following beneficial effects: the present invention controls the moisture content of the mixture to be about 7% by using a vertical intensive mixer to mix pipeline concentrate and quicklime; in the mixing process, the quicklime is digested with the moisture of the pipeline concentrate in the vertical intensive mixer, thereby eliminating the agglomeration phenomenon that occurs in the process of mixing the quicklime with the mineral powder after digestion, preventing the cracking problem that occurs in the roasting process of alkaline pellets produced by using quicklime, and at the same time, when producing high-alkalinity pellets, quicklime is partially substituted for limestone to prevent the problem that the number of pores inside the pellets is too high due to the excessive proportion of limestone, thereby causing the compressive strength to decrease, thereby ensuring that the compressive strength of the high-alkalinity alkaline pellets is at a high level; and then mixed with the dried concentrate and fine-grained limestone to form pellets, the alkalinity of the pellets is adjusted with fine-grained limestone, the porosity of the pellets is increased, the active lime is mixed more evenly, thereby improving the reducibility of the alkaline pellets, and can also inhibit the cracking of the pellets, improve the strength of the alkaline pellets, improve the quality of the pellets, and reduce the carbon emissions of the alkaline pellets. The invention has a wide range of applications and can be promoted to domestic and foreign iron ore pellet production enterprises. Compared with the use of ordinary alkaline pellets, it is more helpful to improve the permeability of blast furnaces and gas utilization. DETAILED DESCRIPTION

[0012] The present invention is further described below in conjunction with specific examples, but the present invention is not limited in any way. To avoid redundant description, the raw materials in the following examples are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified. The compressive strength test is carried out by pressure method, and the testing equipment is a pellet compressive strength tester, which is measured according to the standard GB / T14201-2018 "Determination of compressive strength of iron pellets for blast furnace and direct reduction"; the reducibility is determined according to GB / T13241-2017 "Determination of reducibility of iron ore".

[0013] Example 1

[0014] A method for improving the quality of alkaline pellets comprises the following steps:

[0015] ① Quicklime and pipeline concentrate are charged into a vertical intensive mixer at a mass ratio of 0.4:1 to obtain mixture I;

[0016] ② Drying the concentrate;

[0017] ③ Mix the mixture I obtained in step ① with the concentrate and limestone dried in step ② in a mass ratio of 1.5% mixture I, 98% dried concentrate, and 0.5% limestone, and then use a disc pelletizer to make balls, and the moisture content of the obtained green balls is 9%;

[0018] ④ The green balls obtained in step ③ are roasted in a muffle furnace; the preheating temperature is 925°C, the preheating time is 15 minutes, the roasting temperature is 1230°C, and the roasting time is 25 minutes; and pellets are obtained.

[0019] The moisture content of the mixture I obtained in step ① is 7%, and the basicity of the pellets obtained in step ④ is 0.5; the test results of the compressive strength and medium-temperature reduction degree of the pellets in Example 1 are shown in Table 1.

[0020] Example 2

[0021] A method for improving the quality of alkaline pellets comprises the following steps:

[0022] ① Quicklime and pipeline concentrate are charged into a vertical intensive mixer at a mass ratio of 0.7:1 to obtain mixture I;

[0023] ② Drying the concentrate;

[0024] ③ Mix the mixture I obtained in step ① with the concentrate and limestone dried in step ② in a mass ratio of 1.2% mixture I, 98% dried concentrate, and 0.8% limestone, and then use a disc pelletizer to make balls, and the moisture content of the obtained green balls is 8%;

[0025] ④ The green balls obtained in step ③ are roasted in a muffle furnace; the preheating temperature is 950°C, the preheating time is 20 minutes, the roasting temperature is 1250°C, and the roasting time is 30 minutes; and pellets are obtained.

[0026] The moisture content of the mixture I obtained in step ① is 6%, and the basicity of the pellets obtained in step ④ is 0.6; the test results of the compressive strength and medium-temperature reduction degree of the pellets in Example 2 are shown in Table 1.

[0027] Example 3

[0028] A method for improving the quality of alkaline pellets comprises the following steps:

[0029] ① Quicklime and pipeline concentrate are charged into a vertical intensive mixer at a mass ratio of 0.9:1 to obtain mixture I;

[0030] ② Drying the concentrate;

[0031] ③ Mix the mixture I obtained in step ① with the concentrate and limestone dried in step ② in a mass ratio of 1.0% mixture I, 98% dried concentrate, and 1.0% limestone, and then use a disc pelletizer to make balls, and the moisture content of the obtained green balls is 8%;

[0032] ④ The green balls obtained in step ③ are roasted in a muffle furnace; the preheating temperature is 930°C, the preheating time is 17 minutes, the roasting temperature is 1235°C, and the roasting time is 26 minutes; and pellets are obtained.

[0033] The moisture content of the mixture I obtained in step ① is 7%, and the basicity of the pellets obtained in step ④ is 0.7; the test results of the compressive strength and medium-temperature reduction degree of the pellets in Example 3 are shown in Table 1.

[0034] Example 4

[0035] A method for improving the quality of alkaline pellets comprises the following steps:

[0036] ① Quicklime and pipeline concentrate are charged into a vertical intensive mixer at a mass ratio of 1.2:1 to obtain mixture I;

[0037] ② Drying the concentrate;

[0038] ③ Mix the mixture I obtained in step ① with the concentrate and limestone after drying in step ② in a mass ratio of 0.8% mixture I, 98% dried concentrate, and 1.2% limestone, and then use a disc pelletizer to make balls, and the moisture content of the obtained green balls is 9%;

[0039] ④ The green balls obtained in step ③ are roasted in a muffle furnace; the preheating temperature is 940°C, the preheating time is 18 minutes, the roasting temperature is 1240°C, and the roasting time is 28 minutes; and pellets are obtained.

[0040] The moisture content of the mixture I obtained in step ① is 6%, and the basicity of the pellets obtained in step ④ is 0.8; the test results of the compressive strength and medium-temperature reduction degree of the pellets in Example 4 are shown in Table 1.

[0041] Example 5

[0042] A method for improving the quality of alkaline pellets comprises the following steps:

[0043] ① Quicklime and pipeline concentrate are charged into a vertical intensive mixer at a mass ratio of 1.5:1 to obtain mixture I;

[0044] ② Drying the concentrate;

[0045] ③ Mix the mixture I obtained in step ① with the concentrate and limestone dried in step ② in a mass ratio of 0.5% mixture I, 98% dried concentrate, and 1.5% limestone, and then use a disc pelletizer to make balls, and the moisture content of the obtained green balls is 8%;

[0046] ④ The green balls obtained in step ③ are roasted in a muffle furnace; the preheating temperature is 950°C, the preheating time is 19 minutes, the roasting temperature is 1245°C, and the roasting time is 29 minutes; and pellets are obtained.

[0047] The moisture content of the mixture I obtained in step ① is 7%, and the basicity of the pellets obtained in step ④ is 0.9; the test results of the compressive strength and medium-temperature reduction degree of the pellets in Example 5 are shown in Table 1.

[0048] Comparative Example 01

[0049] Comparative Example 01 uses 97.5-98% concentrate and 2-2.5% quicklime to make pellets; except for the method introduced in the present invention, other conditions are consistent with the embodiment, that is, the green balls are roasted in a muffle furnace; the preheating temperature is 950°C, the preheating time is 15 minutes, the roasting temperature is 1250°C, and the roasting time is 30 minutes; the pellets with a basicity of 0.5 are obtained. The test results of the compressive strength and medium-temperature reduction degree of the pellets of Comparative Example 01 are shown in Table 1.

[0050] Comparative Example 02

[0051] Comparative Example 02 uses 97-98.5% concentrate and 1.5-3% limestone to make pellets. Except for the method introduced in the present invention, other conditions are consistent with the embodiment, that is, the green balls are roasted in a muffle furnace; the preheating temperature is 925°C, the preheating time is 20 minutes, the roasting temperature is 1230°C, and the roasting time is 25 minutes; the pellets with a basicity of 0.5 are obtained. The test results of the compressive strength and medium-temperature reduction degree of the pellets of Comparative Example 02 are shown in Table 1.

[0052] Comparative Example 03

[0053] Comparative Example 03 uses 97.5-98% concentrate and 2-2.5% quicklime to make pellets; except for the method introduced in the present invention, other conditions are consistent with the embodiment, that is, the green balls are roasted in a muffle furnace; the preheating temperature is 925°C, the preheating time is 15 minutes, the roasting temperature is 1250°C, and the roasting time is 30 minutes; the pellets with a basicity of 0.6 are obtained. The test results of the compressive strength and medium-temperature reduction degree of the pellets of Comparative Example 03 are shown in Table 1.

[0054] Comparative Example 04

[0055] Comparative Example 04 uses 97-98.5% concentrate and 1.5-3% limestone to make pellets. Except for the method introduced in the present invention, other conditions are consistent with the embodiment, that is, the green balls are roasted in a muffle furnace; the preheating temperature is 950°C, the preheating time is 20 minutes, the roasting temperature is 1250°C, and the roasting time is 30 minutes; the pellets with a basicity of 0.6 are obtained. The test results of the compressive strength and medium-temperature reduction degree of the pellets of Comparative Example 04 are shown in Table 1.

[0056] Comparative Example 05

[0057] Comparative Example 05 uses 97.5-98% concentrate and 2-2.5% quicklime to make pellets; except for the method introduced in the present invention, other conditions are consistent with the embodiment, that is, the green balls are roasted in a muffle furnace; the preheating temperature is 950°C, the preheating time is 15 minutes, the roasting temperature is 1230°C, and the roasting time is 30 minutes; the pellets with a basicity of 0.7 are obtained. The test results of the compressive strength and medium-temperature reduction degree of the pellets of Comparative Example 05 are shown in Table 1.

[0058] Comparative Example 06

[0059] Comparative Example 06 uses 97-98.5% concentrate and 1.5-3% limestone to make pellets. Except for the method introduced in the present invention, other conditions are consistent with the embodiment, that is, the green balls are roasted in a muffle furnace; the preheating temperature is 950°C, the preheating time is 15 minutes, the roasting temperature is 1250°C, and the roasting time is 25 minutes; the pellets with a basicity of 0.7 are obtained. The test results of the compressive strength and medium-temperature reduction degree of the pellets of Comparative Example 06 are shown in Table 1.

[0060] Comparative Example 07

[0061] Comparative Example 07 uses 97.5-98% concentrate and 2-2.5% quicklime to make pellets; except for the method introduced in the present invention, other conditions are consistent with the embodiment; that is, the green balls are roasted in a muffle furnace; the preheating temperature is 950°C, the preheating time is 15 minutes, the roasting temperature is 1250°C, and the roasting time is 30 minutes; the pellets with a basicity of 0.8 are obtained. The test results of the compressive strength and medium-temperature reduction degree of the pellets of Comparative Example 07 are shown in Table 1.

[0062] Comparative Example 08

[0063] Comparative Example 08 uses 97-98.5% concentrate and 1.5-3% limestone to make pellets. Except for the method introduced in the present invention, other conditions are consistent with the embodiment; that is, the green balls are roasted in a muffle furnace; the preheating temperature is 950°C, the preheating time is 15 minutes, the roasting temperature is 1250°C, and the roasting time is 30 minutes; the pellets with a basicity of 0.8 are obtained. The test results of the compressive strength and medium-temperature reduction degree of the pellets of Comparative Example 08 are shown in Table 1.

[0064] Comparative Example 09

[0065] Comparative Example 09 uses 97.5-98% concentrate and 2-2.5% quicklime to make pellets; except for the method introduced in the present invention, other conditions are consistent with the embodiment; that is, the green balls are roasted in a muffle furnace; the preheating temperature is 950°C, the preheating time is 15 minutes, the roasting temperature is 1250°C, and the roasting time is 30 minutes; the pellets with a basicity of 0.9 are obtained. The test results of the compressive strength and medium-temperature reduction degree of the pellets of Comparative Example 09 are shown in Table 1.

[0066] Comparative Example 10

[0067] Comparative Example 10 uses 97-98.5% concentrate and 1.5-3% limestone to make pellets. Except for the method introduced in the present invention, other conditions are consistent with the embodiment; that is, the green balls are roasted in a muffle furnace; the preheating temperature is 950°C, the preheating time is 15 minutes, the roasting temperature is 1250°C, and the roasting time is 30 minutes; the pellets with a basicity of 0.9 are obtained. The test results of the compressive strength and medium-temperature reduction degree of the pellets of Comparative Example 09 are shown in Table 1.

[0068] Table 1 Compressive strength and medium temperature reduction degree of pellets with different basicity

[0069]

[0070]

[0071] As can be seen from Table 1, with the increase of alkalinity, the compressive strength of the pellets shows a trend of first increasing and then decreasing. The compressive strength of the alkaline pellets of the two comparison examples shows that the strength is highest when the alkalinity of the pellets is between 0.5 and 0.6, and the strength of the pellets decreases more after the alkalinity is greater than 0.6; among them, the pellet strength of the comparison examples 01, 03, 05, 07, and 09 using quicklime is generally low, mainly because the quicklime is difficult to completely digest, resulting in the deterioration of the pellet strength after agglomeration; the pellet strength of the comparison examples 02, 04, 06, 08, and 10 using limestone is generally higher than that of the quicklime series comparison examples, but it decreases more when the alkalinity reaches 0.7, mainly because as the pores inside the pellets increase, the cumulative effect is caused. The strength of the pellets in the embodiment is highest when the alkalinity is 0.7-0.8, and decreases after the alkalinity reaches 0.9, but the decrease is small, so that the compressive strength can be maintained at more than 2500N in the alkalinity range of 0.5-0.9, and the overall strength is good. This is mainly because the quicklime can be better mixed in the present invention, eliminating the agglomeration phenomenon during the quicklime mixing process, and the quicklime can partially replace limestone, reduce the amount of limestone used, and control the number of pores inside the pellets, so that it does not have a significant impact on the compressive strength of the pellets.

[0072] As the alkalinity increases, the medium-temperature reduction degree of the pellets increases. The medium-temperature reduction performance of the comparative examples 01, 03, 05, 07, and 09 using quicklime is the worst, mainly because no limestone is added, the pellets have fewer pores inside, and the number of channels available for the diffusion of reducing gas is small; the medium-temperature reduction performance of the comparative examples 02, 04, 06, 08, and 10 using limestone is good, mainly because the decomposition of limestone increases the pore channels inside the pellets; the medium-temperature reduction performance of the embodiment is significantly better than that of the comparative example using quicklime, and slightly better than that of the comparative example using limestone, mainly because the comparative example using limestone has too many internal pores, and small channels are easily formed into larger channels during the reduction, reducing its specific surface area in contact with the reducing gas, thereby resulting in its reduction degree being inferior to that of the embodiment at high alkalinity.

[0073] In summary, the present invention can effectively improve the compressive strength and medium-temperature reduction degree of the alkaline pellets, thereby improving the quality of the alkaline pellets.

[0074] For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention should still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for improving the quality of alkaline pellets, characterized in that: The method comprises the following steps: ① Put quicklime and pipeline concentrate into a vertical intensive mixer at a mass ratio of 0.4-1.5:1 to mix to obtain mixture I; The pipeline concentrate has a moisture content of 10% to 15% and a basicity of 0.05 to 0.2; the quicklime has a CaO mass content of 85% to 90% and a basicity of 64 to 66; The water content of the mixture I obtained in step ① is 6% to 7%, and its basicity is 19 to 40; ② Drying the concentrate; ③ Mix the mixture I obtained in step ① with the concentrate and limestone after drying in step ② in a mass ratio of 0.5% to 1.5% of the mixture I, 98% of the dried concentrate, and 0.5% to 1.5% of the limestone, and then use a disc pelletizer to make balls, and the moisture content of the obtained green balls is 8% to 9%; The limestone has a CaO mass content of 50% to 54% and a particle size of <0.1 mm, with a proportion greater than 95%; ④ Roasting the green balls obtained in step ③; preheating temperature 925℃~950℃, preheating time 15~20min, roasting temperature 1230℃~1250℃, roasting time 25~30min, to obtain pellets; The basicity of the pellets obtained in step ④ is 0.5-0.9, the compressive strength reaches 2675N, and the medium-temperature reduction degree reaches 77.89%.

2. An alkaline pellet obtained by the method according to claim 1.

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