Low-carbon, low-sulfur, low-cost alkaline particulate cover and method of production thereof

Abstract

The present application relates to a kind of low-carbon low-sulfur low-cost environmental protection alkaline granular covering agent and its production method, using main raw material is 50-70% activated carbon fly ash (or slag), 20-40% lime dust, 6-8% dolomite dust, 2-4% activated carbon dust and other industrial solid waste and 0.2-0.3% methyl silicon oil fluidization treatment, compared with using refractory raw material, substantially reduce raw material cost;At the same time, main raw material does not need to use grinding process, finished product preparation adopts homogenization binderless cold forming preparation process (homogenization treatment, dry extrusion tablet strip, crushing and granulating composite process) instead of wet spray granulation or semi-dry extrusion granulation, further reduce cost.In pouring molten steel has good heat preservation, spreading uniformity, strong adsorption inclusion capacity, does not cause molten steel C, S and other pollution, last liquid slag does not stick bag and other advantages, and has the advantages of convenient operation, ton steel cost is low, is suitable for silicon steel, stainless steel, ultra-low carbon and other special steel.

Description

Technical Field

[0001] This invention relates to the field of metallurgical auxiliary materials technology, and in particular to a low-carbon, low-sulfur, low-cost alkaline particulate covering agent and its production method. Background Technology

[0002] Ladle covering agent is a synthetic auxiliary material added to the ladle during the steelmaking process to cover the surface of the molten steel. It has the following functions: Thermal insulation and prevention of crust formation on molten steel surface. The covering agent has a significant thermal insulation effect. Covering the surface of molten steel with the covering agent prevents the molten steel from being exposed to air, which would cause the temperature of the molten steel to drop rapidly, thereby causing crust formation on the liquid surface and freezing of the nozzle.

[0003] It isolates the molten steel from air and prevents secondary oxidation. After the covering agent is added, it forms a liquid slag layer with poor air permeability, which isolates the molten steel from the air, prevents secondary oxidation of the molten steel, and reduces inclusions in the molten steel.

[0004] The covering agent absorbs non-metallic inclusions on the surface of molten steel, purifying the steel. It forms a slag layer of a certain thickness on the surface of the molten steel, which can adsorb floating non-metallic inclusions, refractory material particles, and other suspended matter, thus purifying the molten steel.

[0005] Currently, most steel mills and most steel grades use ordinary ladle covering agents. These agents are acidic, and their main components are SiO2, Al2O3, CaO, MgO, and C, with w(SiO2) > 40%, w(C) = 15-40%, and w(CaO) / w(SiO2) < 0.5. The biggest advantage of acidic covering agents is their good heat retention, but their biggest disadvantage is that they cannot purify molten steel and may even contaminate it. Therefore, alkaline covering agents that can purify molten steel have been developed. However, the biggest disadvantage of alkaline covering agents is their poor heat retention; their thermal conductivity is twice that of acidic agents.

[0006] Currently, most steel mills use carbonized rice husks as the main raw material for covering agents. The drawbacks of using carbonized rice husks for insulation are: the production process of carbonized rice husks generates a large amount of smoke that pollutes the air; carbonized rice husks have a high melting point and do not easily melt on the surface of molten steel, making it impossible to form a liquid slag layer, resulting in poor spreadability and poor insulation effect, and they do not have the metallurgical function of absorbing impurities floating in molten steel; when using carbonized rice husks, their low density generates a large amount of dust during the addition and slag removal processes, which is not environmentally friendly, and the overall price is relatively high.

[0007] Furthermore, carbon content in steel is one of the elements that must be controlled during the production of clean steel. Domestic steel companies generally use covering agents containing large amounts of carbonaceous materials, which increases the carbon content in the molten steel. To effectively prevent carbon increase in the molten steel inside the ladle, it is best to use carbon-free or low-carbon ladle covering agents, which requires the carbonaceous material content in the ladle covering agent to be as low as possible.

[0008] The purpose of this invention is to provide a low-carbon, low-sulfur, low-cost, environmentally friendly alkaline granular covering agent and its production method. The product can reduce heat loss from molten steel, purify molten steel, and does not cause an increase in carbon or sulfur in the molten steel, and is environmentally friendly.

[0009] The purpose of this invention is achieved as follows: on the one hand, solid waste materials are used to replace refractory materials, which significantly reduces the cost of raw materials; on the other hand, the main raw materials do not need to be ground, and the finished product is prepared by using a homogenized binder-free cold forming process (homogenization treatment, dry extrusion to form strips, crushing and granulation composite process) instead of wet spray granulation or semi-dry extrusion granulation, which further reduces costs. Summary of the Invention

[0010] The purpose of this invention is to address the above-mentioned problems by providing a low-carbon, low-sulfur, and low-cost alkaline particulate covering agent and its production method.

[0011] The objective of this invention is achieved as follows: a low-carbon, low-sulfur, and low-cost alkaline particulate covering agent, characterized by the following composition and mass percentage: CaO: 28-42%, MgO: 3-5%, Al2O3: 12-20%, Fe2O3: 1-3%, SiO2: 25-36%, S: 0.01-0.04%, C < 5%, H2O: < 1%, methyl silicone oil 0.2%-0.3%, the remainder being impurities that do not affect the performance; hemispherical point 1500-1750℃, R (basicity) 1.0-1.5, melting rate 60-120 seconds, bulk density 0.6-0.9, and particle size 0.5-2mm.

[0012] The raw materials for alkaline granular covering agents are 50-70% activated carbon fly ash or slag, 20-40% lime dust, 6-8% dolomite dust, and 2-4% activated carbon dust.

[0013] A method for producing a low-carbon, low-sulfur, and low-cost alkaline granular covering agent includes the following steps: Step 1: Lime dust, dolomite dust, and activated carbon dust are pumped into a raw material silo by a tanker truck for later use; Step 2: After separation by a closed drum screen, the fine powder <0.1mm is sent into the raw material silo by a bucket elevator for later use; Step 3: Various raw materials are mixed in the following proportions: 50-70% activated carbon fly ash or slag, 20-40% lime dust, and 6-8% dolomite dust. The mixture of stone dust and 2-4% activated carbon dust is weighed by a metering auger, then fed into a mixer for uniform mixing, and then sent to an intermediate silo via a bucket elevator for later use; Step 4: The mixture in the intermediate silo falls through a metering feeder with a lock valve to a forced screw feeder with a compression ratio of 5:1, and the pressure of the forced screw feeder is 10-12.5 MPa; Step 5: The raw material after being fed by the feeder is squeezed into a high-pressure strip roller press, and under the pressure of 20-25 MPa, it is extruded into elliptical strips with a length of 100±50 mm, a width of 10±5 mm, and a thickness of 8±4 mm; Step 6: After leaving the roller zone, the elliptical strips are automatically demolded and fall into a blade crusher for further crushing; Step 7: The strip fragments after being crushed by the blade crusher fall into a cage pelletizer, and under the action of the pelletizer with a 2 mm filter screen, the strip fragments are granulated into 0-2 mm particles, which then fall naturally into a multi-layer vibrating screen; Step 8: After being separated into 0.2 mm particles by the multi-layer vibrating screen. The qualified particle size is 5-2mm. The material >2mm and <0.5mm is returned to the intermediate silo by the bucket elevator to participate in the next round of briquetting. Step 9: The qualified particle size finished product is passed through a passivation chamber at 80-130℃ and then subjected to fluidized stirring treatment with 0.2%-0.3% atomized methyl silicone oil to obtain a low carbon and low sulfur alkaline granular covering agent. The methyl silicone oil is heated to 100-130℃ by a heater and atomized through a disc fine nozzle under the action of a 0.5-0.6Mpa booster pump.

[0014] The beneficial effects of this invention are as follows: This invention provides a low-carbon, low-sulfur, low-cost, environmentally friendly alkaline granular covering agent and its production method. It has advantages such as good heat insulation, uniform spreading, no increase in C and S pollution in molten steel, strong adsorption capacity for inclusions, and no sticking of the final liquid slag to the ladle. It also has advantages such as convenient operation and low cost per ton of steel. It is suitable for silicon steel, stainless steel, ultra-low carbon steel, and other special steels.

[0015] The product of this invention forms three layers when poured into molten steel. The functional structure of each layer is clear and achieves its corresponding function. The first layer is the contact surface with the molten steel and is in a molten state, completely isolating the molten steel from secondary oxidation. The second layer is a transition layer that serves as a heat preservation layer. The third layer is a sintered layer that forms a porous covering structure and serves as the main heat preservation layer. Attached Figure Description

[0016] The present invention will now be further described with reference to the accompanying drawings.

[0017] Figure 1 This is a flowchart of the invention. Note: The metering auger is also known as a metering screw feeder. Detailed Implementation

[0018] This invention provides a low-carbon, low-sulfur, low-cost, environmentally friendly alkaline granular covering agent, the composition and mass percentage of which are as follows: CaO: 30-35%, MgO: 3-5%, Al2O3: 12-20%, Fe2O3: 1-3%, SiO2: 30-35%, S: 0.02-0.04%, C < 5%, H2O: < 1%; its melting point ≥ 1500℃, R (basicity) > 1.0, melting rate ≥ 60 seconds, bulk density 0.6-0.9, and particle size 0.5-2mm.

[0019] The low-carbon, low-sulfur, low-cost, environmentally friendly alkaline granular covering agent uses 50-70% activated carbon fly ash (or slag), 20-40% lime dust, 6-8% dolomite dust, and 2-4% activated carbon dust as its main raw materials, which significantly reduces raw material costs compared to using refractory materials.

[0020] A novel method for producing granular covering agents eliminates the need for grinding the main raw materials. The finished product is prepared using a homogenized binder-free cold forming process (homogenization treatment, dry extrusion into strips, and crushing and granulation composite process) instead of wet spray granulation or semi-dry extrusion granulation, further reducing costs. The preparation steps are as follows: (1) Lime dust, dolomite dust, and activated carbon dust are pumped into the raw material silo by a tanker truck for later use. (2) Activated carbon fly ash (or slag) is separated by a closed drum screen, and the fine powder <0.1mm is sent into the raw material silo by a bucket elevator for later use. (3) According to the formula design, the various raw materials are weighed by a metering auger, then fed into a mixer for uniform mixing, and then sent into an intermediate silo by a bucket elevator for later use. (4) The mixture in the intermediate silo falls into a 5:1 forced feeder through a metering feeder with a lock valve. (5) After being fed by the feeder, the raw material is squeezed into the high-pressure roller press and squeezed into 8×10×100mm elliptical strips under the pressure of 25Mpa. (6) After the 8×10×100mm elliptical strips leave the roller area, the pressure is released, the centrifugal force is not on the center line of the material, and it falls into the blade crusher for crushing after automatic demolding. (7) After being crushed by the crusher, the material falls into the cage pellet mill by natural falling. Under the action of the 2mm filter screen, the material falls into the multi-layer vibrating screen. (8) The qualified particle size of 0.5-2mm after multiple vibrating screen separations; the material >2mm and <0.5mm is returned to the intermediate silo by the bucket elevator to participate in the next round of briquetting. (9) The qualified particle size finished product is in the passivation chamber and is treated with 0.2%-0.3% atomized methyl silicone oil fluidization, which greatly improves the fluidity and spreadability of the material.

[0021] 1. To address the problem of low density and excessive dust generation from carbonized rice husks, this invention proposes to use mineral activated carbon fly ash as the main raw material. Its main components are shown in the table below.

[0022]

[0023] Note: Mineral activated carbon fly ash originates from the by-products of activated carbon processing enterprises, namely, the residue from crushing and screening, and the fly ash from dust collectors, which is then burned in boilers at high temperatures during winter to remove carbon. Mineral activated carbon residue and dust collector ash, due to their low calorific value, limited uses, and low price, are generally mixed with fuel coal for sale.

[0024] 2. To achieve the goal of providing products with both high alkalinity and low carbon content, as well as excellent thermal insulation, the main raw materials used in this invention are 20%-40% lime dust and 50%-70% activated carbon fly ash (or slag). The use of lime ensures the high alkalinity of the covering agent, which is beneficial for purifying the molten steel. The mineral activated carbon fly ash contains very little carbon, ensuring that it will not cause carbon increase in the molten steel. The reduction in carbon content does not affect the thermal insulation effect of the covering agent. This is determined by the highly advantageous porous, honeycomb-like microstructure of activated carbon fly ash, which has a lower density than molten steel and a higher melting point, making it less prone to melting. It acts as a skeleton, allowing the insulation layer to maintain a loose, foamy state without significant collapse. The main components of the lime dust are shown in the table below.

[0025]

[0026] 3. To improve fluidity and spreadability, a small amount of dolomite crushing and dust removal ash will be added. Utilizing the thermal decomposition and expansion capacity of the dolomite dust removal ash, the covering agent will spread rapidly after being added to the ladle, effectively covering the surface of the molten steel and preventing leakage. Its main components are shown in the table below.

[0027]

[0028] Note: Dust from dolomite mines: Fine dust collected from environmental dust collectors during the mining, crushing, and processing of dolomite.

[0029] 4. In order to compensate for the heat loss of molten steel, it is proposed to add a small amount of activated carbon dust to the raw materials, but control the finished product w(C) < 5%, and its main components are shown in the table below.

[0030]

[0031] 5. To ensure the homogeneity of the materials, all raw materials are precisely measured according to the formula and then fed into a mixer to be mixed evenly for later use.

[0032] 6. In order to reduce severe dust generation and environmental pollution during use, the raw materials need to be granulated.

[0033] 7. In order to reduce energy consumption and manufacturing costs, it is proposed to adopt a homogenized binder-free cold forming process (homogenization treatment, dry extrusion to form strips, crushing and granulation composite process) to replace wet spray granulation and semi-dry extrusion granulation.

[0034] 8. To improve fluidity and spreadability, methyl silicone oil is used for fluidization (passivation) treatment. Functions of methyl silicone oil: (1) Moisture protection to prevent the granules from absorbing moisture and pulverizing. (2) To reduce particle friction during the addition of the covering agent to molten steel, thereby achieving rapid spreading (fluidization).

[0035] Baseline Implementation

[0036] A method for producing a low-carbon, low-sulfur, and low-cost alkaline granular covering agent includes the following steps: Step 1: Lime dust, dolomite dust, and activated carbon dust are pumped into a raw material silo by a tanker truck for later use; Step 2: After separation by a closed drum screen, the fine powder <0.1mm is sent into the raw material silo by a bucket elevator for later use; Step 3: Various raw materials are mixed in the following proportions: 50-70% activated carbon fly ash or slag, 20-40% lime dust, and 6-8% dolomite dust. The mixture of stone dust and 2-4% activated carbon dust is weighed by a metering auger, then fed into a mixer for uniform mixing, and then sent to an intermediate silo via a bucket elevator for later use; Step 4: The mixture in the intermediate silo falls through a metering feeder with a lock valve to a forced screw feeder with a compression ratio of 5:1, and the pressure of the forced screw feeder is 10-12.5 MPa; Step 5: The raw material after being fed by the feeder is squeezed into a high-pressure strip roller press, and under the pressure of 20-25 MPa, it is extruded into elliptical strips with a length of 100±50 mm, a width of 10±5 mm, and a thickness of 8±4 mm; Step 6: After leaving the roller zone, the elliptical strips are automatically demolded and fall into a blade crusher for further crushing; Step 7: The strip fragments after being crushed by the blade crusher fall into a cage pelletizer, and under the action of the pelletizer with a 2 mm filter screen, the strip fragments are granulated into 0-2 mm particles, which then fall naturally into a multi-layer vibrating screen; Step 8: After being separated into 0.2 mm particles by the multi-layer vibrating screen. The qualified particle size is 5-2mm. The material >2mm and <0.5mm is returned to the intermediate silo by the bucket elevator to participate in the next round of briquetting. Step 9: The qualified particle size finished product is passed through a passivation chamber at 80-130℃ and then subjected to fluidized stirring treatment with 0.2%-0.3% atomized methyl silicone oil to obtain a low carbon and low sulfur alkaline granular covering agent. The methyl silicone oil is heated to 100-130℃ by a heater and atomized through a disc fine nozzle under the action of a 0.5-0.6Mpa booster pump. Example 1

[0037] The formula is designed as follows: 50% activated carbon fly ash, 40% lime dust, 7% dolomite dust, 3% activated carbon dust, plus 0.25% methyl silicone oil. It is produced according to the steps of the benchmark example above, and the product test results are shown in the table below.

[0038]

[0039] After implementation, it is difficult to melt on the surface of molten steel, has poor spreadability, a thin slag layer, poor heat preservation effect, and sticking to the ladle. Example 2

[0040] The formula is designed as follows: 65% activated carbon fly ash, 25% lime dust, 7% dolomite dust, 3% activated carbon dust, plus 0.25% methyl silicone oil. It is produced according to the steps of the benchmark example above, and the product test results are shown in the table below.

[0041]

[0042] After implementation, the molten steel spreads evenly and the slag does not stick to the ladle, but the sintered layer is thin and some parts are red-hot. Example 3

[0043] Preferred formulation: 60% activated carbon fly ash, 30% lime dust, 7% dolomite dust, 3% activated carbon dust, plus 0.25% methyl silicone oil, produced according to the steps of the benchmark example above. Product test results are shown in the table below.

[0044]

[0045] After implementation, the material layer has a clear functional structure, with the melting layer, semi-sintered layer, and sintered layer fulfilling their corresponding functions; when molten steel is added, it has good heat preservation, uniform spreading, strong adsorption of inclusions, does not cause C or S pollution in the molten steel, and the liquid slag does not stick to the ladle.

[0046] The above description is only a specific embodiment of the present invention, but the structural features protected by the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A low-carbon, low-sulfur, low-cost alkaline particulate covering agent, characterized in that: The composition and mass percentage are as follows: CaO: 28-42%, MgO: 3-5%, Al2O3: 12-20%, Fe2O3: 1-3%, SiO2: 25-36%, S: 0.01-0.04%, C < 5%, H2O: < 1%, methyl silicone oil 0.2%-0.3%, and the remainder are impurities that do not affect the performance; hemispherical temperature 1500-1750℃, basicity R 1.0-1.5, melting rate 60-120 seconds, bulk density 0.6-0.9, particle size 0.5-2mm; The raw materials for alkaline granular covering agent are 50-70% activated carbon fly ash, 20-40% lime dust, 6-8% dolomite dust, and 2-4% activated carbon dust. A method for producing low-carbon, low-sulfur, and low-cost alkaline particulate covering agents includes the following steps: Step 1: The lime dust, dolomite dust, and activated carbon dust are pumped into the raw material silo by tanker truck for later use; Step 2: After the activated carbon fly ash is separated by a closed drum screen, the fine powder <0.1mm is sent to the raw material silo by a bucket elevator for later use. Step 3: Various raw materials are weighed by a metering auger according to the ratio of 50-70% activated carbon fly ash, 20-40% lime dust, 6-8% dolomite dust, and 2-4% activated carbon dust, and then fed into a mixer to be mixed evenly. Finally, they are sent to an intermediate silo by a bucket elevator for later use. Step 4: The intermediate silo mixture falls through the metering feeder with an airlock valve to the forced screw feeder with a compression ratio of 5:

1. The pressure of the forced screw feeder is 10-12.5MPa. Step 5: The raw material fed by the feeder is squeezed into the high-pressure strip roller press. Under the pressure of 20-25MPa, it is squeezed into elliptical strips with a length of 100±50mm, a width of 10±5mm, and a thickness of 8±4mm. Step Six: After the elliptical long strips exit the roller zone, they automatically demold and fall into the blade crusher for further crushing; Step 7: The shredded material after being crushed by the blade crusher falls into the cage pelletizer. Under the action of the pelletizer with a 2mm filter screen, the shredded material is granulated into 0-2mm particles and falls naturally into the multi-layer vibrating screen. Step 8: After passing through a multi-layer vibrating screen, the material is separated into qualified particle sizes of 0.5-2mm. The material >2mm and <0.5mm is returned to the intermediate silo via a bucket elevator to participate in the next round of briquetting. Step 9: The qualified particle size product is passed through a passivation chamber at 80-130℃ and then fluidized and stirred with 0.2%-0.3% atomized methyl silicone oil to obtain a low-carbon and low-sulfur alkaline particulate covering agent. The methyl silicone oil is heated to 100-130℃ by a heater and atomized through a disc fine nozzle under the action of a 0.5-0.6MPa booster pump.

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