CN116694862A - A method for resource utilization of fly ash in steelmaking process - Google Patents

Abstract

The present invention relates to three technical fields of thermal insulation technology for molten steel, electrolytic aluminum hazardous waste carbon slag and fly ash produced by garbage incineration, and three technical fields, specifically a method for resource utilization of fly ash in the steelmaking process . The invention adopts an innovative process to produce fly ash and carbon slag into molten steel thermal insulation covering agent, which is added to the top of the ladle after the molten steel refining process is completed, which plays a role in heat preservation and prevention of secondary oxidation for molten steel, and realizes the effect of fly ash and carbon slag The utilization of resources in the molten steel refining process has developed a highly competitive method for the large-scale treatment of fly ash produced by waste incineration in China's iron and steel industry, highlighting the technical advantages of cross-innovation in different technical fields.

Description

A method for resource utilization of fly ash in steelmaking process

technical field

The invention relates to a method for resource utilization of fly ash in a steelmaking process.

Background technique

The solid residue after incineration of waste accounts for 30%-35% of the total waste, of which bottom ash accounts for 25%-30%, and fly ash accounts for 2%-5%. Waste incineration fly ash refers to the trappings of the flue gas purification system of the waste incineration plant and the residue settled at the bottom of the flue and chimney, which contains a certain amount of dioxins, soluble heavy metals and salts, and belongs to the national "National List of Hazardous Wastes" Medium HW18 hazardous waste (772-002-18 domestic waste incineration fly ash) needs to be harmlessly treated in advance before it can be safely landfilled. At present, research on the resource utilization of fly ash has been found in literature and reports. Literature review (1) Luo Renhong published a paper entitled "Overview of Resource Utilization of Domestic Waste Incineration Fly Ash" in the 4th issue of "Environmental Impact Assessment" in 2019. The resource utilization of ash in cement, concrete, ceramic light aggregate, and building materials has been launched. As a new type of material, fly ash can be considered as a part of the base material to replace road construction materials, but it still needs the support of relevant policies. (2) Du Jian published a paper titled "Cement solidification technology for waste incineration fly ash treatment" in the 4th issue of "Henan Building Materials" magazine in 2017. "Use Portland cement to solidify the fly ash produced by municipal waste incineration, and analyze the influence of fly ash content on the solidification strength and heavy metal leaching performance. The strength decreases with the increase of fly ash content; with the decrease of Portland cement content, heavy metal ions such as Pb and Cd are more likely to be leached from the solidified body. In order to improve the solidification effect, it is necessary to further increase the compactness of the cement paste .”; (3) Fan Yanling, Zheng Penghui, and Zhu Wen published a report titled “Summary of Waste Incineration Fly Ash Harmless and Resource Management Technology” in the 4th issue of “Resource Conservation and Environmental Protection” in 2020. In his thesis, “Our country is still in its infancy for the harmless and resourceful utilization of waste incineration fly ash, and many technical difficulties have not yet been overcome, such as the large capacity of cement solidification and the stabilization of dioxins by chemical agents. Destruction, the effect of melting method on heavy metals is unstable and expensive, the effect of hydrothermal treatment technology is unstable, etc., and the recycling of resources is not widely used." The content expression.

According to the above published documents, it can be seen that currently there is no process for utilizing converter steelmaking in conjunction with resource utilization of fly ash.

The refining of molten steel is to carry out deoxidation, desulfurization, degassing and refining of molten steel through LF, LFV, VD, RH and other technological means, and these technological contents are realized by slagging. Each ton of molten steel refining produces 8-15kg of refining slag. These steel slags have high alkalinity and are easy to solidify and encrust after the refining process, resulting in the exposure of part of the molten steel, which can cause secondary oxidation of the molten steel and a decrease in temperature. Therefore, after the refining of molten steel is completed, adding thermal insulation covering agent to the ladle is a process method to reduce the temperature loss of molten steel and prevent secondary oxidation of molten steel;

Consult literature (1) Xu Yongbin and Xu Bing stated in the article "Development of New Ladle Covering Agent" published in "Steelmaking" 2006 (3) that "the composition of the mass percentage of the main component of the new ladle insulation agent is CaO: 5 ～10; SiO ₂ : 40～50; Al ₂ O ₃ <10; Fe ₂ O ₃ <3 fixed carbon <20, belonging to a typical acid ladle covering agent, its binary basicity R(CaO/SiO ₂ <1)". Relevant content; (2) Yu Huacai and Li Shuqing published a paper entitled "Application and Research of Ladle Covering Agent" in the 4th issue of "Steelmaking" magazine in 2001. The alkalinity before the casting is about 0.7, while the residue in the ladle is alkaline, and the alkalinity is about 2.6-3.0. We inspect the residue in the ladle after casting, and the alkalinity is about 1.5, which shows that the covering agent can be combined with the slag A chemical reaction occurs, which changes the properties of the slag and makes the slag brittle, which is conducive to ladle slag turning, the cleanliness of the ladle is obviously improved, and it is also conducive to the increase of the ladle age." The content of the statement.

According to the above literature discussion, it can be seen that there is no technological precedent for producing molten steel thermal insulation covering agent by using fly ash.

In the production process of electrolytic aluminum, the anode carbon block and the cathode carbon lining, under the electrochemical and smelting thermodynamic conditions, and the erosion of the aluminum liquid, can peel off from the carbon block or lining, enter the electrolyte, and form Charcoal.

During the production process of aluminum electrolysis, carbon slag will be burned on the surface of the electrolyte, but in the case of excessive production (as far as the self-baking tank is concerned), it is necessary to manually remove it from the tank in time to reduce the disadvantages of carbon slag to the electrolytic production process Affected, the main components of the fished out charcoal slag are sodium aluminum fluoride, α-A1 ₂ 0 ₃ and carbon based on Na ₃ AlF ₆ ; the carbon content is about 40%, and the electrolyte fluoride is about 60% , the main components of a typical carbon residue are shown in Table 1 below:

;

The components in the carbon slag produced by the electrolytic aluminum plant are not much different. The components of the carbon slag from a factory in Xinjiang are shown in the table below:

.

Carbon slag is a kind of hazardous waste, the national hazardous waste catalog code is 321-026-48, and the definition is "flammable slag produced in the process of aluminum pyrometallurgy".

Literature review (1) Li Hong published a paper titled "Flotation of Carbon Slag from Aluminum Electrolysis" in the 6th issue of "Light Metal" in 2002. Hazardous waste, the carbon residue contains a large amount of fluoride salt. Using flotation to recycle the fluoride salt in the carbon residue can not only reduce the loss of fluoride salt, but also improve the utilization rate of resources. It also avoids environmental damage. There are significant economic and social benefits.” (2) Liang Wenqiang published an article entitled “Disposal and Recycling of Aluminum Ash, Carbon Slag, and Overhaul Slag” in Gansu Metallurgy, No. 4, 2017. In the paper of Utilization Plan, there is in the middle of the abstract: "The dangerous solid wastes such as aluminum ash, carbon slag, and overhaul slag produced by JISCO Group Dongxing Aluminum Company in the electrolytic aluminum production process every year will seriously pollute the ecological environment if they are not treated in time. After sorting and crushing the hazardous solid waste produced by electrolytic aluminum, flotation, chemical reaction and other methods are used to reuse the hazardous solid waste that can be used as a resource, and to make the hazardous solid waste that cannot be used as a resource harmless. treatment to eliminate the pollution to the ecological environment. After the implementation, it will have certain economic benefits and significant social benefits." Content statement; (3) Liu Haixia published a titled "Inorganic Salt Industry" in the 11th issue of 2013 in the magazine "Inorganic Salt Industry" In the paper "Study on Recycling Cryolite Process of Fluorine-Containing Waste Slag", there is "In the process of electrolytic aluminum production, in order to ensure normal production, the electrolyte in the electrolytic cell must be kept at a reasonable height and cleanliness. The traditional method is in the electrolysis process. Extract the excess electrolyte and salvage the carbon blocks floating on the upper part of the electrolyte. These objects form fluorine-containing waste residue after condensation. It is estimated that every 1 ton of aluminum produced will produce 10-12kg of fluorine-containing waste residue, which contains more than 30% Cryolite, about 1% of calcium oxide, about 1% of alumina, and the rest are impurities such as carbon particles, graphite carbon, aluminum carbide and ferrosilicon oxide. Studies in recent years have found that these fluorine-containing waste residues have been artificially After physical treatment such as screening, ball milling, and flotation, crude cryolite can be obtained, but due to its high impurity content, it still cannot meet the raw material requirements for electrolytic aluminum, and quality improvement is urgently needed." The content statement.

According to the above literature introduction, it can be seen that there is no technology for producing molten steel thermal insulation covering agent by using electrolytic aluminum carbon slag.

Contents of the invention

The purpose of the present invention is to provide a method for resource utilization of fly ash in the steelmaking process, which can effectively utilize the fly ash produced by municipal waste incineration, and at the same time fully digest electrolytic aluminum carbon slag, turn waste into treasure, and greatly improve environmental pollution .

The technical solution adopted by the present invention is a method for resource utilization of fly ash in the steelmaking process, which is implemented according to the following steps:

1) Firstly, the hazardous waste carbon slag from the electrolytic aluminum plant is crushed to 0.5-1.0 mm by a crusher, and then transported to the dry powder pelletizing production line for use;

2) Pull and transport the fly ash produced by the municipal waste incineration plant to the dry powder pelletizing production line for use;

3) Mix the fly ash and carbon slag evenly according to the ratio of 85:15 in mass percentage, press them into pellets with a particle size of 15-25mm by using a high-pressure dry powder briquetting machine, and transport them to the steelmaking plant The production line is ready for use;

4) After the molten steel is refined, the pellets are added to the top slag of the ladle as a thermal insulation covering agent for molten steel. The amount of the pellets added is 0.5-1.5kg per ton of molten steel. The process remains the same.

The inventor discovered the following scientific phenomena through research: 1. After the molten steel refining process is completed, the refining slag has a high alkalinity and a temperature above 1400°C, which is the best process platform for the harmless transformation of fly ash. In particular, heavy metals in fly ash can be reduced into molten steel under this temperature condition, and those that have not been reduced can form alkali metal compounds, which become components of refining slag and remain in steel slag. After the steel slag is utilized as a resource, it can undergo hydration reaction to form a cementitious material, realize the mineralization and storage of harmful substances, and achieve the technological purpose of harmless transformation; 2. The high alkalinity and high temperature of molten steel refining slag can make flying The dioxin in the ash undergoes an irreversible decomposition reaction, and the chlorine in the dioxin can exist in the steel slag in the form of chloride, which improves the gelling activity of the converter steel slag and helps to eliminate the instability of f-MgO in the steel slag 3. Fly ash has a small specific gravity and low alkalinity. Adding some acidic substances and heat insulating materials to fly ash can make fly ash an ideal thermal insulation covering agent after molten steel is refined; 4. Electrolytic aluminum hazardous waste carbon slag The fluoride, potassium salt and sodium salt in it can promote the rapid formation of liquid phase of the molten steel thermal insulation covering agent, and the fluoride in it is converted from easily soluble fluoride to insoluble fluoride and cementitious material during the solidification process of steel slag, realizing Harmless transformation of carbon slag; 5. Graphite in carbon slag is a good deoxidizing material and heat insulating material, which can promote the formation of a molten layer on the upper part of the liquid phase layer and a sintered layer on the upper part of the molten steel layer. 6. C and Al in the carbon slag can react with the residual FeO+MnO in the slag, reducing the probability of secondary oxidation of molten steel;

Based on the above findings, the inventors used fly ash as the main raw material, added part of the carbon slag powder to the fly ash, and used a dry powder briquetting machine to produce pellets of 15-25 mm in size, which can be used as heat preservation and covering agents after molten steel refining. Utilization has realized the integrated development of the steelmaking industry's collaborative treatment of hazardous waste. Wherein the composition (mass percentage) of molten steel thermal insulation covering agent sees the following table:

;

The innovations of the present invention are as follows: 1. The inventors have discovered the scientific phenomenon that high-temperature alkaline reducing slag can promote the harmless transformation of harmful heavy metal elements in fly ash, and that alkaline high-temperature steel slag can decompose dioxins and organic matter. The production of molten steel thermal insulation covering agent as the main raw material, and the synchronization of resource utilization of fly ash, complete the harmless transformation of fly ash, which belongs to the industry's first technology; 2. The inventor's fly ash has a large specific surface area and a small specific gravity, which is a good Heat insulation material, adding part of carbon slag powder, producing fly ash into granular molten steel insulation covering agent, in the process of resource utilization, can recover heavy metal elements in fly ash, reduce the alkalinity of refining slag, and optimize refining slag 3. Add carbon slag powder, utilize potassium sodium carbon heat reaction, suppress metal cadmium, lead, zinc from being reduced in the top slag and form metal vapor to escape; 4. The inventors will The fluorine element replaces the fluorine element in fluorite, and the harmless transformation of electrolytic aluminum hazardous waste carbon slag is realized by using refining slag.

Beneficial contributions of the present invention are as follows: 1. Utilize hazardous waste fly ash to produce steel-making molten steel thermal insulation covering agent, realize the harmless transformation of fly ash and carbon slag at the same time of resource utilization in steel-making, and save the cost of hazardous waste The treatment cost solves the land occupation contradiction caused by most of fly ash being used for landfill at present, which is of great significance to the development of society; The molten steel thermal insulation covering agent invented and produced has the advantages of simple processing technology, less dust in the use process, and can optimize the on-site environment of steelmaking production.

Implementation

The embodiment of the present invention is illustrated by taking the converter production line of China Baowu Group Yili Iron and Steel Co., Ltd. as an example.

A method for resourceful utilization of fly ash in a steelmaking process is implemented according to the following steps:

1) Firstly, the hazardous waste carbon slag from the electrolytic aluminum plant is crushed to 0.5-1.0 mm by a crusher, and then transported to the dry powder pelletizing production line for use;

2) Transport the fly ash produced by the Yining waste incineration plant to the dry powder pelletizing production line for use;

3) Mix the fly ash and carbon slag evenly according to the ratio of 85:15 by mass, press them into pellets with a particle size of 15-25mm by using a high-pressure dry powder briquetting machine, and transport them to the steelmaking production line of Yigang stand-by;

4) After the molten steel is refined, the pellets are added to the top slag of the ladle as a thermal insulation covering agent for molten steel. The amount of the pellets added is 0.5-1.5kg per ton of molten steel. The process remains the same.

Claims (1)

1. A method for resource utilization of fly ash in the steelmaking process, characterized in that it is implemented according to the following steps: 1) Firstly, the hazardous waste carbon slag from the electrolytic aluminum plant is crushed to 0.5-1.0 mm by a crusher, and then transported to the dry powder pelletizing production line for use; 2) Pull and transport the fly ash produced by the municipal waste incineration plant to the dry powder pelletizing production line for use; 3) Mix the fly ash and carbon slag evenly according to the ratio of 85:15 in mass percentage, press them into pellets with a particle size of 15-25mm by using a high-pressure dry powder briquetting machine, and transport them to the steelmaking plant The production line is ready for use; 4) After the molten steel is refined, the pellets are added to the top slag of the ladle as a thermal insulation covering agent for molten steel. The amount of the pellets added is 0.5-1.5kg per ton of molten steel. The process remains the same.