A method for utilizing fly ash resources in synergistic cooperation with converter production

Abstract

The present invention discloses a method for resource utilization of fly ash in coordination with converter production, and involves three technical fields of converter steelmaking and resource utilization of fly ash and secondary aluminum ash. The present invention utilizes the process links of the converter and adopts an innovative process method to produce fly ash, secondary aluminum ash and waste magnesium carbon brick particles from steel mills into a slag modifier for the converter, which is used as a slag suppressing agent for the converter foam slag at the end of the converter blowing. While playing the role of slag suppression and defoaming of the converter foam slag, it optimizes the process performance of the converter steel slag splashing furnace protection, which is beneficial to the implementation of the slag splashing furnace protection process after the converter steel is tapped, and at the same time optimizes the performance of the converter steel slag resource utilization, and develops a highly competitive process method for the large-scale treatment of fly ash generated after waste incineration and secondary aluminum ash generated by electrolytic aluminum enterprises in the Chinese steel industry, highlighting the technical advantages of cross-innovation in different technical fields.

Description

Technical Field

[0001] The invention relates to a method for resource utilization of fly ash in coordinated converter production. Background Art

[0002] Background technology 1: The solid residue after the incineration of domestic waste accounts for 30%-35% of the total waste, of which bottom ash accounts for 25%-30% and fly ash accounts for 2%-5%. Fly ash from waste incineration refers to the residues collected by the flue gas purification system of the waste incineration plant and the residues settled at the bottom of the flue and chimney. It contains a certain amount of dioxins, soluble heavy metals and salts. It belongs to the HW18 hazardous waste (772-002-18 Domestic waste incineration fly ash) in the "National List of Hazardous Wastes" and needs to be pre-harmlessly treated before it can be safely landfilled. At present, there are studies on the resource utilization of fly ash in literature and reports. Literature review (1) Luo Renhong published a paper entitled “Overview of Resource Utilization of Fly Ash from Municipal Waste Incineration” in the 4th issue of Environmental Impact Assessment in 2019. The article states that “The resource utilization of fly ash from municipal waste incineration in cement, concrete, ceramic lightweight aggregate and building materials has been launched at home and abroad. Fly ash, as a new type of material, can be considered as a partial base material to replace road construction materials, but it still needs to obtain the support of relevant policies and further research is needed in the future”; (2) Du Jian published a paper entitled “Cement Solidification Technology for the Treatment of Fly Ash from Municipal Waste Incineration” in the 4th issue of Henan Building Materials in 2017. The article states that “The fly ash produced by municipal waste incineration was solidified with silicate cement, and the effect of fly ash content on solidification strength and heavy metal leaching performance was analyzed. The results show that after the fly ash is solidified with silicate cement, the compressive strength of the solidified body decreases with the increase of fly ash content; with the decrease of silicate cement content, the content of Pb and Cd Heavy metal ions such as carbon monoxide and other metals are more likely to leach out of the solidified body. In order to improve the solidification effect, the density of the cement paste needs to be further improved. " (3) Fan Yanling, Zheng Penghui, and Zhu Wen published a paper entitled "A Review of Harmless Treatment and Resource Management Technologies for Waste Incineration Fly Ash" in the 4th issue of "Resource Conservation and Environmental Protection" in 2020. The paper states that "my country is still in the initial stage of harmless treatment and resource utilization of waste incineration fly ash, and many technical difficulties have not yet been overcome, such as the large capacity increase of cement solidification, the incomplete destruction of dioxin-like substances by chemical stabilization method, the unstable and expensive effect of the melting method on heavy metals, the unstable effect of hydrothermal treatment technology, etc., and resource recycling has not been widely used."

[0003] According to the above-mentioned public documents, there is currently no process for utilizing fly ash resources in coordination with the steelmaking process.

[0004] Background technology 2: The key part of converter smelting lies in the blowing in the furnace. Converter oxygen blowing smelting is divided into three stages: 1. 3 to 5 minutes after the converter starts blowing, the silicon, manganese and phosphorus in the molten iron are oxidized in large quantities, which is called the silicon-manganese oxidation period; 2. After the silicon, manganese and phosphorus in the converter molten iron are oxidized in large quantities, the temperature of the converter molten pool rises, and the decarburization reaction begins. This stage is called the carbon-oxygen reaction period. Due to the decarburization reaction of the converter molten steel, CO / CO2 bubbles are generated. During the escape process, the [H] and [N] with smaller partial pressures in the molten iron are merged into the CO / CO2 bubbles to achieve the purpose of removal. At the same time, during the bubble escape process, small bubbles adhere to inclusions and float up into the slag. These functions are important guarantees for improving the quality of converter molten steel, so this stage is also called the decarburization refining period; 3. After the converter decarburization is completed, the temperature and end point composition need to be adjusted. The stage about 3 minutes after the end of decarburization is called the smelting end point control period;

[0005] After the control period of the converter smelting end point, the carbon-oxygen reaction between the slag and the molten steel has not yet reached equilibrium. At this time, there are still bubbles generated by the carbon-oxygen reaction, which makes the slag foaming serious. At the end of the smelting, the converter needs to be temperature-measured and sampled. The converter should be tilted 75-90° in the slag-discharging direction, and part of the slag should be poured out for temperature-measurement and sampling (there are also converters with auxiliary gun systems that do not perform temperature measurement and sampling. After the blowing is completed, no sampling is taken and the furnace is directly poured out for steel.).

[0006] Since the slag is seriously foamed at the end of the converter blowing, no matter which method is used, when the converter is tilted, the seriously foamed slag in the furnace will overflow from the furnace mouth. If no measures are taken, it is necessary to wait for the foaming degree of the slag to decay to a certain extent before the furnace body can be tilted for temperature measurement and sampling or steel tapping. Otherwise, some slag will overflow from the furnace mouth to the platform in front of the furnace or overflow into the ladle ready for steel tapping, or on the ladle car, causing unexpected accidents. In order to solve this contradiction, the converter adds part of the defoaming agent to defoam at the end of the blowing to solve the above contradiction. This defoaming agent is usually called slag pressing agent in the converter. The mechanism of slag pressing agent is based on defoaming the slag. There are two basic principles of defoaming: physical defoaming and chemical defoaming. Physical defoaming is to impact the foam slag by adding defoaming agent to promote the rupture of bubbles in the foam slag; chemical defoaming is to generate gas through carbon-oxygen reaction, enter the bubbles in the foam slag, increase the pressure of the gas in the bubbles, and promote the rupture of the foam in the foam slag to achieve the purpose of defoaming.

[0007] The literature search revealed: (1) Gong Hongjun’s paper “The Practice and Analysis of Using Waste Steel Slag for Slag Pressing and Adjusting in Converter Steelmaking” published in Sichuan Metallurgy, Vol. 31, No. 1, 2009, contains the following statement: “The use of waste steel slag combined with carbonaceous materials for slag pressing and adjusting can achieve a better slag splashing and furnace protection effect, shorten the slag splashing time, and achieve direct steelmaking without turning the furnace over for some furnaces. The direct steelmaking rate without turning the furnace over reached 78.6%, creating favorable conditions for automated steelmaking in new converters.” (2) In the paper “Application of Slag-pressing Balls in Converter Steelmaking” published by Sun Guiping, Ma Zhiwei and Ren Jianbo in the journal Knowledge Economy in 2012 (7), there is a statement that “The appropriate amount of slag-pressing balls is added before pouring or tapping. The process is simple and can effectively inhibit the foaming of slag and reduce the iron loss during slag pouring. For low-carbon and high (FeO) steelmaking, the reduction of (FeO) in the slag is more obvious. In addition, after using slag-pressing balls, the steelmaking cycle is shortened, the working environment is improved, and the amount of slag required for slag splashing can be met. It has been promoted and used in other converters in our factory.” (3) In the paper “Development and Industrial Test of Slag-pressing Rice Husk Blocks” published by Xu Kaili, Dong Lianxing and Liu Shizhou in the journal Steelmaking in 1993 (1), there is a statement that “the slag-pressing agent can eliminate foamy slag at the end of blowing, inhibit or eliminate slag overflow, slag spraying and splashing, and ensure safe production.” (4) Wu Hanyuan published an article titled “Development and Application of Magnesium Slag Depressant in Converter Steelmaking” in the 6th issue of Industrial Heating in 2014. The article states that “The production of this slag depressant mainly involves transporting waste refractory materials (MgO content of 78%) to the production plant, sorting out the industrial waste and iron-containing raw materials, and then using a jaw crusher to crush them into particles <50 mm. They are then processed into powder <3 mm in a Raymond mill, and then limestone powder is added. The slag is pressed into 30±5 mm balls using a steel slag powder briquette machine or a refractory briquette machine. After drying at 30-50°C, they are used in the converter production process.”

[0008] According to the above literature discussion, there is currently no precedent for utilizing fly ash as a converter slag pressing agent for resource utilization.

[0009] Background technology 3: The converter slag splashing furnace protection process is to use high-pressure N2 to splash the slag in the furnace onto the furnace wall to form a certain thickness of slag splashing layer after the converter taps out steel. This slag splashing layer plays a role in reducing the erosion of the furnace lining during the smelting of the next batch of steel, and can greatly increase the life of the furnace lining. Therefore, the physical and chemical properties of the slag in the slag splashing layer have an important influence on the corrosion resistance of the slag splashing layer, the adhesion between the slag and the furnace lining, and the length of the slag incubation time. In order to obtain a better slag splashing furnace protection effect, before the converter slag splashing furnace protection process is implemented, it is necessary to add coke and magnesia materials (dolomite, magnesite, magnesium balls, etc.) into the converter furnace to reduce the FeO in the slag and increase the concentration of MgO in the slag to obtain a better slag splashing furnace protection effect.

[0010] References (1) Zhao Ming, Wang Shuanglong, and Wang Hongsheng published a paper entitled “Research on the Application of Modified Materials for 210 t Converter Slag Splashing Protection” in the 3rd issue of Baosteel Science and Technology in 2008. The paper states: “After the modified materials were used for slag splashing, the thickness of the furnace lining increased, the condition of the furnace body was improved, and good conditions were created for the efficient and stable production of the converter.” (2) Chen Yuanxue and Zhang Yicai published a paper entitled “Optimization of the Slag Splashing Protection Process for Combined Blowing Converter” in the 6th issue of Steelmaking in 2009. The paper states: “The slag modifying agent is prepared by mixing light-burned magnesium powder and deoxidizer in a certain proportion. The addition of the slag modifying agent to the highly oxidizing slag can increase the melting point of the slag and improve the resistance of the slag layer to high-temperature erosion.”

[0011] According to the above literature, there is currently no process for producing converter slag splashing furnace modifier using waste magnesia carbon bricks.

[0012] Technical background 4: Aluminum ash is a solid substance containing metallic aluminum and other components produced during the production, use and recycling of electrolytic aluminum, cast aluminum and other aluminum industries. The basic range of the main components and their content (mass percentage) in primary aluminum ash is: 10% to 30% metallic aluminum; 7% to 20% aluminum nitride; 20% to 40% aluminum oxide; 3% to 15% silicon dioxide, magnesium oxide and iron oxide; 15% to 30% chlorides and other trace fluorides of alkali metals potassium, sodium, calcium and magnesium.

[0013] After screening or aluminum roasting, the remaining aluminum ash after extracting most of the metallic aluminum in the aluminum ash is called secondary aluminum ash. The secondary aluminum ash contains about 5% metallic aluminum, 7% to 20% aluminum nitride, more than 40% aluminum oxide, and soluble fluorides and chlorides. Currently, the National List of Hazardous Wastes (2021 Edition) has listed secondary aluminum ash as hazardous waste.

[0014] Literature review (1) Li Lingling, Yuan Songming, and Yuan Jinqiang published a paper titled "Research Progress in Aluminum Ash Recycling" in the 8th issue of "Inorganic Salt Industry" in 2018. The paper states that "In view of the problem that untreated aluminum ash will cause serious environmental pollution, combined with the characteristics of current technology, it is analyzed that the wet method has more advantages than the fire method in the secondary aluminum ash recovery and treatment. The salt-free fire method for aluminum ash treatment and the recovery of gases generated during the aluminum ash treatment process are future research hotspots. Aluminum ash can be used as a raw material for the production of refractory materials, building materials and environmental materials. The heterogeneity between aluminum ashes determines that aluminum ash treatment requires a systematic and comprehensive treatment method"; (2) Li Yuan Bing, Sun Li and others published a paper entitled "Comprehensive Utilization of Aluminum Ash" in the 6th issue of "China Nonferrous Metallurgy" magazine in 2008. The paper stated, "Aluminum ash contains many substances that may directly or indirectly harm the environment, and direct disposal will cause environmental pollution. Aluminum ash is also a renewable resource with comprehensive utilization value. Aluminum, salt, and alumina can be recovered from it. It can also be used to synthesize water purifiers. It can also be used in refractory materials, road and construction materials, steelmaking desulfurization agents, etc. There are many methods for recycling aluminum ash. It should be treated as comprehensively as possible according to the actual situation, and the selection should be based on the principles of high recovery rate, high economic benefits and no secondary pollution."

[0015] According to the above literature, there is currently no process for producing converter slag splashing furnace modifier using secondary aluminum ash. Summary of the invention

[0016] The purpose of the present invention is to provide a method for the coordinated resource utilization of fly ash in converter production. An innovative process method is adopted to produce fly ash, secondary aluminum ash and waste magnesia carbon brick particles from steel mills into a slag modifier for converter use. The slag modifier is used as a slag suppressant for converter foam slag at the end of converter blowing. While suppressing and defoaming the converter foam slag, the process performance of converter steel slag splashing and furnace protection is optimized, and the environmental protection effect is outstanding.

[0017] The technical solution adopted by the present invention is a method for fly ash resource utilization in converter production, which is implemented according to the following steps:

[0018] 1. First, the magnesia carbon bricks discarded from the steel mill are crushed into particles with a size of 10-15mm by a crusher and transported to the dry powder pelletizing production line for standby use;

[0019] 2. The secondary aluminum ash produced by the electrolytic aluminum plant is transported to the dry powder pelletizing production line for standby use;

[0020] 3. Transport the fly ash generated by the municipal waste incineration plant to the dry powder pelletizing production line for standby use;

[0021] 4. The fly ash, secondary aluminum ash and waste magnesia carbon brick particles are mixed evenly in a mass percentage ratio of 65:15:25, and then pressed into pellets with a particle size of 30-50 mm using a high-pressure dry powder briquetting machine, and transported to the converter production line of the steel plant for standby use;

[0022] 5. Before the converter smelting ends and the slag is discharged, the above pellets are added: for foamy slag defoaming, the addition amount is 3-5kg per ton of molten steel; then the steel tapping operation is carried out according to the normal smelting process; after the converter steel tapping process is completed, there is no need to modify the slag, and the slag splashing furnace protection process can be carried out directly, and the rest of the converter smelting process remains unchanged.

[0023] The inventor discovered the following scientific phenomena through research:

[0024] 1. The slag in the late stage of converter smelting has strong oxidizing properties and high basicity, which is the best process platform for harmless conversion of fly ash. In particular, the three easily gasified heavy metal elements Pb, Zn and Cd in fly ash can be mostly introduced into the molten steel by using appropriate reducing materials under the conditions of strong oxidizing properties and high foaming of slag, while a small part remains in the slag, thus achieving harmless conversion of harmful substances;

[0025] 2. The foamy slag in the late stage of converter smelting has the characteristics of high alkalinity and strong oxidizing property, which can cause irreversible decomposition reaction of dioxins in fly ash, and the chlorine in dioxins can exist in the slag in the form of chloride, which is conducive to eliminating the unstable factor of f-MgO in the slag;

[0026] 3. Utilize aluminum ash and large particles of magnesium carbon bricks discarded by steel mills as materials for converter slag splashing and furnace protection, which can eliminate the reactivity (AlN) and toxicity (soluble fluoride) of harmful substances in aluminum ash and maximize the potential value of discarded magnesium carbon bricks;

[0027] 4. The chloride ions in the fly ash can react chemically with the f-MgO in the converter slag during the slag solidification process, thereby increasing the gelling activity of the converter slag.

[0028] According to the above findings, the inventors used fly ash as the main raw material, crushed the magnesia carbon bricks discarded by the steel mill into 10-15mm particles as aggregate, and used secondary aluminum ash as auxiliary material to produce 30-50mm pellets. In the later stage of converter smelting, it was used as an auxiliary material for steelmaking. It was added before the converter was poured and slag was discharged to play the role of slag pressing and defoaming. While completing the slag pressing and defoaming, the slag was modified, which was conducive to the implementation of the slag splashing furnace protection process after the converter was discharged. The technology of this project optimizes the process content of converter slag tempering while utilizing fly ash and secondary aluminum ash as resources. Finally, most of the fly ash components are converted into steel slag with the characteristics of silicate cement and magnesia cement clinker. It is used as a raw material resource for the building materials industry, road construction field, and cement production, realizing the integrated development of the coordinated treatment of hazardous waste in the steelmaking industry.

[0029] The innovative features of the present invention are as follows:

[0030] 1. The inventor utilized the characteristics of foamy slag in the late stage of converter smelting and the process requirements of slag splashing to protect the furnace, and utilized the thermodynamic and kinetic conditions of converter steelmaking to make resourceful use of fly ash and secondary aluminum ash. At the same time of resource utilization, the harmless transformation of fly ash and secondary aluminum ash was completed, which is the first technology in the industry;

[0031] 2. The inventors found that the magnesia carbon bricks discarded from steel mills have coarse grain structures and lack the activity to undergo metallurgical chemical reactions under the conditions of the slag splashing furnace protection process. This characteristic is retained and crushed to 10-15 mm. In the highly oxidizing converter liquid slag, the small particles of magnesia carbon bricks will undergo surface decarburization reaction, forming an "island" effect. The pores formed on the surface are conducive to the implementation of the slag splashing furnace protection process.

[0032] 3. The metallic aluminum and aluminum nitride in the secondary aluminum ash can react with the heavy metals Ni, Cu, Cr, etc. in the fly ash, and these heavy metals can be reduced to liquid metals and enter the molten steel, thus maximizing the value of the precious heavy metals in the fly ash;

[0033] 4. The aluminum nitride in the secondary aluminum ash, the metal aluminum and the carbon in the magnesia carbon bricks are used to degrade the iron oxide in the foamed slag, which is beneficial to the defoaming during the slag pressing process. After the slag pressing and defoaming operation is completed, the aluminum oxide in the secondary aluminum ash and the aluminum oxide generated by the reaction of metal aluminum and aluminum nitride can react with the MgO in the converter lining and the MgO in the small particles of the magnesia carbon bricks to form a magnesia aluminum spinel phase, which helps to enhance the adhesion between the converter slag and the lining and improve the process effect of slag splashing and furnace protection;

[0034] 5. Taking advantage of the low basicity of fly ash, the basicity of converter slag is reduced, eliminating the hazards of some f-CaO and f-MgO in the converter slag, optimizing the performance of converter slag while realizing resource utilization of fly ash, and ensuring the safety of converter slag resource utilization.

[0035] 6. By utilizing the chloride ions in fly ash and f-MgO in slag, a cementitious material with the characteristics of magnesia cement can be synthesized, which is conducive to the resource utilization of steel slag.

[0036] The beneficial contributions of the present invention are as follows: 1. The production of steelmaking flux using hazardous waste is used to optimize the performance of converter slag, and the harmless transformation of fly ash and aluminum ash is achieved while utilizing it as a resource in steelmaking, saving the cost of hazardous waste treatment and solving the land occupation contradiction caused by the current use of most fly ash for landfill treatment, which is of great significance to the development of society; 2. The resource utilization of fly ash and secondary aluminum ash in converter steelmaking helps to reduce the content of f-CaO and f-MgO in steel slag, which has positive significance for the safety and stability of steel slag resource utilization, and can reduce or eliminate the unstable factors generated after the resource utilization of steel slag. DETAILED DESCRIPTION

[0037] The embodiment of the present invention is described by taking the converter production line of China Baowu Group Yili Iron and Steel Co., Ltd. as an example. A method for fly ash resource utilization in converter production is implemented according to the following steps:

[0038] 1. First, the magnesia carbon bricks discarded from the steel mill are crushed into particles with a size of 10-15mm by a crusher and transported to the dry powder pelletizing production line for standby use;

[0039] 2. The secondary aluminum ash produced by the electrolytic aluminum plant is transported to the dry powder pelletizing production line for standby use;

[0040] 3. The fly ash generated by the Yining City Waste Incineration Plant is transported to the dry powder pelletizing production line for standby use;

[0041] 4. The fly ash, secondary aluminum ash and waste magnesia carbon brick particles are mixed evenly in a mass percentage of 65:15:25, and then pressed into pellets with a particle size of 30-50 mm using a high-pressure dry powder briquetting machine, and transported to the Yigang converter production line for standby use;

[0042] 5. Before the converter smelting ends and the slag is discharged, the above pellets are added: for foamy slag defoaming, the addition amount is 3-5kg per ton of molten steel; then the steel tapping operation is carried out according to the normal smelting process; after the converter steel tapping process is completed, there is no need to modify the slag, and the slag splashing furnace protection process can be carried out directly, and the rest of the converter smelting process remains unchanged.

Claims

1. A method for utilizing fly ash resources in a converter production collaboration, characterized in that Follow these steps to implement: 1) First, the magnesia carbon bricks discarded from the steel mill are crushed into particles with a size of 10-15mm by a crusher and transported to the dry powder pelletizing production line for standby use; 2) The secondary aluminum ash produced by the electrolytic aluminum plant is transported to the dry powder pelletizing production line for standby use; 3) Transport the fly ash generated by the municipal waste incineration plant to the dry powder pelletizing production line for standby use; 4) After the fly ash, secondary aluminum ash and waste magnesia carbon brick particles are uniformly mixed in a mass percentage of 65:15:25, a high-pressure dry powder briquetting machine is used to press them into pellets with a particle size of 30-50 mm, and the pellets are transported to the converter production line of the steel plant for standby use; 5) Before the converter smelting ends and the slag is discharged, the above pellets are added: for foamy slag defoaming, the addition amount is 3-5kg per ton of molten steel; then the steel tapping operation is carried out according to the normal smelting process; after the converter steel tapping process is completed, there is no need to modify the slag, and the slag splashing furnace protection process can be carried out directly, and the rest of the converter smelting process remains unchanged.