Method for synergizing converter double-slag smelting process with fly ash resource utilization

Abstract

The application discloses a method for resource utilization of fly ash in cooperation with a converter double-slag smelting process, and utilizes process conditions of the converter double-slag smelting process to produce composite pellets by adding carbonaceous materials to the fly ash by means of an innovative process method, so that the fly ash has two functions of a reducing agent and a cooling agent, and is applied in the converter double-slag smelting process to reduce a splashing risk generated in a converter slag-remaining process, optimize the converter steelmaking process, and reduce the steelmaking cost, thereby developing a highly competitive process method for the steel industry to process the fly ash generated after garbage incineration on a large scale, and highlighting technical advantages of cross innovation in different technical fields.

Description

Technical Field

[0001] This invention relates to a method for the synergistic utilization of fly ash resources in a converter dual-slag smelting process. Background Technology

[0002] Solid residue from municipal solid waste incineration accounts for 30%–35% of the total waste volume, with bottom ash comprising 25%–30% and fly ash 2%–5%. Waste incineration fly ash refers to the residue collected by the flue gas purification system of waste incineration plants, as well as the residue settling at the bottom of flues and chimneys. It contains certain amounts of dioxins, soluble heavy metals, and salts, and is classified as HW18 hazardous waste (772-002-18 Municipal Solid Waste Incineration Fly Ash) in the National Hazardous Waste List, requiring pre-treatment to render it harmless before safe landfilling. Current research on the resource utilization of fly ash has been documented in literature and reports. (1) Luo Renhong published a paper entitled "Overview of Resource Utilization of Municipal Solid Waste Incineration Fly Ash" in the 4th issue of Environmental Impact Assessment in 2019. The paper stated that "the resource utilization of municipal solid waste incineration fly ash in cement, concrete, ceramic lightweight aggregate and building materials has been carried out at home and abroad. Fly ash, as a new material, can be considered as a substitute for some base materials for road construction, but it still needs to obtain the support of relevant policies and further research is needed." (2) Du Jian published a paper entitled "Cement Solidification Technology for the Treatment of Municipal Solid Waste Incineration Fly Ash" in the 4th issue of Henan Building Materials in 2017. The paper stated that "the fly ash generated by municipal solid waste incineration was solidified with silicate cement, and the influence of fly ash dosage on solidification strength and heavy metal leaching performance was analyzed. The results showed that after the fly ash was solidified with silicate cement, the compressive strength of the solidified body decreased with the increase of fly ash dosage; with the decrease of silicate cement dosage, Pb and Cd Heavy metal ions are more likely to leach from the solidified body. In order to improve the solidification effect, it is necessary to further increase the density of the cement paste. (3) Fan Yanling, Zheng Penghui and Zhu Wen published a paper entitled "A Review of the Technology for Harmless and Resource-based Treatment of Waste Incineration Fly Ash" in the fourth issue of the journal "Resource Conservation and Environmental Protection" in 2020. The paper stated that "my country is still in the initial stage of harmless and resource-based utilization of waste incineration fly ash. Many technical difficulties have not yet been overcome, such as the large increase in capacity of cement solidification, the incomplete destruction of dioxin-like substances by chemical stabilization method, the unstable effect and high cost of the melting method on heavy metals, and the unstable effect of hydrothermal treatment technology. Resource recycling has not been widely applied."

[0003] According to the publicly available literature above, there is currently no process method for the resource utilization of fly ash in the double slag smelting process of converter steelmaking.

[0004] The converter double-slag smelting process involves retaining part or all of the high-basicity, high-temperature, and high-iron-oxide-content steel slag from the previous heat in the converter (referred to in the industry as converter decarburization slag) to be used as slag for the next heat of converter desiliconization and dephosphorization. After the converter desiliconization and dephosphorization are completed, the steel slag in the converter is poured out (referred to in the industry as desiliconization and dephosphorization slag), and then lime and magnesia flux are added to re-form slag and decarburize. After decarburization and temperature adjustment are appropriate, the steel is tapped from the converter, and the steel slag generated in this stage is retained in the converter (referred to in the industry as converter decarburization slag) to be used as slag for the next heat of converter desiliconization and dephosphorization.

[0005] The converter double-slag smelting process can improve the dephosphorization efficiency in the early stage of converter blowing, save the amount of lime and magnesium flux, and improve the thermal efficiency of the converter. It is currently a mainstream method for converter smelting.

[0006] In the converter double-slag smelting process, the decarburized steel slag remaining in the converter after tapping contains a high level of iron oxide and is at a very high temperature. Without appropriate process measures, during the charging of molten iron, the iron oxide in the slag can react with the carbon in the molten iron, producing CO / CO2 bubbles. When these bubbles escape, they can cause a safety hazard as the molten iron being added to the converter splashes from the converter towards the furnace opening. Therefore, appropriate process methods are needed to control this splashing accident in converter double-slag smelting.

[0007] According to literature (1), Wu Ming published a paper entitled "Production Practice of Slag Retention Operation in Converter Smelting of Low Carbon Steel" in the second issue of Steelmaking magazine in 2009. The paper states: "The slag retention operation in converter is a resource-saving steelmaking operation method that uses all or part of the final slag from the previous furnace after slag adjustment and splashing as the initial slag for the next furnace smelting. It meets the requirements of the circular economy. Due to the high basicity, high slag temperature, and high Fe0 content of the final slag, it helps the lime to melt into slag and dephosphorize in the early stage, and its advantages are prominent. However, if the operation is not properly controlled, it is very easy to cause the slag to be mixed with the lime." Problems such as large iron spray, difficulty in ignition during blowing, severe splashing, and rising furnace bottom have been learned from accidents in some steel plants, and should be given high priority. "The content of the article is as follows: (2) Niu Xingming, Liu Wenfei, Li Chao, Wei Chunxin, and Xu Guoyi published a paper entitled "Practice of Slag Retention Operation in 260t Converter" in the magazine "Ansteel Technology". The article states: "The factors affecting the safety of slag retention operation and the impact of slag retention operation on relevant indicators of converter smelting were analyzed. The process parameters for the safety of slag retention operation are: slag retention temperature not higher than 1489℃, iron addition speed less than 1711.57 kg / s, iron addition time greater than 3min, and final oxygen activity of molten steel less than 9×10 -4 The content is expressed as ".".

[0008] Based on the above literature, there is currently no technology for using fly ash in converter smelting of dual slags. Summary of the Invention

[0009] The purpose of this invention is to provide a method for the synergistic utilization of fly ash resources in a converter dual-slag smelting process. This method utilizes the converter dual-slag smelting process to enable the large-scale synergistic utilization of fly ash resources, thus solving the current technological challenge of the difficulty in utilizing fly ash resources.

[0010] The technical solution adopted in this invention is a method for the synergistic utilization of fly ash resources in a converter dual-slag smelting process, implemented according to the following steps: S1. First, transport the waste coal tar, which has a carbon content of more than 80%, to the fly ash storage area of ​​the waste incineration plant for later use. S2. After mixing fly ash and waste coal tar evenly at a mass percentage ratio of 70%:30%, press them into 30-50mm pellets using a high-pressure dry powder briquetting machine. The carbon content of these pellets is greater than 20%, and they are then transported to the converter production line for use. S3. After the converter taps the steel, add the above pellets to the converter decarburized steel slag. Add 160-220 kg of the above pellets to each ton of converter decarburized steel slag. The judgment standard is that the reaction between the pellets and the converter decarburized steel slag is completed and no large amount of flue gas escapes from the converter mouth. The converter can then be smelted according to the traditional double slag smelting process.

[0011] The inventors discovered the following scientific phenomena through experimentation and research: 1. The inventors discovered that in the converter double slag process, controlling the temperature of the converter decarburized steel slag to below 850℃ or controlling the ferrous oxide content in the converter decarburized steel slag to below 5% eliminates the safety hazard of splashing when the converter is charged with molten iron. The decarburized steel slag remaining in the converter during the converter dual-slag smelting process has the following characteristics: a. The temperature of the decarburized steel slag in the converter is between 1620℃ and 1750℃ (the temperature of the steel slag is 50℃ to 150℃ higher than that of the molten steel), which can crack various organic compounds, including dioxins in fly ash. b. The decarburized steel slag left in the converter contains a large amount of heavy metal compounds such as FeO and MnO. At high temperatures, it can undergo a reduction reaction with reducing agents such as carbon and hydrogen, transforming the compounds into a metallic state. Adding a certain amount of reducing material to the steel slag can reduce the content of ferrous oxide in the steel slag and eliminate the safety hazard of splashing when molten iron is charged into the converter. c. The high alkalinity of converter decarburized steel slag allows for the addition of fly ash to the converter decarburized steel slag. This causes the dioxins in the fly ash to decompose into C, H, Cl, and some short-chain organic compounds. Chlorine exists in the steel slag in ionic form, while carbon, hydrogen, and short-chain organic compounds can rapidly react with the oxides in the converter steel slag. Therefore, adding dioxins from fly ash to the steel slag during the converter dual-slag smelting process achieves the harmless transformation of dioxins in the fly ash. 3. To prevent splashing accidents during the double-slag smelting process in the converter, reducing substances are added to the fly ash. The endothermic reduction reaction can achieve two process objectives: reducing the iron oxide concentration and temperature of the steel slag, thereby eliminating the safety hazard of splashing accidents. 4. Fly ash has a low basicity. When added to converter steel slag, the basicity of the converter desiliconization and dephosphorization slag decreases, the slag formation rate is fast, and it is easy to form foam slag. This is beneficial to expand the reaction interface of desiliconization and dephosphorization in the early stage of converter, improve the dephosphorization rate, and the foam slag is easy to pour out of the converter, which facilitates the implementation of the slag retention process.

[0012] 5. During the above process, the heavy metal oxides in fly ash are reduced to a metallic state and enter the molten steel, thus realizing the resource utilization of heavy metal compounds in fly ash. Based on the above findings, the inventors added waste carbonaceous materials to fly ash and compressed it into composite pellets of 30-50mm. In the converter double-slag smelting process, these pellets were added to the decarburized steel slag of the converter as a reducing agent and coolant. By utilizing the reduction reaction of heavy metal oxides (endothermic reaction) and the slag-forming reaction between fly ash and converter decarburized steel slag (endothermic reaction), the temperature of the converter decarburized steel slag and the concentration of iron oxide in the steel slag were rapidly reduced. This solved the process problem of splashing caused when charging molten iron in converter double-slag smelting, and at the same time achieved the harmless transformation of fly ash.

[0013] The innovations of this invention are as follows: 1. Based on the above scientific findings, the inventors proposed adding some carbonaceous materials to fly ash to produce composite pellets (the TC content in the pellets is greater than 20%), which are then added to the slag residue of the converter to reduce the iron oxide concentration and temperature of the decarburized steel slag, thus eliminating the safety hazard of splashing in the dual-slag smelting process; 2. Adding carbonaceous materials to fly ash allows the reducing agents such as carbon and hydrogen to react with heavy metal oxides in the steel slag to form bubbles. When these bubbles escape, they can carry away a large amount of heat energy and expand the reaction interface of the reduction reaction, thereby rapidly reducing the temperature of the steel slag; 3. By utilizing the chemical reaction between the decarburized steel slag and fly ash in the converter, the dioxins in the fly ash decompose, and the carbon and hydrogen elements in the dioxins act as reducing agents to reduce the heavy metal compounds in the steel slag and fly ash. Chlorine becomes a component of the steel slag, eliminating the possibility of secondary dioxin synthesis. 4. Utilizing the low basicity of fly ash, the basicity of the decarburized steel slag in the converter can be reduced, making it easier to form foamy slag during the desiliconization and dephosphorization stage of the converter. This is conducive to the desiliconization and dephosphorization reaction. In addition, the slag has good fluidity, which makes it easier to pour the desiliconization and dephosphorization slag out of the converter, eliminating the hidden danger of converter bottom rise in the dual-slag smelting process.

[0014] The beneficial contributions of this invention are as follows: 1. This invention utilizes the converter double-slag smelting process to achieve large-scale synergistic utilization of fly ash resources, solving the current technological problem of the difficulty in utilizing fly ash resources; 2. Currently, the profit level of the steel industry is low. The process of this invention can co-process more than 16 kg of fly ash per ton of steel. Based on the current hazardous waste disposal fee of 1,500 yuan per ton of fly ash, the converter can earn 24 yuan per ton of steel, increasing the profit level of steelmaking. At the same time, the resource utilization of fly ash in steelmaking increases the social function of steelmaking enterprises and enhances the survival ability of steel plants. Detailed Implementation

[0015] Example: An example of the present invention is a 100-ton converter production line.

[0016] A method for the synergistic utilization of fly ash resources in a converter dual-slag smelting process is implemented according to the following steps: S1. First, transport the waste coal tar, which has a carbon content of more than 80%, to the fly ash storage area of ​​the waste incineration plant for later use. S2. After mixing fly ash and waste coal tar evenly at a mass percentage ratio of 70%:30%, press them into 30-50mm pellets using a high-pressure dry powder briquetting machine. The carbon content of these pellets is greater than 20%, and they are then transported to the converter production line for use. S3. After the converter taps the steel, add the above pellets to the converter decarburized steel slag. Add 160-220 kg of the above pellets to each ton of converter decarburized steel slag. The judgment standard is that the reaction between the pellets and the converter decarburized steel slag is completed and no large amount of flue gas escapes from the converter mouth. The converter can then be smelted according to the traditional double slag smelting process.

Claims

1. A method for the synergistic utilization of fly ash resources in a converter dual-slag smelting process, characterized in that... Follow these steps: S1. First, transport the waste coal tar, which has a carbon content of more than 80%, to the fly ash storage area of ​​the waste incineration plant for later use. S2. After mixing fly ash and waste coal tar evenly at a mass percentage ratio of 70%:30%, press them into 30-50mm pellets using a high-pressure dry powder briquetting machine. The carbon content of these pellets is greater than 20%, and they are then transported to the converter production line for use. S3. After the converter taps the steel, add the above pellets to the converter decarburized steel slag. Add 160-220 kg of the above pellets to each ton of converter decarburized steel slag. The judgment standard is that the reaction between the pellets and the converter decarburized steel slag is completed and no large amount of flue gas escapes from the converter mouth. The converter can then be smelted according to the traditional double slag smelting process.