Method for treating fly ash by using converter steelmaking desiliconization and dephosphorization slag

Abstract

The present invention discloses a method for treating fly ash by using converter steelmaking desiliconization and dephosphorization slag, which is implemented according to the following steps: transporting the waste coating of the tundish of the continuous casting machine in the steelmaking plant, with MgO in the mass percentage > 60%, to the dry powder pelletizing production line for standby; transporting the fly ash from the incineration of domestic waste to the dry powder pelletizing production line for standby; mixing the waste coating of the continuous casting machine and the fly ash generated from the incineration of domestic waste evenly according to the mass percentage of 85:15, pressing them into pellets with a diameter of 30 - 50 mm on the dry powder pelletizing production line, and transporting them to the converter production line for standby; adding the above pellets into the slag ladle along with the slag flow during the slag tapping process of the converter, with the addition ratio being 100 - 250 kg per ton of slag; or after the slag tapping of the converter is completed, adding the above pellets into the slag ladle filled with converter desiliconization and dephosphorization slag; standing the above slag ladle for 30 min, pouring it into the hot splash slag yard, and after continuing to keep warm for 2 h, treating it according to the normal hot splash slag or hot stamping slag treatment process.

Description

Technical Field

[0001] The present invention relates to a method for treating fly ash with a converter steelmaking desiliconization and dephosphorization slag. Background Art

[0002] The solid residue after domestic waste incineration treatment 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 capture of the flue gas purification system of a waste incineration plant and the residues deposited at the bottom of the flue and chimney. It contains a certain amount of dioxins, soluble heavy metals and salts, and belongs to the hazardous waste of category HW18 in the "National Hazardous Waste List" (772-002-18 domestic waste incineration fly ash). It needs to be pre-treated harmlessly before it can be safely landfilled. At present, there are already studies on the resource utilization of fly ash in the literature and reports. Referring to the literature: (1) Zhang Guoliang, Li Zhongfeng, etc. published a paper entitled "Engineering Application of Cement Kiln Co-disposal of Waste Incineration Fly Ash" in the first issue of the "Cement" magazine in 2017. The article states that "in 2012, the demonstration line for the industrialized disposal of fly ash of a certain company was completed and put into operation. The total investment was 80 million yuan. So far, the process has been very smooth, achieving the designed output. The equipment operation has the characteristics of continuity and stability, thus promoting the exemption of the "List of Hazardous Wastes" in China during the revision process, filling and supplementing the blanks that have emerged internationally, and leading the world. At the same time, the fly ash drying and the exhaust gas emissions from the fly ash silo meet the "Integrated Emission Standards of Air Pollutants" in Beijing, and the cement kiln flue gas also meets the corresponding permitted emission concentration limits of relevant standards."; (2) Du Jian published a paper entitled "Cement Solidification Technology for the Treatment of Waste Incineration Fly Ash" in the fourth issue of the "Henan Building Materials" magazine in 2017. The article states that "fly ash generated from the incineration of urban waste was solidified with portland cement, and the effects of fly ash dosage on the solidification strength and the leaching performance of heavy metals were analyzed. The results showed that: after the fly ash was solidified with portland cement, the compressive strength of the solid decreased with the increase of the fly ash dosage; with the decrease of the portland cement dosage, heavy metal ions such as Pb and Cd were more likely to leach from the solid. To improve the solidification effect, it was necessary to further improve the density of the cement paste."; (3) Fan Yanling, Zheng Penghui, Zhu Wen published a paper entitled "Review of the Harmless and Resource Treatment Technology of Waste Incineration Fly Ash" in the fourth issue of the "Resources Conservation & Environmental Protection" magazine in 2020. The article states that "China is still in the initial stage of harmless and resource utilization of waste incineration fly ash, and many technical difficulties have not been overcome, such as large capacity increase of cement solidification, incomplete destruction of dioxin-like substances by the chemical agent stabilization method, unstable effects of heavy metals by the melting method and high costs, unstable effects of the hydrothermal treatment technology, etc., and the resource recycling has not been widely applied."

[0003] According to the above-mentioned public documents, there is currently no process for utilizing converter slag in a coordinated resource-based manner to utilize fly ash.

[0004] The use of double slag smelting technology in converter steelmaking is an innovative technology in the steel industry in the past decade. The double slag smelting process means that after the smelting of a converter is completed, the decarbonized slag is left in the converter as the desiliconized and dephosphorized slag for the next batch. After the desiliconization and dephosphorization are completed, the desiliconized and dephosphorized slag is poured out, and then slag auxiliary materials are added for decarbonization. After the steel is tapped, the slag is left and enters the next batch of circulation. The double slag smelting process is called SGRS in Shougang. The desiliconized and dephosphorized slag produced by this process has the following characteristics:

[0005] (1) The basicity (binary basicity) of conventional converter slag is above 2.8, and the basicity of desiliconized and dephosphorized slag is between 1.4 and 2.2. The slag has a low content of free calcium oxide and contains a large amount of rhodonite and olivine. Its crushing value and strength cannot meet the requirements of surface materials for road construction. The composition of typical desiliconized and dephosphorized slag is shown in the following table:

[0006] ;

[0007] (2) The total iron content in the slag is less than 15%, and the majority of the iron content is small metal iron beads dispersed in the slag.

[0008] References (1) Xu Ying, Wang Qiaoling, Hu Chenguang, and Zhang Zizi published a paper titled "Research Progress of Online Reconstruction Technology of Liquid Steel Slag" in the 2nd issue of "Mineral Comprehensive Utilization" in 2019. The paper states: "This paper briefly describes the characteristics and existing problems of steel slag, and focuses on the effects of tempering components, temperature system, cooling system, atmosphere system, mixing system, process equipment, and thermodynamic and kinetic research on the gelling activity and volume stability of reconstructed steel slag during online reconstructing of liquid steel slag; finally, the problems existing in online reconstructing of steel slag and the more advanced technologies in the steel industry are discussed. Reconstruction of the development trend. ", the article did not mention the use of converter slag to treat overhaul slag; (2) Lv Kaihui published a paper entitled "Innovation and Governance of the Mechanism of Using Converter to Incinerate Combustible Industrial Waste" in the 5th issue of "China Metallurgy" in 2019. The article stated that "As the public's environmental awareness increases and the country pays more and more attention to environmental protection, Fujian Quanzhou Minguang Iron and Steel Co., Ltd. actively studies and explores the path of industrial waste disposal for enterprises, and uses converter incineration to treat combustible industrial waste for enterprises. This is of great significance for recycling resources, reducing social burdens, and reducing environmental risks."

[0009] From the above literature description, it can be seen that there is currently no process for utilizing converter desiliconization and dephosphorization slag to synergistically treat fly ash from the incineration of domestic waste. Summary of the invention

[0010] The object of the present invention is to provide a method for treating fly ash by using the de-siliconized and de-phosphorized slag of converter steelmaking. While solving the problem of resource utilization of fly ash, the waste heat of the de-siliconized and de-phosphorized slag of the converter is utilized, and the economic and environmental benefits are huge.

[0011] The object of the present invention is achieved as follows. A method for treating fly ash by using the de-siliconized and de-phosphorized slag of converter steelmaking is implemented according to the following steps:

[0012] 1) Transport the waste coating of the tundish of the continuous casting machine in the steel mill. The mass percentage of MgO in the waste coating is >60%, and it is transferred to the dry powder pelletizing production line for standby.

[0013] 2) Transport the fly ash from the incineration of domestic waste to the dry powder pelletizing production line for standby.

[0014] 3) Mix the waste coating of the continuous casting machine and the fly ash generated from the incineration of domestic waste evenly in a mass percentage ratio of 85:15, press them into pellets with a diameter of 30 - 50 mm on the dry powder pelletizing production line, and transport them to the converter production line for standby.

[0015] 4) Add the above pellets into the slag ladle along with the slag flow during the slag tapping process of the converter. The addition ratio of the pellets in each ton of the de-siliconized and de-phosphorized slag of converter steelmaking is 100 - 250 kg; or after the slag tapping of the converter is completed, add the above pellets into the slag ladle filled with the de-siliconized and de-phosphorized slag of converter steelmaking.

[0016] 5) Let the above slag ladle stand for 30 min, pour it into the hot splash slag yard, continue to keep it warm for 2 h, and then treat it according to the normal hot splash slag or hot stamping slag treatment process.

[0017] 6) After the slag treatment process is completed, the granulated iron and medium-sized slag iron magnetically separated from the de-siliconized and de-phosphorized slag of converter steelmaking are returned to the steelmaking for resource utilization, and the tail slag is used as a raw material for building materials or road engineering for resource utilization.

[0018] The present invention adds a certain proportion of fly ash and part of the waste coating of the tundish of the continuous casting machine (waste MgO-based refractory material) to the liquid de-siliconized and de-phosphorized slag of the converter, and utilizes each component in the de-siliconized and de-phosphorized slag. During the thermal coupling reaction process of the steel slag, the heavy metal elements in the fly ash are reduced and enter the fine metal droplets dispersed in the steel slag. The de-siliconized and de-phosphorized slag of the converter decomposes the dioxin in the fly ash, and MgO in the waste coating of the tundish of the continuous casting machine forms MgCl with Cl in the fly ash during the solidification process, improving the gelling activity of the steel slag and making it a building raw material with gelling properties. While solving the problem of resource utilization of fly ash, the waste heat of the de-siliconized and de-phosphorized slag of the converter is utilized, and the economic and environmental benefits are huge.

[0019] The innovation points of the present invention are as follows:

[0020] 1. The inventors' research found that during the formation of converter steel slag, when a high-speed oxygen jet impacts the converter metal bath, a large amount of molten iron is splashed out of the bath under the impact. Under the action of gravity, it splashes back into the bath. Since the upper part of the bath is covered with steel slag, some of the molten iron exists in the form of small droplet dispersions in the liquid steel slag. There are more small iron droplets dispersed in the desiliconization and dephosphorization slag of the converter, and the small iron droplets contain relatively large amounts of reducing elements such as [C], [Si], and [P]. At high temperatures, they can undergo metallurgical physical and chemical reactions with the compounds of heavy metals Ni, Cu, Pb, Cr, and Cd, be reduced to metals, melt into the molten iron, and be recovered in the magnetic separation production line of the steel slag, and be resourcefully utilized as raw materials or alloying materials for steelmaking.

[0021] 2. The inventors found that the temperature of the desiliconization and dephosphorization slag is around 1250°C - 1450°C. In this temperature range, dioxins in the fly ash can be completely decomposed. The H and C generated after the decomposition of dioxins can reduce the heavy metal oxides in the slag and fly ash. Chloride ions can form MgCl during the solidification of the steel slag with MgO in the steel slag and the waste coatings of the continuous casting machine. 2 , which can improve the gelling activity of the steel slag.

[0022] 3. The desiliconization and dephosphorization slag of the converter contains relatively large amounts of SiO 2 , which can react with zinc in the fly ash to form zinc silicate and reduce the volatilization pollution of zinc.

[0023] 4. The desiliconization and dephosphorization slag of the converter contains abundant CaO. CaO in the liquid steel slag can effectively inhibit the vaporization and evaporation of Cd, Pb, and Zn, which helps with their recovery after metallization.

[0024] 5. The un-reduced chromium in the fly ash can react with the added MgO to form a magnesium-chromite mineral phase, eliminating the poisoning factor of chromium in the fly ash.

[0025] 6. The steel slag belongs to over-burned Portland cement clinker. After resourceful utilization, the harmful substances that did not participate in the reaction are solid-solved after the resourceful utilization of the steel slag, achieving the harmless purpose of ore-forming and sealing. Detailed implementation method

[0026] The implementation process of the present invention is as follows:

[0027] A method for treating fly ash using the desiliconization and dephosphorization slag of converter steelmaking is implemented according to the following steps:

[0028] 1) Transport the waste coatings from the tundish of the continuous casting machine in the steel mill. The mass percentage of MgO in the waste coatings > 60% and send them to the dry powder pelletizing production line for use.

[0029] 2) Transport the fly ash from the incineration of domestic waste to the dry powder pelletizing production line for use.

[0030] 3) Mix the waste coating of the continuous casting machine and the fly ash generated from incinerating domestic waste evenly in a mass percentage ratio of 85:15, press them into pellets with a diameter of 30 - 50 mm on the dry powder pelletizing production line, and transport them to the converter production line for standby;

[0031] 4) Add the above-mentioned pellets to the slag ladle along with the slag flow during the slag tapping process of the converter, where the addition ratio of the pellets in each ton of converter steelmaking desiliconization and dephosphorization slag is 100 - 250 kg; or after the slag tapping of the converter is completed, add the said pellets to the slag ladle filled with converter steelmaking desiliconization and dephosphorization slag;

[0032] 5) Let the above slag ladle stand for 30 minutes, pour it into the hot splashing slag yard, continue to keep it warm for 2 hours, and then process it according to the normal hot splashing slag or hot steaming slag treatment process;

[0033] 6) After the slag treatment process is completed, the granular iron and medium-sized slag iron magnetically separated from the converter steelmaking desiliconization and dephosphorization slag are returned to steelmaking for resource utilization, and the tail slag is used as a raw material for building materials or road engineering for resource utilization.

Claims

1. A method for treating fly ash with converter steelmaking desiliconization and dephosphorization slag, characterized in that it is implemented according to the following steps: 1) Transport the waste coating of the tundish of the continuous caster in the steelmaking plant, where the mass percentage of MgO in the waste coating > 60%, to the dry powder pelletizing production line for standby; 2) Transport the fly ash from incinerating domestic waste to the dry powder pelletizing production line for standby; 3) Mix the waste coating of the continuous caster and the fly ash generated from incinerating domestic waste evenly in a ratio of 85:15 by mass percentage, press them into pellets with a diameter of 30 - 50 mm on the dry powder pelletizing production line, and transport them to the converter production line for standby; 4) Add the above pellets into the slag pot along with the slag flow during the converter slag discharging process, where the addition ratio of the pellets in each ton of converter steelmaking desiliconization and dephosphorization slag is 100 - 250 kg; or after the converter slag discharging is completed, add the pellets into the slag pot filled with converter steelmaking desiliconization and dephosphorization slag; 5) Let the above slag pot stand for 30 min, pour it into the hot - splashing slag yard, continue to keep warm for 2 h, and then process it according to the normal hot - splashing slag or hot - steaming slag treatment process; 6) After the slag treatment process is completed, the granular iron and medium - sized slag iron magnetically separated from the converter steelmaking desiliconization and dephosphorization slag are returned to the steelmaking for resource utilization, and the tail slag is used as a raw material for building materials or road engineering for resource utilization.