Method for treating fly ash by utilizing ironmaking slag

Abstract

The invention discloses a method for treating fly ash by utilizing ironmaking slag, and relates to the two technical fields of ironmaking slag treatment technology and resource utilization of fly ash generated by waste incineration. According to the method, an innovative technological method is adopted, in the ironmaking slag treatment technological process, the fly ash serves as a tempering raw material of the ironmaking slag and is added into the high-temperature ironmaking slag, harmless treatment is conducted on the fly ash through the high temperature of the ironmaking slag, and the fly ash is converted into a constituent part of the ironmaking slag; harmless conversion and subsequent resource utilization of the fly ash in the ironmaking slag treatment process are achieved, and effective utilization of ironmaking slag heat energy is achieved.

Description

Technical Field

[0001] The invention relates to a method for treating fly ash by utilizing iron-making slag, and relates to two technical fields: an iron-making slag treatment process and resource utilization of fly ash generated by garbage incineration. Background Art

[0002] The solid residue after waste incineration 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 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 fly ash from the incineration of domestic waste) in the National List of Hazardous Wastes. It needs to be harmlessly treated in advance 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 ironmaking slag in synergistic fly ash resource utilization.

[0004] Blast furnace slag is a byproduct of smelting pig iron. When smelting iron in a blast furnace, raw materials such as iron ore, fuel (coke) and flux (limestone and dolomite) need to be added. When the furnace temperature reaches 1400℃~1600℃, the flux reacts with the iron ore at high temperature to become liquid phase, and the gangue, ash, flux and other impurities that cannot enter the pig iron form a slag with good fluidity. Due to different densities (molten iron 6.8~7.0g / cm 3 , slag 2.2~3.2 g / cm 3 ) and separated from the molten iron, the slag floating on the molten iron in the liquid phase is separated by the slag avoider and discharged from the slag outlet.

[0005] There are two main treatment processes for ironmaking slag: hot pouring treatment (dry slag) and water quenching treatment. There are four main water slag processes: bottom filtration, Inba process, Lhasa process, and Tula process.

[0006] Literature review (1) Gao Yang, Gui Yongliang, Song Chunyan, Hu Binsheng, Wang Yawen, five authors published a paper entitled "Current Status and Prospects of Sensible Heat Recovery of Blast Furnace Slag" in the first issue of "Mineral Comprehensive Utilization" in 2018. The paper states: "The traditional water quenching method in my country does not recover the sensible heat of the slag, and a large amount of heat is lost in vain. In response to this situation, domestic and foreign researchers have conducted many experiments, which can be divided into two directions: physical heat exchange method and chemical recovery method. The physical heat exchange method mainly collects blast furnace slag through specific energy carriers to achieve sensible heat recovery. The chemical recovery method directly uses slag and sensible heat to produce high value-added products. Compared with the former, the chemical recovery method is more efficient in recovering sensible heat and can better reflect the comprehensive utilization of blast furnace slag." (2) Wang Haifeng, Zhang Chunxia, ​​Qi Yuanhong, Dai Xiaotian, Yan Dingliu and five authors published a paper titled "The Current Status and New Development Trends of Blast Furnace Slag Treatment Technology" in the 6th issue of "Steel" magazine in 2007. The paper states: "The traditional blast furnace slag water treatment technology has the disadvantages of large water consumption, environmental pollution, air and water pollution, and the inability to recover heat energy. It is proposed to develop a new dry method for blast furnace slag treatment, which can not only greatly save new water, but also recover the sensible heat of blast furnace slag. In addition, after granulation, the blast furnace slag can achieve the same effect as the traditional water treatment of blast furnace slag." According to the above literature discussion, there is currently no process technology that utilizes the waste heat of ironmaking slag to synergistically treat fly ash. Summary of the invention

[0007] The purpose of the present invention is to provide a method for treating fly ash using iron-making slag, which can utilize the waste heat of the iron-making slag to synergistically treat the fly ash produced by the municipal waste incinerator, thereby achieving the technological goal of fully absorbing the urban fly ash in the steel plant, which is beneficial to the coordinated development of the municipal waste incineration industry and urban steel enterprises.

[0008] The technical solution adopted by the present invention is a method for treating fly ash using ironmaking slag, which is implemented according to the following steps: 1) First, purchase calcium carbonate powder with a particle size of 0.5-1.0 mm, and then transport it to the dry powder pelletizing production line for use; 2) Purchase waste edible oil (commonly known as gutter oil) and transport it to the dry powder pelletizing production line for use; 3) After the fly ash, waste edible oil and calcium carbonate powder are mixed evenly in a mass percentage of 90:5:5, they are pressed into 5mm-10mm pellets using a high-pressure dry powder pelletizing machine and transported to a 2500m 3 Standby near the blast furnace slag outlet; 4) When the iron-making slag is discharged, add the above pellets to the liquid iron-making slag in the slag discharge ditch, add 50-150kg of the above pellets per ton of iron-making slag, and the rest of the iron-making slag treatment process remains unchanged.

[0009] The inventor discovered the following scientific phenomena through research: 1. The slag tapping temperature of ironmaking is as high as 1400-1600℃, the specific heat capacity of the slag is about 1.2KJ / (Kg·℃), and the basicity of the ironmaking slag is about 1.0. It is an alkaline low melting point slag with good fluidity, which is conducive to adding fly ash to liquid ironmaking slag and utilizing the physical thermal decomposition of dioxins by the ironmaking slag to achieve the purpose of resource utilization of ironmaking slag heat energy; 2. The formation conditions of fly ash are at high temperatures of about 850℃-1100℃ in the waste incinerator. Under such high temperature environment, the crystal structure of each mineral composition in the fly ash is coarse. When the fly ash is added to the high-temperature ironmaking slag, a slag-forming reaction of mineral recombination occurs between the fly ash and the ironmaking slag. The required chemical reaction heat is less, which can satisfy the secondary slag-forming reaction between the fly ash and the ironmaking slag. 3. Ironmaking slag is a reducing slag, and small iron beads formed during the ironmaking process are dispersed in the slag, accounting for about 2% to 10% of the ironmaking slag. These small iron beads can be recycled through magnetic separation during the resource utilization of ironmaking slag, and most ironmaking slag contains vanadium and titanium oxides. This feature is conducive to the heavy metals in fly ash being reduced and melted into small iron beads for recovery, which is conducive to the cracking and harmless transformation of dioxins in fly ash; 4. Based on the above findings, the inventors used fly ash as the main raw material, added 5% by mass of calcium carbonate powder to the fly ash, used waste edible oil as a binder, and used a dry powder briquette machine to produce fly ash into 5-10 mm pellets. During the slag discharge process of the iron-making blast furnace, the pellets were added to the iron-making slag. The high temperature of the iron-making slag was used to decompose the dioxins in the fly ash. The alkaline characteristics of the iron-making slag were used to reduce the heavy metals in the fly ash and melt them into the small metal iron beads in the iron-making slag to achieve the purpose of recycling and utilization, thereby realizing the integrated development of coordinated treatment of hazardous waste in the iron-making industry.

[0010] The innovative features of the present invention are as follows: 1. The inventor discovered the scientific phenomenon that high-temperature alkaline ironmaking slag can promote the harmless transformation of harmful heavy metal elements in fly ash and decompose dioxins and organic matter. The fly ash is added to the ironmaking slag for harmless transformation, and finally the fly ash is converted into a part of the ironmaking slag, thus realizing the resource utilization of fly ash. This is an industry-first technology. 2. In order to achieve the rapid decomposition of dioxins by adding fly ash to ironmaking slag, the inventors used waste edible oil as a binder and added calcium carbonate to make fly ash into balls. The waste edible oil quickly cracked and burned after being heated, and the calcium carbonate broke up after being heated, so as to increase the reaction interface for the chemical reaction between the fly ash balls and the liquid ironmaking slag and improve the reaction speed. 3. The added calcium carbonate powder is used as a chlorine-fixing agent after the dioxins in the fly ash are decomposed, and the oxides of Ti and V in the ironmaking slag can also act as chlorine-fixing agents, which can eliminate the possibility of re-synthesis of dioxins after the dioxins in the fly ash are decomposed; 4. The inventors took advantage of the fact that iron-making slag contains 2% to 10% small iron beads (most of which are liquid), and reduced the heavy metals in the fly ash so that they can be melted into the small iron beads and recycled in the subsequent magnetic separation production line.

[0011] The mineral structure of fly ash is similar to that of iron-making slag. After eliminating harmful substances in fly ash, fly ash can be converted into components of iron-making slag and utilized as a resource of iron-making slag, thus achieving the purpose of resource utilization of fly ash and having great environmental significance.

[0012] The beneficial contributions of the present invention are as follows: 1. The fly ash is synergistically treated by utilizing the high-temperature liquid slag from ironmaking, which realizes the harmless transformation of fly ash without affecting the ironmaking slag treatment process, saves the treatment cost of hazardous waste, and solves the land occupation contradiction caused by the current use of most fly ash for landfill, which is of great significance to the development of society; 2. The amount of ironmaking slag generated is large. The amount of ironmaking slag generated by producing one ton of molten iron is usually 250 to 500 kg. A 5 million ton long-process steel enterprise generates 1.25 to 2.5 million tons of ironmaking slag. The ironmaking slag can be used to recycle 60,000 tons to 250,000 tons of fly ash each year, realizing the process goal of urban steel mills to fully consume urban fly ash, which is beneficial to the coordinated development of urban waste incineration industry and urban steel enterprises. DETAILED DESCRIPTION

[0013] The embodiment of the present invention is based on a steel enterprise with a capacity of 2500m 3 Take the blast furnace as an example. A method for treating fly ash using ironmaking slag is implemented according to the following steps: 1) First, purchase calcium carbonate powder with a particle size of 0.5-1.0 mm, and then transport it to the dry powder pelletizing production line for use; 2) Purchase waste edible oil (commonly known as gutter oil) and transport it to the dry powder pelletizing production line for use; 3) After the fly ash, waste edible oil and calcium carbonate powder are mixed evenly in a mass percentage of 90:5:5, they are pressed into 5mm-10mm pellets using a high-pressure dry powder pelletizing machine and transported to a 2500m 3 Standby near the blast furnace slag outlet; 4) When the iron-making slag is discharged, add the above pellets to the liquid iron-making slag in the slag discharge ditch, add 50-150kg of the above pellets per ton of iron-making slag, and the rest of the iron-making slag treatment process remains unchanged.

Claims

1. A method for treating fly ash using ironmaking slag, characterized in that Follow these steps to implement: 1) First, purchase calcium carbonate powder with a particle size of 0.5-1.0 mm, and then transport it to the dry powder pelletizing production line for use; 2) Purchase waste edible oil and transport it to the dry powder pelletizing production line for use; 3) After the fly ash, waste edible oil and calcium carbonate powder are mixed evenly in a mass percentage of 90:5:5, they are pressed into 5mm-10mm pellets using a high-pressure dry powder pelletizing machine and transported to a 2500m 3 Standby near the blast furnace slag outlet; 4) When the ironmaking slag is tapped, add the above pellets to the liquid ironmaking slag in the blast furnace slag ditch, 50-150 kg of the above pellets are added to each ton of ironmaking slag, and the rest of the ironmaking slag treatment process remains unchanged.