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What is fly ash?
Small ash particles discharged during the combustion of fuel (mainly coal). Its particle size is generally 1 ~ 100μM. Also known as fly ash or soot. Fine solid particles in flue gas ash produced by fuel combustion. Such as fine ash collected from flue gas in coal-fired power plants. Fly ash is formed after pulverized coal enters the furnace at 1300 ~ 1500 ℃ and is cooled after being absorbed by the hot surface under the condition of suspension combustion. Due to the effect of surface tension, most of the fly ash is spherical, with smooth surface and small pores. Some of them collide with each other in the molten state and become honeycomb composite particles with rough surface and more edges and corners. The chemical composition of fly ash is related to coal composition, coal particle size, boiler type, combustion condition and collection method. The emission of fly ash is directly related to the ash content in coal combustion. According to the situation of coal consumption in China, burning 1t coal produces about 250 ~ 300kg fly ash. If a large amount of fly ash is not controlled or treated, it will cause air pollution. Entering the water will silt the river, and some of the chemicals will cause harm to organisms and human bodies.
Current domestic treatment methods
1）Safe landfill method.
Enter the hazardous waste landfill for final disposal after appropriate disposal; Safe landfill method is a method of sending incinerated fly ash to a safe landfill after simple treatment on site, which is one of the safe and reliable means of incinerated fly ash treatment at present. However, the construction and operation costs of safe landfills remain high, which is difficult for waste incineration plants to bear. At the same time, the purpose of volume reduction and recycling cannot be achieved. Therefore, the application of this method will be gradually reduced in the future.
2）Curing and stabilization.
Cement solidification, asphalt solidification, melting solidification technology, chemical agent solidification and stabilization, etc. if the products treated by fly ash solidification and stabilization equipment meet the leaching toxicity standard or resource utilization standard, they can enter the ordinary landfill for landfill disposal or resource utilization; Solidification / stabilization landfill technology refers to the inclusion and coverage of toxic and harmful components in fly ash, or making it chemically inert, and then entering the landfill for landfill. The purpose of solidification / stabilization treatment is to make all polluting components in hazardous waste chemically inert or contained for transportation, utilization and disposal.
3）Extract heavy metals from fly ash.
Acid extraction, alkali extraction, biological and biological agents extraction, etc., after the extraction of heavy metals, fly ash and heavy metals can be used as resources respectively. Most of the above fly ash treatment methods have been applied to domestic waste incineration plants and achieved certain results.
4）Resource method.
The main component of fly ash belongs to the cao-sio2-a12o3-fe2o3 system, which is very close to the components of auxiliary cementitious materials such as blast furnace slag and fly ash. Therefore, many scholars, researchers and practitioners have carried out the research and application of replacing some cementitious materials with fly ash.
Treatment of fly ash by plasma gasification technology
The pilot plant of plasma high temperature melting technology has a design treatment capacity of 2~3t/d. The process flow of fly ash treatment is as follows: the DC arc plasma torch and coke are used to preheat the melting furnace. When the temperature in the furnace rises to 1250 ℃, the waste incineration fly ash, coke, flux and other auxiliary materials are put into the melting furnace by using a screw feeder. Fly ash and flux melt into liquid state in the furnace, and the molten slag flows out through the slag discharge port at the bottom of the furnace, and forms a glass body after water quenching and quenching. High temperature tail gas is discharged up to standard after purification treatment such as denitration, quenching, neutralization, adsorption, bag dust removal, etc.
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