Study On Melting And Solidification Of Heavy Metals From Fly Ash Of Municipal Solid Waste Incineration

MSWI fly ash is defined as a hazardous waste because of its heavy metal leaching toxicity.As one of the methods of harmless disposal of fly ash,melting treatment can greatly reduce the toxicity of fly ash and the effect of reducing volume and weight is good,and the generated slag can be used at high value.This paper analyzes the physical and chemical properties of fly ash,investigates and analyzes the pilot scale test site of plasma gasification melting treatment of waste fly ash,explores the melting characteristics of the samples with different alkalinity and the solidification effect of the melting treatment on heavy metals.The process of fly ash processing is optimized by simulation calculation and the optimization scheme is put forward.It is found that the melting effect of fly ash is good,but because the melting temperature is too high,the thermal insulation material ZrO₂ in the furnace falls off,which leads to the reduction of the service life of the equipment.In this paper,the fly ash collected by the flue gas purification system of circulating fluidized bed furnace in a waste incineration power plant in North China and the coke obtained from the coking process of Inner Mongolia lignite were selected.The fly ash was mixed with coke powder and silica to form 8 kinds of composite samples with different alkalinity.Melting experiments were conducted to explore the melting characteristics of samples with different alkalinity and the solidification effect of heavy metals.According to the optimized conditions of melting experiment,the pilot site process was set up by Aspen Plus and simplified simulation operation was carried out.The influence of alkalinity on melting energy consumption and the distribution of heavy metals after melting were analyzed.It is found that the addition of coke can provide some energy for the melting process,change the composition of fly ash and reduce the melting temperature of fly ash.The solidification effect of water cooling treatment on heavy metals is better than air cooling treatment during melt cooling.The solidification rate of Cr,Zn and Ni with less volatile properties all reaches more than 70%,and the solidification rate decreases obviously with the increase of alkalinity.The leaching toxicity of all the slag is far lower than the standard of hazardous waste leaching,and the leaching toxicity of the slag after water cooling treatment is even lower.Due to the different melting boiling points of heavy metals in the melting process,heavy metals are partially volatilized into the flue gas after the complete melting of fly ash.In this paper,an optimization process scheme for actual melting treatment of fly ash is proposed:fly ash is pretreated with water washing for dechlorination,forming and drying,then molten slag is collected by melting and water cooling,and the flue gas is cooled step by step to collect the heavy metals in the flue gas.