Research On Wet Pretreatment Of Municipal Waste Incineration Fly Ash

The paper which was based on the analysis and summary of the current wet pretreatment technologies explored the optimal process parameters combination on the removal rate of chlorine for representative Beijing fly ash in single factor and orthogonal experiments when leaching agents was deionized water.Then corresponding characterization analysis was carried out.Based on results of experiments above,optimized continuous countercurrent water-leaching process and corresponding simulation experiment were put forward for engineering applications and preliminary design and analysis was also conducted.The results showed that:(1)Laser particle size analyzer,X-Ray Fluorescence(XRF)and X-Ray Diffraction(XRD)were utilized to analyze the particle size distribution,elemental composition and mineral phase composition respectively.The results showed that fly ash was a kind of material with small particle size and possessed a strong capacity of adsorption and large specific surface area.Substances containing chlorine in the fly ash were mainly soluble chlorides like sodium chloride(NaCl)and potassium chloride(KCl).Characteristic of large specific surface area of fly ash made it easy to fully contact with the extraction agent and target of removing chlorides from fly ash were also relatively easy achieved.(2)Frequency,temperature,time of water-leaching and water to ash ratio were explored during single factor and orthogonal experiments.Then the effects of removing heavy metals and scale inhibition of filtrates after pretreatment of water-leaching were analyzed to direct resource utilization of the filtrates.a.Removal effect of chlorine was significantly obvious by the method of water-leaching treatment.The primary and secondary relationship between each factor affecting the removal effect of chlorine is determined as follows: temperature of water-leaching>water to ash ratio>time of water-leaching.And the optimum combination conditions were also determined as follows: time of water-leaching was 5min,water to ash ratio was 6mL/g(fly ash),temperature of water-leaching was 40? and frequency of water-leaching was one.b.Soluble heavy metal elements and trace amounts of dioxin would dissolve into the filtrates during process of removing chlorine through the method of water-leaching.However,concentration of each heavy metal element was far lower than the most strict emission concentration set by current “Integrated wastewater discharge standard(GB8978-1996)”.Additionally,concentration of dioxin was also lower than the limit set by “Standards for drinking water quality(GB5749-2006)”.Obviously,most of heavy metals and dioxin in fly ash were presented the insoluble state and the other which were not removed would be burned out or cured and stabilized in the crystal lattice at the condition of high temperature when co-processing of municipal waste fly ash in cement kiln were conducted.c.Filtrates after water-leaching exhibited chemical characteristics of high alkalinity and easily scaling.In order to prevent its negative effect on the normal operation of the follow-up equipment like conveying equipment,pipeline and evaporator,pH value of the filtrate was adjusted to 6.8~7.5 by adding quantitative hydrochloric acid solution.Result of static scale experiments showed that the amount of scale afer adding acid solution was65 mg/L while that before adding acid solution was 3082mg/L after the same 24 h.(3)Based on the operation of leaching and extracting of effective components from plant,process plan of continuous countercurrent pretreatment was put forward to remove chlorine during water-leaching process from fly ash.Corresponding simulation experiment under the condition of laboratoryverified the feasibility and efficiency of countercurrentpretreatment,on which the corresponding process plan was designed to be consisted of system for continuous countercurrent pretreatment of water-leaching on fly ash and resource utilization systems on filtrates and fly ash treated.And fly ash after wet pretreatment and filtrates were into different resource utilization system respectively.The crystalline salt could be sold for industry,while the condensed water could be recycled.Therefore,the process plan had good environmental,economic,and social benefits.