Characterization Of Particulate Matter From Sludge Incineration And Formation Mechanism Of PM2.5

Incineration processes are commonly employed for the treatment of sewage sludge due to its advantage of mass and volume reduction,energy recovery and hazardous components sterilization.However,the pollution of particulate matter during incineration is a hot topic.The sludge incineration particle was separated into five different sizes:<1?m,1-2.5?m,2.5-10?m,10-50?m,>50?m.The leaching characteristics of heavy metals in particulate matter were studied by HJT 299-2007-Sulfuric acid nitric acid method,toxicity characteristic leaching procedure?TCLP?and European standard protocol?EN12457-3?.The melting volatilization and kinetics of particulate matter were analyzed by TG-DSC integrated thermal analyzer.The formation mechanism of PM2.5 in sludge incineration flue gas was studied using the method of apparent composition analysis and characteristic time estimation.The results show that,Fe₂O₃-Al₂O₃-CaO-Si O₂-Metal Oxide provide a carrier and active space for the adsorption of heavy metals.The leaching amount of heavy metals decreased with the increasing of particle size.The highest leaching amount of Cu in TCLP was 318mg/kg and the highest leaching amount of Zn HJT 299-2007 method was 195.03 mg/kg.The OPTI of the particle size less than 10?m is greater than the OPTI value of the original particle.It is indicated that the comprehensive toxicity of heavy metal leaching of particles less than 10?m is stronger and more harmful.With the increase of particle size,the initial temperature of the melting volatilization increased,and the apparent activation energy gradually increased:97720.82 k J/mol,99307.27 k J/mol,100802.37 kJ/mol,108634.98 kJ/mol and 107314.32kJ/mol,indicating that the small particle size particles have high reactivity.Ultrafine particles?<100 nm?are formed and grown mainly by volatile-nucleation-condensation-coagulation with volatile metal elements?Na and K?and a very small amount of inorganic compounds?SiO₂ and CaO?.Homogeneous nucleation of the critical nucleation diameter is 0.419 nm,characteristics time of nucleation is 0.1268 ms,which occurred in the entire process of particle generation and growth.When the particle size is less than 1 nm,the characteristic time of heterogeneous condensation is less than the characteristic time of coagulation.As the ultrafine particles size increases from 1nm to 200 nm,the characteristic time of coagulation increases dramatically from 10 ms to 1000 ms.So coagulation becomes the main mechanism of particle growth.