Study On Pollutant Emission Characteristics Of Updraft-Pyrolysis And Combustion System Of Rural Domestic Waste

Decentralized domestic waste pyrolysis system can be used for on-site treatment of rural domestic waste.Pyrolysis technology can not only realize harmless treatment of rural domestic waste,but also convert rural domestic waste into combustible gas,so as to realize waste recycling.However,secondary pollution,including acid gas,organic pollutants and heavy metals,will be generated in the pyrolysis process of rural domestic waste.How to avoid the emission of pollutants has become a key issue in the treatment of rural domestic waste.In this paper,different batches of ash and flue gas samples produced during the operation of rural domestic waste pyrolysis furnace were analyzed to provide basic data analysis for secondary pollution control of rural domestic waste pyrolysis.The slag and fly ash were analyzed by XRF,XRD and SEM-EDX.The results showed that slag mainly contained CaCO₃ and SiO₂,while CaCO₃ was the main component in fly ash.At the same time,the distribution of Cl element was analyzed.No Cl element was found in the results of point energy spectrum of fly ash,while the content of Cl element in slag was about 3%.It was found that Cl element was mainly retained in slag in the form of inorganic chloride,including KCl,KClO₃,etc.Meanwhile,the leaching toxicity,content and speciation distribution of toxic heavy metals（Cu,Pb,Al,Zn,Cr）in slags and fly ash were detected.The results showed that the leaching toxicity of heavy metals in the slags did not exceed the limits in the identification standard for hazardous wastes leaching toxicity identification（GB 5085.3-2007）.And the smaller the slag particle size was,the higher the heavy metal content was.The highest contents of Cd was 33.1 mg/kg,which exceeded the control value of agricultural land soil pollution risk in"soil environmental quality standard for agricultural land soil pollution risk control"（GB 15618-2018）..Combined with the experimental results of improved three-step BCR sequence extraction,the unstable content of Cd was about 25%,which was easy to precipitate into the surrounding environment.The emission characteristics of various pollutants in flue gas were studied.The content of HCl and HF in the flue gas during the operation period exceeded the Standard for Pollution Control of Domestic Waste Incineration（GB 18485-2014）and"Integrated Emission Standard of Air Pollutants"（GB 16297-1996）.The maximum content of HCl and HF in the flue gas of pyrolysis furnace was 1009.9 mg/m³ and 178.6 mg/m³respectively.HCl in flue gas mainly came from the release of organic chlorine,so its content was mainly related to the furnace operating temperature.The liquid products in the operation period and pre-shutdown period of the pyrolysis furnace were collected by condensation and analyzed qualitatively by GC-MS.The results showed that the amount of various substances in liquid products was mainly affected by temperature.In order to reduce the generation of polycyclic organic compounds,it is advisable to ensure that the temperature of pyrolysis layer is higher than 500℃to promote the occurrence of secondary cracking reaction,so that the liquid product can be converted into small molecule combustible gas which is more easily controlled.