Study On The PCDD/Fs Emission Characteristics Of Cement Kilns Co-processing Solid Wastes Such As Aged Refuse

In order to promote the rapid development of solid waste co-processing technology in China's cement kilns.From the perspective of pollutant control,this paper uses a combination of laboratory research and engineering applications to study the emission characteristics of PCDD/Fs and heavy metals in flue gas by co-processing solid waste in cement kiln.This study got some valuable reference data and conclusions,including:?1?The physical and chemical characteristics of aged refuse and simulated refuse-derived fuel had been detected,including composition,calorific value,chlorine content,heavy metal content,proximate analysis,ultimate analysis and thermogravimetric analysis.Among them,the aged refuse has a chlorine content of>1%and a Cu content of>200 mg kg^-1,but the calorific value is as high as 25 MJ kg^-1,so it has the advantage of energy utilization.?2?In this paper,the production and emission characteristics of PCDD/Fs and heavy metals in the flue gas at various levels of the cyclone preheater and in the decomposition furnace when different aged refuse and RDF are added at different points in the cement kiln are carried out in a small-scale cement kiln.The study found that the emission concentration of the first-stage heavy metals in the cyclone preheater all increased,of which Hg increased by 2.5-20 times.The amount of generated PCDD/Fs also increased with the landfill age and the highest is 0.72 ng I-TEQ m^-3.?3?In this paper,our laboratory collected 16 groups flue gas samples of cement kilns without co-processing solid waste and 18 groups co-processing solid waste,and studied the characteristics and distribution of PCDD/Fs emissions.The statistical analysis methods such as principal component analysis and cluster analysis are used to further compare and study the differences in the PCDD/Fs emission characteristics of co-processing solid waste or not.The study found that the toxic equivalent of PCDD/Fs before co-processing of solid waste in cement kilns is between 0.006-0.828 ng I-TEQ m^-3,with an average value of 0.115 ng I-TEQ m^-3;the toxic equivalent of co-processing of solid waste is 0.002-0.559 ng I-TEQ m^-3,the average is 0.12 ng I-TEQ m^-3.The reason why the average value exceeds the national standard of 0.1 ng I-TEQ m^-3 is that the PCDD/Fs emissions of individual plants exceed 0.5 ng I-TEQ m^-3,which improves the overall average value.Therefore,the average value for all research results cannot objectively reflect the true emission levels of all plants.Overall,the median PCDD/Fs toxic equivalent concentration in flue gas after co-processing of solid waste increased from 0.015 to 0.033 ng I-TEQ m^-3.In terms of the PCDD/Fs congener distribution,when without co-processing solid waste,the PCDD/Fs mass concentration contribution in flue gas mainly came from highly chlorinated PCDD/Fs,while the toxic equivalent contribution mainly came from 2,3,4,7,8-PeCDF;After co-processing of solid waste,except for the mass concentration contribution rate of low-chlorinated PCDD/Fs congeners of individual plants are increased,other highly chlorinated are still the main ones.The toxic equivalent contribution of 2,3,7,8-TCDF in some cement kiln is very large,even exceeding 2,3,4,7,8-PeCDF.