EXPERIMENTAL AND PRACTICAL RESEARCH OF DIOXIN EMISSION FROM THERMAL PROCESS OF CO-FIRING COAL AND MUNICIPAL SOLID WASTE

摘要

Differential density circulated fluidized bed incinerator was first developed by Institute for Thermal Power Engineering (ITPE) of Zhejiang University to burn Chinese MSW with low heat value and very complex components. The auxiliary fuel such as coal has to be used to keep stable burning and low pollutants emission in CFB incineration system at present. Experimental and practical research of dioxin emission from incineration process of co-firing coal and MSW are presented in this paper. The tubular furnace experiments using original MSW and mixed with coal within mass percentage rang 0～44% shows that, dioxin emission is strongly related to S/Cl molar ratio in fuel feeding. Dioxin emission inhibition efficiency of 95% is reached when coal was mixed at 16% mass percentage, a higher percentage of coal only led to a slight increase in inhibition efficiency. It seems reasonable for the guideline setting the coal mixing mass percentage no more than 20% when applying co-firing incineration technology. Comparing the PCDD/Fs concentration in fly ash from stoker incinerators and CFB co-firing incinerator, CFB co-firing fly ash is found to have very low PCDD/Fs concentration as 240 ng I-TEQ/kg, which is within the range of guideline values for residential area soil in most countries. Several influencing factors on dioxin formation in fly ash were discussed here. Practical dioxin emission tests on several large-scale using CFB incinerators co-firing technology developed by Zhejiang University showed that dioxin emission in stack gas was dramatically lower than 0.1 ng I-TEQ/Nm 3 . The dioxin inhibition mechanisms for co-firing processes are also discussed briefly in this paper. The experimental and practical results of dioxin emission strongly suggest the dioxin-suppressing phenomenon when MSW was co-fired with coal, and CFB co-firing technology can serve as the main thermal treatment method for Chinese MSW with highly inhibition of potential dioxin emission.