Study on PCDD/Fs Suppressing Phenomenon for Co-Firing Processes of Coal and Municipal Solid Waste

摘要

Incineration as a method of reducing Municipal Solid Waste (MSW) volume and recovery of energy has been developed gradually in China. More attention is now paid on polychlorinated dibenzo-p-PCDD/Fs and polychlorinated dibenzofurans (PCDD/Fs) emission form MSW incinerator. Because of the low caloric value and high moisture content for Chinese MSW, coal and MSW co-firing is used to help self-sustained combustion process. The co-firing process has been found to suppress PCDD/Fs formation during combustion and gas cooling process. Many kinds of experimental data were presented here to confirm the PCDD/Fs suppressing functions from coal and MSW co-firing process. Comparing the PCDD/Fs concentration in fly ash from grate-fired incinerator and CFB co-firing incinerator, fly ash from CFB co-firing was found to have very low PCDD/Fs concentration as 0.24 ng I-TEQ/g. Several impacts on PCDD/Fs formation in fly ash from different incinerators were discussed. Another experiment was done in a tubular stove using pentachlorophenol (PCP) and coal, and the PCDD/Fs suppressing efficiency is up to 98% if only coal was co-fired. Three aspects of reasons were proposed to explain such high suppressing phenomenon. The last experiments showed in this paper were conducted in the same tubular stove using raw MSW and coal. It also strongly revealed the PCDD/Fs suppressing phenomenon that about 20% coal co-firing with raw MSW could get the high suppressing efficiency up to over 95%, and further enhancement of co-fired coal mass percentage promoted little suppressing. From these experiments' results, co-firing suppressed much more PCDDs, which suggested co-firing greatly suppressed the processes of precursors forming PCDD/Fs via gas phase formation.