PCDD/Fs inhibition for co-firing municipal solid waste and coal in circulating fluidized bed incinerators

Series of industrial and laboratory experiments are presented in this paper to discuss the PCDD/Fs inhibition for co-firing municipal solid waste and coal in circulating fluidized bed incinerators. Comparing the PCDD/Fs concentration in fly ash from stoker incinerators and CFB co-firing incinerator, the fly ash from CFB was found to have PCDD/Fs concentration as low 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 PCDD/Fs formation for different combustion mode were discussed here, Practical PCDD/Fs emission tests in several industrial-scale incinerators showed that PCDD/Fs emission in stack gas was dramatically lower than 0.1 ng I-TEQ/Nm(3) with no activated carbon powder injection in air pollution control devices (APCDs). In the laboratory research, experiment was done in a tubular furnace 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 co-firing combustion experiments using original MSW and coal in a tubular furnace showed that, PCDD/Fs emission was strongly related to S/Cl molar ratio in the fuel feeding. The PCDD/Fs emission inhibition efficiency 95% was 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 present guideline setting the coal mixing mass percentage no more than 20% when applying co-firing incineration technology. The PCDD/Fs inhibition mechanisms for co-firing processes are also discussed briefly in this paper.