ORGANIC EMISSIONS FROM COCOMBUSTION OF MIXED PLASTICS WITH COAL IN A BUBBLING FLUIDIZED-BED BOILER

Mixed plastics can be burned safely with coal in modem fluidized bed boilers when flue gas carbon monoxide and dust emissions are kept low. The level of total emissions per thermal unit using plastics is smaller than when using coal. The proportion of mixed plastics incorporated into the plastics/coal fuel blends used in the tests did not affect the emission levels of polychlorinated dibenzodioxines and dibenzofurans (PCDD/Fs). The addition of limestone to the fluidized bed resulted in slightly increased PCDD/F levels, but these nevertheless remained significantly below 0.1 ng/Nm3 TE NORDIC. It is probable that the sulphur contained in the primary fuel poisoned the catalysts responsible for the formation of PCDD/F in all the plastics/coal blends. Limestone affected the formation of PCDD/F by binding sulphur in the gas phase or by increasing the calcium, tin, and chlorine levels of the fly ash. Only a small variation was observed in the copper concentrations of the fly ashes generated.