At first pass, this data might appear confusing, but when differences between cement kilns are taken into account, perhaps this data suggests that there is some type of destruction mechanism associated with some APCD systems. It would not be unreasonable to speculate on the role of increased alkalinity. Evidence for this comes from the comparison of dioxin emission concentrations right after the chain section in the kiln was revamped to dioxin emission concentrations when the chain section was thoroughly worn and nearing replacement time. The concentrations increased from when the chain section was new to when the chain section was well worn. Comparing the two extremes provided an opportunity to investigate the affect of a longer heat exchange zone within the kiln.
Preliminary indications are that the longer heat exchange zone promoted the formation of dioxins.
While not conclusive, the test data discussed here strongly indicates a different temperature relationship associated with dioxin formation in cement kilns than that currently promoted by EPA, yet the hydrocarbon concentration in some raw materials vs. dioxin formation data also confirms that the specific dioxin formation mechanisms are not fully understood. This discussion is almost exclusively based upon the data base that has been collected for municipal waste combustors. No direct relationship has been demonstrated for any of these parameters in cement kilns. This hypothetical MEI is assumed to be exposed to worst case emissions for seventy years but must exhibit no greater risk of cancer than one person in 100,000 people. It is difficult to imagine a more conservative estimate than this.