Emissions of metals and polychlorinated dibenzo(p)dioxins and furans (PCDD/Fs) from Portland cement manufacturing plants: Inter-kiln variability and dependence on fuel-types

Emissions from Portland cement manufacturing facilities may increase health risks in nearby populations and are thus subject to stringent regulations. Direct testing of pollutant concentrations in exhaust gases provides the best basis for assessing the extent of these risks. However, these tests (i) are often conducted under stressed, rather than typical, operating conditions, (ii) may be limited in number and duration, and (iii) may be influenced by specific fuel-types and attributes of individual kilns. We report here on the results of more than 150 emissions-tests conducted of two kilns at a Portland cement manufacturing plant in Portugal. The tests measured various regulated metals and polychlorinated dibenzo(p)dioxins and furans (PCDD/Fs). Stack-gas concentrations of pollutants were found to be highly variable, with standard deviations on the order of mean values. Emission rates of many pollutants were higher when coal was used as the main kiln fuel (instead of petroleum coke). Use of various supplemental fuels, however, had little effect on stack emissions, and few statistically significant differences were observed when hazardous waste was included in the fuel mix. Significant differences in emissions for some pollutants were observed between the two kilns despite their similar designs and uses of similar fuels. All measured values were found to be within applicable regulatory limits.

Research highlights
► We evaluated extensive air toxics emissions data from two Portland cement kilns.
► European Union emission limit values were met in all (> 150) tests.
► Emission rates of most contaminants were greater when the primary fuel was coal rather than petroleum coke.
► Use of waste-derived fuels, including hazardous waste, had little effect on emission rates.
► Small differences in kiln design had significant effects on emission rates of mercury and polychlorinated dibenzo(p)dioxins and furans (PCDD/Fs).