Adsorption of Dioxins on the Entering Raw Meal

Abstract

Cement kilns still emit considerable amounts of dioxins, more precisely polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) whether these kilns co-incinerate waste, or not. The emission level depends on the quality of meals (composition of mixed and ground limestone and shale or clay) on the one hand, the co-firing of waste on the other. Waste can be fired at the lower, discharge end of the rotary kiln, or be introduced to mid-kiln, at the kiln entrance, in the calcination section, or even further downstream along the path of the combustion gases. The temperature/time history of these combustion gases and of the meal are decisive factors in the formation, collection and destruction of dioxins. Still, very little is known on the extent and location of such phenomena along the path of meal, in countercurrent to that of combustion gases. In this study, the adsorption effects of the entering meal on the flows of dioxins were fully investigated in a 4500 ton day -1 clinker production line. The meal was characterised by its Ultimate Analysis, its specific surface and by XRD-and EDS-analysis, indicating that CaO, CaCO 3 and SiO 2 were the main compositions of it. In laboratory experiments, it was observed that the entering raw meal could indeed adsorb 2,3,7,8-substituted PCDD/Fs from combustion gas thus cleaning the raw gas even before its treatment by dust collection. The results revealed that meal could adsorb 2,3,7,8-PCDD/Fs from RDF incineration flue gas, with an efficiency up to 84.8% in wt. units and 71.0% in I-TEQ units.

Suppression of PCDD/Fs by Raw Meal in Cement Kilns

“…Moreover, the formation of PCDD/Fs might be suppressed under an alkaline atmosphere as in the cement kilns with -mainly CaCO 3 and CaO as neutral or basic raw meal (Jing et al, 2015). A high reduction efficiency of PCDD/Fs (84.8%) can be achieved when the flue gas passed through the raw mill of cement kiln due to the existence of CaCO 3 (Zhan et al, 2016a). CaO addition was also proven efficiently to enhance the reduction rate of PCDD/Fs in fly ashes during the thermal treatment at a low temperature, as well as suppress the formation of PCDD/Fs .…”

“…At the same time, the domination of PCDFs shifted from 1,2,3,4,6,7,8-HpCDF to TCDF. The weight average level of chlorination of PCDD/Fs increased from 6.7 to 7.9, indicating a weakened dechlorination effect of PCDD/Fs in the presence of the raw meal ( Zhan et al, 2016a). In I-TEQ units, PCDFs contributed 64% of total toxicity, with 2,3,4,7,8-PeCDF was the largest single contributor, accounting for 39%.…”

Effects of Surfactants on the Removal of Carbonaceous Matter and Dioxins from Weathered Incineration Fly Ash

“…Recently, incineration treatment has become the preferred option for waste treatment because of it yields significant volume reduction (approximately 90%) and mass reduction (approximately 70%), as well as a reduction in the toxicity of infectious materials after incineration (Zhan et al, 2016). However, incineration produces a large amount of medical waste incinerator (MWI) fly ash, which is dust-like particles and has high content of chlorine, dioxin and heavy metal.…”

Cement solidification of the tailings after flotation of medical waste incinerator fly ash

“…Incineration is an effective approach to realize the harmlessness and reduction of medical wastes and has become popular in China [1]. Because of the presence of a large number of chlorine-containing plastics and disposable disinfectants (such as NaCl and KCl), the chlorine level in the typical medical wastes is 1.1-2.1%, which is approximately twice as high as that in domestic wastes [2].…”