Papers by Keyword: Dioxins

Abstract: The article discusses solutions for environmental safety of solid waste incineration technology. Methods of flue gases purification have been evaluated, and two directions of an air purification technology have been considered. The first direction is the precipitation method to remove fly ash, the second direction is the using physic-chemical treatment of toxic substances. Municipal solid waste is a multicomponent mixture, when it is burned, diverse group of substances with different physic-chemical properties produces into the exhaust gases: carbon monoxide, sulfur dioxide, nitrogen oxides, fluorine and chlorine compounds, polychlorinated biphenyls, chlorophenols, polycyclic aromatic hydrocarbons and dioxins. The fly ash that is produced in furnaces contains heavy metal particles. The chemical composition of emissions from waste incineration plants depends on the incineration technology, the morphological composition of waste, and the effective protection against exposure to hazardous chemicals. The authors propose a new approach to the selection of treatment equipment using multi-criteria analysis. Fabric filters, cyclones, scrubbers, electrostatic precipitators, wet cleaning devices were compared to eight criteria. The same criteria were used to compare the efficiency of absorption, adsorption, thermocatalytic treatment, selective catalytic reduction and thermal afterburning.

Abstract: The emission characteristics of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) were evaluated from a grate-type municipal solid waste incinerator (MSWI). The stack flue gas, fly ash and bottom ash samples were sampled and analyzed. Results indicated that the flue gas, fly ash and bottom ash presented their mean dioxin levels of 0.0723 ng I-TEQ/Nm³, 0.614 ng I-TEQ/g and 13.33 ng I-TEQ/kg respectively. The PCDD/Fs congener patterns, in flue gas, fly ash and bottom ash, showed large similarities in both concentration and I-TEQ profiles. The de novo synthesis plays a dominant role in the low-temperature post-combustion zone.

Abstract: In this paper, a small medical waste pyrolysis furnance, which could disposal 1t wastes, is designed for the safe disposal of medical wastes, by in-depth research of pyrolysis, detailed calculation analysis, and considering the experimental results and other factors in general. The flue gas treatment system of the small medical waste pyrolysis furnance is designed applying 3T principle, and the dioxin’s later synthesis is controlled, so the dioxin emissions problem is also resolved. The results show that the small furnance has reasonable configuration, works reliably, and it could self-support freely, its emissions meet the national standards for the dioxin emissions 0.213 ng/m³.

Abstract: With government-depth recognition of scientific development and improvement of people’s living environment, treatments of MSW has become one of the key points of environmental protection. Herein, the formation paths of dioxins and heavy metals during the thermal treatment of MSW were presented detailed, the countermeasures including source control, thermal treatment technology and gas and ash terminal-treat for the emissions control were proposed either.

Abstract: Mesoporous TiO₂ thin films have been prepared with so1-ge1 method by using tetrabutyl titanate(TBT) as precursor and PEG (Molecular weight 3000)as template．The XRD spectrum of the samples of the thin films indicated that the sample crystallized into anatase phase under the 500°C．And the photocatalytic degradation study of dioxins from MSW ash had been carried out. The result showed that the Mesoporous TiO₂ thin films with anatase phase had high photocatalytic efficiency and was in favor of the regeneration and reuse.

Abstract: Co\N codoped mesoporous TiO2 thin films that adhered to the glass slides were prepared with normal temperature complexation method by using tetrabutyl titanate(TBT) , triethylamine(TEA), cobalt dichloride hexahydrate．The XRD patterns of the samples of the thin films indicated that the sample appeared sharp titanium ore and rutile characteristic peaks and characteristic peaks became wide．And the photocatalytic degradation study of dioxins from MSW ash had been carried out. The result showed that the mesoporous TiO2 thin films Co\N codoped had high photocatalytic efficiency and was in favor of the regeneration and reuse.

Abstract: Dioxin is the unintentional synthesized extreme toxic Persistent Organic Pollutants (POPs) in the sintering process. The process of dioxin’s formation and decomposition in the sintering bed layer, as well as the reaction mechanism and related theoretical model of different temperature sector were expounded in this paper. The correlated research indicated that: in the low temperature sector (200-500°C), chlorobenzene and chlorphenol are the representation precursors of dioxin’s precursors catalytic reaction, the dioxin formed in this temperature sector cased by the “de novo” under catalyst (like Cu²⁺) on the surface of smoke particles, its catalytic mechanism of the same phases and heterogeneous all satisfied the four-step reaction model; high-temperature gas phase reaction mechanism of dioxin satisfied the first-order kinetic model, the formation of gas related with suitable precursors, it is the result of chlorinated precursors’ pyrolytic rearrangement like chlorobenzene and chlorophenol in the temperature sector 500-800°C in the gas.

Abstract: Dioxins are extremely toxic, and it is difficult to treat them with the conventional method. When irradiated by light, photocatalysts generate strong oxidative potential and decomposes almost all organic substances containing dioxins to water, carbon dioxide and others. Silica-gel has high adsorptive activity as well as large surface area, and it is transparent to ultraviolet light. Photocatalytic silica-gel was prepared by a dip coating method using TiO2 sol obtained by hydrolyzing titanium tetraisopropoxide on silica-gel bead (about 3mm in diameter) and heat-treated at 550°C. Since the surface area of the photocatalytic silica-gel is 300m2/g, the reaction area is large and allows the highly efficient decomposition of harmful organic substances, unpleasant odors and colored matters contained in waste water. The photocatalytic apparatus for decomposition of dioxins in emission gas from waste incinerators is composed of the catalyst layer consisting of 95dm3 photocatalytic silica-gel and 16 units of UV lamp. The photocatalytic apparatus was connected to the bypass line led from the outlet duct of cyclone, and the concentration of dioxins in the exhaust gas was measured. Decomposition test of dioxins in scrubber water was also performed using a photocatalytic apparatus with 150g photocatalytic silica-gel and 8 units of UV lamp. After 0.5dm3 of scrubber water containing dioxins was circulated in the photocatalytic apparatus for 1, 2 and 24 hour, each concentration of dioxins in the water was measured. As a result, the removal efficiency over 99% of dioxins in emission gas and scrubber water from waste incinerators has been obtained.