Influence of Postcombustion Temperature Profiles on the Formation of PCDDs, PCDFs, PCBzs, and PCBs in a Pilot Incinerator (original) (raw)
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Potential Role of Chlorination Pathways in PCDD/F Formation in a Municipal Waste Incinerator
Environmental Science & Technology, 2004
The role of chlorination reactions in the formation of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) in a municipal waste incinerator was assessed by comparing predicted chlorination isomer patterns with incinerator flue gas measurements. Complete distributions of PCDD and PCDF congeners were obtained from a stokertype municipal waste incinerator operated under 13 test conditions. Samples were collected from the flue gas prior to the gas cleaning system. While total PCDD/F yields varied by a factor of 5 to 6, the distributions of congeners were similar. A conditional probability model, dependent only on the observed distribution of monochlorinated isomers, was developed to predict the distributions of polychlorinated isomers formed by chlorination of dibenzo-p-dioxin (DD) and dibenzofuran (DF). Agreement between predicted and measured PCDF isomer distributions was high for all homologues, supporting the hypothesis that DF chlorination can play an important role in the formation of PCDF byproducts. The PCDD isomer distributions, on the other hand, did not agree well with model predictions, suggesting that DD chlorination was not a dominant PCDD formation mechanism at this incinerator. This work demonstrates the use of PCDD/F isomer patterns for testing formation mechanism hypotheses, and the findings are consistent with those from other municipal waste combustion studies.
Chemical inhibition of PCDD/F formation in incineration processes
Science of The Total Environment, 2004
This review summarises results of our pilot-scale experiments to find suitable inhibitors for preventing the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDyF) during waste incineration and to specify the role of the main factors affecting the inhibition process, and is based on doctoral dissertation of . Results of previous experiments reported by other researchers are also presented and compared with ours. The detailed aims of our experiments were (1) to compare the effects of different inhibitors on PCDDyF formation during incineration in a pilot plant, (2) to investigate the role of the particle size distribution of the flue gas on the inhibition of PCDDyFs, and (3) to find the main parameters affecting PCDDyF inhibition in waste incineration. Prevention of the formation of PCDDyFs with chemical inhibitors and the effects of different supply points, feed temperatures and process parameters were studied in a pilot scale incinerator (50 kW) using light heating oil and refuse-derived fuel as test fuels. Various concentrations of the gaseous inhibitors (sulfur dioxide, ammonia, dimethylamine and methyl mercaptan) were sprayed into the flue gases after the furnace, in addition to which urea was dissolved in water and injected in at different concentrations. The residence time of the flue gas between the furnace and the PCDDyF sampling point was varied in the tests. In another set of urea tests, urea-water solutions at three concentrations were mixed with the RDF prior to incineration. PCDDyF and chlorophenol concentrations, together with other flue gas parameters (e.g. temperature, O , CO, CO and NO), were analysed in the cooling flue gases. The gaseous and liquid 2 2 inhibitors both notably reduced PCDDyF concentrations in the flue gas, the reductions achieved with the gaseous inhibitors varying from 50 to 78%, with dimethyl amine the most effective, while that produced with urea was up to 90%. The PCDDyF reductions were greater at increased inhibitor concentrations and with increased residence time of the flue gas between the furnace and the sampling point. PCDDyF concentrations in the particle phase decreased much more markedly than those in the gas phase. The urea inhibitor did not alter the particle size distribution of the PCDDyFs when the amount of inhibitor was adequate. Chemical inhibitors seem to offer a very promising technique for preventing the formation of PCDDyFs in waste incineration. The addition of urea to the fuel before combustion proved to be very effective approach and could be a useful technique even in the full-scale incinerators. ᮊ
International journal of sustainable development and planning, 2024
Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) are considered the most toxic and most concerning volatile organic compounds in the industrial flue gases. They are formed in various processes involving the combustion of organic materials in the presence of chlorine compounds, including modern and domestic coal burning, waste incinerators, sinter plants, cement industry, and metallurgical processes. The primary objective of this study was to investigate the destruction of PCDD/Fs and polychlorinated biphenyl (PCBs) using effective combustion practices. Flue gas samples were collected from the medical waste incineration plant to analyze PCDD/Fs and PCBs destruction under different temperature intervals, O2 content, residence time, and exhaust gas recirculation. It has been found that, relying solely on good combustion practices is not sufficient to completely destruct PCDD/Fs and PCBs emissions. Even with the implementation of optimal combustion techniques, certain congeners such as 2,3,4,7,8-PeCDF and 1,2,3,7,8-PeCDD were still measured in high concentrations. Consequently, additional techniques such as dry sorbent injections, should be explored to meet the new stringent requirements of 0.1 ng I-TEQ/m 3 .
Waste management (New York, N.Y.), 2003
The toxic equivalency (TEQ) values of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) are predicted with a model based on the homologue concentrations measured from a laboratory-scale reactor (124 data points), a package boiler (61 data points), and operating municipal waste incinerators (114 data points). Regardless of the three scales and types of equipment, the different temperature profiles, sampling emissions and/or solids (fly ash), and the various chemical and physical properties of the fuels, all the PCDF plots showed highly linear correlations (R(2)>0.99). The fitting lines of the reactor and the boiler data were almost linear with slope of unity, whereas the slope of the municipal waste incinerator data was 0.86, which is caused by higher predicted values for samples with high measured TEQ. The strong correlation also implies that each of the 10 toxic PCDF congeners has a constant concentration relative to its respective total homologue con...
Chemosphere, 2009
Formation of polychlorinated dibenzo-p-dioxins (PCDD), dibenzofurans (PCDF), benzenes (PCBz), and phenols (PCPh) was studied during combustion of an artificial municipal solid waste (MSW) in a laboratory-scale fluidized-bed reactor with simultaneous collection of flue gas samples at three different temperatures in the post-combustion zone (450°C, 300°C, and 200°C). PCDF, PCBz, and PCPh were predominantly formed at or above the first sampling point (450°C) with a dominance of the lower chlorinated homologues. PCDDs, on the other hand, were dominated by the intermediately chlorinated homologues with concentrations peaking at 300°C. The dominating PCPh congeners clearly displayed the ortho-para directionality, which is indicative of electrophilic aromatic substitution, as did the PCBz isomer distribution patterns to some extent. Comparison of the observed PCBz isomer distribution patterns to prior work may indicate coupling of aliphatic species in chlorobenzene formation. The PCDDs seemed to be largely influenced by chlorophenol condensation reactions and to some extent chlorination reactions, while the PCDFs displayed a chlorination-oriented pattern for the mono-to tri-chlorinated homologues and a PCPh condensation pattern for the higher chlorinated homologues. Injection of nonchlorinated dibenzo-p-dioxin at 650°C resulted in increased formation of Tri-HxCDD and a decrease in the dibenzofuran levels. The affected PCDD and PCDF congeners were not products expected to form from chlorine substitution, but instead are well known chlorophenol condensation products.
Aerosol and Air Quality Research, 2014
Laboratory wastes are discharged from experimental, testing, or analysis processes, and contain various toxic chemical compounds with a high heating-value and a high chlorine content (> 9%). Elevated PCDD/F (polychlorinated dibenzo-pdioxin and furan) emissions during start-up stages are caused by combustion of waste with high chlorine contents, incomplete combustion, and so called "memory effects". Even though the duration of cold start-up is short compared with the hours of continuous steady operation in a waste incinerator, its negative effects with regard to PCDD/F emissions on both human health and the environment cannot be neglected. A full-scale laboratory-waste incinerator which is operated for 10 days in each run and has 15 to 20 runs annually was investigated in this study. Eleven PCDD/F samples of stack flue gas were collected during the cold start-up periods (for 60.5 hrs). The gas temperature of the primary combustion chamber was above 850°C, and was maintained at between 850 and 900°C by injecting diesel fuel without waste feed. For first 1.5-7.5 hours, the PCDD/F concentration in the stack flue gas was as high as 0.656-1.15 ng I-TEQ/Nm 3. Afterward, during hours 10.5-35.5 and 54.5-60.5, this reduced to 0.159-0.459 and 0.218-0.254 ng I-TEQ/Nm 3 , respectively. Based on principal component analysis (PCA) and the L/H ratio, the results revealed a higher L/H ratio (1.23) before hour 32, indicating that less chlorinated PCDD/F homologues (tetra and penta) dominated, while after hour 32 more chlorinated PCDD/F homologues (hexa, hepta and Octa) had a higher mass concentration and the L/H ratio fell to 0.42. These results indicate that the PCDD/F emissions during cold start-up were caused by memory effects and thermal desorption. Therefore, in order to reduce the PCDD/F emissions from the stack flue gas of waste incinerators, is highly recommended that a higher amount of activated carbon injection is used in front of the bag filters.
Archives of Environmental Contamination and Toxicology, 2007
Formation of chlorinated hydrocarbons and polycyclic aromatic hydrocarbons (PAHs) were determined using a laboratory-scale incinerator when combusting materials at different temperatures, different concentrations of hydrochloric acid (HCl), and when combusting various types of polymers/ newspaper. Polychlorobenzenes (PCBz), polychlorophenols (PCPhs), polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) and their toxic equivalency (TEQ) and PAHs were highlighted and reported. Our results imply maximum formation of chlorinated hydrocarbons at 400°C in the following order; PCBz ‡PCPhs>>PCDFs>PCDDs>TEQ on a parts-per-billion level. Similarly, a maximum concentration of chlorinated hydrocarbons was noticed with an HCl concentration at 1000 ppm with the presence of paraffin powder in the following order; PAHs>PCBz ‡PCPhs>>PCDFs>PCDDs>TEQ an a partsper-billion level. PAHs were not measured at different temperatures. Elevated PAHs were noticed with different HCl concentrations and paraffin powder combustion (range: 27-32 lg/g). While, different polymers and newspaper combusted, nylon and acrylonitrile butadiene styrene (ABS) produced the maximum hydrogen cyanide (HCN) concentration, concentrations of PCDD/FS, dioxin-like polychlorinated biphenyls (DL-PCBs), and TEQ were in a decreasing order: polyvinylchloride (PVC)<newspaper<polyethyleneterephthalate (PET)< polyethylene (PE)< polypropylene (PP)< ABS = blank. Precursors of PCBs were in a decreasing order: PP<nylon<PE<newspaper<ABS<PVC<blank<PET. Precursors of PCDD/Fs were in a decreasing order: newspaper <PP=nylon<PE<ABS<PVC= blank<PET. BTX formation was in a decreasing order; PE<nylon<newspaper<ABS<PP. PAHs formation were elevated with parts-per-million levels in the decreasing order of PP<nylon<PE<newspaper<blank<ABS< PET<PVC. Formation of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) as a result of municipal solid waste incinerators (MSWI) was discovered in 1977 (Olie et al. 1977). Particularly, formation of PCDD/Fs in MSWIÕs and industrial solid waste incinerators (ISWIs) involved complex and heterogeneous chemistry (Huang and Buekens, 1995; Fiedler, 1998; Tuppurainen et al. 1998; lino et al. 1999a, b; 2000; 2001). European Union (EU) member countries have set limit values for PCDD/DF emissions for hazardous waste incinerator plants of 0.1ng I-TEQ/Nm 3. According to the latest inventory of PCDD/DF, emissions from MSWIÕs in Japan were 812 g-TEQ/y until 2001 (Suzuki et al. 2004). Consequently, insight into the formation of toxic contaminants is of the utmost important. The presence of PCDD/ Fs in incinerator fly ash has led to laboratory-scale modeling in the formation process. Earlier reviews summarized the most important trends in formation chemistry (
Environmental …, 2012
This study investigated dioxins and dioxinlike polychlorinated biphenyls in gasses emitted from waste incinerators and thermal processes in central and western parts of India. The concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/DFs) ranged from 0.0070 to 26.8140 ng toxicity equivalent (TEQ)/Nm 3 , and those of dioxin-like polychlorinated biphenyls (PCBs) ranged from 0.0001×10 −1 to 0.0295 ng TEQ/Nm 3 . The characteristics of mean PCDD/F I-TEQ concentration and congener profiles were studied over all the samples of air. In particular, a pattern consisting of a low proportion of dioxin-like PCBs and high proportion of PCDDs/ DFs was common for all the samples from incinerators and high-temperature processes.
Chemosphere, 1992
The formation of chlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) downstream from the combustion zone of a heterogeneous combustor occurred within seconds in the temperature range of 430-380°C, but not at substantially lower temperatures. A spouted bed reactor was used with sand as the heterogeneous medium and a fuel mixture of 1,2dichlorobenzene/heptane. Total PCDD/F-concentrations were in the range of 100 ng m-3; chlorobenzenes other than the starting compound and chlorophenols were formed. The formation of PCDD/F may be mediated by high surface area particles originating from the bed due to attrition. Homogeneous gas phase mechanisms cannot account readily for the levels observed.