Dioxins In Flue Gas Research Articles

The Effect of Adjusting Sinter Raw Mix on Dioxins from Iron Ore Co-Sintering with Municipal Solid Waste Incineration Fly Ash

The inhibition effect of calcined lime (CaO) and limestone (CaCO3) on the formation of dioxins during iron ore co-sintering with fly ash was investigated in a sinter pot in the present work. Experimental results indicated that international total toxicity equivalent concentration of dioxins decreased from 1.4335 to 0.2922, 0.1048, 0.4562, and 0.3098 ng I-TEQ Nm−3 under four different experimental conditions. It can be concluded that 5 wt.% calcined lime with 3 wt.% limestone is the optimal addition to reduce the concentration of dioxins in flue gas, with 92.70% inhibition efficiency. Effects on dioxin distribution was also analyzed. The distribution proportion of low-chlorinated dioxins was found to increase, while that of high-chlorinated dioxins decreased, except for octachlorianted dibenzo-p-dioxins (OCDD). The reason is that the consumption of HCl not only inhibits the de novo synthesis, but also dramatically promotes the condensation and dechlorination to produce more tetrachlorianted dibenzo-p-dioxins and octachlorianted dibenzo-p-dioxins through precursors. Finally, condensation, dichlorination, and inhibition mechanisms of dioxins during co-sintering with municipal solid waste incineration (MSWI) fly ash are proposed.

Formation mechanism and influencing factors of dioxins during incineration of mineralized refuse

Chlorine sources and heavy metal catalysts play an important role in the formation of dioxins during the incineration of mineralized refuse in landfills. Through the use of different external chlorine sources and pretreatment methods, their effects on the formation of dioxins in flue gas from mineralized refuse incineration were studied. The effects of temperature, external chlorine sources, pretreatment methods and metal catalyst ratios on dioxin generation in the flue gas of mineralized refuse incineration were investigated with mineralized refuse. The effects of temperature, atmosphere and external chlorine source on the low-temperature re-synthesis of dioxins from mineralized refuse incineration fly ash were investigated, and the ability of re-synthesis of dioxins from mineralized refuse incineration fly ash and MSWI (Municipal Solid Waste Incineration) fly ash was compared using in situ XPS (X-ray Photoelectron Spectrometer) and heavy metal morphology analysis. The results showed that CuCl2 has the strongest catalytic effect on the formation of gaseous dioxin from mineralized refuse incineration. The components of mineralized refuse and water washing do not interfere with the mass concentration of dioxins in incinerated flue gas. The effect of temperature, atmosphere and external chlorine source on the low-temperature synthesis of dioxin from mineralized refuse incineration fly ash was similar to that of MSWI fly ash. The results of in situ XPS and speciation analysis of heavy metals show that the reducible metals in mineralized refuse fly ash was mainly composed of Fe. The stronger oxidation and chlorination of carbon and the stronger interaction between copper and iron in mineralized refuse fly ash make the dioxin synthesis capacity higher than that of MSWI fly ash. In addition, the concentration of gaseous dioxins produced by mineralized refuse incineration was directly proportional to the amount of CuCl2. However, changing the ratio of heavy metals weakened the de novo synthetic reaction to a certain extent, resulting in the change in 17 toxic dioxin isomers.

Enhancing the degradation of dioxins during the process of iron ore sintering co-disposing municipal solid waste incineration fly ash

Abstract Iron ore sintering is a promising thermal method for co-disposing the municipal solid waste incineration (MSWI) fly ash. To reduce the increased dioxins in flue gas caused by adding fly ash powder, pelletizing was used as a pre-treatment for fly ash to enhance the degradation of dioxins. High specific surface area (5380 cm2 g−1) made the fly ash balls easier to be prepared. Mechanical strength of dried fly ash balls was qualified for further sintering co-disposal as crushing strength reached 145 N P−1 and cracking temperature reached 600 °C. The concentration of dioxins in the flue gas were 4.50 ng I-TEQ m−3 (fly ash balls added) and 4.32 ng I-TEQ m−3 (fly ash balls containing solid fuel added), respectively, both of which were less than 5.61 ng I-TEQ m−3 (fly ash powder added). The degradation rate of dioxins was improved from 93.03% (fly ash powder added) to 96.10% (fly ash balls added) and 96.61% (fly ash balls containing solid fuel added), correspondingly. The improvement of dioxins degradation was realized by reducing the dispersed distribution of the chlorine-containing material, by inhibiting the volatilizing of dioxins before degradation, and by utilizing the suppressing functions of sulfur and calcium compounds from CaSO4 decomposing in the fly ash balls. The method of degrading more dioxins in fly ash during the co-disposing process proved to be feasible.

Simultaneous suppression of PCDD/F and NOx during municipal solid waste incineration

Thiourea was tested as a dioxins inhibitor in a full-scale municipal solid waste incinerator with high capacity (34th−1). The suppressant, featuring a high S- and N-content, was converted into liquor and then injected (35kgh−1) into the furnace (850°C) through the inlets already used for Selective Non-Catalytic Reduction (SNCR) of flue gas NOx. The first results show that thiourea reduces the dioxins in flue gas by 55.8wt.%, those in fly ash by 90.3wt.% and the total dioxins emission factor by 91.0wt.%. The concentration of PCDD/Fs was 0.08ngTEQNm−3, below the national standard of 0.1ngTEQNm−3. The weight average chlorination degree of dioxins decreases slightly after adding the inhibitor, indicating that it suppresses both the formation and the chlorination of dioxins. Analysis of fly ash by scanning electron microscope (SEM) suggests that the particle size becomes larger after adding the inhibitor. Further analysis using an energy dispersive spectrometer (EDS) reveals that the sulphur content in fly ash rises, but the chlorine content declines when adding thiourea. These results suggest that poisoning the metal catalyst and blocking the chlorination are probably responsible for suppression. NOx reduction attains 42.6wt.%. These tests are paving the way for further industrial application and assist in controlling the future emissions of dioxins and NOx from MSWI.

Feasibility of a monitoring system for detecting changes in dioxin concentrations of both in flue gas and fly ash in incineration plants

Surrogate measurements should be low in cost and quick to perform. To examine its feasibility, continuous surrogate monitoring was performed using an organic halogen compound (OHC) analyzer. Surrogates for dioxins (DXNs) from waste incinerators were examined by changing the operating conditions such as the atomized volume of activated carbon added and the temperature at the inlet of the dust collector. OHCs were measured along with DXNs in flue gas at the inlet and the outlet of the dust collector of two waste incinerators over five runs; the fly ash was sampled at the same time. Although the final flue gas concentration of DXNs at the incineration plants was below the regulation criteria, this does not mean complete reduction of DXNs. In addition, the de novo synthesis of DXNs inside the dust collectors was studied by analyzing the mass balance for DXNs concentrations in flue gas and fly ash. Semivolatile chlorinated organic compound concentrations at the outlet of the bag filter were basically well correlated with DXNs levels at the inlet of the bag filter in the test runs. When advanced flue gas treatment is applied by using a bag filter and lime/activated carbon adsorbent, DXNs that may be generated during flue gas cooling processes move to the fly ash, and this amount determines the mass balance of the entire system. It may be useful to monitor surrogate organic halogens for detecting changes in DXN concentrations of both flue gas and fly ash in incineration plants.

Effect of Feed Forms on the Results of Melting of Fly Ash by a DC Plasma Arc Furnace

Fly ash from a municipal solid waste incinerator (MSWI) without preprocessing (original fly ash, OFA) was melted by a direct current (DC) plasma arc furnace to investigate how the feed forms governed the results. Dioxins in flue gas from stack and bag-filter ash (BFA) were detected. The distribution of heavy metals of Pb, Cd, As, and Cr along the flue gas process system was analyzed. Through a comparison of the results for dioxins and heavy metals in this study and previous work, carrying-over of fly ash particles with the flue gas stream can be deduced. Based on the magnetic induction equation and Navier–Stokes equations, a magnetohydrodynamic (MHD) model for the plasma arc was developed to describe the particle-carrying effect. The results indicate that, a. when melted, the feed forms of MSWI fly ash affect the results significantly; b. it is not preferable to melt MSWI fly ash directly, and efforts should be made to limit the mass transfer of OFA from the plasma furnace.

Characteristics of azaarenes and dioxins in gases emitted from waste incinerators

In this study, we propose an analytical method to determine the fourteen of azaarenes present in flue gas samples collected according to Japanese Industrial Standard K 0311, which designates the method for the determination of dioxins in flue gas. Azaarenes can be analyzed using the acidic water phase after shaking extraction with dichloromethane, which is unnecessary for dioxin analysis. Flue gas samples were obtained from 24 waste incinerators in Japan, and azaarenes were detected in all the flue gas samples (0.21–3800 μg/m3N). The most abundant of the detected compounds were quinoline and isoquinoline. The concentration of azaarenes had a tendency to increase with that of polychlorinated dibenzo-p-dioxins and dibenzofurans. The isomer distribution of heptachloro-dibenzofurans (HpCDFs) was calculated using the computed Gibbs energy of formation (ΔGf) obtained by the semiempirical molecular orbital method at various temperatures. The calculated isomer distribution was fitted to the measured value of HpCDFs. It seems that the temperature obtained from the fitting calculations is an indicator of the cooling capacity of the combustion gas in an incinerator. The computed ΔGf also explained the measured isomer distributions of azaarenes. It is suggested that the isomer distribution of azaarenes in the combustion process is thermodynamically controlled.

Evaluation of gas-particle partition of dioxins in flue gas II: Estimation of gas-particle partition of dioxins in dust-rich flue gas by parallel sampling with different conditions

For an accurate determination of the gas-particle partition of polychlorinated dibenzo- p-dioxins (PCDDs), dibenzofurans (PCDFs) and dioxin-like biphenyls (DLPCBs) in dust-rich flue gas, a parallel monitoring procedure with an isokinetic and a non-isokinetic train was used. For four flue gas samples, the two trains gave a significantly different weight of the collected fly ash particles despite the equal gas volume sampled. On the basis of the quantitative values of PCDD/F and DLPCB homologues and the weight of the collected particles, ratios of each homologue in the real flue gas samples in gaseous form were predicted using simultaneous equations. For the four flue gas samples examined, the predicted gaseous ratios were considerably higher that those calculated using a previously reported equation, suggesting that there are some properties which affect partitions of PCDD/Fs in flue gas besides their saturation vapor pressures and fly ash concentration. The partitions for higher temperature flue gases obtained by fractional determinations of each collection device were additionally different from those predicted by the parallel collection, indicating that conventional determination by fractional measurements is subjected to large errors in dust-rich flue gas due to severe adsorption of gaseous PCDD/Fs and DLPCBs onto particles collected on a low-temperature collection device.

Evaluation of gas-particle partition of dioxins in flue gas I: Evaluation of gasification behavior of polychlorinated dibenzo- p-dioxins and polychlorinated dibenzofurans in fly ash by thermal treatment

The gasification behavior of polychlorinated dibenzo- p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in fly ash by thermal treatment has been investigated to estimate gas-particle partition in flue gas. The results obtained in thermal experiments under various conditions showed that gasification of PCDD/Fs depends on air flow rate and treatment weight of fly ash as well as treatment temperature. On the other hand, the results obtained in the thermal experiments using dioxin-free fly ash revealed that during thermal treatment, the de novo synthesis, gasification, and decomposition of PCDFs proceeded at different rates. This difference in the reaction rates indicates that thermal treatment time is also a factor in determining the gas-particle partition of PCDD/Fs in fly ash. Therefore, reasonable thermal treatment conditions were established and applied to three ash samples. For all samples, PCDD/Fs started to gasify at 350 °C treatment, whereas 53–98% of PCDD/F homologs gasified at 400 °C treatment, implying that gaseous PCDD/Fs are dominant in flue gas at temperatures in the range 350–400 °C regardless of particle concentration.

Simplified Monitoring Method for Measurement of Dioxins in Flue Gas Discharged from Municipal Solid Waste Incinerators

Simplified Monitoring Method for Measurement of Dioxins in Flue Gas Discharged from Municipal Solid Waste Incinerators

Experimental research on emission and removal of dioxins in flue gas from a co-combustion of MSW and coal incinerator

This paper describes the experimental study of dioxins removal from flue gas from a co-combustion municipal solid waste and coal incinerator by means of a fluidized absorption tower and a fabric filter. A test rig has been set up. The flow rate of flue gas of the test rig is 150–2000 m 3/h. The system was composed of a humidification and cooling system, an absorption tower, a demister, a slurry make-up tank, a desilter, a fabric filter and a measurement system. The total height of the absorption tower was 6.5 m, and the diameter of the reactor pool was 1.2 m. When the absorbent was 1% limestone slurry, the recirculation ratio was 3, the jet rate was 5–15 m/s and the submerged depth of the bubbling pipe under the slurry was 0.14 m, the removal efficiency for dioxins was 99.35%. The concentration of dioxins in the treated flue gas was 0.1573 × 10 −13 kg/Nm 3 and the concentration of oxygen was 11%. This concentration is comparable to the emission standards of other developed countries.

Formation characteristics of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and coplanar PCBs in fly ash from a gasification-melting process of municipal solid waste

PCDDs/DF and Co-PCB (dioxin) formations were studied with ash from a newly developed gasification and melting process for municipal solid waste. Ash samples were heated in a laboratory-scale fixed-bed reactor. Emphasis was placed on the effects of the type and composition of ash, temperatures, gas residence time, and gaseous organic precursors. Investigations using macroscopic and homologue distribution analyses led to the following conclusion. The ash from the gasification–melting process had the ability to generate dioxins in flue gas. A possible carbon source is unburned carbon in the ash samples, although this was very low (less than 0.01%). An experimental result that the level of dioxins generated from preheated fly ash obtained from a conventional incinerator was much lower than that from nonheated fly ash supported this conclusion. Dioxin concentrations obviously showed temperature dependence and peaked at 350°C. Dioxins formed in a gasification–melting process ash were readily desorbed from the surface, probably because of the low carbon content of the ash. There was no experimental evidence that gaseous organic precursors fed to the reactor generated dioxins. Therefore, an organic precursor was not essential for the formation of dioxins. A good linear relationship obtained between PCDDs/DFs and gas residence time also supported the assumption.