Removal efficiencies of PCDDs/PCDFs by air pollution control devices in municipal solid waste incinerators

Occurrence, profiles, and control of unintentional POPs in the steelmaking industry: A review

The steelmaking industry is an important source of unintentionally produced persistent organic pollutants (UP-POPs). This review summarizes the emission levels, characteristics, and formation mechanisms of UP-POPs, including halogenated dioxins, polychlorinated biphenyls, polychlorinated naphthalenes, and penta- and hexa- chlorobenzenes in the steelmaking industry to improve our understanding of the emissions of UP-POPs from the steelmaking industry. The factors influencing UP-POP formation during the iron ore sintering (IOS) process are also reviewed. The raw materials and temperature during the steelmaking process are important factors influencing UP-POP generation. Raw materials containing plastics, paints, cutting oil, rubber, and iron from electronic waste recycling can contribute to high emissions of UP-POPs during steelmaking processes. Electrostatic precipitator dust contains chlorine, carbon, and metals, which are usually recycled as a component of the raw material, and could also promote dioxin formation and emissions from IOS. Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) are easily formed in high concentrations at temperatures in the range of 200 °C-650 °C. This review also provides a comprehensive summary of the UP-POP emission limits in the steel industry worldwide and the best available techniques and environmental practices for UP-POP emission reduction. The information in this review will be useful for the reduction of UP-POPs in the steelmaking process.

Co-processing of the MSWI flue gas in a lab-scale coal-fired drop-tube furnace

Coal-fired power plants are characterized by high combustion temperature and well-equipped air pollution control devices. The trace organic pollutants in the municipal solid waste incineration (MSWI) flue gas would be completely destroyed if the MSWI flue gas was injected into the high temperature area of a coal-fired boiler. In this study, the emission characteristics of common gas pollutants, heavy metals, and dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in both flue gas and bottom ash when the MSWI flue gas was injected into a lab-scale coal-fired drop-tube furnace were investigated. After co-processing, the concentrations of NOx, SO2, CO, and all heavy metals in the flue gas emitted from the coal-fired drop-tube furnace did not change a lot. However, the concentration of HCl in the flue gas from drop-tube furnace increased after coupling the MSWI flue gas. Moreover, the I-TEQ values of the PCDD/Fs in the flue gas and bottom ash after coupling the MSWI flue gas were 0.037 ng I-TEQ/Nm3 and 0.63 ng I-TEQ/g, respectively. The main formation pathways of PCDD/Fs in the flue gas of drop-tube furnace were suggested to be de novo synthesis and precursor synthesis. Furthermore, the effects of oxygen content and temperature on the formation of PCDD/Fs were also studied. The reduction efficiencies of the total amount of PCDD/Fs in the flue gas from the co-processing system were more than 60%, and even reached 90%. Therefore, co-processing of the MSWI flue gas in coal-fired power plants might be an environmentally friendly technology.

Emission characteristics of dl-PCNs, PCDD/Fs, and dl-PCBs from secondary copper metallurgical plants: Control technology and policy

This study investigated the characteristics of dl-PCNs, PCDD/Fs and dl-PCBs emitted from two typical secondary copper metallurgical plants processing copper sludge equipped with different sets of air pollution control devices (APCDs). Results indicated that the emission factors of dl-PCNs and PCDD/Fs of plant A are 0.00775 and 1.09 μg TEQ/ton, respectively, which are remarkably lower than those of plant B (3.12, 181 and 25.5 μg TEQ/ton for dl-PCNs, PCDD/Fs and dl-PCBs, respectively). Dl-PCNs contributed 0.7-2.7% of total TEQ for flue gases and up to 2.6% of TEQ for ash samples. The TEQ concentration of dl-PCNs in fly ash individually exceeds the regulated level of 1 ng TEQ/g regulated by Taiwan EPA, indicating that emission and discharge of dl-PCNs should be regulated. The combination of semidry scrubber and activated carbon injection (ACI) + baghouse (BH) is effective for simultaneous removals of dl-PCNs and PCDD/Fs in plant A; while the combination of cyclone, secondary combustion chamber, ACI + BH and wet scrubber (WS) is not optimal for removing dl-PCNs, PCDD/Fs and dl-PCBs. Memory effect occurring within BH and WS is responsible for low removal efficiencies of these POPs in plant B. This study suggests appropriate APCDs for simultaneous removal of three POP groups and recommends the inclusion of dl-PCNs in emission standard.

Reduction of polychlorinated naphthalenes (PCNs) emission from municipal waste incinerators in Taiwan: Recommendation on control technology

Emission factor and removal efficacy of PCNs are evaluated via the flue gas sampling of two MWIs equipped with different air pollution control devices (APCDs) in Taiwan. MWI-A is equipped with ESP, wet scrubber (WS) and selective catalytic reduction (SCR), while cyclone (CY), semi-dry absorber (SDA), activated carbon injection (ACI) and baghouse (BH) are employed in MWI-B. The average concentrations of PCNs measured at stacks of MWI-A and MWI-B are 2.1 ng Nm^-3 (0.218 pg TEQ Nm^-3) and 23.2 ng Nm^-3 (0.425 pg TEQ Nm^-3), respectively. The emission factors of PCNs calculated from feeding rates of waste and stack sampling results range from 6.7 to 6.95 μg t^-1 (0.790-1.45 ng TEQ t^-1). PCNs are formed in ESP via chlorination, while SCR and SDA + ACI + BH are effective in removing PCNs with the overall efficacies of 97.6% and 94.3%, respectively. PCN removal efficiencies achieved with SCR and SDA + ACI + BH increase as chlorination level increases. Specifically, around 72% and 82% of Mono-CN are removed by SCR and SDA + ACI + BH, respectively. The removal efficacies of other homologues achieved with SCR are consistently high (96-100%). Dominances of Mono-to Tri-CNs in scrubbing liquid collected from WS and higher removal efficacies of these homologues achieved with WS + ESP compared with ESP alone indicate that WS can capture low chlorinated PCNs to some extent. The results suggest that CY + SDA + ACI + BH should be equipped in MWI for effective removal of PCNs, while ESP, WS and SCR should be utilized with precaution to eliminate PCNs formation and enhance the PCNs removal efficiency.

Characterization of PCN emission and removal from secondary copper metallurgical processes

This study investigates the characteristics of PCN emission and removal from two secondary copper metallurgical processes (plants A and B) equipped with different air pollution control devices (APCDs). Different operating conditions and feeding materials result in varying emission factors of PCNs from two plants. The average PCN concentration emitted from plant B (7597 ng Nm^-3) is significantly higher than that emitted from plant A (32.5 ng Nm^-3) and those reported in China (5.8-2845 ng Nm^-3). Similar trend is found for fly ash samples collected from two plants. Low chlorinated homologues (Mono-to Tri-CNs) are the major contributors to total PCNs measured in flue gas, fly ash and slag samples. Combination of semi-dry absorber, activated carbon injection and baghouse is effective for PCN removal in plant A, with the overall removal efficiency of 98%. The overall removal efficiency of PCNs achieved with APCDs equipped in plant B is 90%, however, increases of some homologues as the flue gases passing through baghouse and wet scrubber are found, suggesting the occurrence of memory effect within baghouse and wet scrubber.

Influence factors and mass balance of memory effect on PCDD/F emissions from the full-scale municipal solid waste incineration in China

Studies are carried out in two wet scrubbing systems (WSSs) subordinated to two similar full-scale (30 t h^-1) municipal solid waste (MSW) incinerators to explore the influence factors and mass balance of memory effect on polychlorinated-ρ-dibenzodioxins and dibenzofurans (PCDD/Fs) emissions. The results show that the memory effect on two WSSs notably increases the TEQ concentrations by 13.6 and 3 times, respectively, through increase in the total mass concentration and the proportions of low-chlorinated PCDD/Fs, directly resulting in the PCDD/F emissions of 1# MSW incinerator over the national standard. PCDD/F adsorption/desorption in WSSs is the reasonable acting mechanisms of memory effect. In addition, memory effect mainly influences gaseous PCDD/F emissions by elevating the percentage of PCDFs, while slightly affects PCDD/Fs in residuals. A mass balance of PCDD/Fs is established to further analyze the influence factors of memory effect on WSSs, indicating filling as the largest potential source discharging PCDD/Fs into outlet flue gas. The results pave the way for further industrial optimization of WSSs design, such as the filling materials with less adsorption capacity on PCDD/Fs and more reasonable operation.

Influences of P-N-containing inhibitor and memory effect on PCDD/F emissions during the full-scale municipal solid waste incineration

Influence of inhibition and memory effect on PCDD/Fs are carried out in a full-scale (23 t h^-1) municipal solid waste (MSW) incinerator under three conditions. Ammonium dihydrogen phosphate (ADP) is injected into the post combustion zone of incinerator. The results show that the inhibition efficiency of PCDD/Fs in flue gas was 53.34% (71% for TEQ), and ADP possibly also didn't have effect on the chlorination reaction of PCDD/F formation. The memory effect phenomenon, PCDD/F adsorption/desorption, is clearly discovered in the wet scrubber system (WSS), resulting in PCDD/F concentration increased by 6.2-19.9 times. Memory effect also changes the distribution of PCDD/Fs by increasing the proportions of low-chlorinated PCDD/Fs, which is easily to be desorbed because of their higher vapor pressure comparing with the high-chlorinated PCDD/Fs. After renewing the scrubbing solution and cleaning the bottom sludge in WSS, the PCDD/F TEQ concentrations decreases from 0.51 to 0.24 ng I-TEQ Nm^-3, further mitigating but still not enough to eliminate the memory effect because the PCDD/F desorption of wall and scrubber fillings in the WSS. The results are paving the way for further industrial optimized design of WSS and assist in controlling the PCDD/F emissions from MSWI.

The effects of green building on construction waste minimization: Triangulating 'big data' with 'thick data'

In contrast with the prolific research examining the effects of green building (GB) on property value, energy saving, or indoor air quality, there has been minimal focus on GB's effects on Construction Waste Minimization (CWM), which is also an important aspect of cultivating sustainability in the built environment. To address this significant knowledge gap, this study has two progressive objectives: (1) to ascertain the empirical effects of GB on CWM and; (2) to identify and understand the causes leading to the ascertained effects. This is achieved by triangulating quantitative 'big data' obtained from government agencies with qualitative 'thick data' derived from case studies and interviews. The study found that BEAM Plus, the latest version of the Building Environmental Assessment Method developed by the Hong Kong Green Building Council (HKGBC), gave rise to a 36.19% waste reduction by weight for demolition works, but no statistically significant waste reduction for foundation or building works. It is because CWM, the basis for a demolition project to obtain GB credits, makes up only one of many ways for foundation or building works to earn credits, e.g., site aspects, lighting. In any case, CWM measures typically prove costlier means of acquiring credit, further causing developers to pay less attention to CWM in their GB tactics. The study's results, i.e., CWM in GB significantly influences demolition, but only marginally for foundation and building works, provide useful scientific evidence to inform GB councils and other responsible bodies and encourage continuous improvement in GB practices. While the study in general sheds light on how the triangulation of big, empirical data with conventional, qualitative data, e.g., interviews with GB professionals, helps to better understand the subject of the investigation, i.e., the effects of GB on CWM.

Comprehensive diagnosis of PCDD/F emission from three hazardous waste incinerators

Comprehensive diagnosis of polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/F) emissions was systematically conducted on three hazardous waste incinerators (HWIs). Results indicated that PCDD/F mainly existed in the solid phase before the bag filter. This was especially true for higher chlorinated dioxin and furan congeners (hexa-, hepta- and octa-). The aged bag filters tended to increase the gas-phase PCDD/F. Emissions also increased due to PCDD/F desorption from circulated scrubbing solution and plastic packing media used in the wet scrubber. The PCDD/F concentrations were elevated during the start-up process, reaching up to 5.4 times higher than those measured during the normal operating period. The ratios of PCDFs/PCDDs revealed that the surface-catalysed de novo synthesis was the dominant pathway of PCDD/F formation. Installation of more efficient fabric filters, intermittent replacement of circulated scrubbing solution will result in reduced PCDD/F emission. Additionally, 2,3,4,7,8-PeCDF correlated well with the international toxic equivalent quantity (I-TEQ) value, which suggests that 2,3,4,7,8-PeCDF could act as an I-TEQ indicator.

Comparative analyses of catalytic degradation of PCDD/Fs in the laboratory vs. industrial conditions

This study investigates the efficiencies and mechanisms of the catalytic degradation of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) first, in simulated laboratory conditions and then, in a commercial municipal solid waste incineration (MSWI) plant. Five commercially available V₂O₅-WO₃/TiO₂ (VWTi) catalysts were tested. The degradation efficiency of PCDD/Fs in the simulated flue gas ranged 22.8-91.7% and was generally higher than that in the MSWI flue gas of 8.0-85.4%. The degradation efficiency of PCDD/Fs in the real flue gas of the MSWI plant was largely hindered by the complex composition of the flue gas, which could not be completely reproduced in the simulated laboratory conditions. Furthermore, the degradation of the higher chlorinated PCDD/Fs was easier compared to the lower chlorinated ones in the presence of the VWTi catalysts, which was primarily driven by the tendency of the higher chlorinated PCDD/Fs to be adsorbed on the surface of the catalyst and further destructed due to their lower vapor pressure. In addition, powdered catalysts should be preferred over the honeycomb shaped ones as they exposed higher PCDD/Fs degradation efficiencies under equal reaction conditions. The chemical composition and a range of the relevant to the study properties of the catalysts, such as surface area, crystallinity, oxidation ability, and surface acidity, were analyzed. The study ultimately supports the identification of the preferred characteristics of the VWTi catalysts for the most efficient degradation of toxic PCDD/Fs and elucidates the corresponding deactivation reasons of the catalysts.

State-of-the-art of recycling e-wastes by vacuum metallurgy separation

In recent era, more and more electric and electronic equipment wastes (e-wastes) are generated that contain both toxic and valuable materials in them. Most studies focus on the extraction of valuable metals like Au, Ag from e-wastes. However, the recycling of metals such as Pb, Cd, Zn, and organics has not attracted enough attentions. Vacuum metallurgy separation (VMS) processes can reduce pollution significantly using vacuum technique. It can effectively recycle heavy metals and organics from e-wastes in an environmentally friendly way, which is beneficial for both preventing the heavy metal contaminations and the sustainable development of resources. VMS can be classified into several methods, such as vacuum evaporation, vacuum carbon reduction and vacuum pyrolysis. This paper respectively reviews the state-of-art of these methods applied to recycling heavy metals and organics from several kinds of e-wastes. The method principle, equipment used, separating process, optimized operating parameters and recycling mechanism of each case are illustrated in details. The perspectives on the further development of e-wastes recycling by VMS are also presented.

A comparative assessment of waste incinerators in the UK

The uptake in Europe of Energy from Waste (EfW) incinerator plants has increased rapidly in recent years. In the UK, 25 municipal waste incinerators with energy recovery are now in operation; however, their waste supply chains and business practices vary significantly. With over a hundred more plant developments being considered it is important to establish best business practices for ensuring efficient environmental and operational performance. By reviewing the 25 plants we identify four suitable case study plants to compare technologies (moving grate, fluidised bed and rotary kiln), plant economics and operations. Using data collected from annual reports and through interviews and site visits we provide recommendations for improving the supply chain for waste incinerators and highlight the current issues and challenges faced by the industry. We find that plants using moving grate have a high availability of 87-92%. However, compared to the fluidised bed and rotary kiln, quantities of bottom ash and emissions of hydrogen chloride and carbon monoxide are high. The uptake of integrated recycling practices, combined heat and power, and post incineration non-ferrous metal collections needs to be increased among EfW incinerators in the UK. We conclude that one of the major difficulties encountered by waste facilities is the appropriate selection of technology, capacity, site, waste suppliers and heat consumers. This study will be of particular value to EfW plant developers, government authorities and researchers working within the sector of waste management.

Removal of PCDD/Fs and PCBs from flue gas using a pilot gas cleaning system

A 100 Nm3/hr capacity pilot scale dual bag filter (DBF) system was tested on the flue gas from an actual hazardous waste incinerator (HWI), the removal efficiency of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) and polychlorinated biphenyls (PCBs) was also studied. The first filter collected most of the fly ash and associated chlorinated organic; then activated carbon (AC) was injected and used to collect phase chlorinated organic from the gas. Concentrations of PCDD/Fs and PCBs after the DBF system were 0.07 and 0.01 ng TEQ/Nm3, respectively, which were both far below the national emission standard. Comparing with the original single bag filter system, the PCDD/Fs concentration dropped a lot from 0.36 to 0.07 ng TEQ/Nm3. Increasing AC feeding rate enhanced their collection efficiency, yet reduced the AC utilization efficiency, and it still needs further study to select an appropriate feeding rate in the system. These results will be useful for industrial application and assist in controlling emissions of PCDD/Fs and other persistent organic pollutions from stationary sources in China.

Quantum chemistry study on the destruction mechanism of 2,3,7,8-TCDD by OH and O(3) radicals

Due to its fundamental importance, the destruction mechanism of the dioxins, as exemplified by 2,3,7,8-TCDD, by OH and O3 radicals was investigated in detail employing Quantum Chemical Calculations in this paper. Theoretical results showed that, OH radical degraded 2,3,7,8-TCDD via substituting chlorine at the 2,3,7,8 positions, while O3 radical degraded 2,3,7,8-TCDD via destructing CC bonds and aromatic ring. Based on the mechanism study, the kinetic parameters of the reactions were also calculated by Transition State Theory. By comparing, the rate constant of the 2,3,7,8-TCDD destruction by OH was found to be much higher than that by O3, which indicated that OH radical have much stronger ability to degrade 2,3,7,8-TCDD than O3 radical. This finding was consistent with the standard electrode potential of OH and O3 radical. The theoretical results in this paper can be believed to supply important theory basis for the further investigation on dioxins removal by using the catalytic oxidation technology.

Enrichment of PCDDs/PCDFs in peripheral utilities of the municipal solid waste incineration facility

This study was performed to suggest the improvements through measuring the amounts of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), re-synthesized in peripheral utilities (PUs) of a commercial-scale municipal solid waste incineration facility (MSWIF) where a few research results existed. The PUs examined in this study consisted of air pre-heaters (APHs) and gas/gas re-heater (GGRH) and kerosene-fired duct burner for selective catalytic reduction (SCR) process. PCDDs/PCDFs in flue gas were simultaneously measured at the inlet and outlet of PUs. Flue gas was cooled down from 380 °C to 249 °C by exchanging the heat with fresh air in APHs, and then heated up to 383 °C by GGRH and duct burner from 164 °C at the outlet of bag filter. The results showed that PCDDs/PCDFs were 3-4 times higher within this temperature range of PUs. In comparison of PCDDs/PCDFs concentrations at the inlet with those at the outlet of PUs, particulate-phase PCDDs/PCDFs were about 9.5-10 times enriched while gaseous-phase ones were decreased by about 33-41%. The PCDDs/PCDFs re-synthesized in the PUs, where PCDDs were relatively higher than PCDFs, showed somewhat different patterns compared to those formed at incinerators and emitted at stack. Through the investigations for PUs, we conclude that the PUs used in MSWIFs was a potential source for de novo synthesis of PCDDs/PCDFs.

Memory effect driven emissions of persistent organic pollutants from industrial thermal processes, their implications and management: a review

Memory effect is delayed emission of certain persistent organic pollutants (POPs). Many of the POP compounds viz. polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) get trapped in the particulate phase deposited in the flue transfer lines and air pollution control systems (equivalent to storage in the memory of a system) and released subsequently. Memory effect driven emission is a combination of real time emission and emission of stored compounds and so is not a true measure of actual real time emission. Memory effect is now realized to have existed for a long time but was not identified and understood until recently. Memory effect has several serious implications e.g. it wrongly depicts emission patterns of POPs; it makes compliance to stipulated emission standards difficult; it could lead to wrong calculations of emission factors and emission inventory estimates of a plant and leads to misinterpretation of efficacy of processes and air pollution control systems. Further, new PCDD/Fs may be formed in the trapped particulate phase via de novo synthesis and the new compounds may be emitted, thereby increasing total PCDD/F emissions, apart from altering the homologue pattern of PCDD/Fs in emissions. Memory effect could be minimized by judicious operational and management (O&M) procedures like optimizing combustion, minimizing unnecessary halts in operations, periodical cleaning of flue transfer lines, application of inhibitors etc.

PCDD/Fs removal efficiency by electrostatic precipitator and wetfine scrubber in an iron ore sintering plant

This study investigates the removal efficiency of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) by the APCDs of an iron ore sintering plant, an electrostatic precipitator (ESP) and a wetfine scrubbing system (WS). The removal efficiencies of the ESP on the total PCDD/Fs concentration and the total PCDD/Fs I-TEQ concentration are 44.3% and 41.4%, respectively, while those of the WS are 66.7% and 68.4%, respectively, but the vapor/solid phase distribution changes after APCDs abatement. At ESP inlet, the PCDD/Fs account for 31.2% in vapor phase and for 68.8% in particulate phase while, at ESP outlet, the PCDD/Fs account for 63.3% in vapor phase and for 36.7% in solid phase. The ESP removes effectively solid-phase PCDD/Fs for its effectiveness to capture the particulate while it is ineffective in removing vapor-phase PCDD/Fs. It, on the contrary, increase for the vaporization within the ESP, especially for these congeners with a lower chlorination degree, and for the PCDD/Fs "stripping" from particulate to gas-phase during the sampling. At WS inlet, the PCDD/Fs account for 63.3% in vapor phase and for 36.7% in solid phase while, at WS outlet, the PCDD/Fs account for 21.4% in vapor phase and for 78.6% in solid phase. Considering that WS outlet temperature is about 40 degrees C, the PCDD/Fs vapor-phase condense to particles: therefore, even if the particulate is removed by WS, the final result is that PCDD/Fs percentage decreases in vapor-phase and increases in solid-phase.

PCDD/F adsorption and destruction in the flue gas streams of MWI and MSP via Cu and Fe catalysts supported on carbon

Catalytic destruction has been applied to control polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/Fs) emissions from different facilities. The cost of carbon-based catalysts is considerably lower than that of the metal oxide or zeolite-based catalysts used in the selective catalytic reduction (SCR) system. In this study, destruction and adsorption efficiencies of PCDD/Fs achieved with Cu/C and Fe/C catalysts from flue gas streams of a metal smelting plant (MSP) and a large-scale municipal waste incinerator (MWI), respectively, are evaluated via the pilot-scale catalytic reactor system (PCRS). The results indicate that Cu and Fe catalysts supported on carbon surface are capable of decomposing and adsorbing PCDD/ Fs from gas streams. In the testing sources of MSP and MWI, the PCDD/F removal efficiencies achieved with Cu/C catalyst at 250 degrees C reach 96%, however, the destruction efficiencies are negative (-1,390% and -112%, respectively) due to significant PCDD/F formation on catalyst promoted by copper. In addition, Fe/C catalyst is of higher removal and destruction efficiencies compared with Cu/C catalyst in both testing sources. The removal efficiencies of PCDD/Fs achieved with Fe/C catalyst are 97 and 94% for MSP and MWI, respectively, whereas the destruction efficiencies are both higher than 70%. Decrease of PCDD/F destruction efficiency and increase of adsorption efficiency with increasing chlorination of dioxin congeners is also observed in the test via three-layer Fe/C catalyst. Furthermore, the mass of 2,3,7,8-PCDD/Fs retained on catalyst decreases on the order of first to third layer of catalyst. Each gram Fe/C catalyst in first layer adsorbs 10.9, 6.91, and 3.04 ng 2,3,7,8-PCDD/Fs in 100 min testing duration as the operating temperature is controlled at 150, 200, and 250 degrees C, respectively.

Baseline levels of dioxin and furan emissions from waste thermal treatment in Colombia

Background data of polychlorinated dibenzodioxin and dibenzofuran (PCDD/Fs) emissions from the incineration sector in Colombia are presented. Monitoring was carried out during a two-year period, 2003-2005. Twelve plants were sampled for stack gas emissions of dioxins and total solid particulate (TSP). Additionally, PCDD/Fs in several fly ash samples were analyzed. Most incinerators burned industrial refuse materials and medical residues. A wide range of PCDD/Fs emission levels were found. In particular, levels ranging from 6.9 to 343.8 ng I-TEQ/N m(3) were determined in plants without any air pollution control system (APCS). In contrast, 0.5-39.2 ng I-TEQ/N m(3) levels were found in plants with APCS while 8.5-67.5 ng I-TEQ/g were measured in fly ash samples. TSP values ranged from 14 to 448 mg/N m(3). This study also evaluated the impact of implementing different control systems in an incinerator. Finally, for comparison purposes several samples were analyzed by both high resolution gas chromatography coupled to high resolution mass spectrometry (HRGC-HRMS) and high resolution gas chromatography coupled to ion-trap low resolution mass spectrometry-mass spectrometry (HRGC-IT LRMS/MS). Overall, I-TEQ values deviated about 20-30% between both techniques.

Adsorption characteristics of carbonaceous adsorbents for organic pollutants in a model incineration exhaust gas

Adsorption characteristics of carbonaceous adsorbents were examined using 1,2,3,4-tetrachlorobenzene, naphthalene and 2,4,6-tribromophenol as adsorbates. The breakthrough and equilibrium adsorption characteristics were evaluated using laboratory-scale adsorption test equipment. A micropore volume of diameter less than 2 nm is the most important factor governing the adsorption capacity of all adsorbates. A kinetic analysis was performed and the adsorption behavior of the adsorbates was analyzed. Diffusion within porous particles controls the adsorption rate in this system, and the diffusion process is a function of pore diffusion. The operating conditions in working incineration facility adsorbers were reviewed and the breakthrough time of these adsorbents in actual adsorbers was estimated using the mass transfer zone method. Information on the optimal operating conditions of adsorbers was derived from the adsorption breakthrough characteristics.

Effect of raw materials on emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans from the stack flue gases of secondary aluminum smelters

The present study was undertaken to investigate the effect of raw materials on PCDD/F emission from secondary aluminum smelters (ALS). Four plants each of aluminum ingot smelters (over 50% ingot) and secondary ALS (over 70% waste or recycled aluminum) were selected and the results compared. The secondary ALS yield much higher PCDD/Fs than the aluminum ingot smelters, or 7.94-22.76ng/Nm(3) versus 0.57-2.67ng/Nm(3), due to the large percentage of waste or recycled aluminum used. As for air pollution control devices (APCDs), the wet scrubber system in one of the aluminum ingot smelters exhibits an adverse effect on PCDD/F removal, due to the continuous recycle of the contaminated water through the scrubber system. Another ingot plant equipped with cartridge filter, there is a significant reduction in PCDD/F TEQ (52%). The powdered activated carbon injection at 2kg/h (110mg/Nm(3)) in one ALS reduces 70% of the total PCDD/Fs. The average emission factor of four secondary ALS is much higher than that of aluminum ingot smelters, or 20-fold higher based on either raw materials or product. Consequently, more attention should be paid to the emission reduction of PCDD/Fs from the secondary ALS, including installation of a secondary burner, additional APCDs and the pre-cleaning of raw materials.

Characterization of PCDD/Fs and heavy metals from MSW incineration plant in Harbin

The characterization of PCDD/Fs and heavy metals in the flue gas and fly ash of Harbin municipal solid waste (MSW) incineration plant, located in the northeast of China, was investigated in this study. The MSW was treated in a twin internal fluidized (TIF) bed incinerator. The results indicate that the emission of PCDD/Fs into the environment is 0.02 ng I-TEQ/m3 and the level of PCDD/Fs in the fabric filter fly ash is 0.7982 ng I-TEQ/g. The leachability levels of Pb, Cd and Hg in the fly ash are below the limits of environmental protection standard in China. However, the contents of Cu, Zn, and Hg are high in the fly ash. This suggests that the fly ash is a hazardous waste that requires special treatment and disposal. The practice of more than four years of operation shows that the TIF bed incinerator is very suitable and practical for China.

Destruction of PCDD/Fs by SCR from flue gases of municipal waste incinerator and metal smelting plant

Partitioning of PCDD/F congeners between vapor/solid phases and removal and destruction efficiencies achieved with selective catalytic reduction (SCR) system for PCDD/Fs at an existing municipal waste incinerator (MWI) and metal smelting plant (MSP) in Taiwan are evaluated via stack sampling and analysis. The MWI investigated is equipped with electrostatic precipitators (EP, operating temperature: 230 degrees C), wet scrubbers (WS, operating temperature: 70 degrees C) and SCR (operating temperature: 220 degrees C) as major air pollution control devices (APCDs). PCDD/F concentration measured at stack gas of the MWI investigated is 0.728 ng-TEQ/Nm(3). The removal efficiency of WS+SCR system for PCDD/Fs reaches 93% in the MWI investigated. The MSP investigated is equipped with EP (operating temperature: 240 degrees C) and SCR (operating temperature: 290 degrees C) as APCDs. The flue gas sampling results also indicate that PCDD/F concentration treated with SCR is 1.35 ng-TEQ/Nm(3). The SCR system adopted in MSP can remove 52.3% PCDD/Fs from flue gases (SCR operating temperature: 290 degrees C, Gas flow rate: 660 kN m(3)/h). In addition, the distributions of PCDD/F congeners observed in the flue gases of the MWI and MSP investigated are significantly different. This study also indicates that the PCDD/F congeners measured in the flue gases of those two facilities are mostly distributed in vapor phase prior to the SCR system and shift to solid phase (vapor-phase PCDD/Fs are effectively decomposed) after being treated with catalyst. Besides, the results also indicate that with SCR highly chlorinated PCDD/F congeners can be transformed to lowly chlorinated PCDD/F congeners probably by dechlorination, while the removal efficiencies of vapor-phase PCDD/Fs increase with increasing chlorination.

PCDD/DF concentrations at the inlets and outlets of wet scrubbers in Korean waste incinerators

To further understand the effects of wet scrubbers on PCDD/DF levels, it was measured the concentrations of PCDD/DF, dust, and other gaseous pollutants at both the inlets and the outlets of seven wet scrubbers. As a result, the concentrations of PCDD/DF at the inlets and outlets of the wet scrubbers ranged from 0.2 to 37.4, and 0.8 to 6.0 ng TEQ N m-3, respectively. With the exceptions of wet scrubbers F and G, the PCDD/DF levels decreased by and large in most wet scrubbers. It was thought that their relatively high removal efficiencies were more increased with heavier loads of dust and particle-bound PCDD/DF. On the other hand, it was also surveyed the increase of gaseous PCDD/DF in wet scrubber, where the total level of PCDD/DF was decreased. However, it was not sure whether it had been resulted from the thermal adsorption/desorption phenomenon between packing materials and emission gases or not. At the very least, however, although there still remains an unexplained aspect for the increase of gaseous PCDD/DF, it is clear that wet scrubbers can be sufficiently applied to remove PCDD/DF to a certain extent, if only removal efficiencies for the particle loads are high, and if a significant part of the PCDD/DF at the inlets is particle associated.

The prediction of PCDD/DF levels in wet scrubbers associated with waste incinerators

Wet scrubber is one of the most conventional types of air pollutant control devices (APCDs), which is specially designed to treat dust and acidic gases in the flue gas simultaneously. In spite of its outstanding ability to control them, however, wet scrubbers have been considered as potential contaminant sources that may increase PCDD/DF concentrations in the flue gas. In this study, we investigated the change of PCDD/DF concentrations at the inlets and outlets of seven wet scrubbers, and compared them with other published data. With a multi-regression analysis of dust concentrations and temperature at the inlets and outlets of given wet scrubbers, we developed an empirical model to understand factors dominating the change of PCDD/DF concentrations. As a result, we confirmed that the changes of PCDD/DF concentrations in wet scrubbers are closely related to their concentrations at the inlets, which would usually be determined by the type of APCDs installed upstream of the wet scrubber.

Reducing PCDD/F formation by adding sulfur as inhibitor in waste incineration processes

The results obtained in this study indicate that addition of sulfur in incineration processes could effectively reduce PCDD/F formation. PCDD/F formation is reduced dramatically (54.1%) when S/Cl molar ratio is controlled at about 2 in a laboratory-scale system (LSS). The XRD analysis of the fly ash confirms the existence of vulcanized metals such as Cu2SO4, Cu2S, SnS and ZnS. The results suggest that the sulfur added would poison Cu-based metals and render the Deacon reaction catalyst less active, thereby reducing PCDD/F formation. In addition, the results obtained from the tests conducted in an industrial waste incinerator (IWI) indicate that the efficiency of reducing PCDD/F formation by adding sulfur was 51.6% at S/Cl mole ratio of 0.4. The results indicate that adding too much sulfur would actually increase particle concentration and also increase PCDD/F yield. This study demonstrates the effectiveness of adding sulfur as an alternative technology for reducing PCDD/F emissions from waste incineration processes. The efficiency of reducing PCDD/F formation by addition of sulfur is strongly influenced by S/Cl mole ratio.

Experimental study on the removal of PAHs using in-duct activated carbon injection

This paper presents the incineration tests of municipal solid waste (MSW) in a fluidized bed and the adsorption of activated carbon (AC) on polycyclic aromatic hydrocarbons (PAHs). An extraction and high performance liquid chromatography (HPLC) technique was used to analyze the concentrations of the 16 US EPA specified PAHs contained in raw MSW, flue gas, fly ash, and bottom ash. The aim of this work was to decide the influence of AC on the distribution of PAHs during the incineration of MSW. Experimental researches show that there were a few PAHs in MSW and bottom ash. With the increase of AC feeding rate, the concentrations of three- to six-ring PAHs in fly ash increased, and the concentration of two-ring PAH decreased. The total-PAHs in flue gas were dominated by three-, and four-ring PAHs, but a few two-, five-ring PAHs and no six-ring PAHs were found. PAHs could be removed effectively from flue gas by using in-duct AC injection and the removal efficiencies of PAHs were about 76-91%. In addition, the total toxic equivalent (TEQ) concentrations of PAH in raw MSW, bottom ash, fly ash, and flue gas were 1.24 mg TEQ kg-1, 0.25 mg TEQ kg-1, 6.89-9.67 mg TEQ kg-1, and 0.36-1.50 microg TEQ Nm-3, respectively.

Evaluation of PCDD/F congener distributions in MWI flue gas treated with SCR catalysts

Partitioning of PCDD/F congeners between gaseous and particulate phases and removal efficiencies of the air pollution control devices (APCDs) for PCDD/Fs at an existing municipal waste incinerator (MWI) in Taiwan are evaluated via stack sampling and analysis. The MWI investigated is equipped with electrostatic precipitators (EP), wet scrubbers (WS) and selective catalytic reduction system (SCR) as APCDs. The average PCDD/F concentration of stack gas is 1.49 ng/Nm3, and the International Toxic Equivalent Quantity (I-TEQ) is 0.043 ng-I-TEQ/Nm3. The EP increases PCDD/F concentration by 174.0% while the average removal efficiency of WS+SCR system for PCDD/Fs reaches 99.1%. In addition, the PCDF removal efficiency achieved with WS+SCR system (97.1-99.8%) is higher than that for PCDDs (96.5-99.3%). The results obtained on gas/particulate partitioning in flue gas indicate that the particulate-phase PCDD/Fs accounted for 65% at the inlet of EP, 20% at the outlet of EP and 50% at the stack, respectively, of the total PCDD/F concentrations. This study also indicates that as the chlorination level of PCDD/F congeners increases, the percentage of PCDD/Fs existing in gas phase decreases in all flue gas samples.

Emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans from stack flue gases of sinter plants

This study investigated four sinter plants, classified into two categories--with selective catalytic reduction (SCR) (S1, S2 and S3) and without SCR (S4) as its air pollution control device. Polychlorinated dibenzofurans (PCDFs) are dominant in the stack flue gases of sinter plants with and without SCR. The polychlorinated dibenzofurans/polychlorinated dibenzo-p-dioxins (PCDFs/PCDDs) ratio exceeds 1 extremely. The degree of chlorination of the sinter plant without SCR is towards hepta and hexa congeners while that of the sinter plant with SCR is towards penta and hexa congeners. PCDD/Fs are indeed decomposed (75.5% and 69% on ng and ng TEQ bases, respectively) and not only reduced in degree of chlorination. The overall concentration in the stack flue gas of sinter plants with SCR (7.97-14.1 ng/Nm(3); 0.995-2.06 ng TEQ/Nm(3)) is lower than that of the sinter plant without SCR (28.9 ng/Nm(3); 3.10 ng TEQ/Nm(3)). In Taiwan, based on the emission factors of 0.970 microg TEQ/ton-feedstock (sinter plants with SCR) and 3.13 microg TEQ/ton-feedstock (sinter plant without SCR), the annual PCDD/F emission of 44.7 g TEQ/year from sinter plants is 60 and 121 times higher than those from municipal solid waste incinerators (0.750 g TEQ/year) and MWIs (0.369 g TEQ/year). These results show that sinter plants have become the dominating PCDD/F emission source since tighter emission limits have been applied to incinerators.