Activated Carbon Injection Research Articles

Formation, migration, and removal mechanisms of PCDD/Fs throughout the temperature range (850°C–150°C) in a full-scale MSW incinerator: The invention of novel high-temperature PCDD/F sampling device

Polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) emitted from municipal solid waste (MSW) incineration have detrimental effects on the ecological environment. This study innovatively invented a high-temperature sampling device for PCDD/Fs, followed by a process tracing experiment conducted in a full-scale MSW incinerator to investigate the formation and migration mechanisms of PCDD/Fs throughout the temperature range (850°C–150°C). The results highlighted the considerable PCDD/F level of 0.446 ng I-TEQ Nm−3 at the @1 furnace outlet (850°C). The distribution characteristics of PCDD/Fs suggested a prevalence of high-temperature homogeneous reactions in the flue zone between sites @1 and #1 (850°C–600°C). In the low-temperature zone, de novo synthesis emerged as the dominant formation mechanism, primarily occurring near the @2 superheater outlet (∼368°C) and inside the SCR system (∼230°C). The impact and removal efficiency of individual air pollutant control devices on PCDD/Fs was systematically analyzed, yielding an overall PCDD/F reduction of 99.7%. Remarkably, the buffering effect of economizer, the co-removal of semi-dry deacidification system, and the adsorption-filtration effect of activated carbon injection and fabric filter individually reduced PCDD/F concentrations by 23.9%, 35.3%, and 99.7%, respectively; while de novo synthesis inside the SCR system negatively impacted PCDD/F removal, demonstrating an efficiency of −43.2%. Consequently, these comprehensive insights inspired industrial operation optimization and ultra-low PCDD/F emission control.

Recyclable magnetic-responsive AC/Fe3O4/UiO-66 adsorbents for removing elemental mercury from flue gas

Activated carbon injection technology has been identified as the leading method for removing elemental mercury (Hg0) in coal-fired power plants. However, this technology can only achieve pollutant transfer, with the disposal of removal products and the inability to recycle adsorbents, and there is an issue of secondary pollutant release. In this work, a series of magnetic composites AC/Fe3O4/UiO-66-X were prepared by adding different amounts of activated carbon during the synthesis process. Activated carbon was introduced into the synthesis process of magnetic metal–organic framework Fe3O4/UiO-66 to enhance its dispersibility and improve its adsorption capacity of Hg0 in simulated flue gas. The porous composites have good stability and magnetism. The elemental mercury removal experiment showed that the addition of activated carbon greatly enhanced the removal performance in the simulated flue gas, with a maximum adsorption capacity was 85.9 μg/g. The spent magnetic composite AC/Fe3O4/UiO-66–1.0 was recycled, and the results showed that the adsorbent remained good mercury-removal performance after four cycles of regeneration. The regenerated adsorbent showed an 8.4 % decrease compared to the fresh adsorbent after four times of recycling. The recovery rate can even exceed 65 % at the high wind speed of 9 m/s in the wind tunnel with magnetic field.

Selenium-modified activated coke: a high-capacity and facile designed Hg0 adsorbent for coal-fired flue gas.

The substantial amount of mercury emissions from coal-fired flue gas causes severe environmental contamination. With the Minamata Convention now officially in force, it is critical to strengthen mercury pollution control. Existing activated carbon injection technologies suffer from poor desulfurization performance and risk secondary-release risks. Therefore, considering the potential industrial application of adsorbents, we selected cost-effective and readily available activated coke (AC) as the carrier in this study. Four metal selenides-copper, iron, manganese, and tin-were loaded onto the AC to overcome the application problems of existing technologies. After 120min of adsorption, the CuSe/AC exhibited the highest efficiency in removing Hg0, surpassing 80% according to the experimental findings. In addition, the optimal adsorption temperature window was 30-120°C, the maximum adsorption rate was 2.9 × 10-2mg·g-1·h-1, and the effectiveness of CuSe/AC in capturing Hg0 only dropped by 5.2% in the sulfur-containing atmosphere. The physicochemical characterization results indicated that the AC surface had a uniform loading of CuSe with a nanosheet structure resembling polygon and that the Cu-to-Se atomic ratio was close to 1:1. Finally, two possible Hg0 reaction pathways on CuSe/AC were proposed. Moreover, it was elucidated that the highly selective binding of Hg0 with ligand-unsaturated Se- was the key factor in achieving high adsorption efficiency and sulfur resistance in the selenium-functionalized AC adsorbent. This finding offers substantial theoretical support for the industrial application of this adsorbent.

Swirl diffusion strategy boosts mercury removal effectiveness of magnetospheres injector

The emissions of mercury from coal-fired flue gas poses a major threat to public health and ecosystems. Modified magnetospheres (CC-MF) mercury removal technology provides an economical, reusable, and eco-friendly solution, overcoming the drawbacks of conventional activated carbon injection (ACI) techniques. To address the issues of inadequate particle diffusion and uneven injection in traditional mercury removal injectors, this study developed a single-hole swirl injector. Furthermore, a mathematical model for mercury removal was developed and imported in the form of a UDF into Fluent for the evaluation of section coverage rate and mercury removal efficiency. The simulation results demonstrated that the section coverage rate of the swirl injector improved by 51.0%, reaching 81.0% compared to the direct injector. Additionally, the mercury removal efficiency increased by 41.3%, reaching 88.7%. This work identified the optimal operational parameters for the CC-MF mercury removal system, providing valuable insights for its practical application.

Effect of flue gas components on the removal of cadmium pollutants by transition metal-modified activated carbon: Density functional theory and thermodynamic study

Removal of cadmium (Cd) pollutants from waste incineration (MSW) flue gas by modified activated carbon (AC) is of great potential, yet the influence of flue gas composition on their interaction mechanism is still unclear. Thus, density functional theory and thermodynamic analyses were combined to explore the effects of typical flue gas compositions (O2, HCl, NO, SO2, CO2, and H2O) on Cd species capture over the Fe/AC and Mn/AC surfaces. All flue gas compositions inhibit the adsorption of Cd species, wherein their inhibitory effects are mainly divided into two categories, i.e., one with moderate inhibition (HCl, CO2, and H2O), and the other with significant inhibition (O2, NO, and SO2). For the first category, HCl forms new active sites after adsorption on the surface, while CO2 and H2O have weak competitiveness with Cd species, resulting in mild inhibitory effects. Nevertheless, O atoms of O2/SO2 and N atoms of NO are highly effortless to bond with Fe/Mn atoms, and strongly exclude the Cd adsorption on the active sites, greatly weakening their binding strength. According to thermodynamic analysis, the fixation of Cd species by Fe/AC and Mn/AC spontaneously proceeds with the interference of flue gas components, while the selectivity to Cd species decreases with the increased temperature. In summary, it is instrumental to adjust the operating parameters and AC injection location to attenuate the negative effects of O2, SO2, NO, and high temperature on Cd capture by Fe/AC and Mn/AC.

Simultaneous removal of PCDD/Fs and mercury by activated carbon from a full-scale MSW incinerator in southeast China.

This study emphasized on the removal performance of polychlorinated-ρ-dibenzodioxins and dibenzofurans (PCDD/Fs) and mercury by different activated carbon injection (ACI) rates from a full-scale (700 t/d) MSW incinerator. The result exhibited that the emission standard of PCDD/Fs and mercury could be met when the ACI rate reached 50mg/Nm3 and 30mg/Nm3, respectively. Lower chlorinated PCDD/Fs and PCDFs showed higher removal efficiencies compared with highly chlorinated PCDD/Fs and PCDDs, which could be attributed to the larger competitiveness of highly volatile congeners in AC adsorption than the lower volatile ones. AC turned out to have different adsorption selectivity for CP-routes PCDD/Fs congeners, among which 1379-TCDD was preferred to be absorbed while others exhibited little or poor selectivity for AC adsorption. The removal efficiency of PCDD/Fs was positively correlated with ACI rate at 99% confidence interval with a linear relationship (R2 = 0.98). Also, the outlet concentration of mercury decreased with the increase of ACI rate in a nearly linear function (R2 = 0.96). These results will be meaningful for the rational use of AC for pollutants control.

Ultra-high adsorption of Hg0 using impregnated activated carbon by selenium.

Activated carbon was one of the main adsorptions utilized in elemental mercury (Hg0) removal from coal combustion flue gas. However, the high cost and low physical adsorption efficiency of activated carbon injection (ACI) limited its application. In this study, an ultra-high efficiency (nearly 100%) catalyst sorbent-Sex/Activated carbon (Sex/AC) was synthesized and applied to remove Hg0 in the simulated flue gas, which exhibited 120 times outstanding adsorption performance versus the conventional activated carbon. The Sex/AC reached 17.98 mg/g Hg0 adsorption capacity at 160 °C under the pure nitrogen atmosphere. Moreover, it maintained an excellent mercury adsorption tolerance, reaching the efficiency of Hg0 removal above 85% at the NO and SO2 conditions in a bench-scale fixed-bed reactor. Characterized by the multiple methods, including BET, XRD, XPS, kinetic and thermodynamic analysis, and the DFT calculation, we demonstrated that the ultrahigh mercury removal performance originated from the activated Se species in Sex/AC. Chemical adsorption plays a dominant role in Hg0 removal: Selenium anchored on the surface of AC would capture Hg0 in the flue gas to form an extremely stable substance-HgSe, avoiding subsequent Hg0 released. Additionally, the oxygen-containing functional groups in AC and the higher BET areas promote the conversion of Hg0 to HgO. This work provided a novel and highly efficient carbon-based sorbent -Sex/AC to capture the mercury in coal combustion flue gas. Graphical abstract Selenium-modified porous activated carbon and the interface functional group promotes the synergistic effect of physical adsorption and chemical adsorption to promote the adsorption capacity of Hg0.

Removing mercury from flue gas by sulfur-doped zeolite-templated carbon: Synthesize and adsorption mechanism

Elemental mercury is harmful to humanity and the ecological environment. It is a simple and feasible method to capture elemental mercury by carbon-based adsorbents. The purpose of this work is to develop zeolite-templated carbon with and without sulfur (ZTC and S-doped ZTC) and to explore their mercury adsorption performance. ZTC and S-doped ZTC were synthesized by chemical vapor deposition (CVD) method and their mercury adsorption performance were tested at 30 and 150 °C. Among all ZTC samples, BEA-ZTC-HS exhibited highest mercury removal efficiency (MRE) whose initial value was 99.99% (150 °C) and 97.39% (30 °C) and decreased to 96.63% and 89.15% after one hour mercury adsorption. The physical and chemical properties of the ZTC samples were characterized by various methods to explain the high MRE of BEA-ZTC-HS. The experimental results shown that BEA-ZTC-HS replicated the crystal structure of BEA zeolite faithfully and exhibited regular microporous structure and doesn’t have obvious elemental sulfur whose existence could block the micropores in ZTC. This was helpful to the mass transfer of Hg0 in ZTC. Moreover, the chemical properties of BEA-ZTC-HS shown that the introduced sulfur were mainly bonded to the carbon framework of ZTC in the form of thiophene, sulfone, sulfoxide and sulfonic acid. Those sulfur-containing functional groups provided main active sites for mercury capture and exhibited higher activity at 150 °C. Finally, Density Functional Theory (DFT) was used to reveal the adsorption mechanism of ZTC and S-doped ZTC on Hg0. Due to its good properties of regeneration, higher MRE, good thermal stability and low cost, BEA-ZTC-HS has a wide prospect for industrial application in the wide temperature ranges compared to the activated carbon injection technology.

Surface sulfidation modification of magnetospheres from fly ash for elemental mercury removal from coal combustion flue gas

Reduction of elemental mercury (Hg0) emission from coal-fired power plants is an enormous challenge. In this work, magnetospheres separated from fly ash was modified through H2S as an efficient sorbent (i.e., S-MS) for Hg0. Elemental sulfur with high affinity towards Hg0 was formed on the S-MS surface through selective catalytic oxidation of H2S. The sulfidation temperature played an important role in Hg0 adsorption over S-MS, ascribing to the variation of sulfur species on S-MS. The S-MS exhibited above 80% Hg0 adsorption efficiency with a sulfidation temperature of 150 °C for 30 min. The optimal Hg0 adsorption performance was obtained at 50 and 75 °C, implying that the S-MS could be adopted by injecting into the duct upstream of wet electrostatic precipitator (WESP) system. The gaseous Hg0 was immobilized by S-MS as stable mercury sulfide (HgS) owing to the presence of abundant sulfur species that is active for binding Hg0. The leaching ratio of mercury from spent S-MS in WESP effluent was as low as 1%, hence minimizing the secondary mercury pollution from the industrial waste. The cost analysis demonstrates that the mercury removal technology on the basis of magnetospheres adsorbents exhibited much superiority in operation cost compared with commercial activated carbon injection technology. Thus, the S-MS, with specific features, such as high Hg0 adsorption performance, minimized environmental hazardous and recyclability, displayed great potential in Hg0 sequestration.

Adsorption of low-concentration organic pollutants from typical coal-fired power plants by activated carbon injection

Activated carbon (AC) injection was applied to remove the organic pollutants from coal-fired power plants. The total hydrocarbon (THC) concentration in flue gases was 0.512–0.998 mg/m3, aromatic hydrocarbons and oxygenated volatile organic compounds (VOCs) were the major components. With the AC injection (150 mg/m3), the THC was removed by 36.52–46.49%. The mesopores could capture some larger organic molecules and facilitate the intrapore diffusion. Improving the AC injection amount promoted the organic pollutant adsorption, but lowered the AC adsorption capacity. Removal performance of organic pollutants was affected by their physicochemical properties. The removal efficiency for most VOCs was within the range of 15–50%, while that was 45–90% for semi-VOCs. Minor amounts of VOCs achieved high removal efficiency through specific interactions, especially oxygenated VOCs. However, the removal efficiency of the total oxygenated VOCs was lower due to competition adsorption with inorganic components. AC injection had no significant effect on the physicochemical properties of fly ash. This work and results provide a feasible method and reference for the reduction of organic pollutants in coal-fired power plants and other combustion exhaust gases.

Adsorption behaviors of VOCs under coal-combustion flue gas environment using activated carbon injection coupled with bag filtering system

Adsorbent injection is a simple and efficient technique for flue gas purification. Performances of volatile organic compounds (VOCs) removal in coal-combustion flue gas environment were investigated by activated carbon (AC) injection coupled with bag filtering (ACI + BF). Results showed that the removal efficiency of toluene and p-xylene was not only related to the micropore volume of AC but also to the pore size distribution and mesopore volume. Waste AC could be reused without desorption, the removal efficiency of mixed ACs was close to the fresh AC when the proportion of waste AC was 25%. Under complex coal-combustion flue gas environment, the adsorption efficiency of p-xylene was decreased by 19.0%. The fly ash in flowing state had less influence on the adsorption of VOCs on AC. On the adsorption layer of filter bag, fly ash decreased the AC concentration and blocked some important mass transfer channels of VOCs, restricting the diffusion of VOCs to the AC outer surface and decreasing utilization efficiency of adsorption sites. Although the concentration of SO2 was high, the inhibitory effect on VOCs adsorption was not significant. As the water vapor and SO2 coexisted, the H2SO4 was formed and blocked some micropores. Then the VOCs diffusion in the AC inner pores was influenced and some micropores could not adsorb VOCs. The removal of VOCs in both pipeline and adsorption layer was influenced by SO2 and water vapor.

Effects of evaporation capacity on the formation and removal of PCDD/Fs in a full-scale municipal solid waste incinerator

Municipal solid waste (MSW) classification has become a hot topic with the requirement of “zero waste city”; however, incinerators are designed unclassified currently. Therefore, it is difficult to keep around the rated value of evaporation capacity. Herein, we investigated the effects of evaporation capacity on the formation and removal of PCDD/Fs in a full-scale incinerator firstly. The formation of PCDD/Fs at the 110 % evaporation was lower than that of 100 % from the primary superheater to economizer, as high oxygen concentration. After flue gas flowed through the position of activated carbon injection, PCDD/F emissions at the 100 % evaporation were lower than that at the 110 % as the primary air volume at 110 % was 1.21 times that of 100 %. It had no significant effects on the PCDD/F emissions of the stack gas for an increase approximate 10 % of the evaporation capacity. Although the removal efficiencies of PCDD/F congeners varied in the four parts of the air pollution control devices (APCDs), while it was similar for the effects of APCDs on the removal efficiencies of PCDD/Fs between the two operating conditions. For the two different operating conditions, the removal efficiencies of congeners were kept at high levels (96.32–99.81 %) after flue gas flowed through APCDs and the removal efficiencies of the less-chlorinated congeners general were higher than those in the more-chlorinated congeners. And the removal efficiencies of PCDFs were much higher than PCDDs. These findings provide some new option for controlling PCDD/F emissions in a full-scale incinerator under the MSW classification.

Emissions of PAHs, PCDD/Fs, dl-PCBs, chlorophenols and chlorobenzenes from municipal waste incinerator cofiring industrial waste

Concentrations and distributions of PAHs and chlorinated aromatic compounds including PCDD/Fs, dl-PCBs, chlorophenols (CPs), and chlorobenzenes (CBz) in the municipal waste incinerator are investigated to characterize their formation and emission via intensive stack sampling. In addition, the toxicity of fly ash contribution by PCDD/Fs and dl-PCBs is evaluated in this study. The results reveal that concentrations of PCDD/Fs and dl-PCBs in flue gas are significantly lower than those of CPs, CBz, and PAHs. Additionally, the removal efficiencies of PAHs and chlorinated aromatic compounds achieved with existing air pollution control devices are evaluated, indicating that the removal efficiencies achieved with activated carbon injection + baghouse (95–99%) are higher than those with semi-dry scrubber (SDS). Besides, PCDD/Fs and PCBs TEQ concentrations in SDS and BH ashes are within 1.61–2.66 WHO-TEQ/g and 0.09–0.19 WHO-TEQ/g, respectively. Furthermore, the calculated mass flow rates suggest that the input rate of PCDD/Fs and dl-PCBs of SDS are 60.24 mg/h and 59.74 mg/h, respectively. The mass flow rates of PCDD/Fs and dl-PCBs after SDS in flue gas are 32.47 mg/h and 49.73 mg/h, respectively. However, the discharge rates of PCDD/Fs and dl-PCBs from SDS are 120.60 mg/h and 27.05 mg/h, respectively, indicating that PCDD/Fs are significantly formed within the SDS. PCDD/Fs formation is attributed to the operating temperature of SDS (240 ± 11.5 °C), which is within the temperature window for de novo synthesis. Thus, operating parameters of the APCDs should be optimized to reduce the formation of PAHs and chlorinated aromatic pollutants from MWI.

Mercury adsorption characteristics of Cl-impregnated activated carbons in simulated flue gases

Activated carbon injection upstream of a particulate matter control device is a general method to control mercury in a coal-fired flue gas. Nitrogen oxides (NOx) and hydrogen chloride (HCl) in flue gas have been reported to increase the efficiency of activated carbon for mercury removal. In a coal-fired power plant, a NOx control device is generally located upstream of a particulate matter control device. In addition, if coal with a low chloride (Cl) content is burned, the concentrations of NOx and HCl may be low in the flue gas upstream of a particulate matter control device. Under these conditions, chemically promoted activated carbon is necessary to effectively control mercury. This study was designed to suggest the best chloride compound impregnated on activated carbon depending on the flue gas composition. HCl, ferric chloride (FeCl3) and cupric chloride (CuCl2) were impregnated with an identical concentration of Cl on activated carbon. Then, each sorbent was tested using a fixed-bed reactor system at 140 °C. CuCl2-impregnated activated carbon (CuCl2-AC) was tolerant of SO2 gas. The mercury adsorption efficiency was higher in the order of CuCl2-AC, FeCl3-impregnated activated carbon (FeCl3-AC) and HCl-impregnated activated carbon (HCl-AC) with 1% Cl for all three sorbents for the tests with a simulated flue gas of 12% CO2, 5% O2, 7% H2O, 60–70 µg/m3 Hg0, 500 ppm SO2, 20 ppm NO and N2 balance gas. However, the mercury adsorption efficiencies among the Cl-impregnated activated carbon sorbents became more similar with the increase in Cl concentration on activated carbon.

Mercury removal performance of brominated biomass activated carbon injection in simulated and coal-fired flue gas

Brominated biomass activated carbon, with impactful gaseous mercury removal performance, has become a novel cost-effective and environment friendly alternative adsorbent for activated carbon. In this paper, the mercury removal behavior of brominated rice husk activated carbon (RHAC-Br) injecting was investigated in a simulated flue gas entrained-flow experimental system, a pilot-scale 0.3 MWth circulating fluidized bed combustion (CFBC) system, and an industrial-scale 75 t/h CFBC boiler system, respectively. For comparison, the mercury removal performance of brominated coconut husk activated carbon (CHAC-Br) and brominated coal-based activated carbon (CAC-Br) was also studied in simulated and coal-fired flue gas. Combined with the nitrogen adsorption-desorption and X-ray photoelectron spectroscopy analyses, the three sorbents were characterized and analyzed on their mercury removal features in different scale experiments. The results showed that in the entrained-flow experimental system, the increase of injection amount and initial mercury concentration promotes mercury removal of RHAC-Br, with the optimum removal temperature of 120 °C, and the following order for Hg0 removal efficiency for the three sorbents: η (CAC-Br) > η (CHAC-Br) > η (RHAC-Br). Further investigation carried out in the pilot-scale 0.3 MWth CFBC facility indicated that both injection temperature and mercury removal behavior of the three sorbents in coal-fired flue gas are quite different from those in the simulated flue gas, mainly as a result of large proportion of Hg2+ and Hgp. The mercury removal performance of RHAC-Br is comparable to that of a commercial activated carbon (CAC-Br). The outcome conducted in the industrial-scale 75 t/h CFBC boiler system demonstrated that the RHAC-Br injection is as efficient as CAC-Br injection, verifying that the brominated biomass activated carbon could be an effectively alternative adsorbent for the brominated activated carbon in the application for large-scale coal-fired boiler systems.

Magnetically recyclable Fe3O4 doped flower-like MoS2: Efficient removal of elemental mercury

At the front end of the Electrostatic precipitator (ESP), activated carbon injection is a common method to remove mercury from flue gas, but the high cost, low efficiency and non-recyclability limit the practical application of activated carbon. MoS2, a transition metal sulfide with a two-dimensional layered structure, was found to have favourable performances in removing contaminant. In this work, Fe3O4 was successfully grown on the surface of flower-like MoS2 by two-steps hydrothermal methods. The experimental results showed that the specific surface area of MoS2/Fe3O4 (MF) was the largest when the ratio is 10 wt% (MF-10). Compared with pure MoS2, the specific surface area of MF-10 increased by 6.7467 m2/g, which was attributed to the growth of Fe3O4. At the same time, the introduction of Fe3O4 made the MF possess superparamagnetism to facilitate its retrievability under an external magnetic field. In addition, MF-10 also showed a mercury removal efficiency of almost 100%. Although the efficiency of the MF-10 has decreased after 5 cycles and 24 h, it could still maintain about 90%, revealing a stable cycle life. Due to its mercury removal performance and recyclability, MF can be considered as a favorable adsorbent for removing elemental mercury.

Near-Zero Air Pollutant Emission Technologies and Applications for Clean Coal-Fired Power

Abstract Coal is the dominant energy source in China, and coal-fired power accounts for about half of coal consumption. However, air pollutant emissions from coal-fired power plants cause severe ecological and environmental problems. This paper focuses on near-zero emission technologies and applications for clean coal-fired power. The long-term operation states of near-zero emission units were evaluated, and synergistic and special mercury (Hg) control technologies were researched. The results show that the principle technical route of near-zero emission, which was applied to 101 of China’s coal-fired units, has good adaptability to coal properties. The emission concentrations of particulate matter (PM), SO2, and NOx were below the emission limits of gas-fired power plants and the compliance rates of the hourly average emission concentrations reaching near-zero emission in long-term operation exceeded 99%. With the application of near-zero emission technologies, the generating costs increased by about 0.01 CNY∙(kW∙h)–1. However, the total emissions of air pollutants decreased by about 90%, resulting in effective improvement of the ambient air quality. Furthermore, while the Hg emission concentrations of the near-zero emission units ranged from 0.51 to 2.89 μg∙m−3, after the modified fly ash (MFA) special Hg removal system was applied, Hg emission concentration reached as low as 0.29 μg∙m−3. The operating cost of this system was only 10%–15% of the cost of mainstream Hg removal technology using activated carbon injection. Based on experimental studies carried out in a 50 000 m3∙h−1 coal-fired flue gas pollutant control pilot platform, the interaction relationships of multi-pollutant removal were obtained and solutions were developed for emissions reaching different limits. A combined demonstration application for clean coal-fired power, with the new “1123” eco-friendly emission limits of 1, 10, 20 mg∙m−3, and 3 μg∙m−3, respectively, for PM, SO2, NOx, and Hg from near-zero emission coal-fired power were put forward and realized, providing engineering and technical support for the national enhanced pollution emission standards.

Partitioning and removal behaviors of PCDD/Fs, PCBs and PCNs in a modern municipal solid waste incineration system

An extensive evaluation on a modern full-scale municipal solid waste incineration system was conducted for characterizing the distribution of highly toxic chlorinated aromatics, polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs) and polychlorinated naphthalenes (PCNs), and their corresponding mass fluxes in post combustion zone. It was found that the flue gas/fly ash partitioning behaviors of chlorinated aromatics could be essentially described by their octanol-air partition coefficients (KOA) and strongly affected by the flue gas temperature. Above 93% of chlorinated aromatics formed in boiler section was partitioned into the flue gas and transported into the subsequent flue gas cleaning system, in which above 92% of Cl3–8DDs, Cl3–7DFs, Cl5–10Bs and Cl4–8Ns in flue gas was removed by the discharge of fly ash. The results of mass flux calculation indicated that the memory effect in flue gas cleaning system remarkably elevated the emission levels of chlorinated aromatics, especially the less chlorinated ones. The memory effect should mainly result from the direct chlorination mechanism mediated by the deposited particles. In addition, activated carbon injection could cause an obvious increase in PCBs emission. The obtained results provided some important implications for further reducing the emission of highly toxic chlorinated aromatics.

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.