Removal effect of the low-low temperature electrostatic precipitator on polycyclic aromatic hydrocarbons

The modification of surface basicity and its role in naphthalene oxidation: The effect of the basic sites introduced by Ce

A series of V-xCe/Ti catalysts was prepared by a step impregnation method with gradual increased Ce amount. Compared to the commercial V-W/Ti catalysts, the V-xCe/Ti catalysts exhibited considerably higher COx selectivity during the oxidation of naphthalene (Nap), and less intermediates or by-products were detected both in gas phase and on the surface of the catalysts. Through a series of characterizations, it was found that abundance of weak basic sites in the form of OH was introduced by Ce, as well as the oxygen vacancies caused by the redox cycle of V4++Ce4+↔V5++Ce3+. The weak basic sites introduced by Ce could greatly enhance the Nap adsorption, and the Nap adsorbed was quickly converted to naphthol on Ce-OH. Furthermore, V existed at a high valence with the interaction of V and Ce, and the oxygen vacancies also increased the Oads and OOH. It improved the redox ability and the regeneration of Ce-OH on V-xCe/Ti catalysts. The intermediates could be further oxidized, and the Ce-OH consumed in the reaction could recover quickly. Therefore, almost 100% Nap conversion and a high COx selectivity was observed in the V-xCe/Ti catalysts system.

Potential Strategy to Control the Organic Components of Condensable Particulate Matter: A Critical Review

More and more attention has been paid to condensable particulate matter (CPM) since its emissions have surpassed that of filterable particulate matter (FPM) with the large-scale application of ultralow-emission reform. CPM is a gaseous material in the flue stack but instantly turns into particles after leaving the stack. It is composed of inorganic and organic components. Organic components are an important part of CPM, and they are an irritant, teratogenic, and carcinogenic, which triggers photochemical smog, urban haze, and acid deposition. CPM organic components can aggravate air pollution and climate change; therefore, consideration should be given to them. Based on existing methods for removing atmospheric organic pollutants and combined with the characteristics of CPM organic components, we provide a critical overview from the aspects of (i) fundamental cognition of CPM, (ii) common methods to control CPM organic components, and (iii) catalytic oxidation of CPM organic components. As one of the most encouraging methods, catalytic oxidation is discussed in detail, especially in combination with selective catalytic reduction (SCR) technology, to meet the growing demands for multipollutant control (MPC). We believe that this review is inspiring for a fuller understanding and deeper exploration of promising approaches to control CPM organic components.

Characteristics of the pyrolytic products and the pollutant emissions at different operating stages from a pilot waste tire pyrolysis furnace

Pyrolysis is considered a highly practical, cost-effective, and environment-friendly technology for waste tires disposal. In this study, pyrolysis processes of waste tires were conducted in a pilot scale furnace feeding at 30 kg/h. The properties of pyrolytic products and the distribution patterns of pollutants generated in different operating stages (start-up, steady, and shut-down) were investigated. The pyrolytic gas in the steady state had a high caloric value of 10799 kJ/Nm3, valuable as heating source for pyrolysis. The elements of sulfur and zinc were effectively fixed as ZnS in the pyrolytic carbon. The basic properties of pyrolytic oil were in line with commercial diesel oil except for the lower flash point. Heavy metals were mainly concentrated in the pyrolytic carbon, with slightly higher concentrations in the steady state. Moreover, polycyclic aromatic hydrocarbons (PAHs) and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) were mainly concentrated in the pyrolytic oil, with predominated low-ring PAHs and high chlorinated PCDD/Fs. The concentrations of PAHs and PCDD/Fs in the gas phase were higher during the start-up stage due to the memory effect, whereas were effectively reduced during the steady stage. The concentration of PAHs in the solid phase was highest during the furnace start-up and lowest in the shut-down stage. In contrast to PAHs, the PCDD/Fs in the solid phase reached their highest concentration during the shut-down stage, which was mainly affected by temperature. The results provide guidance for the reducing of pollutant emissions and the recycling of pyrolytic products.

Role of sulphur and chlorine in condensable particulate matter formation during coal combustion

Condensable particulate matter (CPM) is a major component of primary particulate matter emitted into the atmosphere from stationary sources. However, the factors affecting CPM generation remain unclear. In this study, we systematically investigated the role of sulphur and chlorine in CPM formation during coal combustion. To explore the influence of S, various concentrations of SO₂ (0-2000 ppm) were added to the combustion process of high-S coal. The role of Cl in the generation of CPM was revealed by burning coal with a significant difference in the Cl content (0.51-9.70 mg/g). The results show that addition of SO₂, especially in SO₄^2-, to the combustion process increases the CPM inorganic fraction content from 5.83 to 48.3 mg/m³. In addition, we speculated that the presence of SO₂ may have led post-break oxidation of long-chain alkanes to form esters, especially phthalates. At the same time, in experiments concerning Cl, the opposite trend was observed between S and Cl in the CPM inorganic fraction. As the Cl content in the fuel increased, the S content in the inorganic fraction of CPM gradually decreased. This is because Cl inhibits the conversion of SO₂ to SO₃, therefore, less S forms CPM as SO₃ or as sulphides.

Formation behavior of PAHs during pyrolysis of waste tires

Polycyclic aromatic hydrocarbons (PAHs) formation from the pyrolysis of waste tires is inevitable because of the complexity of tire formulations and the addition of certain chemicals. In this study, the formation behavior and distribution of PAHs in three-phases were investigated from waste tires under pyrolysis conditions. The influencing factors including the temperature, heating rate, holding time, particle size, catalyzer, and atmosphere, were systematically evaluated. The results showed that PAHs were mainly concentrated in pyrolysis oil (94.59-99.03%), followed by the gas phase (0.96-5.34%), and their content was very low in the solid phase (0.01-0.99%). A higher temperature and slower heating rate lead to partial PAHs decomposition, thus reducing their emissions. The overall formation of PAHs can be inhibited when pyrolyzing coarse-grained tire powder. Furthermore, the PAHs formation mechanisms in waste tires were determined through reaction molecular dynamics, electron paramagnetic resonance, and intermediate products. Tires were mainly decomposed into benzene series, *C₂H₃, and *CH₃; therefore, it was determined that PAHs were formed by the joint action of the hydrogen abstraction, and vinyl radical addition and methyl addition cyclization mechanisms. Among them, low and middle-ring PAHs were formed more easily, particularly naphthalene. The generation of PAHs can be inhibited by reducing the concentration of hydrocarbons and monocyclic benzene series. Regarding the distribution law and generation pathways of PAHs, our results provide guidance for reducing PAHs formation and emissions.

The Assessment of Indoor Formaldehyde and Bioaerosol Removal by Using Negative Discharge Electrostatic Air Cleaners

This study investigated the single-pass performance of a negative corona electrostatic precipitators (ESP) in removing suspended particulates (PM_2.5 and PM₁₀), formaldehyde (HCHO), and bioaerosols (bacteria and fungi) and measured the ozone (O₃) concentration generated by ESP. The experimental results revealed that if the operational conditions for the ESP were set to high voltage (−10.5 kV) and low air flow rate (2.4 m³/min), ESP had optimal air pollutant removal efficiency. In the laboratory system, its PM_2.5 and PM₁₀ removal rates both reached 99% at optimal conditions, and its HCHO removal rate was 55%. In field tests, its PM_2.5, PM₁₀, HCHO, bacteria, and fungi removal rates reached 89%, 90%, 46%, 69%, and 85% respectively. The ESP in the laboratory system (−10.5 kV and 2.4 m³/min) generated 7.374 ppm of O₃ under optimal conditions. Under the same operational conditions, O₃ generated by ESP in the food waste storage room and the meeting room were 1.347 ppm and 1.749 ppm, respectively. The removal of HCHO and bioaerosols was primarily attributed to their destruction in the corona, as well as ozone oxidation, and collection on the dust collection plate.

Construction of a regional inventory to characterize polycyclic aromatic hydrocarbon emissions from coal-fired power plants in Anhui, China from 2010 to 2030

The infrastructures of coal-fired power plants in China have changed significantly since 2010, but the magnitude and characteristics of polycyclic aromatic hydrocarbon (PAH) emissions remain to be updated. In the present study, a unit-based PAH emission inventory for coal-fired power plants between 2010 and 2017 was constructed for Anhui Province, China. Atmospheric PAH emissions from pulverized coal (PC) and circulating fluidized bed (CFB) units in 2017 were 8600 kg and 7800 kg, respectively. The emission rates and intensities for CFB units (7.2 kg ton^-1 and 2.1 kg MW^-1) were significantly higher than those for PC units (1.1 kg ton^-1 and 0.19 kg MW^-1), primarily because CFB boilers were operated at lower combustion temperatures and poor combustion conditions compared to PC boilers. The distribution patterns of PAH emissions across different age groups largely reflected the time periods for constructing coal-fired units in Anhui and for the transition of small units to large ones. The accomplishment of ultralow emission technologies and phase-out of outdated coal-fired units were responsible for the decreasing trend of PAH emissions between 2012 and 2017. The warmer summer in 2013 and 2017 and colder winter in 2011 compared to other years probably caused increased use of air conditioners, resulting in increased electricity consumption and PAH emissions. Future PAH emissions would decrease by 45-57% during 2017-2030, benefitting from power plant fleet optimization, i.e., phasing out outdated coal-fired units and replacing them with large ones. With the best available optimized power plant fleets and end-of-pipe control measures accomplished in Anhui's CFPPs, PAH emissions in 2030 would potentially be reduced by 56-65%.

Coordinated effects of air pollution control devices on PAH emissions in coal-fired power plants and industrial boilers

Coal-fired power plants are important sources of polycyclic aromatic hydrocarbon (PAH) emissions in the world. The effects of various air pollution control devices (APCDs) on PAH emissions were investigated by analyzing samples from inlets and outlets of APCDs in six coal-fired power plants (A-F) and two coal-fired industrial boilers (G and H). The APCDs were electrostatic precipitators (ESPs), wet flue gas desulfurization systems (WFGDs), and wet ESPs (WESPs). The PAH congener patterns for the coal-fired plants were similar. Gas-phase PAHs were dominant in flue gases, and the most abundant PAH was naphthalene. Three- and four-ring PAHs were dominant in fly ash. Positive correlations were found between the PAH and total organic carbon contents of fly ash (R² 0.87) and slag (R² 0.92). Plants D-F, equipped with low-low-temperature ESPs (LLT-ESPs) and WESPs discharged the lowest PAHs. Circulating water was an important source of PAHs in the desulfurization except in plant A, which used desalinated seawater rather than circulating water in the desulfurization process. WESPs decreased PAH concentrations by an average of 20.67%, which can be spread to other plants to reduce PAHs.