Evolution of Condensable Fine Particle Size Distribution in Simulated Flue Gas by External Regulation for Growth Enhancement

Variation of nitrate and nitrite in condensable particulate matter from coal-fired power plants under the simulated rapid condensing conditions

In this work, condensation temperature, H₂O vapor, SO₂, SO₃ and NH₃ were studied to explore the formation mechanism of nitrate ions (NO₃^-) and nitrite ions (NO₂^-) in condensable particulate matter (CPM) discharged by ultra-low emission coal-fired power plants. Some important results were obtained: (i) The concentration of NO₃^- and NO₂^- increased with the decrease of condensation temperature, and H₂O vapor could also promote the formation of NO₃^- and NO₂^-. (ii) The effects of SO₂ and SO₃ varied at different saturated states of flue gas, which was caused by the redox reaction of SO₂ and NO_X or the formation of H₂SO₄. (iii) NH₃ could promote the nucleation of NO₃^- and NO₂^-, and the promotion effect also existed in the existence of SO₂ or SO₃. It is worth mentioning that SO₃ and SO₂ might synergistically inhibit the formation of NO₃^- and NO₂^-, regardless of the presence of NH₃. The research results would enrich peoples understanding of the chemical and physical characteristics of NO₃^- and NO₂^- in CPM and provide a basic reference for the control of CPM emitted from coal-fired power plants.

Physicochemical characteristics of polycyclic aromatic hydrocarbons in condensable particulate matter from coal-fired power plants: A laboratory simulation

The objective of this study was to examine the physicochemical characteristics of polycyclic aromatic hydrocarbons (PAHs) in condensable particulate matter (CPM) during fast condensation (within several seconds). The concentration of PAHs increased as the condensation temperature decreased, indicating that the conversion of gaseous PAHs to CPM would be enhanced at low temperatures. PAH concentrations increased in relation to the number of rings in the fragment, with the high-ring (4-,5- and 6-ring) PAHs accounting for 89.70-92.30% and 99.78-99.80% of the total concentration and total toxic equivalent of PAHs. In addition, particulate-phase PAHs (0.1-1.0 μm), developed through the synergistic effect of PAHs and fine particles, were difficult to collect by fast condensation. Inorganic fine particles could be formed when ammonia-rich conditions prevail, reducing PAH condensation further. Furthermore, CPM was morphologically and chemically characterized. During the experiment, fine and well-aggregated CPMs were detected on the membrane, and the diameter of CPMs was further enhanced by the addition of 16 PAHs. Most of the C element was collected in the rinse fluid, thus indicating that PAHs in CPM were collected through condensation. Based on these findings, basic guidelines can be provided for the control of PAHs in flue gas from coal-fired power plants.

Preventing Aerosol Emissions in a CO2 Capture System: Combining Aerosol Formation Inhibition and Wet Electrostatic Precipitation

Aerosol emission from the CO₂ capture system has raised great concern for causing solvent loss and serious environmental issues. Here, we propose a comprehensive method for reducing aerosol emissions in a CO₂ capture system under the synergy of aerosol formation inhibition and wet electrostatic precipitation. The gas-solvent temperature difference plays a vital role in aerosol formation, with aerosol emissions of 740.80 mg/m³ at 50 K and 119.36 mg/m³ at 0 K. Different effects of SO₂ and SO₃ on aerosol formation are also found in this research; the aerosol mass concentration could reach 2341.25 mg/m³ at 20 ppm SO₃ and 681.01 mg/m³ at 50 ppm SO₂ with different aerosol size distributions. After the CO₂ capture process, an aerosol removal efficiency of 98% can be realized by electrostatic precipitation under different CO₂ concentrations. Due to the high concentration of aerosols and aerosol space charge generated by SO₂ and SO₃, the removal performance of the wet electrostatic precipitator decreases, resulting in a high aerosol emission concentration (up to 130.26 mg/m³). Thus, a heat exchanger is installed before the electrostatic precipitation section to enhance aerosol growth and increase aerosol removal efficiency. Under the synergy of aerosol formation inhibition and electrostatic precipitation, an aerosol removal efficiency of 99% and emission concentrations lower than 5 mg/m³ are achieved, contributing to global warming mitigation and environmental protection.

Co-Benefits of Pollutant Removal, Water, and Heat Recovery from Flue Gas through Phase Transition Enhanced by Corona Discharge

Pollutant removal and resource recovery from high-humidity flue gas after desulfurization in a thermal power plant are crucial for improving air quality and saving energy. This study developed a flue gas treatment method involving phase transition enhanced by corona discharge based on laboratory research and established a field-scale unit for demonstration. The results indicate that an adequate increase in size will improve the ease of particle capture. A wet electrostatic precipitator is applied before the condensing heat exchangers to enhance the particle growth and capture processes. This results in an increase of 58% in the particle median diameter in the heat exchanger and an emission concentration below 1 mg/m³. Other pollutants, such as SO₃ and Hg, can also be removed with emission concentrations of 0.13 mg/m³ and 1.10 μg/m³, respectively. Under the condensation enhancement of the method, it is possible to recover up to 3.26 t/h of water from 200 000 m³/h saturated flue gas (323 K), and the quality of the recovered water meets the standards stipulated in China. Additionally, charge-induced condensation is shown to improve heat recovery, resulting in the recovery of more than 43.34 kJ/h·m³ of heat from the flue gas. This method is expected to save 2628 t of standard coal and reduce carbon dioxide emission by 2% annually, contributing to environmental protection and global-warming mitigation.

Study on characteristics of organic components in condensable particulate matter before and after wet flue gas desulfurization system of coal-fired power plants

Wet flue gas desulfurization (WFGD) in coal-fired power plants has a great impact on the emission of particulate matter, including filterable particulate matter (FPM) and condensable particulate matter (CPM). In this paper, CPM and FPM in flue gas before and after WFGD in coal-fired power plants were sampled in parallel. FPM was tested according to ISO standard 23210-2009, and CPM was tested according to U.S. EPA Method 202. A method for quantitatively analyzing fatty acid methyl esters in CPM was established, and the removal capacity of fatty acid methyl esters and phthalate esters by WFGD in a typical coal-fired unit was compared. Results show that WFGD has a significant effect on particle size distribution, concentration, and chemical composition. WFGD has a high removal efficiency of inorganic components in CPM, up to 54.74%. CPM contains a variety of organic compounds, including hydrocarbons, esters, siloxanes, halogenated hydrocarbons, and so on. In particular, esters are an important component in CPM, whose concentration tends to decrease after WFGD. Furthermore, a total of 11 fatty acid methyl esters and 5 phthalate esters were detected in CPM before and after WFGD. Noted that fatty acid methyl esters account for 13.38% of CPM, which make a higher contribution to the concentration of particulate matter than phthalate esters, while WFGD has a stronger control effect on the removal of phthalates.

An online technology for effectively monitoring inorganic condensable particulate matter emitted from industrial plants

The concentration of condensable particulate matter (CPM) has gradually exceeded that of filterable particulate matter emitted from industrial plants equipped with advanced air pollution control systems. However, there is still no available online technology to measure CPM emissions. Based on the significant linear correlations (R² > 0.87, p < 3 × 10^-3) between the electrical conductivity (EC) values and ionic mass concentrations of the CPM solutions when the interference of H⁺ was excluded. We developed an online inorganic CPM monitoring system, including a cooling and condensation unit, pH and EC meters, a self-cleaning unit, and an automatic control unit. The CPM mass concentrations obtained by the developed online monitoring system agree well (mean bias 3.8-20.7%) with those obtained by the offline system according to USEPA Method 202 when used in parallel during real-world studies. Furthermore, individual ion mass concentrations of CPMs can even be retrieved separately with a time resolution of one hour when industrial plants are under steady operating conditions. The newly developed system makes the online monitoring of CPM emissions available and lays a foundation for the control of CPM emitted from industrial sources to further improve air quality.

Adsorption of condensable particulate matter from coal-fired flue gas by activated carbon

Condensable particulate matter (CPM) is a special kind of primary particulate matter and is in a gaseous state before discharge. After discharge, it rapidly forms liquid or solid particles through atmospheric dilution and cooling, which are harmful to the environment and human health. However, current research on controlling CPM is lacking. Therefore, the adsorption effects of activated carbons (ACs) on CPM at different temperatures were studied using EPA Method 202. Results showed that the removal efficiency range of CPM at 90 °C by ACs could reach 19%-22%. The removal efficiency of the inorganic fraction was higher than that of the organic fraction. ACs had obvious adsorption effects on Cl^-, NH₄⁺, and Hg in CPM but had marginal adsorption effects on SO₄²⁺, NO₃^-, and other metal elements in CPM. ACs had prominent adsorption effects on extremely toxic aromatic compounds in CPM. At a flue gas temperature of 35-170 °C, the efficiency of CPM removal through AC adsorption could increase with decreasing flue gas temperature, and this effect was more obvious during the adsorption of inorganic fractions. In addition, the efficiency of CPM removal through condensation and adsorption could reach up to 51% at 35 °C when flue gas at 130 °C was used as the initial flue gas.