Influence of SO3 in flue gas on electrostatic precipitability of high-alumina coal fly ash from a power plant in China

Influence of H2O and SO3 on fine particles coagulation for sintering flue gas after desulfurization in an alternating electric field

Electric coagulation of fine particles has been studied in the simulated sintering flue gas after semi-dry desulfurization to quantify the influence of H₂O and SO₃. The electric coagulation platform has a DC charging zone and an AC coagulation zone. Fine particles were divided into different diameter intervals to deeply explore the impact of H₂O and SO₃, including less than 0.15 μm (PM_0.15), 0.15-0.5 μm (PM_0.15-0.5) and 0.5-1 μm (PM_0.5-1). The particle charge, mass fractions of fine particles, and the mean diameter are measured and compared under water and SO₃ atmosphere. The experiments showed that the increasing AC voltage helps particles larger than 0.5 μm to coagulate but has little effect on the rest particles without H₂O or SO₃. Both H₂O and SO₃ enhance the PM_1.0 AC coagulation. When flue gas relative humidity went up from 20 to 80%, the charge per particle maximally increased by 120%, as well as the mass fraction of PM_0.5-1, PM_0.15-0.5, and PM_0.15 decreased by 83.2%, 64.5%, and 66.6%, respectively. When the SO₃ concentration rose up from 0 ppm to 12.3 ppm, the charge per particle maximally increased by 100%, as well as the mass fractions of PM_0.5-1, PM_0.15-0.5, and PM_0.15 decreased by 54.5%, 28.6%, and 33.3%, respectively. The impact of water and sulfuric mist on the particle intervals was sequenced as: PM_0.5-1 > PM_0.15 > PM_0.15-0.5. The influence on PM_1.0 AC coagulation was sequenced as H₂O > sulfuric mist > AC voltage. Through data regression, H₂O had approximate linear correlation with the particle mass fractions while the impact of sulfuric mist was non-linear. The interparticle forces were calculated to analyze the dominant force of particle AC coagulation with water: liquid bridge force > Coulomb force >  > van der Waals force. The liquid bridge force indicated that liquid film was form on the surface of fine particles when water or sulfuric mist was added into the system which was the main reason enhancing the AC coagulation.

Characteristics of particulate matter from four coal-fired power plants with low-low temperature electrostatic precipitator in China

The performance of traditional electrostatic precipitators (ESPs) is strongly affected by the flue gas temperature. Operating under much lower temperatures (e.g., ~90 °C), the low-low temperature electrostatic precipitators (LLT-ESPs) are considered as an effective technology to improve the particulate matter (PM) removal efficiency in coal-fired power plants (CFPPs). Wet flue gas desulfurization (WFGD) can also be affected by the decrease in the operating temperature of the ESP. This study evaluates the influence of various ESP operating temperatures on ESP performance, PM_2.5 (particles with an aerodynamic diameter of ≤2.5 μm), and total dust emission characteristics at the ESP and WFGD outlets in CFPPs equipped with LLT-ESPs. PM_2.5 and total dust concentrations at the ESP and WFGD outlets in CFPPs installed with LLT-ESPs are much lower than those with traditional ESPs. The PM concentrations at both the ESP and WFGD outlets show a decreasing trend with a decrease in the operating temperature. However, the concentration of total water-soluble ions (mainly SO₄^2-, Cl^-, and NH₄⁺) in the total dust at the outlet of ESPs increases from 0.3 to 0.8 mg/m³ as the temperature decreases from > 90 °C to 80-90 °C, which is contrary to that at the WFGD outlet (decreases from 4.7 to 0.8 mg/m³). The PM_2.5 and total dust concentrations increase by 10.2-80.2% and 13.7-77.0%, respectively, through the WFGD unit due to the entrainment of a gypsum slurry. A relatively lower operating temperature of LLT-ESPs in power plants is also beneficial to decrease the incremental effect of PM emissions in the process of WFGD. The recommended operating temperature for LLT-ESPs is ~90 °C, and limited improvement on PM reduction can be achieved with a further temperature decrease from 90 to 80 °C.

Effects of coal blending in electrostatic precipitation efficiency-Inner Mongolia, China

Based on this study, the Al₂O₃ content of Jungar coal ash is over 45%, and the resistivity of high-Al₂O₃ ash in Jungar reaches up to 10¹² Ω​·cm. These results seriously influenced the electric characteristics of fly ash, and the collection efficiency of electrostatic precipitators (ESPs) evidently decreased. To facilitate the effective collection of fine particle in the flue gas generated before and after coal blending via ESP, the fly ash obtained from a power plant electrostatic precipitation was analyzed in terms of resistivity, size distribution, and cohesive force through a portable dust electrical resistivity test instrument, Bahco centrifuge, and a cohesive force test apparatus invented by the researchers. The mixed ratio of else coal is higher than 50%, the resistivity of the fly ash in the flue gas was lowered to approximately two orders of magnitude, and the size distribution showed an evident decrease in the PM2.5 and PM10 content in fly ash. In addition, the adhesive force and efficiency increase from 95.9 to 99.5% in the electrostatic precipitation. Therefore, the combustion of blending coal is an effective approach to improve the efficiency of ESP used to collect high-Al₂O₃ fly ash.