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

Highlights: • We characterized PM emitted from coal–fired power plants equipped with LLT–ESP. • PM concentration decreases with the decrease in operating temperature of LLT–ESP. • PM concentration at LLT–ESP outlet is lower than those with traditional ESP. • The optimal operating temperature for LLT–ESP is ~90 °C. -- Abstract: 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 SO₄²⁻, 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.