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.

Transformation and removal of ammonium sulfate aerosols and ammonia slip from selective catalytic reduction in wet flue gas desulfurization system

Selective catalytic reduction (SCR) denitration may increase the emission of NH₄⁺ and NH₃. The removal and transformation characteristics of ammonium sulfate aerosols and ammonia slip during the wet flue gas desulfurization (WFGD) process, as well as the effect of desulfurization parameters, were investigated in an experimental system equipped with a simulated SCR flue gas generation system and a limestone-based WFGD system. The results indicate that the ammonium sulfate aerosols and ammonia slip in the flue gas from SCR can be partly removed by slurry scrubbing, while the entrainment and evaporation of desulfurization slurry with accumulated NH₄⁺ will generate new ammonium-containing particles and gaseous ammonia. The ammonium-containing particles formed by desulfurization are not only derived from the entrainment of slurry droplets, but also from the re-condensation of gaseous ammonia generated by slurry evaporation. Therefore, even if the concentration of NH₄⁺ in the desulfurization slurry is quite low, a high level of NH₄⁺ was still contained in the fine particles at the outlet of the scrubber. When the accumulated NH₄⁺ in the desulfurization slurry was high enough, the WFGD system promoted the conversion of NH₃ to NH₄⁺ and increased the additional emission of primary NH₄⁺ aerosols. With the decline of the liquid/gas ratio and flue gas temperature, the removal efficiency of ammonia sulfate aerosols increased, and the NH₄⁺ emitted from entrainment and evaporation of the desulfurization slurry decreased. In addition, the volatile ammonia concentration after the WFGD system was reduced with the decrease of the NH₄⁺ concentration and pH values of the slurry.