Electron beam technology for multi-pollutant emissions control at a coal-fired boiler, current issues

Abstract

Abstract. Coal combustion is the primary means of power generation in Poland. During this process large amount of different pollutants like: particulate matter (PM), sulphur oxides (SO2 and SO3), nitrogen oxides (NOx=NO+NO2), carbon oxides (CO and CO2), volatile organic compounds (VOC) and mercury are emitted. Their harmful effects on human health and ecosystems are well known and documented. The emission of these pollutants has been restricted by newly tightened NOx, SO2 and PM emission limits to reduce pollutants emission and improve the quality of life. The technologies which can treat simultaneously many pollutants are searched for. The conventional technologies are usually designed for removing only a single pollutant. An integrated technology for simultaneous emission control of: SO2, NOx, polycyclic aromatic hydrocarbons (PAHs) and one – ringed aromatic hydrocarbons (benzene, toluene, and xylenes) is presented in the paper. It is a dry-scrubbing process for simultaneous SO2 and NOx removal with generation of byproduct that can be used for agricultural fertilizer production. The technology uses ammonia injection to the flue gas and irradiation of such mixture in the process vessel by a high-energy electron beam from accelerator. This technology has been tested in the pilot plant in the Kawęczyn thermal power plant and then has been implemented on an industrial scale in the “Pomorzany” power station at Szczecin. The Pomorzany industrial plant purifies up to 270 000 Nm3/h of flue gas from two hard coal-fired Benson boilers of 60 MWe and 100 MWth each. The SO2 removal efficiency exceeds 95%, while for NOx it reaches 70%. The byproduct is collected by the electrostatic precipitator and is shipped to the fertilizer factory. The chromatographic analysis indicates that it consists primarily of ammonium sulphate and ammonium nitrate with low traces of ammonium chloride. Content of heavy metals was many times lower than permissible level in agricultural fertilizer.The experiments conducted in the Kawęczyn pilot plant have demonstrated that besides SO2 and NOx, other potentially harmful chemicals, especially polycyclic aromatic hydrocarbons (PAHs) and one-ringed aromatic hydrocarbons (BTXs) were also simultaneously significantly reduced by electron beam irradiation. Overall removal efficiencies of approximately 42% for PAHs and 80% for BTXs were achieved with an irradiation dose 5.3 kGy. The decomposition ratio of these compounds increased with an increase of absorbed dose. Thus, the electron beam flue gas treatment technology ensures simultaneous removal of acid (SO2 and NOx) and organic (PAH and BTX) pollutants from flue gas emitted from coal-fired boiler. The further applications of this technology are presented.