Identification of aluminum fluoride complex in the absorber of a desulfurization system

Abstract

Electric power plants generate energy, but by products in the form of small particles of waste which contain high quantities of sulfides are also produced. Regional law prohibits the expulsion of sulfur into the atmosphere. Because sulfurous acid gas (SO2) becomes concentrated in power plant furnaces owing to the recirculation of flue gas, optimal conditions for efficient sulfation are required. In conventional coal combustion, the indirect sulfation of limestone occurs. The sulfation efficiency in conventional coal combustion is usually low because of sintering of the absorber. Usually preserving values for optimal conditions are set and plant operation is maintained at 100%, but sometimes a 1 or 2% decrease in activity occurs. When [Al]3+ = 0.4 mM and [F]− = 4 mM at pH 5.5, the concentration of [AlF4]− is higher than that of [AlF3]. Under these conditions in the absorber, [AlF4]− is considered to increase in quantity and to form a complex with Ca2+ from limestone. When the pH of the absorber increases, [AlF3] and [AlF4]− decrease and [F]− increases. It is concluded that the concentration of [AlF4]− governs the decrease in activity in the absorber. In the spectra of electrospray ionization mass spectrometry (ESI-MS), five peaks were observed and assigned to CaSO4+ AlF4−, 2CaCO3+ AlF4−, 2CaCO3 + CaF2 + AlF4−, 2CaCO3 + CaSO4 + H2O + AlF4−, and 2CaCO3 + CaF2 + CaSO4 + H2O + AlF4− from the chemical components in the actual absorber.