Post combustion SO_x mitigation in Thermal Power Stations

Air pollution by oxides of Sulphur (SO_x) from thermal stations can be controlled by either in-furnace absorption as in fluidised bed combustion (FBC) based boilers or by post combustion flue gas desulphurisation (FGD). The later method, i.e., FGD would continue to be used for large capacity power stations with pulverized fuel/oil fired boilers. Large number of FGD processes have emerged with newer techniques of increasing SO_x removal efficiencies. Some processes have merits of not generating liquid effluents such as spray dryer and circulating fluidized bed lime reactor. Some processes convert SO_x into marketable by products like gypsum, sulphuric acid or elemental sulphur. A few FGD process regenerate the sorbent as in Wellmenlord process/Magox process/Dual alkali process. Because of high ash content of Indian coals, a dust collector before the absorption tower or reactor is necessary. Comparison of various processes both form point of view of technical and financial aspect as given here in the paper can help process selection for a particular situation. A comparison of SO_x generated per MWH by Indian Coals and foreign coals as given herein shows that very significant amount of SO_x is released in India which would increase with increasing coal fired generation and would require measures to curb it henceforth.