2015 年 30 巻 2 号 p. 93-99
Due to recent higher quality requirement for refined petrochemical products, sulfur content increases even to the range of 4–8% in petrochemical residue, which may be used as boiler fuel from econimical reasons and viewpoint of effective resource utilization, as an alternative of usual heavy oil. When a fuel with high sulfur content is burnt in boiler, SO2 is partly oxidized to SO3 in flue gas, and at the outlet of wet FGD (Flue gas desulfurization) system, it takes the form of liquid mist (SO3 mist), which is ultrafine particulate matter (PM) classified into PM2.5, and causes problems such as sulfuric acid corrosion of the flue gas treatment system or visible bluish plume discharged from stack. In order to remove SO3 from flue gas, two practical methods have been developed firstly in Japan and applied for many years satisfactorily in actual plants using usual heavy oil so far. One is NH3 injection dry electrostatic precipitator (DESP) system and the other is wet electrostatic precipitator (WESP) system. However, these conventional systems may not be applied as they are for the recent cases of using petrochemical residue as boiler fuel, which causes very high SO3 content, over 60–130 ppm, in flue gas. A new technology “salt solution spray WESP system” is recently developed and firstly in Japan put into actual operation. SO3 concentration of the system is reduced from 130 ppm to 1 ppm, equivalent to 99.2% of removal efficiency. Together with the salt solution spray technology, WESP provides the most effective system for SO3 mist removal.
