Abstract: As one of the most critical equipments in wet flue gas desulfurization system, the performance of the demister will directly affect the operation security of the desulfurization system and even compromise the generation unit itself. This paper took the failure scenario of the double tower double cycle desulfurization of a 660 MW coal-fired unit as an example, in which the blockage of demister caused overturn fault on some modules. The comprehensive analysis was also conducted regarding the demister design factors (such as the air velocity within the cooling tower, the mounting space, the pressure of flush water etc.), the concentration of entrance smoke, the rinse water volume of demister as well as the components of slurry, gypsum and fouling materials. It was found that the improper water balance control of desulfurization system and the high pH value settings of the secondary tower were the major culprits of demister failure. In order to reduce the risk of operation failure of the demister, some reasonable suggestions were given for the control of water balance and slurry pH value of the double tower double cycle desulfurization system.

Key words: coal-fired power plant, gas desulfurization, double tower double cycle, demister, water balance