When the flue gas passes through the wet desulfurization of the coal-fired unit

its temperature drops and becomes saturated when it is discharged into the environment through the chimney

and then the condensation is formed

called as "white smoke" phenomenon. The theoretical calculation model of exhaust gas temperature for each white smoke elimination technology of coal-fired units was established. The characteristics of white smoke elimination technology in different regions were calculated by taking Xi'an

Shijiazhuang and Shanghai as examples. Results show that the flue gas directly heating method can effectively eliminate white smoke when the ambient temperature is high. When the ambient temperature is low

the flue gas cooling and reheating method would be more effectively. In spring and summer

the white smoke can be eliminated by directly heating method

and the exhaust flue gas temperature should be controlled between 60℃ and 75℃ according to environmental factors. In autumn and winter

when the ambient temperature is 9℃ and the relative humidity is 60% or less

the white smoke should be removed by the cooling and reheating method. In autumn

the flue gas temperature should be lowered to 45℃ and then heated to 75℃. In winter

it can be lowered to 45℃ and then heated to 85℃.