At present, the vast majority of domestic steel, coking, chemical industry flue gas before discharge mostly spray or wet desulfurization, the temperature drops to 45℃-55℃, at this time the flue gas is usually saturated wet flue gas, flue gas contains a lot of water steam, water steam contains more soluble salt, SO3, gel dust, dust, etc. (are the main components of haze). If the flue gas is discharged directly from the chimney and enters the ambient air with a lower temperature, the water vapor in the flue gas will condense and form a wet plume in the process of reducing the temperature of the flue gas because the saturation humidity of the ambient air is relatively low.