Les gaz de combustion de l'acier, de la cokéfaction, de l'industrie chimique et des chaudières sont principalement pulvérisés ou désulfurés par voie humide avant leur décharge, et la température chute à 45 ~ 80 ℃. À ce stade, les gaz de combustion sont des gaz de combustion humides saturés et les gaz de combustion contiennent une grande quantité de vapeur d'eau, qui contient du sel ablatif, du trioxyde de soufre, de la poussière de gel, des micro-poussières, etc. (tous des composants importants de la brume).
Smoke whitening refers to the removal of some moisture from the smoke before it is discharged into the atmosphere, in order to prevent the chimney from emitting white smoke and reduce its impact on the environment. Normally, smoke whitening involves first cooling and condensing the smoke, followed by heating it. The main component of the air flue gas whitening unit is the BXB plate heat exchanger. In the plate heat exchanger, ambient air is used to cool the flue gas, thereby precipitating water from the flue gas. Afterwards, the flue gas is reheated to increase its temperature, so that there will be no "white smoke" when the flue gas is discharged into the atmospheric environment.