DOWNCOMER DUCT

The down comer duct is located between the top-stage cyclone outlet of the preheating tower and the kiln-induced draft (ID) fan. Hot process gases from the combustion process are pulled down through the duct by the ID fan, where they are cooled by water sprayers. The combustion gases that come out of the top-stage cyclone have a certain dust loading or capturing element based on the cyclone efficiency, thus leading to buildup in the duct work lining. Moreover, gases can be corrosive and slightly abrasive, which causes wear and thinning of the duct. Also, suction pressure from being on the inlet side of the ID fan is an added element in deterioration. This is why periodic thickness testing and inspection schedules of the duct will determine when replacement is necessary.