Sludge dryer

Working Principle

Wet material is transported to a hopper via a belt conveyor or bucket elevator and then fed into the inlet end through a feed pipe. The slope of the feed pipe must exceed the material's natural angle of repose to ensure smooth flow into the dryer.

The dryer consists of a rotating cylindrical shell inclined slightly relative to the horizontal; material enters at the higher end, while the heating medium enters at the lower end, creating counter-current contact (though co-current flow is also possible). As the cylinder rotates, gravity causes the material to move toward the lower end.

As the wet material moves forward within the cylinder, it is dried through direct or indirect heat transfer from the heating medium and is subsequently discharged via a belt conveyor or screw conveyor. Lifting flights (lifters) are installed on the inner wall of the cylinder to lift and shower the material, thereby increasing the contact surface area between the material and the gas stream, enhancing the drying rate, and facilitating material movement.

The heating medium is typically hot air or flue gas. Upon exiting the dryer, the gas usually passes through a cyclone separator to recover any entrained material; if further reduction of dust content in the exhaust gas is required, the gas is passed through a bag filter or wet scrubber before discharge.