ROMSO Cyprus Knowledge Base

--- CONTENT ---
A rotary kiln (DRO) is a cylindrical kiln for continuous processes in process engineering, which rotates continuously about its own axis in normal operation. Combined with a slight inclination of the axis of rotation, the rotational movement ensures product or fuel transport.

Structures
Rotary kilns can be heated both directly and indirectly. In the case of direct heating, the heat is supplied from within the furnace, for example by a burner. Any product in the rotary tube is in direct contact with the resulting flue gas. In the case of indirect heating, the heat is transferred from outside into the reaction chamber. This can also take place, for example, via the exhaust gas from the process.

Construction of directly heated rotary kilns

A directly heated rotary kiln generally consists of the following components:
an inlet housing for feeding or filling the materials to be treated continuously
The rotary tube
an outlet housing or furnace head
a burner equipment which is seated at the furnace head.
the refractory lining;
Mounting on two or more supports, rollers and axles
longitudinal positioning control with an axial roller
the drive means by means of gearing and toothed ring or by frictional entrainment on driven rollers
the seals at the furnace inlet and outlet to seal the rotating rotary tube against the stationary furnace head parts;

In the case of directly heated rotary kilns, a distinction is made between cocurrent and countercurrent firing, depending on whether the exhaust gas and the combustible material move in the same or opposite direction.

Indirectly heated rotary kilns
An indirectly heated rotary kiln generally consists of the following components:
an inlet housing, usually also only an insertion screw with a shield,
The rotary tube
The discharge housing
the sealing systems that seal the product room atmosphere from the air, often with the use of sealing gas
The bearing, traditional with bearing ring and rollers, modern with large ball bearings or plain bearings
the drive by means of compact transmission and toothed ring
the externally insulated heating muffle providing the required amount of heat, usually by flue gas or heating rods

Furthermore, internals may be present in rotary kilns which mainly influence the transport of solids. Lifting blades, for example, ensure trickling of the feedstock through the hot gas atmosphere and thus improve the heat transfer. Retarding rings at the discharge increase the degree of filling in the furnace. Chain internals are particularly suitable for avoiding or eliminating caking in the case of wet feedstock. Geometric bodies introduced in a targeted manner, such as steel balls, improve the mixing and increase the heat transfer.

Procedural features
The product is transported within the rotary kiln by the rotary movement and the N