Whereas rotary dryers are used remove water or solvent from a material, calciners (or kilns) chemically change the material, for example converting limestone into lime. Calciners are very similar in design to rotary dryers, and can likewise be directly or indirectly heated, but much higher temperatures are involved.
As with rotary dryers, rotary calciners are ideally suited to handling a wide range of particle sizes. Product quality and equipment reliability are essential considerations for our design team and manufacturing specialists.
- Simple and robust design
- Shell materials are selected to suit the application
- Air flow direction matched to product
- A wide range of process temperatures can be achieved
- Indirect units are frame-mounted for stability and speed of installation
- Heat source can be matched to local requirements
- Residence times range from minutes to hours
Directly Heated Rotary Calciners
Directly heated rotary calciners are used where roasting, oxidising, reducing or heat treatment is required at temperatures above those normally used for drying. They are widely used for materials such as phosphates, ores, iron oxide, inorganic salts and refractory powders.
The oil or gas burner fires directly into the end of the shell, achieving air temperatures of up to 1,650 degrees C. There are usually two lining materials: high temperature refractory bricks on the inside, and a layer of insulating bricks adjacent to the steel shell. On smaller units a single layer of castable refractory is normally provided.
Heat is transferred to the material by direct convection and radiation from the gases and also by conduction and radiation from the hot refractory lining. The refractory-lined rotating shell has no lifting flights: forward flow of the material is governed by the slope and rotation of the shell.
Indirectly Heated Rotary Calciners
Indirectly heated rotary calciners are used when the material is too fine or too low a density for directed fired units, or when the material must not come into contact with the products of combustion. Typical applications include nickel catalysts, carbon regeneration, molecular sieves and china clay.
Based on the design of the indirectly heated rotary dryer, the calciner can operate at temperatures of 1,100 degrees C.