Direct Fired & Indirectly Heated Calciners are used for applications where it is necessary to change the "state" of the material. Direct fired units are suited to high-temperature applications and indirectly heated units for dusty, finely divided materials and low to medium temperature applications.
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Direct Fired, Refractory Lined Calciners are also supplied for high temperature applications where it is necessary to change the ‘state’ of the material. Since this process usually requires a long residence time, the length to diameter ratio is often in excess of 10:1. In most cases an oil or gas burner fires directly into the discharge end of the unit. The material is heated in three ways - by radiation from the burner flame, conduction from the refractory lining and convection by contact with the hot gases.
Direct fired (usually but not always), refractory lined calcined heat material in three ways - by radiation from the burner flame, conduction from the refractory lining and convection by contact with the hot gases.
Suitable for high temperature applications where it is necessary to change the 'state' of the material or drive a chemical or physical reaction.
Indirectly Heated Rotary Dryers and Calciners are available for dusty, finely divided materials and low to medium temperature calcining applications. The rotary drum is partially enclosed and externally heated by a series of burners mounted in an insulated stationary chamber or jacket. Alternatively, the products of combustion from an external heater may be recirculated to increase thermal efficiency.
Since heat transfer is by radiation and conduction via the cylinder wall, the internal flights are arranged to distribute the material around the inner periphery of the drum. The entrainment of ‘fines’ is minimal as a low air flow is only required for removing the water vapor, little or no de-dusting equipment is therefore necessary.
In the indirectly heated dryer/calciner, there is little or no contact between the product and the drying gases since heat transfer is mainly via the cylinder wall.
This design is therefore more appropriate for fine, dusty materials, including those necessitating an inert atmosphere, or for applications where contamination is to be avoided.
GEA supply a range of Rotary Coolers including Cascade Coolers which are used for lower temperature, coarse product applications, External Spray Type Coolers and Section Coolers that are used dusty and/or high temperature applications often after kilns and calciners and specialized Combined Dryer/Coolers that have specific applications with the sugar and sweetener industries.
The GEA Rotary Dryer is extensively used throughout the process industries and is highly reliable under the most arduous operating conditions.