- Rotary Calciners

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Rotary calciners, also commonly called indirect kilns, are used in thermal processing operations where exhaust gases must be minimized, when processing finely divided solids, or where temperature must be tightly controlled along the length of the kiln.

A calciner is comprised of a rotating drum inside a furnace, which is externally heated. Unlike direct-fired kilns, which utilize direct contact between the material and process gas to carry out processing, in a calciner, heat is transferred from the shell of the externally heated kiln to the bed of material through radiation.

FEECO offers a unique testing facility where we use batch and continuous pilot equipment to simulate production conditions, allowing us to test small samples of your material under various conditions and develop a process around the unique needs of your material. Specifically, we offer a direct batch kiln, indirect batch kiln, direct continuous kiln, and indirect continuous kiln.

The batch and pilot direct-fired equipment can be configured to include the following: combustion chamber, afterburner, baghouse, quench chamber, and wet scrubber.

Rotary calciners are indirectly-heated, continuous-process heat transfer devices for medium to high-temperature processing of bulk solids materials.

The rotary calciner consists principally of an alloy rotary shell, enclosed in and heated on its exterior in a stationary furnace. The process material moves through the interior of the rotary shell, where it is heated through a combined radiative and convective/conductive mode of heat transfer through the rotary shell wall. Operating temperatures of up to 2200 °F can be achieved. Rotary calciners can be small pilot-scale units, or full-scale productions units as large as 10 ft diameter with a heated length of up to 100 ft. Units can be heated by a variety of fuels, or by electric-resistive heating elements. Waste heat sources can also be accommodated for rotary calciners.

Materials of construction of the rotary shell are selected for high-temperature service, corrosion resistance, and compatibility with process materials. A variety of features and auxiliary equipment is available, to accommodate many process requirements.

Rotary calciners are ideal for specialized processing due to the indirect heating mechanism. As the heat source is physically separated from the process environment, specific process atmospheres can be maintained. Processes requiring inert, reducing, oxidizing, or dehumidified atmospheres, or those with a solids/gas phase reaction can be accommodated. Depending on the process requirements, rotary calciners can operate under positive or negative pressure, and a variety of seal arrangements are available. Internal appurtenances affixed to the rotary shell interior can be employed to promote uniform heat transfer and exposure of the material to a process gas. The indirect heating also allows for temperature profiling of the process, which provides the capability of maintaining the material temperature at a constant level for specific time periods. Multiple temperature plateaus can be achieved in a single calciner unit in this manner.

Other advantages of indirect heating are the minimization of process off-gas volume, and a clean flue gas, as these are two completely separate streams, which do not intermix. The flue gas can be exhausted directly to atmosphere (depending on fuel quality and governing emissions regulations), and the low-volume process off-gas can be ducted to whatever gas treatment equipment may be required.

Indirectly-heated calciners are also ideal for fine and/or light-weight materials, as gas flow through the rotary shell is very low, or virtually non-existent. The potential for product entrainment in a gas stream is thus minimized or eliminated altogether with rotary calciners.

Indirectly-heated rotary calciners can be applied in many different processes, handling many different types of materials. Typical applications for rotary calciners include drying, calcinations, oxidation or reduction reactions, desorptions, devolatilizations, decompositions, solids phase changes, etc. Calciners are widely used in the production or processing of ceramics, magnetics, pigments, metals, glass, carbons, catalysts, chemicals, waste/contaminated materials, etc. Many other processes and materials can be accommodated.

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