Using Advanced Rotary Tube Internals to Improve Thermal Processes

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Some designs not only utilize the increased surface area of a tube internal, conducting heat just through the tube wall, but also allow the cooling water to flow inside the internals yet again increasing the total cooling efficiency. In this design, the pipes running through the process area are open to the outside of the tube such that cooling water and flow through without wetting the process material, thus allowing for an increase in cooling surface without relying solely on the heat transfer through conduction with the rotary tube wall.

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Radial Mixing – A Vital Feature for Advanced Materials

Product homogeneity and consistency is vital for all high value advanced materials. When processing in a rotary furnace with specific tube internals, such as flat bar lifters, consistency can be greatly improved by increasing the radial mixing of the material.

The flat bar lifter, when sized below the height of the bed of material, will cause agitation in the bed of material as it is conveyed by the rotary tube and increase envelopment. If the lifter was to be sized larger than the bed of material a greater bed turn-over is achieved, but this may come at a cost. A greater chance of reduced yields of material due to entrainment and dusting can occur if the material particle size is too small and the processing gas velocity is too high.

Improved Gas-Solid Interaction for Improved Thermal Transport

Reaction gas is vital for many of the processes, such as aluminum nitriding and boron nitriding. The need for consistent contact of the material bed with the reaction gas will determine whether or not the reaction takes place. Knowing this, it is not always necessary to reduce the tube fill percent in order to insure gas penetration through the entire bed to obtain the needed gas-solid reaction.

The addition of uniquely designed lifters in the rotary furnace can bring material up along the tube walls to a curtain point of discharge where the material is dropped through the process gas, thus, increasing the time exposure and amount of material exposed to the process gas.

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