The directly heated rotary dryer operates on the principle of lifting and showering the product through a hot gas stream moving either in parallel or counter-flow whereas with the indirect dryer, which is more suited to fine and dusty materials, there is little or no contact between the product and the drying gases since they are heated from the outside, via a stationary jacket fitted with either multiple burners or other external heat source.
The efficiency of the dryer is largely dependant on the differential between the inlet and exhaust gas temperatures, although the heat transfer rate is also influenced by the relationship between the design of flights and the speed of rotation. However, irrespective of the gas and material temperatures the drying (or residence) time may be critical, as this is governed by the rate of diffusion of water from the core to the surface of the material.
For greater thermal efficiency and where inertization is required, recycling of exhaust gases can be used. This can be implemented on all our airstream drying systems and retrofitted on customer's existing drying operations.
For special applications, the rotary cascade design is adapted to provide a shortfall, or 'Cruciform', lifter configuration.
Similarly, Rotary Cascade Coolers and Combined Dryer/Coolers are available as required.