GEA's range of Rotary Dryers are extensively used throughout the process industries and are highly reliable under the most arduous operating conditions. Noted for their process flexibility and robust construction, their design permits the use of the highest possible drying temperatures and in contrast to other dryers, are not sensitive to wide fluctuations in throughput and product size.
The workhorse of industry.
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.
Co-Current Rotary Dryers are the most widely used and are particularly suitable for drying materials containing a high moisture content, which are heat sensitive or have a tendency to stick or cake.
The wet material is in contact with the gas at its highest temperature, which rapidly evaporates surface moisture. The initial heat transfer rate is high, causing an immediate and considerable drop in gas temperature, which prevents overheating of the material and the dryer shell. The final product is in contact with the gas at its lowest temperature, enabling the moisture content to be readily controlled, usually by maintaining the dryer exhaust gas temperature at a pre-set value.
Counter-Current Rotary Dryers are more suitable for materials that must be dried to very low levels of moisture, where the last traces of moisture are difficult to remove, or where an elevated product temperature is desirable.
They are also used effectively as combined dryer / preheaters. However, since the final product is in contact with the gas at its highest temperature the counter-current dryer is often unsuitable for heat sensitive materials. Although this system can be more efficient, moisture which is to remain in the product, is not so readily controlled.
Calciners are used to change the "state" of a material. GEA's direct fired and indirectly heated Rotary Calciners are custom designed to suit your individual product and process requirements.
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.