Rotary coolers are often an integral part of a thermal process, cooling material as it exits a rotary kiln or rotary dryer, to a manageable temperature for the next step in the process. There are two main types of rotary coolers: a convective rotary cooler, and an indirect water deluge rotary cooler.
Convective Rotary Coolers
A convective rotary cooler works like a rotary dryer without heat; Flights lift the material up, and drop it through a stream of ambient, or chilled air. Typically, a convective rotary cooler is counter-current, meaning the material flows in the opposite direction of the air stream. This is a more efficient design from a thermodynamics and heat transfer standpoint than co-current flow (material flows in the same direction as air). Think of it like a hot, windy day. If you are walking against the wind, it is going to cool you off much quicker, than if you were to be walking with the wind.
In some convective rotary coolers, it is necessary to line the inlet of the rotary drum with refractory, because some material temperatures may exceed the design temperature of the rotary drum shell. The refractory is installed in the front end of the rotary cooler until the material has reached a temperature that the shell can handle. At this point, the refractory stops, and internal lifting flights begin to shower the material.
Indirect Rotary Coolers
Indirect water deluge rotary coolers are a unique type of cooler, using cold water to indirectly cool the material. Similar to an indirect fired rotary kiln, a rotary drum is enclosed in a stationary housing. Within this stationary housing, a trough above the rotating drum bathes the rotary drum in cool water. This cool water flows over the rotary drum, and is collected in a sort of funnel at the bottom. As the water is collected, it is funneled into a heat exchanger, which cools the water, and is sent back to the trough to be reused. In the case of an indirect water deluge rotary cooler, the drum is typically made out of stainless steel, in order to avoid corrosion. In some situations, material enters the rotary drum so hot, that it could potentially damage the stainless steel shell. In this case, a special alloy would be used for the inlet part of the rotary cooler. Once the material has reached a certain point in the drum and has cooled off enough, the alloy portion of the drum can stop, and stainless steel can take over for the remainder of the rotary cooler shell. It would be impractical to line the rotary cooler with a refractory, because all of the heat transfer is occurring through the shell, and having a refractory would make it difficult and inefficient to transfer the heat.
Rotary coolers can be a valuable step in the process when thermally processing materials. FEECO International can custom design a high-quality rotary cooler to suit your needs.
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