Rotary Kiln Design: Seals

Holding the appropriate temperature within a rotary kiln is what allows the desired chemical reaction to occur. Sustaining that temperature, however, can be difficult if the right seal is not chosen.

Almost all rotary kilns run at a negative pressure, meaning gas doesn’t leak out, but rather, air leaks in. Because rotary kilns are always running at a higher temperature than the ambient air, any ambient air leaking into the rotary kiln will cause the temperature inside of the rotary kiln to drop. Not only will this result in an unnecessary amount of energy being used and wasted, but if the leak is severe enough, it could potentially disrupt the chemical reaction. This is why it is crucial to have a quality seal.

Sealing the ends of a rotary kiln can be a difficult task, because there is always going to be something rotating attached to something stationary. This breeching, or the stationary part, is typically where leakage will occur. So how do you seal a moving part against a stationary part? One answer is a leaf seal. Leaf seals are the standard seal used on rotary kiln and rotary dryers. But how does a leaf seal work?

Leaf seals are similar to a fanned out deck of cards. The “cards,” or leaves, are made out of a spring steel. These fanned out leaves are bolted to the breeching, and the springy leaves are forced to push against the seal/wear plate of the rotating kiln, naturally keeping pressure on the rotary kiln to create a good seal. Several variations of this seal are also available, such as the purged double leaf seal.

The purged double leaf seal is typically used in situations where maintaining the atmosphere inside the rotary kiln is extremely critical. For example, in cases where the atmosphere inside the rotary kiln cannot tolerate oxygen from ambient air leakage. In this case, the purged double leaf seal would be a viable alternative to a standard leaf seal. The purged double leaf seal is made up of two components. The first is two sets of seals which consist of two layers of leaves on top of each other. The second component is an inert purge gas, such as nitrogen, which is introduced between the two sets of seals. This purge gas pushes outward to ambient, so that there is a flow of gas going out, and therefore, no oxygen is allowed to flow in.

As a leader in the thermal processing industry, Feeco International knows how critical it is to run efficiently. We can supply leaf seals and purged double leaf seals to suit your needs.

Rotary Kiln Design: Leaf Seal

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