The heat source of a rotary kiln primarily comes from gas burners.
These gas burners utilize heat derived from the processed material as fuel.
This method is an energy-saving approach that reuses waste heat as an external heat source.
Gas Burner Type Heating: Reusing Waste Heat for Energy Efficiency
In the gas burner type of rotary kilns, the heat is generated by burning the processed material itself or its by-products.
This method not only provides the necessary heat for the kiln's operations but also serves as a way to recycle and utilize waste heat.
The heat generated is used to superheat steam, which corresponds to the furnace atmosphere.
This facilitates various thermal processes such as calcination, incineration, and thermal desorption.
Direct Rotary Kilns: Efficient Direct Heat Transfer
Direct rotary kilns are particularly efficient due to the direct heat transfer between the material and the heating medium.
In these kilns, process gas passes through the drum either co-currently or counter-currently to the material.
The drum is typically lined with refractory materials and may contain lifting or tumbling flights.
These flights enhance heat transfer by encouraging bed turnover or creating a showering effect of the material through the process gas.
Internal Heat Exchangers: Enhancing Heat Exchange
In some rotary kilns, especially those operating at lower temperatures or in the cooler parts of long kilns without preheaters, internal heat exchangers are used.
These exchangers improve heat exchange between the gas and the feed.
They may include scoops or "lifters" that cascade the feed through the gas stream.
Metallic inserts that heat up in the upper part of the kiln and transfer heat to the feed as the kiln rotates are also common.
Chains hanging in curtains across the gas stream are a common type of heat exchanger.
Electric Heaters: Precise Temperature Control
While less common, electric heaters are used in rotary kilns to achieve high temperatures with precise control over heating rates and temperature distribution.
These heaters allow for uniform temperature control and can operate in various atmospheres such as air, oxygen, nitrogen, argon, etc.
Summary: The Primary Heat Source and Additional Methods
In summary, the primary heat source in rotary kilns is the gas burners that use the processed material as fuel.
This enhances energy efficiency by reusing waste heat.
Additional methods like direct heating, internal heat exchangers, and electric heaters are employed to optimize heat transfer and process efficiency.
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