INDIRECT-HEAT ROTARY DRUM DRYERS

For various reasons, some products dried in a rotary dryer require special conditions that cannot be met by a direct-heat rotary dryer. For example, more control of the atmosphere within the dryer to promote oxidation or reduction may be required. The material may be extremely fine or need to be handled more gently. For other processes like drying food, preventing contamination of the product is important. Each of these issues can be addressed by the use of an indirect-fired rotary drum dryer. For this type of rotary dryer, the heat for drying is applied to the shell of the drum. This may be accomplished by steam jacketing, oil heating, or furnace encasement of the rotary drum.

An indirect-fired rotary dryer also has specialized flights within the drum. These flights are included to provide enough agitation of the material to promote efficient heat transfer. Because the shell itself is heated, the gas velocities within the drum are lower and the size of the gas handling system is smaller.

WHY CHOOSE AN INDIRECT-HEAT ROTARY DRUM DRYER?

Generally speaking, direct-fired rotary drum dryers are more efficient that indirect-fired dryers. However, there are advantages to choosing an indirectly heated rotary dryer.

• Protection of Product from Contamination
• Lower Gas Velocities Produce Less Entrainment
• Gentler Handling of Materials
• Smaller Off-Gas Handling System
• More Precise Temperature Control