Rotary Kilns vs. Rotary Dryers: What’s the Difference?

In the field of industrial thermal processing, rotary kiln and rotary dryer are two common equipments, although they have some similarity in thermal processing principle, but their use, design and operation are significantly different. This article will discuss in detail the main differences between these two types of equipment.

Difference between rotary kiln and rotary dryer

1. working principle and temperature requirements

The rotary dryer is mainly used to extract moisture from the material. The operating temperature is typically between 800ºF and 1400ºF. This equipment through the rotation of the cylinder and the internal lifting plate will be constantly thrown, scattered materials, so that it is fully heated to achieve the purpose of drying. The process is relatively simple and easy to operate.

Rotary kilns, on the other hand, are used to cause chemical reactions or phase changes and therefore need to be operated at higher temperatures, typically between 1000ºF and 3000ºF. While rotary kilns may reduce some moisture during the process, this is usually of secondary importance. The primary purpose of the rotary kiln is to heat the material to the desired temperature for the desired reaction.

2. Design and construction

Because of the need to withstand higher temperatures, rotary kilns must be designed to be more robust. For example, direct-fired kilns are usually lined with refractory bricks or castables to protect the steel shell. In contrast, rotary dryers are usually unlined because they do not operate at such high temperatures.

Indirect rotary kilns and dryers are usually not lined, but instead use a shell made of a high-temperature-resistant alloy to withstand the internal temperatures instead of a steel drum shell. The rotary kiln’s barrel is rotated by a gear unit driven by a pinion gear fixed to the outer diameter of the barrel, and the interior is lined with different types of refractory bricks as required. The cylinder of the rotary dryer is a horizontal rotating cylinder, with various types of plates welded from front to back at different angles.

3. Shape and size

In terms of shape and size, rotary kiln usually has a larger length and smaller diameter ratio, usually more than 10:1, so it looks slender. On the other hand, the length to diameter ratio of rotary dryer is usually less than 8:1, so it looks shorter and thicker.

4. Uses and applications

Rotary dryer is mainly used for low-temperature applications to reduce the moisture content of raw materials, commonly used in mineral processing production of ore raw material drying, such as ball mills and flotation machines after the drying operation. In addition, it is also widely used in agriculture and food processing for drying agricultural products and foodstuffs to extend their shelf life.

The rotary kiln, on the other hand, is used for calcining at high temperatures to change the nature of the material. Typical applications include:

• Cement production: used for calcining cement clinker, through high temperature to make raw materials undergo a series of physical and chemical changes, such as limestone decomposed into calcium oxide at high temperature.
• Metallurgical industry: Used to roast ores and change the chemical properties of the ores for subsequent processing.
• Chemical industry: for the production of chemical products in the high temperature reaction process.

5. Heating temperature

In terms of heating temperature, rotary kiln is able to withstand higher operating temperature, usually between 800℃ and 1300℃, while the heating temperature of rotary dryer is lower, usually around 300℃.

Summarization

To summarize, rotary kilns and rotary dryers have significant differences in shape, process, application, structure and heating temperature. Which equipment to choose depends on the specific process requirements and material characteristics.

Here are some additional tips to help you make your choice:

If your primary goal is to remove moisture from the material, then a rotary dryer is a better choice.

If your process requires chemical reactions or phase changes at high temperatures, then you need a rotary kiln.

Consider the type and characteristics of the material. Some materials may be better suited to one type of equipment than another.

Consult with an experienced engineer or equipment supplier who can help you select the best equipment for your needs.

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As a leading manufacturer of rotary kilns and dryers, TONGLI is known for its superior quality and innovative technology. We offer.

• Advanced rotary dryer solutions
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Whether you are looking to improve productivity or need a customized industrial drying solution, TONGLI can meet your needs.

Contact us today to discuss how we can bring the best rotary kiln or dryer solution to your project!