combined drum dryers-coolers mozer system for processing solids in a production hall | © Allgaier Process Technology 2022
Drum Dryer
Efficient drying of finde and coarse solids

Drum Dryer

The Allgaier drum dryers are used for drying free-flowing bulk solids. High throughput rates and the ability to handle solids with a wide range of particle sizes or fluctuating product properties are distinguishing features of these drying devices. They are particularly suitable for processing minerals, sands, slag, ores, and coal. These extremely robust industrial dryers are available as single-shell, double-shell, or even triple-shell dryers. The design and configuration ensure high performance in a compact space.

combined drum dryers-coolers mozer system for processing solids in a production hall | © Allgaier Process Technology 2022

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Functional principle of the Mozer system

In horizontally oriented Allgaier drum dryers, also known as rotary kilns or rotary dryers, the solid material is moved through the rotation of the drum and the conveying effect of the internal components. Lifting blades pick up the moist solid material from the bottom of the drum and let it fall again, creating intense contact between the hot drying air and the moist solid material. In most applications, the solid material is conveyed in concurrent flow, meaning in the direction of the gas flow. The conveying of the solid material is achieved through so-called guide blades. The lifting blades create a product curtain by dropping the bulk materials in the upper half of the drum, resulting in a combination of concurrent and crossflow between the drying gas and the solid material. Counter-current applications are mainly found in the asphalt industry and in high-temperature applications, such as calcination processes.



drum dryers mozer system infeed drum in a production hall | © Allgaier Process Technology 2022

Multi-pass drum drying

Allgaier Process Technology drying devices are available in single-shell construction, known as continuous dryers, as well as two-pass dryers or three-pass dryers. The use of two or three-pass dryers can depend on the available space and the required solid residence time. Whenever the dried solids are intended to be cooled immediately after drying, the use of a double-shell dryer for combined drying and cooling in a single unit is recommended.

drum dryers mozer system two-pass drum in a production hall | © Allgaier Process Technology 2022

Combined Processes

Allgaier has expanded and perfected the usability of drum dryers. The result of this work is the exploration of new application areas for combined solution processes in a single system, which are particularly effective and profitable for the plant operator.

  • Drying and cooling
  • Drying and cleaning
  • Drying and screening
  • Drying and breaking
combined drying and shredding shredding machine in a production hall | © Allgaier Process Technology 2022

Heating of Drum Dryers

The heating of the drying air is typically done by using gas or light oil burners. The combustion gases are mixed with a portion of ambient air to achieve average drying air temperatures ranging from 600 °C to 900 °C. For thermally robust materials such as quartz sand, the burner flame can directly burn inside the rotating drum. In the case of gentle drying of temperature-sensitive substances such as limestone, clay, bentonite, plastic recyclates, or organic residues and waste materials, combustion chambers are used to ensure that the hot combustion gases are sufficiently mixed with ambient air in the combustion chamber before entering the drum, achieving the desired average drying air temperature.

Combined Drying and Cooling

Allgaier offers combined industrial dryers/coolers in single-shell, double-shell, and triple-shell designs. In all three designs, drying and cooling take place in a single unit, making only one drive and one bearing necessary. Combined drum dryers/coolers are available in three versions: TK, TK+, and TK-D. While the TK type uses ambient air cooling, the TK+ model utilizes the thermal effect of evaporative cooling. The TK-D type is an advancement that combines drying and cooling in a single rotary drum. The TK-D complements the existing systems by offering the capability to cool materials to particularly low temperatures, efficient heat recovery, and resulting energy savings.

Possibilities for Energy Recovery and Efficiency Enhancement  

In order to remain competitive in today's market, it is essential for drum drying processes to incorporate energy recovery and overall efficiency improvement. That is why Allgaier has launched the LeadingEcoSolutions program. Leveraging their extensive experience as a provider of innovative drying systems, Allgaier offers advanced and energy-efficient solution concepts for industrial plants. All possibilities for energy savings are identified in close collaboration with customers to ensure maximum benefits, high quality, and a short payback period.

allgaier employees in front of a dryer in a production hall | © Allgaier Process Technology 2022
Together we determine your potential for energy savings with a view to a high benefit and a short amortization period.
Daniel Mössinger - Machine & Plant Project Planning Drying Technology

Application areas for drying devices with drying chambers

Due to their various model variants and robust operational capabilities, industrial dryers of this type can be used in a wide range of applications. The rugged and simple plant technology is primarily employed in the industrial sector of stones/earth or mining. This allows for the processing of different types of rocks and minerals, such as various types of sand, clay, or limestone. Additionally, the drying devices are also utilized in recycling applications, such as recycling glass. By incorporating a special, wear-resistant lining inside the rotary drum dryer, the highly abrasive behavior of recycled glass can be mitigated. Furthermore, the rotary drum units can also be employed in the production of fertilizers or in the thermal treatment of various chemical products.

Advantages drum drying

  • Suitability for both coarse and fine-grained solids.

  • High resistance to very coarse or heavy solids.

  • Minimal effort required for the air supply equipment due to the burner arrangement on the dryer housing.

  • Resilience to fluctuations in particle size, moisture, throughput, and drying air failure.

  • Low specific electrical energy requirement.

  • Ability to use high drying air temperatures with minimal heat loss.

  • Low heating energy demand, even at partial load, through adjustment of the exhaust air quantity.

  • Easy installation and quick commissioning.

  • Resilience to operator errors.

  • Ability to operate under challenging climatic conditions.

  • Low wear and tear.

combined drum dryers/coolers mozer system for processing solids in a production hall | © Allgaier Process Technology 2022
combined drying and cleaning machine for processing bulk material in a production hall | © Allgaier Process Technology 2022
drum dryers mozer system interior view in a production hall | © Allgaier Process Technology 2022

Limits of the drum dryers

Despite the numerous applications of various advanced technologies, there are also limitations for these dryer models. The robust design of the dryer can have negative effects on the product in some cases. Specifically, for delicate or temperature-sensitive products, the lifting action, the product conveyance within the dryer, as well as the burner flame or combustion gases in direct contact with the product, can have negative impacts on the material properties. Due to the diverse range of machinery offered by Allgaier Process Technology, these limitations can be addressed using other drying techniques such as fluidized bed dryers, flash dryers, rotary bed dryers, or disc dryers.

FAQ - Frequently asked questions

What is a drum dryer?

Drum dryers, also known as industrial dryers, are a type of drying equipment used for drying materials such as granules, powders, or pastes. This system consists of a rotating drum, which is equipped with a burner. The drum is typically positioned horizontally and equipped with lifting blades to move the substance through the drum and ensure that it is fully dried by the hot air flowing through the tube.

At what temperatures does a drum dryer operate?

The operating temperature of drum dryers depends on various factors, such as the type of material being dried and the specific requirements of the drying process. Generally, the operating temperatures range from 600°C to 900°C. In some applications, higher temperatures may be required, such as in the calcination of raw materials, where temperatures of over 1000°C can be reached. However, it is important to ensure that the operating temperature always remains within the limits of the material specifications and safety standards to ensure effective drying and safe operation of the drum dryer.

What kind of wear does an industrial dryer experience?

These drying devices undergo a certain degree of wear during their operation. The extent of wear can vary depending on the application, product characteristics, and specific conditions of the drying process. Some factors that can influence wear include the type of product being processed, operating temperature, drum rotation speed, fill level, and the type of internal components.

The internal components of the drum dryer, such as lifting blades, can become worn or damaged and therefore need regular maintenance or replacement to ensure effective drying. The drum itself can also experience wear over time and, in advanced stages, develop cracks or holes that require repair to maintain the safety and effectiveness of the dryer.

How big is a drum dryer?

The size of such an industrial dryer can vary depending on the application and requirements of the drying process. Our drying equipment can be manufactured in a variety of sizes, ranging from small laboratory models to large industrial plants. Depending on customer and application requirements or the available space, Allgaier can perform the appropriate plant dimensioning. The individual residence time of the material inside the drum dryer and the capacity requirements can be evaluated through trial runs in the Allgaier technical center. The data obtained from these experiments are fundamental for the design and sizing of the future production plant. Small drum dryers often have a diameter of only a few centimeters and are designed for laboratory or pilot-scale applications. However, larger drum dryers for industrial applications can have diameters of several meters and lengths exceeding 30 meters.

How long does it take to deliver a drum dryer?

The delivery time can depend on several factors, such as the size and complexity of the dryer, the availability of materials and components, and the manufacturing capacity of the supplier. Additionally, the specific requirements of the customer also play a crucial role in determining the delivery time.

Typically, the delivery time can span several months, as these are custom-made machines tailored to the specific needs of the customer.