Drum dryer and roll dryer is widely used in industries because of their heat-drying property. In this article learn about principle, constructions, and workings, along with their advantages, disadvantages, and pharmaceutical applications.
Principle of Drum Dryer:
In the drum dryer principle, we use a heated hollow metal drum that rotates on its longitudinal axis. The drum is partially immersed in the solution to be dried. It is a simple and effective method that ensures proper drying of the material. The solution is carried as a film on the surface of the dryer and dries to form a layer that is collected.
Construction of Drum Dryer or Roll Dryer:

- The drum dryer, a moving bed dryer, is constructed using cast iron and stainless steel materials.
- The MOC of the drum dryer has durability, cleanliness, and resistance to chemical attacks.
- It consists of a hollow steel drum of about 0.75 to 1.5 m in diameter and 2.4 m in length.
- It is heated internally, usually by steam, and rotates in its longitudinal axis.
- The external surface of the drum is polished for long sustainability.
- For drying purposes, the materials are fed into the pan.
- The drum is partially dipped in the pan.
- Spreader is used in spreading liquid film eventually on a drum roller.
- The drum is rotated continuously and its speed is adjusted so that all the liquid is fully vaporized.
- Dried deposited or material can be scraped off with the help of a knife and collected in a storage bin.
a. Double Drum Dryer:

- It is utilized for low to medium-viscous materials.
- Two drums are provided to rotate in opposite directions.
- The product is fed in between these two drums and the distance is adjusted as per to get desired material.
b. Vacuum Drum Dryer:
- A vacuum dryer allows for drying at lower temperatures by operating under vacuum conditions.
- In a Vacuum drum dryer, two steam-heated drums rotate within an airtight casing under a high vacuum.
- The liquid is introduced between the drums from the top, dried, and then scraped off before the drums complete a full rotation.
- There is no accumulation of product residues, and no material recirculation occurs.
- It is very easy to inspect and maintain.
- It is useful for heat-sensitive products and the low-temperature evaporation of solvents. Vacuum dryers provide careful treatment for feed materials, preserving thermolabile substances like enzymes and proteins and preventing protein denaturation.
Working of Drum Dryer:
Single Drum Dryer:
- In a single drum dryer, the drum body is heated internally by steam.
- The heat due to steam is transferred by conduction to the materials.
- As we rotate the drum, the liquid materials in the feed pan stick to the drum’s outer surface, forming a thin layer.
- Then materials get dried which is scrapped by the knife which then fall into a storage bin.
Double Drum Dryer:
- In a double-drum dryer, the liquid to be dried is fed into the space between the two drums.
- Then the drum starts to rotate in the opposite direction.
- The contact time between the material and the hot metal surfaces is typically only 6 to 15 seconds
- After that, a knife on each drum removes the dry product.
Advantages of Drum Dryer or Roll Dryer:
- Drying takes place in less time
- Suitable for thermosensitive drugs.
- Occupies less space.
- A vacuum chamber can enclose the drum to lower drying temperatures.
- Rapid drying takes place due to fast heat and mass transfer.
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Disadvantages of Drum Dryer or Roll Dryer:
- High maintenance costs.
- Requires skilled operators to control film thickness, rotation speed, and temperature.
- Not ideal for products with low solubility.
Pharmaceutical Uses of Drum Dryer or Roll Dryer:
- It is used for viscous liquids, slurries, suspensions, and pastes, to turn them into powders or flakes.
- This drying equipment is widely used in Food & Dairy industry, as well as the Chemical & Pharmaceutical industries, for drying various types of pastes and slurries.
Variants:
- Vacuum drum dryers integrate both the drum and feed line into a vacuum chamber, which helps in the drying of heat-sensitive materials.
- On a large-scale, two drums can be arranged in parallel, rotating in opposite directions with a shared feed inlet.
Conclusion:
In conclusion, drum dryers and roll dryers provide an easy solution for drying various materials, including viscous liquids, slurries, and pastes in various industries.
FAQs (Frequently Asked Questions):
Ans: Both drum and roll dryers can easily handle heat-sensitive materials.
Ans: Drum dryers have lots of advantages including reduced drying time, suitability for thermosensitive drugs, compact size, and rapid heat and mass transfer, leading to proper drying processes.
Ans: No. it is not suitable for products with low solubility.
Ans: This equipment is widely used in Food & Dairy industry, as well as the Chemical & Pharmaceutical industries, for drying various types of pastes and slurries.
Ans: Yes, on large-scale production, it is possible to use multiple drums arranged in parallel, rotating in opposite directions.