Drum Dryer | Roll Dryer: Principle, Construction, Working, and Application

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.

Related: Mixing – Pharmaceutical Engineering a Complete Guidance

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):