The drum dryer is an equipment used to convert the solutions and suspensions into the solids. The main purpose of these dryer is placed is to spread the liquid to a large surface area so that drying can occur rapidly.
The drum dryer is also called as an roller dryer or film drum dryer.
The drum dryer consists of a hollow roller with a smoothly polished external surface heated internally by steam.
It rotates on its longitudinal axis. The liquid to be dried is placed in a trough known as feed pan.
The liquid is picked up by the roller as it rotates covering the surface in a thin film is removed mechanically by a scrapper known as doctor knife.
In drum dryer rotates on its longitudinal axis which is heated hallow metal drum , this metal drum is used to dipped in the solution to be dried .
As the dipping process completed the solution on the drum forms as a film on the surface of the dryer and made to dry, to form a layer on the surface of the metal drum. While the drum is rotating the suitable knife which is present just down to the metal drum scraps or peel offs the dried materials from the drum.
The construction of the drum dryer consists of a hollow steel drum of 0.6 to 3 meters diameter and 0.6 to 4.0 m length which is horizontally mounted and its external surface is smoothly polished for the easy removal of the dried cake.
Below the drum pan is placed with the feed in the manner that the drum dips partially in to the pan consisting of feed. One side of the drum a spreader is placed which is used to spread the material on to the drum and on the other side a doctors knife is placed to scrap or peel off the dried materials from the metal drum. After peeling of the material collect the materials in the conveyor or storage bin.
- The drying of the material is done by the process of steam when passed in to the drum. Due to the metallurgic nature of the drum the heat absorption is more.
- By the mechanism of the conduction the heat get transferred in to the drum and drying process takes place, the drying capacity is directly proportional to the drum surface area.
- the liquid material which is present in the pan gets adhere to the drum and gets dried by revolving at the rate of 1 to 10 revolution.
- The materials is completely dried during its journey during its revolutions.
- The dried materials is scrapped by the knife and that falls in to the bin.
- Solutions, slurries, suspensions and more are dried in this dryer.
- Milk products, starch products, ferrous salts, suspensions of zinc oxide, suspensions of the kaolin, yeast, pigments, malt extracts, antibiotics, glandular extracts, insecticides, DDT, calcium and barium carbonates are dried in this dryer.
- It takes les time to dry.
- Thermo sensitives drugs can also be dried.
- Drum dryers occupies less space.
- In order to reduce the temperature of drying the drum can be enclosed in a vacuum chamber.
- Rapid drying takes place due to rapid heat and mass transfer.
- Maintenance cost is high.
- Skilled operators are essential to thickness control of the film.
- It is not suitable less solubility products.
- Mehta RM, Pharmaceutics-I: introduction to the drying process (1996), Page no: 193.
- C.v.s subrahmanyam et al., pharmaceutical engineering principles and practices-filtration, 2001, page no. 393 - 394.