Bulk Drying – Process and Equipment

Bulk drying across process industries is carried out with the help of industrial dryers that best suit industry specifics. Moisture or liquids are removed from the input by evaporation or sublimation, using either direct or indirect drying. Direct dryers are based on convective heating – transferring heat between the product and the immediate environment. Indirect dryers, on the other hand, use a heated wall to lap up moisture from the product. Not all industrial dryers are suitable for all forms of products.

Types of Industrial Dryers for Processing Products in Powder Form

Industrial dryers used for processing powder content tend to vary depending on several factors such as:

• quality, size and consistency of output
• moisture and acid content of the product
• duration of process

Different types of dryers best suited for task include, but are not limited to:

• spray dryers
• fluid bed dryers
• flash dryers
• rotary dryers

Spray Dryers

These are ideal for converting products in liquid form into powders, by atomising them into droplets and then removing moisture to create a fine powder. Products subject to strict quality specifications (food, chemicals, pharmaceuticals, etc.) such as residual moisture content, particle size, and density are good candidates for spray drying. Settings can be fined tuned to achieve precision.

Fluid Bed Dryers

Fluid beds are used to remove excess moisture from powder content to meet quality specifications. A blast of hot air passed through the perforated fluid bed causes fine particles to fluidise and exit the dryer, while the rest of the product is processed to perfection (up to 5 mm). Vibrating fluid beds and back mixing products to increase process efficiency are some variations that help enhance the drying, depending on the type of the product. They find use in processing minerals.

Flash Dryers

The process of flash drying involves feeding the product at a constant rate into a stream of hot air to instantly get rid of the moisture content and collecting the dry powder into a filter. The products are dried in a flash and, hence, the name.

Rotary Dryers

True to the name, these are large, rotating drums into which wet material and hot gases are fed, either from the same or opposite directions to effect the drying process. The end product is usually collected from the bottom of the drum.

Industrial dryers find use in several industries, right from processing food items, health drinks, pharmaceuticals, chemicals, minerals and mining, to fertilisers and cement, etc. The drying process, however, should in no way alter the properties of the end product, must be cost-effective, energy-efficient and environment-friendly. Accordingly, the choice of a suitable dryer will help meet business demands while also helping them comply with safety and quality regulations specific to the industry.