Spray dryers are widely used in the coffee industry

In spray drying, the material to be dried is suspended in air, i.e. the liquid is converted into a mist-like mist (atomization), providing a large surface area. The atomized liquid is exposed to the hot air of the drying chamber. Air and solids can flow in parallel or in countercurrent. Moisture evaporates quickly, so this process is useful for any material that is damaged by prolonged exposure to heat. The solids are recovered as a powder consisting of fine, hollow spherical particles. Heating the dry air can be accomplished with steam or direct gas fired air heaters or indirect gas, liquid or solid fuel heaters. Typically, as part of the process, the exhaust gas is passed through cyclones and/or filters to recover particulate matter (dust) entrained in the exhaust gas. Recycled materials are reincorporated into products.

Spray drying parameters:

The body of the Spray Dryer is large so the particles can settle as they dry without hitting the walls where they might be attached. Commercial dryers can be very large, around 10m in diameter and up to 20m in height. The intake air temperature used can reach about 250°C or higher (depending on the type of product), but the air temperature drops rapidly to about 95°C (air outlet temperature) due to evaporation. The product temperature will be 20 to 30°C lower than the air outlet temperature.

Application fields:

Spray dryers are widely used in dairy and coffee industries.