The third industrial dryer that uses a process air heater for hot gas generation is a spray dryer. Spray dryers are the most widely used drying system in the food and dairy powder industries. Powdered colors, inorganic chemicals, insoluble organic dyes, and instant mixes are just a few of the items that require spray drying. Because spray dryers are known for distributing a consistent particle size, some industrial products (such as catalysts) are also spray dried.
These dryers use an atomizer to feed the liquid into a drying chamber. When the small drops of liquid enter the chamber, they are subjected to hot air, which turns the feed into powder by means of water evaporation. The hot air is generated by either an indirect air heater or a direct fired air heater. Because the air heater utilized depends upon the thermal sensitivity of the feed, an indirect fired air heater is typically used in the food, pharmaceutical and dairy industries.
According to Wikipedia “The hot drying gas can be passed as a co-current or counter-current flow to the atomizer direction. The co-current flow enables the particles to have a lower residence time within the system and the particle separator operates more efficiently. The counter-current flow method enables a greater residence time of the particles in the chamber and usually is paired with a fluidized bed system”. (Fluid bed systems are the topic for next week’s blog!)
After the drying chamber, the material is then separated using cyclones. To meet emission standards, sometimes a scrubber is used with spray dryers.
Below is a picture of a spray drying system.
If you have any questions about how air heaters are used in conjunction with spray dryers or if you have any applications, feel free to contact Stelter & Brinck via our website or give us a call 513-367-9300!