How spray dryer works?
Air inlet is heated by hot air generator. Hot air generator heat source is electric heater, gas burner, steam heat exchangers. The source varies to model of spray dryer. Hot air is vacuum through drying chamber by blower (exhaust fan). Feed pump pumps liquid through special nozzle. Liquid is sprayed become small fine droplet which create high efficient thermal exchange, since area of liquid is increased dramatically. When droplet meets hot air, it evaporate liquid out of solid then become powder. The liquid become steam. The powder is vacuumed to cyclone. Cyclone separate powder and steam. The powder is collected in powder bucket below cyclone. Steam is vacuumed out by blower.
There are two main spraying inlet currents. Co-current spraying nozzle flows top to bottom (in the same direction as air flow). Counter-current flows bottom to top (opposite direction to air flow).
Co-current has shorter heat contact time.Co-current is suitable with liquid which is thermal sensitivity such as sugar-based solvent. Counter-current has advantage in better heat contact time. The droplet is sprayed up against hot air flow then flow down. Longer heat contact time provide higher heat efficient. In huge spray dryer nozzle could be sprayed in both direction to maximize the volume of drying chamber and thermal efficient. For example: ceramic, sodium silicate, chemical solvent. These product is high thermal tolerance. In big industry, spray dryer height is 10-30 meter which increase heat contact time in both direction.