Direct Heat Dryers

Direct heating and drying often refers to combusting the products directly with the process environment. The radiation transmission in a direct process is high and rapid. The process automatically stops at a certain level of combustion. Many process dryers, kilns, calciners, ovens, etc incorporate combinations in forced convection, radiation, and conduction principles as per the product requirement.

The heat supplied must be enough to

• Heat the dryer feed to the "light" component's vaporization temperature.
• Vaporize or free the liquid byproducts above the solids' surface.
• Heat the solids to the final desired temperature
• Heat the solids for the desired duration of time.
• Heat the vapor to the final desired temperature.

Direct heat dryers are of different types including rotary dryers, calciners, multiple hearth furnaces, fluid bed dryers, spray dryers and flash dryers. Their applications range from mineral ores, chemicals, sand and sugar, salts to fine powder slurry such as tea, coffee and catalysts and Gypsum, fine coal, fine crystalline solids.