Factors Affecting Particle Size in Spray Dryers

Spray dryers are the flagship product of Changzhou Mingxing Drying Equipment Co., Ltd. Today, spray drying equipment is widely used in the food, pharmaceutical, and chemical industries. Spray dryers are particularly common in the dairy and ceramics industries. As market demands for products continue to rise, significant changes have occurred in drying processes, presenting considerable challenges for drying equipment manufacturers. For example, in the ceramics industry, slurry is currently dried into granules before being pressed into bricks using a brick press. As the tonnage of brick presses continues to increase, there is a growing need for powder dried by spray dryers to have a larger particle size. How can the structure and operating parameters of spray dryers be adjusted to meet this requirement for larger particle sizes?

Factors Affecting Particle Size in Spray Dryers

  We addressed this topic in our previous article, “How to Increase the Particle Size of Spray-Dried Products.” There are numerous factors that influence the particle size of the final powder, such as the solid content of the feed solution, viscosity, choice of atomizer, inlet air temperature, and outlet air temperature. The extent to which these factors influence the outcome must be verified through experimentation.

  After screening, experiments were conducted focusing on four aspects: material moisture content, viscosity, drying pressure, and atomizer orifice diameter. The experimental equipment used was a pilot-scale spray dryer independently designed by our company, with a material moisture content of 36.2% and a viscosity of 18.5 s.

   First, we varied the moisture content of the material. With all other parameters held constant, a decrease in moisture content led to an increase in the proportion of coarse particles in the product. By plotting a curve, we found that the relationship between moisture content and particle size is not linear. (See figure below)

The figure above shows the effect of feed solution moisture content on product particle size

Effect of viscosity: By altering the viscosity of the feed solution, we found that increasing the viscosity leads to a higher proportion of coarse particles in the product. (See figure below.) However, based on our company’s many years of experience, we have determined that increased feed solution viscosity can cause nozzle clogging and may also result in significant damage to the plunger pump. Conversely, excessively low viscosity can lead to material adhesion to the tank walls. Feed solution viscosity must be adjusted with caution to prevent production accidents.

The figure above shows the effect of feed solution viscosity on product particle size

Effect of Main Spray Drying Tower Pressure: As clearly shown in the figure below, when the pressure in the drying tower increases, the material contains more fine particles; when the pressure decreases, the proportion of coarse particles increases. Pressure affects both yield and atomization efficiency; generally, a pressure setting within the range of 0.8–1.0 MPa is appropriate.

The figure above shows the effect of pressure on particle size.

With all other parameters held constant, we varied the nozzle orifice diameter. We found that selecting a larger orifice diameter resulted in a higher proportion of coarse particles. After appropriately adjusting parameters such as hot air temperature, the product’s moisture content requirements were met. Currently, adjusting the nozzle is a reasonable method for optimizing product particle size.