Spray Drying Case Study

2.2 Spray Drying

The University of Guelph discussed spray drying in the book entitled The Dairy Science and Technology and stated that spray drying is the process which nearly complete removal of water to a level less than 5%. Drying process takes place within a matter of seconds at high temperature, approximately 200°C. Spray dryer that widely used is a type of air convection dryer.

Ift.org (2017) indicated that process steps in spray drying strongly depend on material properties, equipment design and setting of operating parameters. These factors influence final product quality, especially in moisture residues, particle size and powder morphology. Usually, the optimization of these variables achieved by try and error approach.

2.2.1

At the same type of nozzle and feed material concentration, droplet size is decreasing with increasing the atomization pressure (Master, 1991).

The feed viscosity and density have a direct relation to droplet size. Increase in viscosity and density of feed means more energy required to break forces in order to have small droplet size. This situation explained in the equation given below:

Besides that, the feed surface tension also plays an important role in the level of the atomization. In order to achieve atomization, atomizer should overcome the feed surface tension. The higher liquid feed surface tension, more difficult to an atomizer. Therefore, there are criteria for spray dryer design selection in order to enhance spray dryer functionality.

Apart from atomizer parameter, the atomization device also vital to drying process because different types of atomizer contribute to different utilizing spray drying as an economical drying method. This is mean unsuitable atomizer device used for spray drying process may lead to unfavorable powder obtained and cause loss. The major types of atomizers are rotary and nozzle

The inlet temperature is understood as the temperature of the heated drying air also significant in cooling the atomized feed droplets. This inlet temperature often associated with the dryer evaporative capacity and thermal efficiency.

Outlet temperature is the temperature at where solid particles before entering the cyclone. This temperature is the resulting temperature of the heat and mass balance in the drying cylinder. Outlet temperature correlates with the final moisture content and surface topography of powder produced. The higher outlet air temperature will increase the particle temperature.

Glass transition temperature, Tg is the temperature above which the matrix shifts from rigid state to rubbery state. On the other word, Tg is associated with the product stickiness on the spray dryer chamber wall. This property leads to product agglomeration then rise problem on caking and lumping of the powder after