SPRAY DRYER

Oliver Manufacturing Company offers many types of dryers including a spray dryer. What exactly is a spray dryer? It's a machine that transforms feed from a liquid or fluid into a dried form by spraying the feed into a hot drying medium. The actual feed may be in a liquid or solution, suspension or paste. The dried product conforms to powder consisting of single particles or agglomorates, all depending upon the physical and chemical properties of the feed and the design of the dryer and its operation.

There are numerous applications for an Oliver Manufacturing spray dryer. For example spray dryers are used in the food industry for such products as powdered milk or instant coffee or for the production of powdered detergents. The process used in a spray dryer involves the production of highly dispersed powders from a solution or a suspension by evaporating the solvent. A spray dryer uses pressure nozzles or a rotary atomizer that spray the feed down towards the fluid bed where agglomeration incorporating finer, recycled material takes place.

The first step take by the spray dryer is for the solution to be sprayed into a hot air stream. The droplets formed have a large surface when compared with their volume. As the transfer of heat occurring from hot air to the liquid phase is directly proportional to the area of the surface, the temperature of the small droplets is increasing much more rapidly as opposed to one large drop of the same volume. The higher the temperature of the droplet the faster the evaporation of the solvent happens. Considering the droplet phase we will find an increasing temperature due to the heat transfer from the hot air over the phase boundary and consequently so will the evaporation rate. Conversely, the energy for the evaporation of the solvent comes from the liquid drop. The drop temperature is decreasing and heat from the hot air is transferred to the droplet by convection due to temperature gradients. Finally the temperature of the gas phase decreases proportionally to the mass of solvent that has been evaporated.