Material Process 1: Spray Drying
Spray drying is a fast and cost-effective process which produces dry powders from a fluid material by rapidly drying with a hot gas medium (usually air). Spray drying technique is used for a wide variety of processes associating mainly with the food and pharmaceutical industries. Although spray drying has shown its importance, the model of the processes depicting the performance of the spray dryers is poorly developed. As a result, an emphasis has been put on the flow stability of the dryer. Flow stability is a key issue because the spray dryer needs to avoid highly unstable flows, otherwise damages to the machine may occur. In other words, these highly unstable flows can result in partially dried product sticking to the walls of the machine. This results in the buildup of crust and the material can even catch on fire due to overheating. If this happens, then there are more frequent maintenance shutdowns which raises the overall cost and lowers the production rate.
The figure above shows a systematic plan of the conventional spray drying process. The spray drying process consists of four components: the atomization of the liquid feed, the drying of spray with the drying gas, the formation of dry particles, and lastly, the separation and collection of the dry product from the drying gas. The atomization of the liquid feed occurs when the fluid is fed into the drying chamber using a peristaltic pump through a nozzle or atomizer. Atomization is the process of breaking up bulk liquids into droplets and can occur through centrifugal, pressure or kinetic energy. Drying gas, usually air, is also added at the same time when the fluid is being fed into the chamber. This is the drying of the spray with the drying gas. The formation of the dry particles occur when the droplets, in the micrometer scale, are subjected to rapid solvent evaporation. The formation of dry particles are then separated from the drying gas by using the cyclone. The cyclone deposes the dry particles in a glass collector located at the bottom of the device. This is the final component which is the separation and collection of the dry product from the drying gas. Lastly, any exhaust gas is released into the surroundings. The liquid feed can be in the form of solutions, suspensions, emulsions, slurries, pastes or even melts. This gives spray drying more options for different dry particles due to the different viscosity and mixture of the liquid feed. Furthermore, the solid particles produced in the process have a higher chemical and physical stability when compared to its liquid counterparts. These solid particles can even be used as precursors for the production of capsules and tablets in drug delivery systems.