A spray dryer takes a liquid stream and separates the solute or suspension as a solid and the solvent into a vapor. The solid is usually collected in a drum or cyclone. The liquid input stream is sprayed through a nozzle into a hot vapor stream and vaporized . Solids form as moisture quickly leaves the droplets. A nozzle is usually used to make the droplets as small as possible, maximizing heat transfer and the rate of water vaporization. Droplet sizes can range from 20 to 180 μm depending on the nozzle. There are two main types of nozzles: high pressure single fluid nozzle (50 to 300 bars) and two-fluid nozzles: one fluid is the liquid to dry and the second is compressed gas (generally air at 1 to 7 bars). Spray dryers can dry a product very quickly compared to other methods of drying. They also turn a solution (or slurry) into a dried powder in a single step, which simplifies the process and improves profit margins. In pharmaceutical manufacturing, spray drying is employed to manufacture Amorphous Solid Dispersions, by uniformly dispersing Active Pharmaceutical Ingredients into a polymer matrix. This state will put the active compounds (drug) in a higher state of energy which in turn facilitates diffusion of drug spices in patient body. It is a device that can complete drying and granulation at the same time. According to the process requirements, the pressure, flow rate and the size of the nozzle hole of the liquid pump can be adjusted to obtain the required spherical particles in a certain size ratio. A spray dryer is a type of continuous atmospheric dryer. The liquid material is sprayed into a mist with special equipment, and it is dried by contact with hot air. For drying some heat-sensitive liquids, suspensions and viscous liquids, also for drying fuels, intermediates, soap powder and inorganic salts. Generally, it includes electric heating blast drying oven, vacuum drying oven, high-speed centrifugal spray dryer, and sterile spray dryer. The working principle, basic classification, characteristics, technical parameters, application scope and operation process of the spray dryer are introduced in detail.
Drying equipment, also known as dryer, is a device used for drying operations. The moisture in the material (generally refers to moisture or other volatile liquid components) is vaporized and escaped by heating to obtain solid materials with a specified moisture content. The purpose of drying is for the needs of material use or further processing. For example, drying of wood before making wooden molds and woodware can prevent deformation of products, and drying of ceramic blanks before calcination can prevent cracking of finished products. In addition, the dried materials are also convenient for transportation and storage, such as drying the harvested grains below a certain moisture content to prevent mildew. Since natural drying is far from meeting the needs of production development, various mechanized dryers are more and more widely used. The drying process needs to consume a lot of heat energy. In order to save energy, some materials with high moisture content, suspensions or solutions containing solid substances are generally dehydrated or evaporated by heating, and then dried in a dryer to obtain dry solids. In the drying process, it is necessary to complete the transfer of heat and mass (moisture) at the same time, to ensure that the partial pressure (concentration) of the moisture vapor on the surface of the material is higher than the partial pressure of the moisture vapor in the external space, and to ensure that the temperature of the heat source is higher than the temperature of the material. The heat is transferred from the high temperature heat source to the wet material in various ways, so that the moisture on the surface of the material is vaporized and dissipated to the outside space, so that there is a difference in the moisture content between the surface and the interior of the material. The internal moisture diffuses to the surface and vaporizes, so that the moisture content of the material is continuously reduced, and the overall drying of the material is gradually completed.
Vacuum dryer is the equipment with the help of which vacuum drying is carried out. In the pharmaceutical industry vacuum dryer is known by a common name called vacuum oven. Vacuum dryers are sometimes made up of cast iron, but most now are made of stainless steel , so that they can bear the high vacuum pressure without any kind of deformation. The oven is divided into hollow trays which increases the surface area for heat conduction. The oven door is locked air tight and is connected to vacuum pump to reduce the pressure. The materials to be dried are kept on the trays inside the vacuum dryer and pressure is reduced by means of vacuum pump. The dryer door is tightly shut and steam is passed through the space between trays and jacket so that the heat transfer occurs by conduction. Water vapors from the feed is sent into the condenser and after drying vacuum pump is disconnected and the dried product is collected from the trays. The vacuum dryer is composed of a refrigeration system, a vacuum system, a heating system, and an electrical instrument control system. The main components are drying box, condenser, refrigeration unit, vacuum pump, heating/cooling device, etc. Its working principle is to freeze the item to be dried to below the triple point temperature, and then directly sublime the solid water (ice) in the item into water vapor under vacuum conditions, remove it from the item, and dry the item. After pre-processing, the materials are sent to the quick-freezing bin for freezing, then sent to the drying bin for sublimation and dehydration, and then packed in the post-processing workshop. The vacuum system establishes low pressure conditions for the sublimation drying chamber, the heating system provides latent heat of sublimation to the material, and the refrigeration system provides the required cooling capacity to the cold trap and drying chamber.