743 5.7 Continuous dryers Continuous types of direct dryers are spray, flash or rotary designs, where the product enters in a form suitable to be handled properly by that dryer. Spray dryers can accommodate a feed stream in a slurry or solution form, whereas a flash dryer is intended to take a feed cake which can be broken up into individual pieces without coalescing. The feed characteristics uired for flash dryers are that the product must break up if introduced as a cake. If introduced as a paste, it is necessary for the feed to be backmixed with previously dried material so as to firm up the cakess consistency Rotary dryers are more flexible in that they can handle a wide variety of feed consistencies 5.8 Spray Dryers Spray dryers are large cylindrical chambers with a cone or flat bottom They also appear in the form of a large cube or box referred to as a box dryer, Small nozzles are located in the chamber walls through which the feed material, in the form of a slurry or solution, is atomized to a fine droplet. the droplet comes into contact with a hot gas stream and dries to a powder in the time that it takes for it to fall to the bottom of the chamber. Typical residence times in a chamber are 12 to 30 seconds. due to the evaporative cooling effect, the inlet temperature on this type of dryer is normally quite high relative to the dry products temperature limitations. Typical inlet tempera tures for spray dryers range from 400oF to 1000F depending on the application. The higher temperatures are normally for inorganic salt drying and the lower temperatures are normally for organic temperature sensitive products. The resultant individual product is always spherical in shape due to the initial droplet and it will tend to be extremely porous and fracture easil Further processing of spray dried product has been done to achieve instantizing by creating agglomerates of these spheres which retain a relatively high surface area compared to the individual particles. The action of adding this powder to water results in a release of energy from the agglomerated bonding forces and the capillary effect of the water traveling into the porous spheres. The net effect is one of quick dissolution of the agglomerated powder. This is highly desirable when searching for a means of instantizing a product In order to consider spray drying, certain criteria about the material must be met. The feed slurry viscosity must be low enough whereby it can be pumped through either a rotary atomizer, a two fluid nozzle or a highDrying 743 5.7 Continuous Dryers Continuous types of direct dryers are spray, flash or rotary designs, where the product enters in a form suitable to be handled properly by that dryer. Spray dryers can accommodate a feed stream in a slurry or solution form, whereas a flash dryer is intended to take a feed cake which can be broken up into individual pieces without coalescing. The feed characteristics required for flash dryers are that the product must break up if introduced as a cake. If introduced as a paste, it is necessary for the feed to be backmixed with previously dried material so as to firm up the cakes's consistency. Rotary dryers are more flexible in that they can handle a wide variety of feed consistencies. 5.8 Spray Dryers Spray dryers are large cylindrical chambers with a cone or flat bottom. They also appear in the form of a large cube or box referred to as a box dryer. Small nozzles are located in the chamber walls through which the feed material, in the form of a slurry or solution, is atomized to a fine droplet. The droplet comes into contact with a hot gas stream and dries to a powder in the time that it takes for it to fall to the bottom ofthe chamber. Typical residence times in a chamber are 12 to 30 seconds. Due to the evaporative cooling effect, the inlet temperature on this type of dryer is normally quite high relative to the dry products' temperature limitations. Typical inlet tempera￾tures for spray dryers range from 400'F to lOOOOF depending on the application. The higher temperatures are normally for inorganic salt drying and the lower temperatures are normally for organic temperature sensitive products. The resultant individual product is always spherical in shape due to the initial droplet and it will tend to be extremely porous and fracture easily. Further processing of spray dried product has been done to achieve instuntizing by creating agglomerates of these spheres which retain a relatively high surface area compared to the individual particles. The action of adding this powder to water results in a release of energy from the agglomerated bonding forces and the capillary effect of the water traveling into the porous spheres. The net effect is one of quick dissolution of the agglomerated powder. This is highly desirable when searching for a means of instuntizing a product. In order to consider spray drying, certain criteria about the material must be met. The feed slurry viscosity must be low enough whereby it can be pumped through either a rotary atomizer, a two fluid nozzle or a high