SPRAY DRYING METHOD AND APPARATUS FOR PRODUCING GRANULAR PARTICLES FROM STOCK LIQUIDS OF SOLIDS

摘要

A spray drying method comprising forming a layer of solid particles at the bottom of a drying chamber defined by a vertical cylinder, blowing gas into said layer from the underside to agitate the whole of said layer and thereby to form a fluidized bed of solid particles with part of said particles being blown up from the upper surface of said fluidized bed and suspended within said drying chamber, blowing gas into said drying chamber in a direction to form a swirling downward gas flow along the side wall and a swirling upward flow along the center of said drying chamber, whereby said suspending particles are caused to make a circulatory motion while being entrained in said swirling gas flows in such a manner that the fine particles spirally move upward in the center of the drying chamber and at least the major part thereof approach the side wall of the drying chamber under the effect of centrifugal force before they reach the top of said drying chamber and finally spirally move downward along the side wall of said chamber, said particles being partially returned to said fluidized bed and partially being carried upward again in the center of the drying chamber by being entrained in said swirling upward gas flow, spraying stock solution into said drying chamber, the droplets of said sprayed stock solution colliding against and adhered to said circulating particles to form larger sized particles, said larger sized particles being dried by the surrounding gas and partially circulated within said drying chamber and partially falling into said fluidized bed, and discharging said larger sized particles from said fluidized bed while maintaining the depth of said fluidized bed substantially constant.