The Working Principle of Spray Granulation Dryer

The basic principle of spray drying involves the material being pumped through a filter to the atomizer at the top of the spray dryer. The atomizer disperses the liquid material into droplets. Due to their smaller radius, the droplets have a larger surface area and surface free energy, and are highly dispersed. The vapor pressure of moisture on the droplet surface is higher than that of flat liquid surface moisture under the same conditions, leading to rapid evaporation of water and quick drying of the product. Dai Ming and others have derived a one-dimensional, two-way static mathematical model for the spray drying process based on the principles of mass conservation, energy conservation, and Newton's second law. This theoretical study of the heat drying mechanism of spray drying is significant for enhancing the technical level of spray drying.

The Spray Granulation Dryer is a novel one-step granulation equipment that combines spray drying technology with fluidized bed granulation technology. It utilizes a suction fan to draw in negative pressure, drying the droplets and agglomerating them into particles. It can also adjust the particle size as required, making it more powerful in functionality compared to general equipment.

The spray granulation dryer places a certain amount of powdered material into the fluidized bed as a seed during operation. The liquid material is pumped to the nozzle atomizer, where it is first instantaneously removed of some moisture by the high-temperature air used for spraying, with the remaining moisture then dried at the bottom of the fluidized bed at low temperatures while also forming into granules.

Firstly, the liquid (solution, suspension, extract, paste) is uniformly sprayed onto the fluidized inert particles using a nebulizer. The inert particles are located above the distribution plate and are fluidized by the impact of hot air passing through the plate. While fluidizing the inert particles, the hot air also transfers heat to the particles. When the liquid is sprayed onto the particle surface, the heat absorbed by the particles (from the inside out) and the heat from the hot air (from the outside in) cause the moisture to evaporate rapidly, forming a thin shell on the particle surface. The material transitions from elastic to brittle, and due to the vigorous movement of the particles, collisions and friction occur, causing the dried material to detach from the particle surface and be ground into fine powder, which is dispersed and carried away with the exhaust gas, collected by the gas-solid separation unit. The working process can generally be divided into three stages: the liquid is coated onto the surface of the inert particles, the moisture is vaporized by the hot air, and the dried material detaches.