The fluidized bed dryer places fluid materials such as powders and pastes (even suspensions and solutions) on air flow distribution plates such as porous plates, and the drying medium at a considerable speed is fed from the lower part. When the medium flow rate is low, gas flows between the material particles, and the entire material layer does not move; gradually increasing the air flow velocity, the material layer begins to expand, and the gap between the particles increases; further increasing the air flow velocity, a considerable part of the material becomes suspended , forming a gas-solid mixed bed, that is, a fluidized bed. Because the suspended material in the fluidized bed is very similar to a boiling liquid, it is also called an ebullating bed, and it exhibits fluid properties in many aspects, such as an obvious upper interface. , and remain level; if the airflow velocity is further increased, almost all the particles will be taken away by the airflow, and it becomes gas transportation. Therefore, the air flow speed is the most fundamental control factor of the fluidized bed dryer. The appropriate air flow speed should be between the fluidization of the material layer and the taking of the material out.
The heat exchange in the fluidized bed can be through an outer jacket or an in-bed heat exchanger. When using an in-bed heat exchanger, in addition to the general heat exchanger requirements, the impact on the material flow in the bed must also be considered. That is, the form and installation method of the heat exchanger should be as conducive to the normal flow of fluid as possible. . Practice has proved that when using a tube heat exchanger, the tubes are placed 2/5 away from the center of the equipment. Mud-like materials with high viscosity and high moisture content are difficult to disperse and fluidize in the dry medium flow. Put some inert carriers (such as quartz sand, alumina, oxidized pellets, granular salt, etc.) at the bottom of the dryer. When they are fluidized under the action of airflow at a certain flow rate, the wet materials will adhere to their surfaces. Then it becomes a dry crust. Due to the collision and friction of the inert carriers with each other, the dry shell will fall off and be taken away by the medium flow; and the carrier itself will come into contact with new wet materials to form a dry shell. With such a cycle, fine wet and sticky materials can be fully dried in the fluidized bed dryer.
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