The belt dryer is a continuous drying equipment for mass production, which is used for drying flakes, strips, granules and some paste materials with good gas permeability. It is especially suitable for dehydrated vegetables and traditional Chinese medicine decoction pieces with high moisture content and heat sensitive materials. It has the advantages of high drying rate, high evaporation strength and good product quality. Belt dryers are widely used in industry, mainly for drying small pieces of materials and fibrous materials such as cakes, soap chips, wool, cotton, and fibers. In short, the material dried by the belt dryer must have a certain shape and still maintain a certain shape after drying.
Belt dryers are divided into two main forms according to their construction and gas action: dryers with non-porous belts and dryers with mesh belts. The belt of the first type of dryer is made of fabric (canvas, rubber band, coated cloth, etc.). The heat carrier (usually hot air) sweeps over the layer of material being dried evenly over the belt. The flow direction is opposite to the direction of movement of the belt, and the same is cocurrent.
The belt of the second dryer is made of a metal mesh or a non-metal mesh, and the heat carrier flows through the material layer from bottom to top or from top to bottom in the direction of the vertical belt surface. This kind of dryer can only be used to dry the belt on the belt to form a loose porous layer, and the medium through which the heat medium can pass. This is called a through-flow belt dryer, which is the most widely used in industrial production.
Regardless of the configuration, the belt dryer is not suitable for drying unpregnized paste materials.
Second, the basic working principle of the belt dryer
Belt dryers currently have single-layer and multi-layer, single-stage and multi-stage, but the working principle is basically the same. The material in the hopper is evenly spread on the mesh belt by the feeder, moving forward with the conveyor belt. The hot air in the drying unit passes vertically through the material layer to dewater the material. The thickness of the material layer on the mesh belt is determined by factors such as the nature of the material, the manner of the cloth, and the drying temperature, and is generally adjusted within the range of 20 to 100 mm. The mesh belt is 12~16 mesh, made of stainless steel and non-metal materials, and can also be used as a three-dimensional mesh belt. Drag by the actuator to move inside the dryer. The drying section consists of several units (about 2m in length). Each unit of hot air is circulated independently. Some of the exhaust gas is discharged by a special exhausting fan. The amount of exhaust gas discharged from each unit is controlled by a regulating valve. In the circulation unit of the jacket, the hot air from the circulation fan enters the lower chamber of the unit by the side air passage, and the airflow is heated by the heat exchanger and distributed by the distributor, and then the jet is blown toward the mesh belt, and then passes through the material and enters the upper air. Cavity. The drying process is a process in which the hot gas flows through the material layer to complete the heat transfer process. The upper chamber is connected to the fan by a duct, and most of the gas circulates. A part of the gas with a lower temperature and a higher water content is discharged as a tail gas through the exhaust pipe, the regulating valve, and the exhaust fan. In the lower circulation unit, the wind from the circulating fan first enters the upper chamber, is heated upward through the heat exchanger, passes through the material layer and enters the lower chamber, and the lower chamber is connected to the fan inlet by the side air passage and the return air duct, and most of the gas is circulated. Part of it is discharged. The upper and lower circulation units can be flexibly equipped according to user needs, and the number of units can also be selected according to needs.
For use in dehydrated vegetables, several equipments are generally used in series to form the initial dry section, the middle section and the final section, and in the initial dry section, due to the high moisture content of the material and poor gas permeability, a small paving thickness is used. Fast running speed and high drying temperature. When the material temperature is not allowed to exceed 60 ° C, the drying gas temperature in the initial dry section can be as high as 120 ° C or more. The residence time of the material in the final dry section is 3~6 times of that of the initial dry section, and the thickness of the paving is 2~4 times of the initial dry section. For the requirement that the material temperature does not exceed 60 ° C, a drying gas of about 80 ° C can be used. The multi-stage combination can better exert the performance of the belt dryer and the drying is more uniform.
Briefly describe the form and principle of belt dryer
First, the belt dryer overview