Problems to be determined before selection of drying equipment

Because there are many kinds of wet materials in the drying process and the drying characteristics are different, different types of drying equipment and methods are needed This brings about the problem of drying method and equipment selection If it is not properly selected, it will inevitably lead to excessive investment in equipment, or increase in operating costs, or product quality does not meet the requirements, or even cannot operate in extreme cases Therefore, we must pay enough attention to the problem of model selection 1 Material performance and drying characteristics (1) the shape of materials is large to the shape of wood, ceramic products, as well as sheet, fibrous, granular, fine powder, paste and liquid materials, which are all industrial materials that need to be dried Therefore, the selection of dryer should first be based on the shape of materials (2) The physical properties of materials include density, bulk density, particle size distribution, heat capacity and adhesion property The degree of adhesion has a great influence on the operation of feeding and discharging and some forms of dryers When the adhesion is serious, the drying process cannot be carried out (3) The characteristics of materials in drying process include heat sensitivity Some materials will change color and decompose after being heated In addition, the shrinkage of the material in the drying process will make the formed products crack or deform, so that the product quality will be reduced or even discarded (4) The state of the combination of material and water determines the degree of difficulty in drying, the level of energy consumption and the length of stay time required in the dryer, which has a great relationship with the selection For example, for materials that are difficult to dry, a longer residence time is mainly given, rather than the external conditions of intensified drying 2 Requirements for dried products (1) requirements for dried product form, which is particularly important in some cases For example, in food drying, the requirement of product geometry is the key to make the moisture content of the product meet the drying requirements Then, like washing powder and dyestuff, etc., in order to facilitate instant solution and avoid dust flying, spray granulator must be applied when selecting the dryer (2) Requirements for drying uniformity (3) requirements for product hygiene (4) some special requirements for products, such as the drying of coffee, mushroom, vegetables and other materials, require that the product can maintain its unique flavor, so it is not allowed to use the rapid drying with high wind temperature 3 Fluctuation of moisture content of wet materials and dehydration before drying The moisture content of the materials entering the dryer shall avoid large fluctuation as much as possible If the moisture content becomes larger, the output of the dryer will decrease or the dried products will not meet the moisture content requirements If the moisture content becomes smaller, the outlet exhaust temperature will rise and the products will be excessively dried, which will not only reduce the thermal efficiency of the dryer, but also sometimes increase the product temperature, thus affecting the product quality For high humidity materials (moisture content is more than 60%), mechanical dehydration (pressure filtration, centrifugal dehydration, etc.) should be used as much as possible before drying Although the cost of mechanical dehydration equipment is high, its operating cost is low, which can not be compared with hot air drying.