Review of modern drying installations for vegetables and fruits and ways to increase their energy efficiency

Thermal drying, being an integral part of many technologies, is one of the most energy-intensive technological processes. The drying of grain, wood, paper, fabrics, vegetables and fruits, as well as other materials in Russia annually consumes several million tons of reference fuel. The widespread use of drying processes and low (30 - 35%) energy efficiency factors in them determine the relevance of energy saving in drying plants. The production of dried fruits and vegetables is one of the most economical ways to process raw materials. Dried fruits and vegetables have a high energy value, as they contain a significant amount of chemical elements and retain their properties for a long time. They take up less storage space, have a long shelf life and can be used as raw materials for the production of food concentrates in various food industries. In household and low-capacity dryers, as a rule, the convective method of heating the product is used. During the drying process, moisture is removed from the product until a moisture content of 10-12% for vegetables and 18-25% for fruits is reached. Known household electric food dryers in operation discharge with humid air into the surrounding space and the heat obtained from the electric heater, which is a valuable object of reducing costs in the drying process. Thus, the disadvantage of the known dryers is the large loss of thermal energy carried away with moist air into the surrounding space. Also, their disadvantages include the uneven heating of the layers of the product due to stagnation of air and a decrease in its temperature as it moves from bottom to top, as a result of which the products on the lower pallets dry faster than on the upper ones.