Tunnel dryer are the main type of equipment that is applied to dry fruit with a large fruit juice content. Most commonly, the technology is suitable for prunes, dried apricots, raisins, dried peaches, cherries, and other stonefruit manufacturing.
By design and degree of automation, this drying equipment is slightly inferior to belt dryers, but it creates a specific microclimate favorable for juicy fruit drying. Another characteristic of a tunnel drying is relatively high cost of manual labor for maintenance. But this is offset by relatively low cost of the equipment and the lower expenses on salary in rural areas.
In modern constructions of tunnel dryers, indirect air heating is used. In an indirect way air heating occurs through calorifiers of different systems. In this case drying agent is heated air. This method of heating is the most progressive one, as it ensures the sanitary safety of dried fruit produced. Nowadays customers have strict demands to the quality of product so the equipment for fruit drying must meet both Russian and international quality standards.
After the pre-tratment fruit and berries are evenly distributed on special trays, which are placed in trolleys. After that the trolleys are placed in working channel of dryers, where the dehydration process takes place. There are types of dryers, where trolleys are periodically moving through the working channel of the dryer, and there are such, where they are fixed in one place during the whole fruit drying process.
In practice, there are a number of technical solutions for feeding and circulation of hot air in working channel of tunnel dryer.
As a rule there are four types of it:
- straight-flow – the air is moving side-by-side to raw materials traffic in trolleys. The highest temperature of hot air is achieved in the beginning of the work channel;
- reverse-flow – hot air is directed toward the trolleys with fruit. The highest temperature is achieved when the trollyes are at the end of a tunnel dryer;
- combined – both straight-flow and reverse drying installations; the first zone has a straight flow and the second has reverse
- mixed flow type , the hot air is directed perpendicular to the direction of the fruit trolleys traffic (multizone). The heater circulates independently in each zone, maintaining the specified constant parameters. Temperature in the first zone (at the product entrance) is maximum, it is gradually reduced up to the product output from the dryer.
A variety of energy transfer options are available in modern tunnel dryers. They can be dryers using gas, steam, electricity, any liquid or solid fuel.
Experts of Dry Food company always approach the implementation of projects in an integrated manner, and we are able to consider and select for you the most appropriate technology for fruit, berries, fruits and other products drying