Industry: Fruit and Vegetable Preserving and Specialty Food Mfg (NAICS 3114)
Process Brief: Moisture in fruits, vegetables and nuts is removed using hot air.
Energy source: Steam/Natural gas
Energy Intensity: 1,700-28,000 Btu/lb of water in the product
Conveyor or band driers are used to for a range of products, including cereals, fruits, baked goods, vegetables and nuts. In its simplest form, the product is placed on a conveyor that passes through a series of hot air zones. The conveyor is designed to allow air to be blown upward or downward through the conveyor and product. Multiple passes through different conveyor/band driers are common and the product may be piled into deeper beds as the moisture content drops.
Generally, conveyor/band dryers only bring the moisture content to 10%-15% and the drying is completed using bin dryers. Conveyor/band dryers can be very efficient and are one of the most common drier technologies in the food industry. The large range in energy intensities reflects the variety of applications in which conveyor/band driers are used. A typical installation will be 10 feet wide and 60 feet long with three separate zones for drying.
Trough driers are a variation of the conveyor/band drier and are used to produce dehydrated pea and diced vegetables. The small vegetable pieces are piled onto a mesh conveyor belt that is allowed to hang freely between the rollers. The weight of the product causes the belt to take the shape of a trough. Hot air and the progression of the conveyor over the rollers results a constant remixing of the product, which promotes rapid and even drying. Throughput rates for diced vegetables can be 55 minutes, compared to 5 hours in an older tunnel drier.
Tunnel driers are an older version of the basic conveyor/band drier. Tunnel driers are large systems that dry food using hot air inside an insulated housing. The food is loaded onto trays that are set on the moveable trucks that move through the tunnel. Airflow and the number of passes in a tunnel drier can be modified to accommodate a range of fruit and vegetable products. The problem with tunnel driers is the labor needed to load and unload the trays and conveyor/band driers are replacing the systems in many applications. A typical tunnel drier may be 60 feet long and 12 feet wide with electric fans blowing air across steam pipes.
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