IceBits ehf of Iceland explains the process of refrigerated drying.
When man discovered how to catch fish, he soon learned to preserve his harvests through drying (Figure 1).
The abundance of geothermal energy in Iceland made drying of offal from filleting cod commercially viable decades ago (Figure 2).
In cold climates, the absolute moisture content of air – the x-value – is very low and little heating is required to boost drying by reducing the relative moisture content, known as the φ-value (Figure 3).
But humidity is high in warm climates and air for drying must be dehumidified before it is reheated and sent through the goods, much like in air conditioning for comfort. Broiling takes place if temperatures exceed 27°C for extended periods. Due to high investment and operating cost, harvests of low value (pelagic) fish species and offal from processing do not sustain refrigerated drying. However, products of high commercial value sometimes do (bacalhau (salted cod), shark fins, squid, shell meat etc.).
The dryer in Figure 4 is stationary and holds 900 grids, each with a nominal area of 0.8m2, totalling 720m2. Up to 12,000kg of wet produce can be loaded. Drying time varies with the size, shape and consistency of the individual pieces, from less than 36 hours (thin goods) to more than 96 hours (thick material). Similar configurations, though smaller in capacity, can be installed in 40 foot high cube containers, including the refrigerating packages, making them movable with standard equipment for heavy lifting and transport.
One or more containerised facilities can be refrigerated from a central and remote all-in-one package, built up from a compressor, two plate heat exchangers, two pumps and ancillary parts (Figure 5). Refrigeration is transferred through pumping of glycol brine as the cold carrier and condenser water delivering the heat.
Existing cold storage rooms can be converted for refrigerated drying. A reheating unit is added in front of the air cooler and a false ceiling (transparent in the picture) guides the treated air to the front of the stack of goods (Figure 6). Energy for reheating can come from existing refrigerating plant or from an external source.
