Drying and Cooling of Bakery Grist at Its Finest with Carousel Dryer-Cooler (Published in dei-Germany).

Combined drying and cooling

The Idah Carousel Dryer Cooler consists of multiple decks with a tilting floor in each deck to offload the material onto the lower deck. The discharge helps to mix the material and expose it to the drying and cooling air, allowing for effective heat transfer. On the decks, the material rotates in a constant flow of air and thus experiences an even drying and cooling process. The drying and cooling air are guided past the incoming product in a cross-countercurrent flow to achieve maximum heat transfer. A rotary valve in the inlet prevents the uncontrolled intake of ambient air. At the same time, the material is continuously fed into the dryer. With the help of a special mechanical device, dough-like material can be broken up and loosened. This ensures an optimal flow of drying air and effective heat transfer. For cooling, the cooler exhaust air is routed through the dryer section. This offers the simplest possible way to use the waste heat from the cooler without additional equipment.

Process data for baking grist

The graphs show the changes in temperature and humidity of the baking grist in a TK-300 series carousel dryer. The dryer has a diameter of approx. 3 m, the throughput of baking grist is 4.5 t/h, the residence time for drying is 23 minutes, and for subsequent cooling 15 minutes. The inlet temperature of the baking grist is around 87 °C. The product leaves the dryer at a temperature of approx. 13 °C. The direct effect of the special mechanical device installed between Deck 2 and Deck 3 can be seen in the graph on the left. Before installing the device, the temperature dropped to 35 °C. The additional device helped the product flow freely and the product temperature rises from about 43 to about 58 °C just before the grist falls into the cooling zone. The graphic on the right shows the influence of the higher drying temperature under otherwise identical conditions. A similar temperature to Deck 2 can be achieved if the drying temperature is increased to 87°C. This condition results in a high temperature before the grist enters the cooler, which can lower the nutritional value. In addition, the final moisture content is around 1% lower than with a drying temperature of 75 °C. Comparing the combined dryer/cooler with the pure cooler shows that only an air duct with additional heat exchangers between two floors has to be inserted and the main shaft has to be slightly lengthened.