Re-circulating batch dryer
Re-circulating batch dryers have been used for a long time in developed countries. In many Asian countries re-circulating batch dryers are increasingly being used by the private sector for producing better quality grain and for handling large amounts in the peak season safely.
However, the loading, unloading and circulation of grain create dust which needs to be collected in a collection system. In addition, it is recommended to pre-clean the grain prior to loading and drying. As with the flatbed dryer, re-circulating dryers come in a variety of capacities, from 2 tons (for seed production stations) up to 20 tons (for cooperative drying stations).
Depending on the flow of the drying air relative to the flow of the grain re-circulating batch dryers can be classified as cross flow ormixed flow re-circulating batch dryers.
In cross flow dryers the grains are not mixed while they are passing the drying section and being exposed to the hot drying air. This means that a moisture gradient develops in the drying section of the dryer. In the recirculation and tempering process this gradient is reduced because the wet and dry grains are mixed while they are being conveyed and subsequently moisture transfer happens from the wetter to the dryer grains. While this process is not optimal it still produces much better quality than a fixed bed dryer because the moisture gradients are much smaller.