A grain dryer having upright grain passages defined by perforate walls confining grain columns therein, the grain passages having offset portions and common inlets and outlets and vertically spaced plenum chambers, and a duct with a fan and burner drawing air from the lower plenum and applying the air...http://www.google.fr/patents/US4242806?utm_source=gb-gplus-shareBrevet US4242806 - Stacked air dryer with air recirculation
