Cascade air supply system and method for drying section and preheating section of belt type roasting machine

The invention relates to a stepped air supply system and method for a drying section and a preheating section of a belt type roasting machine, the stepped air supply system comprises the belt type roasting machine and five groups of belt type roasting machine air boxes, and further comprises a regenerative fan I, a regenerative fan II and an air mixing device, the five groups of belt type roasting machine air boxes are divided, and a drying section air supply pipeline and the air mixing device are arranged at the upper part of an upper cover of the drying section; the third group of air bellows is connected with a regenerative fan I and a hot air return header pipe I. The hot air return header pipe I is connected with a corresponding air mixing device through a plurality of drying section air supply branch pipes A. The fourth group of air bellows is connected with a regenerative fan II, a hot air return header pipe II, a drying section air supply branch pipe B and a preheating section air supply branch pipe.