Combine harvester with multi-stage grain preparation and related methods for operating a combine harvester

A combine harvester comprising:

• a cleaning arrangement comprising one or more sieves and a main blower;
• and
• a preparation arrangement configured to receive a mixture of grain and residue material from a threshing system and to transport the mixture towards the cleaning arrangement, wherein the preparation arrangement comprises multiple preparation stages, each of said stages being configured to transport the mixture over a given distance between a front edge and a rear edge of the respective stage, with an air gap being present between each pair of consecutive stages, and wherein the preparation system further comprises a separate blower that is separate from the main blower, the separate blower configured to direct air towards at least one of the air gaps, to thereby blow at least a portion of the residue material from the mixture towards the rear of the combine harvester, wherein the preparation arrangement comprises a plate provided with fins mounted transversally with respect to the longitudinal direction of the harvester, each fin representing one of said preparation stages, said plate further comprising one or more openings between at least one pair of consecutive fins, said one or more openings being suitable for allowing the passage of an air stream produced by the separate blower, and directed towards the gap between the pair of consecutive fins,
• wherein the openings are sized to prevent a substantial portion of the grain and residue material from passing through the openings in the direction opposite the air stream produced by the separate blower.