Since a combine normally returns the chaff to the field to be broken down as a source of micronutrients in the next season, you first might want to ask an agricultural agent for a comparative analysis, i.e. the loss of the soil enhancement versus profit as biofuel.
The most efficient way to make use of agricultural waste is shipment to a nearby, combined heat and power plant* capable of accepting such feedstock. Since energy already is invested in separating grain from chaff, another possible approach might be to compress chaff into pellets for pellet stoves.
Note: Not only power generation companies, but also industries and other dedicated physical plants, e.g., hospitals, universities and other forms of congregate housing, are increasingly in the market for less expensive heat and power.
Last winter pellet manufacturers were caught by surprise when increasing demand outpaced supply. Thus, there now may be greater incentive to convert agricultural waste to pellets.
With overall increases in the cost of energy, the challenge is to find cost-effective means of pellet processing, packaging, and delivery. For instance, grass pellets may soon overtake wood pellets as the predominant fuel in the pellet stove market because wood-based pellets have been rising in cost.