Optimization of preprocessing and densification of sorghum stover at full-scale operation

Transportation can be a prohibitive cost in bringing biomass to a preprocessing location or biofuel refinery. One alternative to transporting biomass in baled or loose format to a preprocessing location is to utilize a mobile preprocessing system that can be relocated to the places where biomass is stored and used to preprocess and density the biomass, which is then shipped to the refinery as needed. Idaho National Laboratory (INL) has a full-scale process demonstration unit (PDU) that includes a Stage 1 grinder, hammer mill, drier, pellet mill, and cooler with the associated conveyance system components. Testing at bench and pilot scales has been conducted to determine effects of moisture on preprocessing, crop varieties on preprocessing efficiency, and product quality. INL's PDU provides an opportunity to test the conclusions made at the bench and pilot scales on full industrial-scale systems. Each PDU component is operated from a central operating station where data is collected to determine power consumption rates for each step in the process. The power for each electrical motor in the system is monitored from the control station for problems and to determine optimal conditions for system performance. The data can then be evaluated to determine how changes in biomass input parameters (for example, moisture and crop type), mechanical changes (i.e., screen size, biomass drying, pellet size, grinding speed, etc.), or other variations affect the power consumption of the system. Sorgum, in four-foot round bales, was tested in the system using a series of six different screen sizes, including 3/16 in., 1 in., 2 in., 3 in., 4 in., and 6 in. The effect on power consumption, product quality, and production rate were measured to determine optimal conditions.