(72d) Scale up for a High Solids Loading Aqueous Slurry Formation in a Biorefinery

Corn stover pellets are a promising resource for biofuels production from lignocellulosic biomass, but handling it in a biorefinery requires pre-processing to achieve favorable rheology for conversion into a pumpable slurry that permits transport within a biorefinery in a continuous manner. This is attractive as long as high viscosity is avoided in slurries with high solids concentrations. To address this, a scale-up from benchtop experiments and techno-economic assessment were conducted.

In this study, a slurry was produced by adding corn stover pellets with a moisture content of 16% to a low level of enzyme in deionized water in an agitated bioreactor. Rheology correlated with the slurry concentration was used to calculate the energy usage as a function of the solids content. This was combined with a simulation; at a steady and unsteady state, of the mass and energy balances to determine start-up time and power consumption. The model also provides inputs for techno-economic assessment using laboratory data to estimate bioreactor configuration and volume. In this model, a small tank is used to simulate a mixing junction, with a second much larger tank for retaining the mixture for two to more than six hours until the slurry reaches 300 g/L concentration with a yield stress of less than 400 Pa during the start-up phase. After 6 hours steady state operation occurs.

Our study confirms that it is economically viable to convert corn stover pellets into pumpable slurry without pretreatment to be further processed in the biorefinery, ensuring a steady supply of feed for the biorefinery in a profitable way. The modeling takes a comprehensive approach that includes benchtop scale-up and assessments, establishing the practicality and cost-effectiveness of slurry production. Experimental findings and correlation analysis provide accurate predictions of power consumption, while steady-state energy balance results closely align with predictions. Techno-economic assessments further support the competitiveness of slurry conversion. In essence, this research offers a sustainable solution to challenges in energy generation. The production cost of the pumpable slurry was estimated at 3.4¢/kg slurry containing 300 g/L corn stover resulting in yield stress < 400 Pa, where the slurry was formed without hydrothermal pretreatment. This compares favorably to the NREL process with a cost of 5.5¢/kg of slurry formed from acid-pretreated corn stover.