Impact of Mechanical Refining Conditions on the Energy Consumption, Enzymatic Digestibility, and Economics of Sugar...

Reducing the energy intensity of the mechanical refining-based pretreatment process for producing lignocellulosic-derived sugars without significantly affecting enzymatic hydrolysis sugar yields is challenging. This work investigated the impact of different refining conditions on energy consumption, enzymatic sugar yields, minimum sugar selling price, and environmental impacts for the conversion of corn stover to sugars. A positive proportionate correlation between specific energy consumption and enzymatic sugar yields was observed when changing the refiner plate gap was changed, which agrees with other reported works. However, the correlation between specific energy consumption and enzymatic sugar yields is not straightforward when the rotational speed and refiner plate design change. We observed that, for a corn stover material with low consistency disc refining, specific energy consumption decreased by >50% by decreasing the rotation speed without affecting enzymatic sugar yields. By changing refiner plate designs, a 45% reduction in specific energy consumption could be achieved without affecting the glucose yield, albeit still with a detrimental impact on the xylose yield. Our high-fidelity disc refining model was able to predict the energy consumption for different refiner plate geometry designs and operating conditions. Techno-economic and life-cycle analyses indicate that the plate design and operating conditions have a direct impact on overall process power consumption and sugar yields, with sugar yields strongly dictating the minimum sugar selling price, the life cycle greenhouse gas emissions, and fossil energy consumption. To minimize the environmental impact and maximize process economics, optimization of the mechanical refining process should target maintaining high sugar yields, while lowering refining energy consumption.