Efficiency improvements by geothermal heat integration in a lignocellulosic biorefinery.

In an integrated geothermal biorefinery, low-grade geothermal heat is used as process heat to allow the co-products of biofuel production to become available for higher-value uses. In this paper we consider integrating geothermal heat into a biochemical lignocellulosic biorefinery so that the lignin-enriched residue can be used either as a feedstock for chemicals and materials or for on-site electricity generation. Depending on the relative economic value of these two uses, we can maximize revenue of a biorefinery by judicious distribution of the lignin-enriched residue between these two options. We quantify the performance improvement from integrating geothermal energy for an optimized system. We then use a thermodynamic argument to show that integrating geothermal heat into a biorefinery represents an improvement in overall resource utilization efficiency in all cases considered. Finally, possible future technologies for electricity generation are considered which could improve this efficiency further.