18-03: Potential configurations of a cellulosic biofuel system - global warming and economic perspectives

Cellulosic biofuels require a pretreatment process before hydrolysis. Some pretreatments, including the AFEX™ process, can potentially be physically separated from the other biorefining operations in what we call “Local Biomass Processing Depots” (LBPDs) or simply “depots”. We have examined the economic and environmental impacts of separating pretreatment from other system operations for the case of cellulosic ethanol.  The system configuration plays an important role in determining the greenhouse gas (GHG) profile of the resulting ethanol fuel and the minimum ethanol selling price (MESP). This study investigates two system configurations for the cellulosic ethanol system: localization and integration. The depot system reduces GHG emissions more than does the centralized system without any significant change in MESP. The reduced process energy intensity in a biological conversion facility reduces GHG emissions and also the MESP.
We also consider integrating the cellulosic biorefinery with an existing coal-fired combined heat and power (CHP) plant. The biorefinery provides lignin and biogas to the integrated coal-fired CHP, which supplies electricity and thermal energy to the biorefinery. The integrated system further reduces the MESP because the biorefinery does not require a boiler system and also reduces coal use and the resulting GHG emissions. As the cellulosic biofuel industry emerges, it will be well to consider the functioning of the whole system and to identify ways in which it can leverage existing capital assets and configure itself to achieve both economic and environmental benefits.