3-22: Use of an integrated enzyme use cost model to determine an optimal process design configuration for a stand-alone corn stover to ethanol plant

In 2002, NREL published a design report based upon a comprehensive theoretical study into a biomass to ethanol process using dilute acid pretreatment and enzyme hydrolysis on corn stover (NREL/TP-510-32438).  This n-th plant study suggested such a NREL process could be economically viable given cost optimizations in several key areas of the process, including liquor detoxification, enzyme hydrolysis and fermentation, and since that time has become a baseline for much work in academia, industry and technology development. 

Research and Development organizations have focused efforts within portions of the biomass to ethanol process where they own technical expertise.  However, having met their own development targets, it can be difficult to assimilate improvements into the holistic cost picture in “today’s dollars” so as to evaluate true economic viability.  To date there are still no industrial scale plants in operation or under construction, and as a result, true success in the biomass to ethanol effort is difficult to claim.

An economic simulation model, based upon the 2009 updates made by NREL, will be presented which incorporates AspenPlus process flow correlations to maintain flow integration characteristics in an Excel based format.  A dynamic, non-linear “enzyme use-cost” is used to relate the enzyme hydrolysis cellulose conversion target to the required enzyme dose.  Additional tools are applied for rapid cost simulation capabilities, allowing for a highly flexible and powerful scenario builder and what-if analysis screening method.  A case study with Novozymes’ 2010 biomass enzyme product is presented to illustrate how varying hydrolysis total solids, hydrolysis time and enzyme dose can be used to suggest a biomass to ethanol process that minimizes the ethanol selling price.  Cost sensitivity results from the model and potential development opportunities for further process cost reductions will also be presented.