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Funding from the federal government was provided by the Office of the Biomass Program within the Energy Efficiency and Renewable Energy assistant secretariat as part of the Thermochemical Conversion Platform. The funding for the project was initially provided FY2008 with subsequent funding approved for FY2009 but later rescinded for lack of progress. This report describes the results of the work performed by PNNL using feedstock materials provided by the National Renewable Energy Laboratory, KL Energy and Lignol lignocellulosic ethanol pilot plants. Test results with algae feedstocks provided by Genifuel, which provided in-kind cost share to the project, are also included. The work conducted during this project involved developing and demonstrating on the bench-scale process technology at PNNL for catalytic hydrothermal gasification of lignin-rich biorefinery residues and algae. A technoeconomic assessment evaluated the use of the technology for energy recovery in a lignocellulosic ethanol plant. Feedstock Effects Initial tests in catalytic hydrothermal gasification were performed in a continuous-flow reactor at PNNL. The system required feedstock slurry preparation for pumpable materials in high-pressure feeding systems. Representative feedstocks were provided to PNNL for gasification tests by the participants. The bench-scale tests provided product gas and byproduct materials in sufficient quantity for subsequent analysis and mass and elemental balance. The bench-scale system was used to optimize processing conditions such as temperature, slurry concentration, and residence time. A ruthenium on carbon catalyst was used in all tests. The lignin-rich feedstocks showed varying levels of processing difficulties related primarily to the physical properties of the lignin (melting and viscosity of liquid intermediates) and also to the apparent slower rate of conversion. Plugging in the feed lines and in the transfer lines was a common problem, which stopped several of the tests. The mineral separation step functioned well in most cases with only a small loss of carbon. High conversion of the lignin materials to gas resulted in low contamination levels in the byproduct water. The gas product showed the expected methane and carbon dioxide content (with higher levels of methane) and only low amounts of hydrogen coproducts with minimal amounts of carbon monoxide or hydrocarbon gas products. The algae feedstocks were much more reliably processed. High conversions were obtained even with high slurry concentrations. Consistent catalyst operation in these short-term tests suggested good stability and minimal poisoning effects. High methane content in the product gas was noted with significant carbon dioxide captured in the aqueous byproduct in combination with alkali constituents and the ammonia byproduct derived from proteins in the algae. High conversion of algae to gas products was found with low levels of byproduct water contamination and minimal loss of carbon in the mineral separation step. iv Techno-Economic Assessment...

Biomass is a renewable energy resource that can be converted into liquid fuel suitable for transportation applications and thus help meet the Energy Independence and Security Act renewable energy goals (U.S. Congress 2007). However, biomass is not always available in sufficient quantity at a price compatible with fuels production. Municipal solid waste (MSW) on the other hand is readily available in large quantities in some communities and is considered a partially renewable feedstock. Furthermore, MSW may be available for little or no cost. This report provides a techno-economic analysis of the production of mixed alcohols from MSW and compares it to the costs for a wood based plant. In this analysis, MSW is processed into refuse derived fuel (RDF) and then gasified in a plant co-located with a landfill. The resulting syngas is then catalytically converted to mixed alcohols. At a scale of 2000 metric tons per day of RDF, and using current technology, the minimum ethanol selling price at a 10% rate of return is approximately $1.85/gallon ethanol (early 2008 $). However, favorable economics are dependent upon the toxicity characteristics of the waste streams and that a market exists for the by-product scrap metal recovered from the RDF process.

This study also identified four commercially available and two demonstration MSW gasifiers, two of which involved co-feeding with coal. Three of these gasifiers were used to produce electricity and process heat and consequently were close coupled to combustors and would need to be modified to produce syngas. The other three gasifiers were capable of producing syngas or fuel gas, and would not require modification. There were also a large number of other MSW gasifiers under development that may ultimately be suitable for syngas applications. Overall, this study concludes that MSW should be considered as a potentially viable gasifier feedstock for liquid fuels synthesis. A review of feedstock availability, composition, and handling characteristics along with commercially available MSW specific gasifiers did not identify any obvious insurmountable technical or economic barriers to commercialization. However, further research into the economic issues surrounding tipping fees and process scale is needed to verify economic viability and the appropriate plant scale to achieve it.

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