Integrated evaluation of cost, emissions, and resource potential for algal biofuels at the national scale.

Costs, emissions, and resource availability were modeled for the production of 5 billion gallons yr(-1) (5 BGY) of renewable diesel in the United States from Chlorella biomass by hydrothermal liquefaction (HTL). The HTL model utilized data from a continuous 1-L reactor including catalytic hydrothermal gasification of the aqueous phase, and catalytic hydrotreatment of the HTL oil. A biophysical algae growth model coupled with weather and pond simulations predicted biomass productivity from experimental growth parameters, allowing site-by-site and temporal prediction of biomass production. The 5 BGY scale required geographically and climatically distributed sites. Even though screening down to 5 BGY significantly reduced spatial and temporal variability, site-to-site, season-to-season, and interannual variations in productivity affected economic and environmental performance. Performance metrics based on annual average or peak productivity were inadequate; temporally and spatially explicit computations allowed more rigorous analysis of these dynamic systems. For example, 3-season operation with a winter shutdown was favored to avoid high greenhouse gas emissions, but economic performance was harmed by underutilized equipment during slow-growth periods. Thus, analysis of algal biofuel pathways must combine spatiotemporal resource assessment, economic analysis, and environmental analysis integrated over many sites when assessing national scale performance.

Hydrothermal liquefaction of biomass: developments from batch to continuous process.

This review describes the recent results in hydrothermal liquefaction (HTL) of biomass in continuous-flow processing systems. Although much has been published about batch reactor tests of biomass HTL, there is only limited information yet available on continuous-flow tests, which can provide a more reasonable basis for process design and scale-up for commercialization. High-moisture biomass feedstocks are the most likely to be used in HTL. These materials are described and results of their processing are discussed. Engineered systems for HTL are described; however, they are of limited size and do not yet approach a demonstration scale of operation. With the results available, process models have been developed, and mass and energy balances determined. From these models, process costs have been calculated and provide some optimism as to the commercial likelihood of the technology.

Single-step syngas-to-distillates (S2D) process based on biomass-derived syngas--a techno-economic analysis.

This study compared biomass gasification based syngas-to-distillate (S2D) systems using techno-economic analysis (TEA). Three cases, state of technology (SOT), goal, and conventional, were compared in terms of performance and cost. The SOT case represented the best available experimental results for a process starting with syngas using a single-step dual-catalyst reactor for distillate generation. The conventional case mirrored a conventional two-step S2D process consisting of separate syngas-to-methanol and methanol-to-gasoline (MTG) processes. The goal case assumed the same performance as the conventional, but with a single-step S2D technology. TEA results revealed that the SOT was more expensive than the conventional and goal cases. The SOT case suffers from low one-pass yield and high selectivity to light hydrocarbons, both of which drive up production cost. Sensitivity analysis indicated that light hydrocarbon yield and single pass conversion efficiency were the key factors driving the high cost for the SOT case.