Catalytic Hydrothermal Gasification of biomass provides a highly efficient pathway to medium-Btu fuel gas. This gas product can be used directly in heat and power applications or has potential to be cleaned to pipeline quality gas. As synthetic natural gas, it has potential to displace imported petroleum used in transportation application. Hydrothermal processing utilizes water-based slurries at medium temperature (350°C) and sufficient pressure (3,000 psig) to maintain the water in the liquid phase. The processing option is particularly applicable to wet biomass feedstocks, such as algae.
The algae feedstocks were reliably processed in the bench-scale reactor system. High conversions were obtained even with high slurry concentrations. Consistent catalyst operation in 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.
Hydrothermal processing of biomass to gaseous fuels requires expanded process development to take the technology to a scale for industrial demonstration. Technical challenges associated with hydrothermal processing of biomass will be discussed. They include not only with feeding of high-pressure slurries and pressure let-down; but also the properties of the byproducts, which are highly dependent on the feedstock composition; optimization of the gasification process variables; and demonstrating the effectiveness of separation techniques to remove impurities before catalyst poisoning.
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