The continuous supercritical water gasification of spirulina and the use of a positive displacement feeding system
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] A factorial experiment was designed and conducted to explore the effect of three variables, concentration, temperature, and residence time, on two responses, gasification efficiency and reaction rate. A hydraulic positive displacement pump was used to feed slurries of Spirulina, a blue‐green algae, at 35‐50% dry solids content into the mixing tee, where it combined with a stream of supercritical water. This is the first time that this method has been used to deliver biomass solids into a continuous reactor. Increasing concentration led to a decrease in gasification efficiency, and the effect on rate was on the level of the noise. Increasing the temperature, in the range of 550‐650°C, led to increases in both gasification efficiency and reaction rate. The (relatively) low temperature range was selected to achieve partial, rather than complete, conversion (despite < 10 s residence time). Increasing residence time in the range of 4‐9 seconds led to increases in both gasification rate, and gasification efficiency. Additional low‐conversion experiments were conducted under turbulent flow conditions to evaluate intrinsic reaction rate. Arrhenius parameters were estimated, including an activation energy of 108 kJ/mol. The Arrhenius parameters can be used in rate laws and design equations to predict the performance and estimate the size of plug flow reactors operating at a range of temperatures. The maximum observed rate of gasification was 53 g/L‐s, much higher than previously reported. The results indicate that Spirulina gasify extremely rapidly and efficiently in supercritical water.
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