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 REQUEST OF AUTHOR.] 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[degrees]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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