Fluidized bed gasification of marine microalgae in a spouted bed reactor

Abstract

The sustainable production of biofuels from marine microalgae shows enormous potential. While current research is focused on the cheap and sustainable production of algal lipids, another key technical question is the optimum process option for the residual biomass. One possibility is gasification of the biomass in a fluidized-bed to produce syn-gas which can be used for energy directly, converted to liquid hydrocarbons or converted to other valuable bulk chemicals such as methanol, etc. Possible impediments to this technology include the high concentration of alkali metals in the biomass, high moisture content and the small particle size. This paper presents preliminary attempts to gasify a marine microalga that has been sundried. The dried biomass was sieved to recover a size fraction in the range 1.0-3.35 mm and this was gasified with air and steam in a spouted fluidized bed reactor. Early experiments, utilising the as-received biomass, proved unsuccessful due to rapid bed sintering and blockage of the downstream product lines. Leaching of the algal biomass to remove the extracellular salt was performed, however gasification of the resultant biomass also proved unsuccessful. Co-gasification of the leached biomass with Kingston coal, a low-rank coal from South Australia, at a biomass-to-coal ratio of 1:9 was also unsuccessful. In all cases it appears that rapid attrition of the biomass feed within the screw-feeder led to the almost complete elutriation of biomass from the reactor which resulted in the downstream blockages.