Mass cultivation of microalgae dates back to the mid 20th Century, from when all of the methodologies currently used can be identified, including shallow raceways and enclosed photobioreactors. While the basic principles are well established, significant technological hurdles have persistently constrained the wide scale commercial exploitation of microalgae, except for niche markets. Thanks to recent advances in bioprocess engineering and increased understanding of microalgal physiology, the opportunity now exists to effectively exploit microalgae for combined waste remediation and bioenergy production and significant investment is being made internationally in this arena.
There is currently much global interest and investment in cultivating microalgae as a source of biofuels, as they do not directly compete with food crop-based commodities and are typically grown in non-arable land areas. Potential biofuels from microalgae include direct combustion, pyrolysis, hydrogen, alkanes or “green diesel”, biodiesel alcohols (ethanol) and methane. Some microalgae species contain a much higher percentage of extractable oil than other oil crops – in excess of 50% compared to for example, 25% from rapeseed.
Methods for efficient pyrolytic conversion of intact biomass will be developed where the biomass is to be re-used for energy generation at the site of production (e.g. combined heat and power applications, where microalgae bioreactors have been used to capture flue gas CO2). This work will be carried out at EBRI incorporating EBRI’s patented “Aston zero waste bioenergy cycle”. The core of the downstream processing of microalgal biomass in the project is an intermediate pyrolysis, involving converting algae into pyrolysis liquids, pyrolysis gas and pyrolysis char with typical ratios of 20 to 30 wt % of char and 70 to 80 wt % of vapour phase. The vapour phase is directly coupled to the gasifier which can be gasified and will produce syngas which can be later used for hydrogen synthesis. Alternatively the vapour phase can be condensed to pyrolysis liquids. The total pyrolysis liquids (about 50-60% of the energy of the input material) will be converted to biofuels in a biorefinery. Also another route is to run the pyrolysis gases on dual fuel engines to electric power. The pyrolysis char, as well a CO2 neutral energy resource, can be cofired, or can be spread on the agricultural lands as a fertilizer. The Algae photobioreactor at the EBRI is shown in the figure presented here.