Hydrothermal liquefaction (HTL) is considered as one of most promising techniques for valorization of whole, wet algae biomass. HTL uses subcritical water (270-350 ºC and 8-18 MPa) to convert the organic biomass constituents into an energy-rich bio-crude oil that can be upgraded into liquid fuels. To date, many studies have used batch reactor; shifting to continuous reactors is necessary for progressing to commercial-scale processes due to the higher productivity and lower operating costs of steady-state, continuous systems.
This study reports the modification and preliminary testing of a pilot-scale continuous flow reactor (CFR) for hydrothermal liquefaction of wastewater microalgae at low solids loadings. The goal of this reactor is to perform continuous (>30 liters or >8 hours) HTL on algae slurries with solid algal contents up to 10 wt.%, and to produce char-free bio-crude oils using a dual high-pressure cylinder filter system with blow-down pots to remove solids. CFR systems must address several challenges: smooth flow of homogenous biomass slurry through unit operations, clogging, solid-liquid-gas separation/filtration, multiple unit operations, and process safety and control. Here we report on the progress of the reactor development relative to bio-crude oil production, reaction residence time, and operational stability. In addition to reactor development, HTL product characterization was also conducted using Fourier transform ion cyclotron resonance mass spectroscopy (FT-ICR MS) and fatty acid methyl ester (FAME) analysis by gas chromatography mass spectroscopy (GC/MS for bio-crude oil quality, and oxy-combustion calorimetry and elemental analysis (CHNS) for mass and energy balances.
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