(90f) Hydrothermal Liquefaction of Wastewater Treatment Microalgae in a Pilot-Scale Continuous Flow Reactor

Authors: 
Cheng, F., New Mexico State University
Le-Doux, T., New Mexico State University
Treftz, B., New Mexico State University
Woolf, S., New Mexico State University
Miller, J., New Mexico State University
Jena, U., New Mexico State University
Brewer, C. E., New Mexico State University

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.