a b s t r a c t
Integration of Hydrothermal Liquefaction (HTL) of microalgae biomass with concentrated solar power
thermal processing (CSP) for bio-oil production is a potential processing pathway for energy efficient generation
of renewable biofuels. Solar HTL infrastructure avoids additional bolt-on components of conventional
solar parabolic trough systems used for electricity production including heat transfer fluids,
counter current heat exchangers, fluid transfer interconnectivity and electrical power control systems.
The absence of such capital intensive additional equipment considerably reduces the production costs
of solar HTL biofuels compared to electricity generation from conventional CSP power systems. An economic
and market appraisal of variance and system economic resilience is presented. It is hypothesised
that the combination of nutrient recycling with HTL/CSP unification has the potential for economically
sustainable microalgae bio-oil production. A microalgae biofuel minimum fuel sales price of $1.23/kg
has been modelled. Further experimental work would be able to validate this integrated model.
2016 Elsevier Ltd. All rights reserved.
1. Introduction
As the demand for energy intensifies amid growing concerns for
drastic climate change, biofuels are needed more than ever as an
alternative to fossil fuels. Third generation renewable liquid biofuels
derived from microalgae could potentially supplement incremental
global energy demand. Microalgae grow rapidly, produce
energy dense lipids, are able to utilise marine, freshwater and
wastewater, grow on non-agricultural land and remediate waste
or atmospheric carbon dioxide. Microalgae biomass feedstock for
HTL bio-oil production benefits from reduced energy requirements
for complete dewatering [1–20].
This paper begins with an introduction and review of current
literature, the HTL process and heat integration using CSP are discussed,
then we calculate costs of microalgae derived bio-crude
production from a 1-ha site using a 100 m long parabolic CSP
trough. Working methodology considers established CSP thermodynamics,
heat transfer, present day market prices and the mass
of engineering equipment and associated capital expenditure
(CAPEX). Finally, this theoretical forecast of a commercial operation
is compared to industrially functioning global electricity CSP
and evaluates how this new techno-economic analysis (TEA) can
make strides from being present-day theory to the development
of a new future scenario of commercially implemented technology.
The energetics of the HTL process are dominated by the energy
required to heat the reactor, 6.51 MJ (kg microalgae)1 [21]. Careful
consideration of the EROEI (Energy Returned on Energy
Invested) of HTL as a function of reaction temperature is required
[22]. A sensitivity analysis of base case parameters indicated that
modelled systems were particularly sensitive to the extent of heat
integration from HTL suggesting that optimisation of heat integration
is necessary for minimisation of lifecycle greenhouse gas
emissions [23]. HTL oil yields reported for higher temperatures
(>200 C) exceed the lipid content of the biomass, which