The industrial-scaled system is assumed to be an optimized
process in terms of energy recovery with yields based on the
experimental data. Energy is recovered through the burning of process
gasses used to provide heat to the reactor, and through the
bio-oil stream using a heat exchanger, which transfers heat to
the incoming feed stream with an efficacy of 85%. A process flow
of the modeled industrial-scale HTL system is presented in Fig. 2.
The aqueous phase contains organic carbon, ammonium, and
phosphite which are used to supplement the nutrient demands
in microalgae growth. The catalyst and solids are separated from
the oil through a centrifuge and reused.
The energetics of the HTL process are dominated by the energy
required to heat the reactor, 6.51 MJ (kg microalgae)1. This is
slightly supplemented in the industrial-scale process, 0.61 MJ
(kg microalgae)1, by the implementation of heat recovery and
burning of process gasses. The bio-oil and gasses produced through
HTL were experimentally determined to have a high heating value
(HHV) of 34 MJ kg1 and 1.1 MJ kg1 respectively.