Hydrothermal liquefaction (HTL) has been widely investigated as a suitable process method for the preparation of alternative fuels from algae, due to its mild reaction conditions and environmentally benign reaction medium. HTL requires heat input to a large amount of aqueous phase medium, which accounts for most of the heat consumption in the bio-crude preparation stage; in addition, co-processing requires bio-crude as a feedstock for the fuel refinery system. Therefore, energy consumption in the preparation stage of bio-crude is important for industrial cost control. In this paper, HTL from different types of algae and process methods is evaluated from the perspective of energy consumption. One-step HTL, two-step HTL, and co-solvent system HTL were modelled and calculated using the chemical simulation software Aspen Plus. Five algal species with lipid contents ranging from 6.15 wt% to 47.80 wt% were evaluated. The results showed that both process method and algal species had a significant effect on the energy consumption of the HTL process. The co-solvent system HTL using a methanol:water ratio of 1:19 (v/v) and an ethanol:water ratio of 3:97 (v/v) consumed less heat (based on fatty acids and fatty acid esters (FAFEs)) than one-step HTL while obtaining high quality bio-crude. Two-step HTL has about 20% higher process heat consumption, although there are advantages in bio-crude quality and by-products over one-step HTL.
Dong et al. (Thu,) studied this question.