Continuous Hydrothermal Liquefaction of Biomass in a Novel Pilot Plant with Heat Recovery and Hydraulic Oscillation

Abstract

Hydrothermal liquefaction (HTL) is regarded as a promising technology for the production of biofuels from biomass and wastes. As such, there is a drive towards continuous-flow processing systems to aid process scale-up and eventually commercialization. The current study presents results from a novel pilot-scale HTL reactor with a feed capacity of up to 100 L/h and a process volume of approximately 20 L. The pilot plant employs a heat exchanger for heat recovery and a novel hydraulic oscillation system to increase the turbulence in the tubular reactor. The energy grass Miscanthus and the microalgae Spirulina, both representing advanced dedicated energy crops, as well as sewage sludge as high-potential waste stream were selected to assess the reactor performance. Biomass slurries with up to 16 wt% dry matter content were successfully processed. The heat recovery of the heat exchanger is found to increase with reactor run time, reaching 80% within 5–6 h of operation. The hydraulic oscillation system is shown to improve mixing and enhance heat transfer. Bio-crudes with average yields of 26 wt%, 33 wt% and 25 wt% were produced from Miscanthus, Spirulina and sewage sludge, respectively. The yields also appeared to increase with reactor run time. Bio-crude from HTL of Spirulina was mainly composed of palmitic acid, glycerol, heptadecane and linolelaidic acid, while biocrude from sewage sludge contained mainly palmitic acid, oleic acid and stearic acid. In contrast, biocrude from HTL of Miscanthus consisted of a large number of different phenolics. An energetic comparison between the three feedstocks revealed a thermal efficiency of 47%, 47% and 33% and energy return on investment (EROI) of 2.8, 3.3 and 0.5 for HTL of Miscanthus, Spirulina and sewage sludge, respectively.

Two-stage catalytic hydrotreatment of highly nitrogenous biocrude from continuous hydrothermal liquefaction: A rational design of the stabilization stage

“…In sewage sludge biocrude, oxygenated compounds (mainly fatty acids) are the largest majority, although around 10% of the chromatogram area is explained by amides. Results are in good accordance with previous literature data [3,4,31].…”

“…Details related to the properties and the production of these two biocrudes can be found in Ref. [31].…”

Catalytic upgrading of hydrothermal liquefaction biocrudes: Different challenges for different feedstocks

“…Based also on literature [15], possible reaction products can be represented by ethylbenzene and ethylcyclohexane ( Figure 5), which were both detected among the reaction products. other studies [21,22], where different settings of the instruments were able to detect also other fatty acids up to C20.…”

“…HTL experiments were carried out in a continuous pilot plant operating at subcritical conditions (350 °C, 22 MPa). Details on the production of these biocrudes can be found in [22].…”

Catalytic Hydrotreatment of Microalgae Biocrude from Continuous Hydrothermal Liquefaction: Heteroatom Removal and Their Distribution in Distillation Cuts

“…This biocrude contains~10-15 wt. % of heteroatoms (primarily O and N) with a high heating value (HHV) of~30-38 MJ/kg [17,18]. Biocrude as such cannot be directly utilized in the transportation sector.…”