Simulation model for hydrothermal liquefaction reactions

Abstract

Lately the production of biofuels from renewable sources has aroused interest due to the decreasing number of fossil fuels and preventing the climate change. Especially the replacement of fossil transportation fuels by renewable ones is important, since the use of energy of the traffic sector corresponded to 22.5% of total energy consumption in the European Union in 2015. There are several different process technologies to produce renewable transport fuels from biomass, such as production of biodiesel by NExBTL technology. One of the most promising technology under development is hydrothermal liquefaction, where biomass is converted into liquid biofuel in hot pressurized water. The aim of this thesis was to study the possibility to develop a simulation model for hydrothermal liquefaction of lignocellulosic biomass. The interest of creating the simulation model is that the simulation model will be used as reactor scaling tool in the future. The objectives of the thesis were both to study existing research focusing on both reactions in the supercritical water and existing hydrothermal liquefaction simulation models, and to create a simulation model for modelling the hydrothermal liquefaction reactions. The simulation model will be tested and validated in the future when hydrothermal liquefaction pilot facility is completed. The work included literature research, creating the simulation model and simulating a case study. The literature research focused on both finding the reaction pathways and kinetics in supercritical water related to lignin, hemicellulose and cellulose, and studies that included creation of simulation model. The process layout of the simulation model came from the test facility, which was under construction during the study. The other needed information for the simulation, such as reactions and reaction kinetics, was gathered in the literature research. There were couple of different reaction pathways and kinetics used, before the most suitable one was found. Finally, the simulation model was linked with Excel spreadsheet that works as user interface for the model. The outcome of the study were the simulation model for hydrothermal liquefaction of biomass and case study results. The case study showed that treating Norway spruce by using hydrothermal liquefaction can produce biocrude with good energy and mass efficiency. The results of recoveries of mass and energy were 30 % and 63 % when using 15 minutes residence time. However, the comparison of simulation model results with other studies results showed that the model predicts both biocrude yield and gas yields too low while the char yield is too high. The results showed that the model needs developing before it is suitable for calculation tool for scaling the reactor into desired scale.