CFD Modeling and Simulations of Catalytic Hydrotreatment of Bio-Oil

Abstract

The term biofuel is referred to liquid, gas, and solid fuels produced from biomass. Biofuels include energy security reasons, environmental concerns, foreign exchange savings, and socioeconomic issues related to rural sector. Biofuels include bioethanol, bio-methanol, vegetable oils, biodiesel, biogas, bio synthesis gas, bio-oil, bio-char, and bio hydrogen etc. Whereas, bio-oil refers to the synthetic fuel produced from the seeds like jatropha, karanja, corn etc., by destructive distillation or pyrolysis process at a temperature of 500oC produces both liquids and gases. Further cooling this mixture leads to a liquid form termed as bio-oil. They are also known as second generation bio fuels. These second generation bio-fuels from pyrolysis process are incompatible with the conventional fuels mainly due to the higher oxygen content, high solids, content, high viscosity, high moisture content and chemically unstable, along with higher contents of char formation. Hence upgradation of the bio-oil from the pyrolysis process is highly advisable. Among the various upgradation processes hydrodeoxygenation (HDO) process appears to be the promising technique carried in the presence of a conventional catalysts using H2 gas that is also termed as catalytic upgradation of pyrolytic oil. This Ph.D. dissertation entitled “CFD Modeling and Simulation of Catalytic Hydrotreatment of Bio-oil” deals with the modeling and simulation of lumped kinetics of the HDO process in the presence of three different catalysts, namely Pt/Al2O3, Ni-Mo/Al2O3, and Co-Mo/Al2O3. The simulations are performed using commercial computational fluid dynamics (CFD) based software, Ansys Fluent 14.5, for a wide range of pertinent conditions i.e., weight hourly space velocity ranging between , temperature ranging between and pressure values between . The numerical methodology implemented for the present simulation studies comprising Ranz –marshall, and Gunn for heat interaction,Gidaspow and Schillar Naumann for drag interaction between solid and fluid phases; kinetic theory of granular flow for solid catalyst, turbulence model for flow characteristics, and finite rate/ eddy dissipation method to study the chemical reaction kinetics are implemented and thoroughly validated with the experimental literature and good agreement is observed between two results. From the simulation studies a wide range of results in terms of volume fractions of three phases with respect to the pertinent conditions are presented. Similarly, the lumped reaction kinetics mechanism has been included in order to characterize the mass fraction of the species after the HDO process to estimate the performance of the process. Some of the key findings include that Co-Mo/Al2O3 produces the major desired species of alkanes and aromatics, phenols are higher with the Ni-Mo/Al2O3 catalyst and gaseous streams are dominating with Pt/Al2O3 catalyst. It is also observed that the hydrodeoxygenation of unprocessed bio-oil in the presence of Co-Mo/Al2O3 catalyst yields higher amounts of alkane and aromatics. The amount of LNV is found to be significant during the HDO process of bio-oil compared to HNV in the presence of three catalysts. Finally, the yields of alkanes and aromatics varying with respect to the operating parameters in the presence of catalysts follows the order Co-Mo/Al2O3 > Pt/Al2O3 > Ni-Mo/Al2O3.