Bio-oil, a mixture of complex oxygenated hydrocarbons, is obtained through fast pyrolysis of solid biomass. As biomass is low in energy density and not easily transportable, a novel approach is to convert biomass to bio-oil, transport bio-oil to a centralized facility, gasify bio-oil to syngas, and upgrade syngas to transportation fuels and other high-value chemicals. In this study, a comprehensive numerical model was developed to simulate the gasification of bio-oil at different operating conditions and different reactor geometries.

The present model considers spray, atomization, vaporization, and chemical reactions of bio-oil. Bio-oil was modeled as a multi-component fuel, consisting of ten major components. The Joback method, a group contribution method, was used to calculate the bio-oil thermophysical properties, including enthalpy, latent heat, and vapor pressure. With the bio-oil thermophysical properties, vaporization of single bio-oil drop was simulated, and results show that the heaviest component, i.e., levoglucosan, is the last component which remains in the drop.

A thermodynamic equilibrium approach was used to account for chemical reactions. Gasification of methanol was first simulated for model validation. The numerical simulations of bio-oil gasification at different operating pressures and equivalence ratios were also conducted. Comparisons between the numerical results and experimental data show that the current model can predict gasification process reasonably well. Results show that syngas yield is independent of the ambient pressure while sensible to equivalence ratio. The simulation results show that conversion of bio-oil to syngas occurs gradually along the gasifier.

Using the current model, bio-oil gasification was studied for large reactors with high gasification capacity. It was found that a reactor with 30 cm in diameter and 300 cm in length can gasify bio-oil at a rate of 6 ton/day and the gasification products can reach their equilibrium state at the reactor outlet. It is estimated that a gasifier with 200 cm in diameter and 300 cm in length can allow the use of 20 injectors to gasify 120 ton/day of bio-oil. Therefore, it is suggested that 10 such gasifiers can be assembled in a biorefinery to achieve the capacity of 1200 tons of bio-oil per day. This quantity of bio-oil corresponds approximately to 2000 ton/day of solid biomass that is used for fast pyrolysis to produce 1200 ton/day of bio-oil.