Modelling of bio-oil steam gasification in a fluidized bed reactor

Abstract

This paper reports a three-dimensional CFD model for bio-oil gasification in a fluidized bed reactor. The model considered three-phase hydrodynamics, heat and mass transfer, bio-oil atomization, spray droplet vaporization and thermal decomposition in gas–solid flow. It employed a Euler-Lagrange method, in which gas and solid flow were solved using the Eulerian method and the bio-oil droplets were tracked using the Lagrangian approach. Droplet trajectory was calculated via equation of motion using discrete phase model in the Lagrangian frame, considering the interactions with flow field. Experimental data were obtained for bio-oil injection characteristics and simulations were conducted for generating the Rosin-Rammler distribution function under different injection conditions. As the droplets were injected into a fluidised-bed reactor, the depletion in bio-oil droplet size as a result of evaporation could not be described by the D2-law due to the complex composition of bio-oil. Spray penetration into the reactor increased substantially with increasing droplet size. The predictions from the CFD model for bio-oil steam gasification were in good agreement with the experimental data available in the literature, in terms of cold gas efficiency (CGE) and syngas compositions at various bed temperatures, steam-carbon molar ratios and methane equivalent gas hourly space velocity (GC1HSV) of feed. Sensitivity analyses on these key process parameters were also carried out.