Analysis of biomass gasification in bubbling fluidized bed with two-fluid model

The framework of theoretical method is two-fluid model coupled with reaction process. The k-epsilon model is used for gas phase, and the kinetic theory of granular flow is employed for solid phase. In the simulation, gasification process consists of three parts: pyrolysis, homogenous reaction, and heterogeneous reaction. In the first stage, biomass particles crack into carbon particles and volatile gases upon entering the reactor. Subsequently, the carbon particles and volatile gases react with oxygen, which includes both homogenous reaction and heterogeneous reaction. The effect of equivalence ratio (ER) is studied. It is found that all the products have same tendency with the increase of ER. H-2 and CH4 change linearly with ER; CO and CO2 change cubically with ER. This is because the mechanism of formation of CO and CO2 is more complex than that of H-2 and CH4. H-2 and CH4 are consumed by O-2, so they tend to decrease with the increase of ER, whose value corresponds to the amount of O-2 fed. For CO and CO2, however, things are more complicated: the extents at which CO and CO2 decrease are converse. CO decreases significantly and then reaches a plateau and finally decreases again, while CO2 decreases moderately at the beginning and then decreases sharply and finally becomes flat. The conclusion is that when oxygen concentration is low, increment of oxygen favors production of CO2, and when oxygen concentration reaches a certain level, increment of oxygen favors production of CO, and when oxygen concentration continually increases, increment of oxygen favors production of CO2 again. Published by AIP Publishing.