Study of hydrodynamic characteristics in a circulating fluidized bed gasifier for plastic waste by computational fluid dynamics modeling and simulation

Abstract

For designing an efficient circulating fluidized bed reactor, understanding the complex hydrodynamic characteristics in the reactor is required. Hence, in the present study, the modeling and simulation of the circulating fluidized bed gasifier using plastic waste were carried out with Eulerian-Granular approach. Several cases were investigated as changing superficial gas velocities or sizes of plastic waste particle. Firstly, cases were examined with four different velocities when the particle diameter is 1 mm. At the gas velocity of 6 or 8 m/s, gas volume fraction is more than 95 % throughout the reactor and particle velocity has positive value overall. Therefore, a circulating fluidized bed seems to be formed in both cases. Comparing those two cases, better solid mixing can be expected considering the mass fraction and solid velocity at the superficial gas velocity of 6 m/s. Thus this case was further studied for the effect of particle size. As the diameters of plastic waste particle are 1 or 3 mm, it is considered that a circulating fluidized bed is formed. And plastic waste and sand particles are well mixed throughout the reactor. However, the particle diameter increases over 3 mm then, it is very hard to maintain circulating fluidization condition. List of symbols dParticle diameter (m) F Coefficient for interphase drag force (kg m -3 s -1 ) gGravitational acceleration (m s -2 ) P Pressure (pa) S sj jth solid phase stress tensor (Pa) V Velocity vector (m s -1 )Greek letters e Void fraction q Density (kg m -3 ) s g Deviatoric stress tensor for gas phase (Pa)

Multi-Scale Modeling of Plastic Waste Gasification: Opportunities and Challenges

“…As can be observed in this table, most of the E-E studies specific to PWG are non-reactive. Lee et al have studied the hydrodynamic of a circulating fluidized bed reactor (CFB) to gasify the PW with circulating sand [313]. The goal of this study is to find the optimum condition-in this case, the gas superficial velocity and PW particle diameter-under which the solids create a uniform circulating flow.…”