Three-Dimensional Simulation of Hydrodynamic Mechanism of Fluidized Bed Methanation

Abstract

Organic solid waste (OSW) contains many renewable materials. The pyrolysis and gasification of OSW can realize resource utilization, and its products can be used for methanation reaction to produce synthetic natural gas in the specific reactor. In order to understand the dynamic characteristics of the reactor, a three-dimensional numerical model has been established by the method of Computational Fluid Dynamics (CFD). Along the height of the reactor, the particle distribution in the bed becomes thinner and the mean solid volume fraction decreases from 4.18% to 0.37%. Meanwhile, the pressure fluctuation range decreased from 398.76 Pa at the entrance to a much lower value of 74.47 Pa at the exit. In this simulation, three parameters of gas inlet velocity, operating temperature and solid particle diameter are changed to explore their influences on gas-solid multiphase flow. The results show that gas velocity has a great influence on particle distribution. When the gas inlet velocity decreases from 6.51 to 1.98 m/s, the minimum height that particles can reach decreases from 169 to 100 mm. Additionally, as the operating temperature increases, the particle holdup inside the reactor changes from 0.843% to 0.700%. This indicates that the particle residence time reduces, which is not conducive to the follow-up reaction. Moreover, with the increase of particle size, the fluctuation range of the pressure at the bottom of the reactor increases, and its standard deviation increases from 55.34 to 1266.37 Pa.