关键词: 输送床, 甲烷化, 煤制天然气, 数值模拟, 传热, 动态行为, 反应机制

Abstract:

Numerical simulation based on COMSOL Multiphysics was conducted to understand the heat transfer dynamics and reaction control mechanism over methanation catalyst particles in size of about 100 μm under conditions of transport bed. The high heat transfer efficiency in transport bed makes the catalyst particle into the bed quickly approach its steady state at about 0.1 s, a really very short transient period. For the catalyst particle at steady state there are temperatures sharing little difference among particle center, particle surface and gas flow bulk. However, it was clear that the temperature is still gradually lower from the center to surface of the particle, and on particle surface its temperature is higher than that in gas bulk. This clarifies that the exothermic heat of methanation reaction first heats catalyst particle, and the temperature-raised particle then reaches a balance of heat transfer with its surrounding gas. Calculating the radial profiles of temperature, gas components and reaction rate inside the catalyst particle clarified that for methanation at higher gas bulk temperature and elevated pressure (2 MPa here) the mass transfer into particles is quicker and the CO consumption rate becomes gradually lower from the center to surface of the particle. On the contrary, for atmospheric methanation at lower gas velocity, the reaction rate was conversely lower at the particle center. It demonstrates that the methanation reaction is subject to kinetic control for the former but to mass transfer for the latter.

Key words: transport bed, methanation, coal-to-SNG, numerical simulation, heat transfer, dynamic behavior, reaction mechanism