关键词: 固定床反应器, 接触点处理方法, 压降, 流动传热, 数值模拟

Abstract: Tubular fixed beds are widely used in high-temperature catalytic cracking processes. Investigating the structural characteristics of fixed beds with low tube to particle diameter ratios and the flow heat transfer laws at high temperatures can provide valuable insights for optimizing the fixed bed high-temperature catalytic cracking process. To address the issues of inaccurate particle description in the discrete element method and difficulty in mesh delineation in the particle resolution method, a new contact point method is proposed. This method does not alter the particle and bed size and shape parameters, adapts to various particle shapes, and significantly reduces the difficulty of model contact processing. Three cylindrical particle beds with different ratios of the inner diameter of the reaction tube to the equivalent diameter of spheres of equal specific surface area of the cylindrical particles (tube-diameter ratio D/dp) and one spherical particle bed are generated to investigate the effects of tube size ratio and particle shape on bed structure and flow heat transfer characteristics. The results show that the overall void ratio of the bed layer decreases with increasing tube to particle diameter ratio, the particle stacking is distributed in circles, and the radial distribution curves of radial void ratio and axial mean velocity are highly consistent. Additionally, the pressure drop is generally consistent with Eisfeld modified equation. Furthermore, the bed flow field distribution is highly correlated with the bed structure, and the size of the flow channel voids directly affects the generation of channel flow phenomena, which further impacts its temperature field distribution and heat transfer performance. The sphere particle bed exhibits a more uniform temperature field distribution, but its heat transfer performance is not as good as that of the cylind particle bed.

Key words: Fixed-bed reactor, Contact point method, Pressure drop, Flow heat transfer, Numerical simulation