Scale-up exploration of spout fluidized beds by CFD-DEM simulation

Abstract

This paper is based on the MFiX software platform and employs the CFD-DEM method to conduct a numerical simulation study on a six-nozzle rectangular jetting bed. The focus is on analyzing the flow pattern organization rules and the feasibility of scaling up when the basic unit of dual-nozzle coordinated deflection jetting is expanded to a six-nozzle array. The core issue of the study lies in: when the number of nozzles expands to a higher level from the coordinated basic unit, will the original deflection jetting dynamics still remain stable, and under what conditions can the six-nozzle system re-establish an ordered multi-unit jetting structure.

The numerical results indicate that when the basic unit of the dual-nozzle coordinated deflection jet flow is directly expanded into a six-nozzle array and the deflection flow pattern is used for scaling up, the system is prone to non-ideal flow states such as strong inter-nozzle airflow interference, aggregation of large bubbles, and surge instability, which disrupt the local particle circulation and cause disorder in the bed layer porosity distribution. This shows that the deflection jet flow mode cannot be directly applied to the six-nozzle expansion. To solve this problem, this paper further regulates the operating conditions of the six-nozzle system by taking nozzle spacing and background airflow velocity as the main optimization variables. The results show that when the nozzle spacing is reasonably optimized and the background airflow velocity is precisely controlled within the range of 1.75–2.00 m/s, the six-nozzle rectangular jet flow bed can form multiple independent vertical jet flow units, and stable and mutually non-interfering particle circulation structures are established above each nozzle, resulting in a more uniform and regular porosity distribution in the bed layer. At the same time, the nozzles are not completely isolated but achieve effective gas-solid mixing within the entire bed through weakly coupled bubble interactions, thereby maintaining local independent jet flow while also considering the overall mixing capability.

This study demonstrates that the successful scaling-up of the six-nozzle system does not merely rely on the simple continuation of the original deflection nozzle dynamics, but rather on whether the local jetting units can be reorganized under higher nozzle counts. Through the coordinated optimization of nozzle spacing and background airflow velocity, the rectangular jetting bed amplification path centered on the dual-nozzle collaborative jetting unit is also feasible in the six-nozzle structure. This paper reveals the amplification mechanism of the six-nozzle system from three aspects: porosity distribution, local flow state transformation, and particle circulation organization, providing a numerical basis for the design and optimization of rectangular jetting beds with higher nozzle counts in the future.