A Fundamental Investigation Of Discrete Liquid, Gas And Fines Flow In A Random Packed Bed Along With Applications

Abstract

The discontinuous nature of liquid flow in a random packed bed is observed in many chemical engineering and metallurgical applications like blast furnace and heap leaching. So, to model the liquid flow in these systems, the discrete nature of the liquid flow should be taken into consideration. Moreover, the effect of gas flow on the particles and liquid phase of the packed bed, taking into account the random nature of the bed and the discrete nature of the liquid, is lacking. Therefore, fundamental understanding of the liquid-solid-gas interactions in a random bed is important to improve the processes. To understand the effect of gas-solid interaction, a slow-moving packed bed, inside the reactor, has been considered. Particles are discharged from the bottom and gas is injected laterally. The gas flow has been modelled using continuum-based fluid flow equations. It is found that gas flow is not symmetric inside the reactor due to significant variation in void sizes inside the bed. This along with gas variation also affects the residence time of each particle inside the bed. This work is extended to the liquid flow in random bed using Discrete Liquid Flow (DLF) theory. A novel graph-based recursive Depth First Search (DFS) algorithm is developed to find the shape and size of voids in the random bed. The liquid flow behaviour has been studied in various conditions, like changing the packing size and bed height. This study confirms that the bed topology plays an important role in dictating the liquid flow behavior in a randomly packed bed. Using the DLF, DFS, the various phenomena, which occur in a multiphase flow packed bed, such as rupturing of rivulets, liquid hysteresis have been understood and explained fundamentally. The study is further extended to heap leaching process, where the liquid flows as droplets and rivulets due to very low liquid flow rates. The liquid flow behaviour is studied in terms of tortuosity, liquid distribution, breakthrough time, contact angle etc. The study shows that heap leaching processes can be modelled in more accurate and deterministic way using DLF theory along with DFS algorithm by avoiding the uncertain experimental parameters (like bed permeability etc). Finally, the flow behaviour of the liquid phase in a random packed bed is studied, taking into account the movement of particles due to the lateral gas and fines injection. The deviation of the liquid path due to the gas and fines drag is also captured. It is found that the deviation of the liquid path is higher for the larger particle sizes.