Optimisation of sputnik distributor using numerical method

Abstract

A coal distributor is necessary to mix and split raw coal for subsequent processing in a parallel module coal preparation plant. The sputnik hydraulic distributor, a static device with two internal chambers and tangential water pipes, is widely employed for this purpose. Biased properties in the discharging slurry streams may lead to many problems. It is useful to develop a mathematical model to aid the design, control and optimisation of the operation. For this purpose, we have recently developed a computational fluid dynamics (CFD) model which uses homogeneous two-phase flow method to solve the three-dimensional distribution of water flow and its volume fraction and a discrete element method (DEM) to describe the motion of coal particles in the distributor. In this article, extensive numerical experiments based on the CFD model are conducted and the detailed fluid flow pattern is analysed to understand the main causes for water maldistribution inside a 12-way coal distributor, aiming to identify the optimum operational condition and design for practice. Variables considered include water flow rate and velocity, layout of water inlets, size and position of the inserted table, geometry of orifice slots and outlet size. The initial momentum of tangential inlet jet is found to be most important to minimise biased mass flow rate among outlets. Three mechanisms, namely, geometric distribution, swirl distribution and gravity distribution, are found to be responsible for the water distribution. To test the outcomes, the flow of coal particles is also simulated using DEM. Several cases with different operational conditions are considered to clarify the influence of water flow on particle flow and the relationship between water distribution and particle flow distribution at the outlets. The findings should be useful in the development of a better understanding of this complicated gas-liquid-particle flow system or new designs and control strategies for coal distributors.

Keywords:

• coal distributor
• numerical modelling
• multi-phase flow
• discrete element method

Acknowledgements

The authors are grateful to Dr. A. Vince and Mr. I. Brake of BMA for helpful discussion.