Solving Granular (Particulates) Flow Problems Using Discrete Element Methods

Granular flow processes are practically everywhere in the process industries - and they have been around for a long time too. Some examples of such processes are pneumatic conveying, polymer processing, fluidized bed granulation and coating, tablet coating, spray drying etc. Despite their widespread application, however, the development of such processes is still based on empiricism - largely due to a lack of fundamental understanding of granular flow behavior. The situation gets even more confounded when one or more fluids interact with the granular material. Nevertheless, a good fundamental understanding of granular flow dynamics is key to successful development of such processes.

In this presentation, we describe a class of computational modeling techniques that help engineers realize this goal. The Discrete Element Method (DEM) is a computational technique that can be used to describe granular flows to a high degree of accuracy. The first and key step in this computational techique is material characterization – which is a series of simple tests that are performed to determine the flow properties (coefficient of restitution, heap angle, bulk density) of the granular material. Once these properties are determined, granular flow models over a wide range of complexity can be developed using the DEM technique. Further, DEM models can be coupled to computational fluid dynamics (CFD) models to realistically simulate interactions between granular material and fluids. Such DEM-CFD hybrid analyses have been successful in gaining a fundamental understanding of processes such as granular mixing (and segregation), spray drying, tablet coating and calcination of catalyst support. Examples demonstrating the successful use of DEM-CFD techniques for process improvement in the Oil & gas, Pharmaceutical and Chemical (specialty, fine and consumer) industries will be presented.