Particle damage and subsequent size reduction is characteristic across a wide range of industries including the food, chemical, mineral and pharmaceutical sectors which encompass an even wider range of processed materials. Breakage of particulate materials by repeated low-energy stressing events is an important subject that range from materials handling to comminution. There are many applications where undesirable breakage or degradation can take place such as cyclones, fluidized beds, centrifuges, stirred vessels; and in transport equipment, such as pneumatic, screw and hydraulic conveyors and chutes. For instance, degradation is of relevance from materials such as coal and iron ore lumps, used in steelmaking, to fine powders that are processed in the chemical, food and pharmaceutical industries. Another example in which degradation is actually desirable is the case of crystallization processes as it is used to provide a consistent size distribution, which would not be achieved through controlled crystal growth alone.
Breakage is an essential process in many industries notably for mineral processing
Research has shown that particles are often loaded using insufficient energy to cause breakage inside comminution equipment, being fractured only after repeated low-energy stressing. This has been particularly well-known for autogenous and semiautogenous mills, where rock lumps are broken by a combination of attrition and self-induced impact-fracture. The Discrete Element Method (DEM) has proven to be a great predictive tool to model these mills and it has recently shown that fracture by repeated stressing is also the major mode of breakage for coarse particles. Therefore, this mode of particle fracture is likely to be of significance for a number of crushers as well. This has led to an increased demand in the simulation of particle breakage and degradation to better describe fracture of particles subjected to repeated loading.
At EDEM we have many customers in the mining and mineral processing industries with a need for modelling a number of unit operations in particulate materials processing and handling, where particles are often subject to complex series of loading events. This need has been the driving force for us to include a model that will be able to describe the underlining mechanisms that will lead to weakening and breakage.
Over the years there have been several mathematical models that fail to provide realistic results either because of their empirical nature, large number of fitting parameters, great complexity or poor accuracy.
Up until now EDEM users were able to simulate breakage using the EDEM Application Programming Interface (API) and it consisted in replacing a particle with its daughter particles but that was addressing fragmentation on a very simplified level. While this approach has been sufficient and successfully used by some of our users for specific applications, we wanted to provide a more suitable and advanced model that would include both surface damage (also known as abrasion or weakening) and fragmentation.
To develop this new breakage model we followed the latest advances in research and worked with experts in the field (including Prof. Marcelo Tavares, UFRJ) to deliver a model based on well-established and validated physics. This resulted in a robust breakage model that considers both catastrophic breakage (when particles suffer a great impact) as well as surface breakage (where particles become progressively weaker) by using less fitting parameters.
EDEM’s breakage model is able to describe the underlining mechanisms that lead to the weakening and overall breakage of particles.
This model provides a list of outputs related with the weakening of the particles and their related energies before fragmentation, as well as the final fragmentation and the size distribution of the fragments. The latter is especially of key importance for users as it helps towards the improvement and optimization of equipment as well as understanding better the behavior of materials.
The breakage model is currently available as a BETA from the EDEM User Forum. It is easy to use and includes a .dll file, used as an input in the physics section in EDEM, as well as the preference file with the parameters of the breakable materials. We also provide a guide to breakage parameters for various materials including granulite, limestone and iron ore based on information available in literature and obtained from calibration tests.
On top of the standard analysis available in EDEM, this breakage models provides users with the following information:
- Mass loss per particle type
- Mass loss of the entire system
- New fracture energy per particle type
- Fragment size distribution
- Mill power
We are excited to make this breakage model available to our users and we are already working on the next phase – more details will be made available in due time!