Dynamic Modeling and Simulation of SAG Mill Circuits with Pebble Crushing
Licentiatavhandling, 2020

Grinding is one of the most energy-consuming processes in the mining industry. As a critical part of the comminution process, autogenous grinding (AG) or semi-autogenous grinding (SAG) mills are often used for primary grinding. However, the breakage mechanism of an AG/SAG mill is inefficient in grinding particles of a certain size, typically in the range of 25-55 mm, i.e., pebbles. Therefore, cone crushers are often used as pebble crushers and integrated into AG/SAG mill circuits to break the critical size particles that accumulate in the mill and to increase the performance of the primary grinding circuits.
Many studies have been carried out, mainly focusing on optimizing of SAG mills and cone crushers, respectively, but only a few have investigated the dynamic interactions between a SAG mill and its pebble crushers. The scope of this thesis is to examine the dynamic relations between the SAG mill and the pebble crusher in a closed circuit and thus to optimize the circuit efficiency by controlling the pebble crusher operational settings.
In this thesis, two modeling techniques are proposed for simulating the dynamics in the grinding process. The first method is the fundamental modeling method, where the underlying physics of the comminution process has been considered. The proposed mill model is divided into sub-processes that include breakage behavior in each sub-division, particle transportation within the mill chamber, and the discharge rate from the mill. The dynamic cone crusher model describes the crusher chamber as a surge bin and predicts the product particle sizes based on crusher CSS and eccentric speed. In the simulation model, other production units such as screens and conveyors are included to describe the dynamics of the circuit better. The flexibility of this method allows one to apply this simulation library to a variety of plants with different configurations.
The second modeling technique presented in this study is based on data-driven methods, where two SAG mill power models are developed. The first model calculates the mill power draw by combining several individual data-driven algorithms. The second model uses historical data to forecast the mill power draw in advance. These data-driven methods can make high accuracy predictions based on a specific plant dataset, and find complex nonlinear relations between input variables and target outputs.
The results from both simulations and industrial data analysis show that significant dynamic impact can be induced by altering the pebble crusher operational settings. Therefore, the performance (throughput or specific energy) of an AG/SAG closed circuit can be improved with the optimized utilization of its recycle pebble crusher. While the present work is based on simulation and analysis of plant data, full-scale tests and further model development are needed as part of a future study.

Dynamic modeling

AG/SAG mill

Fundamental modeling method

Data-driven modeling method

Pebble crushing

Cone crusher

Comminution process

VDL, Hörsalsvägen 7A
Opponent: Prof. Malcolm Powell, University of Queensland


Haijie Li

Chalmers, Industri- och materialvetenskap, Produktutveckling

Dynamic modelling and simulation of an AG/SAG mill with multi component ore

Dynamic modeling and simulation of a SAG mill-pebble crusher circuit by controlling crusher operational parameters

A data-driven method to isolate the impact of pebble recycling on AG/SAG mill circuit


Konferensbidrag (offentliggjort, men ej förlagsutgivet)


Annan maskinteknik


Annan elektroteknik och elektronik


Chalmers tekniska högskola

VDL, Hörsalsvägen 7A

Opponent: Prof. Malcolm Powell, University of Queensland

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