Application of TUSSIM with a variable Tromp curve for predicting optimal operation of multi-compartment mills with various ball size distributions

A true unsteady-state simulator (TUSSIM) for ball milling was integrated with a variable Tromp curve for classification to simulate and optimize closed-circuit, multi-compartment cement ball milling. Using representative model–operational parameters from available literature, we first investigated the system dynamics for a two-compartment mill. Then, various simulations examined the impacts of closed-circuit vs. open-circuit operation, number of compartments, and various ball size distributions. Our results suggest that integrating an air classifier into an open-circuit ball mill can increase the production rate by 15% or increase the cement-specific surface area by 13%. A single-compartment mill entails a pre-milled feed for proper operation, whereas a two-compartment mill yields a finer cement product than a three-compartment mill. Uniform mass distribution of balls led to slightly finer product than uniform surface area or number distributions, while the impact of a classifying liner was negligibly small. Finally, we identified optimal ball mixtures in a two-compartment mill using a combined global optimizer–DAE solver, which suggests 14% capacity increase with desirable cement quality. Overall, TUSSIM's results are not only in line with limited, full-scale experimental studies and industry best practices, but also provide fundamental process insights, while enabling process optimization with tailored ball mixtures in different compartments.