Optimizing rice bran ball milling via a friction-coupled population balance model: Integrating comminution theory and energy efficiency

Abstract

Despite rice bran's considerable nutritional and functional potential, its fibrous structure and high oil content complicate efforts to produce uniform, finely milled powders for food and nutraceutical applications. This study addresses that challenge by examining how milling time (30–90 min) and rotational speed (30–120 rpm) influence both the extent of particle size reduction and the associated energy demand. A laboratory ball mill was used to generate a broad range of operating conditions, while mechanical energy usage and particle-size parameters (d₁₀, d₅₀, d₉₀) were recorded. Population Balance Modeling (PBM) served as the primary analytical framework, calibrated through experimental size distributions to yield breakage kinetics. Frictional effects were incorporated to determine net breakage energy, and classical comminution laws (Bond, Rittinger, Kick) were also evaluated for benchmarking. Results revealed two key milling regimes: an early stage with rapid fragmentation of larger particles, followed by a fine-dominated phase marked by diminished breakage rates and agglomeration. Friction-coupled PBM simulations achieved near-unity parity with experimental data, significantly improving upon simplistic energy models. Short, high-speed milling (e.g., 30 min at 120 rpm) delivered moderate fineness (d₅₀ ≈ 70–90 μm) at relatively low energy (≈0.002–0.005 kWh/ton), whereas prolonged milling (≥90 min) could push median sizes below 5 μm but escalated energy consumption (∼5 kWh/ton). These findings highlight the trade-off between achieving ultra-fine bran and managing rising power costs. By integrating friction-coupled PBM insights with empirical measurements, the study provides a rigorous basis for multi-objective process optimization, guiding industrial-scale rice bran milling toward both enhanced product quality and improved energy efficiency.