Kinetic analysis of anaerobic coal desulfurization : impact of particle size on sulfur content, ash and calorific value

Abstract

Kinetic parameters are essential for improving desulfurization efficiency by providing insight into coal properties, reaction rates linked to ash, sulfur content, and calorific value, and for guiding process optimization. The current study develops a kinetic model and evaluates the desulfurization behavior of a bacterial consortium under anaerobic conditions for steam coal. Four particle size fractions (+4.60 mm, -4.60 + 2.30 mm, -2.30 + 1.00 mm, and -0.85 mm) were analyzed. Kinetic parameters were estimated and validated using the AQUASIM software. Over 20 days, total sulfur in the finest coal fraction (-0.85 mm) decreased from 1.45 wt.% to 0.50 wt.% corresponding to a 65.5% desulfurization efficiency under temperature condition of 23 ± 3 °C. Upon increasing the temperature to 30 ± 2 °C, sulfur removal was further improved, with the total sulfur content decreasing to 0.40 wt.%, yielding an overall removal efficiency of 72.4%. Ash in this fraction dropped from 34.2 wt.% to 23.2 wt.%, indicating a 32.2 % reduction. The calorific value improved accordingly, enhancing coal quality. Kinetic analysis showed that reaction rates increased with decreasing particle size, with the -0.85 mm fraction exhibiting the highest reaction rate constant (kmc = 17.474 h⁻¹), while the +4.60 mm fraction recorded the lowest (kmc = 11.105 h⁻¹). Sulfur content and ash removals followed first-order kinetics, confirming that reaction rates were concentration-dependent, while changes in calorific value followed second-order kinetics (R² > 97 %), suggesting more complex dependencies. These findings highlight the critical role of particle size in anaerobic biodesulfurization efficiency and provide a reliable kinetic framework for optimizing microbial coal treatment.

HIGHLIGHTS • Particle size significantly influences desulfurization kinetics. • Sulfur and ash reduction followed first-order kinetics, whereas calorific value enhancement followed second-order kinetics. • Reaction Rate Constants Correlate with Particle Size. • Kinetic parameters (kmc and Kc) were modelled using Monod-type equation. • Desulfurization treatment improved coal quality.