Effect of Reduced Raw Material Moisture Content on Powder Properties and Energy Requirements for Size Reduction

Abstract

This study was conducted to evaluate the potential of single-stage chili milling (SSCM) as a substitute for the conventional multistage milling method to identify improvements that can be made to this process. This included reducing the moisture content of the chili to enhance the milling efficiency by increasing brittleness. Multiple stages were involved, including hammer mills and a pulverizer for chili milling. The initial moisture content of chili, which ranged from 12% to 13% w.b. during storage, was reduced to 3.5-4% w.b. by allowing it to reach the equilibrium moisture content of chili at 20% relative humidity and a 37° C environment created using heat pump air dehumidifiers. SSCM trials were performed using a pulverizer. This study aimed to analyze the particle size distribution and its relationship with the energy consumption and flow indices, such as the Hausner ratio and compressibility index. The particle size distribution was described by parameters such as uniformity index, size range variation coefficient, mass relative span, skewness, kurtosis, size guide number, coefficient of uniformity, coefficient of gradation, and geometric standard deviation. The Rosin-Rammler (RR) model was proven to be a more suitable fit (R² of 0.954-0.967) than the Gaudin-Schumann (GS) model (R² of 0.725-0.808) when describing the particle size distribution across all samples. The energy consumption for grinding was analyzed using classical grinding laws, including Bond, Rittinger, and Kick’s laws. Notably, the energy consumption of SSCM was significantly lower than that of conventional multistage chili milling. Additionally, the powder flowability of the SSCM method was comparatively lower than that of conventional multistage chili milling. However, the Hausner ratio and compressibility index of the SSCM were notably higher than those of the multistage ground powder.