A review on determining the residence time of solid particles in rotary drum dryers

Abstract

Biomass material such as forest and agricultural residues are moist after harvest. Drying is an established operation to prepare them for pelletization. Wood pellet manufacturer involves drying wet biomass from mill residue or forest down to 5–7% wet-basis moisture content. Moisture reduction occurs conventionally in rotary drum dryers operating at high inlet temperatures of 300–600 °C. Although rotary dryers were initially designed to dry nonfibrous materials, these dryers have been used for drying grains, herbs, woody biomass, and agricultural wastes. Biomass materials have heterogeneous size, shape, and density properties, and their flow characteristics inside the drum are not a known phenomenon. This article reviews the researchers’ efforts to determine the residence time of solid material in concurrent rotary drum dryers. This review article analyzes the developed empirical correlations and solid cascading approximation to determine the residence time. The outputs of various empirical correlations are compared for a consistent operating condition.