On the design of conical hoppers for spent coffee grounds: Moisture content and particle-size effects

Abstract

Spent coffee ground (SCG) is a food waste with promising potential for reuse in pilot-to-industrial scale processes provided that storage and handling issues are overcome. Here some key bulk and flow properties of SCGs were determined with FT4 rheometer, for powders with different particle-size distribution (249.1 ≤ dV ≤ 583.1 μm) and moisture content (2.8% ≤ MC ≤ 62.5%). These properties were used to evaluate the design of mass-flow silo hoppers following the classical Jenike theory. The SCGs flowability worsened by decreasing dV and increasing MC, with indexes between 1.09 ≤ HR ≤ 1.92 and 2.5 ≤ FF ≤ 15.0. The minimum hopper inclination and outlet diameter ranged from 9.9° to 17.1° and 0.40–1.00 m. A sensitivity analysis for the hopper design was performed, and a densification equation was coupled to Jenike's method to ease future hopper designs for SCGs with different properties. Ultimately, the results showed that careful consideration must be given to dV and MC to design effective devices to handle SCGs.