Analysis of the performance of an L-valve feeding spent coffee ground powders into a circulating fluidized bed

Abstract

Waste biomass powders are appealing to generate renewable energy and to reduce the dependence on fossil fuels, however, feeding reactors in processing is still a challenge. This paper examines the performance of a non-mechanical L-valve to feed dry and moist Spent Coffee Ground (SCG) powders into a circulating fluidized bed under a broad range of conveying and aeration flowrates. The L-valve performed as a robust feeder, providing stable solids circulation rate (WS) for most of the tested conditions. Solid mass flowrates were not affected by fluctuations in the riser air flowrate up to ±15%. We verified that the L-valve performance is limited by a deterioration of powders' flowability. Lower values of WS and narrower operating ranges were observed when feeding dry SCGs powders and samples containing fine particles. Nevertheless, the feeder can be considered a good option to handle SCGs with moisture content close to 30% w.b. and a mean particle size of 400 μm. This is an appealing result since the moisture content of SCGs burned in the soluble coffee industry ranges from 25 to 50%. Solids feeding was stable and operation was smooth in a range of 1.2 < WS < 10.0 g/s. Finally, a correlation to predict Ws from the pressure drop in the L-valve is proposed, which fitted our data better than other equations available in the literature.