Evaluation of the Drying Characteristics of Coffee Grounds with Electric and Gas Combustion Heat Sources

Abstract

The water content of the coffee grounds discharged from coffee beverage production facilities and coffee stores is about 75 wt.%. When the coffee grounds is used as solid energy source, drying technology is important because the high water content of the coffee grounds causes lower heating values reduction and combustion deterioration. In particular, it is necessary to maintain a constant water content of the dried coffee grounds with low energy consumption. In this study, two types of coffee ground batch dryer were tested: an electric heating and a gas burning system. After coffee grounds were injected into each dryer, vapor evaporation, drying rate, specific moisture evaporation rate, and drying efficiency were measured. The drying systems applied the moisture intensity (pulse, P) sensor and an automatic control program to maintain the moisture content of the dried coffee grounds. The drying performance and efficiency of the electric heating dryer were 21% and 33% higher than the gas burning dryer, respectively. The water content of dried coffee grounds is about 2.1 wt.%, and the ash content is 1.5 wt.%. The lower calorific value of dried coffee grounds is 5,710 kcal/kg, satisfying Bio-SRF (solid refuse fuel, Korea) quality standard. Therefore, when the dried coffee grounds is used as a solid energy source, it is advantageous to reduce the amount of greenhouse gas and save fossil fuels compared to the case of landfilling the dried coffee grounds.