Drying coffee grounds involves high energy consumption and represents an important step in using coffee waste materials as green energy. This study analyzes the drying process using thermogravimetric analysis. The kinetics of the drying process of coffee grounds, containing equal proportions of Arabica and Robusta, were evaluated under isothermal conditions at various temperatures: 50, 60, 70, and 80°C, with sample layer thicknesses of 0.6, 1.2, 1.8, and 2.4 mm. The thermogravimetric curves obtained for the coffee grounds samples under conditions of constant temperature allowed the tracing of the drying curves (moisture content—drying time). The influence of the furnace air velocity on the drying and water evaporation process was analyzed. The drying rate has been established to be about 2.6 times slower than the rate of water evaporation under the same conditions; as a result the overall process is controlled by the effective water diffusion in the layer. This aspect is important in industrial practice for sizing tubular dryers. The activation energy was found to be influenced by the thickness of the coffee grounds layer subjected to the drying process and had values between 8.3 kJ/mol and 10.3 kJ/mol.

中文翻译：

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使用热重分析的废咖啡渣的等温干燥动力学研究

干燥咖啡渣涉及高能耗，是将咖啡废料用作绿色能源的重要一步。本研究使用热重分析分析干燥过程。咖啡渣的干燥过程动力学（含有等比例的阿拉比卡和罗布斯塔）在不同温度的等温条件下进行评估：50、60、70 和 80°C，样品层厚度为 0.6、1.2、1.8 和2.4 毫米。在恒温条件下为咖啡渣样品获得的热重曲线允许追踪干燥曲线（水分含量 - 干燥时间）。分析了炉膛风速对干燥和水分蒸发过程的影响。干燥速率已确定为约 2。比同等条件下水分蒸发速度慢6倍；因此，整个过程由层中的有效水扩散控制。这个方面在工业实践中对于确定管状干燥器的尺寸很重要。发现活化能受经受干燥过程的咖啡渣层厚度的影响，其值介于 8.3 kJ/mol 和 10.3 kJ/mol 之间。