Industrial Heat Pump Dryer For Chestnuts (Castanea Sativa Mill.): Performance Evaluation

Abstract

<abstract><title><italic>Abstract. </italic></title> The production of chestnut flour is a viable alternative to their fresh consumption. The principal step of the flour production process is drying, which can be done by different methods. The traditional method uses coal as a fuel (low and uncontrolled temperature, long time, low energy consumption), whereas the most widely used method is by convection ovens based on forced warm air (temperature controlled, short drying time, high energy consumption). Therefore, an alternative drying system is desired that is energy efficient and able to preserve product quality. Drying by heat pump decreases processing costs and produces a good quality product with high value added. This research studied the performance of an industrial-sized chestnut drying plant based on a heat pump. The system, equipped with a fan, provides air at a temperature of 25°C to 30°C and at a flow rate of approximately 5 m³/s. A total of 9,430 kg (volume of 12 m³) of fresh chestnuts was processed. During the process, chestnut weight was monitored to obtain the drying curves (from 48%-50% to 7%-11% wet basis). Temperature (T) and relative humidity (RH) levels of the circulating air in the Heat Pump Dryer (HPD) were analyzed to investigate the performances. Throughout, an electric analyzer studied the energy consumption of each component of the plant in order to define all the technical parameters of the drying process. Furthermore, indices to measure the energy efficiency of the drying plant (specific consumption of fresh chestnuts regarding evaporated water, flow of water evaporated, and specific moisture extraction rate) were determined. Finally, two sensorial parameters, color (colorimeter) and odor (electronic nose), were evaluated to characterize the final product resulting from two drying methods: traditional (still locally in use) and HPD.