Citrus residue is a large-scale agro-industrial biowaste that can become a source of renewable energy through drying. Drying demands high power consumption due to the low energy efficiency of this process in the industries. In this work, the energy performance of the drying process in a semi-industrial rotary drum of 2.7 m length and 0.45 diameter was analyzed. The main objective was to find the operational condition for the lowest energy consumption and also the highest energy, drying and exergetic efficiencies. The experiments were performed under different solid mass flow rates (0.2 and 0.4 kg/min) inlet air velocities (1 and 2 m/s) and temperatures (135, 145, and 155 °C). The average energy efficiency was 13.1% with 25.1% of drying efficiency, 37291.3 kJ/kg of specific energy consumption, and 37.3% of exergy efficiency. The results showed that the drying technique can be an interesting alternative to add value to the citrus residue.