The rotary reactor efficiently produces high-quality activated carbon from areca spathe at 700–900 °C with 50–100 cm³/min steam for 60–180 min, ensuring uniform activation and well-developed pore structure. It delivers consistent industrial-grade quality with low operating costs (67.35 THB/kg electricity, 0.3 THB/kg water) and a 3.9–5.2-year payback, enabling scalable, sustainable waste-to-resource production.