Techno-economic assessment of forced-convection pre- and drying process for STR 20 block rubber

The present study focused on improving both pre‑drying and drying processes for STR 20 block rubber using a hot‑air dryer. Integrating hot‑air recirculation with controlled humidity in the drying process significantly affected thick rubber drying. Appropriate humidity control can improve the heat and mass transfer within the rubber blocks and reduce case hardening during the initial high‑temperature period. In the final stage, upward airflow provided more effective moisture removal than downward flow. Forced‑convection pre‑drying with hot air at 80 °C for 20 min proved optimal, shortening total drying time from 260 to 180 min. Specific energy consumption (SEC) decreased from 3.09 to 2.42 MJ/kg‑dried compared with natural‑convection pre‑drying. The cost saving of the proposed process was 0.53 million USD, with a payback period of 1.1 years. Overall, the proposed pre‑ and drying strategy is suitable for commercial STR 20 productions, improving both energy efficiency and drying time without compromising product quality.