Performance evaluation of a biomass-fired parallel-flow tray dryer for orthodox black tea processing

The uniform and efficient drying process is still a big problem in the decentralized orthodox tea industry, especially in the field of using cost-effective and eco-friendly thermal drying equipment. In this study, an experimental evaluation of a biomass-fired parallel-flow tray dryer with 15° inclined airflow-guiding plates was conducted to explore the drying performance, moisture uniformity, and energy-efficiency for the drying system. For processing an 11 kg tea batch, seven tea trays with perforations were used, and the temperature, airflow velocity and sample mass were systematically monitored. The drying chamber had a temperature of about 70–100 °C and the process was finished in 199 min, with the increase in the inlet velocity from 2.0 to 2.5 m s⁻¹ by opening the airflow-control valve. Spatial non-uniformity of drying was observed with final moisture contents of 9.18% and 4.63% at 2 monitoring positions. The total moisture removal efficiency was estimated at 3.11%, which shows great potential for thermal optimization. The Page model was selected as the best model over the Lewis model and was not validated independently. This data is preliminary quantitative evidence for engineering decisions related to the regulation of airflow, combustion control and heat recovery. The prototype has potential to be decentralized tea processing system but needs to be replicated for testing and optimize the heat management before commercialization.