Two-stage optimal fixed-bed drying for natural rubber producing STR20 block rubber

Abstract

The objectives of this research were to study effect of drying parameters on two stage drying of natural rubber producing STR20 block rubber and to verify drying model program prediction of moisture transfer and specific energy consumption. The experiment was set-up at the 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> stage drying with upward inlet air temperature between 110 and 150°C (30-60 min) and the 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> stage drying with downward inlet air temperature between 110 and 140°C (100-120 min). Specific air flow rate was varied between 0.07 and 0.25 kg dry air/s-kg dry rubber while natural rubber bed-depth was varied between 0.1 and 0.3 m. The average initial moisture content of the fresh natural crumb rubber was in ranges of 38.1-52.5% dry-basis. As the results of 19 experiments, the drying kinetics exhibited only one falling rate period while drying temperature and bed depth of natural rubber relatively affected drying kinetics of crumb rubber sample. The simulation drying system program including energy consumption analysis was developed using the basic principle of near thermal equilibrium drying model. Simulation was carried out to validate the drying model against experimental results. The results conclude that the predicted results were in good agreement with experimental results. In addition, the qualities of the dried crumb rubber producing block rubber satisfied all standard STR20 criteria. The optimal drying strategy of STR20 block rubber process is the 30 cm. bed depth natural rubber drying operated under the conditions of rapid 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> drying with 130°C and following the 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> stage drying with 110°C for all drying period of 220 min.