Walnut Drying by Combined Drum Catalytic Infrared with a Variable Temperature and Hot Air
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Abstract:
In order to improve the drying efficiency of hard shell nuts, this work developed a new type of multi-unit drum-type catalytic infrared drying equipment with a variable temperature, and adopted a combined drying technology of drum catalytic infrared with a variable temperature and hot air. In this work, the walnut drying effect, energy consumption and kinetic process were studied. The results showed that the catalytic infrared temperature, radiation distance, and rotating speed of the drum all had significant effects on the drying performance. After 22.50 min of infrared radiation pre-drying under the optimal radiation temperature of 300+400 ℃, radiation distance of 30 cm and rotation speed of 25+35+35 Hz, and then 14 h of hot air drying under the temperature of 43 ℃ and speed of 3 m/s, the total drying time was 14.38 h. Compared with that of single hot air drying, the drying time was shortened by 28.10% and the energy consumption was saved 25.04%. The dried walnut shell had no brown spots, the shell opening rate was 0%, the L value was 54.24, the a value was 10.61, the b value was 19.89 and the color was bright red and yellow. In addition, the maximum drying rate (0.28 g/g·min) was significantly higher than that of the single hot air drying (0.11 g/g·min). Correspondingly, the Henderson-Pabis model established can well predict the changes of water content and drying rate of walnut in the drying process and the fitting effect was good with R2 of 0.99 and RMSE of 0.03. Therefore, the combined drying technology of drum catalytic infrared with a variable temperature and hot air is a kind of new type drying method with high efficiency and energy saving, suitable for drying nuts products.
