Bidirectional hot air drying: an effective inhibitor of the browning of biomass similar to thick-layered honeysuckle

Large amounts of Chinese medicinal materials (CMMs) should be quickly dried during the harvest period because improper drying leads to a browning reaction, which deteriorates the medicinal value of CMMs. In this study, a bidirectional alternating hot air drying system was designed for thick-layered CMMs. The drying capacity could be greatly improved by increasing the thickness of the material layer. The time-weighted average temperature (TWAT) was defined to determine the appropriate reverse time of the airflow direction. The two-stage air supply could reduce the moisture content of the sample to a certain degree at a low temperature, and then realizing the rapid drying of the sample at a high temperature. When the moisture content of honeysuckle reduces to 60%, the browning reaction would be effectively inhibited. Moreover, the drying efficiency of the thick layer could be improved by reducing the frequency of changes in the direction of hot air. An equal TWAT could be obtained in each layer by adjusting the ratio of the upward to downward airflow supply duration. When the TWAT of the upper layer was equal to that of the lower layer, the drying uniformity improved. The difference between the moisture content of the middle layer of the sample and that of its upper and lower layers could serve as the standard for drying uniformity; the smaller the difference is, the better the drying uniformity will be. The bidirectional alternating hot-air drying method was applied to thick layer drying of Chinese herbal medicine and grain. On the one hand, it reduces the drying energy consumption, on the other hand, it helps to improve the uniformity of drying for Chinese herbal medicine. Additionally, this drying method can be applied for grain drying.

Automated summary

A bidirectional alternating hot air drying system was designed for thick-layered Chinese medicinal materials, which significantly improved drying efficiency and uniformity by controlling airflow direction and temperature.