Development Of Microwave Fluidized Bed Drying Technology And Equipment

Microwave fluidized drying technology, compared with the traditional drying method, has several advantages such as fast drying speed, high production efficiency, energy saving, cleaner production, automatic control and improvement of the quality of products and so on. Thus, microwave fluidized drying technology becomes more and more attention in the industrial production. In this study, hot air drying (HAD), microwave drying (MD), microwave fluidized drying (MFBD), microwave fluidized and microwave finish drying (MFBD+MD) were applied to tea leaves and pill. The drying characteristics of the four drying methods were studied and drying dynamic models were also established. Meanwhile, effects on qualities characteristics of the four drying methods of pill were studied to get the optimal technological condition.1. Drying fresh Jin Xuan tea was carried out by microwave drying (MD) technology and hot air drying (HAD) method. The effect of drying parameters, namely microwave power and air temperature on drying time and moisture loss were investigated. In the meantime, the rehydration characteristics and the content changes of main chemical compounds were analyzed. It is found that MD resulted in apparent decrease in the drying time and the dried products had better rehydration characteristics as compared to HAD. However, the content of total tea polyphenol and catechin compounds after MD was lower than HAD. Moreover, the tea drying kinetic models of these two methods agreed well with Page semi-empirical equation.2. MD, MFBD and MFBD+MD were carried out using the second generation microwave fluidized bed dryer. The rules of moisture change were given by studying drying characteristics of four drying technologies, including HAD, MD, MFBD and MFBD+MD.(1)During the process of HAD, the required time decreased with an increase of temperature; during the process of MD, MFBD, MFBD+MD, the required time decreased with an increase of microwave power; during the process of MFBD+MD, the required time increased with an increase of air velocity.(2)Among the four drying technologies, the required time of HAD was the longest, MFBD was longer, MD and MFBD+MD were the shortest.3. Experimental results indicate that four drying methods can meet Page equation:MR=exp(-ktN). Drying rate constant k of microwave-assisted drying methods (MD, MFBD, MFBD+MD) is significantly larger than HAD, the greater the microwave power and the larger the k. The magnolol content of dry pills, detected by HPLC, can be used to explore the quality characteristics of dry pills. Among the four drying technologies, magnolol content followed the sequence: HAD> MFBD> MFBD+MD> MD. From the characteristics of rehydration, the size of rehydration ratio followed:600W MFBD>600W MFBD+MD>70℃>600W MD>80℃>90℃>100℃. From appearance, the pills after microwave drying had burning flavour, while the others remained a beautiful shape.4. Effects of drying time, the content of magnolol, the characteristics of rehydration and apparent phenomenon were studied, and MFBD and MFBD+MD, power for600W of dry scheme in a pill dry presented superior advantages.