(146b) Behaviour of Fine Particles in a Cold Plasma-Enhanced Spouted Bed

Atmospheric-pressure nonthermal plasma technology in fluidized bed received a great deal of interest in the processes of fine particles mixing and coating. Cold plasma jet as typical process of the cold atmospheric-pressure plasma technology can be well used for thermally sensitive materials and drug particles at the temperature range of 50-300︒C. Therefore, plasma enhanced fluidized/spouted bed technology can be widely used in the mixing, granulation, and medical pharmaceuticals processes. However, few studies of the fine particles fluidized behaviour in the cold plasma-enhanced spouted bed have been reported.

In this paper, the spouted bed reactor combined with plasma generator by the low frequency (20 kHz) AC electric source was used for the experiment and the effect of plasma condition on the fluidized behavior was evaluated. White fused alumina (WA particle with the average diameter of 58.6μm) was used as the fluidized agent. In the experiments, particle volume, plasma voltage and working gas were changed. The voltage changed from 0kV to 10kV and the working gas changed Ar to N₂. X-ray diffraction (XRD) was also performed to characterize the morphological structure changes. Temperature of the spouted bed was measured by Infrared Camera (FLIR T440).

As a result, minimum spouted bed velocity (u_ms) presented the similar trend regardless of static bed height, however it decreased when the plasma applied. u_ms decreased by applying plasma regardless of the initial height. As the presence of plasma, the u_ms increased with increasing the static bed height, it was consistent with the trend of absence case.

In the case of static height of fine particles and plasma voltage as the constant, the u_ms declined that associated with increment of plasma voltage. Higher plasma voltage decreased u_ms, while higher plasma voltage deteriorated fluidization because of strong ionization. Under situations of setting up static height of fine particles and flow rate to be constant values, the particles maintained as fixed bad until plasma voltage high enough. In the higher flow rate (remain in fixed bed) conditions, lower plasma voltage as required for fluidization. The same trend was obtained compared with the aforesaid study with nuances since ionization easier to form with the stable plasma voltage supplement.

N₂ and Ar, two plasma gases, were investigated in the process of fine particles behaviour in spouted bed. Due to the difference of density, the u_ms with Ar was higher than of N₂. With the addition of plasma, u_ms decreased slightly with increasing plasma voltage as well by N₂. Thus, low voltage was more suitable for fluidization in the spouted bed with plasma-enhanced both by Ar and N₂.

Plasma light under the N₂ atmosphere was weaker than that under the Ar condition though camera and observation. Ar plasma light began to bring out about 3kV with lower flow rate, and N₂ needed around 7-8 kV for plasma. The mixture Ar and N₂ (ratio of 1:1) was taken out to in comparison with the calculated data by pure gas, whose error was within 5%. Meanwhile, the higher plasma resulted in the higher UV light. The surface temperatures in the middle point and top point of the reactor were same. Whereas, temperatures in inlet point were increased to about 40︒C（Ar）and 70︒C（N₂）. It can be taken no account of the temperature effect on the fluidization. XRD results illustrated that there were no significant changes after the plasma treatment for the fine particles.