| Summary: | 碩士 === 國立臺灣大學 === 環境工程學研究所 === 91 === High-gravity rotating packed bed (HGRPB) gas-liquid contactor is characterized by its high mass transfer efficiency, small spatial requirement, low energy consumption, and low capital and operating costs. This technology can be applied to the processes of distillation, absorption, gas stripping, and diffusion-controlled gas-liquid reaction. The present study focuses mainly on the characteristics of the gas-liquid mass transfer and ozonation of reactive dye of Reactive Black 5 (RB5) in the HGRPB.
Four parts of experiments are conducted in this study. Oxygen transfer into water using HGRPB (system A, with bed volume VB of 0.000335 m3) with continuous operation is investigated in the first part. The effects of various operation parameters upon the oxygen mass transfer coefficient ( ) are examined, including rotating speed (N), liquid flow rate (QL), and gas flow rate (QG). The oxygen mass transfer coefficients of HGRPB ( ) of 0.056 — 0.145 s-1 are larger than those of the conventional packed bed ( ) of 0.0004 — 0.07 s-1. The conditions of the experiments of this part are: QL of 0.52 — 1.29 L/min, QG of 1.19 — 4.40 L/min, and N of 400 — 1500 rpm.
The liquid holdups (εL) of HGRPB (system B, with VB of 0.000185 m3) affected by various operation parameters are studied for the continuous system in the second part. The results indicate that εL is proportional to N, superficial gas velocity (uG,1), and superficial liquid velocity (uL,2) with powers of -0.148, -0.015, and 0.646, respectively. Thus, εL is strongly effected by uL,2. The experimental conditions of this part are: QL = 0.15 — 1.29 L/min, QG = 1.19 — 4.40 L/min, N = 300 — 1500 rpm。
The mass transfer of ozone into water using HGRPB (system B) are examined in the third part. For semi-batch operation with recycled liquid, the dissolved liquid ozone concentration (θALb) increases with time and approaches to a steady state value at a certain time tss which decreases with increasing values of N and QL. The mass transfer coefficients of ozone and oxygen are further determined in continuous HGRPB (system B) by simulation. The results show that the ratio of the mass transfer coefficients of ozone and oxygen ( / = 0.0975 s-1/0.111 s-1 = 0.88) with high liquid flow rate (QL = 0.60 L/min) and rotating speed (N = 1500 rpm) is closed to the ratio of the square roots of diffusivities ((DA/ DO)0.5 = (2.0×10-9 m2/s)/(2.5×10-9 m2/s))0.5 = 0.8944) calculated by the penetration theory. This means that the penetration theory is more applicable to HGRPB than the film theory. The results also show that the of 0.0975 s-1 with higher QL of 0.60 L/min, and N of 1500 rpm, is about 4.31 times of of 0.0226 s-1 with lower QL of 0.30 L/min, and N of 300 rpm. Further applying the penetration theory, of 0.0226 — 0.130 s-1 and of 0.0253 — 0.145 s-1 can be estimated in the conditions of the experiments with QL = 0.30 — 1.29 L/min, QG = 1.19 — 4.40 L/min, and N = 300 — 1500 rpm。.
The HGRPB (system B) for semi-batch operation with recycle liquid is employed to the ozonation of RB5 in the fourth part of the experiments. Comparison of the efficiencies of ozonation with ozone introduced in different reactors, say HGRPB and CSTR (continuous stirred tank reactor), is made. The volumes of HGRPB (VB) and CSTR (VT) are 0.185 and 5.5 L, respectively. By considering the effect of VB and VT, the average mineralization rates of RB5 in HGRPB of 0.582 — 3.124 mg/L2-min are about 20.7 — 25.3 times of those in CSTR of 0.023 — 0.151 mg/L2-min. The results indicate that HGRPB is more efficient than CSTR in per reactor volume basis.
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