Shigeo Uchida

Evaluation of dual-bed pressure swing adsorption for CO2 recovery from boiler exhaust gas

Dual-bed CO2 adsorption using zeolite was studied experimentally and theoretically. Boiler exhaust gas (13 vol% CO2, 79 vol% N2 and 8 vol% O2) was used as a feed gas for the eight-step four-bed PSA process. Na-X type zeolite (NaX) and Na-A type zeolite (NaA) were selected in the break-through test. NaX has higher CO2 adsorption capacity than other adsorbents. NaA has the highest selectivity among all adsorbents tested. In the simulations, a NaX-to-NaA ratio affected the recovery efficiency and the concentration of recovery gas. Moreover, in the dual-bed PSA process of NaX-to-NaA ratio=2/1, the recovery efficiency and CO2 concentration of recovery gas were higher than those in a single-adsorbent PSA process. Simulated results by the dynamic model agreed well with the PSA experimental results.

Minimum fluidization velocity of binary mixture of particles with large size ratio

Abstract The minimum fluidization velocities for systems of binary particles of greatly different sizes and densities have been studied experimentally. Particles of different shapes such as wood chips, rubber sheets, glass beads, iron beads, soya beans and small beans were used as coarse particles and nearly spherical fine particles of sands and glass beads were used as a fluidized medium. The correlation for the estimation of the true minimum fluidization velocity at which both coarse and fine particles are completely fluidized was obtained by the modification of the equation of Wen and Yu. This equation provides a good estimate of the minimum fluidization velocity for binary systems.

Cross-sectional distributions of gas and solid holdups in slurry bubble column investigated by ultrasonic computed tomography

Abstract A brief review on recently developed non-invasive techniques for gas–liquid and gas–liquid–solid systems is presented first. The ultrasonic computed tomography (UCT) developed for measuring the time-averaged cross-sectional distributions of gas and solid holdups in a slurry bubble column is then described. The ultrasonic tomography is a coupling of the earlier developed transmission-mode ultrasonic technique with two-parameter sensing (the energy attenuation and the velocity change) and a tomographic reconstruction technique using a filtered back-projection algorithm. The ultrasonic tomographic technique provides a method capable of measuring the cross-sectional distributions of the gas and the solid concentrations simultaneously in a gas–liquid–solid system. The technique has been applied to a slurry bubble column to get the general structures of the distributions of gas bubbles and solid particles in the column. The macroscopic flow scheme of the slurry bubble column is illustrated based on the structure of the gas holdup distribution. And the solid particle concentrating mechanism in the slurry bubble column along with the effects of gas velocity, solid loading and particle diameter is discussed.

Effect of particle diameter on fluidization under vibration

Abstract The effect of particle diameter on fluidization under vibration was studied. Glass beads with diameters ranging from 6 to 100 μm and pertaining to the Geldart groups C and A, were used as fluidizing medium. In order to examine the effect of vibration on the fluidization characteristics of the particles, minimum fluidization velocity ( u mf ), void fraction ( e mf ) at u mf and flow patterns in the bed were measured. For group C powders, u mf decreased with increasing the vibration strength, while for group A powders, u mf remained almost constant. With vibration, the flow patterns in the bed were changed, especially in the case of group C powders. For larger powders of 30 μm, channels and cracks were not observed in the bed. However, for smaller powders than 20 μm, stable channels and cracks were observed under no vibration and they disappeared by vibration. The lower limit of the gas velocity at which the channeling in the bed was not observed was lowered as the vibration strength increases. For smaller powders, the flow pattern in the bed becomes complex as various sizes of agglomerates occur and thus makes vibration difficult to propagate in the bed.

Flow structure and phase distributions in a slurry bubble column

In this paper, the axial and radial distributions of the gas and solid concentrations in a slurry bubble column are measured by an ultrasonic penetration technique, which provides a method capable of monitoring simultaneously the concentrations of the gas bubbles and the solid particles in the system. The macroscopic flow structure of the slurry bubble column is analyzed based on the structures of the phase distributions. The flow structure became important in determining the particle distribution in the column. The relationships among the gas bubble distribution, the flow structure and the particle concentration distribution are discussed. It is found that the solid particles are partly concentrated in the region near but not adjacent to the column wall and in the region between the central bubble stream and the region where the vortical-spiral liquid flow is established.

Analysis of distributions of gas and TiO2 particles in slurry bubble column using ultrasonic computed tomography

The ultrasonic computed tomography (UCT) as a coupling of the ultrasonic transmission method and the image reconstruction technique based on the iterative filtered back-projection was applied to investigate the cross-sectional distributions of gas and particle holdups in a slurry bubble column. The dispersion system of air–water–TiO2 was used in this study. The loading of the titanium dioxide particle has affected on the increase of the gas holdup. The UCT was used to analyze the macroscopic flow scheme of the system under various operating conditions. Based on the experimental results and the observation during the experiments, the macroscopic bubble flow scheme may be considered to be a helical rising flow.

Utilization of Ultrasonic Energy in a Photocatalytic Oxidation Process for Treating Waste Water Containing Surfactants

A system for treating waste water containing surfactants using a photo-oxidation catalyst combined with ultrasonic irradiation was investigated. The system consisted of two reaction chambers installed with ultrasonic transmitters of different frequencies to enhance the photo-catalytic reaction as well as to recover the photocatalyst particles used. An ultrasonic transmitter with a frequency of 200 kHz was used the reaction to enhance in the first chamber. An ultrasonic transmitter with a frequency of 28 kHz was installed for particles recovery in the second chamber. Glass beads (hereinafter GB) were used as the collectors as well as the accelerators of the agglomerated photocatalyst particles under ultrasonic irradiation. Waste water containing a surfactant, i.e., polyoxy-ethylene-alkyl-ether (C14H29O(CH2CH2)7H, hereinafter SS-70) with an initial concentration of 100 ppm and a volume of 1000 ml was used as a sample. It was confirmed that after three times of recycling tests there was no significant loss in catalyst activity.

Simultaneous Measurement of Mean Bubble Diameter and Local Gas Holdup Using Ultrasonic Method with Neural Network

One of the greatest challenges in the characterization of bubbles in a bubble column has been the prediction of the bubble diameter and the gas holdup. In this study a novel technique for predicting the mean bubble diameter and the local gas holdup using a non-invasive ultrasonic method with neural network was investigated. The measurement parameters of the energy attenuation and the transmission time difference of ultrasound are used to obtain the mean bubble diameter and the local gas holdup in an air-water dispersion system using neural network reconstruction. Bubble size distributions in a 2-D bubble column are obtained experimentally by using a photographic method. An adequate selection of the neural network structure has been carried out to represent the training data. The representative results using the present structure show good agreement with the measured data.

Ultrasonic enhancement of photo-catalytic oxidation of surfactant

Photo-catalytic oxidation of surfactant (polyoxyethylene-alkyl-ether, C14H29O(CH2CH2)7H, hereinafter referred as SS-70) enhanced by high power ultrasound is examined. The influences of the ultrasonic power and the stirring speed on the degradation rate are investigated. 1000 ml of 100ppm SS-70 is decomposed totally in about 20 minutes in the photo-catalytic process combined with the ultrasonic irradiation. Without ultrasonic irradiation, the decomposition needs more than 1 hour. The optimum conditions for the hybrid degradation process are discussed. It is found that the stirring speed largely influenced the degradation efficiency. It is considered that the catalyst particles might be localized by ultrasonic standing wave, and caused inhibition to the decomposition in the degradation process. However, by high stirring speed, the inhibition could be overcome.

Sonophotocatalysis of endocrine disrupting chemicals

Sonolysis and photolysis often exhibit synergistic effects in the degradation of organic molecules. An assay of fish oocyte maturation provides an appropriate experimental system to investigate the hormonal activities of chemical agents. Oocyte maturation in fish is triggered by maturation-inducing hormone (MIH), which acts on receptors on the oocyte surface. A synthetic estrogen, diethylstilbestrol (DES), possesses inducing activity of fish oocyte maturation, and a widely used biocide, pentachlorophenol (PCP), exhibits a potent inhibitory effect on fish oocyte maturation. In this study, the effects of the combined treatment by sonolysis with photolysis (sonophotocatalysis) to diminish the hormonal activity of DES and the maturation preventing activity of PCP was examined. By sonophotocatalysis, hormonal activity of DES was completely lost within 30 min and the inhibiting activity of PCP was lost within 120 min. These results demonstrated that sonophotocatalysis is effective for diminishing the endocrine-disrupting activity of chemical agents.