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Yong Kang
Article type: Preface
2008 Volume 41 Issue 7 Pages
531-532
Published: July 20, 2008
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Following the successful achievement of previous nine conferences, the 10th Asian Conference on Fluidized-Bed and Three-Phase Reactors (ASCON-2006) was held in Busan, Korea, during November 26–29, 2006, in order to exchange and share current research ideas, information and experiences on the Fluidized-Bed and Three-Phase Reactors. Needless to say, the conference (ASCON) has grown up in a sense of the high quality of papers presented and the active participation of the top scientists and engineers from neighboring Asian countries.
In the mean time, publication of the papers in the regular international journal has been discussed in the committee of international coordinators of the conference, in order to expand the scientific dialogues and concepts that had been spawned in the fields of topical relevance during the conference.
The encouragements of President Kunio Yoshida (Niigata Sangyo University), Emeritus Professor Wei-Ming Lu (National Taiwan University), Professor Sang Done Kim (Conference Chairman, KAIST), President Shigeo Uchida (Polytechnic College of Hamamatsu) and Professor Lii-Ping Leu (National Taiwan University) had been the basis idea for the preparation of special issue for the latest conference (ASCON-2006). This special issue is the first outcome in the series of Asian Conference on Fluidized-Bed and Three-Phase Reactors having appeared as a special issue in one of the international leading journal,
Journal of Chemical Engineering, Japan (JCEJ). During the selection of the journal, the devotions of President S. Uchida (Polytechnic College of Hamamatsu), Professor A. Tsutsumi (The University of Tokyo) and Professor T. Kojima (Seikei University) had been valuable actions.
All the submitted manuscripts for publication in the special issue were reviewed following the standard procedure for papers submitted to the regular issues of the journal. Finally, 34 papers were accepted for publication in the special issue, covering wide range of research areas from fundamental aspects to the practical applications in the fields of fluidized beds and three-phase reactors.
We have to extend our sincere appreciation to more than 90 professionals in Japan, Korea and Taiwan for their valuable help for peer reviewing the submitted manuscripts. In addition, our deep appreciation has to be expressed to Professor Naoto Ohmura, the Editor-in-Chief of the
Journal of Chemical Engineering, Japan, for his valuable support and to Ms. Yamashita in the editorial office of the journal for her persistent devotion to the preparation of this special issue.
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Hiroki Uchiyama, Toshifumi Ishikura, Mitsuharu Ide
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
533-539
Published: July 20, 2008
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Gas holdup distribution in a gas bubble dispersed phase generated by an impinging gas–liquid two-phase jet was measured with an optical fiber void probe. The effects of structural factors of nozzle and column diameter on gas holdup distribution were investigated.
The effects of structural factors of nozzle and column diameter on gas holdup distribution were similar to the column average gas holdup. Measured values of the probe were validated by a comparison with column average gas holdup. As a result, it was found that gas holdup distribution in the jet absorber was given by the sum of the gas holdup distributions of descending bubbles and ascending bubbles.
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Sang-Wook Park, Byoung-Sik Choi, Kwang-Joong Oh, Jae-Wook Lee
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
540-546
Published: July 20, 2008
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Carbon dioxide was absorbed into an aqueous nanometer sized colloidal silica solution of 0–31 wt% and triethanolamine of 0–2 kmol/m
3 in a flat-stirred vessel with an impeller size of 0.05 m and speed of 50 rpm at 25°C and 101.3 kPa to measure the absorption rate of CO
2. The measured rate of CO
2 absorption was compared with the values estimated from the model based on the film theory accompanied by chemical reaction. The volumetric liquid-side mass transfer coefficient (
kLaL) of CO
2 decreased with increasing silica concentration and was expressed as an empirical correlation formula presenting the relationship between
kLaL and the rheological behavior of the aqueous colloidal silica solution. Reduction of the measured
kLaL was explained by the viscoelastic properties of the aqueous colloidal silica solution.
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Masanori Yoshida, Masaki Minamoto, Kazuaki Yamagiwa, Akira Ohkawa, Shu ...
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
547-552
Published: July 20, 2008
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Gas–liquid mass transfer was studied experimentally for an air–water system in an unbaffled vessel with a liquid height-to-diameter ratio of 2:1 that was agitated by unsteadily forward-reverse rotating multiple impellers which alternated rotation direction. Two kinds of four-bladed impellers were used with different designs of triangular delta blades. One (S impeller) has a straight blade with a downward triangle apex throughout. The other (T impeller) has a twisted blade composed of an inner downward part and an outer upward part. With both the impellers, enhancement of the mass transfer was observed with increases in the liquid-phase mass transfer coefficient as well as the gas–liquid interfacial area that determine the magnitude of the volumetric coefficient characterizing the rate for water to absorb oxygen in air. The respective dependences of mass transfer parameters on the axial position within the vessel were evaluated for the mean bubble diameter and gas hold-up. T impeller produced a gas–liquid interface with a larger area and more uniform distribution than S impeller. The effect of forward-reverse agitation using the delta blade impellers on formation of the gas–liquid dispersion was confirmed in relation to the behavior of gas bubbles within the vessel.
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Kei Mizuta, Yuka Odo, Shiho Yoshimitsu, Hitoshi Kaji, Miwako Murakami, ...
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
553-556
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The mass transfer characteristics of a gas dissolution process around a single stationary bubble were investigated experimentally. The two-color laser induced fluorescence (LIF) technique and particle image velocimetry (PIV) were utilized to evaluate the instantaneous planar pH and velocity distributions, respectively. The results show that the development of the pH and the velocity distribution during the dissolution process were properly evaluated. Moreover, the change in mass transfer characteristics were closely correlated with the development in the pH and velocity field.
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Hideki Tsuge, Takamasa Ogawa, Ryushin Ohmasa
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
557-561
Published: July 20, 2008
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By electrolysis of water using new mixing equipment with low frequency vibratory fins, microbubbles of oxygen and hydrogen were produced for NaOH electrolyte. The effects of operating parameters of the mixing device, that is, vibrating frequency of fins, concentrations of electrolyte and electrolysis current on the average bubble diameter, bubble size distribution and gas holdup were investigated. This operation shows a new microbubble generation method.
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Yoshiyuki Bando, Takashi Yoshimatsu, Wenji Luo, Yufei Wang, Keiji Yasu ...
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
562-567
Published: July 20, 2008
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The flow characteristics and decomposition performance in the cocurrent upflow bubble column dispersed with micro-bubbles were experimentally examined. A micro-bubble generator was installed at the bottom of the column, and for comparison the sintered glass gas sparger was set at the lower part of the column.
When milli-bubbles coexist with dispersed micro-bubbles, micro-bubbles disappear. This is considered because micro-bubbles are absorbed into the wake of milli-bubbles. The volumetric mass transfer coefficient is higher for micro-bubbles than for milli-bubbles, but the mass transfer coefficient is much lower for the former than for the latter. The apparent decomposition rate constant strongly depends on the volumetric coefficient. When the volumetric coefficient is higher, the rate constant of micro-bubbles is higher than that of milli-bubbles.
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Makoto Yoshimoto, Keiji Furumoto, Fumio Azakami, Toru Hasuoka, Tetsuya ...
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
568-577
Published: July 20, 2008
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A triple electroresistivity probe was newly developed to detect the bubbles whose centers moved upwards through it and to measure their rise velocities and sizes (central chord lengths). The probe was designed based on the directional coincidence of the probe axis with the bubble motion, as required to determine the bubble velocity, as well as on the positional determination of the bubble chord detected, as required to obtain the chord length. The conventional double probe has a difficulty in sampling its signals for the bubbles moving vertically and in determining which chord of the individual bubble is detected. The measurements of the behaviors of bubbles with the triple probe were made for two different sizes of normal bubble columns and an external loop airlift bubble column with the liquid and solid phases performed batchwise under a wide range of operating conditions. An analysis of the signal sequences obtained by the probe was proposed which considered the effects exerted by the complicated behaviors of both bubbles and particles. The method gave the results on the local bubble frequency and gas holdup, as well as on distributions of the bubble central chord length and bubble rise velocity at a given radial position of the column. These results suggested an enhanced interaction between bubbles, such as their coalescence and breakup, due to the presence of solid particles. The radial profiles of the bubble frequency, the gas holdup and the mean bubble size and rise velocity, were found to depend on the bubble column type, operating conditions and physical properties of liquid and solid particles.
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Katsumi Nakao, Keiji Furumoto, Fumio Azakami, Toru Hasuoka, Tetsuya Im ...
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
578-584
Published: July 20, 2008
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In the present study, the local superficial gas velocity was calculated as a sum of the contributions of the size and frequency, or the rise velocity and gas holdup, of the individual bubbles rising vertically through the probe. A correction factor
αi for any detected bubble
i was needed to take into account the probability that some of the bubbles vertically approaching the probe might not be detected due to the chaotic behaviors of bubbles and liquid. The reciprocal of
αi was regarded as the bubble detection efficiency of the probe. The value of
αi was assumed to be specific to the gas–liquid flow pattern, i.e., the bubble, churn-turbulent or slug flow. As a result, the effects of the various operating conditions on the radial distribution of the gas velocity were determined. The distribution was found to be more remarkable for the higher superficial gas velocity and for the smaller column diameter.
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Yongwon Seo, Sung-Ho Jo, Ho-Jung Ryu, Chang-Keun Yi, Gyoung Tae Jin
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
585-589
Published: July 20, 2008
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This study investigates one-step dimethyl ether (DME) synthesis from coal-derived, CO-rich syngas over a bifunctional catalyst comprising a methanol synthesis catalyst (Cu/ZnO/Al
2O
3) and a methanol dehydration catalyst (
γ-Al
2O
3). The liquid-phase DME synthesis was carried out in a slurry reactor that provided good mixing and excellent heat removal. Higher CO conversion and DME space time yield (STY) were observed at a higher reaction temperature and a higher pressure. A lower gas hourly space velocity (GHSV) caused higher CO conversion, but a lower DME STY. Excessive content of
γ-Al
2O
3 had an adverse effect on both CO conversion and DME STY. Among various H
2:CO ratios, the maximum DME STY (13.5 mol/kg-cat/h) was observed at a H
2:CO ratio of 1.0. CO
2 in the feed syngas had a negative effect on DME synthesis. The results and data obtained in this study can be used as basic data for the design and operation of a large scale bubble column reactor and for further application to a three-phase fluidized bed reactor.
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Jung hoon Park, Sang do Park
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
590-596
Published: July 20, 2008
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Alaska coals were extracted with sub- and supercritical water (SCW) using a micro reactor. Conversion of coal was studied in the temperature range of 320–400°C, pressure 15–30 MPa and water density 0.06–0.7 g/cm
3 for 0–2 h. The experiments were conducted to investigate the effects of reaction temperature, pressure and water density on gas and liquid products respectively. The results show that the coal conversion in supercritical condition was higher than in sub-critical condition. The hexane soluble liquid product of original coal reaches a maximum 18.8% in the reaction time of 90 min at 400°C and 30 MPa. The contents of CO, CH
4, and H
2 form especially well at supercritical condition. It is seen that supercritical condition was favourable to the hydrogen formation. With the increase of temperature, the sulfur in coal releases into the liquid and gas effluents. And the sulfur removal in liquid effluents is much greater than that in gas effluents. Higher water density causes higher conversion due to promotion of hydrolysis in coal extraction.
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Hee-Chul Yang, Yong-Zun Cho, Hee-Chul Eun, Yong Kang
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
597-601
Published: July 20, 2008
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The destruction of trichloroethylene (TCE) was studied in a bench-scale two-stage molten salt oxidation (MSO) reactor system under oxygen-rich conditions from 1023 to 1173 K, with varying gas residence times from 0.95–1.38 s. Traces of some chlorinated organics such as C
2H
4Cl
2, C
6H
4Cl
2 and C
6H
5Cl were found as by-products during low-temperature test runs (1023 K and 1173 K). However, the major product of an incomplete combustion (PIC) was found to be carbon monoxide (CO), of which emissions were greatly reduced by the increase in the reactor temperature. Destruction and removal efficiency (
DRE) of 99.999972–99.999999% and chlorine retention efficiency (
CRE) of 99.9985–99.9996% were achieved during TCE destruction. The results of this study suggest that the MSO technology is a more promising technology for the control of TCE emissions from industrial cleaning processes, when compared with other currently applicable technologies.
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Pyung Seob Song, Byung Youn Min, Wang Kyu Choi, Chong Hun Jung, Won Zi ...
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
602-606
Published: July 20, 2008
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Characteristics of radionuclide distribution on the melting conditions, flux types, and kinds of radionuclide were investigated in an electric arc furnace. The results of the radionuclide partitioning in the oxidation conditions showed a similar trend with the results in the inert gas conditions. In contrast to the removal of the cobalt in the melting decontamination of the steel wastes, it was easily removed to the slag phase in the aluminum melting process.
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Byung Youn Min, Pyung Seob Song, Wang Kyu Choi, Chong Hun Jung, Won Zi ...
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
607-611
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The partitioning phenomena of radioisotope cobalt-60 (
60Co) and cesium-137 (
137Cs) from a molten ingot, slag, and dust have been investigated for the effect of the slag type, slag concentration and basicity in a plasma arc melting process. A direct current plasma arc furnace was used to melt contaminated stainless steel, and mild steel with an acid, neutral, and basic slag (SiO
2, CaO, Al
2O
3, Fe
2O
3, MgO) containing radioactive
60Co and
137Cs, to measure the partitioning phenomena. Calcium oxide and ferric oxide were added to provide an increase in the slag fluidity and oxidative potential, respectively. Most of the
60Co remained in the ingot phase and was barely present in the slag.
60Co decontamination factor was not highly dependent on the slag composition. The distribution ratio of
60Co the ingot and the slag phase showed that about 90% to 95% was recovered in the ingots.
137Cs was completely eliminated from the melt of the stainless steel as well as the carbon steel, and was distributed to the slag and dust phase. The partition remaining in the slag depended on whether the slag was basic or acidic and had a high oxidative flux (Fe
2O
3). A maximum of 52% of the
137Cs remained in the slag phase with an acid slag.
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Yong-Soo Seo, Sung-Ho Hong, Kyoung-Hee Kim, Il-Kyu Kim, Jea-Keun Lee
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
612-617
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The objective of this study was to investigate the performance of a two-stage biotrickling filter system installed for the control of odorous compounds in the emission gases from a food waste fodder manufacturing process. During long-term operation, 150 days, the removal efficiencies of total hydrocarbons were within the range of 90 to 98%. The major odorous compounds; especially aldehydes and sulfur compounds, were removed by up to 97.9 and 91.6%, respectively. The elimination capacity in the first stage of the system was much higher than that in the second stage. The elimination capacities in the first and second stages were approximately 223 and 73.4 g/m
3-filter bed-hr, respectively.
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My-Le Du, Jun-Heok Lim, Jea-Keun Lee
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
618-623
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A laboratory sequencing batch biofiltration reactor (SBBR) packed with 1 inch zeolite-containing polyethylene media was used to remove organic matter and nutrients from synthetic wastewater. The effects of the anoxic/aerobic time ratio and the mass ratio of chemical oxygen demand to total nitrogen (known as C/N mass ratio) on the performance of SBBR were investigated. Throughout the experiment, the anoxic/aerobic time and C/N mass ratios varied ranging from 0.1–1.0, and 3–10, respectively. The SBBR had a chemical oxygen demand (COD) removal efficiency of 98% as well as a total nitrogen (T-N) removal efficiency of up to 97%, and a total phosphorous (T-P) removal efficiency of 67%. These highest efficiencies were obtained at the anoxic/aerobic time ratio of 0.5 and the C/N mass ratio of 10.
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Joon Sup Park, Woo-Sik Kim, Jong Min Kim, In-Ho Kim
Article type: Short Communication
2008 Volume 41 Issue 7 Pages
624-626
Published: July 20, 2008
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Ibuprofen racemates were separated in a SMB system with 4 chromatographic columns packed with TBB gels. Retention times of
R- and
S-enantiomers of ibuprofen were measured in batch chromatography experiments with hexane/TBME/acetic acid mixed solvent. Isotherm parameters of SMB were calculated from the batch chromatography data, and operation flow parameters obtained from m2 and m3 plane of Morbidelli and coworkers (Abel
et al., 2004). Experimental results are summarized as purities of raffinate. In order to compare experiments with simulations, ASPEN Chromatography Simulator was adopted. Isotherm and operation parameters were inserted to the dialog box of the simulator and output display data was cropped for comparison of experiments and simulations.
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Chang-Sup Oh, Sharad D. Bhagat, Yong-Ha Kim, Bum-Chul Woo, Young Soo A ...
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
627-630
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Because of their extremely large surface area, carbon nano tubes (CNTs) and carbon nano fibers (CNFs) have been widely used to remove heavy metals from water. But the removal of such CNTs and CNFs from water is another important aspect in water purification process. In the present work, we discuss CNT and CNF separation from water using a magnetic separation technique. In order to compare the separation efficiencies, CNTs and CNFs having wide variation in their magnetic properties were selected. The effects of CNT and CNF concentrations in untreated water and water flow velocity on the separation efficiency were investigated systematically.
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Jung hoon Park, Sang do Park
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
631-638
Published: July 20, 2008
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The formation of nano-sized barium titanate powders by hydrothermal reaction between barium hydroxide octahydrate and hydrous titania was studied at various temperatures, times and reactant concentrations without mineralizer. FTIR, TGA, SEM, XRF, BET and XRD were used to investigate the effects of temperature, time and concentration on reactivity, particle size, morphology and secondary phase of BaTiO
3 powder prepared hydrothermally. The main impurities were BaCO
3, TiO
2, surface H
2O and lattice OH
– radical at low conversion while secondary phase such as the lattice hydroxyl radical and trace BaCO
3 remained at high conversion. As the temperature and time increased in low concentration reaction below 0.5 M, the maximum conversion could not exceed 98% but the conversion increased with increasing concentration, reaching over 99% above 1.5 M. In addition, concentration of more than 1.5 M was favorable to smaller particle size, better sphericity and Ba/Ti ratio ≒ 1. Kinetic analysis by the Johnson–Mehl–Avrami plot shows hydrothermal reaction progresses through solidification path. Initially, dissolution-precipitation mechanism takes place to form the nuclei of BaTiO
3 through fast dissolution of TiO
2·
xH
2O and reaction with Ba
2+ ions and then the BaTiO
3 crystal begins to grow.
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Je-Jung Yun, Tae-Young Kim, Sung-Yong Cho, En-Mei Jin, Hal-Bon Gu, Kyu ...
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
639-643
Published: July 20, 2008
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Platinized stainless steel sheet (PSSS) can be used as an alternative counter electrode in dye sensitized solar cells (DSSCs). The conversion efficiency of a typical platinized fluorine-doped tin oxide (PFTO) counter electrode in DSSC was 3.1%. With PSSS, however, an efficiency of 4.7% was achieved. The enhancement of conversion efficiency is approximately 150%. This result was obtained by introducing PSSS as a counter electrode which decreased the resistance of charge transfer on tight bonding between the interface of the platinum particles and stainless steel sheet substrate and large grain size of Pt cluster of counter electrode. These results were supported by measurements by X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy(EIS).
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Chan-Gi Lee, Masato Uehara, Hiroyuki Nakamura, Hideaki Maeda
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
644-648
Published: July 20, 2008
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Microreactors can be used for continuous operation and precise control of heating conditions in chemical synthesis. Therefore, microreactors are expected to offer a more efficient strategy for obtaining homogeneous nanocrystals and easier of size control than the general batch reaction system. CdSe nanocrystals can be turned into emission color by controlling the size of nanocrystals. In this study, we synthesized CdSe nanocrystals by a multiphase microreactor. The CdSe nanocrystals were coated with ZnSe and ZnS by using the multiphase microreactor. The nanocrystals are coated on their surface with a shell of a larger band gap semiconductor, which can improve luminescence efficiency. Furthermore, we investigated the residence time in relation to size of nanocrystals and optimized the coating layer thickness.
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Chang-Hyung Choi, Jae-Hoon Jung, Tae-Ho Yoon, Dong-Pyo Kim, Chang-Soo ...
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
649-654
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The geometric effect of microfluidic channels on the production of monodispersed alginate hydrogels was investigated. The general flow focusing design could not produce stable hydrogels because the synthesis between alginate and calcium chloride at the junction strongly depends on the diffusion limited reaction. The addition of winding microchannels as a mixing line could not perfectly solve the diffusion problem because imperfect mixing of alginate and calcium solutions results in unstable generation of alginate microbeads and merging of the produced alginate beads in the microfluidic devices. The last microfluidic design adopted a mechanism in which the droplet formation was based on a biased shear-force-driven break-off to improve rapid droplet formation and mixing efficiency. The final design of microfluidic device could promptly produce the stable monodispersed-hydrogel beads.
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Sung Mo Son, Suk Hwan Kang, Uk Yeong Kim, Ik Sang Shin, Yong Kang, San ...
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
655-661
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Characteristics of oxygen transfer were investigated in the riser of a viscous three-phase circulating fluidized bed, with a diameter of 0.102 m (ID) and a height of 3.5 m. Effects of gas (0.01–0.09 m/s) and liquid (0.12–0.43 m/s) velocities, fluidized solid particle size (1.0, 1.7, 2.1, 3.0 mm), solid circulation rate (2–8 kg/(m
2·s)) and liquid viscosity (0.96–38 mPa·s) on the volumetric oxygen transfer coefficient in the riser were examined. The oxygen transfer coefficient was found to increase with increasing gas velocity, particle size and solid circulation rate, while it decreased with increasing viscosity of the continuous liquid medium, and changed very little with the variation of liquid velocity. The oxygen transfer coefficients were well correlated in terms of dimensionless groups as well as operation variables.
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Toshio Tsutsui, Kazuya Ijichi, Shin-ichi Miyashita, Hiroaki Kodama, Ya ...
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
662-669
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Effect of fine particle addition on the fluidity of industrial catalyst was investigated. It was found that the fluidity depended not only on particle diameter and particle density, but also surface properties of particles. If the surface was smooth, even if they were Geldart’s group A particles, slugging or channeling tended to arise in the bed. When fine powders of a diameter less than 2 μm were added to poorly fluidizing catalyst particles by 0.015 wt%, the fluidity was drastically improved. This effect was considered due to lowering excessively strong van der Waals force acting between the A-type particles with smooth surface by the existence of fine powders adhering on the surface. It was found that the minimum quantity of the fine powders for improving fluidity depended on the size of the fine powders. The improvement was found continuing for several hundred hours at 0.2–0.4 m/s superficial velocity.
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Jun-Sik Kim, Atsushi Tsutsumi, Yong Kang
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
670-677
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Nano particles (7 nm TiO
2) added coarse particle (100 μm Al
2O
3) fluidization was carried out in a 2-D column. Influences of nano particle addition on hydrodynamics and heat transfer in gas–solid fluidized beds were investigated. The flow behavior and heat transfer were evaluated with Kolmogorov entropy (
K) of the pressure fluctuation and heat transfer coefficient (
h), respectively. It was found that
K is drastically increased as the ratio of nano particle addition increased, whereas
h is exponentially decreased in accordance with the unstable flow behaviors. From SEM images, the sizes of nano agglomerates fragmented and the nano agglomerates on the surface of coarse particle were observed. The flow regimes with the variation of nano particle ratio were classified into a fragmented agglomerate flow and a surface dispersed agglomerate flow. It was also found that the agglomerate film around the surface of heater and coarse particles acted as a dominant resistance source of the heat transfer.
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Tsutomu Nakazato, Kunio Kato
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
678-685
Published: July 20, 2008
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The effects of particle size and weight fraction of fine powder (group C) upon the entrainment rate of bed particles (groups B + C or groups A + C) and fine powder were investigated in a fluidized bed and in a circulating fluidized bed. The entrainment rates and elutriation rate constants of the bed particles and fine powder were strongly affected by the particle size and the weight fraction of fine powder in the bed. A clear difference was observed in the dependence on the weight fraction of fine powder in both the entrainment rate of bed particles and the ratio of the elutriation rate constant of fine powder to that of coarse particles between the B–C and A–C binary particle systems. When fine powder of 6 μm or smaller was added, the elutriation rate constant of fine powder decreased as the mean diameter of the bed particles decreased from 40 μm. On the other hand, addition of group C powder of larger than 10 μm to group A particles showed very good fluidization with the large entrainment rate of the bed particles.
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Jeong Hoi Goo, Myung Won Seo, Dong Kyoo Park, Sang Done Kim, See Hoon ...
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
686-690
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A cold model dual fluidized bed gasifier was designed and constructed to determine the hydrodynamic properties in a bubbling fluidized bed and in a riser using silica sand (260 μm) as the bed material to determine the optimum operating conditions for stable heat supply between the two reactors for the biomass gasifer operation. Solid circulation rate was measured as a function of gas velocity and solid inventory and the obtained data was correlated in terms of Froude number and a ratio of aeration and particle terminal velocities. Flow regimes and the axial solid holdup distribution in the riser were determined as a function of gas velocity and solid circulation rate.
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Chang-Keun Yi, Sung-Ho Jo, Yongwon Seo
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
691-694
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The performance of the CO
2 capture of a potassium-based dry sorbent was investigated in a dual circulating fluidized bed process. The dual circulating fluidized bed process consisted of a carbonation reactor and a regeneration reactor. It was operated in the continuous solid circulation mode between a fast fluidized-bed carbonator of 6 m in height and a bubbling fluidized-bed regenerator. As the solid circulation rate increased from 7 to 36 kg/m
2/s, the CO
2 removal of the potassium sorbent, sorbKX40, increased from 25 to 55% and the mean voidage was maintained from 0.94 to 0.99 representing the dilute phase in the fluidization regime. The continuous solid circulation behavior in a dual fluidized bed process was well expressed by a single closed loop in a pressure balance curve that indirectly explained the direction of the sorbent flow and the mean bulk densities of the gas–solid mixture. The information on hydrodynamics and sorption capacity will be used for the conceptual and scale-up design of the system.
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Tak-Hyoung Lim, Sang Done Kim
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
695-699
Published: July 20, 2008
Released on J-STAGE: July 20, 2008
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The photocatalytic degradation characteristics of TCE, acetone, and toluene have been determined in a circulating fluidized bed (CFB) photoreactor system over TiO
2/silica gel photocatalyst. The conversions of acetone and toluene decrease with the initial acetone and toluene concentrations in the CFB reactor. Water vapor enhances the photo-degradation rate of toluene, but inhibits it for trichloroethylene (TCE) and acetone. The photocatalytic conversions of TCE and acetone exhibit a maximum value at 318 K but that of toluene exhibits a maximum value at 298 K. The optimum oxygen concentration for the maximum degradation of acetone and toluene are found to be approximately 10% and 7%, respectively. The present circulating fluidized bed (CFB) photoreactor system is an effective tool for higher degradation of volatile organic compounds (VOCs) with efficient utilization of photon energy.
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Gook Hee Kim, Sang Done Kim, Soung Hee Park
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
700-704
Published: July 20, 2008
Released on J-STAGE: July 20, 2008
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Plasma Enhanced Chemical Vapor Deposition (PECVD) of TiO
2 thin films on silica gel powders at atmospheric pressure in a Circulating Fluidized Bed (CFB) reactor was carried out. In addition, TiO
2 thin films on silica gel powders were prepared by the sol–gel method and compared with the TiO
2-deposited powders by PECVD. The characteristics of those thin films were determined by X-ray diffraction spectra, Raman spectroscopy, SEM and BET. Without heat treatment, anatase phase was crystallized well by PECVD in a CFB reactor. Specific surface area of the TiO
2-deposited silica gel by PECVD exhibits a larger value than that by the sol–gel method. By the PECVD method, TiO
2 thin films are uniformly deposited on the external surface of silica gel.
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Og Sin Kim, Dong Hyun Lee, Sang Done Kim
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
705-709
Published: July 20, 2008
Released on J-STAGE: July 20, 2008
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The effects of inlet gas velocity (1.53–1.75 m/s), inlet gas temperature (50–80°C), mass ratio between fine powder and inert particle (
F/
I ratio, 0.05–0.2) and initial water content (8.5–31.6 wt%, wet basis) on the drying rate were determined in an inert medium circulating fluidized bed (0.085 m ID × 1.0 m high). Glass beads (
dp = 327.5 μm,
ρs = 2,500 kg/m
3) as inert particles and poly methyl methacrylate (PMMA) beads (
dp = 12.5 μm,
rs = 1,190 kg/m
3) as fine powders were used. The drying rate increases with increasing inlet gas temperature, gas velocity and the
F/
I ratio. The effect of initial water content on the drying rate was negligible compared with the other variables. The obtained drying rate data have been correlated with inlet gas temperature, gas velocity,
F/
I ratio, and the initial water content.
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Jong-Min Lee, Dong-Won Kim, Jae-Sung Kim, Jong-Jin Kim
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
710-715
Published: July 20, 2008
Released on J-STAGE: July 20, 2008
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Detection and clearance of poor fluidization in a simulated fluidized bed ash cooler were studied by analyzing the mixing properties of the bed materials and the pressure fluctuation of the air header distributor. We observed a bridge of large particles at the bed surface which caused the poor fluidization area to form at the entrance of the FBAC. The poor fluidization was caused not only by airflow rates but also by the particle discharge rates as well as particle size distribution in the FBAC. Additionally, we could easily detect the local poor fluidization through a simple method developed in the simulated FBAC and in the FBAC of the Tonghae CFB boiler. As local poor fluidization is detected, it should be possible to clear it up by regulating the flow rate of each air header in the FBAC.
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Ho-Jung Ryu, Gyoung-Tae Jin, Sung-Ho Jo, Moon-Hee Park
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
716-720
Published: July 20, 2008
Released on J-STAGE: July 20, 2008
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Natural gas combustion characteristics of oxygen carrier particles were investigated in a batch type bubbling fluidized bed reactor (0.05 m ID, 0.6 m high). Three particles, NiO/bentonite, NiO/NiAl
2O
4, and Co
xO
y/CoAl
2O
4, were used as oxygen carrier particles. Natural gas and air were used as reactants for reduction and oxidation, respectively. All three oxygen carrier particles showed high gas conversion, high CO
2 selectivity, and low CO concentration during reduction and no NO
x (NO, NO
2, N
2O) emissions during oxidation. Moreover, all three particles showed good regeneration ability during successive reduction–oxidation cyclic tests up to the 10th cycle. The gas conversion, CO
2 selectivity and CO concentration were maintained to 97% of initial values for all three particles. These results indicate that inherent CO
2 separation, NO
x-free combustion, and long-term operation without reactivity decay of oxygen carrier particles are possible in the natural gas fueled chemical-looping combustion system with NiO/beotonite, NiO/NiAl
2O
4 and Co
xO
y/CoAl
2O
4 particles.
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Mi-Ran Kim, Kyoung-Hee Kim, Jeong-Gook Jang, Jea-Keun Lee
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
721-728
Published: July 20, 2008
Released on J-STAGE: July 20, 2008
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In order to prevent bed agglomeration during fluidized bed combustion processes, it is necessary to be able to predict the extent of agglomerate formation. In this study, a thermodynamic equilibrium model is used to predict the extent of agglomerate formation during fluidized bed combustion processes for various wastes and fuels.
According to the simulation results, silicate melts such as sodium silicate melt and/or potassium silicate melt are the main components involved in bed agglomeration. The amounts of silicate melts predicted in the agglomeration and non-agglomeration groups were significantly different. An assessment criterion for predicting bed agglomeration in the fluidized bed combustion process was established using a thermodynamic equilibrium model. This criterion can be used as a tool for predicting the bed agglomeration potential in the fluidized bed combustion of various fuels. Therefore, it was found that control technology for bed agglomeration can be applied to the fluidized bed incineration of wastes and fuels based on the model simulation results.
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Seok Jun Yoa, Yong Soo Cho, Dong In Lee, Byung Huk Kwon
Article type: Research Paper
2008 Volume 41 Issue 7 Pages
729-736
Published: July 20, 2008
Released on J-STAGE: July 20, 2008
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The present study investigates the collection characteristics of a semi-wet type multi-stage porous plate system combined with a water spray. Numerically and experimentally, collection efficiency and pressure drop were estimated with the various operation parameters such as the droplet spray, stage number, hole diameter and inlet velocity, etc. Moreover, a water spray system was adopted to prevent the reentrainment of deposited particles and especially to increase the inertia effect for submicron particles. Pressure drops for 6 stage in a case of a hole diameter of 6 mm were moderately controlled as 200 and 211 mmH
2O showing the high collection efficiency 97.0 and 98.3% at inlet velocity 1.0 and 1.2 m/s, respectively, by the numerical simulation. For 6 stage and an inlet velocity 1.2 m/s, higher collection efficiency was estimated over 99% due to the proper water droplet spray maintaining the pressure drop of 200 mmH
2O, experimentally.
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