Environmental technology & Fluidization technology

Development of CO2 Removal Process in Power Plant
Recently, high efficient CO2 absorption ceramic particles have been developed at the industry in Japan. When the particles are utilized at the effluent process in power plants, the CO2 emission to atmosphere can be reduced. We design the characteristics of the particles and the suitable process.

Sterrization using opt-catalyst particles fluidization
For drinking water, sterrized water for hospital and recycle water in hot springs, the technology of water sterrization is very important. In this study, using infra-violet light as well as optcatalyst to sterrize, a novel sterrization reactors are developped.



Methane fermentation process utilizing unaerobic active sludge
To develop more effective organic efluent waste water treatment process, a novel unaerobic active sludge is utilized.


Gas-Solid Fluidization and Pressure Profile in Circulating Fluidized Bed
Circulating fluidized beds are often used as boilers and FCC process due to good combustion efficiency and reactivity. When the circulating fluidized bed is utilized as a gas-solid catalytic reactor, it is important that reactant gases react stably enough with solid catalyst because of constant composition and yield of products.
So, it is necessary to control quantitatively the feed rate of gaseous reactants and catalytic particle in reactor. Although the control of gas flow rate is not so difficult, the solid particle circulation rate cannot be operated quantitatively enough. There are two principal techniques to control particle flow rate in circulating fluidized bed.
When the catalytic reaction can be separated into consumption and regeneration of catalyst activity, the twin-column circulating fluidized bed system can be utilized to recycle catalysts continuously.
In this study, to design a J-shaped pneumatic valves to control solid particle circulation flow rate, the effect of operating parameters on particle flow rate, pressure drop and gas entrainment through the J-valve was investigated experimentally.



Bioengineering technology

Aerobic Xanthan Production by Xanthomonas campestris
Under construction...





Development of Bioreaction Tower for Bioproducts Having Yield Stress
 n food industries, many kinds of thickeners are produced biologically. For xanthan fermentation, which is one of important products, a stirred tank bioreactor is usually used to keep the oxygen transfer rate up to the demand of aerobic bacterium. However, the local stagnant zone in which oxygen transfer is limited was observed in the stirred tank because of the yield stress. On the other hand, the bubble column has good mixing performance under slug flow operation for high concentration of xanthan aqueous solutions, so that the stagnant zone is little.
In this study, the characteristics of the oxygen transfer into highly viscous non-Newtonian liquids having yield stress in bubble columns were investigated to develop an optimum bubble column fermentor for viscous aerobic cultivation.
Due to the yield stress, the small bubbles could not escape from liquid and they were stagnant. On the other hand, the large slug bubbles, which were observed over the almost all operating range in this work, were rising smoothly without coalescence or breakage after they had been accelerated upward just above a gas distributor. The escapable gas holdups increased with increasing superficial gas velocity and decreasing the column diameter. They were estimated well by the modified equation of Nicklin et al. The effect of apparent viscosity of liquids on gas holdup was hardly observed under the operating conditions.




Development of Soft Material with Multi-Gas Channels  
Under construction....


Development of Bubble Column with Draft Tube Circulated Forcibly Liquid  
In the case of mass transfer into highly viscous liquids by using an internal airlift bubble columns, the performance is reduced. Because the friction between the walls in the column and liquids increases with increasing viscosity. In this study, therefore, the screw type propeller was set in the draft tube. By revolving the propeller, the viscous liquid was forced to circulate in the bubble column. The mass transfer coefficient increased with forced circulation rate of liquid.




Gas distribution into liquid phase


Research on Micro-bubbles for Novel Chemical Processes. 
Micro-bubbles has a great different characteristics from standard size bubbles. So we are developing a novel chemical processes.



Development of Waste Water Treatment Using Micro-bubbles
マイクロバブルの電気的吸着性を利用した廃水中に含まれるカーボン微粒子の吸着による除去プロセスの開発を行っています。
カーボン微粒子は正に帯電しており、マイクロバブルは負に帯電する性質があるので、両者を接触させると吸着が起こり、浮上していきます。これを利用すると水中からカーボン微粒子だけを分離できます。
すでに、液中のカーボン懸濁物の分離についての成果はTV報道されました。


Evaluation of Microbubble Distributors for Industrial Uses.
現在、様々な種類のマイクロバブル発生装置が開発されています。その中のいくつかはすでに市販されています。しかし、マイクロバブル発生器を化学反応装置に使用する場合には、その正確な性能が既知でないと使用することはたいへん危険です。そのため、事前にマイクロバブル発生器の性能を知る必要があります。本研究室では各種マイクロバブル発生器について、化学反応装置への適用の際に重要となるいくつかの点に注目して、化学工学的面から評価を行っています。


Development of Novel Functional Materials Containing Microbubbles
マイクロバブルを利用した新しい材料に関する研究を行っています。マイクロバブルの応用分野としては、現在液相を対象としたものがほとんどですが、本研究室ではマイクロバブルを機能性素材として注目しています。


Development of Novel Microbubble Generators
これまでに市販されているほとんどのマイクロバブル発生器は強力な液ポンプを必要とします。そのため、マイクロバブルの発生には必ず高速の液流が伴います。本研究室では、液ポンプが不要なマイクロバブル発生方法として、蒸気凝縮法を用いた新しいマイクロバブル発生器の開発を行いました。
2005年特許出願中


Development of Microbubble Removers
液中に混入したマイクロバブルは、逆になかなか除去できないなどかえってトラブルの原因になることもあります。マイクロバブルの除去にはろ過、浮上分離、遠心分離、サイクロンなどの方法がありますが、連続処理が可能で、また液流量が小さい場合に使用できる新しい方式の気泡分離装置を開発しました。これは遠心力とろ過を組み合わせた方法で、装置の小型化が容易です。
2005年特許出願中



Simulation of Liquid Velocity Profile around a Single Rising Bubble in Liquid by CFD
Bubble Formation from a Nozzle in Shear Liquid Flow
To distribute gas phase in liquid phase, an aerated stirred tank reactor Is usually used in industry, in which the gas phase was crushed by the Attrition with the blade of impeller. To evaluate the performance of the reactor, the estimations of bubble size and bubble size distribution are essential. However, it is very difficult at the present because of too complicated mechanism of bubble breakage around the impeller.
In this study, therefore, the bubble formation mechanism in simple shear flow conditions was investigated.
The revolving cylindrical rotator was set at the axis on the cylindrical vessel in which the viscous liquid is filled. By revolution of the rotator, the smooth liquid profile was generated in the annual path in the vessel. The bubbles distribute from a horizontal nozzle was deformed strongly by the shear flow. When the uniform bubbles are dispersed in liquid, the bubble volume was measured by the pressure fluctuation in the gas chamber. The bubble size decreased with increasing shear rate. To control the shear rate of the edge of the nozzle, the bubble size can be controlled.


Downward Bubble Formation in Downstream of Liquid
When the termical velocity of a bubble is slower than downward liquid velocity, the bubble flows downward along the liquid flow. In the cases of some gas-liquid operations, gas was downward blown into liquid. In this study, the mechanism of bubble formation at the end of nozzle inserted vertically into the bubble column.

Bubble Formation in Viscous non-Newtonian Liquids Having Yield Stress
Some foods such as mayonnaise and dressing for salad have strange characteristics, i.e., YIELD STRESS or zero-shear stress. The yield stress is sometimes increasing the taste of foods. Some liquidized foods are produced by fermentation.
When the culture liquid has an yield stress, the small bubbles whose buoyant force is smaller than the yield stress cannot rise in the liquid in aerobic fermentors. So, if too small bubbles are distributed in the bubble column, the flooding will be occurred.
In this study, to estimate the bubble size at the gas distributor, the non-spherical bubble formation model was proposed.


Visualization of Gas Flow in Two-dimensional Bubble
To investigate the gas flow in the bubble during bubble formation at the nozzle, the smoke tracer was used. The smoke was inputted with air into the bubble growing in a 2D-bubble column so that the image of bubble growth was photographed using a high-speed video camera with laser beam visualizer.
The smoke tracer was circulated along the gas-liquid interface in the bubble.


Mechanism of Gas Absorption and Reaction from NH3 Gas Bubble Formation in Water
To investigate the mechanism of gas absorption from a bubble containing soluble and insoluble components, a gaseous mixture of ammonia and nitrogen was bubbled into water.
The bubble volume decreased with the increasing composition of ammonia in a bubble, decreasing gas chamber volume and decreasing gas flow rate.
The non-spherical bubble formation model combined with the overall mass transfer resistance estimated well experimental bubble shape, bubble volume at its detachment from an orifice, growth rate and mass transfer rate. Moreover, the change of concentration with bubble growth time and the fractional absorption during bubble formation were simulated.



Measurement of Heat Transfer Coefficient for Direct Contact Condensation
When the vapor constant directly coolant and then it condenses with heat transfer, the heat transfer coefficient is much larger than the standard coefficients. The direct-contact heat transfer coefficient is usually neglected. When the very fast phenomena of vapor bubble condensation are simulated, however, those values become very important.


Two-phase Bubble Formation from a Nozzle with Condensation
When the vapor gas is brown into the immiscible liquid, the bubble is expanding with condensation. If the expansion rate is smaller than condensation rate, the bubble or drop cannot be generated. The phenomena of generation of two-phase bubbles are often observed in the direct-contact heat exchanger. In this study, to produce homogeneous sized liquid droplets, the condensable vapor bubbles are generated constantaneously from a nozzle in a bubble column. at first. Then, by controlling liquid temperature, the size-controlled vapor bubbles are condensed and become droplets. The droplet size is uniform when the specific operating conditions are maintained.
Publiched in News paper, 18 Jul. 2000

Gas-Liquid Separation from Liquid Phase under Microgravity
Left picture: The water flows homogeneously the left side to right side under the ground condition. Bubbles were inputted from three nozzles whose orifice is directed to the downstream. Of course, by the buoyant force, all bubbles rise upward.
Left picture: The experimental conditions are same as the upper picture except for the gravity. The equipments were capsuled and dropped into the drop shaft of JAMIC in Hokkaido, Japan, to obtain micro gravity for 10 seconds. The bubbles could not rise in the liquid so that the size of bubbles increased and the bubble shape became spherical.
Published in Newspape, 25 Jul. 2000



Bubble Formation in Liquid under Microgravity
地上重力での気泡生成 The water is filled in the three neighborhood cells. The gas is blown into water through three downward nozzles. The bubbles rise instantaneously after the detachment from the nozzles under terrestrial gravity.
On the other hand, in the case of micro gravity, the bubbles became spherical and never detach from the nozzles.



On-line Measurement and Simulation of Shape, Velocity and Interface area of Rising Single Bubble
The studies on bubble shape were usually carried out by picture analysis method using still camera, digital camera and high speed video camera. However, by those methods, the bubble size, shape and rising velocity could not measured on real-time so it was difficult to get a lot of data within a reasonable experimental time. Moreover, if the bubble shape is complicated three-dimensionally, only the 2-dimensional shape of the bubble is available.
In this study, by using some laser sensors, the 3-dimensional bubble shape, bubble surface area, bubble volume and bubble rising velocity are measured at the real-time. The coordinates of the bubble surface are recorded of the digital file so that those data can input instantaneously to the CFD software.
By this system, it is very useful and convenient to analyze the bubble behavior.




Simulation of liquid velocity profile around a single rising bubble in liquid by CFD
By the combination of experimental work and computational technology, the flow dynamics around a rising bubble were simulated



Reactor Design by Non-Spherical Bubble Formation Model and CFD Simulators
The non-spherical bubble formation model was proposed by Pinczewski at first. Then, Terasaka modified it and developed for various purposed. At the present, the non-spherical bubble formation model can estimate the various non-Newtonian system, constant flow condition, micro gravitational system, reactive gas system, high pressure system, flowing liquid system, vapor condensation system and liquid-liquid system. When the gas distributor will be designed, the estimation by the model is very useful.