粉体工学

A forced vortex-type centrifugal air classifier has the advantages of fine cut-size and high classification accuracy. It's capacity for classifying submicron particles attracts attention. Various types of classifiers are on the market. However, the classification mechanism has not been clarified. We describe simulation of particle motion in a classifier. Effects of the initial angular position and circumferential velocity of a particle at injection into the classifier and of capturing accuracy are also discussed, based on results of particle trajectories.

Presently there are many projects in progress to construct large-scale coal-fired power plants and coal centers. Coal consumed at these plants amounts to several million tons per year. Prediction of coal particle dispersion caused by handling large amounts of coal is required to assess environmental impact. This report describes the emission rates from coal storage piles and coal dropping processes, and presents simulation method to predict the dust deposition due to coal handling facilities.

Coal-water mixture (CWM), a liquid fuel produced by mixing together coal and water with an aid of surfactant, has many advantages for storage and handling of coal and, moreover, for beneficiation of coal, transforming coal into a more appropriate form to handle and burn. Following the development of the coal-oil mixture (COM), a research program to develop a CWM technology has been made by Mitsubishi Heavy Industries, Ltd. for the past decade, covering the CWM production, transportation, storage and combustion.This paper reviews an outline of the CWM research and it's results, specifically focusing on the handling process of two-CWM consisting of fine particles of coal and water.

In the case of collecting grains and removing muddy deposits, especially those containing contaminants, it is very difficult to lift them up effectively by means of suction alone. Our investigations revealed that effective and smooth collection and transportation can be performed by mounting an injector at the collecting mouth in order to fluidize the settled bed. A sand collector with an injector at the collecting mouth can be applied not only for gases but also for liquids as a carrier and can transport many kinds of grains, such as sand and other relatively small particles. Several variables affect the performance of this device. In this paper, the fundamental characteristics of the system and its application are reviewed.

The density of dust in a tunnel during construction is one of the most important factors among the environmental conditions experienced by construction workers. Dust is caused by blasting, shotcrete, waste-handling, etc. Effectively controlling dust is very difficult, especially during blasting. Thus, an effectively designed ventilation system is needed in order to reduce the density of dust. The behavior of dust in a tunnel is only experimentally understood, but there remain many conditions which affect the efficiency of ventilation. If the behavior of dust in a tunnel could be better understood, ventilation systems would be more effectively designed.

Granulation techniques have been developed to produce granular materials, such as all forms of granules, small compacts, coating particles, and small grains or prills, for demand application in widely differing industries. A primary objective in this review is to present a generalized accouts of the diverse granulation methods in a systematic way. In the case of size-enlargement of fine powders, there are two principal modes of granulation. One is achieved by tumbling, agitating, or fluidizing raw materials in the presence of liquid binders, and the other includes granulation processes in which materials are forced to flow in a plastic or sticky condition through dies or screens or in molds. The former is especially reviewed from a design viewpoint of granulation processes.

Blast furnace involves the complex flow conditions of the upward gas flow and unburnt char/coke fines, and the downward flows of coke and molten iron and slag. Under the recent high rate injection operation of pulverized coal, permeability in the furnace has been prevented due to the accumulation of such fine powder in the lower part. Therefore, it becomes more important to understand the essential flow characteristics of the fine powder in the blast furnace to attain the stable operation. This article discusses the recent development of the analytical method and the numerical modeling of powder behavior, particularly focuses on the combustion behavior of pulverized coal, generation of coke fines and the movement and accumulation of fine powder in the lower part of the blast furnace.

The high speed mixing granulator, the fluidized bed granulator/dryer, the tumbling fluidized bed to which a rotor is added, and the rotating drum type tablet coating equipment are widely used for solid dosage manufacture. Rationalization of operating conditions according to the physical properties of various materials has been a big subject. Therefore, for these equipments, the phenomenon inside these equipment are analyzed especially on particle motion by DEM analysis. Some example data examined about the features of these equipments performance are introduced, and the application to future development of equipments is explored.

The mathematical simulation of blast furnace operation, which uses theories of reaction kinetics and transport phenomena, has been being developed in past four decades. Although blast furnace was once treated as a black-box-reactor, a lot of experimental and numerical efforts have revealed that multiple regions exist within a furnace. The requirements for more detailed information of their functions and characteristics has been increased, as they revealed. Such demands improves the mathematical simulation model of blast furnace from one-dimensional to multi-dimensional, from steady to transient, and from single phase to multiple phases. This paper explains the outline of the latest mathematical model of blast furnace operation, which is based on multi-fluid theories, reaction kinetics and transport phenomena, and its applications. This model treats four materials, that have different flow characteristics and thermo-physical properties, as fluid. These materials are gas (blast and reaction gases), lump solids (coke and ore), liquids (molten metal and slag) and fine particles (unburnt pulverized coal and fine coke). The equations of motion of these four phases have the same form and are solved by same technique. This way of modeling allows efficient process simulation including heat and mass transfer, and reaction analyses. The model has been applied to a variety of operating conditions, and revealed the in-furnace status of blast furnace in detail.

Combustion flows are widely used for the mass production of nanoparticles including fullerenes. Researches concerning with the fullerene formation in combustion flows are introduced and the experimental results are briefly shown in the present report. In the fullerene formation process in the combustion flow the temperature profiles and the chemical reactions of the intermediate chemical species are essential under the reduced pressure conditions. In order to consider the non-equilibrium phenomena in combustion flows the non-equilibrium molecular dynamics method can be applicable and the simulation results for the surface aggregation phenomena of the carbonic nanopraticles are also introduced briefly.

The state-of-the-art of numerical simulation models and methods in gas-solid two-phase flows in powder technology field is briefly reviewed. Eulerian-Lagrangian coupling simulations have been largely developed in the last three decades，especially the DEM-CFD coupling simulation has become popular, and widely used in many operations of powder technology. It is expected that the mesoscopic flow models and two-fluid models will be improved by using the multiscale-modeling strategy.

This study experimentally examined the spouting phenomenon of the cohesive powder from an orifice when air was supplied from the top and the bottom of powder bed in a vessel. The stable discharge of the cohesive powder was obtained as the same flow rate of air was simultaneously supplied at the top and the bottom of the powder bed. Then, it was observed that the flow pattern of powder bed in a vessel became a mass flow, and that the discharged powder jet from an orifice was dispersed in the atmosphere. It was found that the interstitial air pressure affected the change of the void fraction and the discharge coefficient. In addition, it was confirmed that the interstitial air pressure during the spouting of powder greatly influenced the mass flow rate of powder through an orifice.

The rugged surface produced by the nanoparticle coating on a substrate is very effective to prevent water adhesion and maintain the transparent. So, we developed the novel water repellent using nanoparticle for side mirror of a car. The rugged surface by coating is also very effective to prevent powder adhesion too. It was experimentally confirmed to prevent dust adhesion by covering the surface of the glass substrate with nanoparticle. The adhesion force between particle and substrate is measured by the centrifugal method and the relation between the adhesion force and the surface roughness is discussed from experimental and theoretical point of view. The measured and calculated results by Van der Waals force show that adhesion force decreased with the increment of the surface roughness. From the results, nanoparticle coating is very effective to prevent the dust adhesion on the substrate and the various application of nanoparticle coating can be expected.

Dense phase pneumatic conveying in a pipeline is often applied to avoid disadvantage such as high power consumption, particle breakage and pipeline abrasion. This article described mainly the dense phase pneumatic conveying in a horizontal rectangular channel using the fluidizing air. The fluidized powder conveying system consists of a powder supply vessel and a horizontal rectangular channel at the side of vessel. The powder was fluidized by air through the porous membrane at the bottom of a vessel and a horizontal channel. The powder used belongs to Geldart A particle, where the mean diameter is 53 μm, the particle density is 2523kg/m3 and the minimum fluidizing velocity is 4.329mm/s. The mass of transported powder, the bed height of powder in a vessel and the supply air pressure were measured when the fluidizing velocities at the bottom of vessel and horizontal channel were changed. The powder could be transported smoothly when the air was supplied to the bottom of vessel and the velocity of the bottom of horizontal channel exceeded the minimum fluidizing velocity. In this case, the powder was discharged smoothly from vessel to horizontal channel, and then the powder flowed easily toward the exit of horizontal channel. Therefore, the fluidizing air at the bottom of vessel and horizontal channel was important to obtain smooth powder conveying on this system. Also, the mass flow rate of powder and the solid loading ratio were estimated from the mass of transported powder against the elapsed time. As the result, the solid loading ratio had taken a one peak when the fluidizing velocity at the bottom of horizontal channel was larger than the minimum fluidizing velocity. In addition, it is found from the analyzed solid loading ratio that the high dense powder conveying was possible in this system.

The particles emitted from diesel engine exhaust have low resistive in nature and extremely small in the range of 70-120 nanometers. These particles are penetrated into an alveolus and extremely harmful to human health. These particles are generated from various emissions such as diesel automobiles, marine engines, power generation engines, and construction diesel machines. These particulates also exist in tunnel or underground parking. An electrostatic precipitator has been extensively used for the collection of these particles. In the present technical report, the technology of electrostatic precipitator on diesel exhaust particle was explained.

This paper aims to describe an industrial application of the Discrete Element Method (DEM). The DEM is often employed in granular and solid-fluid mixture systems. The DEM is a Lagrangian approach, where individual particles are simulated based on Newton’s second law of motion. In my group, novel models are developed to apply the DEM in industrial powder systems, i.e., coarse grain model of the DEM for efficient calculation of large-scale powder systems and combination of signed distance functions and immersed boundary method for efficient creation of arbitrary shaped wall boundary. These models are shown to be crucial for a numerical simulation of an industrial powder system.