Aggregate structures of a colloidal dispersion composed of polydisperse ferromagnetic particles were investigated by the cluster-moving Monte Carlo method. The internal structure of aggregates was analyzed quantitatively by means of the pair correlation function. The results obtained here are summarized as follows. Under the influence of a strong magnetic field, chain-like clusters are formed in the direction of the magnetic field and become longer and thicker as the magnetic interactions between particles increase. Also, thicker chain-like clusters are formed for a wider distribution of particle diameters. For the very weak external magnetic field, chain-like clusters are formed that have bend-like, small loop-like and branch-like structures. These structures are induced by the interactions between large particles. As the influence of the magnetic field dominates, these structures appear less and less, until straight chain-like clusters are formed in the direction of the magnetic field. The thickness of the clusters does not significantly depend on the strength of the magnetic field but on the distribution of particle diameters.
When the length of an annular liquid film in a circular pipe exceeds a critical length under zero gravity, the liquid film breaks into several lobes periodically, and plugs are formed. The dynamic behavior of the interface deformation of the liquid film under zero gravity was investigated using a three-dimensional simulation based on the finite difference method. For concentric gas-cores with various diameters, the numerical results of the average distance between lobes were in good agreement with those of the linear stability analysis. For eccentric gas-cores, the average distance between lobes was longer in the numerical simulation due to the eccentricity of the gas-core (the lack of uniformity of the film thickness at the transition to zero gravity) and the combination between adjacent lobes during the interface deformation. The numerical results of the distance were in reasonable agreement with those of our drop-shaft experiments under microgravity.
In simulation of spray combustion, the prediction of spray flow is important in order to understand combustion characteristics (temperature and chemical species distribution). To improve the prediction of spray flow, it is necessary to consider the volume fraction of droplets, because the number density is high near the spray nozzle in a spray combustor. Numerical simulation of spray flow was conducted using a Lagrangian method considering the volume fraction of droplets calculated from the residence time of droplets in a control volume, and the validity of this method was evaluated by comparing experimental and calculated results. The calculated data by this method showed good agreement with the experimental results. As a result, this method is effective for spray flow calculation because it is able to calculate when the number density of droplets is high near the spray nozzle.
It is very important for development of a steam-injection type gas-turbine generator system to elucidate the combustion characteristics and flammability limits under high-steam and low-oxygen atmosphere. In the present study, we carried out a numerical analysis using the detailed elementary reaction mechanism for the counterflow diffusion flame under high-steam and low-oxygen atmosphere, and we clarified the flame structure and the flammability limits and examined the mechanism of flame extinction due to the steam addition. The results obtained are as follows. With the increase in the preheating temperature of fuel and oxidizer, the amount of steam that can be added increases and the flammability range extends. Considering the radiation heat loss, the added steam concentrations at identical flame temperatures and the flame temperatures at identical added steam concentrations decrease by about 10%, but the flame temperatures at the flammability limits are almost the same. The major reason for flame extinction due to steam addition is that the large specific heat of steam decreases the flame temperature, but the chemical kinetics due to steam addition also have a considerable effect. In particular, the flame stability near the extinction limit is influenced by the change of heat release rates of the following elementary reactions: O+CH3→H+CH2O (R10), OH+H2→H+H2O (R84), H2O+O→OH+OH (−R86), OH+HO2→O2+H2O (R87) and OH+CH4→CH3+H2O (R98).
By assuming a simple relation between the minimum agitation power input for a solid suspension with aeration and the aeration power input, a new correlation was derived with which to estimate the minimum agitation power input for solid suspension in gas-liquid-solid stirred vessels. The equation obtained is a function of aeration power input, minimum agitation power input for a solid suspension without aeration, and agitator blade angle. The minimum agitation power input for solid suspensions estimated in this work agreed with measured data in the literature. In a stirred aerated slurry reactor, a higher agitation power input than the minimum power input estimated for a solid suspension was necessary to obtain complete reaction.
The air-lift pump and the electrolytic gas-lift pump are potentially usable to collect valuable mineral resources from the deep seabed. The former is considered useless for collection of mineral resources from depths of over 3000 meters due to the power limit of compressors, whereas the latter can be used at any depth. However, design criteria for an electrolytic gas-lift pump have not been established. As a first step, this paper examines the solid lifting velocity of a single coarse particle by an electrolytic gas-lift pump.
Economic evaluation of facilitated transport membranes for separation of CO2 from two kinds of flue gases, i.e., from a natural gas-fired power plant (NGFPP) and a coal-fired power plant (CFPP), was performed by computer simulation. Gel-coated liquid membranes containing aqueous solutions of a novel carrier, 2, 3-diaminopropionic acid (DAPA), were used as facilitated transport membranes. When the CO2 recovery is 50%, the CO2 purity of the recovered gas is 90% and the recovered gas is transported as a gas mixture for sequestration, the energy required was estimated as 8.39% of the energy generated in the case of NGFPP and 10.55% in the case of CFPP. The CO2 separation costs for NGCPP and CFPP were 359 yen/kmol-CO2 and 283 yen/kmol-CO2, respectively. When the CO2 recovery is 50%, the CO2 purity in the recovered gas is 99.9% and the recovered gas is transported as liquefied gas, the energy required was estimated as 11.1% of the energy generated energy in the case of NGFPP and 14.5% in the case of CFPP as 14.5%. The CO2 separation costs from NGCPP and CFPP were 427 yen/kmol-CO2 and 354 yen/kmol-CO2, respectively. The CO2 recovery system by the facilitated transport membrane has an economic advantage in operation energy and CO2 separation cost compared to the polymer membrane system and the chemical absorption system.
Carbon dioxide removal from power station flue gas was tested in a pilot-scale absorber of about 25 m in height, operated at a volumetric gas flow rate from rated 555m3/h to 1100m3/h. The test results revealed that a chemical absorption process using KS-1 solution, which is a hindered type alkanolamine, and an absorber equipped with regular packings could recover double the amount of carbon dioxide as compared to the conventional design. Accordingly, the construction cost of the absorber will be drastically reduced, because the same volumetric flow rate of flue gas can be treated by an absorber with half of the conventional cross-sectional area.
Wincef, an injectable cephalosporin antibiotic, was adapted to the powder filling method as a pharmaceutical process. The effects of temperature, supersaturation degree, stirring rate and seed crystals on the specific volume, crystal size and crystal size distribution of Wincef were studied, and crystallization conditions were established to obtain spherical agglomerate crystals suitable for powder filling. As the degree of supersaturation increased, the specific volume of Wincef decreased. The optimum stirring rate was found from the viewpoint of breakage and agglomeration of products, and power consumption per unit volume was applied as a scale-up factor. Wincef obtained from a 500 l crystallizer was used in a powder filling experiment, and the expected result was obtained. Finally, it was confirmed that the Wincef obtained in a 3000 l commercial crystallizer had the expected powder characteristics.
Recently, the demand for fine particles of μm or sub-μm-order has risen strongly in various industrial fields. In many powder-manufacturing processes, a supersonic jet mill is used for the pulverization of various kinds of fine particles. The improvement of pulverization efficiency is very important, because the jet mill consumes a large amount of operating power. In this study, a new supersonic jet nozzle with a rectangular cross section was proposed, and its flow characteristics and the particle acceleration performance were investigated experimentally by measurement of particle velocity and flow visualization by the Schlieren method. Numerical analysis was also performed for reference. As a result, it was found that the new supersonic jet nozzle has a high performance for particle acceleration, namely, for improvement of pulverization efficiency.
Recent epidemiologic studies have corroborated the relationship between ambient concentration of airborne fine particles and detrimental heath responses. Though dust particles in flue gases can efficiently be removed with bag filters and electrostatic precipitators, the collection efficiency for submicron particles requires improvement. In the present study, a packed bed with applied electric field was connected to the outlet of an electrostatic precipitator of the cylindrical type to collect submicron particles that pass through the precipitator. Since the submicron particles were observed to carry electrostatic charges, the precipitator also functions as an electrostatic charger. Measurement of the collection efficiency of the packed bed for submicron particles revealed that although collection mechanism has puzzling aspects and is more complicated than we expected, the efficacy is clearly enhanced by the electrostatic effects. Owing to the limitation in our high voltage supply, the maximum field strength we applied was only 1 kV/cm, which is much lower than that applicable in practice, namely, 5 kV/cm. Nevertheless, the observed collection efficiency of the packed bed for submicron particles was 98% at a pressure drop of 0.2-0.3 kPa for a superficial velocity of 50 cm/s.
Particles coated with sprayed liquid in a fluidized bed might be kept at relatively high temperature for a long period during drying with high-temperature air. Materials with a low temperature of decomposition should, therefore, be treated for a short time, and hitherto operational conditions have been set empirically. In this study, the relationship among the operational parameters was investigated quantitatively, and the particle temperature was estimated as wet-bulb temperature. It was found that a high coating rate could be obtained from a high feed rate of sprayed liquid and a high temperature or flow rate of inlet air at a given particle temperature.
Macro-sized particles and seamless capsules were prepared in a liquid system with continuous flow. The effect of process parameters was studied on the capsule size and the wall thickness. The experimental data were successfully fitted with equations developed on the basis of force balances. Particle size was found to decrease with increasing dispersed phase velocity at high continuous phase velocity, but to increase with increasing dispersed velocity at low continuous phase velocity. In the case of capsule preparation, larger capsules were formed at higher flow rate of total dispersed phase over the whole range of continuous phase velocity, independently of the flow ratio of dispersed phases. Therefore, it was found possible to increase external and internal capsule diameters by increasing total dispersed flow rate and decreasing continuous phase velocity. Capsules with thicker walls were yielded by increasing the flow ratio of dispersed phases at constant total flow rate of dispersed phase.
Batch fermentations of Rhizopus oryzae AHU 6537 in medium containing granular activated carbon from coal, powder activated carbon from coal or granular activated carbon from coconut were carried out in an airlift bioreactor. As a result, fermentation broths were decolorized by activated carbon, and clearer fermentation broths were obtained than in fermentation without activated carbon. With activated carbon from coal, the cells formed smaller pellets than in fermentation without activated carbon, and fermentation performance was improved. Productivity was further improved by increasing the amount of activated carbon from coal. Therefore, the productivity of lactic acid fermentation could be improved by selecting a suitable activated carbon and by controlling the amount of activated carbon.
To determine whether the tar emission abatement effect of activated alumina is applicable to a circulating fluidized bed gasifier (CFBG), we carried out experiments of ligneous biomass pyrolysis with activated alumina particles as a bed material using a small-scale CFBG at 873 K and 943 K. High tar reduction could be achieved in the CFBG within the investigated range, particularly at high tar yields, for which a decrease of two orders of magnitude was recorded. Total low tar yields also decreased, although some light aromatic hydrocarbons increased slightly. In addition, in the investigated range, the effects of load on the operating conditions for tar emission were sensitive to low tar yield, but were insensitive to high tar yield. With respect to gaseous products, hydrogen and carbon dioxide yields increased. However, this increase resulted in a lower heating value of the produced gas due to a decrease in the carbon monoxide concentration. The use of activated alumina as a bed material has the advantageous effect of increasing the total gas yield and the adverse effect of decreasing the heating value. However, with respect to the simulation of the steam gasification process, the cold gas efficiency is increased by a few percentage points overall. In addition, the use of activated alumina particles allowed stable circulation of the bed material and prevented the “bogging” effect by immediately removing tar in the reactor.
The effects of NaCl, KCl and CaCl2 on chloride volatilization of Pb, Zn and Cu from three different molten fly ashes and model fly ashes were investigated in the temperature range of 873-1173 K and under N2 atmosphere. Results showed that when the model ashes containing PbO, ZnO and CuO were heated at 1023 K after mixing with NaCl, KCl and CaCl2, the effectiveness of inorganic chloride for volatilization of PbO, ZnO and CuO was in the order of CaCl2>NaCl>KCl. The volatilization behavior of Pb in the molten fly ashes showed the same trend as that in the model fly ashes, and the volatilization ratio of Pb increased with heating temperature above 873 K. Also, the chlorination of Pb was favored in the presence of NaCl, KCl and CaCl2, which formed a low temperature eutectic mixture below 923 K. On the other hand, volatilization behavior of Zn from the model fly ash was greatly different from that from the molten fly ash. ZnO in the molten fly ash was thought to be reduced to Zn by unburned carbon or Fe contained in the ash, and the Zn was volatilized at a lower temperature than melting temperature of ZnO. Volatilization ratio of Cu from the model fly ash was low even at 1173 K, and no volatilization of Cu was observed for the molten fly ash. As in the case of Zn, CuO in the molten fly ash was thought to be reduced to Cu by unburned carbon and Fe, and the Cu was hardly chlorinated to form CuCl.
Adsorption gel was prepared by using formaldehyde to crosslink lignosulphonic acid, which is generated in the production of pulp as a by-product of low value or nearly waste. The amount of cation-exchangeable hydrogen ion contained in the gel was measured by titration as 4.83 mol/kg-dry gel, the majority of which was considered to be attributed to hydroxyl groups of phenol moiety of the gel. Batchwise adsorption tests were carried out to elucidate the pH dependency of the adsorption of some metal ions and adsorption isotherms. Adsorption occurred at pH greater than 2 and increased with increasing pH, suggesting that cationic metal ions are adsorbed on the gel by a cation exchange mechanism. The order of the selectivity was as follows: La(III)>Pb(II)∼Fe(III)>Fe(II)∼Cu(II)∼Al(III)>Cd(II)∼Ni(II)>Mn(II)∼Zn(II). The adsorption isotherms were of the Langmuir-type, and the maximum adsorption capacity was evaluated as 0.86, 0.76 and 0.47 mol/kg-dry gel for copper(II), lead(II) and lanthanum(III). With a view to practical use of this gel, the separation of lead(II) from zinc(II) was examined using a column packed with the gel. Satisfactory separation was achieved, suggesting the feasibility of applying the gel to, for example, the removal of lead impurity from a zinc plating bath.
Leachate from landfill contains high concentrations of salts and can not be discarded because it causes environmental pollution. It is treated mainly by a membrane method, by which it is separated into filtered water and condensed salts solution. The condensed salts solution then requires secondary treatment. We have developed one-stage methods of evaporating water from the leachate by spray-atomizing of the leachate or by wetting cloth with leachate and heating it. Experimental results show that reduction of concentration of salts is 93% by the spray-atomizing method and 99.7% by the wetted cloth method, while the thermal efficiency is 56% for the spray-atomizing method and 28% for the wetted cloth method.
A lower temperature method for reforming magfnesite to magnesium oxide was experimentally investigated by heating magnesite powder with and without adding magnesium nitrate hexahydrate. The results demonstrated that the reforming rate of magnesite was greater with magnesium nitrate hexahydrate than without, and in the presence of magnesium nitrate hexahydrate, magnesite was successfully reformed to magnesium oxide at a lower temperature of ∼170 K. In this case, the degradation of magnesium nitrate hexahydrate generates nitrogen oxides, which accelerate the reforming reaction of magnesite to magnesium oxide. This work suggests that it is possible to reform magnesite into a desulfurization agent at lower temperature.