Outstanding Paper Award Subcommittee of Kagaku Kogaku Ronbunshu has assessed the 82 papers published in 2006, corresponding to volume 32, and selected the candidates of the award. As a result, the editorial board finally selected the two papers for Kagaku Kogaku Ronbunshu Paper Awards of 2006; those are the papers on “Correlation Equation of Particle Collision Frequency with Impeller in a Stirred Tank,” and “Improvement of Denitrifying Reaction Rate by Enhanced Substrate Transport within a Cell-Immobilized Space by Electrophoresis.”

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For the tangential velocity u measured in the free vortex flow region in a turbulent non-baffled agitated vessel with a paddle impeller or a pitched blade paddle impeller, the dimensionless velocity (u/v_θ)(βD/md) was well correlated with the dimensionless radius 2r/D, where the correlation parameter m was expressed by m=2.5(r_c/r_d)² using the radius of cylindrically rotating zone r_c and the impeller radius r_d. The tangential velocity near the side wall of the vessel u_D satisfied the relation (u_D/v_θ)(βD/md)≒1.

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From the analysis of the heat transfer coefficient measured by many investigators, the similarity of heat and momentum transfer at the side wall of a fully turbulent agitated vessel without baffles was expressed by j_H(md/βD)≒f/2 using the j-factor j_H for heat transfer and the friction factor f for momentum transfer, in which the correlation parameter m was defined as m=2.5(r_c/r_d)² using the radius of cylindrically rotating zone r_c and the impeller radius r_d.
The correlation of the heat transfer coefficient in an agitated vessel with the power consumption per unit volume P_v proposed by Calderbank and MooYoung (1961) was confirmed to satisfy well the similarity between heat and momentum transfer at the side wall of the vessel for a wide range of impeller dimensions.

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Enhancement of the rising velocity of air bubbles in shear-thinning fluids under oscillatory pressure field was studied experimentally. Application of mechanical pressure oscillations to cause cyclical change of bubble diameters can give rise to strong local flows around the bubbles that are sufficient to decrease the apparent viscosity of shear-thinning fluids and hence bubble rising velocity. Enhancement of the natural air bubble rising velocity of over 400 times has been obtained with shear-thinning fluids, whereas almost no effect is observed with Newtonian fluids. Time-series data of cyclical bubble diameter were obtained experimentally using a strobe scope and a video system to estimate the local shear rate and the local shear viscosity. The enhancement of bubble rising velocity estimated from the shear viscosity behaviour agreed well with the experimental data.

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The conditions for generating rotary sloshing of liquid, and the influence of operational conditions, such as the size of equipment, liquid height and rotational speed of impeller in a stirred vessel with a flat paddle impeller on the rotary sloshing frequency and resonance phenomena were examined. It was found that the rotary sloshing of liquid occurred immediately after the liquid surface touched the lower end of the impeller, and that it was generated when the rotational speed of impeller was greater than the rotary sloshing frequency. Moreover, based on the equation for sloshing frequency in the tank without an impeller, the equation of rotary sloshing frequency was derived considering the influence of the impeller's diameter. Furthermore, in the mixing machine, when rotary sloshing of liquid occurred, the vibration was induced by both rotational speed of impeller and rotary sloshing. It was found that the resonance phenomena occurred when the vibration induced by rotary sloshing of liquid was in agreement with the natural frequency of the mixing machine.

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Soot formation during benzene pyrolysis was investigated experimentally and numerically. In the experiment, soot was formed by pyrolysis of gaseous benzene in an alumina reactor. In the numerical simulation, a new model was constructed by combining the discrete-sectional model and the cluster-cluster aggregation model. The new model describes the rate of benzene pyrolysis, nucleation and the formation, growth and aggregation of primary particles. In the reaction of primary particle growth, fusion of primary particles by sintering in an aggregate is also considered.
Calculated results of the size distribution of primary particles and the shape of aggregates are in good agreement with experimental ones. Furthermore, the calculated results indicate that the fusion of primary particles by sintering significantly affects the primary particle diameter and the shape of aggregates.

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The correlation of fluidity between solid–liquid and solid–gas suspensions was examineed using the thixotropy model proposed by Usui et al., (2000a, 2000b, 2001) Shear-thinning behavior was observed for a solid–gas suspension of calcium carbonate particles. The decrease in apparent viscosity of the solid–gas suspension is attributed to the breakdown of agglomerative structure with the increase in shear rate. It was found that the predicted inter particle bonding energy for the solid–gas suspension corresponded well to that obtained for a solid–liquid suspension. The same tendency was reported previously for the case of silica suspension. Since the suspension viscosity is not greating sensitive the change in inter particle bonding energy, it may be possible to predict solid–gas suspension viscosity by predicting the inter particle bonding energy for a solid–liquid suspension, and by using the thixotropy model proposed by the present authors.

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There is growing demand for simple freeze-concentration equipment which can operate intermittently. We have made freeze-concentration equipment consisting of an ice-making part, which continuously produces ice flakes on a rotating cooling drum, and a continuous centrifuge separating part. The purpose of this study was to evaluate the effect of shortening the residence time of ice flakes in the centrifuge part. Experiments using sea-water (Cl⁻ concentration of the mother liquor 2.04–3.02 wt%) in this equipment led to the following results. The solute recovery rate and the treated quantity of mother liquor in tests with shortened residence time(15 s) compared favorably with those of previous tests with residence time of 60 s. In the previous tests, the solute recovery rate was 0.31–0.40 when the treated quantity of mother liquor ranged from 29.9 to 32.9 kg/h. The present tests gave a solute recovery rate of 0.54–0.73 for a treated quantity of mother liquor from 56.4 to 61.1 kg/h.

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A kinetic model for methane fermentation of animal and kitchen waste was proposed based on the assumption that the biogas production rate is proportional to the concentration of volatile solids (VS) in the waste. The following equation for the biogas production rate was then derived from analysis of published data on a methane fermentation operation for pig manure.
−dC_vs/dt = γ(4.61×10¹¹)(exp(−7.47×10⁴/RT))(C_vs)
The present model was also based on the following assumptions and sequence. (1) The digester was assumed to be a constant-volume batch reactor, and the integration time of the differential equation for the digester was one day. (2) The fermentation of organic waste fed on any given day was assumed to be independent of the waste previously fed into the digester. (3) The amount of waste degraded on a given day was calculated by applying the above rate equation to the residual VS of each batch of waste fed into the digester on each day within the retention time of the digester. (4) The summation of the calculated amounts of degraded waste gave the total amount of the biogas produced on the given day.
It was demonstrated that the present model could be used to predict the biogas production rate for animal waste, kitchen waste and mixtures of both types of waste during the mesophilic and thermophilic anaerobic digestion.
All the actual data used in this paper came from literature published by other researchers.

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Ultraviolet-ray (UV) decomposition is one of the chemical methods authorized in Japan for decomposition of polychlorinated biphenyls (PCBs). The equipment for the UV decomposition consists of photoreactors and UV lamps. Photoreactors are classified as either an internal irradiating reactor (IIE) or an external irradiating reactor (EIR) depending on the lamp location with respect to the reactor. Both types have advantages and disadvantages. For example, an IIR has higher UV-utilizing efficiency than an EIR, but it is generally easier to perform maintenance on an EIR than an IIR. The purpose of this study was to determine which types of reactor is better suited for PCB detoxification plants. Here, we focus on the UV-utilizing efficiency, but to our knowledge, no study has been reported to estimate it quantitatively by means of simulation. First, under our initial experimental conditions, the UV utilizing efficiency was 64% for IIR and 2% for EIR. Next, to estimate UV utilizing efficiency for EIR, we calculated the efficiency by a Monte Carlo simulation in consideration of Fresnel's reflection law, UV self-absorption of lamp and thermal loss. The result was 4%, which is approximately the same as the experimental result (2%). For this reason, we believe this code is reliable. Finally, to improve the UV-utilizing efficiency for EIR, we calculated the rates under different conditions: more lamps and reactors inside a vessel. The results indicated that the absorption efficiency for EIR would reach 30% in the case of 9 reactors and 16 lamps inside the vessel. Because of the higher UV-utilizing efficiency and lower power cost for the UV lamp, we decided to choose IIR for a PCB decomposition plant.

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The development of production and utilization technology of highly reactive coke is significant in order to improve blast furnace reaction efficiency. A basic study of the solution-loss reaction (C+CO₂→2CO) in a CO–CO₂ atmosphere was performed with catalyst-supported high purity graphite to clarify the relation between the carbon and the catalyst.
The presence of a small amount of CO (1.5%) in the CO–CO₂ atmosphere greatly decreased the reactivity of the Ni-supported graphite at low temperature. On the other hand, the reactivity of the Fe-supported graphite increased with increasing CO until its concentration reached 50%. It was confirmed that the solution-loss reaction on the catalyst-supported graphite followed the redox reaction model and the changes in the reactivity with CO concentration could be explained by the equilibrium calculation based on the redox reaction model.
It was also found that the complex Fe–Ni-supported graphite showed high reactivity from low temperature to high temperature in the CO–CO₂ atmosphere. A SEM–EPMA observation revealed that the catalytic Fe–Ni particles did not agglomerate and were finely dispersed. On the other hand, in the case of a single-metal-supported graphite, the catalytic Fe or Ni particles agglomerated at high temperature, where the reactivity decreased. It was suggested that the complex Fe–Ni-supported graphite showed high reactivity because the agglomeration of catalytic particles was inhibited.

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This paper presents a new controller coordination method based on multiple local models for highly nonlinear chemical processes. In the proposed method, a bank of local controllers is designed based on multiple models and run in parallel. Manipulated variables are calculated by the affine combination of the weighted outputs of local controllers. The soft-max function with a tuning parameter is used to determine the weight coefficients of local controller outputs. This method is simulated to control the temperature of a non-isothermal continuous stirred-tank reactor (CSTR) whose liquid level changes according to the operational conditions. The proposed method exhibits good control capabilities over a wide range of operational conditions.

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In batch processes, the processing times of operations may fluctuate due to unforeseen failure of equipment or uncertain quality of the raw materials. Such disturbances affect the starting times of successive batches and force operators to do additional tasks and/or to change the processing order of pre-assigned tasks. Unexpected changes of schedule induce human errors, and affect the schedules for preparation of raw materials, inspection of products and product delivery. Thus, the propagation of such disturbances to successive batches should be suppressed as soon as possible. Usually, the buffer time, which is idle time between batches, is used to adjust the delay caused by the disturbances. However, it is not clear how to assign buffer times between batches. In this research, a systematic procedure deciding buffer times is proposed.
First, a method of calculating the influence of the delay of an operation on subsequent batches is explained. Then, a method of calculating buffer times that can absorb every pre-assigned disturbance within a given number of batches is proposed. In a real process, regular processing times of some operations are decided so as to have some allowance, and the processing times can be shortened by using additional manpower or utilities. The methods of shortening processing times are classified into several strategies, and a procedure for assigning buffer times under the predetermined strategies is also proposed. The effectiveness of the proposed procedure has been verified by simulation study.

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The possibility of preparing microcapsules composed of expanded polystyrene (EPS) in a (W/O)/W′ multiple emulsion system was investigated. Glycerol aqueous solution was employed to control the inner structure of microcapsules, (R)-(+)-limonene solution of EPS was used as the dispersed phase, and ethylene glycol solution of polyvinyl alcohol (PVA) was used as the continuous phase. It was found that the specific surface area of microcapsules increased with the concentration and the loading of glycerol aqueous solution, and also increased with the concentration of PVA in the continuous phase.

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Steam gasification of dried coffee grounds (about 10 wt% water) was investigated in a laboratory-scale bubbling fluidized bed gasifier coupled to a pneumatic transported bed char combustor. The effects of steam-to-fuel ratio and Ca additive in two different forms, physically mixed or impregnated, were tested to examine their potential to increase gasification efficiency and eliminate tars. This examination was also conducted in a two-stage bubbling fluidized bed gasifier having a secondary stage of fluidized particles in the gasifier's freeboard.
The results showed that increasing steam-to-fuel ratio only slightly increased the gasification efficiency expressed by fuel C conversion and cold gas efficiency, while the accompanying decrease in tar evolution was also not significant. Calcium additive exhibited pronounced upgrading effects on gasification efficiency and tar elimination only in the impregnated form. It increased the fuel C conversion from about 70% to 90% and decreased the tar content in the produced gas from 40 to 10 g/m³ N at a reaction temperature of about 1073 K. This kind of high activity to facilitate fuel gasification and enhance tar reforming/destruction was attributed to the high degree of dispersion of impregnated Ca throughout the fuel matrix. The CaO physically blended into the fuel was poorly dispersed, resulting in its low activity to affect gasification reactions. The two-stage bubbling fluidized bed gasifier allowed increased gasification efficiency and suppressed tar evolution to some extent, but it was hard to eliminate further the tars generated in gasifying the Ca-impregnated fuel. This indicates essentially that the tars from the Ca-impregnated fuel are more difficult to degrade than those from coffee grounds only.
This study also found that the fuel C conversion and tar content in product gas correlate with the H₂/CO molar ratio of the produced gas.

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In this study, the effect of water vapor on the hydrogen absorption–desorption properties of a hydrogen-absorbing MmNi₅-based alloy (MmNi_4.04Mn_0.31Co_0.60Al_0.05) was investigated. When pure hydrogen used, the hydrogen-absorbing capacity decreased slightly with the number of absorption–desorption cycles. However, when hydrogen containing water vapor was used, the hydrogen-absorbing capacity decreased significantly, due to a decrease in the rate of hydrogen absorption-desorption, and the rate of absorption–desorption decreased with an increase in cycle number and water vapor concentration. After reactivation of the alloy, the hydrogen-absorbing capacity recovered. However, the hydrogen-desorbing capacity and the rate of hydrogen absorption–desorption did not increase significantly compared with those before the reactivation. Thus, the reactivation tested in this study was effective only for hydrogen desorption from alloy was not completed hydrogen desorption.

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