Kunio Yoshida

Co-liquefaction of coal and cellulose in supercritical water

Co-liquefaction of biomass and coal in supercritical water is proposed with the intention that hydrogen matching between biomass and coal takes place, resulting in enhanced coal liquefaction and preferable liquefaction products. A semi-batch packed-bed reactor is employed to co-liquefy cellulose utilized for a model compound of biomass and Ishikari coal in supercritical water at 673 K and 25 MPa. No interaction between coal and cellulose is observed for the production of residue and water-insoluble product, judging from the yield and its composition. On the contrary, the yield of the water-soluble product increased for the case of co-liquefaction. Both hydrogen to carbon ratio and oxygen to carbon ratio of the water-soluble product increased by co-liquefaction. The mechanism for this interaction is proposed based on the addition reaction of compounds derived from cellulose with coal-derived compounds to increase the recoverable yield of the water-soluble product.

A novel fluidized-bed coating of fine particles by rapid expansion of supercritical fluid solutions

A novel fluidized-bed coating process using the rapid expansion of supercritical fluid solutions (RESS) is described for the coating of fine particles. Experiments were conducted in a 50 mm i.d. circulating fluidized bed with an internal nozzle in the center of the riser. Microspheroidal catalyst particles (average particle size 56 μm) were used as the core particles. Supercritical carbon dioxide solutions of paraffin were expanded through the nozzle into the bed that was fluidized by air. The coating mass and coating rates were measured by a sampling method. Mercury porosimetry was used to determine the quality of the coated particles. A stable coating of fine particles was achieved without the formation of agglomerates at room temperature. The present study examines the effects of hydrodynamics and solute concentration on coating rate and coating efficiency.

Diagnosis of chaotic dynamics of bubble motion in a bubble column

Abstract The motion of bubbles in a two-dimensional bubble column was characterized by the deterministic chaos analysis of time-series data of bubble frequency, measured locally by an optical transmittance probe with a narrowed He Ne laser beam. To diagnose the dynamics of bubble motion, three different methods were applied to the series of time intervals between two successive bubble passages: (i) the correlation dimensions were estimated from the reconstructed attractors, (ii) using the short-term predictability analysis, the deterministic and random features in the bubble motion were characterized in terms of Mann-Whitney statistic, and (iii) the value of the Hurst exponent was computed using the rescaled range ( R/S ) analysis. All three parameters were found to show consistent and significant changes at the transition between homogeneous bubble flow and heterogeneous churn-turbulent flow. These results indicate that at low velocity the motion of bubbles in the bubble column is deterministic chaotic whereas at high gas velocity the random-like motion of bubbles becomes significant.

Solar UT-3 thermochemical cycle for hydrogen production

Abstract The UT-3 thermochemical hydrogen producing cycle is a four step process developed at the University of Tokyo. In the process, only solid and gas reactants/products are used and the maximum temperature is 1033 K. The process has been developed to be coupled with gas cooled nuclear reactors (HTGR). In this article, a new UT-3 process is conceived to be coupled with a solar heat source. In the new process, all four reactions are carried out in a adiabatic equipment where steam (or steam + nitrogen) can be used as a vector. The operation of the process is done continuously. During sunshine hours, the energy to the process is supplied directly from the solar receiver. During cloudy periods and nights, it is supplied from a thermal storage system where the necessary high temperature heat is stored during sunshine hours. The solar UT-3 process has been evaluated using the ASPEN-PLUS code. It is found that the overall thermal efficiency is 49.5%, the exergetic efficiency is 52.9% and the process can be realized using conventional materials. Sizing of a solar hydrogen plant producing 2000 Nm3 per hour hydrogen has been carried out and operation of various equipment has been discussed.

Mechanism of bed-wall heat transfer in a fluidized bed at high temperatures

Abstract Radiant heat transfer in a fluidized bed was investigated experimentally by means of two kinds of heat exchange pipes. It was found that the contribution due to radiant heat transfer would be insignificant at temperature levels in fluidized beds up to 1000°C. The results are interpreted in terms of a model based on the behaviour of bubbles in the fluidized bed.

An artificial neural network as a model for chaotic behavior of a three-phase fluidized bed

Abstract Non-linear hydrodynamic behavior of bubble motion and that of particle motion in a three-phase fluidized bed have been modeled by resorting to an artificial neural network (ANN). The experiments were performed in a transparent acrylic resin column with an inner diameter of 0.184 m and a height of 2.0 m. Subsequently, the ANN was trained with the time-series data comprising temporal intervals, each of which was the period between two sequential signals of bubbles or particles from an optical transmittance probe. By successively adapting its output to input, the ANN has regenerated time-series data at any superficial gas velocity, Ug, thereby yielding the bifurcation diagrams of both bubble and particle motion. These diagrams exhibit complex behavior over a wide range of Ug, thus demonstrating that the ANN is capable of predicting and modeling non-linear dynamics of three-phase fluidized beds often behaving chaotically.

Dependences of laser-induced bulk damage threshold and crack patterns in several nonlinear crystals on irradiation direction

The dependence of the bulk damage threshold of nonlinear crystals, such as KDP, KTP, LBO, BBO, CLBO, LiNbO3, and LiTaO3 on laser irradiation direction and their polarization under a single-shot operation have been investigated. We found that the intrinsic bulk-damage threshold for nonlinear crystals was mainly caused by dielectric breakdown from self-focusing with nonlinear refractive index. LBO single crystals have the highest value studied among nonlinear crystals. For KDP, BBO, and CLBO crystals, the damage threshold when an incident laser was propagated along the axis is approximately twofold that in the {100} or {010} plane at a 1.064 µm wavelength. The damage crack pattern is also suggested to be in the mechanically weak direction due to inner pressure caused a laser-induced plasma in the crystal as a result of the laser breakdown due to electron avalanche breakdown.

Adiabatic UT-3 thermochemical process for hydrogen production

Abstract The UT-3 thermochemical hydrogen producing cycle is a four step process developed at the University of Tokyo. In the process, only solid and gas reactants/products are used and the maximum temperature is 1033 K. In this paper, a new UT-3 process has been developed in which all four reactions are carried out adiabatically using a heat carrier vector (steam or an inert gas). The new process has been evaluated using the ASPEN-PLUS process code. The first law efficiency of the cycle has been determined as 48.9% and the second law efficiency as 53.2%. The process can be realized using conventional materials for the reactors, which can be packed bed, honeycomb or fluidized bed type. In the latter case, it is found that the flow rate of the heat carrier fluid is sufficient to fluidize all four reactors. For a plant producing 30,000 Nm3 per hour or 2.68 × 106 GJ H2 per year, the plant sizing has been carried out, its operation is discussed and its advantages are presented.

Chaotic Hydrodynamics of Continuous Single-Bubble Flow Systems

Abstract The time evolution of bubble motion was studied in continuous single-bubble flow systems. Dynamic changes in rise velocity, shape and orientation of bubbles were simultaneously measured using a flow visualization method. Both deterministic chaos and stochastic analyses were used to diagnose bubble dynamics in gas-liquid two-phase systems. The bubbles were found to have chaotic fluctuations in shape and rise velocity. The Kolmogorov entropy and the correlation dimension of the attractor reconstructed from the time-series data of bubble-shape indices and velocity components by the embedding method were found to be positive and very high, indicating the chaotic-time evolution of bubble motion. On the other hand, the bubble inclined angle exhibited a periodic variation in bubble orientation, reflecting the zigzag motion of rising bubbles. The fluctuation in bubble-rise velocity can be considered to take place in the streamwise direction due to the oscillation of drag force associated with the bubble-shape fluctuation.

Purification of Waste Waters Containing Low Concentrations of Heavy Metals

Abstract Two types of brown coal, oxyhumolite and peat were studied with respect to their ability to remove heavy metals from waste waters. The results showed that the calcium loaded form of these materials can be effectively used for metal extraction by ion exchange with calcium. The proposed method can be recommended for concentrations of metals less than 10 mM.