Hironao Ogura

Effects of heat exchange condition on hot air production by a chemical heat pump dryer using CaO/H2O/Ca(OH)2 reaction

Results of an exploratory experimental study of a chemical heat pump (CHP) assisted convective dryer are presented. The CaO/H2O/Ca(OH)2 gas–solid reversible hydration/dehydration reaction is used to store and recover heat from the dryer exhaust air to enhance the thermal efficiency of the dryer. The CHP unit can be operated to increase the temperature level and also to dehumidify the air, which is a particularly attractive feature for drying. Results are presented for a single cylindrical reactor to study the effects of the heat exchange conditions on hot air production. The results show that the hot air production is improved by enlarging the heat exchanger, increasing the heat transfer rates by use of stainless mesh and increasing the air flow rate.

Frequency analysis of pressure fluctuation in fluidized bed plenum and its confidence limit for detection of various modes of fluidization

Abstract Pressure fluctuations were measured in a fluidized bed plenum and power spectral density functions obtained by fast Fourier transform (FFT) analysis of the pressure fluctuation and its confidence limit for the diagnosis of fluidization were investigated. Various species of fluidized beds, which consist of Groups A, B or D particles of Geldarts classification and their mixtures, were used. Species of fluidizing particles, weight fraction of particles in bed and bed height strongly influenced the mode of fluidization. They were also significantly reflected on the power spectral density function. From experimental results, it is concluded that frequency analysis of pressure fluctuation is useful to obtain information about fluidization and to diagnose the fluidized bed, while it has a limit for its ability for detection of the fluidization mode.

Coating efficiency of seed particles in a fluidized bed by atomization of a powder suspension

Abstract Seed particles were coated with a powder in a fluidized bed by atomizing a suspension of the powder and then measuring the coating efficiency. This depends on the operating conditions, for example, the concentration of the powder and binder in the suspension, the bed temperature, the humidity of fluidizing gas and the feed rate of the suspension. An index, R, which evaluates quantitatively the drying conditions in a fluidized bed, is defined as the ratio of the humidity of outlet gas to its maximum humidity achieved at the saturation. It was confirmed that the effects of bed temperature, humidity of fluidizing gas and feed rate of suspension on the coating efficiency were all correlated by the index. The index proposed here is useful for estimating the coating ability of the materials used and of the fluidized bed coater.

Effect of solid circulation rate on coating efficiency and agglomeration in circulating fluidized bed type coater

Circulating fluidized bed was proposed to be used as a coater, and coating experiments of glass beads with silica powder were performed in a circulating fluidized bed. Glass beads and silica powder were chosen as model particles, because their shape was almost spherical. The respective effects of gas flow rates supplied from a distributor and from an air nozzle for solid circulation, feed rate of powder suspension and particle content in the bed on coating efficiency and agglomeration are mainly discussed. Coating efficiency in circulating fluidized bed coater was correlated well with solid circulation time rather than with gas flow rates or solid circulation rate, while the agglomeration among core particles was mainly governed by solid circulation rate.

SIMULATION OF HYDRATION/DEHYDRATION OF CaO/Ca(OH)2 CHEMICAL HEAT PUMP REACTOR FOR COLD/HOT HEAT GENERATION

ABSTRACT A chemical heat pump (CHP) utilizes reversible reactions involving significant endothermic and exothermic heats of reaction in order to develop a heat pump effect by storing and releasing energy while transforming it from chemical to thermal energy and vice versa. In this paper, we present a mathematical model and its numerical solution for the heat and mass transport phenomena occurring in the reactant particle bed of the CHP for heat storage and cold/hot heat generation based on the CaO/Ca(OH)2 reversible hydration/dehydration reaction Transient conservation equations of mass and energy transport including chemical kinetics are solved numerically subject to appropriate boundary and initial conditions to examine the influence of the mass transfer resistance on the overall performance of this CHP configuration. These results are presented and discussed with the aim of enhancing the CHP performance in next generation reactor designs.

EXPERIMENTAL STUDIES ON A NOVEL CHEMICAL HEAT PUMP DRYER USING A GAS–SOLID REACTION

The authors have been studying Chemical Heat Pumps (CHP) from the viewpoints of energy saving and environmental impact. The CHP can store thermal energy in the form of chemical energy by an endothermic reaction, and release it at various temperature levels during heat demand periods by exo/endothermic reactions. The authors have proposed in an earlier study a novel chemical heat pump (CHP) system for environmentally-friendly effective utilization of thermal energy in drying as a chemical heat pump dryer (CHPD). In this exploratory study, we test the effectiveness of operating the proposed CHPDs experimentally. Basic experiments on the CHPDs such as hot dry air production for convective drying are performed on lab-scale CHPD apparatuses using gas–solid reactions in calcium oxide/calcium hydroxide reactant beds. The proposed CHPDs are found to produce hot air by CHP operation for drying. The temperature levels of the produced hot air and the reaction rates/conversions are as good as in the case of hot water supply system using basically same CHP operation. The cold heat for air dehumidification is also found to be generated/recovered by the same CHPD system. The generated heat amounts can be increased by changing the operating conditions although the heat recovery must be enhanced for practical application of CHPDs.

Fluidization behavior of glass beads under different vibration modules

The expansion of free bubbling gas fluidized beds has been investigated experimentally in a two-dimensional perspex-walled bed. Glass beads were fluidized with dried air at varying gas velocities, while the bed was vibrated at different frequencies, amplitudes and directions to study their effects on the fluidization quality. The experimental results showed that the particle flow pattern depends on the vibration direction, especially at superficial gas velocities less than the minimum fluidization velocity Umf. The effect of horizontal vibration on fluidization behavior of glass beads exists at superficial gas velocities less than Umf, while the effect of vertical vibration on fluidization behavior still exists even at higher superficial gas velocities than Umf.

Powder coating efficiency of small particles and their agglomeration in circulating fluidized bed

The coating efficiency of fluidizing small particles and their agglomeration were investigated to evaluate the possibility of powder coating by the use of a circulating fluidized bed. Glass beads, whose mean diameter was 43 Μm, and silica powder of 1 Μm were used as a core and a coating material. Polyvinyl alcohol was used as a binder and its solution was supplied together with silica powder from a spray nozzle equipped in the circulating fluidized bed. Glass beads of 43 Μm, which had been impossible to coat in a conventional fluidized bed coater, were successfully coated with silica powder in a circulating fluidized bed, and agglomeration among core particles was prevented. From this result, it was confirmed that a circulating fluidized bed performs excellently as a coater, especially for fine core particles, so a circulating fluidized bed coater has bright prospects for particle coating.

The effects of frequency and amplitude on the powder coating of fluidizing particles in a vibro-fluidized bed

Abstract Glass beads were coated in a vibro-fluidized bed by atomizing a fine silica powder and polyvinyl alcohol solution. The coating efficiency and weight fraction of the agglomerated particles were measured under various experimental conditions, and their dependencies on the amplitude and frequency of vibration were investigated. When the humidity of the outlet gas was high, high coating efficiency and agglomeration of core particles were observed. The efficiency of the powder coating decreased as the amplitude and the frequency increased, while the agglomeration was prevented by the addition of vibration. It was confirmed that high-quality and high-efficiency coating, where few agglomerates were produced and silica powder was utilized efficiently, was possible using the vibro- fluidized bed with adequate amplitude and frequency.

EFFECT OF DRYING ON POWDER COATING EFFICIENCY AND AGGLOMERATION IN VIBRO-FLUIDIZED BED

Glass beads of 43 μm were coated in a vibro-fluidized bed by atomizing a fine silica powder together with polyvinyl alcohol aqueous solution. The coating efficiency and weight fraction of the agglomerated particles were measured under various experimental conditions, and their dependencies on the frequency and the direction of vibration were investigated. The coating efficiency and the degree of the agglomeration among core particles correlated well with an index R. The index R was introduced to evaluate quantitatively the drying conditions in a fluidized bed. Application of vertical vibration on the fluidized bed lowered the coating efficiency somewhat, while it prevented agglomeration. From the experimental results it was confirmed that coating with high quality and high efficiency, where few agglomerates were produced and silica powder was utilized efficiently, was possible in a vibro-fluidized bed with adequate vibration frequency and orientation of the vibration vector.