Ryohei Yamazaki

A study on the behavior of bubbles and solids in bubbling fluidized beds

Abstract In present work, a novel bubble distribution model, based on the population balance of bubbles, is proposed incorporating with the Navier–Stokes equation for solid flow in order to predict the solid mixing and circulation as well as the bubble behavior in bubbling fluidized beds. This work is comprised of three sections: The first section is “estimation of solid flow pattern in bubbling fluidized bed”. In this section, we compare the computed values of bubble diameter and solid velocities with experimental values in cylindrical bubbling fluidized bed. The second section is “estimation of solid flow pattern in rectangular fluidized beds”. This section is divided into two parts. In the first part, we apply the simulation model to bubbling rectangular fluidized bed, which is expressed by the rectangular coordinate system in place of the cylindrical coordinate. In the second part, we compute the solid behavior in beds equipped with immersed vertical tubes. Third section is “solid mixing in bubbling fluidized beds”. This section is also divided into two parts. In the first part, we investigate experimentally the solid mixing characteristic in bubbling fluidized beds using the tracer particle. In the second part, we incorporate the simulation model with a solid dispersion model for predicting the solid mixing in bubbling fluidized beds.

Combustion test of refuse derived fuel in a fluidized bed

Abstract Power generation from refuse derived fuel (RDF) is one of the promising technologies for the utilization of municipal solid waste. To understand the combustion behavior of two kinds of RDF burnt in a fluidized bed incinerator, commercial sized RDF was fed continuously into a 0.3×0.3 m 2 and 2.73 m high bubbling type fluidized bed combustor. Gases such as CO, NO x , SO x and HCl concentrations in the flue gas from the combustor were detected by a continuous measurement system. It was found that, for RDF-A which is lower in density and strength than RDF-B, the concentrations of CO in flue gas are high and are strongly affected by the air ratio. When secondary air was injected, the CO concentrations for both RDF-A and RDF-B were decreased. The increase in the air ratio led to an increase of NO x concentration when only primary air was injected at a bed temperature of 1073 K. The addition of secondary air effectively reduced the NO x level for both RDF-A and RDF-B. The temperature where the HCl concentration was the lowest was about 1073 K. Nonetheless the concentrations of HCl were always less than 60 ppm in all experiments. The HCl removal ratio by the calcium compound was higher than 70% even though the bed temperature was higher than 1173K. This indicates that the added calcium compound in the RDFs effectively controlled the HCl emissions.

Fundamental study of the behavior of chlorine during the combustion of single RDF.

A fundamental study of the combustion characteristics and the de-HCl behavior of a single refuse-derived fuel (RDF) pellet was carried out to explain the de-HCl phenomena of RDF during fluidized bed combustion and to provide data for the development of high efficiency power generation technology using RDF. In this research, combustion and pyrolysis experiments were carried out in an electrical furnace using a series of model and actual RDF samples. The de-HCl capability of Ca(OH)2 in RDF was evaluated by measuring the emission fraction of HCl in the flue gas and the capture fraction of Cl in the residue. It was found that the capture fraction of Cl components in the residue increased from 0 to nearly 70% when the molar ratio of Ca/Cl was changed from 0 to around 13. Apparently, the capture fraction also decreased with increasing oxygen concentration in the feed gas. The devolatilization process of RDF was confirmed to be a very important part of de-HCl process. The effect of temperature profile of the RDF pellet on the de-HCl process, as it varies with the heating rate of RDF and the oxygen concentration in the vicinity of the sample, is discussed.

Effect of chemisorbed water on bed voidage of high temperature fluidized bed

Abstract Minimum fluidization voidage in the beds of three kinds of silica is investigated at elevated temperatures up to 1223 K experimentally and theoretically. The bed voidage depends not only upon the operating temperature but also upon the humidity of fluidizing gas. Experimental results and theoretical consideration on the change in the bed voidage with temperature and/or humidity demonstrate that this change is caused by the adhesion force of silica particles originating from the change in the concentration of siloxane groups on the surface of the particles.

Multi-component granulation in a fast fluidized bed

The granulation of multi-component particles was conducted in a fast fluidized bed with an atomizing binder solution. The effects of gas velocity and binder droplet diameter on granulation rate, granule size distribution and granule composition were studied. The granulation rate and granule yield were determined by the balance between the agglomeration rate of feed particles and the disintegration rate of granules because there was no secondary granulation. With the increase in gas velocity and the reduction in binder droplet size, the agglomeration rate of feed particles decreased but the disintegration rate of granules increased, resulting in a reduced granule yield. Despite the larger fraction of small particles in the granules, the homogenous granulation of multi-component particles was achieved.

Numerical Simulation of Particle Behavior in Fluidized Bed Equipped with Immersed Vertical Tubes.

大型矩形流動層内に垂直管群を挿入した場合の層内の粒子挙動を推算した.このシミュレーションモデルは, 気泡の挙動と粒子循環を推定することのできる前報のモデルをベースに伝熱管表面での境界条件を新たに加え修正したものである.管群が粒子挙動に与える影響について検討を行った結果, 層内に管群の挿入がある場合, 層内粒子運動は伝熱管により抑制され, 層内に形成する粒子循環流のフローパターンは, 層内に伝熱管挿入がない場合とは異なるため, 層内粒子温度の均一性を損なう恐れがある。そのため, 伝熱管群を適切に配置することは流動層設計の際非常に重要であることが分かった.

Development of Process for Manufacturing Metal-Nonmetal Composite Particles Using Fluidized-Bed in Electro-Magnetic Field.

非導電性粒子にてコーティングされた金属粒子を製造するプロセスを開発するために, 電磁場内に設置した流動層を用いて実験を行った.コーティング試験は窒素雰囲気のもとで行った.非導電性粒子を用いる流動層を電磁加熱コイルの中に設置し, 窒素ガスを流し, 電磁場を印加した後に, 所定量の金属粒子を上部より投入し非導電性粒子で被覆された金属粒子を回収した.コーティングの原理は, 非導電性粒子の融点が金属粒子の融点より高いか低いかによって, 2通りあることがわかった.プラスチックによるコーティングについてはプラスチックの融点により, 印加出力, ガス流速の最小点が変化すること, またコーティング厚さは印加出力と共に増加することがわかった.

Thermal Energy Storage, Heat Pump and Thermal Energy Transportation Technologies. Solid Mixing Behavior in Bubbling Fluidized Beds.

流動層の軸方向および水平方向の粒子混合特性を調べるため, 矩形流動層を用いてトレーサー粒子の濃度変化の測定をおこなった.実験は, 粒子挙動が二次元とみなせる流動層を用い, 壁面をCCDカメラで撮影し, その画像をイメージデジタイザーで解析することにより流動層内粒子混合の測定を行った.また, 粒子径の混合に及ぼす影響について調べるため, 2種類の粒子径を選択し実験を行った.その結果, 流動化直後層内に大きな渦状の粒子循環流の形成がみられ, 層内での粒子混合は, 層壁近傍においてその層内粒子大循環流の影響を大きく受けていることがわかった.また, 層中心部および層下部においては気泡の移動に伴う混合が支配的であることがわかった.

Simulation modeling of fluidized bed coal gasifier for new topping cycle system

A new topping cycle coal power generation process is to be developed as a Japanese national project of high efficiency power generation process of coal. This process consists of a combination system of a pressurized bubbling fluidized-bed coal gasifier and a pressurized bubbling fluidized-bed combustor in series. To evaluate the performances and also to determine specifications and operation parameters of this process, it is extremely important to analyze the behavior and the performance of this system by a reasonable simulation model. A simulation model of this new process is developed in this paper. It is demonstrated by calculated results from this model that the carbon conversion in the gasifier, the composition and the heating value of produced gas are strongly dependent on operating conditions. Heat recovery by the steam in the combustor is also estimated as the function of coal feed rate.

The effect of ring-shaped baffles on bubble behavior in a gas-solid fluidized bed.

気固系流動層内にリング状バッフルを設置して, バッフルの位置, 数, 気泡挙動への影響を実験的に検討した.リング状バッフルは, 気泡のほとんど無い塔壁近傍に設置した場合にも気泡挙動に大きな影響を与え, 気泡の空間分布を均一にし, 平均気泡径を小さくする効果があることを見いだした.この機構を明らかにするために, 半円筒可視モデルを用いて粒子挙動を測定し, リング状バッフルが粒子下降流を変え, 気泡挙動に影響を与えることを明らかにした.