Attrition of char agglomerates

A 15.2 cm diameter fluidized bed system with single- and multiple-jet distributors was designed and constructed to study the attrition behavior and mechanism of Kentucky No. 9 char from IGT's U-GAS fluidized bed gasifier. The effects of the jet and auxiliary gas velocities, the number of jets, the bed height, and the roughness of the fluidized bed wall on the attrition of char particles were studied. Particle shape variation during attrition was calculated by comparing our experimental data on pressure drop for a packed bed with the Ergun equation prediction. A mathematical procedure was developed to translate the size distribution variation of particles in the fluidized bed to the attrition rate expression.     

Numerical simulation of gas-particle flow with a second-order moment method in bubbling fluidized beds

Flow behavior of gas and particles is performed by means of gas-solid two-fluid model with the second-order moment model of particles in the bubbling fluidized bed. The distributions of velocity and moments of particles are predicted in the bubbling fluidized beds. Predictions are compared with experimental data measured by Jung et al. (2005) in a bubbling fluidized bed and Patil et al. (2005) experiments in a bubbling fluidized bed with a jet. The simulated second-order moment in the vertical direction is on average 1.5-2.3 times larger than that in the lateral direction in the bubbling fluidized bed (Jung et al., 2005). For a bubbling fluidized bed with a jet, the ratio of normal second-order moment in the vertical direction to in the lateral direction is in the range of 0.5-2.5 (Patil et al., 2005). The bubblelike Reynolds normal stresses per unit bulk density used by Gidaspow et al. (2002) are computed from the simulated hydrodynamic velocities. The simulated bubblelike Reynolds normal stresses in the vertical direction is on average 4.5-6.0 times larger than that in the lateral direction in the bubbling fluidized bed (Jung et al., 2005). The predictions are in agreement with experimental second-order moments measured by Jung et al. (2005) and porosity measured by Patil et al. (2005).     

IMPORTANCE OF DISPERSED SOLIDS IN BUBBLES FOR EXOTHERMIC REACTIONS IN FLUIDIZED BEDS

Ignition of activated carbon particles were measured in a vertical tube reactor of 4 cm ID, where single particles fell consecutively through a gas mixture containing oxygen.

A two dimensional fluidized bed reactor 24 cm wide, 51 cm high and 2.5 cm in thickness was used for visual observation through a wide front window 24 cm × 35 cm covered with a silica glass plate 1 cm thick. Activated carbon particles were fluidized incipientiy by air, and a gas mixture containing oxygen was injected upwards into the bed through a nozzle positioned 5 cm above the distributor, forming single bubbles intermittently.

It was observed that carbon particles dispersed in rising bubbles were ignited abruptly at emulsion phase temperatures above 550°C. Experimental findings from the fluidized bed were compared with those from the tube reactor, suggesting that the igniting conditions for particles dispersed in bubbles are nearly the same as for single particles falling in the tube reactor.     

IMPORTANCE OF DISPERSED SOLIDS IN BUBBLES FOR EXOTHERMIC REACTIONS IN FLUIDIZED BEDS

Ignition of activated carbon particles were measured in a vertical tube reactor of 4 cm ID, where single particles fell consecutively through a gas mixture containing oxygen.

A two dimensional fluidized bed reactor 24 cm wide, 51 cm high and 2.5 cm in thickness was used for visual observation through a wide front window 24 cm × 35 cm covered with a silica glass plate 1 cm thick. Activated carbon particles were fluidized incipientiy by air, and a gas mixture containing oxygen was injected upwards into the bed through a nozzle positioned 5 cm above the distributor, forming single bubbles intermittently.

It was observed that carbon particles dispersed in rising bubbles were ignited abruptly at emulsion phase temperatures above 550°C. Experimental findings from the fluidized bed were compared with those from the tube reactor, suggesting that the igniting conditions for particles dispersed in bubbles are nearly the same as for single particles falling in the tube reactor.     

A novel induction heating fluidized bed reactor: Its design and applications in high temperature screening tests with solid feedstocks and prediction of defluidization state

A novel mini induction heating fluidized bed reactor (IHFBR) is introduced which was developed to carry out screening tests of high temperature reactions up to 1500°C particularly for solid feedstocks. Despite conventional mini reactors, this reactor mimics real scenario of solid feeding in industrial reactors: cold feedstock is injected within 1 s from a lift tube, then particles reach reaction temperature in less than 5 s in a reaction zone. The lift tube (9.5 cm diameter) is also the gas distributor of the fluidized bed (2.5 cm diameter) so that the bed is completely fluidized with uniform gas distribution. Beside facilities to perform tests in a fluidized bed, another important feature of this reactor is prediction of the defluidization state in the bed. Not only reproducible data are generated, but also many tests can be conveniently carried out, that is, one test per hour. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1507–1523, 2015     

Numerical simulation of horizontal jet penetration in a three-dimensional fluidized bed

The introduction of reactant gas as a jet into a fluidized bed chemical reactor is often encountered in various industrial applications. Understanding the hydrodynamics of the gas and solid flow resulting from the gas jet can have considerable significance in improving the reactor design and process optimization. In this work, a three-dimensional numerical simulation of a single horizontal gas jet into a cylindrical gas-solid fluidized bed of laboratory scale is conducted. A scaled drag model is proposed and implemented into the simulation of a fluidized bed of FCC particles. The gas and particles flow in the fluidized bed is investigated by analyzing the transient simulation results. The jet penetration lengths of different jet velocities have been obtained and compared with published experimental data as well as with predictions of empirical correlations. The predictions by several empirical correlations are discussed. A good agreement between the numerical simulation and experimental results has been achieved.     

Geometrical and hydrodynamical study of gas jets in packed and fluidized beds using magnetic resonance

Magnetic resonance (MR) was used to image the motion of particles and gas just above the distributor of 3D beds of particles fluidized by air. Three different distributors were used: (i) a single‐orifice distributor, with orifice diameters 1.0–4.0 mm, (ii) a plate, drilled with a triangular array of 79 holes, each of 0.35 mm diameter, with a central nozzle containing a single hole of diameter 1.0, 2.5, or 9.0 mm, (iii) distributors with two or three orifices and diameters of 1.0 or 2.5 mm. It proved possible to extract geometrical information, such as the length of a jet, from MR images, each averaged over ～5 min. Also, light was shed on the question of why is there such a discrepancy between reported jet‐lengths. The fluidization state, the “start‐up” procedure and also the number of holes all play a significant role in determining the measured distance a jet penetrates into a bed. The question as to whether the observed voids represent permanent jets or streams of bubbles was considered. The evidence from ultra‐fast MR measurements strongly suggests that only the lower part of a jet from an orifice in a multi‐orifice distributor is permanent; bubbles form at the top of the jet. Consequently, the top of each jet is transient. However, most of the jet from a single orifice is a permanent cavity when the bed of particles is not fluidized. The length of a jet was successfully correlated with operating variables using dimensional analysis. Finally, the flow of particles around a single jet was measured with high resolution MR.     

Numerical and experimental study on spout elevation in spout‐fluidized beds

The effect of elevating the spout on the dynamics of a spout‐fluidized bed, both numerically and experimentally is studied. The experiments were conducted in a pseudo‐two‐dimensional (2‐D) and a cylindrical three dimensional (3‐D) spout‐fluidized bed, where positron emission particle tracking (PEPT) and particle image velocimetry (PIV) were applied to the pseudo‐2‐D bed, and PEPT and electrical capacitance tomography (ECT) to the cylindrical 3‐D bed. A discrete particle model (DPM) was used to perform full 3‐D simulations of the bed dynamics. Several cases were studied, that is, beds with spout heights of 0, 2, and 4 cm. In the pseudo‐2‐D bed, the spout‐fluidization and jet‐in‐fluidized‐bed regime, were considered first, and it was shown that in the spout–fluidization regime, the expected dead zones appear in the annulus near the bottom of the bed as the spout is elevated. However, in the jet‐in‐fluidized‐bed regime, the circulation pattern of the particles is affected, without the development of stagnant zones. The jet‐in‐fluidized‐bed regime was further investigated, and additionally the experimental results obtained with PIV and PEPT were compared with the DPM simulation results. The experimental results obtained with PIV and PEPT agreed mutually very well, and in addition agreed well wtih the DPM results, although the velocities in the annulus region were slightly over predicted. The latter is probably due to the particle‐wall effects that are more dominant in pseudo‐2‐D systems compared with 3‐D systems. In the jet‐in‐fluidized‐bed regime, the background gas velocity is relatively high, producing bubbles in the annulus that interact with the spout channel. In the case of a non elevated spout, this interaction occurs near the bottom of the bed. As the spout is elevated, this interaction is shifted upwards in the bed, which allows the bubbles to remain undisturbed providing the motion of the particles in the annulus near the bottom of the bed. As a result, no dead zones are created and additionally, circulation patterns are vertically stretched. These findings were also obtained for the cylindrical 3‐D bed; although, the effects were less pronounced. In the cylindrical 3‐D bed the PEPT results show that the effect on the bed dynamics starts at h_spout =1 4 cm, which is confirmed by the ECT results. Additionally, ECT measurements were conducted for h_spout =1 6 cm to verify if indeed the effect happens at larger spout heights. The root mean square of the particle volume fraction slightly increased at h_spout =1 2 cm, whereas a larger increase is found at h_spout = 4 and 6 cm, showing that indeed more bubbles are formed. The presented results have not been reported so far and form valuable input information for improving industrial granulators. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2524–2535, 2012     

Solids entrainment into gas, liquid, and gas-liquid spray jets in fluidized beds

The injection of liquid into a fluidized bed is a crucial step in many processes such as fluid coking, fluid catalytic cracking, or gas-phase polymerization, whose performance greatly depends on good and rapid contact between the injected liquid and the fluidized particles. The liquid spray, created by two-phase (gas-liquid) nozzles, forms a jet, i.e. a gas-rich cavity within the fluidized bed. Past studies have shown that good liquid-solid contact requires a large entrainment rate of particles into the jet, followed by intensive mixing of liquid droplets and entrained particles within the jet. The objective of this study is the experimental measurement of solids entrainment into spray jets. The specific application of interest is the enhancement of solids entrainment under conditions relevant to the fluid coking process.A novel and accurate experimental technique has been developed to measure the solids entrainment from a fluidized bed into two-phase gas-liquid jets, gas jets and liquid jets. The effects of operating conditions of the nozzle (sonic versus subsonic) and of the fluidized bed on the solids entrainment have been investigated. The differences between the mechanisms of solids entrainment for two-phase gas-liquid, gas and liquid jets have been analyzed.This experimental tool has been applied to the design and testing of a mixing chamber consisting of a cylindrical tube placed at a certain distance downstream of the nozzle tip, resulting in a confined, turbulent jet with enhanced liquid-solid mixing properties.     

带内置水平管的大颗粒振动流化床流体力学研究

以大颗粒MAP（磷酸-铵）为试验物料对带内置水平管的大颗粒振动流化床流体力学进行了试验研究,结果表明,振动的引入对床层临界压降有明显的降低作用;同样床层条件下振动频率越大床层临界压降越低,振幅的改变对床层压降影响不大;低气速下振动使床层孔隙率降低而导致压降高于普通流化床;在带内置水平管的大颗粒振动流化床中,振动对大粒径颗粒的影响小于小粒径颗粒;由试验拟合出经验公式,与试验数据吻合良好。     

沉浸管式流化床的颗粒尺度模拟

为模拟具有复杂几何结构的气固流动系统,文中将计算流体力学和离散单元法与边界元方法结合起来,对沉浸管式流化床内颗粒及气泡的运动行为进行了数值模拟。模拟计算得到的瞬态流型图揭示了气泡绕流沉浸管束时出现的合并和破碎状态及颗粒群的详细运动行为,发现床内气固二相的流动受到沉浸管束存在的显著影响。当颗粒及气相的流动受到沉浸管的阻碍而绕管流动过程中气泡会发生变形,变得扭曲狭长且易被撕碎。同时颗粒与管道壁面碰撞会造成气固二相复杂的动态运动形式,床内的管道大部分时间会被气穴包围,将严重阻碍管道与颗粒之间的传热。     

内热式惰性粒子流化床中膏状物料干燥模型

通过对惰性粒子流化床中膏状物料干燥机理的分析,得到了干燥时间及单位面积床层水分汽化量的数学计算式,可对干燥器的性能进行预测。采用带浸没加热管的惰性粒子流化床对膏状钛白物料进行干燥中试研究,采用气流式喷嘴将膏状物料分散成200～400μm的小液滴喷洒在惰性粒子表面进行干燥,探索了适宜的干燥条件,测定和确定了最佳的干燥工艺参数、操作参数和设备参数。结果表明:该干燥工艺能强化床内传热传质,促进高黏性膏糊状物料很好地分散,床层温度分布均匀,干燥器的操作弹性大,热量消耗低,干燥强度高,传热系数可达300W·m-2·K-1以上。     

Particle-scale simulation of fluidized bed with immersed tubes

In order to simulate gas-solids flows with complex geometry, the boundary element method was incorporated into the implementation of a combined model of computational fluid dynamics and discrete element method. The resulting method was employed to simulate hydrodynamics in a fluidized bed with immersed tubes. The transient simulation results showed particle and bubble dynamics. The bubble coalescence and break-up behavior when passing the immersed tubes was successfully predicted. The gas-solid flow pattern in the fluidized bed is changed greatly because of the immersed tubes. As particles and gas are come in contact with the immersed tubes, the gas bubbles will be deformed. The collisions between particles and tubes will make the tubes surrounded by air pockets most of the time and this is unfavorable for the heat transfer between particles and tubes.     

Magnetic Resonance Imaging of fluidized beds

This paper reviews recent developments in Magnetic Resonance Imaging (MRI) which enable it to follow particle motion in fluidized beds. Imaging with a spatial resolution of 400 μm and a temporal resolution of 1 ms is now feasible; particle velocities of order 1 m/s can be measured with good accuracy. The technique provides voidage fractions on a motion-picture basis and particle velocity fields. Limitations are: (i) the particles must contain appropriate atoms e.g. C or H; and (ii) currently the fluidized bed diameter cannot exceed 50 mm, though measurements from larger units will doubtless become available. MR studies on fluidized beds are described: results are reported for (i) air jets entering the bed (ii) bubbling and slugging beds and (iii) dispersion in a bubbling bed. The data are consistent with published measurements. Study (i) helps to resolve the longstanding puzzle about the behaviour of an air jet entering a fluidized or partly-fluidized bed, answering the question: does the entering air form bubbles or a continuous jet?     

Use of piezoelectric pressure transducers to determine local solids mass flux in the riser of a cold flow circulating fluidized bed

A method to determine local mass flux measurements within the riser of a circulating fluidized bed using the rate of impingement of particles on the surface of a piezoelectric pressure transducer is described. Statistically designed experiments with various solids circulation rates and riser gas velocities were conducted in the riser of a cold flow circulating fluidized bed to verify the accuracy of the method. Also, various techniques to relate the impingement rate to mass flux were employed. It is believed that this method delivers results in situations where more standard methods, such as isokinetic sampling, fail.     

Effect of injection-nozzle operating parameters on the interaction between a gas-liquid jet and a gas-solid fluidized bed

The objective of the present study was to provide insight into the effect of operating conditions on the performance of gas-assisted nozzles injecting liquid into gas-solid fluidized beds. Acquisition of such knowledge is relevant to many industrial applications where liquid injections into fluidized beds of solid particles are performed via spray nozzles. In the fluid coking process, for example, product yields and reactor operability strongly benefit from a rapid and uniform distribution of the liquid feed on fluidized solid particles, which, in turn, is greatly affected by the performance of the liquid-injection system used.A novel experimental technique was employed to investigate the effect of varying the air-to-liquid ratio (ALR), the liquid mass flow rate, and the nozzle size on the contact efficiency of injected liquid on fluidized bed particles. Increasing the ALR or the liquid flow rate increased the nozzle spraying efficiency. On the contrary, increasing the nozzle size while keeping the gas and the liquid flow rates constant, and hence decreasing the pressure at the nozzle tip, lowered the liquid-solid contact efficiency.The effect of increasing the ALR on the liquid-solid contact resulting from nozzle-injections into the fluid bed, was correlated to both the nozzle atomization performance, as determined by open-air tests using a laser-photocell equipment, and the solids entrainment into the gas-liquid jet, as predicted by a model.     

流化床灰熔聚煤气化器中高速射流区的颗粒分离

本文研究了垂直射流喷入流化床时固体颗粒从喷口排出的稳定分离过程及初始分离速度U_(IJ)的确定;考察了射流区的几何结构对床层流动特性与分离过程的影响;提出用结构流动参数C_s来作为选取射流区合理几何结构的重要判据;指出了细粒组份对颗粒分离的改善作用.     

Enhancement of the liquid feed distribution in gas‐solid fluidized beds by nozzle pulsations (induced by solenoid valve)

In this work, it was found that spray nozzles pulsations greatly improved the liquid feed spray distribution on fluidized bed particles. Pulsating a spray nozzle doubled its nozzle performance index at various operating conditions. The objective of this study was to impose fluctuations of well‐defined frequency and amplitude on the liquid spray to investigate potentially beneficial effects of fluctuations on the liquid feed distribution on the particles in the fluidized bed. Three sets of experiments were conducted to study the quality of the spray jet‐bed interaction using a conductance probe method. The jet penetration for each experiment was calculated theoretically. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

Particle-scale simulation of fluidized bed with immersed tubes

In order to simulate gas-solids flows with complex geometry, the boundary element method was incorporated into the implementation of a combined model of computational fluid dynamics and discrete element method. The resulting method was employed to simulate hydrodynamics in a fluidized bed with immersed tubes. The transient simulation results showed particle and bubble dynamics. The bubble coalescence and break-up behavior when passing the immersed tubes was successfully predicted. The gassolid flow pattern in the fluidized bed is changed greatly because of the immersed tubes. As particles and gas are come in contact with the immersed tubes, the gas bubbles will be deformed. The collisions between particles and tubes will make the tubes surrounded by air pockets most of the time and this is unfavorable for the heat transfer between particles and tubes. __________ Translated from Chemical Engineering, 2007, 35(11): 21–24 [译自:化学工程]     

A two-dimensional gas fluidized bed for hydrodynamic and elutriation studies

A two-dimensional fluidized bed having the dimensions of 52.1 cm (20.5 in) by 2.00 cm (0.787 in) is designed and tested for its use in hydrodynamic and elutriation studies. The fluidization column is provided with a calming section and freeboard which are 45.7 cm (18.0 in) and 129.5 cm (51.0 in) high respectively. A porous distributor plate is provided whose pressure drop is found to vary linearly with air velocity in the range of current interest. Fluidization experiments with three sand particles (788, 488 and 167 μm), glass beads (427 μm), millet (2064 μm) and green peas (4578 μm) are reported. Bed expansion and bubble growth characteristics are examined in some detail. Variations of bed height and pressure drop with fluidization velocity are analyzed to establish bed voidage as a function of gas velocity, and minimum fluidization velocity. The latter is also measured for three particles in a 0.305 m square fluidized bed. These studies reveal that two-dimensional fluidized beds are great tools for making novel qualitative investigations for mechanistic details of processes taking place in three-dimensional fluidized beds. Currently, investigations are underway for elutriation phenomenon.