Predicting Transition Velocities from Bubbling to Turbulent Fluidization by S-Statistics on Vibration Signals

Vibration signatures as the representatives of the fluidized bed nonlinear hydrodynamics were measured in a lab-scale fluidized bed of sand particles operated at ambient conditions. The experiments were carried out for three particle sizes, different velocities, and three probe heights. The S-statistic method was applied to the vibration signatures for the chaotic attractor comparison. The measured signatures of two different consecutive velocities in similar conditions were compared based on null hypothesis that they have same origin. According to this method, when the value of S is larger than 3, the null hypothesis is rejected with the confidence level of 95% indicating that the two signals are originated from different hydrodynamics. The results are compared with results obtained from common statistical methods and it is shown that attractor comparison can be a reliable method for detecting regime transition velocity.     

Advanced m-CHP fuel cell system based on a novel bio-ethanol fluidized bed membrane reformer

Distributed power generation via Micro Combined Heat and Power (m-CHP) systems, has been proven to over-come disadvantages of centralized generation since it can give savings in terms of Primary Energy consumption and energy costs.The FluidCELL FCH JU/FP7 project aims at providing the Proof of Concept of an advanced high performance, cost effective bio-ethanol m-CHP cogeneration Fuel Cell system for decentralized off-grid applications by end of 2017. The main idea of FluidCELL is to develop a new bio-ethanol membrane reformer for pure hydrogen production (3.2 Nm³/h) based on Membrane Reactors in order to intensify the process of hydrogen production through the integration of reforming and purification in one single unit. The novel reactor could be more efficient than the state-of-the-art technology due to an optimal design aimed at circumventing mass and heat transfer resistances. Moreover, the design and optimization of the subcomponents for the BoP could also be improved. Particular attention has to be devoted to the optimized thermal integration that can improve the overall efficiency of the system at >90% and reducing the cost due to low temperature reforming. The main results obtained until now in terms of performance of the catalysts, membranes and the membrane reactors will be presented in this work.     

Segregation of char and silica sand particles in a hot-fluidized-bed steam gasifier

Understanding the behavior of coal char particles in a hot fluidized bed is essential for the design and operation of low-temperature gasifiers. The segregation of char as flotsam is the main focal point of this work. Segregation is generally unfavorable; however, it is attractive if the char holdup can act advantageously as a strong promoter of in-bed decomposition of tar and its conversion to syngas. This study first demonstrates the segregation of char during its gasification in a hot fluidized bed at a relatively low U₀/U_mf and at a steady state under continuous feeding and discharge of lignite and char, respectively. The distribution of char and its conversion from the bottom to the top of the bed are obtained from the motion of the char particles and the distribution of the gas components.     

Influence of process variable and physicochemical properties on the granulation mechanism of mannitol in a fluid bed top spray granulator

This study investigated the influence of specific process variables, including the hydroxypropyl cellulose (HPC) binder solution atomization, on the fluidized bed top spray granulation of mannitol. Special attention was given to the relationship between wetting and the granule growth profile. The atomization of the HPC binder solution using a binary nozzle arrangement produced droplets of decreasing size as the atomization pressure was increased, while changes in the spray rate had little effect on the mean droplet size. Increasing the HPC binder concentration from 2 to 8% w/w increased the binder droplet size and was most likely attributed to higher solution viscosity. The top spray granulation of mannitol showed induction type growth behavior. Process conditions like high spray rate, low fluidizing air velocity and binder solution concentration that promote the availability of HPC binder solution at the surface of the particles appeared to be key in enhancing nucleation and growth of the granules. Increasing the bed moisture level, up to a certain value, reduced the contribution of attrition to the overall growth profile of the granule and, more significantly, produced less granule breakage on drying. It was observed that the mean granule size could be reduced as much as 40% between the end of granulation and the end of drying for lower initial bed moisture level despite a shorter drying phase. High atomization pressure, especially when maintained during the drying phase, contributed substantially to granule breakage.     

TRANSITION OF FLOW REGIME IN FLUIDIZED BEDS WITH SLANTING BLADE BAFFLES

A flow model is proposed to investigate the transition of flow regime from bubbling to turbulent fluidization postulating that the flow in the emulsion phase follows the Richardson-Zaki equation.

Void fraction of the whole bed ε_f and the mean velocity of bubbles U_b were measured in fluidized beds of 0.3 and 0.5 m ID, in which slanting blade baffles were positioned. Mo-catalyst, silica gel, sand and glass beads with size between 135-443 μm were fluidized by air.

Void fraction of the emulsion phase ε _e was calculated on the basis of the above model. Correlating ε _e with superficial gas velocity U_ƒ, we found that ε _e was very close to ε _mƒ in the bubbling regime and that e, increased with increasing U_ƒ in the turbulent regime.

Calculated values of the volume fraction of bubble phase δ were correlated with U_ƒ, from which apparent transition point from bubbling to turbulent regime was estimated. Combining information obtained, transition of flow regime in the above type of fluidized beds is discussed     

快速流化床截面平均空隙率轴向分布及其影响因素

根据在直径0.186m、高8m和直径0.14m、高12m两台快速流化床装置的实验结果，并综合文献研究报道，研究了操作气速、颗粒循环速率、颗粒物性、床层直径以及进口、出口结构等因素对床层截面平均空隙率轴向分布的影响。表明一般情况下，快速流化床截面平均空隙率轴向分布的基本形式是上部空隙率高、下部空隙率低的单调指数函数。在特定的床结构条件下，快速流化床截面平均空隙率轴向分布曲线可能发生变异，即在出口结构有强约束作用时，可能呈反C，在入口结构有弱约束作用时，可能呈S型。     

新型三相循环流化床蒸发器的实验研究

开发了一种新型三相循环流化床蒸发器。以饱和盐卤为工质 ,研究了其防、除垢性能。结果表明 ,该蒸发器具有优良的防、除垢效果 ,并且有效地强化了传热。工业应用证明这是一种行之有效的在线防、除垢蒸发装置     

Removal of hydrogen sulfide, benzene and toluene by a fluidized bed bioreactor

The dominant off gases from publicly owned treatment works include hydrogen sulfide, benzene, and toluene. In this research, hydrogen sulfide oxidized byBacillus cereus, and benzene with toluene were removed by VOC-degrading microbial consortium. The optimum operating condition of the fluidized bed bioreactor including both microorganisms was 30 ‡C, pH 6–8, and 150 cm of liquid bed height. The critical loading rate of hydrogen sulfide, benzene and toluene in the bioreactor was about 15 g/m³h, 10 g/m³h and 12 g/m³h, respectively. The fluidized bed bioreactor showed an excellent elimination capacity for 580 hours of continuous operation, and maintained stable removal efficiency at sudden inlet concentration changes.     

Attrition due to mixing of hot and cold FCC catalyst particles

The formation of fines in a fluidized catalytic cracker unit (FCCU) due to catalyst attrition and fracture is a major source of catalyst loss. In addition to the generation of fine particles, a significant amount of aerosols have been identified in the stack emission of FCCUs. To determine the source of these aerosols, samples of fresh and equilibrium (e-cat) type catalysts were heated up to 600 °C and mixed with cold samples, simulating the thermal shock and particle fracture, which occurs inside an FCCU when catalyst is added. The thermal shock in the experiments produced fine particles and aerosols, which were captured on filters and analyzed using scanning electron microscopy (SEM) imaging and atomic absorption tests. It was found that significant quantities of metal rich aerosols were generated by the thermal shock. This production of fine particles and aerosols is a new phenomenon that can help explain excessive catalyst emissions from operating FCCUs.     

Agglomerate behavior in a recirculating fluidized bed with sheds: Effect of sheds

A Radioactive Particle Tracking (RPT) technique was used to study the effects of the internal baffles in the stripping section of the Fluid Coker?, called sheds, have on the behavior of wet agglomerates that are formed when residual oil is injected into the Coker. Vapor emitted by reacting wet agglomerates below the sheds rises and causes shed fouling. The release of vapor from agglomerates can be estimated by combining the RPT results with a coking reaction model. The study found that the sheds reduce the time agglomerates spend in the shed zone, which in turn reduces the amount of organic vapor that reaches the sheds, but at the same time increase the wetness of the agglomerates that exit to the recirculation line, which results in the loss of valuable liquid. The research also found that the best type of shed, from the point of view of agglomerate motion, is the mesh-shed. Finally, experimental data indicate that reducing the cross sectional area of the sheds from 50% to 30% increases the time that the agglomerates spend above the shed zone, and thus reduces the flow of vapor emitted below the sheds.