Experimental investigation of gas‐liquid flow in monolith channels using monofiber optical probes

Two‐phase hydrodynamics has been experimentally investigated using optical fibre probes in individual channels of a laboratory scale monolith bed. Experimental investigations were carried out to validate the optical probe measurements in a single capillary. Optical probes were positioned at selected single channels of a monolith block, and the signals were processed to assess the local hydrodynamics under cocurrent gas‐liquid downflow configuration, using air and water as fluids. The investigations were performed for three different distributors, viz. single pipe, multipipe, and packed bed distributor configurations. The different distributor configurations were evaluated on the basis of void fraction and bubble frequency for a wide range of flow velocities. The specific novelty aspect of this study comes from the fact that we have undertaken channel scale investigations in monoliths under conditions where we have also reported the global gas‐liquid distribution. Thus, one can readily correlate the bed‐scale hydrodynamics with the local channel‐scale hydrodynamics. © 2016 American Institute of Chemical Engineers AIChE J, 63: 327–336, 2017     

Development of an optical fiber monolith reactor for photocatalytic wastewater Treatment

A photocatalytic reactor, which employs a ceramic multi-channel monolith as a support for TiO₂ and bare quartz fibers inserted inside the monolithic channels as both a light-transmitting conductor and a support for TiO₂, was constructed and tested for water treatment by investigating the photocatalytic degradation of o-dichlorobenzene (DCB) and phenanthrene (PHE). This configuration provides a higher surface area for catalyst coating per unit reactor volume compared to the continuous annular reactor (CAR) and optical fiber reactor (OFR). The light distribution profile inside each cell of the monolith is analyzed. Exponential decay of light was observed in propagation along the quartz fiber core and penetration into the TiO₂ film. Optimum thickness of TiO₂ layer on the optical fiber was found to be ≈ 0.4 μm in this study. The kinetics of DCB and PHE degradation were pseudo-first order. The effect of the water flow velocity was investigated and showed that the operation was in the mass transfer control regime. Overall rate constants were extracted from the experimental data; and these were then used to calculate the apparent quantum efficiency of photocatalytic degradation. Greater apparent quantum efficiency was observed for the optical fiber monolithic reactor (OFMR) compared with that of the CAR.     

利用光导纤维表征并流下行流化床中颗粒聚凝体的动态特征

利用光导纤维来表征并流下行流化床中颗粒聚凝体的动态特征。下行床的直径为0.1m、床高10m,操作气速为3.5～10m·s-1,颗粒流率为50～200kg·m-2·s-1。所用颗粒为催化裂化FCC颗粒,直径67μm,密度为1500kg·m-3。研究中首先用灵敏度分析方法建立起确认颗粒聚凝体的最佳条件,由此从所测得的瞬时颗粒浓度数据来获得颗粒聚凝体的各种特性(频率、时间分率、存在时间及平均浓度)。研究发现颗粒聚凝体的性质明显地受到操作条件的影响(气体速度与颗粒流率)以及局部颗粒浓度的影响。颗粒聚凝体的性质亦沿着下行床的轴向与径向发生很大变化。在充分发展段,下行床中心比近壁处有着更强的形成颗粒聚凝体的趋势。靠近下行床的底部,颗粒聚凝体性质沿轴向分布的变化比较缓和。     

Testing of a spherical dual-tipped optical fiber probe for local measurements of void fraction and gas velocity in two-phase flows

An alternate and easy method of constructing an optical liber probe tip is presented for the study of different two-phase flow variables such as local time-averaged void fraction, gas velocity and interfacial bubble passage frequency. The proposed probe tip has similar response characteristics to the “U-bend” single fiber probe and is easier to construct than the 90° wedge tipped probe. The signal from the spherical tip seems to be insensitive to changes in bubble velocity as opposed to the 90° wedge and is more advantageous at higher velocities. The signal from the spherical tip has the same time duration as the signal changes from liquid to gas and vice versa for the same bubble velocity. A simplified model is presented to describe the balance of forces around the spherical tip when a bubble is penetrated. The model offers a qualitative explanation of why the non-dimensional response intensity decreases as the bubble velocity increases.     

A study on hydrodynamic characteristics in a Φ38 pulsed extraction column by four‐sensor optical fiber probe

Accurate prediction of dispersed phase droplet behavior is crucial to the design and scaling‐up of an extraction column. In this article, the dispersed droplet velocity algorithm and the diameter algorithm in a liquid–liquid two‐phase flow have been developed based on the bubble velocity model in gas–liquid two‐phase flow of Lucas [Measurement Science & Technology. 749, 758(2005)] and Shen [International Journal of Multiphase Flow. 593, 617(2005)]. Hydrodynamic characteristics, including droplet diameter, holdup and droplet velocity, were measured using a self‐made four‐sensor optical fiber probe in a 38 mm‐diameter pulsed sieve‐plate extraction column. Water and kerosene were used as continuous and dispersed phases, respectively. The influences of the pulsed intensity, the continuous and dispersed phase superficial velocities on the hydrodynamic characteristics were investigated. The experimental results show that it is reliable to use a four‐sensor optical probe to measure the hydrodynamic characteristics of a pulsed extraction column. © 2016 American Institute of Chemical Engineers AIChE J, 63: 801–811, 2017     

四传感器光纤探针测量气泡速度矢量模型

光纤传感器作为纤维光学领域中的新技术,在两相流动局部参数测量中得到了越来越广泛的应用。在假设气泡对称面垂直于气泡运动方向的基础上,对四传感器探针测量局部瞬时气泡速度的数学原理进行了详细推导,给出了新的计算气泡速度矢量的方法和模型,并运用自制的四传感器光纤探针,对气液两相流动中的气泡运动速度和方向进行了测量。实验中通过探针方法测得气相流速相对于流量计测量值的平均偏差为9%,表明新的探针测量方法精度较高,能够用于两相流中气泡速度矢量测量。进一步的实验研究表明,不同流动条件下,局部空泡份额及界面面积浓度(IAC)沿通道径向呈“壁峰型”或“核峰型”的分布规律。     

Measuring local droplet parameters using single optical fiber probe

This article proposes a new single optical fiber probe (OFP) sensor method for measuring local droplet parameters such as droplet fraction, droplet velocity, and droplet diameter. To this end, we developed a stretched conical optical fiber probe (SC-OFP) sensor that minimizes the wetting of the sensing tip at a high droplet velocity, a discrimination algorithm based on the first and second derivatives of the output of the raw signal of the OFP sensor, and a method that uses neural network training to determine local droplet velocity independently of droplet size. In the experiments conducted, the developed SC-OFP sensor measured local droplet velocity with a mean absolute percentage error (MAPE) smaller than 4.1% for velocities ranging from 2 to 32 m/s, and droplet diameter with a MAPE smaller than 4.9% for diameters ranging from 0.29 to 1.78 mm.     

Influence of ash agglomerating fluidized bed reactor scale‐up on coal gasification characteristics

To study the influence of fluidized‐bed reactor scale‐up on coal gasification characteristics, a model of the ash agglomerating fluidized‐bed reactor has been developed using an equivalent reactor network method. With the reactor network model, the scale‐up effects of a gasifier were studied in terms of the characteristics of the chemical reactions in the jet zone, the annulus dense‐phase zone and the freeboard zone. Results showed that the changes occurred in the inequality proportion of the volume of the jet zone during the reactor scale‐up. Taking into consideration the utilization of a portion of the backflow gas, the expansion of the jet zone volume and the coal particle residence time, the temperature of the jet zone was increased from 1592 to 1662 K. Also, both the annulus dense‐phase zone temperature and the freeboard zone temperature decreased, causing subsequent decrease in the carbon conversion efficiency. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1821–1829, 2014     

高气液化下分布器设计对结构化床层气液分布的影响(英文)

Experiments were carried out to investigate the liquid flow distribution at high gas/liquid ratios in a cold model monolith bed of a 0.048 m diameter with 62 cells per cm2.Three types of distributor for the liquid distribu-tion were used to evaluate their distribution performance.Local liquid saturation in individual channels was meas-ured using 16 single-point optical fiber probes mounted inside the channels.The results indicate that 1) The optical fiber probe technique can measure phase distribution in the monolith bed;2) Liquid saturation distribution along the radial direction of the monolith bed is not uniform and the extent of non-uniformity depends on the distributor de-sign and phase velocities;and 3) The tube array distributor provides superior liquid distribution performance over the showerhead and nozzle distributors.     

Computational study of spout collapse and impact of partition plate in a double slot‐rectangular spouted bed

Gas‐solid hydrodynamics in a three‐dimensional slot‐rectangular double‐spouted bed was numerically investigated by a combined approach of discrete element method and computational fluid dynamics, and the knowledge gained was extended to understand the mechanisms leading to operational instability due to the collapse of a spout, along with the beneficial impact of inserting a vertical partition plate. The setup investigated has two diverging bases and contains up to 2,590,000 particles. The computational results show different behaviors of pressure drop, in terms of average value, fluctuations, and power spectral trends, in the five distinct flow regimes corresponding to various superficial gas velocities. Two types of spout shapes are observed under stable spouting conditions, and the spout sizes are quantified. When one of the spouts chokes then collapses, complex interactions between the chambers are identified. Furthermore, the insertion of a vertical partition plate between two chambers appears to be an effective way to prevent the interactions between adjacent fountains, which is advantageous for improving the operational stability of such systems upon scale‐up. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4087–4101, 2015     

Experimental characterization of the flow pattern in an annular fluidized bed

The annular fluidized bed combines a long solids residence time and a good heat and mass transfer. To experimentally characterize the flow pattern in the system, pressure drop and capacitance probe measurements have been carried out under ambient conditions in two plants of inner diameters of 0.19 and 0.74 m. Depending on the interaction between gas velocity in the central jet and ratio of bubble to central nozzle diameter, the ratio of internal to external solids circulation can be regulated.     

Droplet velocity,size, and local holdup measurements in an extraction column by tri‐sensor optical probe

The tri‐sensor optical probe was applied to study the hydrodynamic characteristic in a pulsed sieve plate extraction column. Two immiscible liquids consisting of the dispersed phase (kerosene) and continuous phase (water) were introduced in countercurrent operation. Local parameters such as droplet velocity, drop size, and holdup of the dispersed phase were obtained. It was found that the tri‐sensor optical probe could be used as an efficient and convenient technique for measuring local hydrodynamic parameters inside the pulsed sieve plate extraction column. Furthermore, the results indicated that pulsation intensity imposed more influence on these hydrodynamic parameters than two‐phase superficial flow rates in the investigated ranges. Experimental results were found to be in good agreement with the empirical correlations reported in literature. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3958–3963, 2015     

Measurement of bubble size distribution using a flying optical probe technique: Application in the highly turbulent region above a distillation plate

A flying optical probe technique has been developed and employed to measure bubble size above sieve trays in an air-water facility simulating cross-flow distillation (CRODIS). Despite the highly turbulent conditions occurring in the flows investigated, successful measurements were made of bubble size distributions at a series of levels above the trays. Using this technique, experiments are carried out on the CRODIS facility covering a range of gas and liquid flowrates and several tray configurations and the results are presented in this paper. Gas flowrate, sieve hole size and weir height were found to exhibit a significant effect on bubble size distribution, whereas liquid flowrate was shown to have negligible influence.     

提升管中颗粒局部流率和速度的改进的光纤测量方法

在一套高约18 m、内径φ100 mm的提升管冷态实验装置上,根据PV-6D光纤探头的测量结果,提出了一种基于整个采样时间计算提升管颗粒局部流率和速度的改进方法,并与文献方法进行了对比。结果表明,两种方法计算的颗粒局部流率和速度相差较大,本文和文献两种方法计算的截面平均颗粒流率与实测值间的最大、最小和平均相对偏差分别为606.9%、241.3%,221.4%、89.5%和388.9%、145.6%,本文方法测量的颗粒流率偏差相对较小。文献方法计算的截面平均颗粒速度均大于操作气速,其气固间滑落速度和滑落系数分别在-1.6～-4.7 m·s^-1及0.56～0.90间变化,与提升管内的气固实际流动存在很大差别;本方法计算的截面平均颗粒速度均小于操作气速,其气固间滑落速度和滑落系数分别在0.6～9.6 m·s^-1及1.11～2.14间变化。反射型光纤探头在测量颗粒浓度时存在的一些问题是导致本文方法测量的颗粒流率、滑落速度和滑落系数偏大的主要原因。此外,根据光纤测量结果,提出了两个计算提升管颗粒循环强度的关系式,可以替代现有的容积法测量。     

A comparative study of a fluidised bed reactor and a gas lift loop reactor for the ibe process: Part III. Reactor performances and scale Up

Continuous fermentations using Clostridium spp. DSM 2152 immobilised in calcium alginate beads to produce butanol and isopropanol from glucose were carried out in a fluidised bed reactor with liquid recycle (FBR, 10.9 dm³ working volume, 41 % solids) and in a gas lift loop reactor (GLR, 11.4 dm³ working volume, 32% solids). In the FBR in-situ produced non-coalescing gas bubbles had a negligible influence on the fluidisation pattern and the steady state results of the fermentation were in accordance with those predicted by a reactor model. The FBR was operated reliably for 5 weeks without decrease of activity. The GLR behaved as a three phase reactor because of the recycled fermentation gas. The steady state fermentation results were as predicted by the GLR model. Scale up to a 50 m³ FBR and a 65 m³ GLR led to development of a plug flow with recycle model for the FBR and a stirred tank model for the GLR. On the basis of overall reactor performance and ease of integration with a simultaneous product recovery the FBR is preferred to the GLR for application in a large scale butanol/isopropanol process using immobilised Clostridia spp.     

湍动流化床过渡段固含率分布特征的实验及数值模拟

在湍动流化床中,过渡段对于包括甲醇制烯烃在内的气固催化快反应有着重要的作用。采用PV6D反射型光纤探针对内径95 mm的湍动流化床内过渡段的固含率分布和脉动参数进行了测量,分别考察了表观气速和静床高的影响,并采用修正的基于颗粒动力学的三段曳力双流体模型进行模拟。实验表明,湍动流化床过渡段中固含率的轴向分布呈现S型和指数型两种类型,固含率轴向与径向分布都在过渡段内出现最大梯度,表明过渡段中固体浓度分布比稀相段和密相段更不均匀。表观气速和静床高的变化将导致S型和指数型分布的相互转变,并且对过渡段底部与壁面附近的固体高浓度区影响最为显著。局部固含率脉动概率密度分布表明,在静床高较小时,随着气速的增大,床层下部气含率最大值位置将从中心区移动至环隙区,呈现气含率的双峰型分布。本文提出的修正三段曳力模型考虑了颗粒团聚的影响,对过渡段中分布板影响区之外的固含率分布均能较好地模拟。     

Systematic study on heat transfer and surface hydrodynamics of a vertical heat tube in a fluidized bed of FCC particles

Bed‐to‐wall heat transfer properties of a vertical heat tube in a fluidized bed of fine fluid catalytic cracking (FCC) particles are measured systematically using a specially designed heat tube. Two important surface hydrodynamic parameters, i.e. the packet fraction (δ_pa) and mean packet residence time (τ_pa) based on the packet renewal theory, are determined by an optical fiber probe and a data processing method. The experimental results successfully reveal the axial and radial profiles of heat‐transfer coefficient, the effects of superficial gas velocity, and static bed height on heat‐transfer coefficient, most of which can be explained successfully by the measured τ_pa, an indicator of packet renewal frequency. τ_pa is found to play a more dominant role than δ_pa on bed‐to‐wall heat transfer. With a fitted correction factor, the modified Mickley and Fairbanks model is able to predict the heat‐transfer coefficients with enough accuracy based on the determined packet parameters. © 2014 American Institute of Chemical Engineers AIChE J, 61: 68–83, 2015     

Study of gas–solids flow in a short CFB riser by statistical and chaotic deterministic analysis of optical fibre probe signals

In this work, a short CFB riser with a height of 2.42 m and an ID of 82 mm was operated under different dilute operating conditions to study the fluid dynamics of FCC catalyst particles (d_p = 80 µm, ρ_p = 902 kg/m³) in air. The electrical signals from the optical fibre probe were sampled at a frequency of 1000 Hz for a period of 30 s and were obtained at different positions along the radius and height of the riser. Data were analysed using both statistical methods (time average, standard deviation and frequency distribution) and chaos methods (construction of attractors; correlation dimension, D_ML; and Kolmogorov entropy, K_ML). Some results on solids holdup deduced from the electrical signal are also presented for the developed zone of the riser. It was verified that for very dilute conditions, increasing gas velocity produces more complex and less predictable fluctuations in solids concentration, while increasing solids flux generally reduces complexity and increases predictability. However, results for the most dilute condition used shows that for the radial position where solids holdup is higher (near the wall), the increase in solids concentration does not affect the mean free path of the particles, resulting in higher values of D_ML than in the dilute region (core). © 2012 Canadian Society for Chemical Engineering