Particle-liquid mass transfer in three phase sparged reactor

Particle-liquid mass transfer in a three phase sparged reactor has been studied over a wide range of particle sizes, for the chum-turbulent regime. The particle-liquid Sherwood number has been correlated in the usual form with the Reynolds and Schmidt numbers. Use of the hindered particle settling velocity in the Reynolds number yields good agreement (±20%) with the present as well as most of the literature data. The proposed correlation also holds for power law non-Newtonian liquids when the effective viscosity is used.     

固体颗粒对三相气升式环流反应器流动特性的影响

将液相视为连续相,气相和固相视为分散相,同时考虑各相之间的相互作用,结合气液固三相流体的动力学理论,建立气液固三相环流反应器三流体湍流流动的Eulerian模型.采用计算模拟软件Fluent对三相环流反应器的流动状况进行模拟,考察表观气速、固含率、颗粒大小对反应器的气含率以及液体流动速度的影响.模拟结果较好地解释了气升式环流反应器内的三相流体行为,模型与实验结果较好地吻合,表明了模型的可行性.     

Optimal design and operation of an industrial three phase reactor for the oxidation of phenol

Among several treatment methods catalytic wet air oxidation (CWAO) treatment is considered as a useful and powerful method for removing phenol from waste waters. In this work, mathematical model of a trickle bed reactor (TBR) undergoing CWAO of phenol is developed and the best kinetic parameters of the relevant reaction are estimated based on experimental data (from the literature) using parameter estimation technique. The validated model is then utilized for further simulation and optimization of the process. Finally, the TBR is scaled up to predict the behavior of CWAO of phenol in industrial reactors. The optimal operating conditions based on maximum conversion and minimum cost in addition to the optimal distribution of the catalyst bed is considered in scaling up and the optimal ratio of the reactor length to reactor diameter is calculated with taking into account the hydrodynamic factors (radial and axial concentration and temperature distribution).     

The development of a high throughput reactor for the catalytic screening of three phase reactions

The design and utilisation of a reactor for the optimisation of multiple heterogeneous catalytic reactions in liquid phase is described. With the ability to screen up to 25 samples simultaneously at a maximum pressure of 50 bar, the reactor is one of the first to be designed specifically for what is termed stage II, the optimisation phase, of catalytic high throughput experimentation (HTE). Experiments demonstrating the reliability and reproducibility of the reactor are described, including the use of the reactor to study the catalytic hydrogenation of crotonaldehyde (CrAld) over bimetallic samples based on a commercial 5 wt.% Pt on activated carbon catalyst. Modification of the mono-metallic Pt sample by the impregnation of aqueous metal salts and various pre-treatments, resulted in 140 bimetallic catalysts that were used in the hydrogenation study. The changes observed in both selectivity and reactivity of the modified catalysts are described and show, by way of example, how the speed of catalyst screening can be increased by at least an order of magnitude.     

三相淤浆床冷态特性研究──空气─水─石英砂系统

本文研究了空气─水─石英砂三相淤浆床的流体力学特性．同时回归山含气率与其影响因素的关联式：εｇ＝０．０４９７ｕｇ１．０３７Ｃｓ－０．２５７．本文为研究三相淤浆床甲醇合成提供了流体力学数据。     

CFD analysis of hydrodynamic, heat transfer and reaction of three phase riser reactor

Catalytic cracking reaction and vaporization of gas oil droplets have significant effects on the gas solid mixture hydrodynamic and heat transfer phenomena in a fluid catalytic cracking (FCC) riser reactor. A three-dimensional computational fluid dynamic (CFD) model of the reactor has been developed considering three phase hydrodynamics, cracking reactions, heat and mass transfer as well as evaporation of the feed droplets into a gas solid flow. A hybrid Eulerian-Lagrangian method was applied to numerically simulate the vaporization of gas oil droplets and catalytic reactions in the gas-solid fluidized bed. The distributions of volume fraction of each phase, gas and catalyst velocities, gas and particle temperatures as well as gas oil vapor species were computed assuming six lump kinetic reactions in the gas phase. The developed model is capable of predicting coke formation and its effect on catalyst activity reduction. In this research, the catalyst deactivation coefficient was modeled as a function of catalyst particle residence time, in order to investigate the effects of catalyst deactivation on gas oil and gasoline concentrations along the reactor length. The simulation results showed that droplet vaporization and catalytic cracking reactions drastically impact riser hydrodynamics and heat transfer.     

An evaluation of the pneumatic transport reactor

In a pneumatic transport reactor, a dilute suspension of the reacting solid particles is conveyed by the gas stream through the reactor. The system is characterized by very short particle residence times. The relative flow rates of gas and solids are determined by the thermodynamic and kinetic requirements of the reacting conveyed systems. Design considerations for co-current gas and solids flows are presented and a comparison between co-gravity and counter-gravity flow reactors is discussed for the case of iron ore reduction by hydrogen. Kinetic data from single particle studies have been used to predict the performance of a pilot-scale reactor.     

内循环三相厌氧生物流化床降解精对苯二甲酸废水的研究

以火山岩为载体,制作了内循环式厌氧生物流化床,通过好氧预挂膜、快速排泥、逐步提高负荷法启动,启动时间约47 d。运行稳定后,当精对苯二甲酸(PTA)废水的COD为(4 752.3±41.2)mg/L时,在水力停留时间(HRT)为(17.3±1.2)h、有机负荷(OLR)为6.5kg COD/(m3.d)条件下,COD去除率达(64.0±4.4)%,对苯二甲酸(TA)去除率达(65.1±1.3)%,生物膜量达(13.3±0.2)mgVSS/g载体。对载体进行扫描电镜分析(SEM)得知,载体内为封闭孔,厌氧生物主要生长于载体表面孔内。观测产量为Yobs0.057gVSS/g COD,载体生物基质利用速率为0.83g COD/(gVSSd)。     

Fractal analysis of pressure fluctuations in a three phase bubble column reactor operating at low pressure

Pressure fluctuations in a three phase bubble column reactor operating at relatively low pressure (92 KPa) have been analyzed by adopting the spectral and fractal analyses to get the engineering informations for the on-line control and fault diagnosis of the reactors. The mean value, standard deviation, skewness and kurtosis of the pressure fluctuations have been obtained. The local fractal dimension has been determined from the Pox diagram obtained by means of the rescaled range analysis of the pressure fluctuations based on the fractional Brownian motion. The local fractal dimension of pressure fluctuations has increased and thus the pressure fluctuation signals have become less persistent and irregular, with increases in the gas flow rate reaction temperature, particle size and solid content in the slurry phase. The local fractal dimension has been well correlated in terms of the operating variables.     

The production of the antibiotic patulin in a three phase fluidized bed reactor I. Effect of medium composition

The continuous and semi-batch production of the antibiotic patulin by immobilized Penicillium urticae cells in a three phase fluidized bed reactor was investigated. A key factor for the success of the process was the limitation of the nitrogen source which increased the longevity of the biocatalyst while keeping cell growth at a low level. The continuous reactor was operated for 360 h during which time the effluent concentration of patulin was maintained at 0.25 mmol/L for 192 h. The total amount of patulin produced by the continuuous run was 35% greater than that obtained in a semibatch run. The pathway efficiency was 0.35 for 192 h indicating the biosynthetic pathway was operating at a high catalytic efficiency.     

Evaluation of hydrodynamic behavior of the perforated gas distributor of industrial gas phase polymerization reactor using CFD-PBM coupled model

A 2D computational fluid dynamics (Eulerian–Eulerian) multiphase flow model coupled with a population balance model (CFD-PBM) was implemented to investigate the fluidization structure in terms of entrance region in an industrial-scale gas phase fluidized bed reactor. The simulation results were compared with the industrial data, and good agreement was observed. Two cases including perforated distributor and complete sparger were applied to examine the flow structure through the bed. The parametric sensitivity analysis of time step, number of node, drag coefficient, and specularity coefficient was carried out. It was found that the results were more sensitive to the drag model. The results showed that the entrance configuration has significant effect on the flow structure. While the dead zones are created in both corners of the distributors, the perforated distributor generates more startup bubbles, heterogeneous flow field, and better gas–solid interaction above the entrance region due to jet formation.     

Scalar transport in a milli-scale metal foam reactor

We present an investigation on species mass transfer in a milli-scale plug flow reactor using metal foams to enhance the mixing process. In the current design the reactor consists of a pipe with an inner diameter of 7 mm and metal foam inserts with different pore sizes of 20, 30 and 45 ppi. Simultaneous PIV and LIF measurements were performed in orthogonal planes normal to the radial and axial direction downstream of a foam element of 50 mm length. The investigated Reynolds numbers range from 600 to 7600 defined with the empty tube diameter and the bulk velocity. We discuss the influence of the pore sizes on the scalar mixing efficiency and compare the results to the reference empty tube case. A strongly intermittent flow caused by the metal foam was observed over the whole range of Reynolds numbers. The increased radial velocities lead to an enhanced mixing performance. Coefficients of Variation in the order of 0.1 were achieved.     

Simulation of ethylene epoxidation in a multitubular transport reactor

It has been demonstrated that increased yields of ethylene oxide are obtained with a fixed-bed reactor operating with multiple injection of oxygen and cyclic adsorption-desorption of the desired reaction product. In certain conditions, this reactor simulates the operation of a larger two-tube transport reactor; the latter reactor may, in turn, be used to simulate large-scale commercial multitubular transport reactors. The small fixed-bed reactors may also be used for optimization of the process. The reaction of ethylene epoxidation on a silver catalyst is a good illustration of the advantages of a multitubular transport reactor and of this new method of simulation and optimization.     

钼酸盐在两相厌氧反应器分相中的应用研究

在两相UASB反应器动力学启动成功的条件下,对选用钼酸盐作为产甲烷菌抑制剂进行分相的可行性和效率进行了实验研究。实验的前3d在酸化反应器进水中投加2.0mmol/L的钼酸钠溶液,出水直接排放。3d后停止投加钼酸钠溶液,出水依然直接排放。6d后酸化反应器出水开始进入甲烷化反应器。实验表明,投加钼酸盐后产酸相的酸化率从50%提高到60%,产甲烷相出水水质也进一步提高,从而实现了两相厌氧反应器的相分离。同时投加钼酸盐对产甲烷相负面影响很小,获得了很好的分相和污染物去除效果。钼酸盐作为两相厌氧反应器的分相抑制剂可行。     

基于计算流体力学的气相烯烃聚合反应器模拟综述

气相聚合过程以流化床为核心反应器,其混合、传递和化学反应过程规律对工艺研发具有指导意义。计算流体力学是一种模拟流体流动的方法,可节省大量人力和物力并提供更全面的反应过程信息,在气固流态化领域得到广泛应用。基于计算流体力学的流态化模拟的难点在于如何建立能够恰当描述颗粒团聚过程的曳力模型,关于热量传递甚至聚合反应过程的模拟工作都是基于此发生的。随着计算机运算能力的提高,研究工业尺度的流化床反应器以及由粒径分布而带来的传递过程的影响可能成为模型广度及深度发展的方向。     

Simulating a multiphase reactor with continuous phase transition

A novel multiphase fixed-bed reactor with continuous phase transition for benzene hydrogenation to cyclohexane has been presented by Cheng et al. (A.I.Ch.E. J. 47 (2001a) 1185; Chem. Eng. Sci. 56 (2001b) 6025; 57 (2002) 3407; A.I.Ch.E. J. 49 (2003) 225) which makes use of evaporation of volatile components to remove the reaction heat. This paper investigates issues related to the numerical simulation of the model for this novel fixed-bed reactor. The reactor is supposed to be divided into two parts subject to the phase transition point on the bed level, that is, the liquid-contacted zone at the lower part and the gas-contacted zone at the upper part. A steady-state mathematical model for the reactor is developed. All external mass and heat transfer resistances can be neglected in the case investigated, as well as temperature differences in the particles. The effects of feed inlet temperature, inlet benzene concentration, gas flow rate and liquid flow rate on the reactor performance are theoretically studied. Reliability of the model is verified by bench-scale experiments. The results show that dryout phenomena will occur in the reactor both on the bed-scale and on the pellet-scale under certain conditions.     

Gas and liquid phase distribution and their effect on reactor performance in the monolith film flow reactor

Nuclear magnetic resonance imaging (MRI) has been applied to study the phase distribution in the monolith film flow reactor. The accumulation of the liquid in the corners of the square channel with an arc-shaped gas–liquid interface has been determined. The average liquid saturation is in good agreement with model calculations. Non-uniformities of the liquid distribution over the four corners of the square channel were apparent, besides the maldistribution over the cross-section of the monolith. Computational fluid dynamics (CFD) calculations applying the measured liquid distribution predict a broadening of the residence time distribution and a shorter break-through time, due to the maldistribution, which is in very good agreement with experimental results. The impact on the modeled gas–liquid mass transfer performance seems to be negligible, due to the nearly linear relation between k_GLa_V and u_Ls.     

Noncatalytic gas-solid reactions in a vertical pneumatic transport reactor

A heterogeneous model is developed to account for noncatalytic gas-solid reactions in a vertical pneumatic transport reactor. The model takes into consideration both the positive and negative variations of the solid porosity and the variation of the gas diffusivity with the reaction. The method of lines utilizing the second order centered finite difference scheme for the spatial discretization is employed to obtain the model solution. Experiments utilizing a vertical pneumatic transport reactor of a laboratory scale are performed to study the reaction between limestone and sulfur dioxide generated from coal combustion. The reactor is of 16.2 cm ID and 610 cm in length. The experimental data for sulfur retention are reported for various superficial gas velocities and calcium-sulfur molar ratios. Verification of the model with experimental data is conducted. The agreement between the model prediction and experimental data is satisfactory.     

Mass transport characterization of a novel gas sparged photoelectrochemical reactor

The photoelectrochemical treatment of waste water using immobilised TiO₂ electrodes has been demonstrated to be an attractive alternative to TiO₂ slurry reactors; however, it is generally believed that the diffusion of species to the surface of the catalyst imposes severe mass transfer limitations and hence is a disadvantage of the photoelectrochemical approach. To challenge this view, this paper reports the characterization of the mass transport properties of a novel gas sparged photoelectrochemical reactor. It is shown that passing a constant stream of nitrogen gas through the reactor increased the mass transfer coefficient by an order of magnitude above that in the absence of gas and this was attributed to the turbulent flow regime imposed by rising gas bubbles. It is also demonstrated that the gas–liquid transfer coefficient was greater than that for the rate of liquid diffusion and this has important implications for heterogeneous processes.     

Modeling and simulation of an industrial slurry phase ethylene polymerization reactor: effect of reactor operating variables

A hierarchical and computationally efficient mathematical model was developed to explain the polymerization of high-density polyethylene (HDPE) in an isothermal, industrial, continuous stirred tank slurry reactor (CSTR). A modified polymeric multi-grain model (PMGM) was used. Steady-state macroscopic mass balance equations were derived for all species (namely, monomer, solvent, catalyst and polymer) to obtain the final particle size and the required monomer and solvent input rates for a given catalyst input and the reactor residence time. The interphase mass transfer coefficients were calculated for the industrial CSTR using the operating data on the reactor. The present model was tuned with some data on an isothermal industrial reactor and the simulation results were compared with data on another set of industrial reactor. The comparison revealed that the present tuned model is capable of predicting the productivity and the polymer yield at various catalyst feed rates and the mean residence times. The effects of variation of two operating variables (catalyst feed rate and mean residence time) on the productivity, the polymer yield, the polydispersity index (PDI) and the operational safety were analyzed. The present study indicated that an optimal value of the reactor residence time (for maximum productivity per catalyst particle) exists at any catalyst feed rate.