Methanol steam-reforming in a catalytic fixed bed reactor

Designing an appropriate methanol steam reformer requires detailed knowledge about the processes within such a reactor. Thus, the axial temperature and concentration gradients and catalyst ageing were investigated. It was found that for a fresh catalyst load, the catalyst located in the reactor entrance was most active during the experiment. The activity of this part of the catalyst bed decreased after some time of operation due to ageing. With further operation, the most active zone moved through the catalyst bed. From the results concerning hydrogen production and catalyst degradation, the necessary amount of catalyst for a mobile PEMFC-system can be estimated.     

An experimental study of a single layer packed bed cathode in an electrochemical flow reactor

Experimental measurements are reported for a packed bed electrode consisting of a single planar layer of uniform copper plated spheres located between platinum anodes and restrained by two plane porous PVC diaphragms. Two mass transfer controlled reactions, namely the reductions ofm-nitrobenzene sulphonic acid and copper sulphate, were investigated and the electrochemical mass transfer data in the range 23 <Re < 520 correlated by the equationShSc ^?1/3 = 0-83Re ^0.56, the Reynolds and Sherwood numbers being defined in terms of a particle diameter. Variations of electrode potential throughout the bed were found to be small enough to ensure reaction selectivity in the system.     

固定流化床反应器内气体分布方式的优化

传统小型固定流化床反应器采用烧结板作为气体分布装置,利用中控螺栓将分布器压紧固定在流化床反应器底部。在较高的操作温度条件下,由于密封垫与反应器材质的不同而产生不同程度的膨胀,导致密封部分或者环隙出现气流短路的问题,造成流化状态的不稳定,导致部分催化剂未参与实际反应,影响了催化剂评价数据结果的准确性。为了解决这一难题,文中采用堆砌的不锈钢珠作为分散介质,利用规则不锈钢珠气阻小、易于安装和拆卸的特点,降低了密封要求。文中通过流化床冷模实验比较了烧结板气体分布器和规则填料气体分布器的阻力大小和流化状态,通过流化床热模比较了烧结板气体分布器和规则填料气体分布器的温度分布。实验表明本文的方法大大改善了流化床流化状态,获得了良好的固定流化床评价结果。     

Catalyst poisoning and fixed bed reactor dynamics

The poisoning kinetics of thiophene on Ni-kieselguhr catalysts and the deactivation behavior of nonisothermal fixed bed reactors have been studied experimentally using benzene hydrogenation as a model exothermic reaction. The time dependent axial temperature profiles in the reactors were measured and compared with values evaluated from a dispersion model, the parameters of which have been determined in separate experimentation.Poisoning kinetics were measured in a series of differential reactor experiments at atmospheric total pressure, thiophene partial pressures of 0·037-0·19 torr, hydrogen to benzene molar ratios >$\text{8}\text{1}$ and temperatures from 60–180°C. Excellent agreement was found with a power law equation for the rate of change of activity with time, first order in catalyst activity and in thiophene concentration, with an experimental activation energy of 1080 kcal/kmole.This correlation of poisoning kinetics, however, was not able to predict the propagation of the zone of activity (hot-spot) on poisoning of an integral fixed bed reactor. Initial (steady state) temperature profiles were modeled satisfactorally, but the rate of migration of the hot spot was found experimentally to be more rapid than that predicted from the correlation of poisoning kinetics. A semi-empirical two site deactivation model is shown to resolve the discrepancy.     

数学模型在固定床反应器中的应用

化学反应器是整个化工生产过程的核心装置，其中固定床反应器是应用较为广泛的反应设备，建立能准确描述其特性的数学模型，不但可以给反应器设计和最优化操作提供理论依据，更减少了工作量。实现其优化操作，具有重要意义。主要介绍了固定床反应器中各种吸附过程数学模型的建立及其相应解法。     

Thermal stability in a flow reactor containing a fixed catalyst bed

Biisk. Translated from Fizika Goreniya i Vzryva, Vol. 26, No. 4, pp. 68–74, July–August, 1990.     

Modelling of a photocatalytic reactor with a fixed bed of supported catalyst

This work intends to develop a mathematical model of a fixed bed reactor and tests this model with experimental data. For this reason, we introduce some specific knowledge about light absorption from the catalyst, about the hydrodynamic interpretation of the reactor and the kinetic behaviour of photocatalytic reactions. Afterwards, we summarise this information and set up a complex mathematical model. We use this model in order to identify the kinetic constants of some reactions. We also formulate some simplified models to be used in particular circumstances and we compare the results of the complex model and the simplified models. Moreover, we compare experimental data of conversion and the results estimated with our model.     

Air oxidation of aqueous cyanides in a countercurrent fixed bed reactor

This study was conducted to discuss the removal of cyanides from water by air oxidation. Experiments were carried out in a countercurrent fixed bed reactor for three different values of temperature, concentration, gas and liquid flow rates. It was operated at pH 12 by using delrin (formaldehyde polymer) as packing material. Effects of some operating parameters on the conversion were studied, and it was observed that the conversion percent increased by increasing temperature and decreasing gas and liquid flow rates. Effect of concentration was not steady. A conversion of 89% was achieved under optimum conditions while it ranges from 44 to 79% at room temperature.     

一种CO优先氧化装置的实验研究

质子交换膜燃料电池需要CO含量低于10μL/L的富氢合成气作为燃料。CO优先氧化是一种深度脱除CO的有效方法。设计了一种CO优先氧化反应器,考察了催化剂装填方式、CO空速和氧碳比对反应器性能的影响。结果表明:对于所测试的操作条件,催化剂稀释之后分三段装填有利于反应器床层温度的均匀分布和出口CO浓度的降低;氧碳比越高出口CO浓度越低,当氧碳比为2.8时出口CO浓度为7μL/L。连续20 h的测试表明,反应器床层温度分布均匀,出口CO浓度保持在10μL/L以下。     

An experimental laboratory fixed bed study on the atmospheric pressure gasification of poplar bark with steam

An experimental study has been made of the gasification of poplar bark particles exposed to a helium/water vapor atmosphere in a fixed-bed reactor at 873–973 K. with and without silica catalyst. The effect of temperature on gas yields, calorific value and carbon conversion was evaluated for the pyrolytic conversion and steam-char gasification stages. The kinetics of the production of various gases in catalytic steam-char reaction has been studied.     

Simulation of fixed bed reactor for dimethyl ether synthesis

Dimethyl Ether (DME) is considered as one of the most promising candidates for a substitute for LPG and diesel fuel. We analyzed one-step DME synthesis from syngas in a shell and tube type fixed bed reactor with consideration of the heat and mass transfer between catalyst pellet and reactants gas and effectiveness factor of catalysts together with reactor cooling through reactor wall. Simulation results showed strong effects of pore diffusion. We compared two different arrangements of catalysts, mixture of catalyst pellets (methanol synthesis catalyst and methanol dehydration catalyst) and hybrid catalyst. Hybrid catalyst gave better performance than a mixture of pellets in terms of CO conversion and DME productivity, but more difficulties with reactor temperature control. Use of inert pellets and inter-cooling was also simulated as a means of controlling maximum reactor temperature.     

An experimental study of oscillatory states in a stirred reactor

Instabilities of the type which lead to sustained oscillations (limit cycles) were studied experimentally in a nonadiabatic, well-stirred, continuous-flow reactor. The study included: (1) the stabilization of unstable states by means of conventional feedback control, (2) the construction of phase-plane diagrams showing experimental limit cycles and other time-dependent behavior, and (3) comparisons of experimental results with theoretical predictions.The exothermic liquid-phase reaction between sodium thiosulfate and hydrogen peroxide was employed in all experiments. An empirical reaction rate expression for use in the describing equations was obtained from batch reactor experiments.Experiments were carried out with two reactors which differed only in wall thickness. The mass of the reactor with the thicker wall was sufficiently large to cause all oscillations to be damped, but for the other reactor, the mass of the wall did not seem to affect the reactor dynamics appreciably. The agreement between theoretical predictions and experimental observations was good, though there were some noticeable quantitative discrepancies in the time-dependent state.     

Deactivation of an adiabatic fixed bed reactor by a Langmuir-Hinshelwood fouling mechanism

Fouling of an adiabatic fixed bed reactor has been simulated for a process where both the main reaction and the fouling reaction occur by a Langmuir-Hi mechanism. Series and parallel fouling mechanisms were investigated assuming a pseudo -steady state in the simulation and results were obtained in the where only unique solutions were possible. Comparison with first order fouling showed that Langmuir-Hinshelwood fouling is generally more severe and in case fouling by this means gives results contrary to previous predictions. An analysis of this abnormal behaviour was made by varying the activation en of the fouling reaction, the Thiele modulus and the adsorption constants.     

固定床反应器内气体预分布器研究

研究了直径1 000 mm,高3 000 mm的固定床冷模装置中气体预分布器对反应器内气流分布的影响。结果表明:气体分布器可改变床层内气流流形并使径向气流的速度分布趋于均匀;随着表观气速的增加,反应器内气流的不均匀程度增加;分布器的环隙高度在一定的范围可使反应器内气流的不均匀程度相对较好。应用计算流体力学软件CFX对固定床反应器内的流场进行模拟计算,并与大型冷模试验测试结果进行比较,模型计算值和冷模试验测量值吻合较好。     

Comparison between twodimensional fixed bed reactor calculations and measurements

Radial temperature profiles and the average conversion have been measured at various axial distances in a fixed bed reactor. The reaction applied was the synthesis of vinyl acetate from acetic acid and acetylene.The measurements are compared with twodimensional reactor calculations. The rate expression of the vinyl acetate synthesis and the parameters describing heat and mass transfer in packed beds were measured separately. The agreement between measurements and calculation is good at a low molar ratio of acetylene and acetic acid (1·5) but less satisfying at a molar ratio of 4. In the last case the reactor operated in a more “critical region”. It is shown that slight variations in the various parameters and/or operational conditions can easily explain the differences observed.     

Hydrodynamic study of a toroidal fluidized bed reactor

Hydrodynamic behavior of a newly developed toroidal fluidized bed reactor is studied in this work. The reactor has a gas distributor consisting of angled blades in an annular ring at the reactor bottom. The driving force for particles to move over the distributing blades comes from the velocity head of gas jets accelerated upon entering the blade spacing. Relevant hydrodynamic behaviors are measured with various inert materials in a pilot scale 400-mm toroidal fluidized bed reactor. The observed hydrodynamic behavior is found to be essentially predictable at ambient temperature by conventional hydrodynamic models. Fine particle tracking on the reactor wall is clearly observed through oxidation of zinc dross at a bed temperature of around 1120°C, and is simulated on the basis of a simplified mathematical model. Hydrodynamic issues, such as particle flying trajectory and retention time in the reactor, are discussed based on the developed model.     

绝热多段固定床甲烷化反应器设计中几个问题的研究

相比一般固定床反应器的设计,绝热多段固定床甲烷化反应器的设计具有一定特殊性。针对甲烷化反应器运行中诸如床层热点穿出、床层超温、催化剂结构性破坏、反应器冷热位移等影响,以及甲烷化反应器安全稳定运行的问题进行了研究,分析了这些问题产生的原因,并给出解决问题的建议。     

The pyrolysis of individual plastics and a plastic mixture in a fixed bed reactor

Six thermoplastics, which represent more than two-thirds of all polymer production in western Europe, were pyrolysed in a static batch reactor in a nitrogen atmosphere. These were high density polyethylene (HDPE), low density polyethylene (LDPE), polystyrene (PS), polypropylene (PP), polyethylene terephthalate (PET) and polyvinyl chloride (PVC). The heating rate used was 25°C min⁻¹ to a final temperature of 700°C. These six plastics were then mixed together to simulate the plastic fraction of municipal solid waste found in Europe. The effect of mixing on the product yield and composition was examined. The results showed that the polymers studied did not react independently, but some interaction between samples was observed. The product yield for the mixture of plastics at 700°C was 9·63% gas, 75·11% oil, 2·87% char and 2·31% HCl. The gases identified were H₂, CH₄, C₂H₄, C₂H₆, C₃H₆, C₃H₈, C₄H₈, C₄H₁₀, CO₂ and CO. The composition of oils were determined using Fourier Transform infra-red spectrometry and size exclusion chromatography. Analysis showed the presence mainly of aliphatic compounds with small amounts of aromatic compounds. ©1997 SCI     

固定床生物油气化反应数学模拟

生物油气化对提高生物质能利用和保护环境具有重要意义。生物油气化选择乙酸、丙酮、丙三醇、苯酚、糠醛组成的混合物作为生物油模型物,在固定床圆柱形管式反应器进行气化模拟,用吉布斯自由能最小化法对其水蒸气催化重整制氢过程进行热力学分析。应用热动力学方程和质量平衡原理推算反应器模型,估算了反应热力学参数,通过Aspen Plus中的Gibbs反应器模拟生物油在不同温度下产物的平衡组成,计算出化学平衡体系的摩尔定压热容,利用Runge-Kutta法结合Matlab软件进行求解得出催化剂床层气化转化率;考察了反应温度对平衡时气体产物的影响。在固定床圆柱形管式反应器进行气化模拟实验,得出不同反应温度时反应产物气体产率和生物油气化反应较佳反应温度,通过比较得出实验结果与模拟计算值较一致。