管式固定床反应器柱状颗粒床层流体流动模拟与实验研究

针对管式固定床反应器内管束数量多、规模大等特点,选取单个管束作为特征结构。对装填不同直径柱状颗粒的管束,采用程序坐标定位的方法,建立柱状颗粒床层的物理模型。采用DEM与CFD联合数值仿真方法,探究反应管内径与柱状颗粒的等比表面积球当量直径之比(管径比Di/dp)对柱状颗粒床层流体流动的影响,并建立单管固定床反应器试验台,采用差压测试方法进行实验研究。结果表明,当Di/dp由5.37增至12.75时,床层空隙率和流体分布均匀性均得到改善,壁面效应的影响由床层中心减弱到管壁。基于数值模拟及实验结果对Di/dp=12.75的柱状颗粒床层进行床层压降Ergun公式常系数修正,CFD模拟计算的结果与拟合公式吻合较好。研究结果能为固定床反应器压降预测提供参考。     

Electro-oxidation of benzene in a fixed bed reactor

A fixed bed electrochemical reactor was used in the laboratory to oxidize benzene to quinone. The reactor consisted of a 3 mm thick bed of 1 mm lead shot, 0.5 m long by 0.05 m wide, sandwiched between a lead feeder plate and an asbestos diaphragm which was compressed against a stainless steel cathode plate. A dispersion of benzene in aqueous sulphuric acid was passed through the reactor and the rates of production of quinone, hydroquinone, carbon dioxide, oxygen and hydrogen, together with the cell voltage and pressure drop, were obtained for a range of operating conditions.Concentrations of quinone in the benzene product varied from 0.04 to 0.31 M and current efficiencies for quinone were in the range 22 to 55%. In a single pass of 1 M acid and benzene through the reactor at 25° C the quinone efficiency fell from 53% to 39% as the average superficial current density increased from 0.4 to 2.0 kA m^–2. At an average superficial current density of 2.0 kA m^–2 the quinone efficiency decreased with an increase in process temperature (25 to 50° C), but increased with increases in acid concentration (1 to 4 M), acid flow (0.5 to 1.0 cm³ s^–1), benzene flow (0.05 to 10 cm³ s^–1) and co-current nitrogen gas flow (0 to 32 cm³ s^–1 at STP). Recycling the 4 M sulphuric acid at 25° C raised the concentration of quinone in the product benzene but decreased the net current efficiency for quinone. Corresponding changes were observed in the cell voltage and in the current efficiencies for hydroquinone, carbon dioxide and oxygen. The results are discussed in terms of the process stoichiometry, electrode kinetics and mass transfer for three-phase flow in a fixed bed reactor.Nomenclature A Acid flow - a ₁ Liquid/liquid specific interfacial area - a _s Liquid/solid specific interfacial area - B Benzene flow - d ₃₂ Sauter mean drop diameter - d _P Particle diameter - E Current efficiency - F Faraday number - I Total current - i _l Superficial transfer-limited current density - K Liquid/liquid distribution coefficient - k _c Liquid/liquid mass transfer coefficient in continuous phase - k _s Liquid/solid mass transfer coefficient - L _c Superficial liquid load — continuous phase - L _d Superficial liquid load — disperse phase - Q _A Quinone concentration in aqueous phase - V ⁰ Standard electrode potential - z Number of electrons per equivalent     

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.     

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.     

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。     

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.     

Complex nonlinear behaviour of a fixed bed reactor with reactant recycle

The fixed bed reactor with reactant recycle investigated in this paper can exhibit periodic solutions. These solutions bifurcate from the steady state in a Hopf bifurcation. The Hopf bifurcation encountered at the lowest value of the inlet concentration turns the steady state unstable and marks the emergence of a stable periodic solution. This periodic solution in turn undergoes a period doubling leaving it unstable and giving rise to a stable period 2 solution. It is know that if the system possesses one period doubling it often also has the possibility of posessing a chaotic attractor. It is shown, that the dynamic behaviour of a fixed bed reactor with reactant recycle is much more complex than previously reported.     

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.     

Cold flow experimental study and computer simulations of a compact spouted bed reactor

Spouted beds are a very interesting class of gas–solid contactors that possess excellent heat transfer and mixing characteristics, while they are particularly suited to process coarse particles. Proper design of such beds requires the prediction of various hydrodynamic characteristics, such as the minimum spouting velocity and maximum spoutable height. Contrary to their typical initial applications, spouted beds have been finding recently more frequent use on the one hand at endothermic processes and on the other hand using much finer particle sizes. In the current work, the hydrodynamic characteristics of a laboratory scale spouted bed of 0.05 m diameter have been investigated via cold flow studies using olivine particles of 3.55–5.00 × 10⁻⁴ m size. Hydrodynamic parameters have been measured at this compact geometry and fine particle size and were compared with common literature correlations. An empirical correlation was derived to predict the fountain height for the studied fine particle spouted bed. Computer simulations have been further used to investigate the heat transfer characteristics of the bed under endothermic reactive conditions, using methane reforming as a case study. Given sufficient external heat supply, a spouted bed operating at a well-mixed regime can efficiently drive even highly endothermic reactions.     

Kinetics study on cnt‐supported RuKCo FTS catalyst in a fixed bed reactor

The rate of syngas (H₂/CO) consumption over a RuKCo/CNT Fischer–Tropsch synthesis (FTS) catalyst was measured in a fixed bed microreactor at 210–225°C, 2–3.5 MPa, H₂/CO feed molar ratios of 1–2.5, and gas hourly space velocity (GHSV) range of 2700–3600 h^?1. The data have been used to model the kinetics of the FTS reactions within the range of the studied conditions. One empirical power law model and four semi‐empirical kinetic models based on Langmuir–Hinshelwood‐type equation have been evaluated. The best fitting was obtained with the equation: similar to that proposed by Brötz et al. The estimated activation energy (E = 80–85 kJ/mol) is lower than that is reported in the literature. The validity of these results are restricted to fixed beds with the given catalyst in the tested conversion regime.     

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 innovative reaction heat offset operation for a multiphase fixed bed reactor dealing with volatile compounds

Hydrogenation of benzene to cyclohexane was conducted in an adiabatic fixed-bed reactor under a phase transitional condition. In which process, a mixture of benzene and cyclohexane was fed into the reactor at the bottom under the liquid condition, however, the liquid phase disappeared and turned into gas phase at the reactor outlet through vaporization. It follows from this novel idea that the problems associated with reaction heat removal and low catalyst efficiency of the liquid-filled catalyst could be solved simultaneously with emptying of the liquid from the catalyst. However, the benzene concentration in the mixture should not exceed 14% if simple phase transition is employed, since the reaction heat is seven times the liquid vaporization heat. To optimize this primitive operation, a side stream quenching operation was proposed and attempted experimentally, and it was found that the side stream quenching with double injection points could be an acceptable operating strategy.     

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.