Encapsulation of nanoparticles by polymerization compounding in a gas/solid fluidized bed reactor

For the first time, a fluidized bed reactor was used for encapsulating nanoparticles by the polymerization compounding approach using Ziegler–Natta catalysts. The polymerization reaction was carried out using a solvent-free process in a gas-phase reactor. This direct gas–solid reaction greatly simplified collecting the particles of interest after polymerization because none of the extra steps often found in encapsulation processes, such as filtering and drying, were performed in this work. The grafting of the catalyst to the original surface of particles was confirmed by X-ray photoelectron spectroscopy. Micrographs obtained by transmission electron microscopy confirmed the presence of a thin layer of polymer, in the order of a few nanometers, around the particles. The thickness of this coating was affected by the operating conditions of the process. The characterization of the modified particles with electron microscopy also revealed that zirconia nanoparticles tend to be coated in an agglomerated state, whereas aluminum particles were mostly individually encapsulated by the polymer. In addition, the effects of temperature and pressure were studied on the encapsulation process and a kinetic analysis was presented based on the available models in the literature. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Modelling of non-catalytic gas—solid reactions—II. Transient simulation of a packed bed reactor

A Transient model for packed bed non-catalytic reactors, which avoids many of the simplifying assumptions of the earlier models, has been developed. The model includes the effects of inter- and intra-pellet transfer resistances and the additional effects of axial dispersion in the bulk fluid. The solution procedure to the system of equations is based on the orthogonal collocation method. The effects of various parameters on the temperature rise encountered in the bed and the possibility of reducing this rise by perturbing the inlet concentration and temperature of the gas are examined.     

Feedback linearizing control of a fluidized bed reactor

The design of an adaptive nonlinear controller for the control of a fluidized bed reactor is derived by using exact linearization techniques. Reset action and parameter adaptation are used to make more robust the precise compensation of nonlinear terms, which is called for in the linearization technique. A nonlinear antiwindup mechanism is introduced to handle reset windup problem and to provide fast response without large overshoot. Simulation results show that the proposed adaptive controller guarantees good setpoint tracking. The developed estimation algorithm allows accurate estimation of the parameters for which the regressor component is not zero.     

三氯氢硅合成流化床反应器工艺改造

针对三氯氢硅生产过程中存在的流化床反应器指形管磨损漏油问题,通过对布风板改造、指形管改造、消除局部涡流、监测漏油等措施,收到了良好的效果。     

Two-phase modeling of a gas phase polyethylene fluidized bed reactor

A two-phase model is proposed for describing the behavior of a fluidized bed reactor used for polyethylene production. In the proposed model, the bed is divided into several sequential sections where flow of the gas is considered to be plug flow through the bubbles and perfectly mixed through the emulsion phase. Polymerization reactions occur not only in the emulsion phase but also in the bubble phase. Voidages of the emulsion and bubble phases are estimated from the dynamic two phase structure hydrodynamic model. The kinetic model employed in this study is based on the moment equations. The hydrodynamic and kinetic models are combined in order to develop a comprehensive model for gas-phase polyethylene reactor. The results of the model are compared with the experimental data in terms of molecular weight distribution and polydispersity of the produced polymer. A good agreement is observed between the model predictions and actual plant data. It has been shown that about 20% of the polymer is produced inside the bubble phase and as such cannot be neglected in modeling such reactors.     

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。     

Kinetics and mechanism of solid reactions in a micro fluidized bed reactor

A novel gas–solid Micro Fluidized Bed Reaction Analyzer (MFBRA) was developed to deduce reaction rates and kinetic parameters through measuring time‐dependent composition changes of evolved gases from the reactions. Application of the MFBRA to the decomposition of CaCO₃ powder resulted in an apparent activation energy of 142.73 kJ/mol and a pre‐exponential factor of 399,777 s^?1. This apparent activation energy was much lower than the thermogravimetry‐measured value of 184.31 kJ/mol, demonstrating a quicker reaction in the MFBRA. This was further verified by CuO reduction in CO, as accelerated by the fast diffusion and high heating rate in the MFBRA. Measurement of pyrolysis of coal and biomass in MFBRA found that the reaction process was completed in about 10 s, a time much shorter than the literature‐reported values in larger fluidized bed reactors. By monitoring the release of gas species from reactions at different temperatures, the MFBRA also allowed deeper insight into the mechanism of pyrolysis reactions. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Unipol工艺气相法聚乙烯流化床反应器回路压降的控制

Unipol气相法聚乙烯生产工艺中,反应器循环回路系统压降的控制是制约装置长周期运行的主要因素之一,对循环回路压降进行系统分析,探讨影响回路压降的关键因素,减缓压降上升的速率,对装置稳定生产有非常积极的意义.结果表明:通过设置合理出料时间、优化异戊烷浓度、调节循环气表观流化气速,以及控制粉料的质量等措施可以有效控制循环...     

Electrostatics and gas phase fluidized bed polymerization reactor wall sheeting

Reduction of electrostatic charge accumulation in fluidized bed polymerization reactors can reduce the frequency of reactor wall sheeting incidents and decrease the cost of operating fluidized bed polymerization reactors. The accumulation of excess electrostatic charge in fluidized bed polymerization reactors causes the fluidized polymer particles to adhere to the reactor wall and form wall sheets. Reactor wall sheets are described in order to characterize the problem. Electrostatic forces are compared to other forces influencing fluidization, such as drag forces and van der Waals forces. Literature values of measured particle electrostatic charges are compared to the maximum theoretical values predicted by Gauss’ law applied to the particles and to the entire fluidized bed. Electrostatic charge mitigation techniques are reviewed and future research areas are suggested based on the theoretical analysis and identified knowledge gaps.     

Flue gas desulfurization in an internally circulating fluidized bed reactor

An internally circulating fluidized bed reactor (ICFBR) was used as a desulfurization apparatus in this study. The height of the bed was 2.5 m, and the inner diameter was 9 cm. The bed materials were calcium sorbent and silica sand. The effects of the operating parameters of the flue gas desulfurization including relative humidity, particle size of the calcium sorbent, inlet concentration of SO₂, difference between the superficial gas velocities in the draft tube and the annulus, and superficial gas velocity in the draft tube on SO₂ removal efficiency (RE) were investigated. It was found that when the relative humidity (RH) was varied from 40% to 80%, the steady state RE had a largest value of approximately 15% when the relative humidity was 60%. When RH = 50%, 60% and 70%, RE decreased initially and then increased. After that RE decreased again until a steady state was reached. In addition, RE decreased with increasing calcium particle size or inlet SO₂ concentration. A larger difference between the superficial gas velocities in the draft tube and the annulus had a higher RE resulting from increasing reactivity of the calcium sorbent caused by a higher attrition rate. Moreover, a higher attrition rate had a higher total volume of the flue gas treated. Finally, a model to predict the steady state RE in ICFBR was proposed. It assumed that the draft tube section was a bubbling fluidized bed while the annulus section was a moving bed. In addition, the effects of the calcium sorbent conversion, attrition rate and gas-bypassing fractions on RE were also taken into account in this model. It was found that the values of RE predicted by this model agreed with the experimental results.     

Propenoxide isomerization in a fluidized bed reactor

Propenoxide isomerization, over lithium orthophosphate as a catalyst, was investigated in a fluidized bed reactor. A mathematical model of the process was developed and its kinetic parameters identified. There is a high degree of selectivity for allyl alcohol.     

Three-dimensional numerical simulation of a circulating fluidized bed reactor for multi-pollutant control

Circulating fluidized bed adsorber (CFBA) technology is regarded as a potentially effective method for simultaneously controlling emissions of sulfur dioxide, fine particulate matter, and trace heavy metals, such as mercury vapor. In order to analyze CFBA systems in detail, a gas mixture/solids mixture model based on the three-dimensional Navier-Stokes equations is developed for particle flow, agglomeration, physical and chemical adsorption in a circulating fluidized bed. The solids mixture consists of two solids, one with components of CaO and CaSO₄, and the other being an activated carbon. The gas mixture is composed of fine particulate matter (PM), sulfur dioxide, mercury vapor, oxygen and inert gas. Source terms representing fine particulate matter agglomeration onto sorbent particles, sulfur dioxide removal through chemical adsorption onto calcined lime, and mercury vapor removal through physical adsorption onto activated carbon are formulated and included into the model. The governing equations are solved using high-resolution upwind-differencing methods, combined with a time-derivative preconditioning method for efficient time-integration. Numerical simulations of bench-scale operation of a prototype CFBA reactor for multi-pollutant control are described.     

Synthesis of linear alkylbenzene in a liquid–solid circulating fluidized bed reactor

The alkylation reaction of benzene with 1-dodecene was investigated in a liquid–solid circulating fluidized bed reactor (LSCFBR) using HY zeolite as catalyst. The conversion of 1-dodecene, the apparent reaction rate constant, the activity of catalyst and the product distribution in the LSCFBR were analysed and compared with the values obtained using a stirred tank batch reactor (STBR).     

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.     

硅粉氮化输送床内气固反应过程数值模拟

以单个硅颗粒氮化反应缩核模型为基础,本文建立了硅颗粒在输送床内反应、辐射与对流传热耦合的数学模型,并借助CFD软件FLUENT对输送床内能质传输过程进行了数值模拟,分析了输送床壁面温度、氮气流量、预热温度、硅粉粒径等因素对输送床内温度场和硅粉氮化率的影响。在数值计算域内将单个颗粒反应过程转化为颗粒群整体反应过程,实时监测颗粒粒径及未反应硅颗粒粒径,为数值模拟颗粒流反应提供一种新思路。当壁面温度高于1723K时,输送床内会出现一高温区加速硅粉氮化反应;反应温度越高、颗粒粒径越小,氮化过程越剧烈,硅粉到达完全氮化所需时间越短。模型表明为使粒径为2.5μm的硅粉达到完全氮化且输送床内最高温度不超过氮化硅的分解温度2173K,应控制输送床壁面温度在1773K,氮化时间在170s以上,预热温度在1273K,粉气质量比为0.2,稀释剂比例为0.5~1。     

Forced bed mass oscillations in gas–solid fluidized beds

A second-order mechanical vibration model is proposed to explain the oscillation phenomena and pressure fluctuations in gas–solid fluidized beds. Experiments were conducted in a 0.1-m ID gas–solid fluidized bed driven by periodic gas pulses with the frequency varying from 0.2 to 10 Hz. Experimental results indicate that the proposed mechanical vibration model, which considers the pressure fluctuation as the results of the response of the fluidized bed to the external excitation forces related to the bubble behavior in the bed, can reasonably explain the pressure fluctuations of the gas–solid fluidized bed. The behavior of pressure fluctuations is correlated with characteristics of both the bed system and excitation forces.     

Measuring and modelling lateral solid mixing in a three-dimensional batch gas—solid fluidized bed reactor

A 0.27 m diameter fluidized bed reactor has been designed to allow experimental measurement of the axial and radial mixing behaviour of the solids. A unique method has been developed which permits the continuous determination of solid tracer concentration with time at different radial and axial positions within the fluidized bed. Solids mixing has been described by a model in which vertical mixing is instantaneous and lateral mixing occurs by dispersion. The lateral solids dispersion coefficients have been evaluated at various operating conditions from the experimental results of tracer concentration versus time. Based on the results, a modification of an existing correlation is proposed.