Three-Phase Model of a Fluidized-Bed Catalytic Reactor for Polyethylene Synthesis

2016 ◽  
Vol 14 (1) ◽  
pp. 93-103 ◽  
Author(s):  
R. A. Bortolozzi ◽  
M. G. Chiovetta
Keyword(s):  
Gas Phase ◽  
Fluidized Bed ◽  
Solid Particle ◽  
Active Sites ◽  
Supported Catalysts ◽  
Plug Flow ◽  
Solid Particles ◽  
Particle Phase ◽  
Three Phase ◽  
Bubbling Fluidized Bed

AbstractA mathematical model of a bubbling fluidized-bed reactor for the production of polyolefins is presented. The model is employed to simulate a typical, commercial-scale reactor where the synthesis of polyethylene using supported catalysts is carried out. Results are used to follow the evolution of temperature within the reactor bed to avoid conditions producing polymer degradation. The fluidized bed is modeled as a heterogeneous system with a bubble gas phase and a solid-particle emulsion. The catalyst active sites are considered located within a growing, solid, ever changing particle composed of the support, the catalyst and the polymer being produced. The model sees the reactor as a three phase complex: (a) the bubble phase, transporting most of the gas entering the reactor; (b) the solid-particle phase, where polymerization takes place; and (c) the interstitial-gas phase among solid particles. Both gaseous phases move continuously upward, with different velocities, and are modeled as plug flows. For the solid-particle phase, modeling alternatives are explored, ranging from a descending plug-flow limiting case to the opposite extreme of a perfectly mixed tank related to the particle drag-effect the rising bubble produces in the bed. In the scouting process between these limits instabilities are predicted by the model. The most realistic representation of the bed is that of the two gas phases moving upward in two plug-flow patterns and the solids moving with ascending and descending trajectories due to back-mixing.

scholarly journals Biological treatment of water contaminated by hydrocarbons in three-phase gas-liquid-solid fluidized bed

2013 ◽  
Vol 8 (1) ◽  
pp. 9-15
Keyword(s):  
Mass Transfer ◽  
Fluidized Bed ◽  
Biological Treatment ◽  
Plug Flow ◽  
Point Of View ◽  
Operating Conditions ◽  
Solid Particles ◽  
Hydrodynamic Characteristics ◽  
Intimate Contact ◽  
Three Phase

Biological treatment has been carried out in two different systems: aerated closed and threephase fluidized bed reactors for hydrocarbons removal from refinery wastewaters. For the two systems, hydrodynamic study allowed the determination of operating conditions before treatment experiments. Then, in a second time, biological treatments have been conducted in the same operating conditions. The obtained results showed that in the three-phase fluidized bed we can degrade hydrocarbons more rapidly than in a closed aerated bioreactor. Among the different appropriate techniques available to create efficient contacts between phases, the three-phase fluidization G/L/S where carrier particles are moving inside the reactor seems very interesting. It allows an intimate contact between phases and present many advantages concerning hydrodynamic and mass transfer phenomena. In fact, depending on operating conditions and the bubble flow behaviour, the three-phase fluidized bed could display different flow regimes In these systems called bioreactors the solid particles covered with a biofilm are fluidized by two ascending flows of air and contaminated water. With favourable operating conditions, from a hydrodynamic and mass transfer point of view, the pollutant can be biologically degraded up to 90%. Until this date, the three-phase bioreactors modelling remains very complex because it required taking into account several factors: the pollutant biodegradation rate in the biofilm, the bioreactor hydrodynamic characteristics, and the reactant interfacial gas-liquid and liquidsolid mass transfer. Thus the essential purpose of modelling is to integrate the microbial kinetics with the reactor hydrodynamics. We can notice that a few models have incorporated both bioreactor hydrodynamics and microbial kinetics. For the steady state bioreactor model, we generally assume that the particles are uniform in size, the biofilm is uniform in thickness, and the biofilm can be considered as homogeneous matrix through which oxygen and substrate diffuse and are consumed by the microbes. The liquid phase in the bioreactor substrate is considered to be axially dispersed while the gas phase is assumed to be in plug flow [2]. Rittmann (1997) proposed a model based on wake theory for predicting bed expansion and phase hold-ups for three-phase fluidized bed bioreactors. In this model he modified the correlation for the computation of the bioparticles drag coefficient CD [3]. He also attempted to explain the biofilm detachment which can occur with three broad patterns: erosion, sloughing and scouring and assumed that the factors affecting detachment rates can be grouped into two categories (physical forces and microorganisms physiology in the biofilm).

Mass transfer between solid particles and liquid in a three phase fluidized bed

1987 ◽  
Vol 65 (2) ◽  
pp. 228-236 ◽  
Author(s):  
A. Prakash ◽  
C. L. Briens ◽  
M. A. Bergougnou
Keyword(s):  
Mass Transfer ◽  
Fluidized Bed ◽  
Solid Particles ◽  
Three Phase

Biological wastewater treatment by three-phase fluidization - characteristics and basic design method

1994 ◽  
Vol 30 (11) ◽  
pp. 91-100 ◽  
Author(s):  
Akira Hirata ◽  
Motoharu Noguchi
Keyword(s):  
Fluidized Bed ◽  
Design Method ◽  
Research Work ◽  
Plug Flow ◽  
Oxygen Absorption ◽  
Basic Design ◽  
Fluidized Bed Bioreactor ◽  
Particulate Media ◽  
Flow Type ◽  
Three Phase

A three-phase fluidized bed bioreactor is expected to treat wastewater quite efficiently, because the reactor has large specific surface area of biofilm, and oxygen for the biodegradation is simultaneously supplied from gas to liquid with oxygen consumption for biooxidation. However the reactor design and operation had been quite difficult particularly with a plug flow type fluidized bed, because of complicated behavior in the reactor. This paper concerns the current research work by the authors in focusing on the following characteristics and basic design method: (1) Behavior of biofilm immobilization on particulate media, fluidization of immobilized biofilm media and characteristics of oxygen absorption and substrates biodegradation. (2) Characteristics of biological treatment by immobilized biofilm. (3) Basic design method of a plug flow type three-phase fluidized bed bioreactor.

scholarly journals Numerical simulation of non-conventional liquid fuels feeding in a bubbling fluidized bed combustor

2013 ◽  
Vol 17 (4) ◽  
pp. 1163-1179
Author(s):  
Milica Mladenovic ◽  
Stevan Nemoda ◽  
Mirko Komatina ◽  
Dragoljub Dakic
Keyword(s):  
Numerical Simulation ◽  
Fluidized Bed ◽  
Liquid Waste ◽  
Liquid Fuels ◽  
Three Phase ◽  
Bubbling Fluidized Bed ◽  
Detailed Simulation ◽  
Calculation Results ◽  
Gas Fuel ◽  
Jet Penetration

The paper deals with the development of mathematical models for detailed simulation of lateral jet penetration into the fluidized bed (FB), primarily from the aspect of feeding of gaseous and liquid fuels into FB furnaces. For that purpose a series of comparisons has been performed between the results of in-house developed procedure- fluid-porous medium numerical simulation of gaseous jet penetration into the fluidized bed, Fluent?s two-fluid Euler-Euler FB simulation model, and experimental results (from the literature) of gaseous jet penetration into the 2D FB. The calculation results, using both models, and experimental data are in good agreement. The developed simulation procedures of jet penetration into the FB are applied to the analysis of the effects, which are registered during the experiments on a fluidized pilot furnace with feeding of liquid waste fuels into the bed, and brief description of the experiments is also presented in the paper. Registered effect suggests that the water in the fuel improved mixing of fuel and oxidizer in the FB furnace, by increasing jet penetration into the FB due to sudden evaporation of water at the entry into the furnace. In order to clarify this effect, numerical simulations of jet penetration into the FB with three-phase systems: gas (fuel, oxidizer, and water vapour), bed particles and water, have been carried out.

scholarly journals INCORPORATION OF A TWO-FLUX MODEL FOR RADIATIVE HEAT TRANSFER IN A COMPREHENSIVE FLUIDIZED BED SIMULATOR PART I: PRELIMINARY THEORETICAL INVESTIGATIONS

2003 ◽  
Vol 2 (1) ◽  
pp. 64 ◽  
Author(s):  
J. A. Rabi ◽  
M. L. De Souza Santos
Keyword(s):  
Heat Transfer ◽  
Mathematical Model ◽  
Thermal Radiation ◽  
Fluidized Bed ◽  
Radiative Heat ◽  
Radiation Heat Transfer ◽  
Basic Structure ◽  
Solid Particles ◽  
Particulate Media ◽  
Bubbling Fluidized Bed

Over the last two decades, a comprehensive mathematical model and its corresponding computational program, aimed to simulate steady-state operations of bubbling fluidized bed equipments, has been continuously improved and tested. Despite its success, the simulator has employed a simple approach for radiative heat transfers. In cases of high temperatures, thermal radiation becomes an important energy transfer mode and the original model could lead to deviations above acceptable levels. The purpose of the present work was to improve the model for thermal radiation heat transfer between all solid particles in the bed section by applying a two-flux method to a non-homogeneous polydispersed particulate media in radiative equilibrium. Gases in the emulsion and in the bubbles were assumed transparent to thermal radiation. This first part of the paper presents and discusses the basic structure of the former mathematical model and of the new one.

Particle pressures generated around bubbles in gas-fluidized beds

2002 ◽  
Vol 455 ◽  
pp. 103-127 ◽  
Author(s):  
KHURRAM RAHMAN ◽  
CHARLES S. CAMPBELL
Keyword(s):  
Fluidized Bed ◽  
Bubble Size ◽  
Fluidized Beds ◽  
Gas Flow ◽  
Solid Particles ◽  
Particle Phase ◽  
Fluid Mixture ◽  
Maximum Value ◽  
Particle Pressure ◽  
Gas Fluidized Beds

The particle pressure is the surface force in a particle/fluid mixture that is exerted solely by the particle phase. This paper presents measurements of the particle pressure on the faces of a two-dimensional gas-fluidized bed and gives insight into the mechanisms by which bubbles generate particle pressure. The particle pressure is measured by a specially designed ‘particle pressure transducer’. The results show that, around single bubbles, the most significant particle pressures are generated below and to the sides of the bubble and that these particle pressures steadily increase and reach a maximum value at bubble eruption. The dominant mechanism appears to be defluidization of material in the particle phase that results from the bubble attracting fluidizing gas away from the surrounding material; the surrounding material is no longer supported by the gas flow and can only be supported across interparticle contacts which results in the observed particle pressures. The contribution of particle motion to particle pressure generation is insignificant.The magnitude of the particle pressure below a single bubble in a gas-fluidized bed depends on the bubble size and the density of the solid particles, as might be expected as the amount of gas attracted by the bubble should increase with bubble size and because the weight of defluidized material depends on the density of the solid material. A simple scaling of these quantities is suggested that is otherwise independent of the bed material.In freely bubbling gas-fluidized beds the particle pressures generated behave differently. Overall they are smaller in magnitude and reach their maximum value soon after the bubble passes instead of at eruption. In this situation, it appears that the bubbles interact with one another in such a way that the de uidization effect below a leading bubble is largely counteracted by refluidizing gas exiting the roof of trailing bubbles.

scholarly journals INCORPORATION OF A TWO-FLUX MODEL FOR RADIATIVE HEAT TRANSFER IN A COMPREHENSIVE FLUIDIZED BED SIMULATOR PART I: PRELIMINARY THEORETICAL INVESTIGATIONS

2003 ◽  
Vol 2 (1) ◽  
Author(s):  
J. A. Rabi ◽  
M. L. De Souza Santos
Keyword(s):  
Heat Transfer ◽  
Mathematical Model ◽  
Thermal Radiation ◽  
Fluidized Bed ◽  
Radiative Heat ◽  
Radiation Heat Transfer ◽  
Basic Structure ◽  
Solid Particles ◽  
Particulate Media ◽  
Bubbling Fluidized Bed

Over the last two decades, a comprehensive mathematical model and its corresponding computational program, aimed to simulate steady-state operations of bubbling fluidized bed equipments, has been continuously improved and tested. Despite its success, the simulator has employed a simple approach for radiative heat transfers. In cases of high temperatures, thermal radiation becomes an important energy transfer mode and the original model could lead to deviations above acceptable levels. The purpose of the present work was to improve the model for thermal radiation heat transfer between all solid particles in the bed section by applying a two-flux method to a non-homogeneous polydispersed particulate media in radiative equilibrium. Gases in the emulsion and in the bubbles were assumed transparent to thermal radiation. This first part of the paper presents and discusses the basic structure of the former mathematical model and of the new one.

scholarly journals Axial holdup distributions of gas and solid particles in three-phase fluidized bed for gas-liquid(slurry)-solid systems.

1985 ◽  
Vol 18 (4) ◽  
pp. 308-313 ◽  
Author(s):  
YASUO KATO ◽  
SHIGEHARU MOROOKA ◽  
TOKIHIRO KAGO ◽  
TETSUYA SARUWATARI ◽  
SHOU-ZHI YANG
Keyword(s):  
Fluidized Bed ◽  
Solid Particles ◽  
Three Phase ◽  
Liquid Slurry

Cluster-Based Modeling of Fluidized Catalytic Oxidation of n-Butane to Maleic Anhydride

2006 ◽  
Vol 4 (1) ◽  
Author(s):  
Hamid Reza Hakimelahi ◽  
Rahmat Sotudeh-Gharebagh ◽  
Navid Mostoufi
Keyword(s):  
Mathematical Model ◽  
Maleic Anhydride ◽  
Fluidized Bed ◽  
Flow Reactor ◽  
Plug Flow ◽  
Fluidized Bed Reactor ◽  
Solid Particles ◽  
Reactor Model ◽  
Two Phase ◽  
Cut Method

A mathematical model is proposed for the partial oxidation on n-butane to maleic anhydride (MAN) in a gas-solid fluidized bed reactor. The reactor consists of two regions, i.e., a lower dense region and an upper dilute region. The dynamic two-phase structure was used for modeling the lower dense bed hydrodynamics. The upper region hydrodynamics was modeled by a cluster based approach. This allows the porosity distribution to be calculated for plug flow reactor model assumed for the gas phase in this region. The basic assumption in the cluster based approach is that the solid particles move only as clusters and the amount of single particles in the upper region is negligible. The mathematical model was obtained from coupling the kinetic sub-model, obtained from the literature, with this hydrodynamics sub-model. Comparing the results of the model with the experimental data available in the literature showed close agreement. Two other methods (i.e., particle based approach and short-cut) were also tested in this work. However, it was found that the cluster based approach modeling is quite suitable for the fluidized bed reactor used in this study. The short-cut method seems reasonably applicable for the prediction of the overall conversion but does not provide any local information (such as concentration profiles, yield, etc.) within the fluidized bed reactor.

scholarly journals Fuzzy-GMC Control of Gas-Phase Propylene Copolymerization in Fluidized Bed Reactor

2018 ◽  
Vol 156 ◽  
pp. 07002
Author(s):  
Nazratul Fareha Salahuddin ◽  
Ahmad Shamiri ◽  
Mohd Azlan Hussain ◽  
Navid Mostoufi
Keyword(s):  
Gas Phase ◽  
Fluidized Bed ◽  
Fuzzy Logic Controller ◽  
Fluidized Bed Reactor ◽  
Solid Particles ◽  
Phase Model ◽  
Regulatory Control ◽  
Generic Model ◽  
Two Phase ◽  
Model Control

A modified two-phase model for gas phase propylene and ethylene copolymerization was chosen to represent the process in a fluidized bed reactor. This model considered the entrainment of solid particles in the reactor, as a modification to the original two-phase model assumptions. The non-linearity of this process makes it difficult to control just by using conventional controller such as PID. A hybrid control strategy (a simple designed fuzzy logic controller (FLC) integrated with generic model control (GMC)) is designed to control the temperature of the reactor. This advanced control system was compared with the GMC and conventional PID controller. The simulation results showed that the hybrid controller (Fuzzy-GMC) performed better than both GMC and PID in terms of both servo and regulatory control.

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