Copyright (c) 2008 All rights reserved. http://works.bepress.com/sotudeh Recent documents in Rahmat Sotudeh-Gharebagh en-us Thu, 03 Jan 2008 17:39:14 PST 3600 http://works.bepress.com/sotudeh/35 http://works.bepress.com/sotudeh/35 Thu, 07 Dec 2006 02:07:16 PST A model is developed based on a two-stage hydrogenation of pyrolysis gasoline to obtain a C6-C8 cut suitable for extraction of aromatics. In order to model the hydrogenation reactors, suitable hydrodynamic and reaction submodels should be solved simultaneously. The first stage hydrogenation takes place in a trickle bed reactor. The reaction rates of different di-olefines as well as hydrodynamic parameters of the trickle bed (i.e., catalyst wetting efficiency, pressure drop, mass transfer coefficient and liquid hold-up) have been combined to derive the equations to model this reactor. The second stage hydrogenation takes place in a two compartment fixed bed reactor. Hydrogenation of olefines takes place in the first compartment while sulfur is eliminated from the flow in the second compartment. These reactions occur at relatively higher temperature and pressure compared to the first stage. The key component in this stage is considered to be cyclohexene, of which the hydrogenation was found to be the most difficult of the olefines present in the feed. The Langmuir-Hinshelwood kinetic expression was adopted for the hydrogenation of cyclohexene and its kinetic parameters were determined experimentally in a micro-reactor in the presence of the industrial catalyst. The model was solved for the whole process of hydrogenation, including hydro-desulfurization. The predictions of the model were compared with actual plant data from an industrial scale pyrolysis gasoline hydrogenation unit and satisfactory agreement was found between the model and plant data. Navid Mostoufi Process Modeling and Simulation http://works.bepress.com/sotudeh/25 http://works.bepress.com/sotudeh/25 Thu, 07 Dec 2006 02:06:41 PST A predictive model is developed in order to define the hydrodynamics of the acceleration zone in the riser of a circulating fluidized bed (CFB). The riser is divided into three distinct zones, i.e., acceleration, fully developed and deceleration zones. The acceleration zone is the region between the top of the dense bed and the fully developed zone. This study has employed both fundamental principles and empirical correlations in order to predict the hydrodynamic parameters in the acceleration zone. It is assumed that the solids move up in the riser as clusters (cluster-based approach, CBA) rather than single particles (particle-based approach, PBA). The model is thus based on the force balance on a single cluster. The cluster properties were estimated from the existing correlations from the literature. The model predictions were compared with the data obtained from the literature in term of pressure drop against riser height. Unlike the particle-based approach, there is a good agreement between the proposed model predictions and the experimental data. Therefore, it has been concluded that clusters are the key controller of the acceleration zone hydrodynamics. Hashen Sabbaghan Fluidization http://works.bepress.com/sotudeh/19 http://works.bepress.com/sotudeh/19 Thu, 07 Dec 2006 02:06:20 PST A sequeantail modular method for the simulation of fluidized bed reactors is proposed. The model consists of two submodels, hydrodynamic and reaction submodel. The hydrodynamic submodel is developed based on the dynamic two-phase model, which considers existence of particles in the bubbles and emulsion not being in minimum fluidization. This sub-model allows the concentration of particles in the bubble and emulsion phase to be determined. The reaction submodel considers the typical highly exothermic reactions reported in the literture. These two submodels are combined together so that the fluidized bed reactor to be presented. This model is developed based on a proper combination of CSTRs and PFRs, which reflects the real physical phenomena occuring within a fluidized bed reactor. The fluidized bed eractor is divided into several stages. The number of stages is determined based on the concept drived from the experimental data reported in the literature. Results of this model are compared with the experimental data and it was shown that the model provides appropriate explanation of the performance of the fluidized bed reactors based on this sequential modular approach. The results of the work may be used to predict the conversion in the fluidized bed reactor based on dynamic behavior of buuble-emulsion phase recently proposed in the fluidization literature. Rouzbeh Jafari Fluidization Process Modeling and Simulation http://works.bepress.com/sotudeh/18 http://works.bepress.com/sotudeh/18 Thu, 07 Dec 2006 02:06:18 PST 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 40% of the polymer is produced inside the bubble phase and as such cannot be neglected in modeling such reactors. Ali Kiashemshaki Fluidization Process Modeling and Simulation http://works.bepress.com/sotudeh/17 http://works.bepress.com/sotudeh/17 Thu, 07 Dec 2006 02:06:16 PST The synthesis section of urea production plant (high-pressure section) has been simulated with process simulation software. Wilson and ideal gas equations were used as equations of state for liquid and gas phases, respectively. The binary interaction coefficients of Wilson equation were modified to fit the actual data. This set of equations shows satisfactory results in all parts of the studied section with the exception of CO2 compressor. For which Peng-Robinson equation of state was used. Existing units of urea synthesis section have been simulated with standard modules from HYSYS with the exception of the reactor. The reactor has been simulated with sequential CSTRs model. Temperature dependence formula of equilibrium constant of ammonium carbamate reaction has been corrected using the data in the literature as well as those at the exit of the real reactor. Comparison between simulation results and plant data shows good consistency between the model and reality. Mohsen Hamidipour Process Modeling and Simulation http://works.bepress.com/sotudeh/15 http://works.bepress.com/sotudeh/15 Thu, 07 Dec 2006 02:06:10 PST A mathematical model is proposed to simulate the starch converter. The converter was hydrodynamically divided into six zones and material and energy balances were established in each zone. Due to the fact that the converter is a laminar flow reactor, it was necessary to apply the equation oriented simulation approach to simulate the converter. Therefore, four partial differential equations were solved together by finite difference in each section. Thermophysical properties of the corresponding fluid were calculated by using various correlations and data from the literature. In order to predict accurate concentrations of glucose, the kinetics was determined with the aid of the data in the literature. A set of actual plant data from the industrial converter is used to validate the proposed model. The agreement between the model prediction and the experimental data is quite satisfactory and the model could be used to predict the performance of industrial converters at a wide range of operating conditions. Arash Iranshahi Process Modeling and Simulation http://works.bepress.com/sotudeh/14 http://works.bepress.com/sotudeh/14 Thu, 07 Dec 2006 02:06:09 PST Combustion of natural gas in fluidized bed reactors is considered as an economical way for producing energy and food-grade CO2 largely needed in food and chemical industries. Therefore, their simulation and modeling could be of great industrial importance. In this study, a model is developed based on the sequential modular approach for combustion of natural gas in a catalytic turbulent fluidized bed (TFB) reactor. The proposed model integrates hydrodynamic parameters, reaction model and kinetic data necessary to simulate the combustion of natural gas in the catalytic turbulent fluidized bed reactor. For the purpose of this study and based on hydrodynamic considerations, a number of ideal reactors have been considered to simulate the overall performance of the reactor. The validity of the proposed model was demonstrated using the pilot plant experimental data from the literature. The agreement between the simulation results and the experimental data was found to be satisfactory. Rahmat Sotudeh-Gharebagh Fluidization Process Modeling and Simulation http://works.bepress.com/sotudeh/13 http://works.bepress.com/sotudeh/13 Thu, 07 Dec 2006 02:06:08 PST A model is developed for evaluating the performance of industrial-scale gas-phase polyethylene production reactors. This model is able to predict the properties of the produced polymer for both linear low-density and high-density polyethylene grades. A pseudo-homogeneous state was assumed in the fluidized bed reactor based on negligible heat and mass transfer resistances between the bubble and emulsion phases. The nonideal flow pattern in the fluidized bed reactor was described by the tanks-in-series model based on the information obtained in the literature. The kinetic model used in this work allows to predict the properties of the produced polymer. The presented model was compared with the actual data in terms of melt index and density and it was shown that there is a good agreement between the actual and calculated properties of the polymer. New correlations were developed to predict the melt index and density of polyethylene based on the operating conditions of the reactor and composition of the reactants in feed. Ali Kiashemshaki Fluidization Process Modeling and Simulation http://works.bepress.com/sotudeh/12 http://works.bepress.com/sotudeh/12 Thu, 07 Dec 2006 02:06:06 PST Modeling of a bubbling/turbulent fluidized bed reactor has been studied for catalytic reactions in the presence of different catalysts. The performance of the fluidized reactor has been investigated by three different hydrodynamic models: (i) simple two-phase model, (ii) dynamic twophase model and (iii) generalized bubbling/turbulent model. It has been shown that the simple two-phase model is suitable only for slow reaction rates. The dynamic two-phase model and generalized bubbling/turbulent model are able to predict the performance of the fluidized bed reactor satisfactorily over a wide range of gas superficial velocities. The performance of the dynamic two-phase model could be further improved by choosing the proper constants. In the case of the generalized bubbling/turbulent model, a more realistic distribution function for the probability of being in the turbulent regime of fluidization would further enhance the performance of this model. Rouzbeh Jafari Fluidization http://works.bepress.com/sotudeh/11 http://works.bepress.com/sotudeh/11 Thu, 07 Dec 2006 02:06:05 PST Particle-wall contact behavior of the solids in a gas-solid fluidized bed was experimentally studied using the radioactive particle tracking (RPT) technique in which the position of a radioactive tracer is monitored when moving freely in the bed. The solids were sand particles, fluidized by air at room temperature and atmospheric pressure at various superficial velocities, covering both bubbling and turbulent regimes of fluidization. The motion of individual particles near the wall of the bed was studied based on the position of the tracer. The contact time, contact distance and contact frequency of the particles at the wall were evaluated. It was found that the distribution functions of these three parameters become wider by increasing the superficial gas velocity. Axial profiles of contact time and contact distance were also studied in this work. Axial profiles of the overall heat transfer coefficient in the fluidized bed were estimated based on the formulas reported in the literature and the experimental particle-wall contact time evaluated in the present study. Based on such profiles, in order to benefit from the maximum heat transfer coefficient along the bed, it is recommended to place the heat exchanging surface in the middle of the bed, i.e., not very close to the gas distributor as well as far from the top of the dense bed. Mohsen Hamidipour Fluidization