Copyright (c) 2008 All rights reserved. http://works.bepress.com/navid_mostoufi Recent documents in Navid Mostoufi en-us Thu, 03 Jan 2008 11:46:57 PST 3600 http://works.bepress.com/navid_mostoufi/25 http://works.bepress.com/navid_mostoufi/25 Wed, 24 Oct 2007 09:59:38 PDT A mathematical model is developed to optimize the performance of the radial flow reactors of styrene production through an oxidative reheat process. The model integrates the hydrodynamic configuration of the reactors with the underlying chemical reactions where the kinetic expressions were found in the literature. The predictions of the model were compared with the actual plant data and satisfactory results were obtained. In order to optimize the performance of the plant, a combination of yield and selectivity styrene was adopted as the objective function. The global criterion multi-objective method using Levenberg-Marquardt algorithm was used in order to search for the optimal solution of the process. Three main process variables, i.e., the flow rate of steam injected to the second and third reactor and the fraction of oxygen injected to the secondary injection port of the second reactor, were determined in the optimization. The results show that the optimal operating conditions may lead to 2.6 % increase in the styrene yield and 1.5% increase in styrene selectivity, which significantly improves the profitability of the whole styrene production process. Navid Mostoufi Process Modeling http://works.bepress.com/navid_mostoufi/24 http://works.bepress.com/navid_mostoufi/24 Wed, 24 Oct 2007 09:56:39 PDT Although extensive studies have been conducted on convective heat transfer from a heat exchanger surface to a gas fluidized bed, the contribution through particle convection has not been adequately described, especially in turbulent fluidized beds. In this study, the role that dense bed hydrodynamics play on particle convection has been outlined. The existing models in the literature suggest a constant decrease of particle-wall contact time with an increase in the gas velocity. It has been experimentally demonstrated, however, that the contact time increases, both in bubbling and turbulent regimes, upon increasing the gas velocity. A comprehensive model has been developed to represent such a trend and improve agreement with experimental data presented in literature. The proposed model includes two constants for taking into account the wall effect on bubbles and clusters. The constants of the model have been evaluated based on the radial profiles of the distribution of bubbles and clusters using a radioactive particle tracking technique. A comparison of the predicted results with the experimental data from the literature confirms the validity of the present model for the dense bed region of a fluidized bed of sand particles. Reza Zarghami Fluidization http://works.bepress.com/navid_mostoufi/23 http://works.bepress.com/navid_mostoufi/23 Wed, 24 Oct 2007 09:51:02 PDT A two phase model is proposed for describing the behavior of fluidized bed reactor of polyethylene production. In the proposed model the bed is divided into several serial sections. The flow of the gas is considered as plug flow through the bubbles and perfectly mixed through the emulsion phase in each section. Polymerization reactions occur not only in the emulsion phase but also in the bubble phase. The concentrations of particles in the emulsion and bubble phase are estimated from the dynamic two phase hydrodynamic model. The kinetic model are employed in this study is based on the moment equations. The results of the simulation are compared with experimental data in terms of melting index of the product. A good agreement was observed between the simulation results and the actual data. Ali Kiashemshaki Fluidization http://works.bepress.com/navid_mostoufi/22 http://works.bepress.com/navid_mostoufi/22 Wed, 24 Oct 2007 09:46:07 PDT An industrial steam reformer of a methanol plant was modeled at a dynamic condition in which a one dimensional homogeneous model was coupled with a verified kinetics from the literature. A close agreement was observed between the results of the model and industrial data from a real plant at steady state conditions. The open loop response of the system to switching etween two operating conditions was investigated and shown that the produced synthesis gas during the transition period would be unsuitable for the downstream methanol converter. The genetic algorithm was then employed to perform a multi-objective dynamic optimization on the reactor performance in case of switching the feed and operating conditions. Maximization of methane conversion and minimization of a stoichiometric parameter, were considered as the two objectives' functions that were optimized for a fixed feed rate of methane to the existing unit. The results of the dynamic optimization for the specified reformer configuration were achieved after switching the operating condition. Results of the optimization showed that the produced synthesis gas would stay in its acceptable limits in terms of quality of the feed of the methanol converter and also, the final conversion of the reformer would be improved compared to the steady state condition. This procedure could be applied to the advanced process control of the methanol plant. Ali Alizadeh Process Modeling http://works.bepress.com/navid_mostoufi/21 http://works.bepress.com/navid_mostoufi/21 Mon, 18 Dec 2006 03:59:54 PST The concept of temperature penetration depth is used to investigate the heat transfer behavior near the wall of fluidized beds, according to the cluster-based approach. The process of heat transfer through clusters which exist adjacent to the wall was viewed in context of partial and total heat penetration. In the case of partial heat penetration, the heat flux applied to the wall side of the clusters has not reached its bed-side, while in the case of total heat penetration the heat flux has completely crossed the cluster, and the temperature of its bed-side would differ from the bed temperature. Based on the heat balance equation inside the cluster, two different expressions were derived for heat transfer coefficient for each penetration period. The predictions of the proposed model are in close agreement with experimental values and to some extent better than existing models. Shayan Karimipour Fluidization http://works.bepress.com/navid_mostoufi/20 http://works.bepress.com/navid_mostoufi/20 Mon, 04 Dec 2006 20:45:31 PST Alkis Constantinides http://works.bepress.com/navid_mostoufi/19 http://works.bepress.com/navid_mostoufi/19 Mon, 04 Dec 2006 20:37:43 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 http://works.bepress.com/navid_mostoufi/18 http://works.bepress.com/navid_mostoufi/18 Mon, 04 Dec 2006 20:36:07 PST A pseudo-homogeneous model is proposed for describing the behavior of fluidized bed reactor for linear low density polyethylene (LLDPE) production. The kinetic model employed in this study is based on the moment equations. The average concentration of particles in the bed is estimated from the dynamic two-phase structure hydrodynamic model. A tanks-in-series model was adopted to describe the flow pattern in the reactor. The hydrodynamic and kinetic models are integrated to the reactor model to make a comprehensive gas-phase LLDPE production reactor model. It has been shown that the results of this model fit the actual data in terms of melt flow index of the produced polyethylene, satisfactorily. The proposed model is capable of predicting the performance of the reactor as well as polymer physico-chemical properties. Mahmoud Alizadeh Fluidization http://works.bepress.com/navid_mostoufi/17 http://works.bepress.com/navid_mostoufi/17 Mon, 04 Dec 2006 20:31:56 PST Simulation of chemical processes involving nonideal reactors is essential for process design, optimization, control and scale-up. Various industrial process simulation programs are available for chemical process simulation. Most of these programs are being developed based on the sequential modular approach. They contain only standard ideal reactors but provide no module for nonideal reactors, e.g., fluidized bed reactors. In this study, a new model is developed for the simulation of fluidized bed reactors by sequential modular approach. In the proposed model the bed is divided into several serial sections and the flow of the gas is considered as plug flow through the bubbles and perfectly mixed through the emulsion phase. In order to simulate the performance of these reactors, the hydrodynamic and reaction submodels should be integrated together in the medium and facilities provided by industrial simulators to obtain a simulation model. The performance of the proposed simulation model is tested against the experimental data reported in the literature for various gas-solid systems and a wide range of superficial gas velocities. It is shown that this model provides acceptable results in predicting the performance of the fluidized bed reactors. The results of this study can easily be used by industrial simulators to enhance their abilities to simulate the fluidized bed reactor properly. Rouzbeh Jafari Fluidization http://works.bepress.com/navid_mostoufi/16 http://works.bepress.com/navid_mostoufi/16 Mon, 04 Dec 2006 20:28:53 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