Copyright (c) 2009 Berkeley Electronic Press All rights reserved. http://www.bepress.com/cppm Recent documents in Chemical Product and Process Modeling en-us Fri, 06 Nov 2009 23:22:25 PST 3600 http://www.bepress.com/cppm/vol4/iss1/46 http://www.bepress.com/cppm/vol4/iss1/46 Thu, 05 Nov 2009 22:14:33 PST The complex flow patterns induced in fluidized bed catalytic reactors and the competing parameters affecting the mass and heat transfer characteristics makes the design of such reactors a challenging task to accomplish. The models of such a process rely heavily on predictive empirical correlations for mass and heat transfer coefficients. Unfortunately, published empirical based correlations have the common shortcoming of low-prediction efficiency compared with experimental data. In this work, an artificial neural network approach is used to capture the reactor characteristics in terms of heat and mass transfer based on published experimental data. The developed ANN-based heat and mass transfer coefficients relations were used in a conventional FCR model and simulated under industrial operating conditions. The hybrid model predictions of the melt-flow index and the emulsion temperature were compared to industrial measurements as well as published models. The predictive quality of the hybrid model was superior to other models. This modeling approach can be used as an alternative to conventional modeling methods. Ahmmed Saadi Ibrehem Modeling and ANN http://www.bepress.com/cppm/vol4/iss1/45 http://www.bepress.com/cppm/vol4/iss1/45 Fri, 30 Oct 2009 09:12:09 PDT Process control in the field of chemical engineering has always been a challenging task for the chemical engineers. Hence, the majority of processes found in the chemical industries are non-linear and in these cases the performance of the linear models can be inadequate. Recently a promising alternative modelling technique, artificial neural networks (ANNs), has found numerous applications in representing non-linear functional relationships between variables. A feedforward multi-layered neural network is a highly connected set of elementary non-linear neurons. Model-based control techniques were developed to obtain tighter control. Many model-based control schemes have been proposed to incorporate a process model into a control system. Among them, model predictive control (MPC) is the most common scheme. MPC is a general and mathematically feasible scheme to integrate our knowledge about a target, process controller design and operation, which allows flexible and efficient exploitation of our understanding of a target, and thus produces optimal performance of a system under various constraints. The need to handle some difficult control problems has led us to use ANN in MPC and has recently attracted a great deal of attention. The efficacy of the neural predictive control with the ability to perform comparably to the non linear neural network strategy in both set point tracking and disturbance rejection proves to have less computation expense for the neural predictive control. The neural network model predictive control (NNMPC) method has less perturbations and oscillations when dealing with noise as compared to the PI controllers. Senthil Kumar Arumugasamy Process Control http://www.bepress.com/cppm/vol4/iss3/13 http://www.bepress.com/cppm/vol4/iss3/13 Tue, 27 Oct 2009 20:46:21 PDT A novel supervisory control system was developed for a boutique, walking beam-type, natural gas-fired industrial reheating furnace for steel slabs. The control system was developed to provide furnace temperature set points for the operators. The system development ideology was to utilise the considerable and inexpensive computing resources available today, to solve problems in real time in a discrete and digitised manner in place of complex analytical solutions. The control system utilises an entirely iterative regime to calculate the required furnace heating profiles to ensure that slab delivery temperatures are optimised. A two-dimensional slab conduction and radiation model was developed to fulfil the supervisory control function. The results are promising with estimated control performance at least as good as current manual achievement but with the benefit of additional information being provided to the expert human operator in the control loop. A. A. Waelen Control http://www.bepress.com/cppm/vol4/iss3/12 http://www.bepress.com/cppm/vol4/iss3/12 Tue, 27 Oct 2009 20:35:21 PDT This paper presents a systematic computational study of the inhibition of premixed flames of short chain hydrocarbons with CF3I, focusing on sensitivity analysis of the (normalized) burning velocity and reaction pathway analysis using the "iodine-flux" approach. A comprehensive kinetic mechanism was obtained by combining the GRI, hydrofluorocarbon and CF3I sub-mechanisms, and updating the rates of some of the elementary reactions. Calculations were performed using the PREMIX computer code in the CHEMKIN suite of computer codes. The updated mechanism yielded estimates of the normalized laminar burning velocities which concurs closely with published measurements. The sensitivity analysis resulted in a positive coefficient for CF3I + M → CF3 + I + M, confirming the promoting effect of CF3I on the laminar flame velocity and is consistent with previous studies. Reaction pathways were drawn for stoichiometric, fuel-lean and fuel-rich flames doped with 1 and 2% of CF3I at atmospheric pressure. The reaction pathway analysis served to identify four major inhibition cycles, denoted as HI → I → HI, HI → I → I2 → HI, HI → I → CH3I → HI and HI → I → C2H5I → HI. Furthermore, the paper developed a linear expression linking the normalized rate of heat release with the ratio of laminar burning velocities of mitigated and non-mitigated flames, and verified the efficacy of this expression for flames inhibited with CF3I. Caimao Luo Combustion modeling http://www.bepress.com/cppm/vol4/iss1/44 http://www.bepress.com/cppm/vol4/iss1/44 Fri, 23 Oct 2009 22:33:55 PDT Modeling for hydrocarbon methane was carried out during the warm-up period. A one-dimensional model based on its catalytic combustion reaction was formed. The mass and energy balance equations derived for the gas and the solid phase are a set of partial differential equations. All these equations are solved using Backward Implicit Scheme. The variation of gas concentration, temperature and solid temperature along the length of the converter during the warm-up period was analysed. Also, the effects on time while changing various parameters--like inlet gas temperature, catalyst loading, surface area, and converter length--for methane conversion, were studied. Sanchita Chauhan environmental process modeling http://www.bepress.com/cppm/vol4/iss1/43 http://www.bepress.com/cppm/vol4/iss1/43 Fri, 23 Oct 2009 03:18:24 PDT This paper presents the results of numerical modeling of temperature distribution and flow pattern in a block radiator used in power transformer cooling system. Each block radiator consists of eighteen plane radiators which are parallel together and a typical power transformer (like a 30MVA) has 6 radiator blocks in each side which means it has 12 blocks totally. The numerical study using fluent software has been conducted to find the explanation of low cooling efficiency in this especial power transformer currently used in industry. Our main desire is the study of relation between radiator block characteristics and cooling behavior of system which can be used for its optimization in the future studies. The results indicate that recirculation occurs whenever pressure increase at the end of a radiator block that consequently prevents the enough oil flow through the last radiator of block. Experimental data taken from company and technical data extracted from transformer documents have been used for model calibration and results verification. Hamid Nabati Modelling http://www.bepress.com/cppm/vol4/iss1/42 http://www.bepress.com/cppm/vol4/iss1/42 Thu, 22 Oct 2009 13:34:10 PDT The potential impacts of additional flow and organic loads resulting from the production of cellulosic ethanol on an existing integrated newsprint mill were simulated in this paper. It was found that depending on the ethanol production rate and the existing spare capacity for additional biochemical oxygen demand (BOD), treatment plant modifications may be required. In terms of operating costs, it was found that nutrients use could increase by 50% to 150%, while aeration flow could increase by 5% to 140% depending on the desired level of dissolved oxygen in the aeration basin. Significant increases in polymer use for mixed sludge dewatering could result due to additional biosolids production. Additional capital costs for air blowers could also be necessary unless the mill has existing spare capacity. It was also found that ethanol recovery efficiency and production rate had little impact on BOD removal up to a certain ethanol production level, and that the impact on operating costs decreased with increasing recovery. Jean-Martin Brault Wastewater treatment http://www.bepress.com/cppm/vol4/iss1/41 http://www.bepress.com/cppm/vol4/iss1/41 Wed, 14 Oct 2009 22:30:09 PDT Hydrogen atom transfer (HAT) underlies free-radical chain-breaking by phenolic compounds. Using linear free energy relationship (LFER) analysis, proton transfer kinetics was hypothesized as a surrogate rate process for HAT. Phenol red is a probe that is easily oxidized to highly absorbing specie by hydroxyl ion. Absorbance decay of oxidized phenol red was induced by incremental proton transfer from a model phenolic (resorcinol). Global best-fit kinetics profile of resorcinol approximates a mono-exponential decay model (R2 = 0.991) as a limiting law. Proton transfer rate constant (Kptt) versus concentration reveal the utility of the slope (αaoc) of the linear plot (r2= 0.990) as a sensitive predictor of phenolic antioxidant capacity. Superior antioxidant capacity profile of a polyphenol-rich dietary supplement: Garcinia kola seed extract, optimally obeyed a mixed linear/mono-exponential decay equation. Model robustness and selectivity for phenolics was achieved by specifying mathematical constraints as acceptance criteria. The method is more biologically relevant for chain-breaking antioxidants than free-radical-based assays because it captures antioxidant structure-function relationships. Further validation studies, using structurally diverse polyphenols, are warranted to ascertain general utility of the kinetic assay for achieving quality by design (QbD) in phenolic dietary supplement products. Sunday O. Idowu Antioxidant capacity assays http://www.bepress.com/cppm/vol4/iss1/40 http://www.bepress.com/cppm/vol4/iss1/40 Mon, 12 Oct 2009 22:27:23 PDT The major issues in anaerobic treatment are discharge standard accomplished by post-treatment facilities. Model tanks have been designed for post treatment of anaerobic effluents. Tracer studies by KMnO4 have been employed on model tanks to know hydrodynamics and mixing inside the tanks. The existence and arrangement of baffles in the tanks and higher tracer density can result in much more complex flow pattern which includes turbulent mixing, dead zones and short circuiting. The objective of the paper is to present the result of a numerical study undertaken to investigate the flow inside the reactor and effect of hydraulic parameters on the extent of mixing. The computational fluid dynamics (CFD) study was also performed on the velocity distribution within the model tanks. Thus, several 2D steady-state and time-variable numerical simulations were performed with in the model tanks geometry. Tracer transport was analyzed in case of burst of concentration. The CFD study shows how velocity, pressure and their vector notations were useful to predict the dead spaces inside the tanks which affect the mixing behavior inside the tank. Khushbu Patel Chemical Reaction Engineering http://www.bepress.com/cppm/vol4/iss3/11 http://www.bepress.com/cppm/vol4/iss3/11 Thu, 01 Oct 2009 10:34:43 PDT Two-dimensional numerical simulations for the ohmic heating of whole milk solutions in an annular geometry were performed using a general-purpose partial-differential equation solver, FlexPDE software. The flow, energy, and concentration equations were developed and solved for laminar flow. The reaction kinetics model for beta-lactoglobulin proposed by Toyoda and Fryer (1996) was adopted to solve for the native, denatured, and aggregated protein concentrations in the full-flow domain. The aim of this work is to investigate how the applied voltage and flow rate affect the temperature field, and the effects on the concentration profile of each protein type in the solution. Despite what is usually expected of the ohmic heating as a uniform heating method, temperature gradients were seen to be significant from the wall to the bulk solution. The results show that a higher voltage causes a faster disappearance of native protein concentration, especially near the wall. Depending upon the applied voltage, the denatured protein concentration initially increases along the axial distance, then starts to decrease at different axial locations. The aggregated protein concentration was found to be much higher at the wall then in the bulk. In addition to describing the protein concentration distributions in the heater, the fouling tendency of the milk components on the walls is also discussed in this paper. H.J. Tham Modeling and Simulation