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  • Chemical Engineering  (17)
  • SPACE RADIATION
  • 1995-1999  (18)
  • 1
    Electronic Resource
    Electronic Resource
    Modeling and dynamic simulation of a bleach plant (1995)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 2603-2613 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A dynamic model of five-stage (C+D)EDED bleach plant was developed using SIMNON a dynamic simulation language developed at Lund Institute of Technology, as a platform. The model is composed of individual modules that represent each bleaching stage. Each module includes chemical addition and mixing, diffusion and reaction in a retention towel, and washing. These unit operations are coupled with chemical kinetics for each bleaching stage using appropriate models. A relationship between the (C+D)E Kappa number and the input absorption coefficient to the D1 stage was used to link the delignification and brightening partial sequences of the bleach plant. The model, verified using steady-state data, was used to model the dynamic response of the plant to step changes in production rate, (C+D) chemical addition, and incoming Kappa number, as well as the open-loop response of the plant to a simulated variation in incoming Kappa number. The modular structure of the program allows a variety of bleach plants to be assessed once flow parameters and chemical kinetics are known. The dynamic model can also be used to develop and compare control strategies before being implemented at the mill.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690411209
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of operating conditions on stability of gas-phase polyethylene reactors (1995)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 868-879 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Fluidized-bed polyethylene reactors are prone to unstable behavior and temperature oscillations (Choi and Ray, 1985b). Their work is extended to show the effects of ethylene feed system operation, reactor cooling system design, catalyst properties, and gas composition on reactor stability and dynamics. The analysis is performed using a well-mixed model, because heat- and mass-transfer resistances between multiple phases are small and are not required to account for the observed bifurcation phenomena. The addition of a gas recycle and heat exchanger system to the model significantly affects dynamic performance, including the formation of limit cycles. The size and dynamics of the heat exchanger, however, have little effect on the overall stability. In contrast, automation of the ethylene feed system to replace the monomer in the reactor as it is consumed leads to substantially different dynamic behavior than if the ethylene feed is maintained at a constant rate. Catalyst properties (multiple sites, activation energy, and deactivation) significantly affect dynamics and stability, whereas comonomer and other gases affect them only mildly. The results confirm that without proper temperature control, gas-phase polyethylene reactors are prone to instability, limit cycles, and excursions towards unacceptable high-temperature steady states.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690410414
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  • 3
    Electronic Resource
    Electronic Resource
    Measure of closed-loop nonlinearity and interaction for nonlinear chemical processes (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2261-2278 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new approach for assessing nonlinear interaction effects and closed-loop nonlinearity in multivariable processes is presented. It is based on a differential geometric interpretation of the relative gain array that leads naturally to systematic procedures for describing interaction effects of higher order and for assessing closed-loop nonlinearity effects in nonlinear processes. Two types of nonlinear effects associated with the behavior of a process are introduced. Between-channel nonlinearity is associated with the nonlinear dependence of an output channel on other input - output pairings. Withinchannel nonlinearity is used to identify the nonlinear effects that result from the inherent nonlinearity of an individual output channel. A root-mean-squared measure of nonlinearity is introduced and is used to evaluate the significance of local nonlinear effects. Nonlinear interaction measures are derived that provide tools for assessing input - output pairings in a nonlinear process. This new approach extends the standard techniques and provides an estimate of the effect of nonlinearity on closed-loop interactions.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430912
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  • 4
    Electronic Resource
    Electronic Resource
    Determining porosity profiles during filtration and expression of sewage sludge by NMR imaging (1996)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 953-959 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The formation of a filter cake during mechanical dewatering (filtration and expression) of sludge is studied using one-dimensional nuclear magnetic resonance (NMR) imaging of porosity profiles. The experiments clearly showed the formation of a porosity gradient during filtration and the disappearing of this gradient during expression, forming a cake with a uniform porosity. This technique makes it possible to investigate the material behavior of the porous medium, which is needed before any model calculations can be performed. The results indicate that NMR imaging is useful in nondestructive monitoring of the filtration and expression process of sludge.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690420408
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  • 5
    Electronic Resource
    Electronic Resource
    Study of instabilities in film blowing (1996)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 1388-1396 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Bubble instabilities observed in film blowing using four different polyolefins are discussed: high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and polypropylene (PP). Special attention is given to the effect of the frost line height on the bubble stability, an effect mostly ignored in the literature. A video-camera system was used to record the bubble shape and oscillations. In general, three forms of instabilities and combinations were observed: (1) axisymmetric periodic variations in the bubble diameter; (2) helical motions of the bubble; and (3) variations in the position of the solidification line. The four resins show different stability behaviors. The LDPE has the most stable operating space and the PP is the most unstable one. No correlation was observed between bubble stability and oscillatory shear rheological properties of the resins. Instability is enhanced by increasing take-up ratio, increasing blow-up ratio, and decreasing frost line height. Furthermore, for the LDPE, some operating points were not attainable and multiple steady states were observed. Our results are in a poor agreement with the predictions Cain and Denn's 1988 analysis.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690420519
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  • 6
    Electronic Resource
    Electronic Resource
    Numerical and experimental study of a homogenizer impinging jet (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1100-1107 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: High-pressure homogenization is a key unit operation used to disrupt cells containing intracellular bioproducts. Modeling and optimization of this unit are restrained by a lack of information on the flow conditions within a homogenizer valve. A numerical investigation of the impinging radial jet within a homogenizer valve is presented. Results for a laminar and turbulent (k - ∊ turbulent model) jet are obtained using the PHOENICS finite-volume code. Experimental measurement of the stagnation region width and correlation of the cell disruption efficiency with jet stagnation pressure both indicate that the impinging jet in the homogenizer system examined is likely to be laminar under normal operating conditions. Correlation of disruption data with laminar stagnation pressure provides a better description of experimental variability than existing correlations using total pressure drop or the grouping 1/Y2h2.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430423
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  • 7
    Electronic Resource
    Electronic Resource
    Design analysis for refolding monomeric protein (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2123-2132 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Renaturation of protein expressed as inclusion bodies within Escherichia coli is a key step in many bioprocesses. Operating conditions for the refolding step dramatically affect the amount of protein product recoverd, and hence profoundly influence the process economics. The first systematic comparison of refolding conducted in batch, fed-batch and continuous stirred-tank reactors is provided. Refolding is modeled as kinetic competition between first-order refolding (equilibrium reaction) and irreversible aggregation (second-order). Simulations presented allow direct comparison between different flowsheets and refolding schemes using a dimensionless economic objective. As expected from examination of the reaction kinetics, batch operation is the most inefficient mode. For the base process considered, the overall cost of fed-batch and continuous refolding is virtually identical (less than half than of the batch process). Reactor selection and optimization of refolding using overall economics are demonstrated to be vitally important.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430819
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  • 8
    Electronic Resource
    Electronic Resource
    Temperature dependence of one-component permeation through a silicalite-1 membrane (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2203-2214 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The one-component steady-state permeation of gases through a silicalite-1 zeolite composite membrane as a function of the temperature is studied from 190 to 680 K for light hydrocarbons, noble gases, and some inorganic gases. In general, with increasing temperature the permeance shows a maximum followed by a minimum. For gases weakly adsorbed the permeance has only a minimum and for gases strongly adsorbed only a maximum is observed in the permeance. The permeance for various gases, for a feed pressure of 101 kPa, span four orders of magnitude. The lowest permeation is for i-butane at 300 K: a permeance of 0.07 × 10-8 mol. m-2.s-1.Pa-1. The highest value is observed for methane: a permeance of 70 × 10-8 mol. m-2.s-1.Pa-1 at about 240 K. A comparison between the isobars and the temperature dependence of the steady-state permeance, both at 101 kPa, shows that at the temperature where the amount adsorbed vanishes the permeance starts to increase. The temperature dependence of the steady-state fluxes through the silicalite-1 membrane can be described only if two diffusion mechanisms are taken into account. For high occupancies the mass transport can be described by equilibrium adsorption followed by surface diffusion and for low occupancies the mass transport can be described by activated gaseous diffusion. With increasing temperature the mass-transport mechanism shifts from the surface diffusion regime to the activated gaseous diffusion regime. With these two diffusivities modeling results agree well with experimental results for the one-component flux through the silicalite-1 zeolite membrane.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430907
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  • 9
    Electronic Resource
    Electronic Resource
    Simulation of diffusion in zeolitic structures (1995)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 2399-2414 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Using Maxwell-Stefan equations, experimental and computational results of binary diffusion in pore- and cage-type zeolitic structures are described. In the generalized Maxwell-Stefan (GMS) formulation, the Fick diffusivity is written as the product of two separate contributions, the GMS or corrected diffusivity and the thermodynamic factor. The concentration dependence of the GMS diffusivity for one- and two-component diffusion in zeolitic structures is investigated. From the Maxwell - Stefan equations, different models for the Fick diffusion coefficient matrix for the description of binary mass transport in molecular sieve materials are derived. Various models used predict binary diffusion in zeolitic structures. First, theoretical predictions of binary apparent diffusivities as a function of the occupancy are compared to results from Monte Carlo simulations. Second, theoretical results of binary uptake profiles are compared to experimental results for the system ethylbenzene/benzene/ZSM-5. For different zeolitic structures, that is, pore- and cage-type structures, results of the Monte Carlo simulations agree well with the theoretical predictions. In cage-type structures, the effect of counterexchange between sorbed molecules is demonstrated. Experimental results of transient uptake profiles of a mixture of benzene and ethylbenzene in ZSM-5 follow predictions of the theoretical single-file diffusion model.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690411107
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  • 10
    Electronic Resource
    Electronic Resource
    Heat and mass transfer along a wetted porous plate in an air stream (1996)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 1833-1843 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This experimental study examines 2-D effects on long plate drying due to heat and moisture transfer through boundary layers and porous medium interaction. Many innovative techniques are used to measure accurately boundary layers (velocity, temperature, moisture), the wall surface (infrared sensors for temperature and moisture), and the medium (water content). Gradual decrease in surface saturation measured for several kinds of materials shows that their behavior is more complex than described by the Suzuki-Maeda model, which does not predict the mass exchange sufficiently. Based on the analysis of the transfer between the surrounding air and the porous medium at the scale of the pore on a rough surface, a flow classification is defined and other characteristics are proposed. The drying rate depends on the mass-transfer coefficient, which varies along the plate with the air flow. The study of boundary layers gives the corresponding profiles with an acceptable accuracy. The laminar-to-turbulent transition increases mass-transfer rates resulting in two drying fronts. The diffusive model proposed here predicts a gradual change in the drying rate along the plate similar to the experimental one.
    Additional Material: 21 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690420705
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