摘要:

AbstractExperimental measurements have been conducted of Knudsen diffusion through a model porous medium fabricated by the pelleting of monodisperse silica spheres. Tortuosity factors for this random‐assemblage‐of‐spheres porous solid are calculated and compared with values obtained from both theory and measurements made in the bulk diffusion regime. Evidence is presented to support the use of a mean pore radius calculated as twice the ratio of pore volume to surface area, as opposed to values obtained from mercury porosimetry or sorption isotherm ana

ISSN:0001-1541    

DOI:10.1002/aic.690320102

出版商:American Institute of Chemical Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractA comparison was made of the equilibrium mixing/segregation behavior of binary mixtures of different‐sized, equal‐density glass beads in two‐ and three‐dimensional fluidized beds. Several empirical equations for mixing index were examined, all involving a dimensionless function of excess gas velocity. This function, which appeared to largely account for the effect of aspect ratio, was found to optimally correlate the data for both types of beds. However, a much better fit was obtained for the threedimensional bed data, most probably because wall effects significantly retarded mixing in the two‐dimens

ISSN:0001-1541    

DOI:10.1002/aic.690320103

出版商:American Institute of Chemical Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThermal gasification has been proposed as one technical option for the conversion of coal to gaseous fuels and/or chemicals to supplement supplies presently derived from petroleum and natural gas. In the present study, a bench‐scale fluidized bed reactor was used for the gasification of coal with steam as the fluidizing medium. A mixture of sand and limestone used as the bed material made it possible to gasify a caking coal without the problem of agglomeration. The gas composition and yield of the hydrogen‐rich product gas were studied as a function of temperature.To study the heterogeneous reactions taking place in the reactor and also the transient behavior of the system, a mathematical model was developed. The model assumed a reaction mechanism that accounted for the devolatilization of coal, cracking of volatiles, char gasification, and the water‐gas shift reaction. Both the dynamic behavior and steady state performance of the gasifier were simulated based on the model. The steady state results of the simulation were compared with the experimental data. This comparison enabled us to ascertain that the proposed reaction mechanism and dynamic model predicted the correct t

ISSN:0001-1541    

DOI:10.1002/aic.690320104

出版商:American Institute of Chemical Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThe literature abounds with the application of optimization methods for estimating model parameters in equation systems. The utility of these methods is frequently demonstrated on pathological examples using simulated data generated from a known model with a random error component and a known statistical distribution. Unfortunately, parameter estimation problems encountered in practice do not have this advantage. The true model is frequently not known. In fact, one is faced with choosing among various candidate models, all of which may be wrong. Moreover, the error structure is generally unknown and must be estimated from the data. Finally, a great deal of mathematical expertise is required to transform the model and select meaningful starting guesses before parameter estimation can be successful.In order to demonstrate the difficulties of parameter estimation in the industrial environment and the limitations of existing methods, a parameter estimation problem formulated by the Dow Chemical Company is presented and solved. This test problem consists of a stiff differential/algebraic (DAE) model that describes complex kinetics and requires the estimation of nine parameters from batch reactor data. Here the model was inadequate to describe the data, the error structure was not specified and the starting guesses led to a nontrivial optimization problem.The Dow parameter estimation problem was distributed in 1981 to 165 researchers as a followup to the 1980 FOCAPD conference. Of those researchers, eleven agreed to apply their methodologies and expertise to this problem. However, only five acceptable solutions were finally submitted. Here we present and compare these results. Each solution was obtained using different strategies. In most cases the form of the model was also changed to accommodate the algorithms used and to ease the solution procedure. Therefore, while this case study does not present a direct numerical comparison of algorithms, it does offer guidelines and insight towards the solution of difficult parameter estimation problems.

ISSN:0001-1541    

DOI:10.1002/aic.690320105

出版商:American Institute of Chemical Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractPrevious models of noncatalytic gas‐solid reactions are based primarily on parallelpore representations, thus excluding important topological effects of the porous medium. This paper utilizes network representations and percolation theory to develop expressions for pore closure time and the evolution of accessible volume, effective diffusivity, and conversion rate

ISSN:0001-1541    

DOI:10.1002/aic.690320106

出版商:American Institute of Chemical Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractAir lift pumps are finding increasing use where pump reliability and low maintenance are required, and where corrosive, abrasive, or radioactive fluids must be handled. Although air lifts are used in nuclear fuel reprocessing plants, no general, theoretically sound equation has been proposed in the literature for tall air lift design. Such an equation is developed from two‐phase flow theory to predict the height to which an air lift pump operating in the slug flow regime can lift a given volumetric flow rate of liquid, given the air flow rate and pressure at the point of gas introduction. The widely used drift‐flux model for the prediction of holdup is combined with an approximate relationship to predict pressure loss, and is substituted into the total pressure differential. Integration of the resulting equation provides an explicit formula for the calculation of lift. Experimental work using a variety of liquids in a 38 mm dia. air lift test installation supports the new design equation and demonstrates its flexibil

ISSN:0001-1541    

DOI:10.1002/aic.690320107

出版商:American Institute of Chemical Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractA study is presented of the application of a self‐tuning regulator to the control of the level of wood chips in a Kamyr digester, used in the production of wood pulp. Following an initial phase of experiments and model structure selection, two control schemes were studied, using respectively the blow flow and the outlet device speed as manipulated variables. The approach finally adopted uses the outlet device as the primary control. The control has been in operation for several months and has provided significantly improved control and a high degree of operator acceptanc

ISSN:0001-1541    

DOI:10.1002/aic.690320108

出版商:American Institute of Chemical Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractAn optimal averaging level control problem is defined and solved for a surge tank system. Two averaging level controllers, the ramp controller and the optimal predictive controller are developed utilizing the optimal control policy. These controllers are compared with previously reported averaging level controllers for step and sinusoidal disturbances in inlet flow rate. The OPC results in improved disturbance filtering characteristics for most of the disturbances considered and is very simple to implement.

ISSN:0001-1541    

DOI:10.1002/aic.690320109

出版商:American Institute of Chemical Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractTemperature programmed desorption (TPD) of methanol and ethanol from fresh and Na‐poisoned γ–Al2O3has been employed to investigate experimentally the separability of reaction‐deactivation kinetics. The analysis of the TPD spectra has provided both an energetic characterization of the nonhomogeneous catalytic surface and the kinetic parameters of the desorption reaction, and has allowed quantitative discussion of the separability of the expression for the rate of desorption. The results obtained have been related to the chemical causes of nonseparability of reaction‐deactivation kinetics; they also demonstrate the influence of catalyst decay on selectivity. For the systems considered, it appears that the assumption of separable deactivation kinetics is generally not a satisfactory appro

ISSN:0001-1541    

DOI:10.1002/aic.690320110

出版商:American Institute of Chemical Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractA unified statistical mechanical treatment is developed for adsorption and surface diffusion on homogeneous surfaces. Using molecular parameters, the model accounts for all physical effects of adsorbent‐adsorbate, adsorbate‐adsorbate, and adsorbate‐gas interactions at submonolayer cove

ISSN:0001-1541    

DOI:10.1002/aic.690320111

出版商:American Institute of Chemical Engineers    

年代:1986

数据来源: WILEY