摘要:

AbstractEarlier work of Sinclair and Jackson on the flow of gas‐particle suspensions in vertical pipes is extended to the case of ducts of arbitrary inclination. As a result of the compaction due to gravity, it is necessary to take into account forces transmitted between particles at points of sustained, rolling and sliding contact, and a simple frictional model of this contribution to the stress is introduced. The resulting theory is shown to predict fully developed flows with the qualitative features to be expected, even in horizontal ducts. The effects of flow rates, duct inclination, and duct width on the solution are explore

ISSN:0001-1541    

DOI:10.1002/aic.690390802

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractAn instability analysis has been carried out to elucidate the unsteady flow conditions encountered in the typical circulating fluidized bed units in light of the conveyor‐solids feeder interaction. The results successfully predict the critical velocity and the maximum solids circulation rates reported in the literature and explain the origin of such unstable conditions. Furthermore, the simulation, for the first time, reveals the importance of unit structure in improving the performance of circulating fluidized bed systems. Finally, the concept of a high‐density circulating fluidized bed is propo

ISSN:0001-1541    

DOI:10.1002/aic.690390803

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractA mechanistic model of slug flow based on a set of mass and momentum conservation equations and a number of empirical closure relations is presented. It is then shown that a simplified version of the model, which physically corresponds to the flow of long liquid slugs(long slug model, LSM), can be immediately derived from the general model. The LSM is much simpler than the general model; at the same time, the predictions obtained in the two cases are very similar, when the comparison is limited to the computation of the pressure gradient and the mean liquid holdup. The LSM successfully correlates a large set of experimental measurements relative to three pipe diameters(18, 50 and 90 mm), four inclinations (0°, ±3°, 0.3°), and two pipe lengths(17 and 34

ISSN:0001-1541    

DOI:10.1002/aic.690390804

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractA simple model presented for cross‐flow filtration of liquid suspensions was formulated on the premise that among the particles convected to the filter medium surface in cross‐flow filtration, only a fraction of them become deposited. A criterion based on the interplay of the geometry of the cake‐suspension interface and various forces acting on a particle as it moves toward the interface was established and an expression of the adhesion probability of impacting particles developed. The model was then formulated by incorporating the adhesion probability information together with conventional cake filtration theories. Through sample calculations, the model was found to display behavior consistent with the observed phenomena of cross‐flow filtration and capable of representing experimental

ISSN:0001-1541    

DOI:10.1002/aic.690390805

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe product compositions in single‐feed distillation columns can be specified only in certain regions of the composition space, which depend only on the pressure, feed, and vapor‐liquid equilibrium for the mixture. In nonideal mixtures, even without azeotropes, the regions may allow unusual product distributions. For example, the distillate in a “direct split” is composed primarily of the lightest component. Intuition and experience with relatively ideal mixtures suggest that the next most plentiful component is the intermediate boiler. In nonideal mixtures, however, with or without azeotropes, the next most plentiful component may be the highestboiling species with only trace amounts of the intermediate boiler. For azeotropic mixtures, distillation boundaries may give rise to additional restrictions on the product compositions. We describe how simple distillation boundaries deform into continuous distillation boundaries and, in a limited number of cases, how the simple distillation boundaries can be crossed in continuous columns for certain ranges of the design variables. Unfortunately, such designs may be quite sensitive to model uncertainties or to disturbances in the par

ISSN:0001-1541    

DOI:10.1002/aic.690390806

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractWe present a theoretical study of the adsorption kinetics of particles with a continuous distribution of sizes. If the particles interact with short‐ranged forces, the diminishing rate of adsorption with increasing surface coverage can be attributed to a geometrical blocking effect of the preadsorbed particles. We exploit the fact that at low coverages the blocking effects result from isolated adsorbed particles to develop an analytic description of the adsorption kinetics using a moment expansion approach. We evaluate the time‐dependent surface coverage, density and the average size of the adsorbed particles and compare these quantities with those of the bulk phase. The effect of desorption is studied by introducing a size‐independent desorption constant, and the corresponding adsorption equilibria properties, which are valid at low coverages, are derived. Simulation results for irreversible adsorption are obtained and compared with the theoretical predic

ISSN:0001-1541    

DOI:10.1002/aic.690390807

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

ISSN:0001-1541    

DOI:10.1002/aic.690390808

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractA computationally fast technique accurately estimates process variables when conditions are dynamic due to changes in steady states. The process variable estimators are unbiased and have known distributions. Thus, confidence intervals for true values of process variables are provided. The formulation of this technique was motivated by a recursive, dynamic data reconciliation technique that obtains very accurate estimators. These two techniques are compared in terms of computational speed and accuracy of estimators. The proposed technique is computationally faster, but not as accurate when variances of process measurements are large. However, the accuracy of the proposed estimators is shown to approach that of the recursive technique by iteratively recalculating estimates and when measurement variances decrease.

ISSN:0001-1541    

DOI:10.1002/aic.690390809

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractEquations introduced here identify measurement biases and process leaks, when gross errors exist in measured process variables and the variance‐covariance matrix of the measurements, Σ, is unknown. Σ is estimated by the sample variance, S, using process data.For an unknown Σ, the global test statistic is the well‐known Hotelling T2statistic. Its power function has a noncentral F‐distribution. For component tests used for specific identification of measurement biases and nodal leaks, two tests are presented with Σ unknown. The first test is independent of the number of component tests, k, and is given by a statistic with an F‐distribution. The second test depends on k and has a student t‐distribution. The power functions for both component tests are provided. Process examples and a Monte Carlo simulation study presented demonstrate the use and performance of these statistical equations in identifying biases and

ISSN:0001-1541    

DOI:10.1002/aic.690390810

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractN2O decomposition and formation during the oxidation of NH3and HCN were studied in a quartz flow reactor in the presence of CO, NO and other gases. The emphasis is on the influence of CO and NO. In addition, the homogeneous nitrogen chemistry of fluidized bed combustion and the selective noncatalytic reduction of NO (SNR) are discussed. The rate of N2O decomposition in N2agrees with a first‐order rate expression. The presence of CO or H2increases the decomposition rate regardless of the additional presence of O2For the formation of N2O, HCN oxidation is more efficient than NH3oxidation. The presence of NO increases the amount of N2O formed during the oxidation of HCN or NH3.CO moves the N2O formation toward lower temperatures. H2O increases the reaction rate where few components are present, whereas H2O has little influence in the presence of large amounts of a combustible component such as CO. There are indications that NO is a necessary intermediate for any significant formation of N2O during the oxidation of NH3and HCN. NO reduction is obtained when NO is initially present during oxidation of both NH3and HCN. These results are comparable to the respective SNR results with reductant ammonia and ure

ISSN:0001-1541    

DOI:10.1002/aic.690390811

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY