ISSN:0001-1541    

DOI:10.1002/aic.690360102

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractA method to calculate the compression zone height in continuous thickeners is presented. With this method, it is necessary to know the variations of the pulp‐supernatant interface and the sediment height vs. time in a batch test. This method is discussed considering the following aspects: relationship between the settling rate of solids and their concentration in the settling zone; and the compression of solids due to the squeeze transmitted by the upper layers—unbuoyed weight of particles minus force of friction due to the Darcian flow. When the variation of the sediment height vs. time becomes linear, it is possible to calculate the maximum solids concentration which can be reached by sedimentation. The change of the solids matrix permeability and its influence on the method proposed are also analy

ISSN:0001-1541    

DOI:10.1002/aic.690360103

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractFlow‐induced crystallization experiments are made in a capillary apparatus modified with a downstream reservoir under pressure. Capillary length, diameter, and entrance angle are changed, as well as flow rate. The results show that the crystallization temperature is influenced both by the elongational flow at the capillary entrance and by the shear flow along the capillary. The independent effect of the pressure equals that obtained under static conditions. The effect of shear is correlated in terms of shearing wor

ISSN:0001-1541    

DOI:10.1002/aic.690360104

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractA biosensor electrode system with unique configuration and a thin layer of immobilized yeast cells, set on the surface of an amperometric oxygen membrane electrode, was developed for rapid screening of toxic chemicals in a variety of pollution and process control applications. Measurement is based on the instantaneous detection of changes in oxygen respiratory activity of biofilm of yeast cells upon exposure to toxic chemicals.The design of this electrode system, referred to as biofilm electrodes, was based on a mathematical model of oxygen transport in the biofilm and the electrochemical current response. The biofilm, which consists of three sublayers—boundary layer, filter pad, and yeast cell layer—was modeled as a one composite diffusion layer, or three separate layers in series. While the three layer model is more theoretically complete, the one layer model was more reliable and simpler to

ISSN:0001-1541    

DOI:10.1002/aic.690360105

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractA kinetic model is developed for the drying of solids in fluidized beds, assuming a falling rate period following a constant rate period. Experimental data obtained using batch and continuous single and spiral fluidized beds are satisfactorily matched with the assumed drying kinetics and the residence time distribution of solids appropriate for the type of dryer.

ISSN:0001-1541    

DOI:10.1002/aic.690360106

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractA new dynamic model has been developed for heterogeneous azeotropic distillation columns, which is capable of automatically detecting and accounting for multiple liquid phases on trays at each instant of time. Extensive dynamic simulations have been carried out for the heterogeneous distillation of ethanol, water and benzene. Our results are in general agreement with prior work, which shows that this class of separations can be expected to exhibit multiple steady states, complex dynamic behavior, and parametric sensitivity. One of the most unexpected results was that these systems exhibit parametric sensitivity with respect to small changes in column pressure. For systems vented to the atmosphere, small increases in the barometric pressure lead to loss of interface in the decanter over a 24‐hour period. If small pressure variations of this sort are left uncontrolled long enough, the entire separation will fail. Small decreases in the barometric pressure do not have such a disastrous effec

ISSN:0001-1541    

DOI:10.1002/aic.690360107

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractThe backfill cycle in the pressure swing adsorption (PSA) separation of air to produce an enriched oxygen product using a zeolite 5A molecular sieve was studied theoretically and experimentally. The effects of the backfill cycle, cycle configuration, backfill rate, pressurisation rate, and product rate were studied. The theory agreed well with the experimental results in predicting the product oxygen concentration over a wide range of backfill pressures, thus giving a basic understanding of the bed dynamics of the backfill cycle. The theory showed that the backfill rate and adsorption capacity of the adsorbent were the most important parameters governing the efficiency of the PSA process. We showed that, given an adequate backfill pressure, a separate pressurization step could be omitted by incorporating it with the product release step with no detrimental effect on the product oxygen concentrations while increasing adsorbent productivity.

ISSN:0001-1541    

DOI:10.1002/aic.690360108

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractA stability condition is developed for multivariable, nonlinear feedback systems. The method is based on a modified sector condition and is combined with a polynomial expansion of the nonlinear system to create viable approximations that can be exploited within the sector bound setting. An example demonstrates the utility of the method in defining stable operating regimes for chemical processes.

ISSN:0001-1541    

DOI:10.1002/aic.690360109

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractA volatiles release model has been developed to predict the location and quantity of coal volatiles that are released into a bubbling fluidized‐bed combustor, using overbed, in‐bed or underbed feed systems. This model not only considers time resolution of the simultaneous processes of coal devolatilization and coal particle movement after injection, but also takes account of the stochastic nature of this particle movement. Volatiles release is nonuniform, occurring throughout an industrial‐scale bed, but only in restricted parts of a laboratory‐scale bed. For the industrial‐scale bed, 32% of volatiles are released directly into the freeboard while the particle is devolatilizing at the surface, whereas 24% are released there for the laboratory scale bed. The model predicts the formation of numerous discrete volatiles regions within the bed, in agreement with a new interpretation of experimental measurements from an in‐bed oxygen probe. The model is shown to be consistent with other experimental in‐bed measurements obtained during combustion of “simul

ISSN:0001-1541    

DOI:10.1002/aic.690360110

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractMeasurements of effective diffusivity by the chromatographic method are shown to be biased by nonuniformity of the external porosity in a cross‐section of the column. A very simple model is proposed to interpret experimental results. A modified Van Deemter method is given to extract the axial dispersion and effective diffusion coefficients from chromatographic peaks. This method allows one to ignore the external porosity distribution. Experiments show that even though axial dispersion obeys classical correlations, the internal mass transfer parameters may be strongly affected by the external porosity distributio

ISSN:0001-1541    

DOI:10.1002/aic.690360111

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY