摘要:

AbstractResults of a computer study are reported applying data reconciliation and interpretation techniques to a single‐stage flash operation. Measured errors in the process variables are significantly reduced. The techniques are successfully extended to estimate flash efficiency. The flash efficiency is estimated using two methods: (1) a statistically rigorous simultaneous data reconciliation and efficiency estimation procedure, and (2), a faster, nonrigorous sequential procedure. It is found that the simultaneous procedure provides better measured variable and flash efficiency estimate

ISSN:0001-1541    

DOI:10.1002/aic.690340102

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe effect of supercritical ethane on the high‐pressure phase behavior of the polystyrene‐toluene system is experimentally investigated. Adding 17.8 wt. % ethane to the polystyrene‐toluene solution lowers the temperature of the lower critical solution temperature (LCST) curve by 162°C, 22.5 wt. % lowers the temperature of the curve by 231°C, and with 24.9 wt. % the curve is shifted to such low temperatures that it merges with the upper critical solution temperature curve. In practice this means that polymer solutions can be separated at lower temperatures where thermal degradation of the polymer is less. Also, more than 99 wt. % of the polystyrene is recovered in the polymer‐rich phase after the solution phase splits. Patterson's corresponding states treatment is used to model the

ISSN:0001-1541    

DOI:10.1002/aic.690340103

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractReaction schemes for the thermal cracking of paraffins, naphthenes, olefins, and aromatics, and the associated rate equations, are generated by an algorithm based upon Boolean relation matrices. In order to reduce calculation times for the heavier components, a self‐learning system is introduced. This self‐learning system avoids repetition of identical calculations by recognizing intermediate species, for which the reaction schemes have already been generated. The software includes routines for standardizing the representation of the species, an information retrieval system, and libraries containing the necessary information for recognition of the species and the reaction schemes for these spec

ISSN:0001-1541    

DOI:10.1002/aic.690340104

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe problem of diagnosing faults in chemical plants can be efficiently addressed by a hierarchical procedure involving successive narrowing of the space in which the fault search is conducted. A technique is presented for narrowing diagnostic focus useful in the first stages of a diagnostic search. Based on a decomposition of the process according to function, the technique assesses the functionality of process systems based on measurements of controlled and manipulated variables. A procedure for identification of possibly faulty systems and units from the system states is outlined. Detailed diagnosis, not treated in this paper, would be applied after candidate systems or units are located. An example is presented using a hypothetical chemical reaction process.

ISSN:0001-1541    

DOI:10.1002/aic.690340105

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractSteady states with different flow rates and temperature profiles may exist in a monolith or multitube packed‐bed reactor operating under a prescribed pressure drop, due to the coupling among the species, energy, and momentum balances, and the change of physical properties with temperature and pressure. Criteria are derived predicting the conditions under which thermoflow multiplicity can occur for a gaseous reaction involving a change in the number of moles. In general, a reaction‐induced volume increase enables thermoflow multiplicity to occur for reactions with a lower adiabatic temperature rise. A surprising finding is that thermoflow multiplicity may be found for an isothermal reaction involving a volume decrease. This point emphasizes the difference in the feedback mechanism leading to thermoflow and thermokinetic multiplic

ISSN:0001-1541    

DOI:10.1002/aic.690340106

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractA theoretical and experimental study on the dissolution of porous media by flowing acid has been carried out. Dissolution of the media results in an evolution of the pore geometry and the formation of random flow channels. The goal is to predict the range of conditions under which channels will form, and the effects of various parameters on the structure of the channels and on their rate of propagation through the media. A random network model is used to describe the behavior of the stochastic, rootlike channels that form during flow and dissolution in carbonate rock and in other systems. The structure of the flow channels that form as a result of acid attack are characterized and studied using a Wood's metal casting technique. A comparison of model results shows that the rates of channel formation and growth are intimately related to the developing structure of the channels (size of branches and degree of branching), which in turn is controlled by factors such as the fluid velocity and the rate of reaction. Depending on the experimental conditions, the channels range from a single conduit with a minimum of branching to a highly branched, spongy network of channels. The dependence of permeability increase and channel branchedness on injection rates and acid diffusion rates is described by the Damkohler number for flow and reaction.

ISSN:0001-1541    

DOI:10.1002/aic.690340107

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractMass transfer coefficients for the solution, without reaction, of oxygen in cyclohexane over a wide range of temperature and pressure have been measured in a flat interface reactor (FIR) and a gas sparged stirred‐tank reactor (STR). Solubilities have also been measured and it is suggested that a modified Henry's law coefficient of 1.09 × 10−2kmol/m3· bar can be regarded as constant over the temperature range 293–435 K. The physical mass transfer coefficient in the STR shows very little variation over this temperature range and a value of 3.5 × 10−4m/s can be assumed for 423–435 K. However, coefficients in the FIR increase with agitation rate as expected. The difference is ascribed to interference by neighboring bubbles in the transfer process, when diffusivities are high, and also to the lowering of surface tension at high temperatures. A model proposed by Gal‐Or and Resnick is reviewed in its application to the

ISSN:0001-1541    

DOI:10.1002/aic.690340108

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractLiquid phase oxidation of hydrocarbons is a major source of organic chemicals. This paper concerns itself with the oxidation of cyclohexane. The process is one in which gas absorption is accompanied by chemical reaction, but little information has been reported. A major factor has been safety considerations, the Flixborough explosion being a constant reminder. In this paper attention is given to the kinetics and to the interaction of kinetics and mass transfer, showing that in this autocatalytic system the dissolved oxygen level rises to saturation and falls as the rate of reaction increases. Initially zero order in oxygen, the reaction becomes first order at low oxygen levels. Oscillations and enhancement due to reaction within the boundary layer are noted. A kinetic model is developed based on simplification of the accepted free radical scheme and it is reasonably successful in accounting for the results reported. Experiments at temperatures up to 170°C and 70 bar using uncatalyzed reaction are reported from three different reactors: a homogenous batch reactor, a flat interface reactor, and a sparged agitated bubbling reactor

ISSN:0001-1541    

DOI:10.1002/aic.690340109

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractIn an industrial gas‐liquid reactor both mass transfer and kinetics have, in principle, a role to play. This paper describes studies on the oxidation of cyclohexane in two‐phase, gas‐liquid reactors. Regimes of absorption have been clarified by measurements of dissolved oxygen concentrations. The behavior is found to be complex, arising from the fact that the reaction is autocatalytic, and zero order in oxygen over almost the entire absorption range. As reaction velocity increases, due to the autocatalytic kinetics, enhanced physical mass transfer rates arise. Bubble swarms have properties that prevent the simple application of mass transfer and enhancement from flat‐surface systems. A theory is developed here that accounts qualitatively for the enhancement found in bubble swarms in the present case. The theory is also shown to predict quantitatively the appropriate physical mass transfer coeff

ISSN:0001-1541    

DOI:10.1002/aic.690340110

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractViscoelasticity, nonisothermality, and fountain flow influence the microstructure development during injection mold filling of polymer melts and, therefore, the ultimate properties of a molded article. A comprehensive two‐dimensional mathematical model is developed to evaluate the effects of these factors on the structure of the flow field. Special consideration is given to the shape of the flow front, which is crucial in determining the structure of flow in the fountain region. The effects of slip and crystallization are also considered and their influence on model predictions are analyzed. Simulations using the no‐slip and slip boundary conditions show that a slip boundary condition is necessary to alleviate the singularities in the flow structure. The results also indicate that the predicted stress profiles are significantly influenced by the viscoelasticity of the polymer melt. Furthermore, the nonisothermality and subsequent deposition of a solid layer next to the mold walls considerably alter the moldability parameters and the flow fi

ISSN:0001-1541    

DOI:10.1002/aic.690340111

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY