摘要:

Pentane and hexane hydroisomerization were studied in detail in a microreactor system. This information was very useful for scale-up of catalyst production capaity arid isomerization reactors. In our work, properties of catalysts produced in different amounts were reproduceable and hydroisomerization results in the microrector, lab scale reactor and pilot plant were compatible. It was shown a easy way has been paved to develope a new alkane isomerization catalyst.

ISSN:0098-6445    

DOI:10.1080/00986449308936134

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Visibility in Grand Canyon National Park has shown degradation during the last decade. The Penn State University/National Center for Atmospheric Research (PSU/NCAR) regional atmospheric model is applied to the diagnosis of atmospheric transport in the region in order to better understand how air-pollution transport, and thus visibility, may be influenced by the complex terrain. Both idealized and real-data model simulations are used to examine the local topographic forcing. Significant transport of air pollutants is produced by the differenlial thermal forcing and channeling associated with the orography. It is also demonstrated that the combination of a meteorological model and observations via four-dimensional data assimilation provides the most accurate and complete wind-field information for air-quality applications in regions of complex terrain.

ISSN:0098-6445    

DOI:10.1080/00986449308936135

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The steady state and dynamic behaviour of an adiabatic packed bed reactor for the selective hydrogenation of ethyne and ethene mixtures was studied experimentally. Different methods to achieve adiabatic conditions on a laboratory scale were tested. Temperature profiles of both the gas and solid phase as well as local temperature differences between the two phases were measured. For hydrogenation in the absence of carbon monoxide the selectivity was always poor. Also, in that case, the temperature in the reaction zone exhibited oscillatory behaviour. On addition of CO, the oscillations disappeared and the selectivity improved. For a given set of operating conditions there existed a relatively small range of CO contents with good selectivity and satisfactory conversion. This range depends strongly on the inlet temperature. The dynamic response of the reactor to changes in the CO content showed a considerable wrong-way behaviour. This high sensitivity to fluctuations in the CO content, found for our experimental reactor, indicates a probable cause for a thermal runaway in industrial practice.

ISSN:0098-6445    

DOI:10.1080/00986449308936136

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The steady state and dynamic behaviour of an adiabatic packed bed reactor for the selective hydrogenation of mixtures of ethyne and ethene is studied. A heterogeneous model with axial dispersion of heat is solved numerically by means of a fully implicit discretisation scheme. From an analysis of the inlet and outlet boundary conditions, it follows that in order to avoid an influence of the type of boundary condition on the reactor behaviour, sufficiently long inert zones before and after the active bed should be present. Using preliminary kinetic expressions adapted from Mcn'shchikov ct al. (1975), the model calculations show a reasonable agreement with the experiments performed in a laboratory scale reactor and demonstrate the importance influence of small amounts of carbon monoxide both on the steady state as well as on the transient behaviour of the reactor. However, using the rate expressions derived from our own kinetic experiments in a Berty reactor, the behaviour under runaway conditions and the transition from non-runaway to runaway conditions can not be described well. Several factors that contribute to this discrepancy are discussed. This work shows that, in particular for a complex reaction system such as the selective hydrogenation of ethyne in ethene, the limited accuracy of the kinetic model and kinetic parameters dominates the precision attainable with packed bed reactor models.

ISSN:0098-6445    

DOI:10.1080/00986449308936137

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The viscous flow behaviour of four sets of suspoemulsions (mixtures of suspensions and emulsions) is investigated. Three sets were aqueous systems and one set was a non-aqueous system. In any given set the starting components, i.e. the pure suspension and the pure emulsion, had the same dispersed-phase concentration (volume fraction) and the same continuous-phase, and they were mixed in various proportions to obtain the suspoemulsions. The rheological behaviour of the pure emulsions, in all four sets, was nearly Newtonian. The pure suspensions were Newtonian, yield-pseudoplastic, yield-pseudoplastic, and shear-thickening, respectively. The suspoemulsions are found to exhibit non-ideal behaviour i.e.. the viscosity of the suspoemulsions does not vary linearly with the volume percentage of emulsion droplets in the mixed dispersed-phase. Both positive and negative deviations from ideal behaviour are observed. The reasons for the observed non-ideal behaviour are discussed in terms of heteroflocculation (flocculalion between emulsion droplets and solid particles), dilution, and screening effects.

ISSN:0098-6445    

DOI:10.1080/00986449308936138

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A new model is presented to describe the heat transfer process occurring in fluidized beds under the limiting condition of very short contact times between the heat transfer surface and the emulsion phase. Unlike other work in this area the proposed model assumes that the particles are in constant motion close to the surface throughout the heat transfer process. The effect of the non-continuum gas film assumption (the Smoluchowski effect) when particles are very close to the surface is found to be of secondary importance when compared with the movement of particles close to the surface. Expressions for both the instantaneous and time averaged heat transfer coefficients for individual and a spatial distribution of parlicles are presented.

ISSN:0098-6445    

DOI:10.1080/00986449308936139

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Thermal detoxification of conlaminated soils requires heating the soil to the destruction temperature for an adequate period of time. The process is expensive, partially due to the heat wasted by expelling high temperature effluent streams from the process. The staged fluidized bed contactor (SFBC) is an energy efficient cascaded system that is intended to recover energy from both the spent soil and hot gases leaving the combustion zone of SFBC. Models of the SFBC were developed to assess the impact of incineration stage flow regime, and to show the adequacy of the shallow SFBC as a cost-effective thermal decontaminator.

ISSN:0098-6445    

DOI:10.1080/00986449308936140

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The heat transport in a wall-cooled packed tube in which a hot gas is cooled down is often described with a pseudo-homogeneous one-dimensional or two-dimensional model. Assuming a radially flat inlet temperature profile at the bed entrance can lead to erroneous results, if the actual profile at the entrance is curved. It can cause an apparent length dependence of the effective heat transport coefficients, the so called “length effect”. The reason being that the amount of heat entering the packed bed is overestimated, which is compensated for by higher values for the heat transport coefficients. Using a parabolic inlet temperature profile, as measured in the packed bed at a certain minimal bed length, eliminates the length dependence of the heat transport coefficients. An experimental investigation showed that for the gas flow rates applied. Peps= 52 to 785, a wall heat transfer coefficient αwhas to be used for modelling the heat transport with a two-dimensional model. Confidence intervals are given for the effective radial heat conductivity λe,rthe wall heat transfer coefficient αwand the overall heat transfer coefficient Uu,v. It is shown that λe,rand αware strongly cross-correlated and have large confidence intervals. Especially at low gas flow rates αwis difficult to determine accurately. The confidence intervals for Uu,vare much smaller. It is shown that although values for λe,rand αwcan scatter much for different measurements due to the cross-correlation of these coefficients, the scatter in Uu,vis reduced significantly if this coefficient is calculated with the so called “lump equation”

ISSN:0098-6445    

DOI:10.1080/00986449308936141

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Experiments were carried out to determine the gas-solid mass transfer coefficient for the air-naphthalene system under fast-fluidized conditions. The data were obtained under conditions of high voidage (as high as 98%) and high gas velocities (0·5 m/s-2·2 m/s). The results indicate that the correlation for the mass-transfer coefficient in a gas-solid fluidized bed under low voidage conditions established by previous investigators can be extended to the fast fluidization regime. Significantly lower mass transfer coefficients were, however, obtained under high voidage compared to low voidage conditions.

ISSN:0098-6445    

DOI:10.1080/00986449308936142

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

This paper extends and broadens our present knowledge concerning hydro-dyanmics and heat transfer during boiling of liquids in a thin-layer evaporator equipped with a spiral element. The application of the spiral element in the thin-layer evaporator of static type (STLE) radically changes the hydrodynamics and consequently the rate of heat transfer. Measurements were carried out on distilled water and ethylene glycol. 416 measurements of individual heat transfer coefficients (IHTC) were performed which included 86 measurements in the STLE, 77 measurements in the thin-layer evaporator equipped with immovable spiral element (TLE) with (ISE), and 253 measurements in the thin-layer evaporator with movable spiral element (TLE) with (MSE). Experimental data were correlated using similarity theory and dimensional analysis. The experimental results obtained in the TLE with MSE were compared with adequate data obtained in the TLE with ISE. In the investigated range of frequency and amplitude the increase of IHTC amounted to 10·1% for distilled water and for ethylene glycol 30·7%.

ISSN:0098-6445    

DOI:10.1080/00986449308936143

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor