摘要:

AbstractThe mean crystal size of coarse crystalline products is determined by secondary nucleation and crystal growth. Secondary unclei are mainly produced by contacts of crystals with parts of the crystallizer or with other crystals. As a consequence, attrition effects are very important. In this paper, a model is proposed in order to calculate the attrition rate of crystals, depending on the physical properties of the crystalline product, the geometry of the crystallizer and on the operating conditions such as the stirrer speed or the suspension density. The effective rate of secondary nucleation can be expressed in terms of the attrition rate by introducing effective values for number and size of attrition particles. Finally, a scale‐up criterion based on this model is derived. This criterion allows to predict effective rates of secondary nucleation and mean crystal sizes if data obtained in a laboratory crystallizer are availabl

ISSN:0930-7516    

DOI:10.1002/ceat.270110112

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractA number of topped crude oil residues were subjected to mild thermal cracking in the temperature range between 613 and 673K at N2pressure of one atmosphere. It was found that the thermal stability of the six topped crude oils decreased in the order Brent

ISSN:0930-7516    

DOI:10.1002/ceat.270110113

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractSettling characteristics of four different suspensions were measured by batch settling tests (glass spheres in glycerol‐water mixtures and CaCO3) and by continuous settling test in a bench‐scale vertical flow tank (activated sludge and kaolin in water), including the measurement of solids concentrations inside the tank. The characteristics could be described by different correlation functions which now include all the information about the settling behaviour of ideal suspensions. Continuous settling experiments in a bench‐scale vertical flow tank were carried out with the same four material systems. These results correspond with sufficient accuracy to those from the theory of limiting flux if the settling characteristics determined earlier are consi

ISSN:0930-7516    

DOI:10.1002/ceat.270110114

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractNOxemissions from different commercial gas burners for metal heat treatment applications were measured for a research project of the Gaswärme‐Institut. The burners, rated at up to 50 kW, were installed for the tests in a laboratory combustion chamber operated at temperatures of up to 1400°C. The air for combustion was preheated to maximum temperature of 600°C. Following the tests, the potentials of different NOxcontrol techniques were investigated. Methods explored included staged combustion air injection, staged fuel injection and fuel gas injection into the flue for NOxreduction. The results showed that it is feasible to reduce the NOxcontent of flue gases by as much as

ISSN:0930-7516    

DOI:10.1002/ceat.270110115

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThermal deactivation can be described either by deactivation kinetics or by the isokinetic effect. The latter expression is used synonymously with the “compensation effect” and the “Theta‐Rule”. An examination of the original literature shows that only the compensation effect is applicable to thermal deactivation but not the Theta‐Rule. The introduction of the preparation temperature as a parameter of the compensation effect results in a “modified Theta‐Rule”, which describes the experimental data and is proposed for the non‐separable kinetics. The consequence of the observed deviations from the validity range of the Theta‐Rule is that the activation energy cannot be used as a univers

ISSN:0930-7516    

DOI:10.1002/ceat.270110116

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe kinetics of non‐catalytic as well as catalytic oxidation of Isobutyraldehyde has been investigated. Reaction rate equations for the formation of the main product isobutyric acid and of the side products acetone, CO and CO2were derived. Kinetic parameters, namely the order of reaction, preexponential factor and activation energy were estimated by non‐linear regression. The influence of selectivity and activity of the different type of catalysts employed was investigated quantitativ

ISSN:0930-7516    

DOI:10.1002/ceat.270110117

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractTheoretical modelling of heat transfer to particle beds comprises two sequential steps: transfer from the heating surface to contacting particles followed by transfer to the interior of the bed. Two different limiting case can be formulated for the second step: unmixed and homogeneously mixed bed. In the case, heat is transferred gradually via a repeated sequence of heat transfer in the gap between adjacent particles and conduction in the particulate material. In the second case, heat is transferred to the interior of the bed by mixing of particles which have previously attained the temperature of the heating surface. On the other hand, the mixing motion maintains a homogeneous lower temperature throughout the bed. Theory predicts a significant and easily measurable difference in the behaviour of heat transfer coefficients for the two regimes at long contact timest: unmixed beds ∝\documentclass{article}\pagestyle{empty}\begin{document}$$ \sqrt t $$\end{document}and homogeneously mixed beds ∝ 1/t. For short timest, both regimes show the same behaviour, namely oft.From a theoretical standpoint, it makes sense to differentiate further between the behaviour patterns of unmixed beds: at long timest, instantaneous heat transfer coefficients are independent of heat transfer form the heating surface to adjacent particles. Comparison with experimental result from literature shows that the derived models, which are consistent, are suitable for describing the heat transfer from submerged surfaces to unmixed and mixed beds of partic

ISSN:0930-7516    

DOI:10.1002/ceat.270110118

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe suitability of any item of equipment for a given thermal separation process cannot always be judged solely in the light of efficient and loading range data. In vacuum rectification, involving a large number of theoretical stages, the vapour pressure drop per transfer unit exerts a considerable effect on the energy consumption and thus largely governs the choice of column fittings. Furthermore, the pressure drop per transfer unit determines the temperature at the bottom of a rectification column and, hence, the suitability of the equipment for the separation of heat‐sensitive products. It is also an important criterion for compressor requirements in absorption processes. Another factor of considerable importance in separating heat‐sensitive mixtures by distillation is the time during which the product, particularly the liquid phase, is exposed to a given temperature in the column. Therefore, a standardized liquid residence time has been adopted to evaluate the systems in their entirely. This residence time depends on the hydrodynamic conditions in the column and is thus closely related to pressure drop and efficiency. Further important factors, which may decide the selection of column internals, are the specific volume and mass of the column. Based on theoretical considerations, a flow model is derived for describing the main loading range of countercurrent packed columns; the relationships between the above mentioned parameters are presen

ISSN:0930-7516    

DOI:10.1002/ceat.270110119

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractExperimental investigation of stirring processes require the measurement of temperature changes and concentration profiles in all the zones of the mixing volume. The conversion of simultaneous chemical reactions during the mixing process depends on the local temperature and concentration. The time‐dependent temperature and concentration fields can be recorded for the entire mixing volume with the use of optical tomography and correlated with time. This technique offers the possibility of continuous measurement of temperature and concentration changes during the mixing process throughout the measurement volume. In the described investigations, optical tomography is used to examine the transport and equalization processes during mixing in stirred vessel

ISSN:0930-7516    

DOI:10.1002/ceat.270110120

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractA report is presented on the influence of liquid flow rate, NaOH concentration, column length and presence of 5 × 10‐3wt‐% of the surfactant SLS on the rate of absorption of pure SO2by aqueous NaOH solution in a sphere‐and‐cylinder column. The presence of sodium lauryl sulphate (SLS) prevented axial turbulence which increased mass transfer in longer columns and was almost independent of the flow rate. The enhancement factor due to the reaction between SO2and NaOH with respect to the process of physical absorption was analyzed for the systems with excess OH‐in the outflow. The results obtained in the presence of a surfactant are satisfactorily explained by film theory with a single reaction plane model. Those obtained in the absence of surfactant are best described by a two‐plane model using re

ISSN:0930-7516    

DOI:10.1002/ceat.270110121

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY