摘要:

AbstractThis contribution presents the prediction of maximum heat transfer coefficients in bubbling fluidized beds, which takes into account thermal and fluid‐dynamic properties of particulate material and fluidizing agent. The analysis suggests that heat transfer between heating or cooling surfaces and bubbling fluidized beds consists mainly in a particular manifestation of convective heat transfer. Another feature is an appropriate modelling of the particle convective component leading to a two‐phase Prandtl num

ISSN:0930-7516    

DOI:10.1002/ceat.270150302

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe heterogeneous CaO/SO2reaction has been thoroughly investigated by developing a series of new experimental techniques including the TGA reactor, the volulmetric reactor and the entrained flow reactor. The heterogeneous system is designed in such a way that most of the gas film and pore diffusion resistances are reduced. The modelling of each step related to the reaction is discussed while the chemical reaction and product layer diffusion are emphasized as the main influences on the SO2removal. The unchanging size shrinking core model is used to describe the reaction progress with a two stage assumption which has been confirmed in the TGA reactor: first, a very fast surface reaction, followed by a product layer diffusion controlled reaction. It was found from the experiments that the SO2‐partial pressure aat the very beginning is very important for a high removal efficiency during the initial reaction perio

ISSN:0930-7516    

DOI:10.1002/ceat.270150303

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractA new model is derived to establish the effective nucleation rate in terms of the MSMPR‐theory. The model is based on the concept of two‐step crystal growth, secondary nucleation, nuclei activation and metastable supersaturation. A comparison between model prdictions and experimental data from different crystallizers is presented. This model, which integrates hydrodynamics directly into its theory, proves to be extremely suitable for describing the MSMPR‐crystallization pr

ISSN:0930-7516    

DOI:10.1002/ceat.270150304

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe design and performance of fixed beds are greatly influenced by fluid dispersion. Unfortunately, the existing design data do not provide an accurate picture of this phenomenon. This paper presents an attempt to characterize the dispersive features of packed beds by obtaining reliable estimates of the associated coefficients in the axial (DL) and radial (DR) directions. Such an objective is achieved by developing a representative two‐dimensional pseudo‐continuous dispersed flow model which is subsequently employed to compute the desired coefficients using data obtained from a refined experimental approach. The established values have been correlated to allow such coefficients to be reliably predicted under a variety of physical and operating conditi

ISSN:0930-7516    

DOI:10.1002/ceat.270150305

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractA novel method for measuring local deviations from perfect mixing of two non‐reative tracers is presented. It is based on the partially quenched fluorescence of one fluorescent tracer by a second tracer. When the concentration fluctuations are small, the deviation from the linear behaviour yields the cross‐correlation of the fluctuating components of the concentrations of both traces from an – easy to record – average value of fluorescence intensity obtained in the focus of a laser beam. The method was proven to be suitable for measuring these quantities in a 1125 cm3well‐stirred tank as a function of location and stirr

ISSN:0930-7516    

DOI:10.1002/ceat.270150306

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractA study was made of mass trasfer rates from single large oscillating drops of pure liquid‐liquid systems, in the size range of 5 to 10 mm. A thrermostatically‐controlled, 50 mm in diameter, 1000 mm long, rising drop column was used, in which mirrors in the jacket enabled front and side views of drops to be photographed simultaneously. The systems studied were (1) toluene and acetone (dispersed)‐water (continuous), and (2)n‐heptane and acetone (dispersed)‐water (continuous). High concentrations of acetone (up to 3.75 kmol/m3) were used to examine the effect of different parameters on the mass transfer rate, frequency and amplitude of oscillation in countercurrent operation. Previous theories and empirical correlations [2–6, 12, 13, 15] for the prediction of overall mass transfer coefficients showed large deviations from measured values. These may have aarisen because the models do not represent droplet oscillation accurately, and/or apply only to oscillations of small droplets. Fair agreement was obtained for small oscillating droplets as low solute concentrations. The oscillations of a travelling drop were asymmetrical; the period of oscillation was uniform for mutually‐saturated systems but changed when mass transfer was taking place. The periods were longer than those predicted by the Lamb [7]and Shroeder and Kintner [37] correlations. Terminal velocities predicted from literature correlations [32, 34]did not give reasonable agreement with experimental data when there was mass transfer of solute. The drag coefficient increased with increasing mass transfer rate from the drop. Correlation of the results and the dispersed phase mass trasfer coefficients by dimensional analysis resulted in the correlationList of symbols at the end of the paper.\documentclass{article}\pagestyle{empty}\begin{document}$$ k_d = 1.6 \times 10^6 \varepsilon ^{2.82} Eo^{1.15} Sc^{ - 2.0} \sqrt {D_d \omega _{\exp } } $$\end{document}with a mean deviation of ±23%, by insertion of experimental oscillation frequency data. This will facilitate more accurate prediction of the dispersed phase mass transfer coefficients relating to equipment containing droplets in the oscillating regime, e.g. pulsed columns or

ISSN:0930-7516    

DOI:10.1002/ceat.270150307

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractA laboratory fixed‐bed reaction column is presented, in which a heterogeneouslyl catalyzed reversible fluid‐phase reaction and the separation of the reaction product from unreacted or inert components by distillation are performed simultaneously. The rection studied, the formation of methyl tertiary butyl ether (MTBE) from methanol and isobutylene, is catalyzed by strongly acidic macroreticular ion exchange resins. Packing elements are Raschig rings, manufactured for the first time from the above‐mentioned ion exchange resins. This in‐house made catalyst shows practically the same ion exchange capacity as the commercial products. The control system installed in the equipment is capable of correcting strong disturbances os the steady state. As shown by expwrimental results, the superimposed distillation process occurs in such a way that the chemical equilibrium of the MTBE synthesis does not limit isobutylene con

ISSN:0930-7516    

DOI:10.1002/ceat.270150308

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe reaction of methonol with ammonia over catalysts, used commercially today, to give methylamines, does not occur with the desired dimethylamine selectivity. Both a thermodynamically and kinetically controlled reaction over conventional catalysts permits a maximum dimethylamine selectivity (DMA selectivity) of only about 30 mol‐%. In addition to monomethylamine (MMA), a large amount of the undesirable trimethylamine (TMA) is formed. By using zeolites and taking advantage of their shap‐selective properties, it is possible to achieve high MMA and DMA selectivities. Shape‐selective catalysis can only take place at catalytically active centrs in the inteerior of the por system. The proportion of non‐shape‐selective catalysis at the active centres on the outer surfaces of zeolites is not negligible. Treatment of ZK‐5 zeolite with tetramethoxysilane deactivates the outer surface of the crystallite and increases the shape‐selectivity of the ZK‐5 zeolite with rgard to the amination reaction. Computer simulation of the zeolite skeleton in conjuction with investigations of the reaction leads to some conclusions with respect to the reaction mechanisms and

ISSN:0930-7516    

DOI:10.1002/ceat.270150309

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractWood chips were treated with gaseous mixtures of monomethylamine and water vapour at temperatures between 160 and 120°C and pressurs ranging between 1.5 and 7.0 MPa. The degradation products were subsequently extracted with different solvents at ambient pressure. First, The degradation products of lignin were extracted with highly selective organic solvents such as diethyl ether or2‐butanone. Then, the remaining decomposition products were extracted with water or an aqueous solution of monomethylamine. The latter extract contains the degradation products of the hemicelluloses in a relatively high concentration. After a three hour digestion, the residue obtained from spruce had a lignin content of 3.1 wt‐% (pine: 3.7 wt‐%; birch 0.3 wt‐%). The total yield of unbleached cellulose was approximately

ISSN:0930-7516    

DOI:10.1002/ceat.270150310

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY

ISSN:0930-7516    

DOI:10.1002/ceat.270150301

出版商:WILEY‐VCH Verlag    

年代:1992

数据来源: WILEY