Showing papers in "Chemical Engineering & Technology in 1993"
TL;DR: In this article, a theoretical model is presented that allows mass transfer to be described in terms of packing geometry and physical properties which influence the gas-liquid or vapour-liquid systems in absorption, desorption and rectification columns.
Abstract: Countercurrent-flow columns are widely used in production processes in the chemical industry and their application in ecological engineering is of increasing importance. A theoretical model is presented here that allows mass transfer to be described in terms of packing geometry and physical properties which influence the gas-liquid or vapour-liquid systems in absorption, desorption and rectification columns. The relationships derived from the model can be applied to all countercurrent-flow columns, regardless of whether the packing has been dumped at random or arranged in a geometric pattern.
241 citations
TL;DR: In this article, a cyclone was used for the separation and classification of solids in a gas flow and a new method of calculating the separation efficiency was developed based on this experimental device and the theory of momentum transfer between solids and gas flow.
Abstract: Large recirculation cyclones with high concentrations of particulate solids have gained considerable importance in the field of circulating fluidized bed technology. To calculate a combustion process, the influence of the cyclone on the circulating quantity of solids and their grain size distribution must be known. Measurements in a 105-MW-plant in 1989 showed that the existing cyclone theory was not sufficient for this purpose. In a laboratory cyclone (900 mm in diameter), the separation and classification of solids in a gas flow was investigated. The cyclone was fed from a fluidized bed and operated with cold air and quartz of various grain size distributions. Based on this experimental device and the theory of momentum transfer between solids and gas flow, a new, more accurate method of calculating the separation efficiency was developed.
70 citations
TL;DR: In this paper, power consumption under non-aerated and aerated conditions was measured in a 0.45 m diameter tank containing a range of xanthan gum solutions, using the Scaba 6SRGT impeller.
Abstract: Power consumption under non-aerated and aerated conditions was measured in a 0.45 m diameter tank containing a range of xanthan gum solutions, using the Scaba 6SRGT impeller. Well-mixed caverns were measured in a transparent Carbopol solution. The data are compared with previous results obtained with a Rushton turbine in the range of Reynolds numbers, Re, between 1 and 2000. In each case, the non-aerated power numbers were similarly related to Re except that the Po values of the Scaba 6SRGT were 3 to 4 times smaller. Under aerated conditions, the aeration rate does not affect the power number, Pog, with the actual value falling as a result of increasing xanthan concentration. The Pog/Po vs Re curve passes through a minimum which is lower at higher xanthan concentrations. At the same Reynolds number, the decline in power consumption of the Scaba agitator due to aeration is 20 to 50% smaller than that observed with a Rushton turbine. Well-mixed cavern shapes and sizes are also very similar to those observed with Rushton turbines and can be predicted from equations available in literature. However, instabilities in torque could present a problem in broths containing xanthan in concentrations above 35 kg m–3. Nevertheless, the Scaba agitator offers an interesting retrofitting possibility for xanthan fermentation, which could lead to improved performance.
62 citations
TL;DR: In this paper, an approach based on the concepts of pinch technology for total site targeting for fuel and power is described, which takes account of the trade-offs between process fuel and steam, between steam, site fuel and cogeneration, and of fuel mix.
Abstract: This paper describes an approach based on the concepts of Pinch Technology for Total Site targeting for fuel and power. If specific CO 2 emissions for fuel and power are known, the approach will also target for CO 2 emissions for any given site in the industry. The approach takes account of the trade-offs between process fuel and steam, between steam, site fuel and cogeneration, and of fuel mix. A case study is described where an 18 % reduction in global CO 2 emissions is possible through the correct use of these trade-offs
59 citations
TL;DR: In this paper, a practical definition of the circulating fluidized bed (CFB) regime has been proposed based on a comprehensive hydrodynamic analysis, and two flow regimes are involved in a CFB: fast fluidization and dense phase conveying.
Abstract: Based on a comprehensive hydrodynamic analysis, a practical definition of the circulating fluidized bed (CFB) regime has been proposed. It was established that two flow regimes are involved in a CFB: fast fluidization and dense phase conveying. By demonstrating the variation of pressure gradient in both the lower and the upper section of the bed versus superficial gas velocity, the criteria for the determination of transition velocities have been obtained. Literature data which over wider operating conditions, particle properties and bed diameters from the basis of the obtained generalized correlations of transition velocities. A quantitative flow diagram is presented.
44 citations
TL;DR: In this paper, the authors present the determination of liquid hold-up in gas/liquid two-phase countercurrent columns filled with random or structured packings, with only slight deviations.
Abstract: We present the determination of liquid hold-up in gas/liquid two-phase countercurrent columns filled with random or structured packings. The equations resulting from the established physical relationships are verified against the values for liquid hold-up determined experimentally on 56 different column packings and 16 gas/liquid systems. The experimental and calculated results agree well, with only slight deviations. This also applies to the range between the loading and flooding points for two-phase countercurrent flow
37 citations
TL;DR: In this paper, the authors presented a humidification-dehumidification (H.D.) process suitable for desalination of sea and brackish water, which correlates performance characteristics of the combination of different components in such a loop.
Abstract: This article presents a humidification-dehumidification (H.D.) process suitable for desalination of sea- and brackish water. The work correlates performance characteristics of the combination of different components in such a loop. Water yield, energy requirement and design data are evaluated as functions of different parameters. The investigation covered water to air mass ratios ranging from 60 to 80, concentration ratios between 2 and 5, at a temperature difference of between 10 and 16 °C, along the liquid for dehumidification. The results showed that 76% of energy consumed in the humidifier is recovered by condensation. Increase of the concentration ratio to 5 can reduce the make-up water and rejected brine by about 58% and 24% respectively. Cost calculations show that the H.D. process has significant potential as an alternative for small capacity desalination plants and permits to operate systems as small as 10 m3/day in output.
35 citations
TL;DR: In this article, the effects of gas velocity (032 to 067 m/s), inlet gas temperature (25 to 100 °C) and the mass ratio of starch to inert particles (01 to 04) on the drying rate of starch in a 0083 m-ID × 080 m-high inert medium fluidized bed were investigated.
Abstract: The effects of gas velocity (032 to 067 m/s), inlet gas temperature (25 to 100 °C) and the mass ratio of starch to inert particles (01 to 04) on the drying rate of starch in a 0083 m-ID × 080 m-high inert medium fluidized bed were investigated The drying mechanism in an inert medium fluidized bed can be classified into adhesion-dispersion, evaporation and disintegration steps The drying rate increases with the increasing inlet gas temperature and velocity; the rates being about 10 times those reported for an agitated pan dryer However, the drying rate decreases slightly as the mass ratio of starch to inert particles increases Also, the drying rate exhibits a maximum at an optimum bed porosity The drying rate data obtained in an inert medium fluidized bed have been correlated with the relevant dimensionless groups, ie Stefan and particle Reynolds numbers based on the theory of isotropic turbulence
34 citations
TL;DR: In this paper, the authors analyzed the importance of the internal and external multicomponent mass and heat transfer phenomena on the catalyst under boiling conditions and showed that decomposition of MTBE can occur accompanied by boiling processes inside the catalyst macropores.
Abstract: The octane enhancer methyl tertiary butyl ether (MTBE) can be produced very efficiently from methanol and isobutene in a reactive distillation column where the heterogeneous catalyst also acts as distillation packing. Some mathematical models have been published for the simulation of such a process but they focus on the physical transport processes between the vapour and liquid phases. However, the aim of this paper is to analyze the importance of the internal and external multicomponent mass and heat transfer phenomena on the catalyst under boiling conditions. Therefore, experiments were carried out in a reactive distillation column at different compositions of feed, column pressures and reflux ratios using a Raschig ring shaped acidic ion exchange resin as the catalyst. The temperature and composition of the liquid phase entering and leaving the catalytic column section were measured. These data were used to evaluate the effectiveness factor of the catalyst with a rigorous macrokinetic model. It is shown that the effectiveness factor varies significantly along the column length. Under certain operating conditions, decomposition of MTBE can occur accompanied by boiling processes inside the catalyst macropores.
28 citations
TL;DR: In this article, a new model is presented which takes into account the structure of packing (cylinder model) as well as the structural structure of the liquid hold-up, which allows the separation of liquid flow through packings into its main constituents.
Abstract: In order to predict mass transfer in packed columns, it is necessary to know the interfacial area. The well-known and often cited equations (Onda, Kolev, Zech, etc.) do not yield precise values for the mass transfer coefficient β L a e or the interfacial area a e , especially for modern packing elements. A new model will be presented which takes into account the structure of packing (cylinder model) as well as the structure of the liquid hold-up. This model allows the separation of liquid flow through packings into its main constituents, i.e. rivulets and drops (freely falling). The determination of the structure of liquid flow allows the prediction of effective interfacial areas as well as of volumetric mass transfer coefficients for irrigated large packing elements manufactured from plastics, metals or ceramic. The applicability to novel future packings is one of the advantages of the new model
21 citations
TL;DR: In this article, the authors reviewed the models for equilibrium and kinetics of the system Zn/D2EHPA/n-dodecane (and other diluents), published during the past decade, as well as values of the appropriate model parameters, i.e. of equilibrium and reaction rate constants.
Abstract: This contribution reviews the models for equilibrium and kinetics of the system Zn/D2EHPA/n-dodecane (and other diluents), published during the past decade, as well as values of the appropriate model parameters, i.e. of equilibrium and reaction rate constants. The reviewed kinetic models comprise those for kinetic, diffusional and mixed mass transfer regimes. It is shown that, under certain conditions, the rate equation within the kinetic regime has the same mathematical structure as the equations for the overall mass transfer rate within the diffusional and mixed mass transfer regimes
TL;DR: In this article, a theoretical analysis of the relationship between the rate of energy dissipation per unit volume and the mean kinetic energy of turbulence in a mechanically agitated gas-liquid system was presented.
Abstract: This contribution presents a theoretical description of the relationship between the rate of energy dissipation per unit volume and the mean kinetic energy of turbulence per unit volume in a mechanically agitated gas-liquid system. For agitated systems with standard (Rushton) turbine impellers, the effect of the aeration rate on the distribution of the rate of energy dissipation per unit volume in the system was investigated. It follows from the experiments carried out that the gas flow rate significantly affects the rate of energy dissipation per unit volume in the impeller region as well as in the bulk of the agitated batch. In the impeller region, the investigated rate of energy dissipation markedly increases with increasing gas flow rate and, in the remaining part of the agitated batch, it decreases. Moreover, the rate of energy dissipation near the impeller depends strongly on the local gas hold-up which corresponds to the regime of two-phase flow behind the impeller blades (i.e. to the occurrence of clinging of ragged cavities).
TL;DR: In this article, the bulk density of a catalyst bed in two-dimensional reactor model has been measured by a radiogauging method and three ways of introducing the catalyst were used. Attention was paid to bulk density near the wall and the bottom of the model.
Abstract: The bulk density of a catalyst bed in two-dimensional reactor model has been measured by a radiogauging method. Three ways of introducing the catalyst were used. Attention was paid to bulk density near the wall and the bottom of the model. A homogeneous distribution of the catalyst was obtained in the case of the “rainy” (uniform) filling method using a grid distributor.
TL;DR: In this article, a kinetic model for the oxidation of phenol in high pressure water has been developed and compared with experimental data taken from literature, assuming a chain reaction propagated by O and OH.
Abstract: A kinetic model for the oxidation of phenol in high-pressure water has been developed and compared with experimental data taken from literature The model assumes a chain reaction propagated by O and OH Production of the hydroxyl radical by the reaction of atomic oxygen and water induces a chain-branching effect, which is particularly effective at low temperatures and high pressures The proposed model gives a fair correlation of the experimental data in the whole examined temperature and pressure range and appears significantly better than a simpler, power-law kinetic model The reliability of the model is strengthened by the consideration of values obtained for the kinetic parameters (in particular for the activation energies) which compare well with the literature
TL;DR: In this article, the wall factor for spheres in the acceleration and terminal velocity ranges was determined experimentally for very high Reynolds numbers (13 500 < Re < 70 000) for spheres falling in water inside cylinders 3.4, 4.9, 7, 10, 14 and 19 cm in diameter.
Abstract: The wall factor for spheres in the acceleration and terminal velocity ranges was determined experimentally for very high Reynolds numbers (13 500 < Re < 70 000). Experiments were performed with 12, 15, 18, 21, 25 and 31.75 mm spheres, falling in water inside cylinders 3.4, 4.9, 7, 10, 14 and 19 cm in diameter. A published empirical equation was found to yield good results for the terminal velocity wall factor in the range of studied Reynolds numbers.
TL;DR: In this article, a commercial FCC regenerator, 5.76 m in diameter, was investigated for the mixing of gas, solids and heat in a commercial FD regenerator.
Abstract: Mixing of gas, solids and heat in a commercial FCC regenerator, 5.76 m in diameter, was investigated. This regenerator was operated at a high superficial gas velocity (>1.2 m/s) and high temperature (650–710°C). It is classified as a highly efficient regenerator. The profiles of coke content in the catalyst, gas composition, temperature and pressure were obtained by sampling and instrumental measurement. It was confirmed that a proposed axial dispersion model could be used for a satisfactory prediction of these experimental profiles. The values of gas and solids dispersion coefficients are also presented.
TL;DR: In this article, the emulsion liquid membrane (ELM) separation technique was used for zinc recovery in a multicomponent cationic mixture, and experimental apparatus and conditions were described.
Abstract: Treatment of a given multicomponent cationic mixture was studied applying the emulsion liquid membrane (ELM) separation technique for Zn recovery. Experimental apparatus and conditions are described. Comparative studies using two zinc-selective ion exchangers (thio-DEHPA and dithio-DEHPA) were carried out whereby the composition of the liquid membrane and the operating conditions were investigated for both extractants. A useful method of representing the concentrations of the feed and the receiving aqueous phase is proposed, which allows the occurrence of break-up and/or osmosis to be easily detected.
TL;DR: In this article, the effects of metal exchange between zeolites and alkali metals (Li, Na, K; zeolite Y, ZSM-5, T), alkaline earths (Mg, Ca, Sr, Ba; ZSM, 5), transition metals (La, Ce, Cr, Mn, Fe, Co, Ni, Pd, Cu, Zn, 6, 7), and aluminium (ZSM,5) on the conversion of ethanol were studied.
Abstract: The effects of metal exchange between zeolites and alkali metals (Li, Na, K; zeolite Y, ZSM-5, T), alkaline earths (Mg, Ca, Sr, Ba; ZSM-5), transition metals (La, Ce, Cr, Mn, Fe, Co, Ni, Pd, Cu, Zn; ZSM-5) and aluminium (ZSM-5) on the conversion of ethanol were studied. Activities of the catalysts and selectivities for ethene, C3+ olefins, paraffins and arenes strongly depended on the cation, chosen for the modification. Only ethene was formed by alkali exchanged zeolites, the most active being Li-Y. This could be confirmed by a long-term ageing test with Li-Y pellets under semi-industrial conditions. The exchange of ZSM-5 with alkaline earths or transition metals permitted the formation of a wide variety of products, raning from high ethene to high aromatic yields. A correlation between certain product selectivities and electronegativity was only possible in a rough approximation.
TL;DR: In this paper, the distribution of pressure and velocity in a radial flow cold model of a moving bed reactor, 500 mm in diameter, was studied in four different gas flow modes, inward Z gas flow, inward Π gas flow and outward Z flow, and it was found that the axial non-uniformity of the gas is at a minimum.
Abstract: Distributions of pressure and velocity in the main channels were studied in a radial flow cold model of a moving bed reactor, 500 mm in diameter, in four different gas flow modes, inward Z gas flow, inward Π gas flow, outward Z gas flow, outward Π gas flow. It has been found that, in outward Π gas flow mode, the axial non-uniformity of the gas is at a minimum. The following correlations are proposed for the momentum recovery factors K a and K b : K a = 0.684 + 0.0128 (du/dx)/u, K b = 1.135 + 0.0158 (du/dx)/u. Pressure distributions in the main channels can be accurately predicted using K a and K b
TL;DR: In this article, the Gibbs adsorption equation was used to estimate the surface excess of supercritical components with the aid of Gibbs adaption equation and showed that the excess concentration increases with increasing gas activity, runs through a pronounced maximum, later decreasing rapidly to very small values.
Abstract: Interfacial tension of the binary systems pelargonic acid/ethane, pelargonic acid/carbon dioxide, linoleic acid/ethane, and linoleic acid/carbon dioxide was measured at 313, 333, and 353 K and pressures ranging up to 250 bar, using the capillary rise and Du Nouy ring methods. Both these methods yield similar values. The surface excess of supercritical components is deduced from the measurement results with the aid of Gibbs adsorption equation. The surface excess concentration increases with increasing gas activity, runs through a pronounced maximum, later decreasing rapidly to very small values. Near the surface excess minimum, a falling film of fatty acids disintegrates into a mist of tiny droplets
TL;DR: In this paper, a VCA was designed and constructed for the preparation of sulphamethoxazole (SMZ) microcapsules using gelatin as a coating polymer, which was characterized by physico-chemical methods.
Abstract: Vibrating capillary apparatus (VCA) was designed and constructed for the preparation of sulphamethoxazole (SMZ) microcapsules using gelatin as a coating polymer. The microcapsules were characterized by physico-chemical methods. The apparent diffusion coefficient D a and diffusion rate constant K BL of the drug were measured at pH of 1.2 and 7.2. Better controlled release products were obtained in the VCA
TL;DR: The methods of precipitation, chromatography and foam fractionation are investigated in detail in order to obtain high product yields without loss of quality in downstream processing.
Abstract: Enzymes are of growing interest to the chemical and pharmaceutical industries as highly specific biocatalysts. An obstacle to a large-scale application of such proteins is the expenditure on recovery operations which can amount up to 80% of the total production costs. Therefore, it is necessary to investigate in detail the individual stages of downstream processing in order to obtain high product yields without loss of quality. After a survey of recovery operations and information on some special features of proteins which are relevant to downstream processing, this paper deals with the methods of precipitation, chromatography and foam fractionation
TL;DR: The aim of the studies was to develop an innovative concept of reactor design and engineering called “biocatalyst” (Biokatalysator) that lies in between the conventional biofilter and bioscrubber, using biomass immobilized on macroporous, tubiform supports installed in parallel to the air flow.
Abstract: Biological processes are becoming increasingly popular in dealing with waste air problems. Compared to chemical and physical treatment methods, they offer several advantages, especially in handling of waste air contaminated with low concentrations of biodegradable organic and, occasionally, inorganic substances. Two types of commercial systems are currently in use: biofilters and bioscrubbers. The aim of our studies was to develop an innovative concept of reactor design and engineering called “biocatalyst” (Biokatalysator). Our biocatalytic three-phase system lies in between the conventional biofilter and bioscrubber, using biomass immobilized on macroporous, tubiform supports installed in parallel to the air flow. In laboratory-scale investigations, a bioreactor was continuously fed with solvent-laden air, which produced a more cost-effective mode of operation than the conventional bioscrubber systems.
TL;DR: In this article, a new experimental technique with periodic laser heating is described and applied to the measurement of local heat transfer coefficients at the inner surface of an agitated vessel, where only radiative surface temperature measurements on the outer wall of the vessel are necessary.
Abstract: A new experimental technique with periodic laser heating is described and applied to the measurement of local heat transfer coefficients at the inner surface of an agitated vessel. Only radiative surface temperature measurements on the outer wall of the vessel are necessary.
TL;DR: In this article, the ion exchange equilibria of binary systems on Amberlite IR-120 resin, at different temperatures and total ionic concentrations in aqueous solutions, were reported.
Abstract: Experimental data are reported for ion exchange equilibria of binary systems on Amberlite IR-120 resin, at different temperatures and total ionic concentrations in aqueous solutions. These systems exhibit non-ideal behaviour in both phases, and the equilibrium characterization has been based on the law of mass action, using Wilson and Meisssner, and Kusik equations to correlate the activity coefficients in the resin and aqueous solutions, respectively. Equilibrium constants, standard thermodynamic properties (Gibbs free enthalpy changes, enthalpy and entropy) and Wilson binary parameters were obtained as functions of temperature.
TL;DR: In this paper, the theory and mechanism of electrostatic sparking, parameters needed to assess the respective hazard in a plant, safety measures to combat electrostatic problems, common operations where such problems exist and measures to eliminate or mitigate these problems.
Abstract: Static electricity is a frequent source of fires and explosions in industry A variety of operations may generate static electricity leading to such fires and explosions This requires adequate preventive and protective measures against this hazard The present paper describes the theory and mechanism of electrostatic sparking, parameters needed to assess the respective hazard in a plant, safety measures to combat electrostatic problems, common operations where such problems exist and measures to eliminate or mitigate these problems
TL;DR: The use of ozone as initiating agent in the liquid phase oxidation of α-pinene has been investigated in this article, where the first intermediate product of the reaction is the hydroperoxide of αpinene.
Abstract: The use of ozone as initiating agent in the liquid phase oxidation of α-pinene has been investigated. The first intermediate product of the reaction is the hydroperoxide of α-pinene. Both, ozone partial pressure and its initiation time exert an inhibiting effect on the conversion of α-pinene but yield higher selectivities for the hydroperoxide of α-pinene compared with those of oxidation without ozone. In all cases, temperature was found to be the most important variable affecting the oxidation rate. From a mechanism of radical reactions, kinetic equations, consistent with the experimental results, corresponding to α-pinene oxidation rate and net formation rate of its hydroperoxide, were obtained. The rate constants are given as functions of temperature. The results also suggest that a fraction of the hydroperoxy radicals decomposes to yield other products such as verbenol and verbenone, identified in the work, and whose kinetics will be reported in a later paper
TL;DR: In this paper, a simple model of liquid homogenization in a mixing tank is presented, based on the pumping capacity of impellers and the degree of homogeneity, which is valid for turbulent mixing.
Abstract: This paper presents a very simple model of liquid homogenization in a mixing tank. The model, based on the pumping capacity of impellers and the degree of homogeneity, is valid for turbulent mixing; however, it has been extended to transient regime of mixing (Re = 100 to 1000).
TL;DR: Acidianus brierleyi was also found capable of catalyzing the removal of what is normally reported as organic sulphur from coal 171US34 as discussed by the authors, which allowed a comparison with literature data for Thiobacillus ferrooxidans.
Abstract: Acidianus brierleyi was demonstrated to remove pyritic sulphur from coal. A. brierleyi was also found capable of catalyzing the removal of what is normally reported as organic sulphur from coal 171US34. A kinetic analysis was performed by assuming a first order reaction. The first order kinetics allowed a comparison with literature data for Thiobacillus ferrooxidans. Also, formation of jarosite was taken into account in the analysis. The simple first order kinetics was observed to fit the data on removal of sulphur satisfactorily.
TL;DR: In this paper, the authors provided the first quantitative experimental confirmation of the thermocoustic convection properties of wave propagation in the presence of a second parallel surface, where the wave is predicted to be reflected repeatedly from both surfaces and to decay slowly due to viscous and thermal dispersion.
Abstract: Approximate as well as reasonably exact numerical solutions of the equation of conservation have previously predicted that sudden heating of a solid surface adjacent to a region of gas will generate a slightly supersonic wave with small positive amplitudes in pressure, temperature and density, and thereby a small mass velocity in the direction of wave propagation. If the gas is confined by a second parallel surface, the wave is predicted to be reflected repeatedly from both surfaces and to decay slowly due to viscous and thermal dispersion. This process, which has been termed thermoacoustic convection, is presumed to result in transient heating of the confined gas and heat transfer through it at rates greatly exceeding that of pure thermal conduction. The current work constitutes the first quantitative experimental confirmation of this behaviour. Numerical solutions obtained for support and guidance of the experimental work define for the first time the conditions required for the generation of a wave of significant strength.