Ernst-Ulrich Schlünder

Thermodynamics of multi-solute adsorption from dilute aqueous solutions

Abstract Experimental adsorption data at 20°C are given for six dilute aqueous bi-solute systems adsorbing on activated carbon. The three-parameter Toth adsorption isotherm gives good representation of the data for aqueous single-solute adsorption. Using the thermodynamic ideal-adsorbed-solution method, total and partial adsorptions are calculated for the bi-solute systems; agreement with experimental data is good. Prediction for total adsorption is within about 2–10% and for adsorption of individual components within about 3–20%. In the prediction calculations only single-solute data are used. A new three-parameter adsorption isotherm is presented. This new isotherm also represents the single-solute data well. For bi-solute systems where dissociation is negligible, calculated individual adsorptions agree with experiment within 2%. Systematic deviations between calculated and observed results may be due to the acidities of the solutes. In the future, adsorption experiments should be done under controlled pH conditions.

Competitive adsorption of two dissolved organics onto activated carbon—I: Adsorption equilibria

Abstract Prediction of multi-solute adsorption, using the ideal adsorbed solution (IAS) theory [1,2], may be greatly simplified by representing the single-solute data with several Freundlich adsorption isotherms. Accuracy of the proposed method is tested by comparing experimental with predicted adsoption data for five, dilute, aqueous bi-solute solutions and for four different activated carbons. The simplified method permits rapid and accurate calculations of multi-solute adsorption equilibria; it is suitable for engineering-design applications.

Competitative adsorption of two dissolved organics onto activated carbon—II: Adsorption kinetics in batch reactors

Bi-solute adsorption of dissolved organics by activated carbon was studied in a finite bath system. The batch tests with strongly adsorbable species show that at low concentrations (X < 0.1 mmol/1) only external mass transfer resistance is rate-determining. For higher concentrations internal mass transfer becomes increasingly important. This behavior indicates that the diffusional process within the particle occurs predominantly in the adsorbed phase. Bi-solute calculations were performed, using only single-solute data. Systems with differing equilibrium behavior, but similar diffusive properties of both solutes, were described adequately by a model which takes into account diffusion in the liquid-filled pores and in the adsorbed phase, as well as external mass transfer. Deviations between measured and predicted rates can be observed for systems with large differences in the mobility of the diffusing molecules, or if counter diffusion inside the particles occurs. It is likely that the discrepancies in these cases are caused by diffusional interactions between the two different species in the adsorbed phase.

The scale-up of activated carbon columns for water purification, based on results from batch tests—II: Theoretical and experimental determination of breakthrough curves in activated carbon columns

Abstract Based on the adsorption-rate equation derived in Part I of this investigation, a differential equation has been obtained for the prediction of the concentration distribution in activated carbon columns. This differential equation derived without the constant pattern assumption has been solved analytically. The solution includes both the transition region and the range of the constant pattern which is fully developed in a finite time and finite column length. The comparison of predicted data with experimental values indicates that film resistance has a considerable influence on the concentration history and should never be ignored.

Particle growth and droplet deposition in fluidised bed granulation

The aim of the presented work is the investigation of the growth process in a continuously operated fluidised bed granulator. For that purpose, granulation experiments were performed and system hold-up and particle size distributions were measured. For the interpretation of the results, a model was developed taking into consideration the particle exchange between nozzle jet and fluidised bed as well as the wetting and drying process. In contrast to the commonly found assumption that droplet deposition is analogous to dust deposition in fluidised bed filters, this model was developed to describe the processes in the nozzle region of a submerged nozzle that leads to a system comparable to that of a wet scrubber. Consequently, the growth rate as a result of the droplet deposition is found to increase with particle size.

Temperature Distribution and Heat Exchange in Multipass Shell-and-Tube Exchangers with Baffles

Abstract A model predicting the temperature distribution and the mean temperature difference in multipass shell-and-tube heat exchangers with baffles is presented. The exchanger is treated as a cascade of cells with mixing taking place in each fluid. From the computed results, design rules are deduced to enable the choice of the construction that leads to the highest efficiency. The effect of leakage currents on exchanger effectiveness is ignored in this analysis and is treated separately in another paper.

Competitive adsorption of two dissolved organics onto activated carbon—III: Adsorption kinetics in fixed beds

Adsorption breakthrough curves for bisolute systems of dissolved organics on activated carbon are measured in fixed beds. Results for strongly adsorbable species indicate that at low liquid concentrations (X<0.1 mmol/l.) only external mass transfer resistance is rate determining. However, at higher liquid concentrations internal mass transfer becomes increasingly significant. Breakthrough behaviour is predicted using alternatively three different models with different assumptions about diffusion in the liquid filled pores and diffusion on the surface in series with external film diffusion. Multi-solute adsorption equilibria are predicted from single-solute data using the ideal adsorbed solution theory developed by Myers and Prausnitz, while the single-solute equilibria are represented by Freundlich isotherms. The external mass transfer coefficient for each component is calculated by a general correlation for heat and mass transfer in fixed beds. The internal diffusion coefficient for each component is determined in batch reactor tests with the single-solute system. Systematic deviations between measured breakthrough curves and those calculated from different models using only single-solute data are observed in all experiments with mixed solutes if there is significant internal diffusional resistance and marked displacement of one component inside the carbon particles. The deviations may be due to mutual interference of diffusing molecules. A better agreement between calculated and observed breakthrough curves can be obtained using an extended model in which mixture data are required.

Heat transfer between an impinging jet and a continuously moving flat surface

Experiments have been carried out to determine heat transfer rates from a continuously moving belt to an air jet impinging normally. The parameters that were varied included the jet velocity (4 < VN < 40 m/s), the jet width (4.8 < B < 19 mm), the nozzle-to-plate distance (3 < H/2B < 11) and the belt speed (0. 15 < VB < 5. 5 m/s). An infrared thermometer was used for the measurement of temperature of the moving belt. The average heat transfer coefficients increase with belt speed steeply initially to a maximum value and then remain almost constant for all higher belt speeds. The maximum heat transfer coefficients are about 1.5 to 2.0 times higher than those predicted for the stationary surface. The present data on continuously surface in still air and in impinging jet flow are well compared with the data on rotating cylinders reported in the literature.ZusammenfassungExperimentell bestimmte Wärmeübergangskoeffizienten für Düsengeschwindigkeiten zwischen 4 m/s und 40 m/s, sowie Düsenbreiten zwischen 4,8 mm und 19 mm lagen bei Bandgeschwindigkeiten zwischen 0, 15 m/s bis 5, 5 m/s ca. 50 % bis 100 % höher als bei unbewegtem Band. Die gemessenen Daten bei bewegtem wie bei unbewegtem Band schließen gut an bekannte Werte aus der Literatur an.

Heat transfer and pressure drop for boiling nitrogen flowing in a horizontal tube: 2. Pressure drop

Abstract The pressure drop of boiling two-phase nitrogen flow in a smooth horizontal tube has been studied experimentally. The results show in principle the well-known dependence of the local pressure drop from the vapour quality, the mass flow rate, and the heat flux. A comparison of the measured frictional pressure drop shows a sufficient agreement with predicted values using published correlations. The accelerational pressure gradient can also be predicted taking into account a suitable void fraction relationship.

The influence of HCl on SO2 absorption in the spray dry scrubbing process

To examine the influence of HCl on SO 2 removal in the spray dry scrubbing process, preliminary experiments on the effect of adding CaCl 2 to the lime slurry on SO 2 absorption efficiency were performed in a laboratory scale spray dryer. It was found that the SO 2 removal efficiency is augmented at CaCl 2 concentrations up to 1.2 g/l in the lime slurry. This is ascribed to the influence of the prolonged drying process. However, SO 2 absorption efficiency cannot be improved further at higher CaCl 2 concentrations. A simple estimation shows that this cannot be ascribed solely to the influence of the drying behavior of the droplets and more complex explanations have to be found. Subsequently, experiments on the simultaneous absorption of SO 2 and HCl were performed. It was found that the SO 2 removal efficiency is enhanced at low HCl concentrations in the flue gas. This is ascribed to the formation of CaCl 2 in the droplets, resulting in a prolonged drying process. After reaching a maximum, the SO 2 removal efficiency falls again at higher HCl concentrations. This can be explained with the competing absorption process in which HCl is thermodynamically favored.