Effect of impeller geometry on drop break-up in a stirred liquid—liquid contactor

Drop size measurements were made in the break-up zone at the tip of three 6 bladed disc turbines of different geometries in a 0·30 m dia. vessl. Three systems kerosene, methyl iso-butyl ketone (MIBK) and n-butanol at a volumetric fractional hold-up of 0·05 in water were examined. Power input and circulation time characteristics were determined and a new dimensionless group (?^{?$\text{1}\text{3}$}t_c/T^{$\text{2}\text{3}$}) is proposed to account for the effect of geometric parameters in the correlation of the drop size.     

Size of bubbles and liquid circulation in a bubble column with a draught tube and sieve plate

The size distribution of bubbles and the liquid circulation in a bubble column with a draught tube and sieve plate were studied experimentally. The size of bubbles is well correlated with the previous result of the authors; the size distribution data are fitted reasonably well by a logarithmic normal probability distribution. Gas holdup in the draught tube and annulus and pressure drop were measured and correlations for these parameters are obtained. An energy balance is used to predict liquid circulating velocity using gas holdup and pressure drop correlations. Reasonable agreement is found between the calculated and measured circulating velocity.     

Terminal composition control of a binary distillation column

Terminal composition control of a pilot scale binary distillation column operated under the control of an IBM 1800 digital computer has been studied for disturbances in feed flow rate. Conventional two point control, whereby the overhead composition is controlled by reflux flow rate and bottom composition by means of steam rate, was demonstrated to be unsatisfactory. Two alternate control systems, namely a noninteracting control system and a ratio control system were evaluated. The noninteracting control system was constructed from a transfer function representation of the distillation column dynamics, determined from a series of on-line pulse tests. The results show that a very significant improvement in the control of both compositions is achieved by using noninteracting control or the ratio control scheme suggested by Rijnsdorp compared to the behavior that results using conventional two point feedback control. However, the control performance obtained using noninteracting control was only marginally better than that using the ratio control scheme.     

Sampled-data feedback control of a binary distillation column

The design of sampled-data controllers for a binary distillation column was studied for several types of controllers and for various control tray locations, sampling rates and disturbances. Minimal prototype control was superior to continuous PI control under some conditions but, as expected, was only satisfactory for a specified disturbance. dual “A” control scheme that compensates for both setpoint and load disturbances was developed. Two separate algorithms are implemented simultaneously, one receiving its input signal from the setpoint and the other from the measured variable. Dual control is superior to continuous control, particularly when both disturbances are encountered at the same time, and is superior to the “switching” method proposed by Mosler et al.     

The second law optimal state of a diabatic binary tray distillation column

A new numerical procedure to minimize the entropy production in diabatic tray distillation columns has been developed. The method was based on a least square regression of the entropy production at each tray. A diabatic column is a column with heat exchangers on all trays. The method was demonstrated on a distillation column separating propylene from propane. The entropy production included contributions from the heat transfer in the heat exchangers and the mass and heat transfer between liquid and vapor inside the distillation column. It was minimized for a number of binary tray distillation columns with fixed heat transfer area, number of trays, and feed stream temperature and composition. For the first time, the areas of heat exchange were used as variables in the optimization. An analytical result is that the entropy production due to heat transfer is proportional to the area of each heat exchanger in the optimal state. For many distillation columns, this is equivalent to a constant driving force for heat transfer. The entropy production was reduced with up to 30% in the cases with large heat transfer area and many trays. In large process facilities, this reduction would ideally lead to 1-2 GWh of saved exergy per year. The most important variable in obtaining these reductions is the total heat transfer area. The investigation was done with a perspective to later include the column as a part in an optimization of a larger process. We found that the entropy production of the column behaved almost as a quadratic function when the composition of the feed stream changed. This means that the feed composition is a natural, easy variable for a second law optimization when the distillation column is a part of a process. The entropy production was insensitive to variations in the feed temperature.     

Optimal two point control of a binary distillation column

Optimal two point control and operating policies have been developed for a semi-works scale 10 tray distillation column separating methanol and water. Two controllers, based on different control philosophies were synthesized. They are:

• 1 The controller that will bring the product compositions to their desired values while keeping off-specification products to a minimum.
• 2 The controller that will bring the product compositions to their desired values while maintaining the average product composition of the control period at the desired level.

Two types of disturbances were studied, namely disturbances in the feed stream and changes in product specifications. The column operation was represented by a linearized dynamic mathematical model based on a component material balance. The solution of the problem was obtained by application of the minimum principle of Fontryagin and the modified Riccati transformation technique. Simplified optimal control schemes can be developed from the results of this work. These control schemes are simple enough to be used for direct digital computer control.     

On-line multivariable adaptive control of a binary distillation column

An experimental evaluation of the simultaneous control of top and bottom product compositions of a binary distillation column utilizing multi-variable self-tuning control algorithms is presented. The study was carried out using an 8-tray, 22.86 cm diameter methanol–water pilot scale column with continuous capacitance analysis of top product composition and bottom composition analyzed on a 3 minute cycle, by a gas chromatograph. Column control is studied for ±25% step disturbances in feed flow rate. Terminal composition regulation using both ‘positional’ and ‘incremental’ forms of a generalized minimum variance self-tuning control algorithm is compared with that achieved using a conventional digital PI/PID multiloop control strategy.     

Control of a binary distillation column utilizing a simple control law

Multivariable control of overhead and bottoms composition of a binary distillation column subjected to feed flow disturbances has been studied. The study has been performed using a pilot scale column, equipped with overhead and bottoms composition analyzers, operated under the control of an IBM 1800 digital computer. The column dynamic behavior, for control law calculation, was approximated by a two state variable model. Experimental results employing multivariable feedback and multivariable feedforward-feedback control laws are presented.     

Flow regimes for condensation of a vapour inside a horizontal tube

Experimental data are reported for local heat transfer coefficients during condensation of a pure vapour inside a horizontal tube. Approximately 800 lo     

Adaptive control of a binary distillation column using quadratic programming

A quadratic cost function for the optimal control of binary distillation column was minimized using quadratic programming. An input-output model was used and its parameters were recursively updated by instrumental variable method. A control experiment was conducted for the performance appreciation of the control technique. The performance of the adaptive control was found to be much improved comparing with the conventional PID control. The technique was capable to obtain fast solution and easy to apply for the multi-input-multi-output systems. And also the algorithm was stable for a long term operation which is very critical for the industrial application.     

The break-up of thin liquid films due to the intensity of mass transfer in absorption

The break-up of thin liquid films during gas absorption has conventionally been attributed to the Marangoni effect. Point-to-point variations in surface tension are thought to arise as a result of the absorption process, the consequent surface convection leading to the break-up of the film into rivulets. In this paper, attention is drawn to a relatively unknown type of instability induced by high intensity interphase mass transfer. This type of instability may occur during the absorption of highly soluble gases and should be considered in conjunction with any associated Marangoni phenomena. In the case of absorption of pure vapours or gases, point-to-point variations in surface tension cannot occur and, under such conditions, film break-up may be the result of instability induced by high interphase flux of solute. Experiments on absorption of acetone into a spherical water film were carried out to support the above hypothesis, and a photographic study demonstrated the behaviour and break-up of the film.     

Simultaneous heat and mass transfer in a packed binary distillation column

A simultaneous heat and mass transfer model was applied to a binary system in a 3-in. distillation column packed with $\text{1}\text{4}$in. Raschig Rings. MaThe experiments carried out with the toluene-trichloroethylene system show that the liquid phase is saturated, indicating no resistance to mass transfe     

Numerical and experimental study of a falling liquid column

The collapsing liquid column phenomenon has been experimentally and theoretically studied. The experimental data demonstrated the development and travel of a shock wave. Point velocities within the flow regime were measured using a hot film probe. The numerical simulation was performed using a finite difference code similar to the Marker and Cell technique. The results were in good agreement with the experimental data. The numerical technique therefore promises to be a valuable aid in studying highly convective, incompressible flows.     

Silicic acid column chromatography: Parameters for a binary solvent system

The elution characteristics of methanol-benzene solvent systems were determined by separating a mixture of polar and nonpolar fatty methyl esters by liquid chromatography on silicic acid columns. A series of curves were plotted showing the relationship between the elution volume of each component and methanol concentration of the stationary phase. The resulting graphs serve as a basis for predicting elution conditions for separating other polar materials. Adsorption isotherms were plotted from equilibrium studies of methanol-benzene systems on silicic acid. Methanol concentrations of the effluents from various columns were determined by refractive index. An abrupt concentration change occurs in the methanol content of the effluent when the mobile solvent is either richer or poorer in methanol than the equilibrated solvent. Elution position of this abrupt change depends upon the concentration of methanol in both the mobile and the stationary phases. The procedure has been rigorously standardized because small variations in the amount of methanol on the column create large differences in elution volumes. No. Util. Res. and Dev. Div., ABS, USDA.