Column evaluation pressure drop

The border profile was studied in order to analyse qualitatively the influence of various foam parameters (surfactant kind and foam film type, foam column height, pressure drop, etc.) on the drainage process as well to check the validity of drainage models [12], The foam was placed in a cylindrical vessel (diameter 2.5 to 4 cm), similar to vessel 6 in Fig. 1.4. It was covered with a lid to prevent evaporation. The pressure above the foam was equal to the atmospheric pressure. The border profile was determined by simultaneous measurement of the capillary pressure at various levels of the foam column, i.e. the r(H) dependence in the direction of liquid flow was evaluated. Thus it was found that the best approximation (among the discussed in Section 5.3.3) appears to be the parabolic model of border profile. 

The vertical thermosiphon reboiler is a popular unit for heating distillation column bottoms. However, it is indeed surprising how so many units have been installed with so little data available. This indicates that a lot of guessing, usually on the very conservative side, has created many uneconomical units. No well-defined understanding of the performance of these units exists. Kern s recommended procedure has been found to be quite conservative on plant scale units yet it has undoubtedly been the basis for more designs than any other single approach. For some systems at and below atmospheric pressure operation, Kern s procedure gives inconsistent results. The problem is in the evaluation of the two-phase gas-liquid pressure drop under these conditions. 

Other parameters that have been used to characterize column performance include the column pressure drop and the column flow resistance.1617 The column pressure drop is simply the difference in pressure observed when the column is or is not in-line. The column flow resistance normalizes for particle diameter, solvent viscosity, and column length. One may also wish to compare issues of cost per analysis and column lifetime in evaluating a column.18... 

Mechanical and chemical stability of novel stationary phases are basic requirements concerning their application. A lack in stability generally causes a loss in resolution and thus reduces column efficiency. In addition, the reproducibility of retention times, being important for qualitative analysis, may be affected. Evaluation of the mechanical stability of polymeric stationary phases is usually accomplished by the determination of the pressure drop across the column, when employing solvents of different polarity within a wide range of flow rates. A stationary phase can be considered as mechanically stable if a linear relationship between applied flow rate and resulting back pressure is obtained. 

Apparatus and Procedure. It was necessary to design more definitive tests to further evaluate the better candidate surfactants. This was accomplished by means of a multi-phase dynamic-fiow test that consists of a small packed bed through which surfactant solution can be passed followed by gas to produce in situ foam. The pressure drop through the column is measured as the fiuid is drawn through the column at a constant volumetric fiow rate. From the recorded data, relative mobilities of the liquid and gas phases may be calculated. The change in gas mobility due to the presence of the surfactant is very closely related to the effectiveness of that surfactant for mobility control in oil core studies. A schematic drawing of the apparatus is shown in Figure 2. 

In the present study, experiments have been performed on a preparative column using pure CO2 as the mobile phase. Experiments have been performed at four different back pressure levels. For each back pressure setting, runs were performed both at low flow rates, i.e. where the pressure drop was negligible and at high flow rates. The main process aspects, i.e. pressure drop, mass transfer and retention have been experimentally evaluated and analysed. 

This data collected for determination of the Knox parameters can also be used to establish the linearity of the pressure versus linear velocity curve to evaluate compression of the bed. Lastly, these data can be used to estimate the effective particle size from the pressure drop. The pressure drop data are aseful to assess the effective particle size with the vendors nominal particle size and particle size distribution data. Calculation of the effective particle size is given by Eq. (7.9), where dp is the particle size in cm, u is the linear velocity in cm/s, p is the viscosity in cP, L is the bed length in cm, k[) is the column permeability (e.g. 1 x 10 for irregular particles and 1.2 x 10 for spherical), and AP is the pressure in psi. 

Another value of the pressure versus flow rate data is when the column is. scaled-up, the plate count and pressure drop can be compared with laboratory data to evaluate their comparability. The plate count provides a means to know how well the column is packed. Developing procedures to pack a laige column well are not obvious. Thus, measurement of the plate count is a u.seful tool for collecting quantitative performance information. 

The internal flow of liquid and vapor must be re-evaluated from the standpoint of column capacity, both in the design and performance studies of columns. The physical dimensions of a column can handle only limited ranges of vapor and liquid flow rates. The objective of this chapter is to evaluate the hydraulic aspects of fluid flow in trayed columns. The column performance is examined with regard to factors such as flooding, entrainment, pressure drop, mass transfer, and tray efficiency. 

For mixtures which behave as ideal solutions, the K values and the vapor and liquid enthalpies of the pure components Kjiy Hjiy h i depend upon the temperature 7 and pressure Pj of each plate j. Methods for taking the effect of pressure into account in the evaluation of the Kj- s, Hj- s, and h s are to be found in standard thermodynamic texts, handbooks, and the scientific literature as described in Chap. 14. The effort required to account for the effect of pressure on the K values and enthalpies may be reduced by taking advantage of the following observations. First, for columns operating at relatively high pressure, the pressure drop across the column is small relative to the total pressure. Thus, in many instances, it is possible to use a single column pressure in the evaluation of the Kji s, Hji s, and h s, and these quantities may be curve fit as a function of temperature alone. 

The formula refers to a reflux ratio v = oo, i.e., for a liquid-vapour ratio FID = 1. Beck [244] evaluated 115 experiments on the system water-air and derived new equations for packing sizes from 8 to 80 mm and column diameters from 150 to 1200 mm. Savkovi5-Stevanovi6, Simonovic and Popovic [244 a] examined the efficiency of a laboratory column (diameter, 25 mm separating length, 1.2 m) by determining the HETP values for various pressure drops and vapour velocities. The packing units were of 0.35 nmi steel wire with a diameter of 4 mm. The system benzene/carbon tetrachloride (30 mol% carbon tetrachloride) was used as test mixture. 

W The feed to a sieve-tray distillation column operating at 1 atm is 700 Ibmol/hr of 45 mol% benzene and 55 mol% toluene at 1 atm and its bubble-point temperature of 201°F. The distillate contains 92 mol% benzene and boils at 179°F. The bottoms product contains 95 mol% toluene and boUs at 227T. The column has 23 trays spaced 18 in. apart, and its reflux ratio is 1.25. Column pressure drop is neglected. Tray efficiency is 80%. Estimate the total bare-module cost of the column, condenser, reflux accumulator, combined reflux and distillate pump, reboiler, and reboiler pump. Also, estimate the total permanent investment Results should be computed using (1) the equations in Chapter 16, and (2) Aspen IPE (Icarus Process Evaluator). Compare the results. 

Tray temperature control is used in most distillation columns to infer product composition, but changes in pressure on the control tray can adversely affect the estimation of composition. Pressure is typically controlled in the condenser, not on the control tray, so changes in vapor flow rates will change tray pressure due to changes in tray pressure drops. Pressure-compensated temperature control was proposed over four decades ago to solve this problem. Measurements of both temperature and pressure on the control tray are used to estimate composition. The method has been qualitatively described in many practical distillation control books, but the author is not aware of any quantitative evaluation of its effectiveness that has appeared in the open literature. 

Different evaluation criteria prove to have an opposite influence. For example, the requirement of good separation efficiency leads to a higher pressure drop and higher costs. The selection of column inter-... 

Before continuing to discuss the buoyancy results, the data for flow induced mobilization, which will be compared with the buoyancy data, are presented in Table 7 and represent experiments performed with Systems 1, 2, and 3. Reported in columns (3), (4), and (5) are the measurements of volume, mobilization flow rate, and the mobilization cell pressure drop which was measured across 12 spheres. Next, it is necessary to evaluate terms in equation (8). This can be obtained from columns (4) and (5), and from the dependence of pressure drop on flow rate for a ganglion-free cell, i.e. ... 

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