Column pressure drop

In chemical engineering the Ergun equation (Equation 2.21) is well known for the estimation of friction numbers and corresponding pressure drops for fixed beds with granular particles  

It covers the broad span from fine particles to coarse materials (Brauer, 1971). For chromatographic columns small, more or less spherical particles are used. Therefore, the Reynolds numbers are very small and inertial forces can be neglected. Equation 2.21 then reduces to its first term, which represents the pressure drop because of viscous forces only. 

Introducing Equation 2.22 in the reduced Equation 2.21 leads to Equation 2.24  

This equation is identical to Darcy s law (Equation 2.25), which is well known among chromatographers (Guiochon, Golshan-Shirazi, and Katti, 1994)  

The coefficient feo typically lies between 0.5 x 10 and 2 x 10. This agrees with Equation 2.26 where a void fraction of 0.4 results in a corresponding value of 

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A vapor feed is favored when the stream leaves the upstream unit as a vapor or when most of the column feed leaves the tower as overhead product. The use of a vapor feed was a key component in the high efficiency cited previously for the spHtter, where most of the feed goes overhead. Low Column Pressure Drop. The penalty for column pressure drop is an increase in temperature differential ... 

Example 13 Packed Column Pressure Drop Air and water are flowing coiinterciirrently through a bed of 2-inch metal Pali rings. The air mass velocity is 2.03 kg/s-m (1500 Ihs/hr-fd), and the liquid mass velocity is 12.20 kg/s-m (9000 Ihs/hr-fr). Calculate the pressure drop hy the generalized pres-... 

Figure 1. F Factor as a function of column pressure drop and tray spacing.

Allowing 10 psig column pressure drop, bottoms pressure = 20 psig (1,800 mm Hg abs)... 

Lower pressure drop and greater usable capacity allow use of smaller diameter columns. Pressure drop per stage is 30-50% less than either size Pall ring. 

For highly varying vapor loads through the column, pressure drop may be estimated for differences in latent heats from one point in the column to another, the pres-... 

Neglects effect of distillation column pressure drop. 

Solution Ideal gas behavior is a reasonable approximation for the feed stream. The inlet concentrations are 287mol/m of methane and 15mol/m of carbon dioxide. The column pressure drop is mainly due to the liquid head on the trays and will be negligible compared with 8 atm unless there are an enormous number of trays. Thus, the gas flow rate F will be approximately constant for the column as a whole. With fast reaction and a controlling gas-side resistance, c = 0. The gas-phase balance gives everything that is necessary to solve the problem ... 

The viscosities of supercritical fluids are intermediate between those of a gas and a liquid, but this tine, are much closer to those of a gas than a liquid. For a fixed column pressure drop much longer columns or higher flow rates are possible in SFC compared to liquid chromatography. Liquids, however, are virtually incompressible while gases and... 

The viscosity of the carrier gas determines the column pressure drop for a given velocity. For hydrogen, helium, and nitrogen it can be approximated by equations (1.53 to 1.55) in the temperature range of interest for gas [Pg.545]

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... 

Where a large number of stages is required, it may be necessary to split a column into two separate columns to reduce the height of the column, even though the required separation could, theoretically, have been obtained in a single column. This may also be done in vacuum distillations, to reduce the column pressure drop and limit the bottom temperatures. 

Fluid flow in packed columns Pressure drop... 

Much of the recent impetus for temperature control has focused on exploiting the effects of elevated temperature on viscosity and diffusion coefficients [2], These lead to faster separations and also allow smaller particle diameters to be employed with conventional HPLC hardware. As the viscosity of solvents decreases, the column pressure drops. This can be exploited by using faster flow rates and smaller particle diameters. All of this leads to faster separations. In one experiment in this laboratory, a separation which required 8 min at room temperature was reduced to 2 min at 50°C without changing the column. Speed enhancements of as much as 50-I00-fold have been reported [13] as shown in Figure 9.1. 

Figure 12 shows the flow rate stability versus load (input pressure drop). A variable orifice connected to the sampler was used to adjust the pressure drop over a range of 0-16 inches water column pressure drop. Flow rate was monitored by a rotometer. The flow rate was constant to within i 2 percent(3). ... 

As the liquid holdup increases, the effective orifice diameter may become so small that the liquid surface becomes continuous across the cross section of the column. Column instability occurs concomitantly with a rising continuous-phase liquid body in the column. Pressure drop shoots up with only a slight change in gas rate (condition C or C ). The phenomenon is called flooding and is analogous to entrainment flooding in a tray column. 

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