Gas capacity factor

The effects of liquid and gas flow rates for this absorption are given by Equation 3-13 using the exponents applicable to Uquid-fflm-controlled systems. Because 1-normal sodium hydroxide for the standard test system has been replaced with a 3-normal MEA solution as the liquid phase, the values of the overall mass transfer coefficients will be twice those shown for the standard system in Tables 3-3 through 3-6 for lean solvent containing 0.15 mol CO2 per mol MEA. These values are based on a liquid rate of 10 gpm/ft and a gas capacity factor (Fg) of 0.94 Ib - /ft s. 

The phenomenon is best viewed on plots of pressure Ap versus gas load Vq, witii liquid load Ul a parameter (Figure 8.5). Such plots are routinely featured in the promotional material of packing manufacturers. Abscissa values are also often reported in terms of the so-called gas-capacity factor C = yG[PG/(PLPG)]° - This occasions a shift of the plots toward the ordinate but does not alter their appearance. 

Figure 2-2a. Hydraulic characteristics of random 25 mm metal Biatecki rings, valid for the system air/water under normal conditions. Pressure drop Ap/H as a function of the gas velocity uy or gas capacity factor Fy, ul with the specific liquid load ul as a parameter...

If the gas capacity factor Fv,f1 at the flooding point is determined in relation to a given packing element, it is possible to ascertain the operating point marked by the gas capacity factor Fy. The following applies ... 

Fv,u < Fy < Fypi- Depending on the separation process, the gas capacity factor Fy is set at approx. 10—80% of the value at the flooding point. This leads to the following correlation for the column diameter dsi... 

For simplification purposes, it also assumed that the influence of deflections within the packing element on the pressure drop is negligible, compared to the pressure drop in channels dh- Acc. to Fig. 3-12, the ratio of the pressure drops Apojx and Apoj in relation to the gas flow through channels with a diameter of dh can be equated to the ratio of the equivalent channel lengths lx/1, assuming the gas capacity factor Fy is the same, Eq. (3-22) ... 

Figure 4-4. Total liquid hold-up as function of gas capacity factor Fy for various specific liquid loads UL, valid for random 25 mm Intalox saddles, 50 mm NSW rings, Hiflow rings Super and Mellapak 250Y made of sheet metal. System air/water under normal conditions...

Typical curves showing the total liquid hold-up hL can be seen in Fig. 2-2b for 25 mm metal Bialecki rings and Fig. 4-4a-d for selected types of packings with different gas capacity factors Fy, and the specific liquid load ul as the parameter. The influence of the liquid load ul on the liquid hold-up of randomly filled Pall rings is shown in Fig. 4-5a-c, the influence of the packing size in Fig. 4-5a,b and the influence of the material in Fig. 4-5c. 

In order to ascertain the operating range, the relative column load (Fv/Fv,pi)uL=const was determined for each test point The gas capacity factor at the flooding point Fv,pi was derived by iteration, using the method (2-67), and the hquid hold-up in the loading range was determined based on the method presented in Chap. 4.2.6.2. 

Figure 4-12 shows the correlation between the liquid hold-up hL and the specific liquid load Ul, with the gas capacity factor Fy as the parameter. Below the loading line, the liquid hold-up hL increases with ul to the power of 2/3, whereas above the loading line, the influence of the liquid load on the liquid hold-up hL is bigger, hL ul with an increasing exponent n, n > 2/3. 

The correlation between the parameter Cb and the relative gas capacity factor Fv/Fv,f1 and specific liquid load up, acc. to Fig. 4-15, leads to the following correlation at the flooding point ... 

Based on the data given in numerical Example 3.2, the aim is to determine the pressure drop of the packing Mellapak 250Y in a column with ds = 1.0 m for the test system air/water at ambient conditions. The pressure drop will be determined for a liquid load of Vl = 15.7 m3 h- and for the gas capacity factors Fy = 1.6 /Pa and Fy = 2.3 V -The experimentally derived values are as follows, acc. to Kuzniar and Nizahski [25, Chap. 3] ... 

When describing the pressure drop and the liquid hold-up for counter-current two-phase flow, it is recommended to use the gas capacity factor Fy relating to the maximum value at the flooding point Fv,fi- The liquid hold-up hp as well as the parameter Cb, Fig. 4-15, are dependent on the relative gas capacity Fv/Fyn- The liquid hold-up can be determined using Eq. (4-39), and the parameter Cb based on Eq. (4-55). The calculation of the pressure drop above 65% of the flooding point, based on Eqs. (4-48) and (2-72), can be performed with an accuracy of approx. 20%, Fig. 4-17. 

The value Fq is also called vapour (gas) capacity factor. The maximal permissible value of the capacity factor depends on a dimensionless flow parameter if/ equal to the ratio of values proportional to the dynamic pressures of the liquid and the gas phase, m- to be precise, to the square root of this ratio. 

Fg = vapour (gas) capacity factor, without taking into account the... 

Fig. 10. Pressure drop of metal Raschig Super Rings No. 3 dp=lQ mm versus the gas capacity factor Ffs.

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