Loading region

For Figure 9-21A the loading region is centered about the 0.75 in/ft pressure drop curve the preferred design range being 0.35 to a maximum of 1.0 in. of water/ft. 

Figure 9-21D indicates the loading region as centered about line B, which is a reasonable upper design condition. 

Figure 9-21F is the most current updated version of the GPDC as presented by Strigle [139] to facilitate interpolation of the ordinate and pressure drop curves on the chart. The flooding and loading regions are not identified. For this chart ... 

Below the loading region, the pressure drop can be read from appropriate system curves if they are a ailable, as Figure 9-20. However, for general use the data have been well correlated. Figures 9-21B-9-21F. The slope of most of the curves for pressure drop indicate a proportionality of 1,8 to 2.8 power of the superficial gas mass... 

Comparison with Figure 9-21C gives 3 in. water/ft (parameter) or a total of (3) (45) = 135 in. water. Neither of these values represents a condition (flooding) that should be considered for tower operation, except under known experience studies. Distillation operations sometimes operate above flooding, but other types of contacting normally require operations in the loading region (or below) for stable performance. 

This indicates operation in the loading region. The expected pressure drop is 0.5 in. water/ft. 

For all liquid flow rates, as gas flow rate is raised, a point is reached when the gas velocity begins to interfere with the free drainage of liquid. Liquid will start to accumulate or load the bed, giving this region the name the loading region. The accumulation of liquid reduces the crose-section area available for gas flow and therefore... 

Raising gas velocity past point B moves column operation into the loading region. Initially, efficiency improves because of the greater liquid holdup (region B-E), but this improvement is short-lived. As the flood point is approached, the efficiency passes through a maximum (point E), and then drops (region E-C) because of excessive entrainment. 

Vapor maldistribution may be induced by liquid maldistribution (66) when vapor flows are high. Regions of high liquid holdup impede vapor rise and channel the vapor into the lighter-loaded regions (66). Since liquid tends to accumulate near the wall, vapor will tend to channel through the center. 

Data show a clear loading region (ses Figure 8.16a). HETP in the loading region is lower than the listed HETPs. 

Values are based on countercurrent flow of liquid and air at atmospheric pressure. In the range between the loading region and the flooding point, an approximation of pressure drop Ap at gas mass velocity G can be obtained from Ap = ApF(G/Gm). The pressure drop at the loading point is usually in the range of one-fourth to one-sixth of the pressure drop at the flooding point... 

For each packing, sketch an empirical curve such that (a) its upper end passes through the point Fsf, APF with a slope approaching infinity, and (b) its lower end becomes tangent to the straight, wet-pressure-drop line at an abscissa value of Fsf/2. These two pressure-drop curves for the loading regions are shown by the dashed lines of Fig. 11.1. 

Locating 0.0756 and 0.0563 on Figure 9-21C reading the intersection indicates a condition in the lower loading region, and a pressure drop of approximately 0.60 in. water/ft of packing. 

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