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PackView™ - quantitative analysis of packing mal-distribution

The last issue of Tracerco Insight (Vol 6 Ed 1) featured our patent pending FrothView™ technology illustrating how using Tracerco’s new measurement detector technology and analysis of gamma scan data provides quantitative information about the useful capacity of trayed towers. In this article you will learn how applying this technology to packed towers can determine the % liquid fraction providing a measure of the maximum useful capacity of the packing.

Enhanced quantitative analysis of Tracerco Diagnostics™ Scan results
Once beyond questions concerning damage to internals and flooding within a packed tower, the next big concern is the state of liquid distribution through the beds. Historically gamma scan analysis has relied upon performing two sets of parallel scanlines (given the tower diameter is sufficiently large) through the packing as shown in Figure 1, commonly referred to as a grid scan.

The reasoning goes that all scan parameters being constant, particularly the length or path of radiation through the column, uniform liquid distribution can be confirmed by all four scans detecting identical radiation. Figure 2 is a typical example of grid scan results showing all four scanlines matching, implying good liquid distribution.

On the other hand, Figure 3 represents a grid scan where the lines do not seem to match very well but is this liquid mal-distribution? If so, what is the quantity of liquid mal-distribution? Up until now the available qualitative analysis of a gamma scan is not able to answer this very well.

Tracerco has developed an enhancement in detection capability and data presentation that is termed a liquid retention scale. Figure 4 shows typical scan results through a bed of packing. Overlaid on the data is a density scale.

The density scale begins at the density of the dry or non-operating packing. To derive this value it is necessary to know the packing type to reference its dry bulk density. The density scale to the left of the dry packing density is the calculated density of the liquid retained in the bed of packing. As with the normal gamma scan analysis, if the four scanlines have matching liquid retention densities then the implication is the liquid distribution is good. However, if there is a difference between the scanlines, the retention density gives a numerical comparison from which to gauge the extent or severity of any liquid mal-distribution.

Back to Figure 3 – how “bad” is this liquid mal-distribution? Figure 5 shows the scan results from Figure 3 with the liquid retention scale in place. The spread in density from the lightest density, 104 kg/m3, scanline (blue) to the heaviest density, 136 kg/m3, scanline (black) is 32 kg/m3. Scans of dry towers (tower is not operating so presumably no liquid mal-distribution!) have shown that we naturally get a variation of radiation readings corresponding to a 16-32 kg/m3 difference. Based on this guideline a 32 kg/m3 difference among scanlines would hardly seem to be a significant operational problem.

Figure 6 is an example of liquid mal-distribution seemingly becoming a bigger concern. As seen from the liquid retention scale in Figure 6 the spread in density from the lightest density, 24-32 kg/m3, scanline (blue) to the heaviest density, 120 kg/m3, scanline (black) is 88-96 kg/m3. This is a relatively large difference in liquid density so would represent significant liquid mal-distribution.

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