9.4.7 Concluding comments on design philosophy
The design proposed in Sec. 9.4.6 was shown to satisfy all the performance criteria, and is optimized for Pall® rings. The next section will speculate how it can be further optimized using third-generation packings.
The example reflects a major difficulty often encountered in packed-tower design: the inability to tell whether a correlation will give a suitable prediction for the service under consideration. For many years, this difficulty was circumvented by grossly oversizing packed towers. With the recent renaissance of packed towers, which was coupled by a fierce competition among the suppliers, the over-sizing eroded away. The prediction problem remained. While in the past this problem stayed hidden in an oversized column, it raised its ugly head once the oversizing eroded. The result was a relatively large number of designs failing to meet their performance objectives.
It is important to recognize that working with packed-tower correlations alone is not sufficient for ensuring that a design will work. Data interpolation is far superior to our present correlations, and is the only reliable design tool. When no data are available to interpolate for a given packing in a given service, the designer has only two options: either to grossly oversize the column or to gamble.
The design strategy in Sec. 9.4.1 has been tailored to this state of the art. Chapters 10 and 11 contain all the data that the author could find in the published literature, and present them in a manner that can be readily interpolated.
The above also has strong implications when it comee to selecting a supplier of proprietary packing. Proven track record of a packing in a given service should always be a major consideration, especially when backed by actual performance data. Remember, the availability of good performance data can—and often does—make a difference between success and failure.
9.4.8 Column sizing example: speculation on suppliers' modifications to the preliminary design
As per step 4 in Sec. 9.4.1, the preliminary design in Sec. 9.4.6 will be sent to the suppliers of third-generation packings. The inquiry will request a quote for an alternate design. Below is a speculation on the response of a typical packing supplier. The estimate is based on a typical metallic third-generation packing with a packing factor of 18 in the bottom section and 24 in the top section. All major suppliers market packings that roughly have these packing factors.
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