Kaibel columns

Due to the tremendous costs associated to distillative separations, many alternate schemes to the simple column shown above have been proposed over the past several years both to improve on some of its inherent costs. Traditionally, when purifying a multicomponent mixture, an entire series of distillation columns are used in series, and the way in which these columns are sequenced may make a tremendous difference in the eventual process costs. However, due to the large energy requirements of even the most optimal sequence, more complex column arrangements have been proposed and subsequently utilized. These arrangements include thermally coupled columns such as side rectifiers and strippers, the fully thermally coupled columns (often referred to as the Petlyuk and Kaibel columns). 

Examples of such complex distillation structures are thus columns that have more than one feed point and/or more than two product streams, like distributed material addition/removal columns, and thermally coupled columns. Obviously, as the complexity of the distillation structure increases, so does the design itself thereof. This chapter will, as an introduction to complex column design, treat the design of elementary complex columns such as distributed feed and sidestream withdrawal columns, and side rectifiers, and strippers, before discussing more intricate complex columns like fully thermally coupled columns (sometimes referred to as the Petlyuk and Kaibel columns) in the subsequent chapter. Despite... 

In this section, we will briefly discuss properties and insights of the four-component Kaibel column by looking at some general column properties and specifically investigating the consequences of imposing a sharp product distribution. It should be noted that this section is based largely on work of Abbas in his Ph.D. thesis (Abbas, 2011) [30]. Throughout this book, we have mainly considered ternary separation problems because they are easily presented in a 2D space which lends... 

FIGURE TAX Column section breakdown of a Kaibel column. 

Due to the fact that the Kaibel column falls under the same class of column as the Petlyuk column, namely fully thermally coupled columns, much of the design ideas introduced in Petlyuk design are applicable to Kaibel design too. A typical Kaibel column with its associated CS breakdown is shown in Figure 7.41. Here one can see that four products are produced for a certain feed, only requiring the use of a single reboiler and condenser set. 

The fundamental difference between the Petlyuk and Kaibel columns is the removal of an additional sidestream in the Kaibel column, allowing one to theoretically obtain four pure component product streams (D, Su B),... 

The immediate consequence of removing an additional sidestream is that an extra CS is created. For the sake of consistency, we have kept the numbering format of CSs the same to that of the Petlyuk column, and simply labeled the additional CS in the Kaibel column as CS7. 

The resemblance between the Petlyuk column and the Kaibel column are quite blatant from a structural point of view. The addition of another sidestream however means that there are now 12 external degrees of freedom, assuming the feed stream is known 16 unknown material flowrates minus 4 independent material balances. This essentially requires that the compositions of each product stream be specified from... 

FIGURE 7.42 Topical difference point behavior for die Kaibel column. 

Finally, the designer is required to specify an internal composition variable. We elect to use X 3 largely because we understand the basic requirements of this CS, transporting mainly light intermediate (X2) toward the Si product stream. Xa3 should thus be chosen to lie as close to the X2 vertex as possible. The same linear relationship between the difference points between adjacent CSs exist (by mass balance), as shown for a typical Kaibel column in Figure 7.42. 

FIGURE 743 Six different global FPs for the Kaibel column, labeled 1 6. 

FIGURE 7.44 Representation of FP transition in 4> space for the Kaibel column. 

FIGURE 7.45 Difference point behavior for the sharp split Kaibel column. 

This result provides some insight into the often reported control problems of the Kaibel column. It is simply extremely difficult to obtain high purity product when the bounds on operation are so tight. Any deviation off the line in Figure 7.46 dming... 

FIGURE 7.46 Typical operating line for the Kaibel column operating at sharp spht condition. 

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