Distributed feed columns design

It is apparent that the single feed column is the one limit on the distributed feed column. At the other end of the design spectrum, one may theoretically choose to split the feed stream in infinitely many substreams, resulting in infinitely many CSs. Although this may seem like a purely academic or impractical limit, it does have some use because the feasible region resulting from this will show us all possibilities when deciding on a column. Thus, the profiles of any feed stream division will lie in... 

Try this for yourself Reproduce Figure 6.10 using DODS-DiFe and the given parameters. Try and find other minimum reflux designs for a distributed feed column by changing parameters such as a, Rai f< < product compositions. 

The reader should be aware that the minimum reflux scenarios presented here are just one of three possible ways the minimum reflux limit can be obtained in distributed feed columns. The designs shown thus far all depicted minimum reflux when the vertex of the internal CS adjacent to the topmost rectifying section lies exactly on its profile, that is, a pinch occurs on the topmost rectifying CS. It is perfectly valid for the minimum reflux condition to be determined by the bottommost stripping profile, or indeed where the TTs of the internal CSs do not overlap one another. The latter case is shown in Figure 6.12 where the column reflux has been reduced and TTs cascade around one another, thereby limiting any further column reflux reduction. The general requirement for minimum reflux is however the same as for simple columns any reflux value below the minimum reflux value will lead to a discontinuous path of profiles, and minimum reflux is therefore the last reflux where a continuous path is still maintained. 

F Feed stream designation or molar flow rate H Vapor stream molar enthalpy h Liquid stream molar enthalpy K Distribution coefficient L Liquid stream designation or molar flow rate N Number of equilibrium stages in a column P Pressure... 

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... 

It is also interesting to note that, from a mathematical point of view, these strange positions of X that may be created through distributed feed addition allow the roots of the DPE to be complex. The profiles are in such cases, of course, still perfectly valid and it is still possible to design a feasible column if the roots of the DPE happen to be complex in a particular CS. 

What should be clear from the illustrations presented in Ingures 6.5 6.8 is that the concept of distributed feed addition columns presents unique opportunities to the designer. Each stream addition gives the designs an additional degree of freedom that may be used to manipulate profiles to suit the separation. However, although... 

It should be mentioned that the majority of the work presented here is graphically based simply because it is easier to grasp column into-actions and behavior when approached from this point of view. However, this need not be a limitation for the methods. The authors would also like to stress that it is not necessarily the specific material and problems presented in the book that are important, but more the tools that the reader should be equipped with. The concepts we present simply put tools into the designer s hand for him/her to create a unique column or separation structure that may solve his/her particular separation problem. For instance, both distributed feed and reactive distillation columns are discussed independently, although it is of course entirely possible to conceive of a reactive distributed feed system, which is not discussed. The tools in this book will thus first allow the reader understand, analyze, and design well-known and frequently encountered distillation problems. Second, the tools can be used to synthesize and develop new systems that peihaps have not even been thought of yet. This principle applies to virtually all the work in this book and the reader is urged to explore such concepts. 

The entrance of a liqmd-flashing vapor mixture into the distillation column feed location requires a specially designed distribution tray to separate the vapors from the liquid, w hich must drop onto the packing bed for that section in a uniform pattern and rate. 

The C4 Olex process is designed with the full allotment of Sorbex beds in addition to the four basic Sorbex zones. The C4 Olex process employs sufficient operating temperature to overcome diffusion limitations with a corresponding operating pressure to maintain liquid-phase operation. The C4 Olex process utilizes a mixed paraffin/olefin heavy desorbent. In this case it is an olefin/paraffin mix consisting of n-hexene isomers and -hexane. A rerun column is needed to remove heavy feed components such as Cs/C because they would contaminate or dilute the hexene/hexane desorbent. Table 8.5 contains the typical feed and product distributions. 

FBed composition variation. One way of allowing for design uncertainties and fesdstock variation is by installing alternate feed points. In packed columns, every alternate feed point requires expensive distribution equipment. 

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