Distributed feed columns limitations

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... 

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. 

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 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. 

This subsection describes how to generate the feasible combinatorial possibilities of distillation column configurations for separation of mixtures that do not form azeotropes. Components are named A, B, C, D,. . . and they are listed in the order of decreasing volatility (or increasing boiling temperature). We limit our considerations to splits where the most volatile (lightest) component and the least volatile (heaviest) component do not distribute between the top and bottom product. For simplicity we consider only separations where final products are relatively pure components. Systems containing simultaneously simple and complex distillation columns are considered. Simple columns are the conventional columns with one feed stream and two product streams complex columns have multiple feeds and/or multiple product streams. 

Note that we limit our discussions in this book to a single liquid feed that is split and distributed at various points along the column length. The method described can easily be adapted for wapor feeds, as well as for different feed compositions at each addition point. 

Specify the Feed Distribution/Quality. The DiFe package limits the user to only three feed distributions. The fractions of feed split to each part of the column can be set here, along with the quality of that particular feed stream. Each split firaction must be greater than 0 and less than 1, and they must sum to 1. The feed fractions in (b) are equivalent to the feed fraction in (f). Both are linked, so setting a feed fraction at (f) will change the values in (b), and vice versa. Feed qualities should simply be positive scalar quantities. 

As mentioned above, fish larvae have a limited window of opportunity to catch the microdiet particles before they sink to the bottom of the tank and become unavailable. It is also a current practice in modem hatcheries to establish long photoperiod during the larval production (from 16-24 h light). Therefore, it is extremely important that the distribution of the microdiet be split over time in very frequent feeding events. This will give the larvae a chance to catch fresh microparticles in the water column. 

We have a considerable limitation of sharp extractive distillation process in the column with two feeds the process is feasible if the top product components number is equal to one or two. This Umitation arises because, in the boundary element formed by the components of the top product and the entrainer, there is only one point, namely, point iV+, that belongs to the trajectory bundle of the intermediate section. If Eq. (6.11) is valid, then the joining of the trajectories of the intermediate and top sections takes place as at direct split in two-section columns in the mode of minimum reflux. If Eq. (6.12) is valid then joining goes on as at split with one distributed component. 

In general, at intermediate sphts and splits with a distributed component, the calculation from one of the ends of the column for such splits encounters large difficulties. Determination of possible compositions in the feed cross-section of the column is of great importance for overcoming these difficulties. To estimate correctly the limits of change of component concentrations at the trays above and below feed cross-section, this limits have to be determined at sharp separation ([ / i] and [x/] ). 

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