Reflux ratio side strippers

The optimization can be carried out using nonlinear optimization techniques such as SQP (see Chapter 3). The nonlinear optimization has the problems of local optima if techniques such as SQP are used for the optimization. Constraints need to be added to the optimization in order that a mass balance can be maintained and the product specifications achieved. The optimization of the side-rectifier and side-stripper in a capital-energy trade-off determines the distribution of plates, the reflux ratios in the main and sidestream columns and condition of the feed. If a partitioned side-rectifier (Figure ll.lOd) or partitioned side-stripper (Figure 11.lid) is to be used, then the ratio of the vapor flowrates on each side of the partition can be used to fix the location of the partition across the column. The partition is located such that the ratio of areas on each side of the partition is the same as the optimized ratio of vapor flowrates on each side of the partition. However, the vapor split for the side-rectifier will only follow this ratio if the pressure drop on each side of the partition is the... 

To redistribute the stages in the remaining sections, a shortcut simulation is used to find out the required number of trays, the feed tray location and the minimum reflux ratio for each column in the sequence. To make use of the existing column with the same number of trays (24 trays) iterations are required to adjust the sum of the rectifying sections in each column equal to 24 (number of trays in the main column). Finally, the sequence of the simple columns is merged into a complex column. The main column is not changed, but the side strippers and pump arounds need to be relocated or adjusted. 

Earlier chapters use simplified and binary models to analyze in a very informative manner some fundamentals such as the effect of reflux ratio and feed tray location, and to delineate the differences between absorption/stripping and distillation. Following chapters concentrate on specific areas such as complex distillation, with detailed analyses of various features such as pumparounds and side-strippers, and when they should be used. Also discussed are azeotropic, extractive, and three-phase distillation operations, multi-component liquid-liquid and supercritical extraction, and reactive multistage separation. The applications are clearly explained with many practical examples. 

The existence of a methane peak is not considered a phenomenon that will always occur with intermediately permeable gases in multicomponent mixtures. Rather, the peak is thought to be the result of a combination of factors. These factors include composition of the feed mixture, pure-gas permeabilities, and the internal reflux ratio. For instance. Figure 3 indicates that the intermediate-gas composition profile will steadily decrease in a stripper 1.0 m long, but otherwise identical to the column used in this study, fed with a 63.6% N2 - 32.3% CH - 4.1% CO2 mixture under similar total reflux conditions. The presence of an intermediate peak, however, is reminiscent of multicomponent distillation profiles and raises the possibility of withdrawing a side stream enriched with an intermediate gas. 

While the net flows patterns for each structure are now clearer, it still remains difficult to comprehend the effects of changing the reflux in one CS in the rest of the column. The reflux ratio in a specific CS is an important parameter in finding feasible structures and therefore it is necessary to fully understand these effects. As shown in previous chapters, the reflux in a specific CS is a limitless parameter valid anywhere from negative to positive infinity. Notice howev that in the side-stripper configuration, for example, that the liquid stream is split into two parts. 

Both these split ratios govern the amount of material sent to the side column and are bound between 0 and 1. Thus, for the side stripper, the refluxes of all the remaining CSs can be determined by specifying the reflux of the topmost CS (/ ai)> and its associated liquid split ratio, as shown in Equations 6.13 6.15... 

The two internal degrees of fi eedom of each column have been specified through the appropriate split ratio and a single, reference reflux. Both Rm in the side stripper and Rm in the side rectifier have been chosen as the respective reference refluxes since they lie the closest to the thermally coupled sections. This choice is of course arbitrary, and one may equivalently choose any CS to serve as the reference CS. 

Specify the reference reflux and a split ratio (/ and in side stripper, and... 

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