Cascades stripping section

Application. In addition to providing a relatively simple means for estimating the production of separation cascades, the separative capacity is useful for solving some basic cascade design problems for example, the problem of determining the optimum size of the stripping section. 

Equations 27 and 28 can be used in conjunction, along with the corresponding equations for the stripping section, to produce an ideal plant profile such as is shown in Figure 4 where F is plotted against for the example of an ideal cascade to produce one mol of uranium per unit time enriched to 90... 

Our example system has a flow-controlled feed, and the reboiler heat is controlled by cascade from a stripping section tray temperature. Steam is the heating medium, with the condensate pumped to condensate recovery. Bottom product is pumped to storage on column level control overhead pressure is controlled by varying level in the overhead condenser the balancing line assures sufficient receiver pressure at all times overhead product is pumped to storage on receiver level control and reflux is on flow control. 

The triple-point crystallization of carbon dioxide is illustrated in Figure 7, which shows a schematic carbon dioxide phase diagram expanded about the triple-point and a closed-cycle triple-point crystallizer operating with pure carbon dioxide. The operation of this closed-cycle unit is identical to that of a unit in the stripping section of a continous crystallizer cascade, except that in the cascade vapor would pass to the unit above, and liquid would pass to the unit below. 

The scrub solution joins the aqueous waste feed stream to constitute the aqueous phase in the extraction section of the contactor cascade its low flow rate and low electrolyte concentration have little effect on the extraction section. The scrubbed solvent passes to the strip section of the cascade, where it is contacted with 1 mM nitric acid to transfer the cesium to the aqueous phase. This concentration of nitric acid was chosen to minimize the DCs for best stripping efficiency, while maintaining sufficient acidity to keep the amine protonated and sufficient ionic strength for adequate coalescence. 

Figure 19.15. Staged permeation cascade with rectification and stripping sections. The individual membrane modules may be operated concurrently or counterconcurrently, or perfect mixing may be assumed to occur.

FICURE 30.2 Recycling cascade with enriching and stripping sections. 

Stages of the cascade are numbered consecutively from 1 at the waste end of the plant to n at the product end. The highest stage of the stripping section is numbered ng. 

The streams that move away from the ends of the cascade, that is, the tails stream in the enriching section and the heads stream in the stripping section, are known as reflux. 

This is the equation usually used to estimate the start-up time of a separation cascade. In most cases, it overestimates the time somewhat, because tw for a plant without stripping section is usually negative. 

How many stages are needed in the stripping section In the enriching section Where in the cascade does the maximum value of the reflux ratio (tails to product) occur What is this maximum value ... 

If heavy water containing 99.8 a/o D costs 150/kg D2O when made from natural water containing 0.015 a/o D in an ideal cascade without stripping section, what would be the cost in dollar per kilogram of contained DjO in water containing 1 a/o D 0.1 a/o D Assume that natural water costs nothing and that the unit cost of separative work is constant between 0.015 and 99.8 percent D. 

Stages / + 1 through n constitute the raffinate stripping section of the cascade, where the raffinate solution is exhausted of its C content. The primary raffinate product Rn is divided into two streams Pr, the saturated raffinate product, may be further treated to remove solvent and to provide the finished raffinate and operation not concerned with the extraction operation and which when mixed with the extracting solvent S, provides the raflSnate reflux Pn, Bn, and Pr are of the same composi-... 

Sa = solvent removed from the raffinate, B-free basis, s = a stage in the raffinate-stripping section of a cascade. X = weight fraction. 

The equation used to calculate SWU for a cascade with enriching and stripping sections is as follows ... 

An arrangement for this is shown in Fig. 10.27. The feed to be separated into its components is introduced at an appropriate place into the cascade, through which extract and raffinate liquids are passing countercurrently. The concentration of solute C is increased in the extract-enriching section by countercurrent contact with a raffinate liquid rich in C. This is provided by removing the solvent from extract to produce the solvent-free stream E part of which is removed as extract product and part returned as reflux Rq. The raffinate-stripping section of the cascade is the same as the countercurrent extractor of Fig. 10.18, and C is stripped from the raffinate by countercurrent contact with solvent. 

For solute 1, the cascade to the left of the feed stage is called the scrubbing section or the stripping section since solute 2 is stripped/scrubbed away by phase R from the extract phase product at the left end. The cascade to the right of the feed section is called the extraction section since solute 1 is extracted from phase R into phase E in this section. Employing some simplifying assumptions, we can determine the extent of separation achieved in this cascade. First, we assume that phases E and R are completely immiscible. Second, we are dealing with dilute solutions and constant partition coefficients for both solutes. Third, both the extract and the raffinate phases have no solute (i = 1,2), as they are introduced into the cascade. 

These basic results allow us to determine the number of stages needed in the stripping section and the enriching section to achieve a certain difference in the composition from the top product Xiu to the bottoms product Xi26 in the ideal cascade having a feed of composition xy. For the enriching section, we can start from stage 1 ... 

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