Column section side strippers

Similarly, Fig. 5.15a shows a thermally coupled indirect sequence. The condenser of the first column is replaced by a thermal coupling. The four column sections are again marked as 1, 2, 3, and 4 in Fig. 5.15a. In Fig. 5.156, the four column sections are arranged to form a side-stripper arrangement. ... 

The side-rectifier and side-stripper arrangements have some important degrees of freedom for optimization. In these arrangements, there are four column sections. For the side-rectifier, the degrees of freedom to be optimized are ... 

The partitioned thermally coupled prefractionator in Figure 11.14c can be simulated using the arrangement in Figure 11.14b as the basis of the simulation. However, like side-rectifiers and side-strippers, fully thermally coupled columns have some important degrees of freedom for optimization. In the fully thermally coupled column, there are six column sections (above and below the partition, above and below the feed in the prefractionator and above and below the sidestream from the main column side of the partition). The degrees of freedom to be optimized in partitioned columns are ... 

By eliminating the reboiler and condenser in the prefractionator column in Fig. 13-67a (the column containing sections 1 and 2) we obtain a thermally coupled system, also known as a Petlyuk system, shown in Fig. 13-67b [Petlyuk, Platonov, and Slavinskii, Int. Chem. Eng., 5, 555 (1965)]. Side stripper, side rectifier, and Petlyuk systems can also be built as divided wml columns, as explained in detail in the subsection below on thermally coupled systems. 

The internal modifications to retrofit the distillation system consider the distillation column and its internals. In this level of retrofit, some changes are made in the internals or nozzles of the main column and the side strippers. Moreover, the reboilers and pump around loops are examined and adjusted as required. Therefore, more complex modifications are required at this level that lead to higher investments. The objective of these modifications is to find out the ideal distribution of stages for each section in the main column [4]. This ideal design is applied to the existing column by modilying its internal to the niinimrim extent to reduce the costs. 

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. 

Module 2 models the draw tray and consists of a mixer and an equilibrium stage. Module 3 is a splitter that takes the liquid from the draw tray and splits it into side draw SD and the remaining liquid flowing down to the bottom column section. The side-stripper and the upper column section are modeled with column sections, modules 4 and 5, and the condenser is modeled with an equilibrium stage, module 6. Using computational sequence 1,2, 3,4, 5, 6 requires initialization of streams L3, L5, OH, and R. 

By thermal coupling the heat is transferred by direct contact between vapour and liquid flows that connect sections of different columns. This is a major difference with heat integrated columns , where the heat exchange takes place by condenser/reboilers. Hence, thermal coupled columns have a more complex behaviour. Figure 11.21 illustrates two basic arrangements with side-columns. The first is the side-rectifier, derived irom a direct sequence. The second one is the side-stripper that corresponds to... 

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. 

Notice that in both configurations that they are very closely related to simple columns. For the side stripper, for instance, the simple column has a feed of flowrate F and quality q, a bottoms product of flowrate B and composition x. One can show by mass balance that CS2 produces a distillate product, or a pseudo distillate, of flowrate A2 = V2 — L2 and composition Xa2. Thus, for all practical purposes the CS above and below the feed is just a simple column with one feed and two products. One can in a similar way deduce that the CS2 in the side rectifier acts as a conventional product producing stripping section with a flowrate of — A2 =L2 — V2 (since product flowrates have to be positive) and bottoms composition of X. ... 

FIGURE 635 Column section breakdown across the feed stage for (a) a side stripper and (b) a side rectifier. 

The RadFrac block can be used for the ordinary distillation column and also for the extractive distillation column as shown in the example in Section 3.1. It can also be used as strippers (with a reboiler but no condenser), rectifiers (with a condenser but no reboiler), absorbers (with neither), and more complex columns with side pmnp-around. In the following, several columns other than the ordinary distillation will be outlined. The RadFrac can also be used as a heterogeneous azeotropic distillation column with decanter replacing the reflux drum at top of this column. The vapor-liquid-liquid calculation can be performed inside the column if needed. 

Understand Process Characteristics H2, H2S, and NH3 and light ends are removed from reaction effluents through a series of separation and flashes, resulting in the reaction products in a liquid form, which goes to the stripper, the feed heater, and then to the main product fractionator. The task of the product fractionation is to separate different products based on their product specihcations such as distillation endpoint, ASTM D-86 T90% or T95% point, and so on. Side draws from the column go to the product strippers where kerosene and diesel products are made. The net draw from the column bottom is called unconverted oil (UCO), which is recycled back to the reaction section for nearly complete conversion. There are two pump-arounds, namely, kerosene and diesel pumparounds, as a main feature of heat recovery from the main fractionation column. 

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