Vapor-splitting ratio

Similarly for the side rectifying column, a vapor split ratio... 

In the same way, for the side rectifier, aU refluxes can be written in terms of the bottommost reflux (/ a3) and the vapor split ratio, given in Equations 6.16 6.18... 

After the compressor in the stripper vapor line, the vapor line splits into two lines, one going to the prefractionator and the other going to the sidestream side of the wall. Control valves were inserted in both lines. A ratio control system is used to keep the vapor split constant. The total vapor from the stripper is determined by the compressor (to hold pressure in the stripper) and is measured. This flow signal is sent to a multiplier, whose other input is the desired ratio of vapor to the prefractionator to total vapor (the vapor split ratio). The output of the multiplier is the set point signal of a flow controller that controls the flow of vapor to the prefractionator by changing the position of the control valve in the line. 

Split Injection2 In the split injector, the injected sample is vaporized into the stream of carrier gas, and a portion of the sample and solvent, if any, is directed onto the head of the GC column. The remainder of the sample is vented. Typical split ratios range from 10 1 to 100 1 and can be calculated from the equation ... 

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... 

Split vent. The sample vapors that do not enter the column are ejected through the split vent. A needle valve on this line regulates the total flow of carrier gas into and from the inlet, generating the split ratio, which determines the portion of sample that enters the column. The split ratio is the ratio of the split vent flow to the column flow and provides a measure of the amount of sample that actually enters the column from the injection. A split ratio of 100 1 indicates that a lpl injection from the syringe results in approximately 10 ml of liquid sample reaching the column. 

The total condenser consists of a stage with heat rejection, and a splitter that splits the condensed vapor into a reflux and a liquid product. The stage heat rejection rate is one degree of freedom, and the splitter split ratio is another. Hence, a total condenser adds two degrees of freedom to the column. 

The partial condenser with vapor and liquid products is represented by an equilibrium stage and a splitter, each of these units having one degree of freedom The heat rejected at the equilibrium stage and the splitter split ratio. This type condenser also adds two degrees of freedom to the column. 

The second type of inlet, called a splitter (Fig. 22.7), again uses a syringe to inject the sample. The sample is vaporized and effectively mixed with carrier gas in the mixing tube, after which the vapor passes over a tapered hollow needle. Because of the difference between the inside diameter of the mixing tube outlet and that of the tapered needle, a fraction of the total sample is introduced into the column as a narrow zone. The splitting ratio is a function of the pressure in the inlet, and can be varied. Such a sample splitter is used with capillary columns and high-resolution columns because of their relatively low capacity. 

The flow rate through the column and the split valve changes in various ways, so that the split ratio varies. The effect of the sample splitting depends on the moment at which the cloud of vapor passes the split point. If the needle discharges the sample near to the column inlet, the pressure wave delivers most of the sample vapor into the column, but if the sample is discharged at a point above the column inlet, the cloud of vapor passes the split point just when the pressure drop begins (Period B). The pressure at the inlet of the column is then... 

The term linearity is used today to indicate that the split ratio is identical for all sample components. This is the basic precondition for ensuring that the small amount of sample material analyzed by the column has the same composition as the sample in the injector. However, it does not mean that the true split flow must be the same as the pre-set split flow. A complementary concept is the idea of discrimination, which is the opposite of linearity. Discrimination is not a very important effect in the headspace technique as the sample is already in vapor form, but it is considerably more significant in liquid injection [11]. 

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