Columns dual-stream

FIGURE 2.1 Flow diagram for dual-stream HPLC with guard column regeneration. 

FIGURE 2.3 Autosampler set-up for performing dual-stream HPLC with guard column regeneration (A) overall view, (B) zoomed view of the valving configuration. 

The results of the mass balance are summarized in Table VI. The ratio of the mercury found in the gas stream to the amount of mercury released from the coal but not recovered in the ash is given in the third column. The average of this ratio is 1.19, with a standard deviation of 0.24. Within one standard deviation unit there is not a significant difference between the measured ratio and the expected ratio of 1.0. Therefore, based on 14 ratios at one plant, there is not a statistically significant difference between the total mercury found in the stack gas and the amount expected in the stack gas from the coal and ash determinations. Dual tests 13 and 14 showed close ratios of 0.88 and 0.95. 

Let us consider a CSTR/separator/recycle system, where the first-order reaction A —> P takes place. Figure 4.3(a) presents the conventional control of the plant. The fresh feed flow rate is kept constant at the value F0. The reactor holdup V is controlled by the effluent. The reaction takes place at a constant temperature, which is achieved by manipulating the utility streams. Dual-composition control of the distillation column ensures the purities of the recycle and product streams. 

Distillate purity is controlled by manipulating reflux flow. Note that we have chosen to use dual composition control (controlling both distillate and bottoms purities) in the distillation column, but there is no a priori reason for holding the composition of the recycle stream constant since it does not leave the process. It may be useful to control the composition of this recycle stream for reactor yield pur-... 

Let s look again at the simple reaetor/column process in Fig. 2.5. In Sec. 2.4.2 we proposed two control structures where both the bottoms composition xB it he plant product) and the distillate composition xD (the recycle stream) are controlled, i.e., dual composition control. Bottoms composition must be controlled because it is the product stream leaving the plant and sold to our customers. However, there is a priori no reason to control the composition of the recycle stream since this is an internal flow within the plant. 

For the reversible case, we are interested in the composition of the bottoms stream from the DIB column. We may consider dual composition control (controlling both the n.C-4 impurity in the top and the zC impurity in the bottom). Logic would dictate that the distillate composi-... 

Step 8. The previous steps have left us at this point with two unassigned control valves, which are the reflux flows to each column. As discussed in Chap. 6, these are independent variables and can be fixed by flow controllers. We do not need dual composition control for the irreversible case because only one end of both columns is a product stream leaving the process. These two reflux flowrates are available in Step 9 to use as optimizing variables or to improve dynamic response. However, we may need dual composition control in the DIB column for the reversible case as mentioned in Steps 4 and 5. 

The development of in situ electrolytic methods by Allied Chemical resulted in a novel unit, the electropulse column, in which mass transfer and electrolytic reduction are carried out simultaneously (25). The basic feature of the electropulse column, (Fig. 3), is the dual function of the horizontal perforated plates, acting as cathodes as well as pulse plates, and the introduction of vertical anode screens contained in porous ceramic sleeves. This design was found particularly suitable for Pu-U partitioning, since it permits operation with an aqueous-continuous phase, which is needed to maintain adequate electrical conductivity, while the organic to aqueous flow ratio is kept quite large to obtain a high plutonium concentration in the exiting aqueous stream. 

The reflux flow rates on both columns are fixed dual composition control is not used to keep the column control systems as simple as possible. In some situations better control may be achieved by using dual composition control in the columns to prevent the impurity levels in the recycle streams from becoming so large that they affect conditions in the reactor. 

Figure 11 Illustrates a simplified arrangement of components and the magnitude of operating parameters for the concentration of deuterium by dual-temperature exchange between hydrogen sulfide gas and liquid water. H2S Is circulated In a closed loop counter-current to a descending stream of water. In the colder column deuterium concentrates In the liquid phase the equilibrium constant for the exchange at the cold temperature, 30°C, is 2.20.

Heat removal at intermediate points on the tower can be attained by withdrawing an internal liquid stream from the tower, cooling it and returning it to the column. The cooling medium is usually the crude oil charge which is being preheated before entering the furnace. Thus, a dual benefit is reaUzed. This can be done in one of two ways. 

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