Tower-bottom product temperature

The tower-bottom product temperature and composition is the same as the temperature and composition of the feed to the reboiler. 

Regardless of the type of reboiler used, the tower bottom product temperature has to be the same, so as to make product specifications. This is shown in Fig. 5.5. However, the reboiler outlet temperature must always be higher in the circulating reboiler than in the once-through reboiler. This means that it is more difficult to transfer heat in the former than in the latter. 

Solvent oil is a by-product of the platinum reforming plant of petrochemical factories. The target of optimization is to increase the recovery of solvent oil. There are six affecting factors for the recoveiy of solvent oil reflux rate (X]), flow rate of the first side line (X2), pressure at tower top (X3), temperature of reflux (X4), temperature at solvent oil tower bottom (X5), temperature of the 35th-tower plate of solvent oil tower (Xe). Some data from the industrial records are listed in Table 14.2. 

Heavy hydrocarbons, such as vacuum tower bottom products, tar, and pitch, are frequently pumped and stored in tanks above their auto-ignition temperatures. The process reason for this is to prevent these fluids from "setting up" or solidifying in the pipelines or tanks. At ambient temperatures, even in hot climates, these fluids would normally be either solid or extremely viscous. 

But if valve A is opened, and the feed to the reboiler is coming from the bottom of the tower, then the reboiler outlet temperature must be hotter than the tower bottoms temperature. This temperature difference would be quite small if we had essentially a pure component (like butane) as the tower bottoms product. But with a wide boiling... 

In two stage units, it is often economical to distill more gas oil in the vacuum stage and less in the atmospheric stage than the maximum attainable. Gas formed in the atmospheric tower bottoms piping at high temperatures tends to overload the vacuum system and thereby to reduce the capacity of the vacuum tower. The volume of crude vaporized at the flash zone is approximately equal to the total volume of distillate products. Of course, the vapor at this point contains some undesirable heavy material and the liquid still contains some valuable distillate products. The concentration of heavy ends in the vapor is reduced by contact with liquid on the trays as the vapor passes up the tower. This liquid reflux is induced by removing heat farther up in the tower. 

Figure 6-5 shows a stabilizer with reflux. The well fluid is heated with the bottoms product and injected into the tower, below the top, where the temperature in the tower is equal to the temperature of the feed. This minimizes the amount of flashing. In the tower, the action is the same as in a cold-feed stabilizer or any other distillation tower. As the liquid falls... 

Figure 1.9 illustrates the operation of a simple propane-butane splitter. The tower controls are such that both the pressure and bottoms temperature are held constant. This means that the percent of propane in the butane bottoms product is held constant. If the operator increases the top reflux flow, here is what will happen if... 

As a minimum, a distillation assembly consists of a tower, reboiler, condenser, and overhead accumulator. The bottom of the tower serves as accumulator for the bottoms product. The assembly must be controlled as a whole. Almost invariably, the pressure at either the top or bottom is maintained constant at the top at such a value that the necessary reflux can be condensed with the available coolant at the bottom in order to keep the boiling temperature low enough to prevent product degradation or low enough for the available HTM, and definitely well below the critical pressure of the bottom composition. There still remain a relatively large number of variables so that care must be taken to avoid overspecifying the number and kinds of controls. For instance, it is not possihle to control the flow rates of the feed and the top and bottom products under perturbed conditions without upsetting holdup in the system. 

The main difference between the simple rectification and two-step rectification is the presence of the second rectification tower (T2) in the two-step unit. In the latter case, the feed passes to the first rectification tower at a temperature of approximately 200-240°C. Because of the low temperature used, the volatile product from the first tower only forms part of the gasoline fraction. The bottom product from T1 (Fig. 3.16) passes to the oven for heating until it reaches a feed... 

The hydrogen is distilled in the primary tower into a bottom product enriched in deuterium and an overhead product depleted in deuterium. Final concentration of the bottom product is effected by distillation either of liquid hydrogen or water (not shown in Fig. 13.1). The depleted hydrogen flows back throu the feed exchanger system where it is warmed to room temperature. It is returned to the ammonia plant at the supply pressure, being compressed if necessary. 

The bottoms from the primary tower are fed into the upper half of a smaller secondary tower, where fractionation into a bottom product of nearly pure HD is completed. This HD is warmed to room temperature in a heat exchanger and passed throu a catalytic exchange reactor where its disproportionation into an equilibrium mixture of Hj, HD, and Dj is catalyzed. The product of the exchange reaction is cooled to liquid hydrogen temperatures in the heat exchanger and fed to the bottom half of the secondary tower where it is fractionated into an overhead product of HD + Hj and a bottom product of pure deuterium. This is warmed to room temperature in the heat exchanger and constitutes the product of the plant. The HD and Hj overhead from the bottom of the secondary tower is fed to the top of the secondary tower for recovery of HD. 

Distillate and bottoms were controlled by accumulator and sump levels, respectively, feed and reflux on flow control and boilup was temperature-controUed Tower pall rings were replaced by higher-capadfy rings (bottom) uid wire-mesh structured packing (top) to increase c )acity and reduce reflux. The column was sensitive to ambient disturbances (e.g., rainstorms). The reflux reductions escalated this sensitivity to an extent that annulled the revamp benefits. The temperature control was ineffective due to its narrow range of variation. Problems were solved by controlling boilup on sump level and bottom product on flow control. 

Since this design was completed, the potential for DTBP to decompose explosively at temperatures above 255°F was brought to our attention. At 250 psia, DTBP is present in the bottoms product of tower D-104 at 480.2°F. Given this crucial safety concern, a design team would seek clear experimental evidence. If positive, lower pressures would be explored, recognizing that the distillation boundaries are displaced less at lower pressures. I... 

H2 The feed to a distillation tower consists of 14.3 kmol/hr of medianol, 105.3 kmol/hr of toluene, 136.2 kmol/hr of ethylben-me, and 350.6 kmol/hr of styrene. The bottoms product is to MUain 0.1 kmol/hr of ethylbenzene and 346.2 kmol/hr of (yrene. Determine a suitable operating pressure at the top of the lower noting that the bottoms temperature is limited to 145°C to prevent the polymerization of styrene. 

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