Distillation columns reboiler

Let us now consider a few examples for the use of this simple representation. A grand composite curve is shown in Fig. 14.2. The distillation column reboiler and condenser duties are shown separately and are matched against it. Neither of the distillation columns in Fig. 14.2 fits. The column in Fig. 14.2a is clearly across the pinch. The distillation column in Fig. 14.26 does not fit, despite the fact that both reboiler and condenser temperatures are above the pinch. Strictly speaking, it is not appropriately placed, and yet some energy can be saved. By contrast, the distillation shown in Fig. 14.3a fits. The reboiler duty can be supplied by the hot utility. The condenser duty must be integrated with the rest of the process. Another example is shown in Fig. 14.36. This distillation also fits. The reboiler duty must be supplied by integration with the process. Part of the condenser duty must be integrated, but the remainder of the condenser duty can be rejected to the cold utility. 

The steam supplied to the shell of a distillation column reboiler was very wet, as there was only one steam trap on the supply line although at least three were needed. In addition, condensate in the reboiler drained away only slowly because the level in the drum into which it drained was only 1.4 m below the level in the reboiler. 

Consider now a few examples of the use of this simple representation. A grand composite curve is shown in Figure 21.2a. The distillation column reboiler and condenser duties are shown separately and are matched against it. The reboiler and condenser duties are on opposite sides of the heat recovery pinch and the column does not fit. In Figure 21.2b, although the reboiler and condenser duties are both above the pinch, the heat duties prevent a fit. Part of the duties can be accommodated, and if heat integrated,... 

To illustrate the disturbance rejection effect, consider the distillation column reboiler shown in Fig. 8.2a. Suppose the steam supply pressure increases. The pressure drop over the control valve will be larger, so the steam flow rale will increase. With the single-loop temperature controller, no correction will be made until the higher steam flow rate increases the vapor boilup and the higher vapor rate begins to raise the temperature on tray 5. Thus the whole system is disturbed by a supply-steam pressure change. 

Path 1 is intended to carry heat from exothermic reactions that must he dissipated from the process. This path, shown in Fig. 5.12, goes through all three distillation column reboilers as well as the three preheaters before it terminates in the water cooler. An enthalpy disturbance in the reactor propagates through the entire plant. 

The condenser temperature of 100 °F corresponds to a pressure of 187 psia in the primary column and 222 psia in the secondary tower. The recovery column reboiler temperature then comes to 495°F, while the extractive distillation column reboiler temperature varies from about 300° to 425°F. The temperature of the solvent-addition plate in the main tower varied from 100° to 220°F. 

A distillation column reboiler in a room, as shown in the figure, had been eleaned, but the... 

Edmister applied the group method to complex separators where cascades are coupled to condensers, reboilers, and/or other cascades. Some of the possible combinations, as shown in Fig. 12.24, are fractionators (distillation columns), reboiled strippers, reboiled absorbers, and refluxed inert gas strippers. In Fig. 12.24, five separation zones are delineated (1) partial condensation, (2) absorption cascade, (3) feed stage flash, (4) stripping cascade, and (5) partial reboiling. 

Conventional versus cascade control, (rt) Distillation-column-reboiler temperature... 

CHP production The solid residue from the beer column and me concentrated syrup from the evaporation plant can be used to generate heat to the process and electricity in a CHP plant. If necessary, bark from the debarking unit can also be used. The CHP plant (back-pressure steam turbine unit with steam extraction at appropriate pressme levels to supply utility and process steam) was simulated in Aspen Plus (for input dam, see Figure 4.5). Utility steam is used for process heating in, for example, distillation column reboilers and can be merefore replaced by another hot utility at me same temperature. Process steam is used in the process directly as, for example, in the pretreatment step where steam is used for steam explosion to separate to wood components. As steam in this case is an essential part of the process, it cannot be replaced by another utility. 

Another variable that needs to be set for distillation is refiux ratio. For a stand-alone distillation column, there is a capital-energy tradeoff, as illustrated in Fig. 3.7. As the refiux ratio is increased from its minimum, the capital cost decreases initially as the number of plates reduces from infinity, but the utility costs increase as more reboiling and condensation are required (see Fig. 3.7). If the capital... 

Consider again the simple process shown in Fig. 4.4d in which FEED is reacted to PRODUCT. If the process usbs a distillation column as separator, there is a tradeofi" between refiux ratio and the number of plates if the feed and products to the distillation column are fixed, as discussed in Chap. 3 (Fig. 3.7). This, of course, assumes that the reboiler and/or condenser are not heat integrated. If the reboiler and/or condenser are heat integrated, the, tradeoff is quite different from that shown in Fig. 3.7, but we shall return to this point later in Chap. 14. The important thing to note for now is that if the reboiler and condenser are using external utilities, then the tradeoff between reflux ratio and the number of plates does not affect other operations in the flowsheet. It is a local tradeoff. 

The dominant heating and cooling duties associated with a distillation column are the reboiler and condenser duties. In general, however, there will be other duties associated with heating and cooling of feed and product streams. These sensible heat duties usually will be small in comparison with the latent heat changes in reboilers and condensers. 

The consequences of placing distillation columns in different locations relative to the pinch will now be explored. There are two possible ways in which the distillation column can be integrated. The reboiler and condenser can be integrated either across the pinch or not across the pinch. 

Establish the heat integration potential of simple columns. Introduce heat recovery between reboilers, intermediate reboilers, condensers, intermediate condensers, and other process streams. Shift the distillation column pressures to allow integration, where possible, using the grand composite curve to assess the heat integration potential. 

The composite curves for this flowsheet are shown in Fig. 14.86. The composite curves are dominated by the reboilers and condensers of the two distillation columns and the feed vaporizer for the acetone feed. It is immediately apparent that the two distillation columns are both inappropriately placed across the pinch. Linnhoflf and Parker ... 

Kayihan, F., Optimum Distribution of Heat Load in Distillation Columns Using Intermediate Condensers and Reboilers, AfC/iS Symp. Ser., 192(76) 1, 1980. 

Example A.4.1 The purchased cost of a distillation column is 1 million, and the reboiler and condenser are 100,000. Calculate the annual cost of installed capital if the capital is to be annualized over a 5-year period at a fixed rate of interest of 5 percent. 

Acryflc acid, alcohol, and the catalyst, eg, sulfuric acid, together with the recycle streams are fed to the glass-lined ester reactor fitted with an external reboiler and a distillation column. Acrylate ester, excess alcohol, and water of esterification are taken overhead from the distillation column. The process is operated to give only traces of acryflc acid in the distillate. The bulk of the organic distillate is sent to the wash column for removal of alcohol and acryflc acid a portion is returned to the top of the distillation column. If required, some base may be added during the washing operation to remove traces of acryflc acid. 

The dominance of distiHation-based methods for the separation of Hquid mixtures makes a number of points about RCM and DRD significant. Residue curves trace the Hquid-phase composition of a simple single-stage batch stiHpot as a function of time. Residue curves also approximate the Hquid composition profiles in continuous staged or packed distillation columns operating at infinite reflux and reboil ratios, and are also indicative of many aspects of the behavior of continuous columns operating at practical reflux ratios (12). 

The use of high or low limits for process variables is another type of selective control, called an override. The feature of anti-reset windup in feedback controllers is a type of override. Another example is a distillation column with lower and upper limits on the heat input to the column reboiler. The minimum level ensures that liquid will remain... 

A more complex unit is shown in Fig. 13-24, which is a schematic diagram of a distillation column with one feed, a total condenser, and a partial reboiler. Dotted hnes encircle the six connected elements (or units) that constitute the distillation operation. The variables N, that must be considered in the analysis of the entire process are just the sum of the Nfs for these six elements since here Nr = 0. Using Table 13-5,... 

Effects. Trays can become damaged several ways. A pressure surge can cause damage. A slug of water entering a heavy hydrocarbon fractionator will produce copious amounts of vapor. The author is aware of one example where all the trays were blown out of a crude distillation column. If the bottom liquid level is allowed to reach the reboiler outlet line, the wave action can damage some bottom trays. 

The column internals are housed within a vertical shell, and together with the condenser and reboiler, constitute a distillation column. A schematic of a typical distillation unit with a single feed and two product streams is shown in Figure 1. 

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