Flowsheets condensation

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 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 ... 

The process engineer identifies heat exchange equipment in a process by the operation or function it serves at a particular location in the flow cycle. For example, the bottom vaporizer on a product finishing distillation column is usually termed Finishing Column ReboUer E-16, or Reboiler E-16 the overhead vapor condenser on this column is termed Condenser E-17 etc. The usual operations involved in developing a process flowsheet are described in Table 10-11, or Chapter 1, Volume 1. 

The fundamental question regarding representation of the part of the flowsheet in Figure 19.8 as heat sources and heat sinks is at what temperature the heat becomes available for heat recovery opportunities. Even though the reactor effluent is at 120°C, it is not available at this temperature because the reactor effluent needs to be quenched. The heat only becomes available at 100°C as a vapor stream that needs to be condensed and cooled to 40°C and as a quench liquid at 100°C that needs to be cooled to 30°C. 

It is usually uneconomic to compress a gas in order to bring about the condensation of VOC. Figure 25.11 shows a flowsheet in which the VOC-laden vent gas is compressed in order that condensation can take place using... 

A depressant system developed for beneficiation of Ta/Nb-Zr ores involves oxalic acid-hydro fluoro silicic acid and depressant SHQ. SHQ is a mixture of a low-molecular-weight acrylic acid and condensation product of disulphonic acid (Suspendol PKK, manufactured by Cognis, Germany). After the development of the final reagent scheme, a series of locked-cycle tests were performed using the flowsheet shown in Figure 23.7. 

The above considerations lead to the conceptual flowsheet presented in Figure 8.5. Acid and alcohol enter countercurrently at the top and bottom of the reaction zone. The bottom product consisting of ester and some alcohol goes to an evaporator, from which the alcohol is recovered and recycled. The top vapor is condensed, and separated into two phases after decantation. The water leaves the decanter as a byproduct, while the alcohol-rich phase is sent as reflux into the column. 

The SR method can be applied to distillation columns, but the equations of the algorithm do not allow the solution of the condenser and the reboiler with the other stages in the column. Because only the energy balances are used as independent functions, reboiler and condenser duties, reflux ratio, and the boilup ratio have to be specified. This overspecifies the column and the solution cannot be found. The condenser and the reboiler can be solved as separate unit operations in a flowsheet as demonstrated by Fonyo et al. (39). The SR method is used in the ABSBR step of FLOWTRAN of Monsanto, St. Louis, Missouri, and also in both the public release version of ASPEN and in ASPENPlus of AspenTech, Cambridge, Massachusetts. 

There are P I diagrams for individual utilities such as steam, steam condensate, cooling water, heat transfer media in general, compressed air, fuel, refrigerants, and inert blanketing gases, and how they are piped up to the process equipment. Connections for utility streams are shown on the mechanical flowsheet, and their conditions and flow quantities usually appear on the process flowsheet. 

On a process flowsheet, distillation towers, furnaces, reactors, and large vertical vessels often are arranged at one level, condenser and accumulator drums on another level, reboilers on... 

The feed to the plant consists of pure A. This is mixed with the recycle gas stream consisting of almost pure A, and preheated (Cl) before entering the reactor. After reaction, the mixture of A, B, C, and D passes through an aftercooler prior to distillation. In the first column, A is recovered and recycled, while in the second column, the desired product B is separated from CD, which is used as fuel. The distillation columns are assumed to operate with a constant temperature difference between reboiler and condenser temperatures (Andrecov-ich and Westerberg. 1985). The reflux ratios are fixed and the column temperatures are functions of the pressure in the column, which is variable so that efficient heat integration can be attained between the distillation columns and the rest of the process. The reactions involved in this flowsheet are as follows ... 

Fig. 1. Flowsheet of the process for recycling water and ammonia from condensates in ammonia processing...

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