Flowsheets between

The program is run to make sure everything works okay without a lag or a deadtime in the loop. Now we back up and insert a deadtime element on the flowsheet between the column and the temperature controller. The reason for installing the controller initially without the deadtime element is to avoid initialization problems that sometime crop up if you attempt to install the deadtime and the controller all in one shot. 

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. 

Also, if there are two separators, the order of separation can change. The tradeoffs for these two alternative flowsheets will be different. The choice between different separation sequences can be made using the methods described in Chap. 5. However, we should be on guard to the fact that as the reactor conversion changes, the most appropriate sequence also can change. In other words, different separation system structures become appropriate for different reactor conversions. 

Figure 14.8a shows a simplified flowsheet for the manufacture of acetic anhydride as presented by Jeffries. Acetone feed is cracked in a furnace to ketene and the byproduct methane. The methane is used as furnace fuel. A second reactor forms acetic anhydride by the reaction between ketene from the first reaction and acetic acid. 

Figure 10.16 presents the refining flowsheet of the two decades between 1950 and 1970. An optional unit, visbreaking, appears there. 

Classification Process simulation refers to the activity in which mathematical models of chemical processes and refineries are modeled with equations, usually on the computer. The usual distinction must be made between steady-state models and transient models, following the ideas presented in the introduction to this sec tion. In a chemical process, of course, the process is nearly always in a transient mode, at some level of precision, but when the time-dependent fluctuations are below some value, a steady-state model can be formulated. This subsection presents briefly the ideas behind steady-state process simulation (also called flowsheeting), which are embodied in commercial codes. The transient simulations are important for designing startup of plants and are especially useful for the operating of chemical plants. 

In practice, the production of vanadium by aluminothermic reduction is also governed by some other considerations. The reduction has to be carried out under an inert atmosphere (helium or argon) to avoid nitrogen pick-up from the air by vanadium metal. The composition of the oxide-aluminum charge has to be so chosen that the thermit (metal obtained by aluminothermic reduction) contains between 11 and 19% aluminum. This is necessary for the subsequent refining step in the vanadium metal production flowsheet. Pure vanadium pentoxide and pure aluminum are used as the starting materials, and the reduction is conducted in a closed steel bomb as shown in Figure 4.17 (C). 

A flowsheet for this part of the vinyl chloride process is shown in Figure 28.56. The reactants (ethylene and chlorine) dissolve in circulating liquid dichloroethane and react in solution to form more dichloroethane. Temperature is maintained between 45 and 65°C, and a small amount of ferric chloride is present to catalyze the reaction. The reaction generates considerable heat. 

To illustrate the difference between SSN and STN, consider a simple batch process flowsheet shown in Fig. 1.9 (Ierapetritou and Floudas, 1998). The process involves 3 consecutive tasks, i.e. reaction, mixing and purification, and 4 consecutive states. The corresponding STN for this flowsheet is shown in Fig. 1.10a, whilst the SSN is shown in Fig. 1.10b. The existence of the arc between state 1 and state 2 signifies the presence of a task, which corresponds to mixing in this particular case. 

Figure 3.2 shows the flowsheet for the illustrative example. The data for the example is given in Table 3.1, where i, fc, and is are consecutive processing units, while d2,3 is a dedicated intermediate storage vessel between processing units and is. The time horizon of interest in this example is 9 h. 

A number of different reagent combinations were examined, along with different flowsheet combinations. The Ta/Nb-Zr separation was strongly related to the amount of Fe-hydroxide decoated. Figure 23.15 shows the relationship between Fe-hydroxide removed, Ta/Nb concentrate grade and Zr content of the Ta/Nb concentrate. 

To execute a sequential solution for a set of modules, you have to tear certain streams. Tearing in connection with modular flowsheeting involves decoupling the interconnections between the modules so that sequential information flow can take place. Tearing is required because of the loops of information created by recycle... 

Heuristic based approaches are more relevant for structured products. The most well known heuristic based approach is the hierarchical decomposition method developed by Douglas (Douglas, 1988). In the first level of this method one only looks at the input-output structure of the process. In subsequent levels more detail is added, finally ending with the entire flowsheet. Design decisions are made by using heuristics and short-cut models. An alternative method is due to Siirola (1996) means end analysis. In this method the properties of the feedstock and the desired products are compared. Tasks are defined to eliminate the property differences between the feedstock and the desired product. 

Under suitable pulp potential in the OPCF process, the flotation speed of galena is very fast and most galena has been floated just in rougher flotation stage. So the flotation cell of galena scavenger flotation operation can be diminished and the flotation circuit is further optimized. The comparison of operation parameters between traditional flowsheet and OPCF flotation is presented in Table 10.13. As can be seen, the flotation potential and time are lower in OPCF than in traditional flowsheet. 

In many synfuel refinery flowsheets, the acid-gas partial pressure is borderline between obvious preferance for hot carbonate and physical solvent-based acid-gas removal systems. In these... 

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