Design Spec

Figure 6.93 Setting up a design spec defining variables.

Cf si Properties (fl si flowsheet FJ a Streams. Q Utflifes Itl di Blocks Fl Gfl Reactions f l a Convergence El Qj Fbwsheebng Options 1=1 a Design Spec... 

Figure 7.22 (a) Defining flowsheet variable in design spec (b) editing variable. 

Instead, the simulation programs allow the designer to impose constraints on the model. In the preceding example, this would be a constraint that the product flow rate is equal to a target value. Constraints are imposed using controller functions, known as a Design Spec in Aspen Plus or a Set or Adjust in UniSim Design. Controllers are specified either as... 

Pattern recognition techniques lend themselves to synthetic designs of molecules for those problems for which the design specs require that a molecule is a member of a certain class. 

To determine the solvent flow and other conditions required to achieve 99 percent toluene recovery, we merely need to change the specification of the recovery Design Spec block from 98 to 99 percent and reconveige the simula-... 

The products did not meet design specs. Replacing the liquid distributor by a hi -performance distributor solv the problem. 

Level 4 Design Rep, HCI design Software and hardware design specs Test plans and results... 

To set up the Design SpecA ary function, click on Design Spec under the Cl block in the Data Browser window. The window shown in Figure 3.37a opens up. Clicking the New button opens the window shown in Figure 3.37b. Click OK and another window... 

Figure 3.37 (a) Setting up the Design Spec, (b) Set Design Spec number. 

Then, click the second page tab Components. Click the IC4 in the left column under Available components. Clicking the > button moves IC4 over to the right Selected components column (Fig. 3.39b). Click the third page tab Feed/Product Streams, select D1 in the left column and click the > button to move it to the right column. The Design Spec is now completed. Notice that the number 1 in Figure 3.39c is blue. 

Figure 3.42 (a) New stream results, (b) Setting up second Design Spec, (c) Selecting propane, (d) Selecting bottoms. 

The second Design SpecA ary is set up in the same way. Clicking Design Spec opens a window on which you specify a new Design Spec 2 . Then, the mole purity of the bottoms 61 is specified to be 0.01 mol fraction propane. See Figure 3.42 for the three steps on the three-page tabs. 

Now that we have some reasonable guesses for the values of the recycle streams, the Design Spec/Vary capability can be used to drive the compositions of the two product streams to their desired values. The key feature in the first column is to keep enough benzene in the column to entrain out the water so the bottoms is high-purity ethanol. On the other hand, if too much benzene reflux is fed to the column, it will go out the bottom and drive the bottoms off-specification. A Design Spec/Vary is set up to maintain the benzene composition of the bottoms at 0.5 mol% by manipulating the REFLUX stream, which is consider a Feed rate on the list of choices given in the Vary, Specifications, Adjusted variable, and Type. 

The initial guessed value of the reflux ratio in the second column was 2. The bottoms purity was very high. The reflux ratio was reduced to about RR = 0.2 without affecting the bottoms purity significantly. A second Design Spec/Vary is set to maintain the ethanol composition of the bottoms of the second column at 0.1 mol% by varying the bottoms flow rate B2. 

One way to do this is to manually adjust the feed split in Tl until (2ri is equal to Qc -This can be automated by going to Flow Sheeting Options on the Data Browser window and selecting Design Spec. This is similar to the Design SpecA ary in the column blocks,... 

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