Specifying Chemical Components And Physical Properties

Figure 3.14 Data Browser window.

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Figure 3.14 Data Browser window.

(N/m2), which are quite inconvenient for most chemical processes because typical pressures are very large numbers in pascals (1 atm = 101,325 Pa). Therefore we will use pressures in atmospheres in most of the examples. However, make sure that you select the correct units when you enter data.

The second preliminary item is to indicate what properties we want to see for all the streams. The defaults do not include compositions in mole fractions, which are very

Figure 3.15 Selecting units.

useful in distillation calculations. To include mole fractions in the list of stream properties, click on the last item on the Setup list at the left of the window, which is labeled Report Options. This opens the window shown in Figure 3.16a. Click the page tab labeled Stream. This opens the window shown in Figure 3.16b. Select Mole under the Fraction basis column in the middle of the window.

With these bookkeeping issues out of the way, we can select the chemical components by clicking Components on the left of the Data Browser window. This opens the window shown in Figure 3.17a. Clicking the Find button near the bottom of the window opens another window shown in Figure 3.17b. Type in propane and click Find now as shown in Figure 3.18. A list of components is opened at the bottom of the window. Click

Figure 3.16 (a) Modifying reported stream properties; (b) specifying mole fractions.

PROPANE and click the Add button at the bottom of the window. Repeat for ISOBUTANE and click Close.

The two components have now been selected (see Fig. 3.19). It is often desirable to change the name of a component. For example, suppose that we want to use "C3" for propane and "IC4" for isobutane. This can be accomplished by highlighting the name listed under Component ID and typing the desired name. Click anyplace on the window, and the message shown in Figure 3.20 will appear. Click Rename. Repeat for isobutane.

Now we are ready to select a physical property package. Click Properties and Specifications on the left side of the window. Figure 3.21 shows the window that opens. Under

Find now

Close

New search

Databank

Figure 3.17 (a) Specifying chemical components; (b) finding components.

Name or Formula | Advanced |

Component name orforrnula: |j |7 Match alternate names

V Match only components beginning with this string

Figure 3.18 Type in components.

Property methods & models click the arrow on the right of Base method. A long list of alternatives appears as shown in Figure 3.22. Scroll down and select CHAO-SEAD.

It should be noted that different physical property packages can be used in different unit operations in a flowsheet. For example, we may be simulating a distillation column and a

Component Vle
Figure 3.19 Two components selected.
Figure 3.21 Specifying physical properties.

decanter. The best VLE package should be used in the column, while the best LLE package should be used in the decanter.

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