Figure 3.26 Alternative choices of operating specifications.

Figure 3.26 Alternative choices of operating specifications.

Figure 3.27 Configuration page with all data.
Figure 3.28 Specifying the feed stage.

The last page tab is Pressure. Clicking it opens the window shown in Figure 3.29, in which we specify the pressure in the reflux drum (condenser) and the pressure drop through each of the trays in the column. As discussed above, we set the reflux drum pressure at 14 atm (be careful to change from N/m2). A reasonable tray pressure drop is about 0.0068 atm per tray (0.1 psi per tray).

Figure 3.29 Specifying pressure and tray pressure drop.

All the items in the C1 block are now blue, so the column is completely specified. Next, the design parameters of all the valves and pumps must be specified.

3.4.2 Valves and Pumps

We assume that both pumps generate a pressure difference of 6 atm between suction and discharge. Click Setup under pump P11 and enter these data. Figure 3.30 shows the input

Figure 3.30 Pump P1 specifications.
Figure 3.31 Valve V1 specifications.

form for pump P11 with the Pressure increase button selected and 6 atm pump head entered. Pump P12 is handled in the same way.

The pressure at the exit of the feed valve (V1) must be equal to the pressure on the feed tray (stage 16). We do not know exactly what this is at this point, but we guess it to be about 14.2 atm. Clicking Setup for the V1 block opens the window shown in Figure 3.31. The outlet pressure is set at 14.2 atm. We will come back and adjust this pressure after the flowsheet has been converged and when we know exactly what the pressure on the feed tray is.

Note that under the Flash options the Valid phases has been set to Liquid-Only. This is not necessary for a steady-state simulation, but it will become useful when we move into dynamic simulation in Chapter 7. The other two control valves are each given a pressure drop of 3 atm, as shown in Figure 3.32, and the Flash options for Valid phases are set to Liquid-Only.

The flowsheet is fully specified at this point. All the read buttons are blue, and we are ready to run the simulation.

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