Pressure Checking and Exporting

Under the Dynamics item, the vessel is specified to have CSTR-type dynamics with a diameter of 1 m and a length of 2 m, as shown in Figure 3.107. This corresponds to a residence time of 5 min for the given feed flowrate (0.1 kmol/s). The file is pressure-checked and exported as a pressure-driven dynamic simulation. 

The hie is pressure checked and exported into Aspen Dynamics. Figure 6.101 shows the default control structure. The pressures in each reactor and the liquid level in the separator are controlled. 

The file is pressure checked and exported into Aspen Dynamics. A flow controller is installed on the feed. A pressure controller is installed that holds reactor pressure by adjusting valve V24 in the process discharge line. Figure 7.30 shows the flowsheet with these controllers installed. 

The reflux drum and column base are sized to provide 5 min of liquid holdup when half full. The file is pressure checked and exported to Aspen Dynamics. The initial control scheme that opens is shown in Figure 11.26. Note that there is a level controller (LCW1) that pulls off free water from the reflux dmm. The other level controller (LC12) manipulates reflux flow rate to hold the liquid level of the organic phase in the reflux dmm. Since the reflux ratio is only 0.344 in this column, we change the control structure to hold reflux-dmm level with the NAPHTHA flow rate (valve V12). Pressure controller PCI manipulates the valve V14 in the vapor line. 

The file is pressure checked and exported into Aspen Dynamics. 

The usual sizing calculations are performed, the flowsheet is pressure checked, and the file is exported to Aspen Dynamics. Flow controllers are installed on the feed, distillate, and sidestream. Base level is controlled by manipulating bottoms flow rate. Reflux-drum level is controlled by manipulating reflux flow rate. 

The program in Aspen Plus is run and pressure-checked. It is then exported to Aspen Dynamics as a pressure-driven dynamic simulation as was done in Chapter 3 with CSTRs. The Aspen Dynamics file is opened, giving the window shown in Figure 6.37. The default control scheme has a pressure controller manipulating the valve in the reactor exit line. The simulation is run until all variables stop changing. 

With the equipment sized and the flowsheet pressure checked, it is exported into Aspen Dynamics. Figure 8.37 shows the initial flowsheet that opens in Aspen Dynamics. Pressure controllers are already installed on each column. In column Cl, pressure is held by manipulating the position of valve VI3 in the overhead vapor line upstream of the condenser. Note that the Reflux recycle loop is not closed. 

The flowsheet is exported to Aspen Dynamics after all the parameters required for a dynamic simulation are specified (equipment sizes), and the flowsheet is pressure checked so that a realistic pressure driven dynamic simulation can be used. Reflux drums and column bases are sized to provide 5 min of holdup when half full. Pump heads and control valve pressure drops are specified to give reasonable plumbing. Typical design control valve pressure drops are 3 bar with the valve half open at design flowrates. 

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