Configuring the Pipestill in Aspen Plus

Installing all the equipment and setting up all the conditions discussed above is a fairly involved procedure. We will go through the details step by step. The pipestill is installed on the flowsheet by clicking Columns and PetroFrac on the Model Library toolbar at the bottom of the Aspen Plus window. As shown in Figure 11.33, the "CDU10F" icon is selected (third row, middle column) and pasted on the flowsheet. This configuration has a furnace, multiple sidestream strippers, and multiple pumparounds. Figure 11.34 shows the final flowsheet with all the equipment installed, including the pumps and valve required for dynamic control.

The first step is to connect the bottoms from the preflash column to the furnace of the pipestill. As we did with the preflash furnace, the red input arrow that appears at the bottom of the column (shown at the top of Fig. 11.35) must be dragged over to the furnace (shown at the bottom of Fig. 11.35).

A similar procedure of clicking an arrow and dragging it to the desired location must be performed on the strippers to connect the steam lines and the product withdrawal lines at the base of the stripper. Figure 11.36 gives an example in which a material stream is selected to be installed as steam to the third stripper. Figure 11.36a shows blue arrows appearing at the top stripper. We click on the input arrow pointing to the side of the stripper and drag it to the side of the third stripper. When the blue arrow is in the desired location (see Fig. 11.36b), the mouse button is released and the connection is made. This procedure is repeated for the steam inputs of the other strippers and for the product streams leaving the bottom of each stripper.

Material streams for the heavy-naphtha distillate (HNAPH), water from the reflux drum decanter (CU-WATER), steam to the column base (CU-STM), and the bottoms (RCRUDE) are made in the normal way.

Figure 11.33 PetroFrac palette.

Now we must set up the pumparounds and the strippers. On the Aspen Plus Data Browser under the CDU block, there are items for pumparounds and strippers. Clicking the Pumparounds item opens a window on which New is clicked, an identification label is selected, and the window shown at the top of Figure 11.37a opens. On the Specifications page tab, a number of items are specified. For pumparound P-1, the stage from which the hot liquid is removed is stage 8. The stage to which the cool liquid is returned is higher in the column at stage 6. The flowrate is specified to be 49,000 b/d, and the heat removed is set at 40 x 106 Btu/h. Clicking the Results page tab (after the simulation has been run) gives useful information about pumparound P-1, as shown in the bottom window of Figure 11.37a. Note that the temperature of the return pumparound liquid is 331 °F.

The setup and results for the second pumparound P-2 are shown in Figure 11.37b. The stage from which the hot liquid is removed is stage 14. The stage to which the cool liquid is returned is stage 13. The flowrate is specified to be 11,000 b/d, and the heat removed is set at 15 x 106 Btu/h.

The three strippers are installed in a similar manner. The Stripper item under the CDU block is clicked, the New button is clicked, the new stripper is identified, and the window

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