Steadystate Design Of Preflash Column

The first petroleum fractionator simulated is a simple distillation column that removes some of the light material in the crude. Figure 11.16 gives the Aspen Plus flowsheet of this unit. There are two crude feedstreams that are combined and heated in a furnace in which the feed is partially vaporized before entering the bottom of the column. There is no reboiler. Live steam is introduced in the bottom of the column to strip out some of the light components in the bottoms stream, which is fed to a pipestill that is considered in the next section.

The valves and pumps are standard equipment, but the column is different from the typical RadFrac that is used when specific chemical components are employed. A petroleum fractionator is selected from the model library menu on the bottom of the Aspen Plus window by clicking Columns and then PetroFrac. Figure 11.17 shows the palette of possible configurations. We choose the fourth from the left on the top row, which is a rectifier with a furnace.

It is a little tricky to attach the stream from the tee where the two crudes are mixed to the furnace. When a material stream is selected at the bottom of the Aspen Plus window and the cursor is moved to the flowsheet, a red input arrow appears at the bottom of the column, as shown in Figure 11.18a. Place the cursor over the red arrow and drag it to the left until it points to the furnace. Then click this arrow, which attaches the stream (see Fig. 11.18b).

The total crude feed to the preflash column is 100,000 b/d, with each of the two crudes (Oil-1 and Oil-2) set at 50,000 b/d. Their temperatures are 200°F. The furnace outlet temperature is specified to be 450°F, which requires a heat input of 203 x 106 Btu/h. The crude is ^30 wt% vaporized in the furnace.

Selecting Setup under the column block (PREFLASH) opens the window shown in Figure 11.19, where we see page tabs of Configuration, Streams, Pressure, Condenser, and Furnace. The column is set up to have 10 stages, no reboiler, and a partial condenser.

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