Characterization Of Crude

The information available for a crude oil typically consists of "assay" data: a TBP curve, a gravity curve, and a "light-ends analysis." These are illustrated below. The material in this section is taken from the very useful and detailed documentation available from Aspen Technology,2 and the example used in this book is based on the example presented in that source. Petroleum English units are used in the steady-state design here because they are used in that report. When we move into dynamics, metric units will be used because the current version of Aspen Dynamics (version 12) does not offer Petroleum English units.

We will consider a crude oil called Oil-1. The assay data for Oil-1 are given in Table 11.3. We have already discussed TBP distillation information. In petroleum refining, the term "light ends" refers to specific light hydrocarbons, such as methane and ethane. You can see that there are small amounts of these light component dissolved in the crude oil, even though it is at atmospheric pressure and ambient temperature. The API gravity data give the density of the various cuts as they are produced in the TBP distillation.

A Template is set up in Aspen Plus that takes this data and generates pseudo-components. These will then be used in simulating a simple petroleum distillation column called a preflash unit and a second, more complex petroleum pipestill with multiple sidestream products.

The program is started in the normal way by clicking on Start, Programs, AspenTech, Aspen Engineering Suite, Aspen Plus 12.1, and Aspen Plus User Interface. The window shown at the top of Figure 11.5 opens and the Template option is selected. Clicking OK opens the window shown at the bottom of Figure 11.5 with the Simulation page tab open. We select Petroleum with English Units from the list of options on the left. At the bottom right of the window, we select Assay Data Analysis and click OK.

A Data Browser window opens, and clicking Setup and Specifications gives the view shown in Figure 11.6. A title can be inserted in the appropriate box. Next, the Components item is clicked in the Data Browser, then Specifications is clicked, which opens the window shown at the top of Figure 11.7 with the Selection page tab selected. The individual components from water to n-pentane are typed in the first column (Component ID) and the third column (Component name). The Type and Formula columns are automatically filled in, as shown at the bottom of Figure 11.7.

Now a crude oil is specified. We will use the assay data for Oil-1 given in Table 11.3. On the next line of the Selection page tab we type in OIL-1 in the first column. Clicking the second column opens a dropdown menu (shown in Fig. 11.8), and Assay is selected. Clicking the Petroleum page tab and sequentially clicking Assay/Blend, OIL-1, and Basic Data in the Data Browser opens the window shown at the top of Figure 11.9.

2Aspen Technology, Inc., Getting Started Modeling Petroleum Processes.

TABLE 11.3 Crude Oil Assay Data for Oil-1 (31.4┬░API)

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