Generating Pseudocomponents

If a petroleum mixture is represented by pseudocomponents corresponding to its TBP curve, its properties can be estimated by the same methods that apply to mixtures of chemical species. For instance, the mixture enthalpy and phase behavior can be predicted by the methods discussed in this chapter. 

FIGURE 1.19 True boiling point curve of a mixture with a limited number of components. 

the TBP temperature, can be expressed as a mathematical function of V, the integral may be evaluated analytically. More commonly, the integration is done based on some curve htting technique. Once the pseudocomponents are generated, their properties are estimated from correlations that are functions of the components boiling points and specihc gravities. 

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A Template is set up in Aspen Plus that takes these data and generates pseudocomponents. These will then be used in simulating a simple petroleum distillation column called a preflash unit and a second more complex petroleum pipestiU with multiple sidestream products. 

All the assay data have been entered, and we are ready to generate pseudocomponents. Clicking the blue N button opens the window shown in Figure 11.12a. We select Specify options for generating pseudocomponents. A new browser window opens called... 

Step 13 Click calculate to enable the Aspen HYSYS Petroleum Refining s calculation for working curves which are used to generate pseudocomponents. 

Several features make this algorithm particularly attractive for the optimization of a formulation response. The algorithm requires only the input of the lower and upper limits of the individual components and the equation describing the response. Both of these must be expressed in either normal or pseudocomponent form. A randomization procedure generates the initial simplex within the individual component constraints by ... 

Generating the pseudocomponents from a TBP curve is accomplished by breaking the curve into a number of cuts, as shown in Figure 1.21. Temperatures Tci, Tq2, Tc3> define the cut points. Thus, the first pseudocomponent boiling range is from... 

Components Petro Characterization Generation (see Fig. 11.12b). Clicking New opens the window shown at the top of Figure 11.13 on which we enter an identification name such as Crude 1. Clicking OK opens window shown at the bottom of Figure 11.13 on which OIL-1 is selected from the drop-down menu to be included. Finally, the blue N button is clicked and OK is clicked on each of the windows that come up sequentially (shown in Fig. 11.14). This completes the generation of the pseudocomponents, called Assay Data Analysis. 

In this case, it is useful to use the whole molecular weight distribution (see [60]) or a higher number of pseudocomponents for the modeling. As an example. Fig. 18 shows the molecular weight distributions of polystyrene in the two coexisting phases observed with cyclohexane/carbOTi dioxide solvent mixture [63]. An initially bimodal mixture of two polystyrene samples (40 kg/mol and 160 kg/mol) was mixed with cyclohexane and carbon dioxide at 170°C and different pressures to generate two hquid phases. 

Pseudocomponent Generation Based on Boiling-Point Ranges... 

Figure 1.5 Comparison of the pseudocomponents generated from constant Watson K factor and density distribution (data obtained from [1]).

Step 15 Select assay-1 and click add to use the assay we input to generate the corresponding pseudocomponents. 

Once we have obtained the boiling point, density or specific gravity, molecular weight and critical properties of a particular pseudocomponent, we can also generate estimates for other required properties for process simulation shown in Table 1.3. The accuracy of these predictions is largely a function of the accuracy of the molecular weight and critical property predictions. In addition, depending on the thermodynamic method chosen, we may not require any correlations for certain properties. For example, if we choose an equation-of state approach, we do not require any additional correlations for the vapor pressure (Pvap) heat of vaporization (AHvap), since these values will be calculated directly by the equation... 

Figure 3.2 Typical pseudocomponents generated by commercial simulator.

Figure 6.150 Create new hypo list for Pseudocomponents generated by delumping.

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