Component specification pseudocomponents

The results are summarized in the table below. Using a volume basis of 1 of sample, the masses of the pseudocomponents are also calculated from their specific gravities. The overall specific gravity calculated from the component gravities is 0.801, in close agreement with the measured value hence no normalization of the component specific gravities is necessary. 

Example 4.27 Assessment of separation of a 15-component mixture in two columns The feed for the separation system is a 15-component mixture containing a pseudocomponent, which is specified with an American Petroleum Institute (API) degree of API = 48.6 or a specific gravity of 0.786 (see Figure 4.34). The first column operates at 13.26 atm with 30 stages. The feed enters at stage 8. The top product is rich in propane and the mixture of isobutene... 

If T, 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 sort of curve fitting technique. Once the pseudocomponents are generated, their properties are estimated from correlations that are functions of the components boiling points and specific gravities. 

Stream properties required for solving material and energy balance equations and other process calculations are predicted from component properties. The properties of petroleum pseudocomponents can be estimated from their boiling points and specific gravities. The component properties include the molecular weight, critical constants, acentric factor, heat of formation, ideal gas enthalpy, latent heat, vapor pressure, and transport properties. These are predicted mainly by empirical correlations based on experimental data. Many of these correlations are documented in the American Petroleum Institute Technical Data Book (API, 1983). 

Once we obtain the TBP and density curve, we can cut the components into a number of pseudcomponents. Each of these pseudocomponents has at least a TBP and density, by definition. The number of pseudocomponents for each cut point range can vary depending on the product range of the fractionation system. We have suggested the number of pseudocomponents for a few product ranges in Table 1.2. Subsequent chapters of this text include more information for specific fractionation systems. 

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