HYSYS - Pseudo Critial Properties

[danago]

I am very new to using the HYSYS process modelling software and would appreciate if somebody could possibly answer a simple question.

For an assignment i was working on, i needed to reference the critical temperature and pressure for a hydrocarbon mix. For the particular stream, i used the "critical properties" utility, which displayed "true" and "pseudo" temperatures and pressures. What is the difference between these values? How is the pseudo value calculated?

If anybody is able to shed some light on this issue, i'd be greatly appreciative

Thanks,
Dan.

 

[Navin A S]

The critical temperature and pressure of a hydrocarbon mixture can be estimated by either true or pseudo-critical values. True critical values are calculated from the actual boiling points of the components in the mix, whereas pseudo-critical values are calculated from correlations rather than actual values. Pseudo-critical values are generally more accurate estimates of the critical properties of a hydrocarbon mix and are usually used when true critical values are not available. The pseudo-critical values are typically calculated using an equation of state such as the Peng-Robinson equation of state.