How is the vapor phase determined in VLLE calculations for DEWPT flashes?
One vapor is calculated for each liquid phase and the vapors are combined to one vapor phase.
One vapor is calculated for each liquid phase and the vapors are combined to one vapor phase.
solves the liquid-liquid equilibrium in the inner loop. This means that
once the equilibrium compositions of the two liquid phases are found, they
are used to calculate the vapor - liquid K-values. A very simplified
logical scheme of this algorithm is as follows:
1. Solve the LLE equations for xliq1(i) and xliq2(i) (i denotes component i).
2. Get two sets of vapor - liquid K-values. One set is obtained by using
xliq1(i) and the other set is obtained by using xliq2(i). Let's call
these two sets K1(i) and K2(i)
3. Combine the two sets of K-values into a single vapor-liquid K-value
according to the relation:
K1(i) * K2(i)
K(i) = ---------------------------------
frac_liq1*K2(i) + frac_liq2*K1(i)
In this way, only one vapor composition is obtained.
Therefore, the customer will easily obtain the compositions of the two liquid
phases that are in equilibrium with the vapor (provided that the
liquid - liquid phase splitting occurs at his conditions and the thermo model
is capable of reproducing it). If the same parameters are used for VLE and LLE
calculations, the obtained three phases are exactly in thermodynamic
equilibrium. If different parameters are used for VLE and LLE (which is
frequently done to improve the fit to experimental data), the thermodynamic
equilibrium in the three-phase system is approximate, but the algorithm
gives the best approximation.
About PRO/II: PRO/II is the major product in the Process Engineering Suite (PES). This process simulation software optimizes plant performance by improving process design, operational analysis, and performing engineering studies. It is designed to perform rigorous heat and material balance calculations for a wide range of chemical processes. PRO/II allows users to evaluate the use of heat integration with case studies, rigorously evaluate process improvements with the help of a process flow diagram (PFD), or model crude distillation units. PRO/II offers a wide variety of thermodynamic models to virtually every industry and is incredibly cost effective, decreasing both capital and operating costs.
Technical Support: As always, feel free to reach out to your local technical support team for more information.
About PRO/II: PRO/II is the major product in the Process Engineering Suite (PES). This process simulation software optimizes plant performance by improving process design, operational analysis, and performing engineering studies. It is designed to perform rigorous heat and material balance calculations for a wide range of chemical processes. PRO/II allows users to evaluate the use of heat integration with case studies, rigorously evaluate process improvements with the help of a process flow diagram (PFD), or model crude distillation units. PRO/II offers a wide variety of thermodynamic models to virtually every industry and is incredibly cost effective, decreasing both capital and operating costs.
Technical Support: As always, feel free to reach out to your local technical support team for more information.
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