Exercise 8 Text

Pagina 1

1 Department of Energy Politecnico di Milano Via Lambruschini 4 - 20156 MILANO Exercises of “Fundamentals of Chemical Processes” Prof. Gianpiero Groppi Exercise 8 Estimation of the composition of the liquid and va por streams exiting a flash unit with a supercritical component A mixture of hydrogen, n-heptane, n-hexane and n-butane (molar composition z i reported in the table) is sent to a flash unit. zi Ai Bi Ci H2 0.40 ‐ ‐ ‐ n‐heptane 0.30 15.8737 2911.32 ‐56.51 n‐hexane 0.20 15.8366 2697.55 ‐48.78 n‐butane 0.10 15.6782 2154.90 ‐34.42 For each specie, A i, B i and C i are the parameters of Antoine’s equation for the estimation of the vapor pressure. The mixture is initially at 10 bar. Assuming ideal gases, ideal liquid mixture and assuming that H 2 is absent from the liquid phase (H2 is an incondensable component), estimate:  the dew temperature of the mixture at 10 bar  the vaporization ratio and the composition of the liquid and vapor streams obtained in a flash unit maintained at a temperature of 350 K and at a pressure of 10 bar. Re-estimate the flash unit (vaporization ratio and outlet streams composition) assuming that the H2 dissolves in the liquid phase according to the Henry’s law. The Henry’s constant of H2 varies with the temperature and the composition of the liquid mixture, accounting the data reported in the table and the equations listed below. H0 H2,i(298K) [bar] HDES/R H2 in n‐heptane 1268.8 ‐ 734.4 H2 in n‐hexane 1054.7 ‐ 397.7 H2 in n‐butane 1677.2 ‐ 1418.0 2 Variation of the Henry’s constant with the temperature for H2 in the i-th specie: H is bar, T is K              298 11exp2980 ,, 22 TR HKHH DES iHiH Variation of the Henry’s constant with the composition of the liquid mixture:       NC Hi iHimixH HxH 2 22 ,,…