20210623 Past exam paper Results

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1 Chemical Processes and Technologies (Ing. Giorgia De Guido) Exam June 23rd, 2021 – Exercise: Solution Exercise no. 1 (of 3) A saturated liquid mixture, having the flow rate and the composition reported in the Data section below, is available at 1 atm and has to be separated in a flash drum operated at atmospheric pressure and 280 K. Please, determine: 1. the vaporization ratio, α; 2. the composition (mole fractions) of the vapour and liquid products; 3. the thermal duty [kW] to be supplied to the flash drum. Data: Molar flow rate of the feed stream = 6(8 36)100 2 M⋅−+ [kmol/h] M6 = sixth digit of student number from the left (Student number/matricola = XXXXXX) The vapour pressure is calculated with the Antoine equation: ln( [ ]) [] ev BP mmHg A TK C= − + . Component zF [mol/mol] A B C TNBP [K] TC [K] ΔHev (@TNBP) [kcal/kmol] <cPV> [kcal/(kmol∙K)] <cPL> [kcal/(kmol∙K)] propane 0.1500 15.7260 1872.46 -25.16 231.1 369.90 4491 15.06 28.670 n-butane 0.5000 15.6782 2154.90 -34.42 272.7 425.20 5351 21.99 34.140 n-pentane 0.3500 15.8333 2477.07 -39.94 309.2 469.60 6160 31.02 37.614 Results The results are reported in the following assuming M6 = 0. Therefore: • molar flow rate of the feed stream = 82 [kmol/h]. Point no. 1 Using the Rachford-Rice equation: α = 0.485365. Dipartimento di Chimica, Materiali e Ingegneria Chimica “Giulio Natta” POLITECNICO di MILANO 2 Point no. 2 Then, the following composition (mole fractions) of the vapour and liquid products is obtained. Component x y [-] [-] propane 0.045537 0.260763 n-butane 0.434579 0.569366 n-pentane 0.519884 0.169871 Point no. 3 By writing the energy (enthalpy) balance, it is possible to write the following expression for the thermal duty to be supplied to the flash drum: ( ) ( ) ( ) ( ) ( ) ( ) @@ @ @ (1 ) @ @ VLL flash…