Exercise 03 Solution ENG

Page 1

Page 1 of 8 Dipartimento di Chimica, Materiali e Ingegneria Chimica “Giulio Natta” POLITECNICO di MILANO Practical class (informatic laboratory) of Chemical Processes and Technologies (Prof. Stefania Moioli) Results 1. Multicomponent vapour-liquid equilibrium (VLE) Figure 1. System layout. • Flowrate and composition of the two outlet streams from the first flash-drum (D-101) From the given vaporization ratio α = V/F = 0.25, it follows that: V = 0.25 [kmol/h], L = 0.75 [kmol/h]. By solving the Rachford-Rice equation: ( ) 101 1 ( 1)( ) 0 11 NC Fi i D i i zKfT K − = −== +− the operating temperature is obtained (i.e., 344.90 [K]), as well as the composition of the two outlet streams (Table 1). Q Page 2 of 8 Table 1. Composition of the streams leaving the first flash-drum (D-101). Component xi yi propane 0.044584 0.150249 i-butane 0.193807 0.278578 n-butane 0.349461 0.379617 i-pentane 0.328347 0.158958 n-pentane 0.083801 0.032598 • Flowrate and composition of the two outlet streams from the second flash-drum (D-102) Given the operating pressure (4 [bar]) and temperature (325 [K]), the Rachford-Rice equation ( ) ' 1 ( 1)( ') 0 1 ' 1 NC F i i i i zKf K = −== +− can be solved to find the vaporization ratio α’ = V’/F’ = 0.4628. It follows that: V’ = 0.3471 [kmol/h], L’ = 0.4029 [kmol/h]. The composition of the outlet streams is reported in Table 2. Table 2. Composition of the streams leaving the second flash-drum (D-102). Component xi’ yi’ propane 0.017418 0.076111 i-butane 0.143257 0.252474 n-butane 0.307903 0.397692 i-pentane 0.417013 0.225445 n-pentane 0.114409 0.048278 • Thermal power transferred to the second flash-drum D-102 From the energy balance over the sub-system enclosed by the dashed box in Figure 1: 102 102 101' ( ) ' ( ) ( )V L L D D DQ V H T L H T L H T− −…