Exercise 03 Solution ENG

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Assignment #3: Results Adiabatic flash The pressure of the mixture before the valve is the bubble -point pressure at the given temperature TF of 20 °C. It can be determined as: 2 1 ()b Fi i i P z P T     Pb = 3.3528 bar. The temperature of the flash -drum, T, the degree of vaporization , α, and the compositions of the vapor stream (y) and of the liquid stream (x) leaving the flash -drum can be determined, under the assumption that the operation is adiabatic, by solving the following system of two equations: 1 1 2 ( 1)( , ) 0 1 ( 1) ( , ) ( ) (1 ) ( ) ( ) 0 Nc ii i i V L L F zKfT K f T H T H T H T                   Since the feed mixture contains compounds with a narrow range of volatility, the problem can be solved by means of an iterative procedure which starts by assuming a value of α(0). The Rachford-Rice equation is , then, solved for T and a new value for the degree of vaporization is obtained, by solving the energy balance, and it is used to initiate the next cycle. Once convergence has been reached: T = 267.18 [K] α = 0.2055 Table 1. Composition of the streams coming out from the adiabatic flush-drum. Component xi yi C3 0.170308 0.558074 i-C4 0.148435 0.156051 n-C4 0.342344 0.233621 n-C5 0.338913 0.052254 The operating temperature of the flash -drum is then used, along with the operating pressure of 1.2 bar, to solve a simulation problem assuming the mixtures to have a real behavior and using the Peng-Robinson Equation of State (PR EoS) for computing the par tial molar fugacity coefficients of each component in the vapor and in the liquid phase. By solving the problem iteratively, the following final results are obtained: α = 0.1866 Table 2. Composition of the streams coming out from the flush-drum (simulation problem solved using…