20180706 Past exam paper Results

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1 Chemical Processes and Technologies (Ing. Giorgia De Guido) Past exam paper July 6th, 2018: Results In the following, the results are given for M4 = M6 = 0, so that Pflash = 4.08 [atm] and the % Recovery of n-butane in liquid phase = 74 %. 1. Determine which is the state of the feed stream (liquid, vapor or mixed). By solving the Rachford- Rice equation in the unknown vaporization ratio for the feed stream, α = -1.2e11. Therefore, the feed stream is a subcooled liquid. 2. Determine the temperature range in which vapor- liquid equilibrium conditions exist for the considered mixture, assuming that the flash drum is operated at the pressure P flash reported in the data section. The bubble-point equation and the dew-point equation can be solved to determine the corresponding temperatures, at the given pressure Pflash. As a result, the temperature range in which VLE conditions exist for the considered mixture is 315.1665 - 333.3495 [K]. 3. Determine the molar flow rates and the compositions (mole fractions) of the outlet streams, the temperature of the flash drum, and the duty required to achieve a recovery of n -butane in the liquid phase as re ported in the data section , assuming that the flash drum is operated at the pressure Pflash reported in the data section. This is the case of a flash problem at given pressure , Pflash, and recovery of one component in the liquid phase. The following equation can be solved in the unknown temperature of the flash drum: ( ) ( )1 1 () 0 NC jj rj jr r r zK fT VyKK K Fz = − = = −+ ∑ after calculating the recovery of n-butane (the r-th component) in the vapour phase: 0.26r r Vy Fz = . As a result: Tflash = 321.2360 [K]. 2 The problem is now reduced to the case in which the temperature of the flash drum and the recovery of a component…