# Chap9prac - Chapter 9 Practice Problems(p9.01 The stream...

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Chapter 9 Practice Problems (p9.01) The stream from a gas well consists of 90 mol% methane, 5% ethane, 3% propane and 2% n-butane. This stream is flashed isothermally at 233 K and 70 bar. Use the shortcut K-ratio method to estimate the L/F fraction and liquid vapor composisitons. (ANS. L/F = 0.181) … Solution By short-cut vapor pressure eqn. y x K T P i i i i i ri =≅ +− F H G I K J L N M O Q P L N M M O Q P P 10 7 3 11 1 ^ ?, , ω af y x K ii i = Though not required, the table below also shows bubble T and dew T calculations at 70 bar. For the bubble calculations, in each column, the temperature at the top of the column is used to calculate the K-ratio. Then y i = x i K i . The temperature is adjusted until the sum of y’s is unity. This is an iterature calculation.

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To accompany Introductory Chemical Engineering Thermodynamics 1 of 8 © J.R. Elliott, C.T. Lira, 2004, all rights reserved, (3/17/04) For the dew T calculations, in each column, the temperature at the top of the column is used to calculate the K-ratio. Then x i = y i /K i . The temperature is adjusted until the sum of x’s is unity. This is an iterative calculation. For the isothermal flash calculation, the T = 233K and the pressure is 70 bar, so the K-ratio is fixed, as tabulated in the column under ‘233’. Equation 9.63 is programmed in the cells below the value of L/F=0.181 below the ‘Flash’ title. Each row holds the value of the term ‘D i = z i (1-K i )/[K i + (L/F)(1-K i )]’ from equation 9.63. These values are summed at the bottom of the column. The criteria for the isothermal flash is that L/F is adjusted until the sum goes to zero, as is shown at L/F = 0.181. Once the value of L/F is found, the xi values and yi values in the last columns are generated separately using equations 9.57 and 9.58 respectively. pMPa= 7.000 BUBT DEWT FLASH z Tc Pc w 210.9 y 300.5 x 233 0.181 x y C1 0.9 190.6 4.6 0.011 1.108 0.997 4.7949 0.188 1.767 -0.424 0.553 0.977 C2 0.05 305.4 4.88 0.099 0.049 0.002 0.6332 0.079 0.111 0.1632 0.184 0.020 C3 0.03 369.8 4.25 0.152 0.006 0.000 0.1456 0.206 0.016 0.152 0.155 0.002 nC4 0.02 425.2 3.8 0.193 8E-04 0.000 0.0379 0.527 0.003 0.1088 0.109 0.000 1.0000 0.9997 5E-07 1.000 1.000
To accompany

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Chap9prac - Chapter 9 Practice Problems(p9.01 The stream...

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