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EXAMPLESFT

By Tyler Young,2014-12-10 08:03
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EXAMPLESFT

     H83 MCS

Examples sheet 1

Bubble Points and Dew Points

1. Determine the Bubble Point Temperature of the following hydrocarbon mixture, at a

    pressure of 690 kN/m?.

    Component Moles Molecular weight

     C 10 44.1 3

    iC 30 58.1 4

     C 50 58.1 4

    iC 40 72.1 5

     C 10 72.1 5

     Total Moles: 140

Answer: 63? C

2. Determine the Dew Point Temperature of the mixture in Question 1 at the same

    pressure.

Answer: 77? C.

    Make use of a DePriester K-value chart (attached).

     H83 MCS

Examples sheet 1 Solution

1. The Boiling Point of the middle component, C, can be found by checking the temperature 4

    when the K value is 1.

From the De Priester chart, this is about 64? C.

    As a first guess, assume T = 65 ?C.

    K-values and mol fractions are:

    Component K-value, K Mole fraction, x ii

     C 2.9 10/140 = 0.071 3

    iC 1.4 0.215 4

     C 1.05 0.357 4

    iC 0.5 0.286 5

     C 0.41 0.071 5

     Sum of mole fractions: 1.000

At the Bubble Point: we need ; Kx = 1.0 i i

    Component Kx i i

     C 0.2059 3

    iC 0.301 4

     C 0.3749 4

    iC 0.143 5

     C 0.0291 5

     Sum of Kx: 1.0539 i i

Thus the assumed temperature is a little too high. Assume a temperature of 63? C

    Component x K Kx iii i

     C 0.071 2.80 0.1989 3

     iC 0.215 1.34 0.2881 4

     C 0.357 1.00 0.3570 4

     iC 0.286 0.47 0.1344 5

     C 0.071 0.38 0.0270 5

     Sum of Kx: 1.0054 i i

This is close enough to 1 to be OK.

Answer: 63? C

2. Dew Point temperature will be somewhat higher than the bubble point.

    Make a guess of 70? C.

At the dew point, we need: ; y/K = 1.0 ii

    Component y K y /K iiii

     C 0.071 3.1 0.0229 3

     iC 0.215 1.55 0.1387 4

     C 0.357 1.15 0.3104 4

     iC 0.286 0.54 0.5296 5

     C 0.071 0.46 0.1534 5

     Sum of y/K: 1.1550 ii

Temperature is too low. Reguess 77?C.

    Component y K y /K iiii

     C 0.071 3.45 0.0206 3

     iC 0.215 1.73 0.1243 4

     C 0.357 1.31 0.2725 4

     iC 0.286 0.640 0.4469 5

     C 0.071 0.53 0.1340 5

     Sum of y/K: 0.9983 ii

Close enough to 1.

     Answer: 77? C.

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