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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

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

pressure.

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.

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.