Assignment 1 OCT 2015

Question 1

The overhead from a distillation column of a gas processing plant has the overall composition as shown in Table 1. This system conforms closely to Raoult’s law.

Table 1: Compositions and Antoine Equation parameters for the overhead components

ln P1sat /kPa=A− B

T +C where T

is in Kelvin

Composition Parameters for Antoine Equation

Z A B C

n-Butane 0.5 13.9836 2292.44 -27.8623

n-Pentane 0.30 13.9778 2554.60 -36.2529

n-Heptane 0.20

13.9008 2932.72 -55.6356

Determine the maximum operating temperature at the condenser when the entire overhead products from the distillation column need to be condensed completely at 6 bars.

(12 marks)

Question 2

A stream from a gas well contains n-butane(1) and n-pentane(2) is to be separated in a single stage liquid-vapor separator. It is desired to obtain high purity of propane in the liquid stream. Assuming that the liquid phase is non ideal, the correlation for the activity coefficients are given as:

ln γ1 = 0.88x22 ln γ2 = 0.88x1

2

a) At 65 °C, the liquid composition of n-butane is 0.35, determine the pressure and vapor composition of n-butane and n-pentane.

(6 marks)b) At 65 °C, the vapor composition of n-butane is 0.75, determine the pressure and liquid

composition of n-butane and n-pentane. (8 marks)

Question 3

In a petroleum refinery, a stream containing 10 mole% ethane, 30 mole% propane and 60 mole% n-butane is fed to a flash separator operating at 400 kPa. If 55 % of the feed on mole basis is condensed, determine the temperature at which this separator should be operated. Verify your answer.

Assignment 1 OCT 2015

(13 marks)