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Liquid Flow Rate of NH3 Solution

Question

Water is used to absorb NH3 (mole fraction 0.1) from air at 1 atm in a counter current operation. The gas mixture at 313 K is fed to the bottom of the column at a flow rate of 0.556 m3/s and a velocity of 1.2 m/s. Water is introduced to the column from the top. Due to the enthalpy of dissolution, the temperature of the ammonium water is higher at the bottom of the column. The temperature and composition distribution in the liquid phase from top to bottom of the column, with corresponding gas phase equilibrium compositions are described by Table 1.

Table 1.

 

 

 

temperature of NH3 solution

 

 

composition of NH3 solution

gas phase composition

 

 

 

 

deg C

 

X, kmol (NH3) / kmol (H2O)

Y*, kmol (NH3) / kmol (air)

20

 

0

0

23.5

 

0.005

0.0056

26

 

0.01

0.01

29

 

0.015

0.018

31.5

 

0.02

0.027

34

 

0.025

0.04

36.5

 

0.03

0.054

39.5

 

0.035

0.074

42

 

0.04

0.097

44.5

 

0.045

0.125

47

 

0.05

0.156

 

 

1. If the recovery of NH3 is 95%, assuming air is totally inert, please determine the theoretical minimum liquid flow rate Lmin, (kg/s)

2. If the real liquid flow rate is 1.1 times of the theoretical minimum, and if the KGa is known to be 0.0556 kmol/(m3.s), please determine the diameter of the column, (m).

3. Please determine the height of the packings (m), based on the above information

Summary

This question belongs to thermal engineering and discusses about mass transfer and absorptions.

Word count: 204

 

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