# Determination of Minimum Gas Flow Rate

Question

A packed tower is to be designed to remove ammonia from an aqueous liquid stream by stripping with air. The entering liquid has an NH3 mole fraction of 0.0425 and a flow rate of 0.4 kmol/min; the gas is pure air, 80% of the ammonia is to be removed from the liquid. The figure below shows the equilibrium concentrations at 400 C, 1.0 atm.

1. Plot a point on the diagram corresponding to the stream entering and leaving the bottom of the column.
2. What is the minimum gas flow rate for this situation?
3. If the gas leaving has a mole fraction of 0.048 moles NH3 /mol , what is the gas flow rate ?
4. Using the log-mean concentration difference method, estimate the number of overall, gas phase transfer units required to produce the gas with a mole fraction of 0.048. discuss whether you think the actual number needed would be higher or lower than this value. Based on your observations of the given diagram.
5. Determine the height and diameter needed for the column to operate at 80% of the flooding velocity, using values of: Hy = 1.3 meters, Hx = 0.9 meters, flooding velocity is 2.5 m/s.

Summary: This question belongs to heat transfer and discusses about a packed tower which is designed to remove ammonia from an aqueous liquid. Determines minimum gas flow rate for this situation and height and diameter needed for the column to operate at given percentage of the flooding velocity.

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