Stripping Columns: Summary
The answers to the ConcepTests are given below and will open in a separate window.
Key points from this module:
- A stripping column is usually modeled at steady state.
- Henry’s law can be used to relate the gas concentration to the amount absorbed for the solute when absorbed concentrations are low.
- The number of stages in a stripping column decreases as:
- the temperature increases (for most gases, stripping decreases as temperature increases).
- the pressure decreases.
- the gas flow rate increases.
- On a y-x diagram (solute concentration in gas phase vs. solute concentration in liquid phase) for stripping,
- the slope of the equilibrium line is the Henry’s law constant, which has units of atm in this module.
- the operating line is below the equilibrium line.
- the slope of the operating line is L/V, where L is the liquid molar flow rate and V is the gas molar flow rate.
- the top of the column is at the top of the diagram.
- The liquid stream in an absorption column flows down the column and its molar flow rate is much larger than the gas molar flow rate (the gas flows up).
- For a desired separation in an absorption column at a given temperature and pressure and gas low rate, a minimum liquid flow rate is required; otherwise an infinite number of stages is required.
- The liquid and gas streams leaving a stage in an absorption column are assumed in equilibrium.
From studying this module, you should now be able to:
- Carry out mass balances on a stripping column.
- Determine the number of stages needed to carry out a process to remove an impurity (solute) from a liquid stream by mass transfer to a gas stream.
- Explain how changing pressure and temperature affect absorption/desorption and the number of stages needed for separations.
- Explain where the solute concentrations are high and where they are low in a stripping column.
Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder.