Suggested Response - Q8

*/**Describe the principle of operation of a CO2 stripper.

Response:

An earlier question asked us to name the principle by which a CO2 stripper reduces oxygen in liquid CO2, which was distillation. Here, we are asked to describe it.

With a solution of CO2 and O2, pure CO2 has a higher boiling point (250 K at 18 bar) than pure O2 (130 K at 18 bar). When we boil a mixture of the two, the first vapour formed will be richer in O2, and conversely, the remaining boiling liquid mixture will be leaner in O2, i.e. we will have reduced the dissolved oxygen in the boiling liquid by boiling off some of the oxygen and creating purification.

A simplified schematic for this process is shown below.

Figure: The purification of impure liquid CO<sub>2</sub> by boiling

Figure: The purification of impure liquid CO2 by boiling

Two streams coming from the boiling process: a vapour stream which is higher in oxygen and a liquid stream which is lower in oxygen.

A high level of CO2 purification via distillation will result if we:

  • Have ten or more theoretical distillation processes stacked on one another in a single column

  • Include a single input of heat, at the bottom of the column

  • Have a single exit of oxygen-rich gaseous CO2 at the top of the column

Figure: A simplified CO<sub>2</sub> stripper unit

Figure: A simplified CO2 stripper unit

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