Question

In an absorption tower (or absorber), a gas is contacted with a liquid such that one or more components in the gas is transferred in the liquid. A stripping tower (stripper) also involves a gas contacting a liquid but components are transferred from the liquid into the gas.

A process consisting of an absorber and a stripper is used to separate the components of a gas containing 35.0 mole% CO2 and the balance CH4. This gas is fed to the absorber. A liquid containing 0.800 mole% CO2 and the balanced methanol is recycled from the stripper and also fed to the absorber.

The effluent gas leaving the absorber contains 1.50 mole% CO2 and all the CH4 in the feed gas. The effluent solvent leaving the absorber is fed to the stripper (the same stripper that supplies the recycled CO2-methanol liquid mixture) together with a stream of nitrogen gas. Ninety percent of the CO2 in this effluent solvent is removed in the stripper and the nitrogen/CO2 stream leaving the stripper passes out to the atmosphere. Methanol may be assumed to be nonvolatile and nitrogen may be assumed insoluble in methanol. Taking 100 mol/h of the gas fed to the absorber.

(a) Draw a flowchart and place labels on the diagram for all of the known variables along with the basis.

(b) Conduct the degree of freedom analysis.

(c) Calculate the fractional CO2 removal in the absorber (moles CO2 absorbed/mole CO2 in gas feed).

(d) Molar flow rate and composition of the liquid feed to the stripping tower.

(e) Molar feed rate of the gas to the absorber required to produce an absorber product gas flow rate of 1000 kg/h.

Answer 1

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