A gas containing 25 mol% CO2 and 75% CH4 is treated in a gas conditioning plant. The stream is fed to an absorber at a rate of 50Kmol/h and is contacted in the absorber with a recycle solvent containing 0.50% CO2 and the balance methanol. The gas leaving the absorber contains 1.0 mol% CO2 and essentially all the methane fed to the unit. The CO2-rich solvent leaving the absorber goes to a stripping column. A stream of nitrogen gas enters the stripping column and contacts the solvent, removing 90% of the dissolved CO2. All nitrogen leaves the stripping column in the gas stream. The regenerated solvent is the stream that is recycled to the absorption column. Methanol can be assumed to be non-volatile (that is, no methanol enters the gas phase in either process unit).
(a) Perform the degree-of-freedom analysis for the above described process.
(b) Calculate the fractional CO2 removal (moles absorbed/moles fed), and the molar flow rate and
composition of the liquid feed to the stripping column.
(c) Calculate the molar feed rate to the absorber required to produce an absorber product gas flow rate of 1000 Kg/h.
(d) Re-draw the process flow chart for the case that the volatility of methanol could not be neglected (if there is some methanol in the gas streams).