Question

The heavier component has to be removed from a gas stream by absorption. The absorption column operates at 2 550 kPa. The entering liquid is high molecular mass oil which contains 0.45% of the heaviest component but none of the lighter components. The total molar flowrate of the oil entering the absorber is 150 kmol/hr. The effluent gas that enters the absorber at 800 kmolhr contains 20 mol% C, 46 mol% C2, 30 mol% C3, 4 mol% n-C4. There are 6 stages in the column (N-6). The heaviest component (n-C4) is required to be removed from the effluent gas. It can be assumed that A and S values can be based on the entering values of L and V, and K- values are constant and estimated at an average of the entering and exiting temperatures and provided in Table 2 below. Table 2. Ki-values for components Component Ki-values Ca C3 n-C OIL 5.08 2.45 1.34 0.075 0.0001 2.1. Draw a schematic diagram that depicts the absorption process showing all the entering 2.2. Determine the molar flowrates of the components in the liquid stream and the effluent 2.3. Determine the compositions and flowrates of the vapour (V1) and liquid (L7) streams and leaving streams with the given information. gas entering the absorber. Tabulate your answers. leaving the absorber. Tabulate your answers in an appropriate table. (15) 20 Marks]

Answer 1

In the question it is given that,

L_oX_o=V₇Y₇ $\times$ 0.45%

=>L_oX_o= 800 $\times$ 0.04 $\times$ 4.5 $\times$ 10^-3=0.144 kmol/hr

therefore, X_o=0.00096

	Inlet gas(kmol/hr)	Inlet liquid(kmol/hr)
Molar flow rate	800	150
C1	160(20%)	0
C2	368(46%)	0
C3	240(30%)	0
n-C4	32(4%)	0.144(0.096%)