In Example 10.4, temperatures of the gas and oil, as they pass through the absorber, increase substantially. This limits the extent of absorption. Repeat the calculations with a heat exchanger that removes 500,000 Btu/h from: 

(a) Stage 2; 

(b) Stage 3; 

(c) Stage 4. 

How effective is the intercooler? Which stage is the preferred location for the intercooler? Should the duty of the intercooler be increased or decreased, assuming that the minimum-stage temperature is 100F using cooling water? The absorber oil is nC₁₂.

EXAMPLE 10.4 
Calculate stage temperatures and interstage vapor and liquid flow rates and compositions by the SR method for the absorber specifications in Figure 5.11.

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Absorbent oil To = 90°F 10, Ibmol/h 0.05 0.78 164.17 40 = 165.00 n-Butane (C4) n-Pentane (C5) Oil Feed gas T7 = 105°F Ibmol/h 160.0 370.0 240.0 25.0 5.0 V7 = 800.0 Methane (C₁) Ethane (C₂) Propane (C3) n-Butane (C4) n-Pentane (C5) 1 N=6 Lean gas V₁ 400 psia (2.76 MPa) throughout Rich oil L6