Absorption factor control — To increase the absorption factor A (where A = S / (m * G), with S = solvent liquid rate, G = gas rate, and m = slope of the equilibrium line), what change is appropriate?

Introduction:
The absorption factor A is a convenient nondimensional parameter used in gas absorption design to compare the operating line slope with the equilibrium line slope. Adjusting A can strongly influence stage requirements and approach to the loading point.

Given Data / Assumptions:

• A = S / (m * G), where S is solvent molar (or mass) flow rate, G is gas molar (or mass) flow rate, and m is the slope of the equilibrium relation y* = m x (for dilute systems).
• Equilibrium slope m is taken as fixed by system chemistry and temperature.
• Objective: increase A.

Concept / Approach:
Because A is directly proportional to S and inversely proportional to G (for fixed m), the most direct way to increase A is to raise S and/or reduce G. Increasing A typically moves the operating line farther from equilibrium, improving driving force and reducing tray count, at the expense of larger solvent circulation and associated recovery costs.

Step-by-Step Solution:
Start from A = S / (m * G).Hold m constant (property of system and temperature).To increase A, increase S and/or decrease G → select “Increase S and decrease G”.

Verification / Alternative check:
McCabe–Thiele constructions for absorption show fewer stages and larger approach margins as the operating line is steepened by higher S/G ratios (equivalently, higher A).

Why Other Options Are Wrong:

• (a) Increasing both S and G proportionally keeps A approximately constant.
• (b) Decreasing both reduces throughput without necessarily increasing A.
• (d) Opposite effect: lowers A.
• (e) Changing m by heating is system-specific and not a reliable lever; the prompt asks for certain increase.

Common Pitfalls:
Ignoring downstream solvent recovery/regeneration costs when increasing S; overlooking pressure drop and flooding limits when altering G.

Final Answer:
Increase S and decrease G