Exercise set

Gas Absorption, Stripping, and Adsorption Separation Exercises

Solved gas-separation exercises for absorber removal, solvent circulation, stripping, equilibrium margin, adsorber capacity, breakthrough and release gates.

Branch: Chemical Engineering
Content: Exercise set
Updated: Jul 03, 2026
Revision: v1.0.0 · reviewed

These exercises focus on gas-contacting separations: absorption, stripping and adsorption. They cover contaminant removal, outlet load, solvent circulation, equilibrium margin, transfer height, pressure-drop margin, stripping duty, adsorbent capacity, breakthrough service time, regeneration flow and release evidence.

Assume simplified screening calculations unless an exercise states otherwise. Real design must check thermodynamic model, gas composition, temperature, pressure, packing or tray hydraulics, foaming, solvent degradation, adsorbent aging, fire and toxicity hazards, emissions monitoring and interlock state.

Release Evidence Notes

Gas-separation evidence must preserve inlet load, outlet load, removal efficiency and operating envelope. A high percent removal is not enough if the residual emission load exceeds the permit or downstream process limit.

Absorption and stripping evidence should include solvent rate, solvent condition, equilibrium approach, temperature, pressure, flooding margin, pressure drop and sample basis.

Adsorption evidence should include bed inventory, working capacity, breakthrough criterion, humidity or poisoning risk, regeneration status, bypass position and analyzer proof.

Engineering Boundary Notes

These calculations do not replace rigorous rate-based column design, vendor adsorption curves, hazardous-area review, relief design, emissions certification or operator procedures. They are release and design-screen exercises.

Common Release Mistakes

reporting percent removal without outlet load or permit margin;
using clean solvent capacity after solvent has accumulated contaminant;
ignoring pressure drop, flooding and foaming in packed absorbers;
extending adsorber service from ideal capacity while breakthrough data are missing;
treating bypass or standby-bed alignment as an operator note instead of a release gate.

Scenario Map

Scenario	Exercises	Primary check	Engineering decision
Absorption removal	1, 2, 3, 4, 5, 8, 9	load, solvent circulation, transfer and equilibrium	Decide whether absorber performance is credible.
Stripping service	6, 7, 10	stripping flow, removal and heat load	Decide whether regeneration or stripping can support operation.
Adsorption service	11, 12, 13, 14, 15	capacity, breakthrough, utilization, regeneration and standby	Decide whether adsorber operation can continue.
Release gate	16, 17, 18	emissions closure, evidence and all-of gate	Decide whether the gas-separation package can close.

Exercise 1: Absorber Contaminant Removal

A gas stream contains $120\ \text{kg/h}$ of contaminant. The absorber removes $88\%$ . Compute outlet contaminant load.

Solution

\dot{m}_{out}=120(1-0.88)=14.4\ \text{kg/h}

Engineering Comment

Removal fraction should be tied to solvent condition, gas rate, temperature and sampling location.

Plausibility Check

Twelve percent of one hundred twenty kilograms per hour remains.

Exercise 2: Outlet Load Permit Margin

Outlet load is $14.4\ \text{kg/h}$ and the permitted maximum is $18.0\ \text{kg/h}$ . Compute margin.

Solution

\text{margin}=\dfrac{18.0-14.4}{18.0}=0.20=20\%

Engineering Comment

A positive margin can still be weak if analyzer uncertainty, feed spikes or solvent degradation are large.

Plausibility Check

The outlet is $3.6\ \text{kg/h}$ below an $18\ \text{kg/h}$ limit, one fifth of the limit.

Exercise 3: Solvent Circulation From L/G Ratio

Gas flow is $9500\ \text{kg/h}$ . Target solvent-to-gas mass ratio is $1.8$ . Compute solvent circulation.

Solution

\dot{m}_L=1.8(9500)=17100\ \text{kg/h}

Engineering Comment

The circulation target is useful only if the pump, distributor and solvent quality can maintain it.

Plausibility Check

The solvent rate should be a little less than twice the gas mass rate.

Exercise 4: Absorbent Circulation Volume

Solvent circulation is $17100\ \text{kg/h}$ and solvent density is $1020\ \text{kg/m}^3$ . Compute volumetric circulation.

Solution

Q_L=\dfrac{17100}{1020}=16.8\ \text{m}^3/\text{h}

Engineering Comment

Pump curves and distributor wetting should be checked at the volumetric rate, not only mass rate.

Plausibility Check

A density near water makes tonnes per hour numerically similar to cubic meters per hour.

Exercise 5: Packed-Bed Pressure Drop Margin

Measured packed-bed pressure drop is $2.9\ \text{kPa}$ and the high-pressure-drop action level is $4.0\ \text{kPa}$ . Compute margin.

Solution

\text{margin}=\dfrac{4.0-2.9}{4.0}=0.275=27.5\%

Engineering Comment

Pressure drop trend can reveal fouling, flooding, foaming or liquid maldistribution before outlet concentration rises.

Plausibility Check

The measured value is below but not far from the action level, so the margin is moderate.

Exercise 6: Stripping Gas Requirement

A stripper treats $6.5\ \text{m}^3/\text{h}$ of liquid. Required stripping gas ratio is $28\ \text{m}^3$ gas per $\text{m}^3$ liquid. Compute gas flow.

Solution

Q_G=6.5(28)=182\ \text{m}^3/\text{h}

Engineering Comment

The ratio should be checked against off-gas treatment capacity and vapor flammability.

Plausibility Check

Tens of gas volumes per liquid volume over several cubic meters per hour gives hundreds of cubic meters per hour.

Exercise 7: Stripping Removal

Liquid contaminant load entering a stripper is $42\ \text{kg/h}$ and stripping removes $76\%$ . Compute remaining liquid contaminant load.

Solution

\dot{m}_{out}=42(1-0.76)=10.1\ \text{kg/h}

Engineering Comment

The stripped contaminant becomes an off-gas or condensate load; it must appear somewhere in the release package.

Plausibility Check

About one quarter of forty-two kilograms per hour remains.

Exercise 8: Equilibrium Approach Screen

For a dilute absorber, equilibrium gas fraction at the outlet liquid condition is $y^*=0.012$ . Measured outlet gas fraction is $y=0.018$ . Compute approach ratio $y/y^*$ .

Solution

R=\dfrac{0.018}{0.012}=1.50

Engineering Comment

The outlet gas is above equilibrium. The ratio is a screen for contact limitation or insufficient solvent rate.

Plausibility Check

The measured fraction is fifty percent higher than equilibrium, so the ratio is $1.5$ .

Exercise 9: Solvent Loading Capacity

Lean solvent can accept $0.045\ \text{kg contaminant/kg solvent}$ before the release limit is threatened. Solvent flow is $17100\ \text{kg/h}$ . Compute contaminant capacity.

Solution

\dot{m}_{cap}=0.045(17100)=769.5\ \text{kg/h}

Engineering Comment

Working capacity should be corrected for lean loading, degradation, temperature and foaming risk.

Plausibility Check

Five percent of about seventeen thousand kilograms per hour is about eight hundred kilograms per hour.

Exercise 10: Stripper Reboiler Heat Screen

A solvent regenerator evaporates $1250\ \text{kg/h}$ of stripping vapor. Latent heat is $2250\ \text{kJ/kg}$ . Estimate heat duty.

Solution

\dot{Q}=1250(2250)=2812500\ \text{kJ/h}

\dot{Q}=\dfrac{2812500}{3600}=781\ \text{kW}

Engineering Comment

Regeneration heat can become the utility constraint that limits absorber operation.

Plausibility Check

Thousands of kilograms per hour times thousands of kilojoules per kilogram gives megajoules per hour and hundreds of kilowatts.

Exercise 11: Adsorbent Working Capacity

A carbon bed contains $1800\ \text{kg}$ adsorbent. Working capacity is $0.12\ \text{kg contaminant/kg carbon}$ . Compute usable contaminant capacity.

Solution

M_{cap}=1800(0.12)=216\ \text{kg}

Engineering Comment

Working capacity is lower than theoretical capacity when humidity, temperature swing or co-contaminants compete.

Plausibility Check

Twelve percent of $1800$ kilograms is a few hundred kilograms.

Exercise 12: Breakthrough Service Time

Contaminant load to an adsorber is $9.0\ \text{kg/h}$ and usable capacity is $216\ \text{kg}$ . Estimate service time to breakthrough.

Solution

t=\dfrac{216}{9.0}=24.0\ \text{h}

Engineering Comment

The service estimate should be shortened if outlet analyzer trend or humidity indicates early breakthrough.

Plausibility Check

A bed that holds a few hundred kilograms at a load of about ten kilograms per hour lasts about one day.

Exercise 13: Carbon Bed Utilization

At changeout, contaminant captured is $168\ \text{kg}$ and usable capacity estimate is $216\ \text{kg}$ . Compute utilization.

Solution

U=\dfrac{168}{216}=0.778=77.8\%

Engineering Comment

Low utilization may indicate conservative changeout, channeling, sampling uncertainty or a poor breakthrough criterion.

Plausibility Check

Captured mass is about three quarters of capacity, so utilization near $80\%$ is plausible.

Exercise 14: Regeneration Purge Flow

Regeneration requires $5$ bed volumes of purge gas. Bed void volume is $22\ \text{m}^3$ and regeneration time is $2.0\ \text{h}$ . Compute purge flow.

Solution

V_p=5(22)=110\ \text{m}^3

Q=\dfrac{110}{2.0}=55\ \text{m}^3/\text{h}

Engineering Comment

Purge flow should be checked against off-gas handling, inerting and flammability limits.

Plausibility Check

Moving about one hundred cubic meters over two hours gives a few dozen cubic meters per hour.

Exercise 15: Duty-Standby Bed Availability

Two adsorber beds are arranged duty and standby. Each bed availability is $0.94$ . Estimate probability that at least one bed is available, assuming independent failures.

Solution

Both unavailable:

P_f=(1-0.94)^2=0.0036

At least one available:

A=1-0.0036=0.9964

Engineering Comment

Shared valves, analyzers or bypass dampers can defeat the independence assumption.

Plausibility Check

Two independent beds should be much more available than one bed.

Exercise 16: Gas-Separation Emissions Closure

An emissions closure package requires absorber outlet load, pressure drop, solvent circulation, adsorber breakthrough trend and bypass status. Four of five records are complete. Compute completion.

Solution

C=\dfrac{4}{5}=80\%

Engineering Comment

Missing bypass status or breakthrough trend should hold release even if outlet load is currently below limit.

Plausibility Check

Four of five is exactly eighty percent.

Exercise 17: Gas-Separation RPN

A bypass-open failure mode has severity $8$ , occurrence $3$ and detection $4$ . Compute RPN.

Solution

RPN=8(3)(4)=96

Engineering Comment

High severity makes bypass interlocks and position proof important even when occurrence is not frequent.

Plausibility Check

Multiplying single-digit ratings should give a two- or three-digit score.

Exercise 18: Gas-Separation Release Gate

A release gate requires outlet load below $18\ \text{kg/h}$ , pressure-drop margin above $20\%$ , adsorber service time above $20\ \text{h}$ , no bypass and evidence completion above $90\%$ . Current values are $14.4\ \text{kg/h}$ , $27.5\%$ , $24.0\ \text{h}$ , no bypass and $80\%$ completion. Decide release status.

Solution

Outlet load, pressure drop, service time and bypass status pass. Evidence completion fails:

80\%<90\%

Release status:

\text{hold}

Engineering Comment

The process may be performing, but the release package cannot close without complete operating evidence.

Plausibility Check

An all-of release gate fails when one mandatory evidence threshold fails.

Validation Package Checklist

Inlet load, outlet load, removal efficiency and permit basis are reconciled.
Solvent circulation, solvent condition, equilibrium approach and pressure drop are recorded.
Adsorber capacity, breakthrough, regeneration and bypass status are documented.
Release decisions preserve emissions, safety and interlock evidence instead of relying on percent removal alone.

REF