Chemical Process Design, Scale-Up, and Commissioning Exercises

These exercises practise first-pass calculations used in chemical process design, scale-up, and commissioning. They connect scale factor, heat-transfer scaling, pilot conversion, reactor sizing, utility load, commissioning flush volume, critical path, punch-list readiness, material-balance acceptance, and scale-up risk ranking.

Assume simplified nominal values unless an exercise states otherwise. Real process scale-up requires representative pilot data, verified properties, design-basis control, process safety review, equipment specifications, vendor data, utility confirmation, commissioning procedures, operator training, and post-startup validation.

How to Use These Exercises

For each problem:

1. state the scale, design basis, and operating case;
2. separate laboratory evidence, pilot evidence, vendor assumption, and plant validation;
3. keep material, energy, volume, schedule, and readiness metrics on explicit bases;
4. identify which commissioning record proves the assumption;
5. check whether the calculation creates a safety, quality, utility, waste, or schedule constraint.

The most common mistake is scaling a successful experiment by production rate alone. Heat transfer, mixing, residence time, fouling, control delay, waste handling, and startup sequencing often scale differently from mass throughput.

For each result, state whether it supports a design basis, a scale-up risk screen, a utility check, a commissioning hold point, a release gate, or a handover record. A calculation is not ready for plant use until the supporting evidence and acceptance criterion are visible.

Exercise 1: Batch Scale Factor

A laboratory batch produces 2.0\ \text{kg} of product. The plant target is 1500\ \text{kg/day} with three batches per day.

Estimate plant batch size and scale factor relative to the laboratory batch.

Solution

Plant batch size:

Scale factor:

Engineering Comment

A 250\times scale-up is not only a mass increase. Mixing time, heat removal, charging time, sampling, cleaning, operator workload, and abnormal inventory all need review.

Exercise 2: Area-to-Volume Change

A pilot vessel has heat-transfer area A_p=0.10\ \text{m}^2 and volume V_p=0.010\ \text{m}^3. A plant vessel has heat-transfer area A_f=8.0\ \text{m}^2 and volume V_f=5.0\ \text{m}^3.

Compare area-to-volume ratios.

Solution

Pilot ratio:

Plant ratio:

Relative reduction:

Engineering Comment

The plant has much less heat-transfer area per unit volume. Exothermic reactions, crystallization, viscosity rise, and emergency cooling should be reviewed with plant-scale heat removal, not pilot intuition.

Exercise 3: Pilot Conversion to Plant Product Rate

A pilot reactor feeds 200\ \text{mol/h} of reactant A and reaches 85\% conversion. Desired product selectivity is 92\% on converted A. The proposed plant feed is 1200\ \text{mol/h} of A under similar chemistry.

Estimate expected desired product formation rate.

Solution

Converted reactant at plant scale:

Desired product:

Engineering Comment

The estimate assumes conversion and selectivity transfer to plant scale. That assumption should be validated against mixing, heat removal, residence-time distribution, catalyst state, impurity profile, and sampling basis.

Exercise 4: Reactor Working Volume with Design Margin

A continuous reactor requires nominal residence time \tau=2.2\ \text{h} at design flow Q=3.5\ \text{m}^3/\text{h}. Add 20\% design margin to working volume.

Estimate required working volume.

Solution

Nominal volume:

With margin:

Engineering Comment

The margin helps with uncertainty, but it can also increase hazardous inventory and residence time. Review conversion, side reactions, cleanability, relief basis, and startup inventory before simply oversizing.

Exercise 5: Utility Load Scale-Up

A pilot unit needs 145\ \text{kW} of cooling at feed rate 2500\ \text{kg/h}. The plant design feed rate is 9000\ \text{kg/h}. Assume heat load scales linearly with feed rate.

Estimate plant cooling duty.

Solution

Scale factor:

Plant cooling duty:

Engineering Comment

Linear scaling is a screening assumption. Plant cooling should be checked against reaction heat, fouling, utility temperature, exchanger area, emergency cooling, and simultaneous users on the same utility header.

Exercise 6: Commissioning Flush Volume

Before water trial, a process section contains pipe inventory 0.35\ \text{m}^3, vessel holdup 1.80\ \text{m}^3, and heat-exchanger holdup 0.45\ \text{m}^3. The commissioning plan requires three system volumes of flushing.

Estimate flush volume.

Solution

System volume:

Flush volume:

Engineering Comment

The flush volume is only useful if the flow path reaches dead legs, low points, bypasses, sample lines, and heat-exchanger channels. Wastewater handling and acceptance criteria should be defined before flushing starts.

Exercise 7: Commissioning Critical Path

A commissioning sequence includes:

• mechanical completion: 6 days;
• loop checks after mechanical completion: 5 days;
• utility readiness in parallel: 7 days;
• water trial after loop checks and utilities: 4 days;
• process introduction after water trial: 2 days.

Estimate earliest process introduction.

Solution

Mechanical and loop-check path:

Utility path:

Water trial starts after both are ready:

Earliest process introduction:

Engineering Comment

The critical path runs through mechanical completion and loop checks. Pulling process introduction earlier would require changing real readiness, not only changing a schedule date.

Exercise 8: Punch-List Readiness Gate

A unit has 42 open punch-list items, including 5 safety-critical items. The release gate requires zero open safety-critical items and no more than 10 open noncritical items. After closure work, 8 noncritical items remain and all safety-critical items are closed.

Check readiness against the gate.

Solution

Safety-critical items remaining:

Noncritical items remaining:

The criteria are:

The unit meets this simplified release gate.

Engineering Comment

Release is only valid if the remaining noncritical items do not affect operating limits, emergency access, inspection, sampling, environmental controls, or temporary bypasses.

Exercise 9: Material-Balance Acceptance During Performance Test

During a performance test, measured feed is 18{,}000\ \text{kg}. Product is 15{,}650\ \text{kg}, vented material is 120\ \text{kg}, wastewater is 2150\ \text{kg}, and inventory increase is 60\ \text{kg}. The acceptance criterion is balance closure within 0.5\% of feed.

Check balance closure.

Solution

Measured output plus inventory increase:

Residual:

Closure error:

Engineering Comment

The balance passes the simplified acceptance criterion. The record should still state meter calibration, sample timing, inventory measurement, vent estimate, wastewater basis, and whether the test was at steady operating conditions.

Exercise 10: Scale-Up Heat-Transfer Risk Ranking

A scale-up review identifies insufficient heat removal as a failure mode. Initial rankings are severity S=9, occurrence O=5, and detection D=4.

After a pilot heat-release test, larger exchanger area, emergency cooling validation, and startup hold points are added, occurrence is estimated at O=3 and detection at D=2. Compare traditional risk priority numbers.

Solution

Initial risk priority number:

Revised risk priority number:

Reduction:

Engineering Comment

The revised ranking is lower only if the new evidence is real. The pilot data, exchanger sizing, emergency cooling, alarm response, interlock tests, and startup hold points should all be included in the commissioning handover.

Design and Commissioning Review Checklist

Before using these calculations to justify scale-up or process introduction, check:

• Is the design basis frozen, versioned, and linked to the latest mass and energy balance?
• Are laboratory, pilot, vendor, and plant assumptions separated rather than merged into one estimate?
• Are scale-sensitive phenomena such as heat transfer, mixing, residence-time distribution, fouling, rheology, and venting explicitly reviewed?
• Are utility loads checked against simultaneous demand, turndown, emergency cases, and header limitations?
• Are commissioning flushes, water trials, loop checks, and process-introduction steps tied to written acceptance criteria?
• Are punch-list items classified by safety, quality, environmental, access, temporary bypass, and maintainability impact?
• Are performance-test balances supported by calibrated instruments, synchronized samples, and inventory measurement?
• Are residual scale-up risks assigned to hold points, alarms, interlocks, procedures, training, or design changes?

Strong scale-up engineering keeps the design basis, evidence record, commissioning gate, and startup decision connected. The calculation should make clear what remains uncertain before the plant is allowed to run.