Question 3 of 6: Process Design & Development Items; Batch-Reactor Procedures

Question 3: Process Design & Development Items; Batch-Reactor Procedures (20 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Part (a) — Ten items covering process design and development

A complete process design and development package moves from a verified flow scheme to a fully specified, costed and reviewed plant. Ten major items are:

1. Process flow diagrams with material and energy balances — the quantitative backbone fixing every stream's flow, composition, temperature and pressure.
2. Equipment sizing and specification — duty calculations and datasheets for reactors, columns, exchangers, pumps, vessels.
3. Materials of construction selection — matching alloys, linings and gaskets to corrosion, temperature and pressure service.
4. Piping and instrumentation diagrams (P&IDs) — showing every line, valve, instrument and interlock.
5. Instrumentation and process-control scheme — control loops, alarms, and the safety-instrumented functions.
6. Equipment layout and plot plan — spacing for operability, maintenance access and hazard separation.
7. Utilities and services design — steam, cooling water, refrigeration, electrical, instrument air and inert gas requirements.
8. Structural, civil and building design — foundations, supports, structures and buildings.
9. Cost estimation and economic evaluation — capital and operating cost estimates and profitability analysis.
10. Safety, health and environmental review — HAZOP/hazard studies, relief and effluent design, and regulatory (WHMIS, provincial OH&S, environmental) compliance.

(Two further items often listed — a start-up/operating manual and a waste-treatment/pollution-control design — round out the package.)

Part (b) — Batch-reactor start-up, operation, shutdown and safety

Start-up. Confirm the vessel and services are ready: verify the reactor is clean, leak-tight and pressure-tested, that agitator, jacket/coil, relief valve, rupture disc and instrumentation are functional, and that the emergency-cooling and quench systems are armed. Purge with inert gas to remove air where a flammable or oxygen-sensitive charge is involved. Charge the reactants in the specified order and quantity (often the limiting reagent last, added slowly), start the agitator before heating to avoid a local hot-spot, then bring the batch to reaction temperature under controlled heating.

Normal operation. Hold temperature and pressure at set point using the jacket/coil, watching that the cooling capacity always exceeds the reaction's heat-release rate. Control the addition rate of any semi-batch feed so the accumulation of unreacted material — and therefore the potential adiabatic temperature rise — stays bounded. Monitor temperature, pressure, agitation and conversion (sampling or in-line analysis) until the reaction reaches its endpoint.

Shutdown. Stop any feed, cool the batch in a controlled manner, and relieve pressure to a safe location. Transfer the product to downstream hold or work-up, then drain, vent and (if required) wash/purge the reactor. Isolate energy and material sources and return the vessel to a safe, de-energized standby state.

Safety requirements. The governing hazard of a batch reactor is thermal runaway, so the controlling principles are: keep cooling capacity above the maximum heat-release rate; never heat without agitation; limit reagent accumulation (semi-batch dosing interlocked to temperature); provide independent high-temperature/high-pressure trips, emergency cooling or quench (dump/kill), and adequately sized relief to a scrubber or flare; inert flammable atmospheres; and follow permit-to-work, lock-out/tag-out and operator training under the plant's process-safety-management system.