Question 3 of 6: Top Five Items in a Pilot-Plant Investigation

Question 3: Top Five Items in a Pilot-Plant Investigation (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.

Given / Find. A qualitative design-methodology question: identify and describe the five most important items a pilot-plant programme must resolve before a full-scale plant can be designed with confidence. The pilot plant exists to supply data that neither the laboratory (too small, idealised) nor pure calculation can give reliably.

A pilot plant bridges the gap between bench chemistry and a commercial plant: it is large enough to expose the real-fluid, real-material and real-control behaviour that governs scale-up, yet small enough to fail cheaply. The five items below are the ones that most often decide whether the full-scale design succeeds.

1. Reaction kinetics, catalyst life and deactivation. The pilot plant runs long enough to measure how conversion and selectivity change over weeks or months of continuous operation — catalyst ageing, coking, poisoning by feed impurities and the regeneration cycle. Laboratory runs are too short to reveal deactivation, yet it directly sets reactor size, catalyst inventory and the reactor replacement/regeneration schedule.
2. Heat- and mass-transfer scale-up. Mixing, heat-transfer coefficients, temperature and concentration gradients, and residence-time distribution all change with vessel size. The pilot unit provides the transport data needed to size heat exchangers and agitators and to confirm that hot spots, mass-transfer limitations or poor mixing found at scale will not degrade yield or safety in the commercial reactor.
3. Materials of construction and corrosion/erosion. Extended operation on the real (not idealised) process fluid, including trace corrosive impurities, reveals corrosion, erosion and fouling rates that short laboratory exposure cannot. Coupons and instrumented sections identify the correct alloys and linings and establish realistic maintenance and equipment-life expectations.
4. Recycle and impurity build-up. A closed, continuously recycled system lets trace by-products, inerts and unconverted species accumulate to steady state — behaviour invisible in single-pass bench work. The pilot plant quantifies these build-ups and fixes the necessary purge rates, so the commercial recycle loops can be designed to hold impurities below the level that harms the reaction or the product.
5. Separation performance and product quality. The pilot plant verifies that the separation train (distillation, absorption, filtration, drying) actually delivers on-specification product from the real process streams, including the effect of trace components on relative volatility, foaming, emulsions and phase behaviour. It confirms recovery, purity and the final product properties that the market and any regulatory limits demand.