23-Chem-A5 Chemical Plant Design and Economics · December 2016
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 2016 — 04-Chem-A5 Chemical Plant Design and Economics. Three-hour, closed-book exam; one two-sided aid sheet and an approved calculator permitted. Six equally weighted (20-mark) questions are posed and the candidate answers any five; only the first five are marked. All six are answered below for completeness. Question 1 combines conceptual process-synthesis (reactor and recycle structure for a series-reaction chlorination) with a short economic-potential calculation; Question 2 is a numerical retrofit-costing problem (replacing distillation trays with structured packing); Questions 3–6 are qualitative essays on equipment design procedures, materials of construction, inherently safer design, and equipment-selection factors.
Reference texts: R. Smith, Chemical Process Design and Integration (2nd ed., Wiley) — reaction path, reactor conversion and the recycle structure of the flowsheet, and the economic-potential screen behind Question 1 (the monochlorodecane example is worked there); R.K. Sinnott & G. Towler, Chemical Engineering Design (Coulson & Richardson vol. 6, 6th ed., Butterworth-Heinemann) — the equipment cost correlations and retrofit factors of Question 2, the heat-exchanger and cyclone design procedures (Ch. 12, Ch. 10), materials of construction (Ch. 7), and equipment selection (Ch. 10, 18); T.A. Kletz & P. Amyotte, Process Plants: A Handbook for Inherently Safer Design (2nd ed., CRC) — the inherently-safer-design changes of Question 5; M.S. Peters, K.D. Timmerhaus & R.E. West, Plant Design and Economics for Chemical Engineers (5th ed., McGraw-Hill). Canadian practice per CCOHS and CSA Z767 (Process Safety Management) where jurisdiction matters.
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.
Plastics resist the wet, chloride-bearing and dilute-acid environments that attack steels, and they are light and easily fabricated; against this they are temperature-limited, have low strength and stiffness relative to metals, may be attacked by specific solvents, and (unfilled) creep under sustained load. The right choice balances chemical resistance, temperature and mechanical duty for the service, as summarised below.
| Plastic | Key properties | Typical areas of use |
|---|---|---|
| (a) PVC | Good resistance to acids, alkalis, salt solutions and oils; cheap; available rigid (uPVC) or flexible (plasticised); temperature-limited (max ≈ 60 °C); poor resistance to aromatic and chlorinated solvents. | Pipework and ducting, chemical and cold-water drainage, tank linings, plating and pickling tanks, fume ducting. |
| (b) Polyolefins (PE, PP) | Polyethylene and polypropylene: excellent resistance to acids, alkalis, salts and most solvents; cheap, tough, low density; PP usable to ≈ 120 °C (PE lower, ≈ 60–80 °C); attacked by strong oxidisers; poor UV resistance unless stabilised. | Pipes and fittings, small tanks and tank linings, ducting, valve bodies, packaging, food-contact parts. |
| (c) PTFE | Outstanding chemical inertness (resists virtually all chemicals); very wide service range (−200 to +250 °C); very low friction and non-stick; excellent electrical insulator; expensive; low strength and cold-flows (creeps) under load. | Gaskets, seals and gland packing, valve seats, bearings, pump and valve linings, diaphragms, non-stick coatings. |
| (d) PVDF | Excellent resistance to acids, halogens and oxidisers to ≈ 140 °C; stronger, stiffer and more abrasion-resistant than PTFE; readily fabricated and weldable; costlier than the polyolefins. | Process pipework, pump and valve components, vessel and tank linings for hot or aggressive (e.g. chlorine, strong-acid) duties. |
| (e) GRP | Glass-fibre-reinforced thermosetting resin (polyester, vinyl-ester or epoxy): high strength-to-weight, corrosion resistant (resin-dependent), mouldable into large seamless shapes, suitable for site fabrication and repair; temperature and chemical limits set by the resin (≈ 100 °C); quality depends on lay-up; can be abraded and, with the wrong resin, attacked. | Large storage tanks and vessels, ducting, chimneys and stacks, scrubbers, pipes and pipe fittings, corrosion-resistant structures and gratings. |
| (f) Rubber | Natural and synthetic elastomers (neoprene, butyl, nitrile, Hypalon) used chiefly as linings; elastic and abrasion-resistant; ebonite (hard rubber) resists many acids; each elastomer has its own resistance profile (butyl for acids, nitrile for oils); temperature-limited (≈ 60–90 °C). | Linings for tanks, vessels and pipes handling acids, brine and abrasive slurries; hoses, expansion joints, gaskets and flexible connections. |
