23-Chem-A5 Chemical Plant Design and Economics · May 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — May 2014 — 04-Chem-A5 Chemical Plant Design and Economics. Three-hour, closed-book exam; any non-communicating 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. Questions 1, 5 and 6 are conceptual design / management / safety questions answered as organised prose; questions 2, 3(i) and 4 contain the numerical work (cost–capacity scaling of a heat exchanger, sinking-fund depreciation, and simple/compound loan interest), and every boxed figure.
Reference texts: M.S. Peters, K.D. Timmerhaus & R.E. West, Plant Design and Economics for Chemical Engineers (5th ed., McGraw-Hill) — the exam's named primary text (cost estimation Ch. 6, interest and investment Ch. 7, depreciation Ch. 9, profitability Ch. 10, optimum design Ch. 11, plant safety and loss prevention); R. Turton et al., Analysis, Synthesis, and Design of Chemical Processes (4th ed., Prentice Hall) — flowsheet synthesis and process development; T.M. Duncan & J.A. Reimer, Chemical Engineering Design and Analysis (Cambridge, 1998) — the source of the boiling-point data used in Question 1; supporting Canadian tax practice from the Canada Revenue Agency Capital Cost Allowance classes and the half-year rule.
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.
Profitability is the net outcome of what the venture earns against what it costs and how those cash flows are timed, so the governing factors group naturally into revenue, cost, and financial-timing categories. On the revenue side, the dominant levers are the product selling price and the size and durability of market demand (which together set the sales income), the plant capacity, and the achieved capacity utilisation — a plant that runs at 60 % of nameplate earns far less than its design case. On the cost side, the total capital investment (fixed plus working capital) fixes the money at risk, while raw-material, utility, labour, maintenance and overhead costs determine the operating margin; for an ammonia plant, energy (compression and refrigeration) and feed costs are decisive. Bridging the two are financial and timing factors: the cost of capital and interest rate (money has a time value, so profit earned later is worth less), the depreciation schedule and tax regime (accelerated CCA improves early cash flow), the project schedule and time-to-market, and the plant's economic life. Finally, external factors — competition, technology obsolescence, regulatory and environmental-compliance costs, and general economic conditions — can shift any of the above. A rigorous evaluation folds all of these into discounted-cash-flow measures (net present value, discounted-cash-flow rate of return, payout period) rather than judging any single factor in isolation.
The following table lists five representative risks encountered when judging the feasibility of a plant-design project, together with the practical mitigation a design team would adopt for each:
| Risk factor | Mitigation |
|---|---|
| Market / price risk — product price or demand falls below forecast. | Sensitivity and break-even analysis, secure off-take contracts, stage the capacity, diversify products/markets. |
| Technology / scale-up risk — a novel process under-performs at full scale. | Pilot-plant demonstration, use proven/licensed technology, build in design margins and a contingency. |
| Capital-cost and schedule overrun — construction runs late or over budget. | Detailed (Class 1) estimates with a contingency allowance, firm EPC contracts, critical-path scheduling and change control. |
| Feedstock / supply risk — raw material or utility cost or availability is volatile. | Long-term supply agreements, dual sourcing, on-site utilities, hedging of key input prices. |
| Regulatory / environmental & safety risk — permits, emission limits or a major incident. | Early HAZOP and environmental assessment, design to Canadian codes and CEPA limits, insurance and community engagement. |
(A sixth common risk — financing / interest-rate risk — is mitigated by fixing borrowing rates and maintaining a healthy equity ratio.)
