23-Chem-A5 Chemical Plant Design and Economics · December 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 2013 — 04-Chem-A5 Chemical Plant Design and Economics. Three-hour, open-book exam; any non-communicating calculator permitted. Six equally weighted questions are posed and the candidate answers any five; only the first five are marked. All six are answered below for completeness. Questions 1, 3 and 6 are conceptual design / management questions answered as organised prose; questions 2, 4 and 5 contain the numerical work (production capacity and pricing, simple- and compound-interest loan accounting, and sinking-fund depreciation) 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, interest and investment, depreciation, profitability, process synthesis, and plant safety); R. Turton et al., Analysis, Synthesis, and Design of Chemical Processes (4th ed., Prentice Hall) — flowsheet synthesis, separation selection, and safety; W.D. Seider et al., Product and Process Design Principles (3rd ed., Wiley) — separation-train synthesis; 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.
Between the decision to invest and a plant running on-spec, several years pass and many things can move against the project. Four important risk factors, with the action taken against each, are:
1. Market / economic risk — the forecast product price, sales volume, or feedstock cost proves wrong, eroding revenue or margin. Mitigation: test the economics with sensitivity and Monte-Carlo analysis to find the break-even price and the probability of a loss; secure long-term off-take and feedstock supply contracts; size the plant conservatively and phase capacity so commitment tracks confirmed demand.
2. Technical / scale-up risk — an unproven reaction, catalyst, or separation performs worse at full scale than in the laboratory (lower conversion, faster catalyst deactivation, unexpected impurities). Mitigation: prove the technology through bench and pilot-plant trials before committing capital, prefer licensed and demonstrated process routes, and build design margin into the critical equipment.
3. Capital-cost and schedule risk — the fixed-capital estimate is exceeded or start-up is delayed, destroying the return. Mitigation: advance the estimate to a definitive (Class 1–2) basis before sanction, carry an appropriate contingency, use firm or lump-sum contracts, and manage the schedule with critical-path tools and staged design reviews.
4. Health, safety and environmental / regulatory risk — a process hazard, an inability to obtain a permit, or a change in regulation. Mitigation: carry out HAZOP and other hazard studies, design inherently safer processes with adequate protective systems, engage regulators early, and confirm the plant can meet emission and effluent limits before construction.
Other risks routinely considered include feedstock-supply security, foreign-exchange and interest-rate exposure, and force-majeure events; each is handled by an analogous mix of analysis, contracts, and design margin.
Strictly, risk in a multi-year project is never eliminated — it is quantified and reduced to an acceptable, demonstrable level. One proves this by a combination of evidence and formal review rather than by assertion. Market and cost risks are demonstrated to be under control by re-running the discounted-cash-flow model with the mitigations in place and showing that the probability of a negative NPV (from the Monte-Carlo output) has fallen below the corporation's threshold, and by pointing to signed supply and off-take contracts that fix the previously uncertain prices. Technical risk is proven closed by successful, documented pilot-plant runs that reproduce the design conversion and product quality at representative conditions. Safety and environmental risks are demonstrated through completed and signed-off HAZOP and risk-assessment records, a hazard register in which every identified hazard has an assigned and verified safeguard, and third-party or regulatory approval of the design. Finally, the whole package is subjected to independent stage-gate design reviews (front-end loading gates), so that an approving body other than the project team confirms the residual risk is acceptable before capital is released. The audit trail — analyses, test data, contracts, review sign-offs — is the proof.
