23-Chem-A5 Chemical Plant Design and Economics · May 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — May 2013 — 04-Chem-A5 Chemical Plant Design and Economics. Three-hour, open-book exam; any non-communicating calculator permitted. The paper poses seven equally weighted essay questions and the candidate answers any five; only five are marked. All seven are answered below for completeness. These are conceptual design-and-economics questions — the solutions are written as organised prose (clarity and organisation are explicitly marked). The one numerical illustration (a Canadian Capital Cost Allowance schedule in Q2) is worked from stated assumptions.
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, profitability, depreciation, optimisation); R. Turton et al., Analysis, Synthesis, and Design of Chemical Processes (4th ed., Prentice Hall) — process synthesis, safety, and economics; W.D. Seider et al., Product and Process Design Principles (3rd ed., Wiley) — separation-train synthesis and heuristics; 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.
These four areas overlap but address distinct concerns; one representative aspect of each is described below.
Health — industrial hygiene / occupational exposure control. A representative aspect is the control of worker exposure to a toxic chemical against its occupational exposure limit (e.g. a threshold limit value, TLV). For a stream containing benzene, a known carcinogen, "what is involved" is measuring airborne concentrations, engineering the exposure down by closed handling and local exhaust ventilation, providing respiratory personal protective equipment where residual exposure remains, and instituting medical surveillance of exposed staff. The goal is chronic-health protection — keeping time-weighted exposures below the regulated limit — as distinct from preventing acute accidents.
Safety — process safety / overpressure protection. A representative aspect is protecting pressure equipment from overpressure with a pressure-relief system. What is involved is identifying every credible overpressure scenario (blocked outlet, external fire, thermal expansion), sizing a relief valve or rupture disc to the governing case (e.g. per API 520), and routing the discharge safely to a flare or scrubber. More broadly, process safety uses structured hazard studies such as HAZOP to find hazards before they cause incidents. The focus is preventing sudden, acute releases of energy or material.
Loss protection (loss prevention) — fire protection and containment. A representative aspect is spill containment and fire protection around a flammable-liquid storage tank. What is involved is a dike or bund sized to hold the tank's full inventory so a leak cannot spread, adequate inter-tank spacing, a firewater and foam/deluge system, and explosion venting where vapours may accumulate. Loss prevention aims to limit the consequences — property damage and business interruption — of an incident once initiated, and is closely tied to the site's insurance requirements.
Environmental — emissions and effluent control. A representative aspect is treating a plant discharge to meet regulatory limits — for instance a caustic scrubber removing an acid gas (SO2 or HCl) from a vent before it reaches the atmosphere, or biological treatment of process wastewater before it is released to a receiving water. What is involved is characterising the pollutant load, selecting and sizing treatment to achieve the permitted discharge concentration, and monitoring to demonstrate compliance. The focus is protecting the surrounding community and ecosystem over the plant's operating life.
