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.
Beyond the steady-state flowsheet simulator, a modern project relies on several other software categories. Two are described in detail, with others noted briefly.
Type 1 — Detailed equipment / mechanical design software. The flowsheet simulator gives duties and stream conditions but not the mechanical detail of the hardware. Specialised programs take over: rating and design of tubular and air-cooled heat exchangers (e.g. HTRI Xchanger Suite or Aspen EDR), and pressure-vessel and column-body design to a code such as ASME VIII (e.g. Codeware COMPRESS or PV Elite). What is involved is entering the process duty and mechanical constraints and having the software iterate geometry — tube count and passes, vessel diameter, or wall thickness, nozzle reinforcement and flange ratings — to meet thermal, hydraulic and code requirements. These tools turn a heat-and-material balance into buildable, code-compliant equipment and feed accurate weights and dimensions back to the cost estimate.
Type 2 — Capital-cost estimation and economic-evaluation software. A second essential category converts the sized equipment list into a capital cost and a profitability analysis (e.g. Aspen Capital Cost Estimator / Icarus). What is involved is mapping each equipment item to a costing model, applying installation ("Lang" or module) factors, escalating to the project location and date, and rolling the result into a discounted-cash-flow evaluation — NPV, DCFROR, sensitivity. This closes the loop between design and economics that this exam is about, and lets alternatives be compared on a consistent cost basis.
Other essential types (briefly): dynamic simulation and process-control software (e.g. Aspen Dynamics) for controllability studies and controller tuning; 3-D plant-layout and piping design software (AVEVA E3D, SmartPlant) with associated pipe-stress analysis (CAESAR II); physical-property databases (DIPPR, NIST) underpinning every calculation; project scheduling and cost control (Primavera P6, MS Project); and, for operation, plant data historians (OSIsoft PI) and computerised maintenance-management systems. Each addresses a stage the flowsheet simulator does not.
