Process Design, Economics and Project Management
This domain covers conceptual design and project economics. Concepts: process flow diagrams (PFD) and piping and instrumentation diagrams (P&ID); equipment sizing and selection; capital cost estimation (factored, Lang factors, capacity exponent rule); operating cost; profitability measures (payback, NPV, IRR, ROI); depreciation; and project scheduling (Gantt, critical path). Also know the role of HAZOP and design basis documents.
Traps: confusing capital cost (one-time) with operating cost (recurring); misapplying the six-tenths rule for capacity scaling (cost ratio = (capacity ratio)^0.6); and forgetting that NPV uses discounted cash flows while payback does not. Questions on project scheduling often test whether you can identify the critical path - the longest sequence of dependent activities.
Worked example (rule of thumb): the six-tenths rule: C₂ = C₁·(Q₂/Q₁)^0.6. Doubling capacity multiplies cost by about 1.52, not 2. For profitability, NPV = Σ CF_t/(1+r)^t − initial investment; a positive NPV indicates a viable project. Payback period is simple but ignores the time value of money.