Explain pinch analysis for heat exchanger network synthesis and optimization.

Pinch analysis (Linnhoff method) minimizes external utility requirements by maximizing heat recovery between process streams. Steps: Extract stream data (supply/target temperatures, heat capacity rates); Construct composite curves (hot streams releasing heat, cold streams requiring heat) on T-H diagram; Identify pinch point (minimum approach temperature ΔT_min, typically 10-20°C) where curves closest; Calculate minimum hot utility (above pinch) and cold utility (below pinch) from composite curve end-points; Design network following pinch rules: no heat transfer across pinch, no external cooling above pinch, no external heating below pinch. Grand composite curve identifies utility levels and potential for heat engines/pumps. For complex networks: mathematical optimization (MINLP) finds cost-optimal configurations considering capital/operating cost tradeoffs, forbidden matches, and controllability. Industrial applications achieve 20-40% energy savings through systematic retrofit or grassroots design.