What is pinch analysis and how is it used in heat exchanger network design?

Pinch analysis identifies the minimum energy requirement for a process by constructing composite curves of all hot and cold streams. The pinch point is where curves are closest - it divides the process into heat sink (above pinch) and heat source (below pinch) regions. Design rules: do not transfer heat across the pinch, do not use external cooling above pinch, do not use external heating below pinch. The method determines minimum hot/cold utility requirements and guides heat exchanger network synthesis to approach these targets.