Pinch-Point Targeting of Organic Rankine Cycle Waste-Heat Recovery from the Exhaust Streams of a Cement Plant: A Numerical Study on Measured Plant Data and the Effect of False Air

Pinch analysis and cycle modeling assess heat recovery from the measured preheater, bypass and cooler exhaust streams of a dry-process cement line, which release 39.85 MW above 150 °C with the raw mill stopped. At a 5 K minimum approach in the source exchangers, the evaluated cycles have nominal net power targets of 10.49 MW for supercritical cyclopentane, 10.43 MW for cyclohexane, 10.11 MW for toluene, and 10.00 and 8.28 MW for toluene–cyclohexane 50/50 and n-pentane–toluene 30/70 by mass. The minimum approach lies at the bubble point in the subcritical cycles and at the 227 °C composite breakpoint for cyclopentane. The steam reference gives 9.25 MW at its adopted 120 K superheat bound; the extended search reaches 9.32 MW at 144.6 K. Cyclopentane’s 0.063 MW lead over cyclohexane is smaller than twice the paired standard uncertainty, so their ranking remains unresolved. For single-stage turbines, applying a screening threshold of 50 to the volume flow ratio leaves cyclohexane with the highest power target of 9.61 MW; no cyclopentane design meets that threshold within the search domain. In series, three source exchangers transfer 83 to 89% of the heat targets at target mass flows; idealized split flow comes within 0.2% of the power targets. Modeled removal of 5983 Nm3/h of excess false air from the preheater raises the reoptimized targets nominally by 0.09 to 0.14 MW. At retained cycle states and recalculated mass flows, only the paired gain of steam exceeds twice its standard uncertainty. False air reduction remains primarily a fuel-saving measure.