Simulation Driven Decision Framework for Heat Exchanger Retrofits: A Case Study of a Multi Pass Naphtha Cooler

Abstract

A modular decision framework that integrates process simulation, fouling uncertainty quantification, and lifecycle economics is presented for prioritizing heat exchanger retrofits in petrochemical plants. A multi pass shell and tube cooler used to cool a C₆–C₁₂ naphtha stream was modelled in Aspen HYSYS Exchanger Design and Rating and optimized over tube count, baffle spacing, and cooling water flow to minimize total annual cost subject to hydraulic and mechanical constraints. Fouling was modelled with a combined resistance and a Monte Carlo ±5% sampling quantified economic sensitivity. The optimized retrofit (220 tubes, 0.45 m baffle spacing, 28,000 kg·hr⁻¹ cooling water) increased heat duty from 2,205 kW to 3,150 kW (+42.7%), raised LMTD from 42.3 °C to 58.1 °C (+37.4%), and reduced shell and tube side pressure drops to 0.70 bar and 1.00 bar, respectively. Despite a 6.8% CapEx increase, TAC fell by 10.2% to $115,000/yr, yielding a 2.1 year payback under base economic assumptions. Fouling uncertainty produced a TAC sensitivity of ≈4.8%, shifting payback by ±0.3 years. The framework is transferable across plant exchanger inventories and supports data driven retrofit prioritization.