Optimal cascade phase change regenerator for waste heat recovery in a batch industrial dryer

Abstract Waste heat recovery is one of the main strategies to reduce the use of primary resources. This work develops a cascade phase change regenerator to recover energy from exhaust air to fresh air of a natural gas-fired batch dryer in an existing industrial laundry, taken as a case study, where an experimental campaign is conducted. The regenerator comprises two vertical stoves made of horizontal rod bundles in an aligned configuration to mitigate the fouling. The rods are hollow smooth cylinders that are grouped into sectors, each of which is filled with a phase change material properly selected among paraffins. The number of cylinders per row and the cylinder diameter are investigated by a parametric analysis; the number of sectors and the materials filling each sector are optimized by two alternative algorithms, one based on the process physics and the other on a statistical method. At last, an economic analysis is applied to the optimal configuration. This optimal configuration turns to be an 8-sector regenerator that attains an energy recovered of 61.5% and a net annual saving of 3340 €/year and that requires a total cost of about 9500 €, yielding a payback time lower than 3 years.