Waste heat recovery solution based on a heat pipe heat exchanger for the aluminium die casting industry

An analysis of the end use of energy in the EU reveals that industry is one of the three dominant categories, which accounts for 26.1% of the final end use of energy. In the case of the aluminium industry, approximately 70% of energy consumption is due to heat and thermal processes, highlighting a vast potential for waste heat recovery technologies. Within the aluminium die casting industry, liquid aluminium is cast, formed, cooled, and further processed within a thermal heat process, which includes three sub-processes: solubilising, quenching, and ageing. In the case presented, a thermal heat process is the second most energy intensive process within the factory, and the ageing heat treatment furnace accounts for 15% of the thermal heat process. The thermal heat treatment generates a significant amount of waste heat. The recovery of that waste heat, with minimal risk of cross contamination between streams and reduced chance of equipment failure, has been achieved via the use of a heat pipe heat exchanger (HPHE). The HPHE has been designed, manufactured, and installed in the solution furnace exhaust stack. The HPHE was designed to recover up to 88.6 kW in steady state operating conditions at 400 °C. The return on investment has been evaluated at 35 months with an expected CO2 emissions reduction of 86 tCO2/year when best engineering practices are applied. Furthermore, a theoretical modelling tool to predict the thermal performance of the HPHE was developed and validated within a ±20% deviation from the experimental results. This paper further presents the development of the theoretical model to allow a characterisation of HPHE technology and will act as a guideline for the design of HPHEs within the aluminium industry.