System configurations for shuttle kiln waste heat recovery: comparing and combining a packed-bed thermal storage system and a heat exchanger

Shuttle kilns (SKs) are industrial furnace-type equipment used in sanitaryware production, and commonly consume natural gas. The resulting waste heat (WH) is often rejected into the environment. This study compares three distinct system configurations for waste heat recovery to preheat the combustion air, which are: a standalone heat exchanger (HEX), a packed-bed thermal storage (PBTS) system and a combination of both. All three configurations are evaluated based on the amount of the recovered WH per SK cycle, the equipment's payback period (PBP) and the levelized cost of heat (LCOH). For analyzing the PBTS system, a 1-dimensional numerical model, validated with experimental data from literature, is used. In the first configuration, a HEX can recover up to 8.54 GJ of WH, with a PBP and LCOH of 0.93 years and 0.0170 €/kWh_th. In the second configuration, a PBTS system, sized so that it can be fully discharged by the combustion air, can recover around 15 GJ of WH, achieving a PBP and LCOH of 0.17–0.32 years and 0.003–0.006 €/kWh_th, respectively. The third configuration aims at maximizing the recovered WH, which reached 15.8 GJ. The accompanying PBP and LCOH were 0.81 years and 0.0148 €/kWh_th. Additionally, the reduction in annual CO₂ emissions for the three configurations is up to 16.6 % (HEX), 29.3 % (PBTS) and 30.7–30.8 % (combination). This study highlights that an optimally sized PBTS system can outperform a HEX system, recovering 28 % of the SK's total heat input and achieving lower PBP and LCOH values.