Synergistic deep flue gas heat recovery using corrosion-resistant wall-type condensing heat exchangers coupled with absorption heat pumps

Enhancing the recovery of sensible and latent heat from flue gas provides a direct and effective approach to improving the energy efficiency of gas boiler systems. To address challenges associated with low-temperature corrosion and insufficient heat recovery efficiency, a practical deep waste heat recovery system integrating a corrosion-resistant wall-type flue gas condensing heat exchanger (FGCHE) with an absorption heat pump (AHP) has been developed. Field measurements were conducted to evaluate its thermodynamic performance, and the heat and mass transfer mechanisms governing flue gas-side convective condensation were systematically analyzed. The flue gas exhaust temperature was reduced from 59.7-70.4 °C to 23.8–34.1 °C, achieving a waste heat utilization ratio of 72.1–94.2% and an overall energy-saving efficiency of 10.1–12.8%. Latent heat transfer via condensation played a dominant role, contributing 5.9–8.4 times more than sensible heat transfer, and was significantly influenced by flue gas velocity and water vapor content. Based on field data, empirical correlations for flue gas condensation heat transfer and pressure drop within the FGCHE were established, exhibiting reliable engineering applicability. The system achieved a payback period of 2.61 years, along with significant reductions in natural gas consumption and pollutant emissions, demonstrating strong potential for widespread application in high-efficiency, low-carbon heating systems.