Waste heat recovery from flue gas in glass furnaces: a review

The glass industry is one of the most energy-intensive manufacturing sectors with melting furnaces accounting for most of the total energy consumption. Glass melting and refining require sustained high temperatures and a large share of the energy input ultimately leaves the furnace as hot flue gas with limited recovery particularly in oxyfuel furnaces. This waste heat represents both an efficiency gap and an opportunity because its recovery can substantially reduce fuel consumption, greenhouse gas emissions and operating costs. In recent years, tightening decarbonization targets and the availability of proven retrofit solutions have made flue gas waste heat recovery (WHR) one of the most attractive levers for efficiency improvement in container, tableware and flat-glass production. Primary WHR technologies including combustion air preheating, batch and cullet preheating, oxygen/natural gas preheating and thermochemical recuperation capture sensible heat from exhaust gases and return it directly to the melting process which will reduce specific energy consumption while improving furnace productivity and thermal stability. Complementing these approaches, secondary WHR technologies including waste heat boilers, Organic Rankine Cycle (ORC), Kalina and supercritical CO₂ (sCO₂) cycles, thermoelectric generators (TEGs), direct thermal use and Power-to-X pathways offer additional routes to utilize residual flue gas energy after primary recovery. This review evaluates these options through furnace-specific exhaust characteristics, temperature and exergy hierarchy, recoverable heat, integration constraints, technology maturity and techno-economic feasibility. It concludes that WHR should follow a furnace-specific, process-integration-first cascade, with downstream options selected according to the condition of the residual exhaust and the resulting net plant benefit.