Performance and economic comparison of heat recovery systems for regenerative glass furnaces

Glass industry produces a large amount of medium temperature flue gas that is commonly released to the atmosphere after it has been filtered. This paper summarizes the thermodynamic and economic performance of three different heat recovery systems applied to an existing hollow glass furnace with a production capacity of 150 ton/day, which generate electricity and the compressed air required by the furnace. The aim is to find the best commercially attractive system for medium temperature heat recovery. Different configurations of Organic Rankine Cycles (ORC), supercritical CO2 Brayton cycle and an innovative regenerative air Brayton cycle are modeled, optimized and compared. The economic analysis is then performed using the module costing technique. ORC systems working with cyclopentane results the best choice for the case study. It shows a Return of Investment (ROI) lower or equal than five years, which makes this system commercially attractive. The utilization of the air Brayton cycle is effective only when the efficiencies of the turbomachinery are very high. The system configuration including a supercritical CO2 Brayton cycle and a preheating system of the furnace combustion air shows higher performance than the ORC system but also higher cost (ROI is higher than five years). However, results show also that sCO2 cycle is a promising technology that could overcome the ORC cycle performance for medium to high temperature heat sources and medium to large flue gas mass flow rates.