Divide and conquer: Spectral-splitting and utilization of thermal radiation from waste heat in the steel industry

Approximately 35 % high-temperature waste heat in the steel industry is carried by blast furnace slag and steelmaking slag, and thermal radiation is a primary pathway for this waste heat to dissipate into the ambient environment. Thermophotovoltaic (TPV) systems can convert short-wavelength thermal radiation into electrical energy, but the long-wavelength radiation is still wasted. Here, this work introduces a concept of spectral-splitting (SS) for full-spectrum thermal radiation utilization, allowing simultaneous waste heat recovery by TPV and heat-to-power methods such as Stirling engine (SE). To further demonstrate this concept, an SS TPV-SE system is designed. An optical transmission window of 0–1.7 μm is applied for TPV, and an over 5 μm absorption window is applied for SE. Results show that, with a 0.1 × 1 m molten slag chute, the SS TPV-SE system yields an output power of over 1300 W and achieves an overall efficiency of around 19 %, resulting in an about 58 % improvement compared to the standalone TPV system, and leads to a CO₂ emission reduction of 7516 kg/year. Provided the improved energy efficiency and environmental sustainability, the spectral-splitting concept presented in this work provides a promising approach to enhancing waste heat recovery in the steel industry.