Charging bucket scrap preheating is a method that utilizes the high-temperature off-gas from electric arc furnaces (EAFs) to directly preheat scrap steel placed in the charging bucket. The main goal is to recover waste heat before the scrap enters the furnace, thereby saving energy and reducing production costs.
Development and Application Background
This technology was first implemented in Japan in 1980 on a 50-ton electric arc furnace (EAF) and extended to a 100-ton furnace the following year. Within a decade, over 50 such systems had been commissioned across Japan. In China, companies like Tianjin Steel Pipe (150t electric arc furnace) and Fushun Special Steel (50t electric arc furnace ) also adopted charging bucket preheating systems.
In terms of energy efficiency, this method can recover 20–30% of the heat carried away by exhaust gases. It reduces electricity consumption by 20–25 kWh per ton of steel, lowers electrode consumption by 0.3–0.5 kg/t, and boosts productivity by approximately 5%. These benefits once made it a favored solution for improving electric arc furnace (EAF) performance.
Key Drawbacks and Technical Challenges
Despite its energy-saving potential, charging bucket scrap preheating also poses several challenges:
- Environmental Hazards: The process produces large amounts of white smoke, foul odors, and toxic compounds such as dioxins and furans, which severely pollute the working environment and contribute to occupational health risks.
- Reduced Equipment Lifespan: Prolonged exposure to high-temperature exhaust gases can lead to localized overheating of the bucket, significantly shortening its service life.
- Limited Preheating Effectiveness: Due to heat loss before charging, the final temperature of the scrap often drops to just 100–200°C, limiting the actual efficiency gains.
Improvement Measures and Their Limitations
To mitigate these issues, the industry has explored various solutions:
- Recirculation systems, pressurization, multi-stage preheating, water spray cooling, and post-combustion were introduced to control harmful emissions.
- Water-cooled buckets and tighter limits on preheating time and temperature were used to extend equipment life.
However, these improvements often further reduced the already modest preheating temperatures, resulting in minimal net benefits. In many cases, the overall efficiency remained unsatisfactory.
Conclusion
In summary, charging bucket scrap preheating once showed great promise in energy savings for electric arc furnace (EAF) operations. However, environmental concerns, equipment durability issues, and limited heating efficiency have significantly restricted its widespread adoption. Despite various technological improvements, the overall results have been underwhelming. As a result, some steel plants have already discontinued the use of this technology. Given the lack of meaningful improvements and dwindling industry interest, its future application appears unpromising and unlikely to see widespread adoption again.
