Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

Direct reduction (DR) furnaces are highly sensitive to pellet size distribution; fines (<5.0 mm) raise bed pressure drop and sticking risk, impacting plant productivity and more frequent shutdowns. Conventional vibrating screens, commonly used to handle hard particles, struggle in screening efficiency due to blinding, screen media wear behavior, and impact-induced degradation. This work presents and evaluates a roller-screen solution adapted for hard particles, tested with iron ore fired pellets and pellet screening. Laboratory trials used 20 rolls of 300 mm length deck, operating at intense laboratory loading (∼221.1 t h−1 m−2 of screening surface) and confirmed the effectiveness of the process. Further, industrial prototyping employed a 30-roll unit of 1200 mm length. Data was collected over 17 days of operation, processing more than 3000 t of material with controlled variation of the feed rate, roll speed and gap opening. Wear test using iron ore fired pellets was also performed to assess the roll’s lifespan. Industrial trials using roller screening technology conducted with fired pellets showed an average screening efficiency of 95.1%, combining 91.6% undersize removal with 97.3% good-size retention. For the pellet screening type of material (feed containing 89.5% <6.3 mm fines), average global efficiency was 82.5% with 85.1% of screening efficiency to remove fines, what is explained by the higher amount of near-size pellets contained in the pellet screening feeding the equipment, presenting a higher amount of goodsize particles to the recirculating load. Results indicate that an optimal gap opening seems to be between 5.0 and 7.1 mm. Rolls showed no damage visually after 40 hr of closed-loop lab operation and after the industrial campaign. Collectively, the industrial data demonstrated that fired-pellet classification with the roller screen adapted to handle hard particles is feasible, efficient, and provided softer handling, providing higher screening efficiencies if compared with conventional vibrating screens. Future research should focus on developing numerical models to enhance process understanding and optimization of roller screen handling hard particles, investigate the optimization of roller screen gap settings for pellet screening, assess performance with other hard materials and evaluate roll lifespan under real operating conditions.