Metso recently reported that Samarco Mineração S.A. set a monthly production record during August 2023 of 824,829 metric tons (mt) of high-grade pellets in a single pelletizing line with its 816-m2 Metso Pelletizing Plant Indurating Machine #4 at the company’s Ubu site in Brazil. On an annual basis, the production is equivalent to approximately 8.8 to 9 million mt/y of pellets in a single machine.
Samarco has installed three additional Metso pelletizing plants at its Ubu site. Currently, only the Plant #4 is in operation, and Samarco and Metso are discussing the revamp of the three other plants to continue increasing pellet production and decarbonizing using sustainable technologies according to Samarco’s gradual production revamp plan. Related test work and studies are currently being performed at Metso’s R&D facility in Frankfurt, Germany.
Metso’s traveling grate pelletizing process consists of a green balling section where, after the mixing stage, green pellets are formed either by rolling on discs or in drums. The green pellets are then screened and heat-hardened in the indurating furnace. The process comprises four steps:
• Raw material preparation and mixing;
• Green pelletizing;
• Pellet hardening (indurating);
• Hearth layer and product screening.
To adjust the moisture content, water is added in the initial step. The ore is then mixed with small amounts of binding agents; fluxes such as limestone, olivine, and dolomite give the pellets the necessary physical and metallurgical properties for further processing. The green pelletizing step shapes the pellets by use of pelletizing discs or drums. According to Metso, drums use a two-stage process where undersized pellets are returned to the drum via a roller screen – in contrast to discs using a single process step to discharge pellets from the disc rim within a very narrow size range. Pellet size can be precisely adjusted by varying the disc inclination, circumferential speed, and feed or water addition rates.
During induration, the green pellets are distributed evenly across the traveling grate and then hardened in a furnace where they pass through updraft drying, downdraft drying, preheating, firing, afterfiring, and cooling zones. Metso said its updraft and downdraft drying sequence significantly reduces fuel consumption. The homogeneous pellet charge on the grate reduces the pressure drop within the furnace, which further reduces energy consumption and enables an even heat treatment, resulting in high-quality pellets.
According to the company, the traveling grate machines can be operated with a variety of different fuels, including heavy fuel oil (HFO), natural gas (also in Low-NOX configuration), mixed off-gases from steel plant facilities, coal and gas mixed with fuel oil, and coal tar.
Metso recently unveiled a hydrogen variant of Ferroflame LowNOX burners as part of its NextGen Pelletizing plant product range. According to the company, it is the first-of- its-kind burner to use hydrogen and operate on the LowNOX combustion principle.
Hydrogen-powered Ferroflame LowNOX burners use the same combustion principle as that of the Ferroflame LowNOX burners for natural gas launched in 2022. Metso said they can replace traditional burners in a traveling grate pelletizing plant, and the Ferroflame LowNOx burners for natural gas can be modified to run on hydrogen.