Optimum temperatures for carbon deposition during integrated coal pyrolysis–tar decomposition over low-grade iron ore for ironmaking applications

• Temperatures of pyrolysis and tar decomposition were studied for carbon deposition.
• Highest carbon was obtained in pyrolysis at 800 °C and tar decomposition at 600 °C.
• Gasification decreased carbon deposition at high decomposition temperatures.
• The pore size distribution was a more important factor than the surface area.

Deposited carbon within low-grade iron ore which was produced using integrated coal pyrolysis and tar decomposition showed high reactivity as a reducing agent. However, pyrolysis and tar decomposition were both highly sensitive to temperature and exhibited contrasting behaviors during carbon deposition. In these experiments, the optimum temperatures for pyrolysis and tar decomposition were determined to obtain maximum carbon deposition. High-temperature pyrolysis generated large amounts of volatile matter (tar and gases), which caused high tar decomposition and produced larger deposited carbon and gases. The deposited carbon was major product of tar decomposition at lower temperatures (400–600 °C), whereas mainly gases were produced at higher temperatures (700–800 °C), because of carbon gasification. The highest amount of deposited carbon was obtained at a pyrolysis temperature of 800 °C and a tar decomposition of 600 °C. Hamersley ore gave higher amounts of deposited carbon than Robe-river ore because of its large pore size of less than 4 nm, which was suitable for carbon deposition. The pore size distribution was a more important factor than the surface area. Based on these results, the proposed system could achieve maximum carbon deposition and solve problems related to reducing agents, tar materials, and the use of expensive materials in the ironmaking industry.