Synergistic optimization of thick-bed sintering process by segregated addition of return fines and fuel ratio adjustment

Thick-bed sintering is an important approach for reducing energy consumption and carbon emissions in the sintering process because it enhances heat accumulation within the bed and improves productivity under existing operating conditions. However, increasing bed height promotes heat accumulation in the lower bed region, resulting in excessive liquid phase formation and local over-melting, which deteriorates bed permeability and limits the effectiveness of segregated addition of return fines. To clarify the matching relationship between segregated addition of return fines and thermal regime under thick-bed sintering conditions, a series of 950 mm sintering pot tests were conducted, combined with cold-state permeability measurements, infrared thermal imaging, and flue gas analysis. The effects of the synergistic regulation of return fines segregation and fuel ratio on the sintering process were systematically investigated. The results show that the segregated addition of return fines alone exhibits limited improvement in sintering performance under 950 mm bed height. Reducing the fuel ratio appropriately alleviates heat accumulation and excessive liquid phase formation in the thick bed, thereby enabling the permeability-enhancing effect of the return-fines skeleton structure to be fully realized. Under a total return fines ratio of 20%, the optimum performance is achieved at a critical particle size of 1 mm, segregated addition ratio of 62%, and fuel ratio of 4.0%, yielding sinter yield of 83.17%, tumble strength of 74.64%, and solid fuel consumption of 48.09 kg/t. The enhancement effect of segregated addition of return fines is found to depend not only on the particle size and segregation ratio of return fines, but also on the fuel ratio. The return-fines skeleton structure improves gas flow distribution and moisture migration, while a reduced fuel ratio suppresses excessive liquid phase formation. The synergistic effect of these factors enhances bed permeability, combustion efficiency, and sintering performance simultaneously, providing theoretical guidance for quality improvement and energy conservation in thick-bed sintering.