RH Refining Furnace: Enhancing the Injection Process through Advanced Post-Combustion

RH Refining Furnace: Enhancing the Injection Process through Advanced Post-Combustion

Post-combustion technology in steelmaking is applied through specific equipment such as converter oxygen lances (with post-combustion functionality), RH top-blowing lances (exemplified by RH-KTB technology), and secondary combustion oxygen guns in electric arc furnaces.

While this technology has been implemented during molten steel blowing and refining stages, the refining phase has not yet fully developed specialized post-combustion oxygen lance injection processes akin to those used in converters or electric furnaces. In current refining operations, top-blown oxygen lances are primarily employed for forced decarburization.

The principle of post-combustion involves injecting a supersonic oxygen jet from a top lance into the molten bath. A portion of the oxygen reacts with dissolved carbon [C] to form carbon monoxide (CO), while another portion dissolves into the steel, reacting with [C] as dissolved oxygen.

The rising CO subsequently reacts with oxygen in the upper region of the molten bath. This secondary combustion generates carbon dioxide (CO₂) and releases significant heat, which is then transferred to the charge or molten metal, thereby improving the overall thermal efficiency of the process. In converter and electric furnace operations, dedicated equipment and techniques have been established to promote this CO oxidation reaction.

In RH refining, the Japanese-developed RH-KTB method involves top oxygen injection, allowing a portion of the rising CO to react with the oxygen atmosphere within the furnace. This approach has seen partial adoption in domestic steel plants.

However, this technology has not yet fully capitalized on the substantial volume of CO present in the vacuum chamber. To address this limitation, a novel system has been developed featuring specialized post-combustion equipment and process technology tailored for RH refining furnaces. This innovation aims to increase the post-combustion rate—currently between 40% and 60%—within the RH vessel, thereby more effectively utilizing the latent heat in the furnace to reheat the molten steel. This advancement introduces a new technological pathway for molten steel treatment in RH refining.

Technical Implementation

The objective of this development is to provide an injection process that enhances post-combustion efficiency within the RH refining furnace, consequently improving internal heat utilization. This is achieved by implementing a top-blown post-combustion oxygen lance, equipped with auxiliary oxygen ports, in the RH furnace. This lance design promotes more thorough contact between the CO gas generated from the carbon-oxygen reaction and the oxygen present in the vacuum chamber, thereby increasing the post-combustion rate.

When the converter's final tap carbon content [C] is approximately 0.05%, adopting this RH top-blown oxygen injection vacuum operation process can increase the post-combustion rate by 20–30% compared to conventional top-lance oxygen blowing decarburization processes. This results in a molten steel temperature compensation of approximately 4–6°C.

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