Basic Research on Hydrogen Plasma in Green Steelmaking

Understanding and Optimizing Hydrogen Plasma Steelmaking

In our work we try to develop insights into the Hydrogen Plasma Smelting Reduction (HPSR) process, a foundational technology for CO2-lean steel production.

Our studies leverage Optical Emission Spectroscopy (OES) to monitor and optimize the HPSR of hematite ore. The work establishes a framework for real-time process control, which is essential for scaling this sustainable steelmaking route to industrial application.

Some Key Findings on Hydrogen Plasma Control in Sustainable Metallurgy

The investigation focused on how key furnace parameters—specifically arc current and arc length—impact the plasma characteristics and the efficiency of iron ore reduction.

The Role of Arc Current in Reduction in the Hydrogen Plasma 

Low Current Impact 100 A: Experiments at lower currents showed more intense optical emissions for non-ionized elements. This is due to a lower level of ionization in the plasma. However, this current level resulted in a significantly lower degree of metallization, indicating insufficient energy for effective reduction.

High Current Impact 200 A : Higher currents introduced more energy, leading to significantly higher average plasma temperatures and a corresponding higher electron density (greater ionization). This condition was necessary to achieve effective ore reduction.

Arc Length and Process Monitoring in the Hydrogen Plasma 

The study demonstrated the potential of OES data to act as a vital monitoring tool in large-scale reactors where direct visual access is often impossible:

Arc Length Estimation: The electron density calculated from the optical emissions was identified as a potential proxy for estimating the arc length. This is critical for maintaining process stability.

Temperature Relationship: Increasing the arc length was found to decrease the average plasma temperature due to a reduction in energy density.

Reduction Efficiency: For fluxed hematite, the degree of metallization showed a positive correlation with arc length, suggesting that a longer arc provides a larger contact area, which aids in the reduction process.

 Optical Emission Spectroscopy for Slag and Impurity Monitoring

A major contribution of this research is validating OES as a tool for monitoring slag formation, which is key to process stability and product quality:

Distinct Slag Signatures: The optical emissions of common slag components were found to be highly distinct in the fluxed hematite experiments. This confirms OES as a viable technique for real-time monitoring of slag composition in future industrial settings.

Evaporation Insights: The addition of fluxing agents was unexpectedly linked to an increase in the evaporation of metal. This is attributed to plasma-induced turbulence that exposes iron oxides to the high-energy plasma, highlighting a phenomenon that must be managed in industrial designs.

Setup Importance: The study stresses that the precise positioning of the optical fiber is paramount for capturing reliable and consistent OES data, underscoring the need for careful industrial sensor placement.