Development and Application of Carbon Deposition State Diagram for H-C-O Systems

In both preparing and using hydrogen-rich reducing gas (H₂RG) in direct reduction, carbon deposition occurs if operating parameters are improperly controlled, affecting the entire process. Therefore, a universally applicable method is needed to determine carbon deposition in the CH₄-H₂-CO-H₂O-CO₂ system, especially the broader H-C-O system. This study establishes a novel method based on the H-C-O system's mass balance and chemical equilibrium diagram, alongside multi-phase/multi-reaction equilibrium principles. Critical carbon deposition point coordinates (O/C, H/C) were determined under varying conditions including temperatures typically ranging from 550 °C to 900 °C, total pressures from 0.1 to 2.0 MPa, and H₂/CO ratios of approximately 2.0-6.9. Connecting points under identical parameters generated critical carbon deposition curves, forming a comprehensive "carbon deposition state diagram for H-C-O system". This diagram allows precise determination of system state and carbon deposition occurrence, providing a theoretical basis for optimizing process parameters to avoid deposition. To overcome complex diagram calculations, specialized analysis software was developed. Validation using experimental and industrial data confirmed the diagram's rationality and practicality. The diagram offers a simple, rapid, and accurate means to predict carbon deposition under specified conditions. Crucially, it guides efforts to prevent deposition while simultaneously minimizing energy consumption and costs in natural gas-based hydrogen production processes. Consequently, the "carbon deposition state diagram for H-C-O system" effectively guides actual production towards cost reduction, lower consumption, stability, and smooth operation.