Comprehensive particle behaviors in an impinging entrained-flow gasifier: from atomization to deposition

The behavior of coal particles in an entrained-flow gasifier is critically linked to the stable operation of the gasifier. However, observing these particles has been a significant challenge due to the high temperatures and complex atmosphere within the gasifier. In this study, utilizing a bench-scale opposed multi-burner (OMB) coalwater slurry (CWS) entrained-flow gasifier and a visualization system equipped with high-temperature endoscopes and high-speed cameras of varying specifications, the comprehensive behaviors of particles within the gasifier are thoroughly investigated. The imaging region of the visualization system spans all axial areas of the gasifier, from the dome above the burner plane to 300 mm below it. Detailed discussions are provided on CWS atomization, particle fragmentation, conversion, and deposition behaviors. The findings reveal that as the relative velocity between oxygen and CWS increases, the primary atomization mode transitions from a Rayleightype breakup to a superpulsating atomization mode. A synergistic atomization mode, accounting for 30.1 % of the secondary atomization mode, is identified for impinging entrained-flow gasification. The probability of particle fragmentation peaks at 16.84 %, influenced by the combined forces of the upward impinging-flow from the burner plane and the reverse flow from the dome at approximately 400 mm (4/3 height-diameter ratio of the gasification chamber) above the burner plane. The study concludes with an integrated analysis of the thermal behavior and conversion characteristics of particles across different reaction stages. Deposition behaviors in the gasifier are categorized into three droplet deposition modes and four particle deposition modes. Ultimately, a comprehensive particle evolution model corresponding to the droplet/particle deposition stage is established. Additionally, it is noted that within the gasifier, the char oxidation process typically has the longest duration, ranging from 200 to 2000 ms. Novelty and Significance Statement: The thermal behaviors of coal particles in entrained-flow gasifiers are critical for stable operation but challenging to observe due to extreme high-temperature and complex atmospheric conditions. This study addresses this gap by developing an advanced in-situ visualization system, enabling multiangle observation of particle dynamics-including atomization, fragmentation, conversion, and deposition-in a bench-scale OMB CWS gasifier. By integrating high-speed imaging and advanced image processing algorithms, a comprehensive particle evolution model was established, providing a theoretical foundation for optimizing gasification processes. Furthermore, the scalable visualization technology, validated on an OMB CWS gasifier, is adaptable to other industrial reactors, particularly complex entrained-flow systems, marking a significant advancement in characterizing multiphase thermal processes and supporting the development of efficient and sustainable energy systems.