Effect of Temperature and Atmosphere on Agglomeration of Bed Particles in a Bubbling Fluidised Bed Burning Na‐Enriched Coal

ABSTRACT Agglomeration of bed materials during circulating fluidised bed (CFB) combustion or gasification of high‐alkali fuel is a practical challenge in industrial practice. This work investigates experimentally the effect of temperatures (700°C–900°C) and atmosphere (air equivalence ratios 1.61–0.53) on agglomeration in a lab‐scale bubbling fluidised bed burning Na‐enriched Zhundong coal. The critical Na/Si ratio leading to defluidisation was uniquely quantified, and the role of residual char being as a key precursor initiating agglomeration was revealed. Results show that under oxidising atmospheres, agglomeration of quartz particles did not occur at 700°C but occurred at 800°C–900°C, driven by the formation of Na‐silicates bridges between quartz particles, highlighting the effect of temperature and Na in initiating agglomeration. In contrast, under reducing atmospheres, defluidisation of quartz particles occurred earlier compared to those in oxidising atmosphere conditions, with residual char enriching in Na/Ca/Fe/S were found to be the main precursor for agglomeration initiation. This is proved by separate experiments by sending either Na 2 CO 3 ‐doped Zhundong coal or coal ash into BFB. FactSage calculation revealed that incorporating quartz into the coal ash lowers the slag‐liquid phase formation temperature by approximately 250°C, highlighting the role of ash‐bed particle mineral interactions in promoting agglomeration. These results suggest practical measures to mitigate agglomeration: minimising reduction atmospheres, controlling the bed Na/Si ratio below the critical threshold, managing char accumulation and considering alternative bed materials or additives (e.g., Al‐ or Mg‐rich compounds).