Experimental Study And Quantitive Estimate On Thermal Expansion And Fragmentation Characteristics Of Coal Particle In Fluidized Bed

The size distribution of coal particles is crucial for the combusting signatures, operating condition and efficiency of the Fluidized Bed Boiler. The thermal expansion and fragmentation of coal particles determine their size distribution in the Fluidized Bed Boiler. Moreover, devolatization has been proved to be the major reason for the expansion and fragmentation process. In this study, we focus on the role of devolatilization which causes the expansion and fragmentation of coal particles during the combustion. The findings will be very helpful to improve the use of the Fluidized Bed Boiler in nowadays applications.We use Static Thermo-mechanical Analyses (TMA) and High Temperature Microscope to investigate the shaped coals and raw coals. By performing Static Thermo-mechanical Analyses, we revealed the expansion characteristics of the coal particles in shielding gas atmosphere during the devolatilization. By using High Temperature Microscope, we observed the whole process of expansion till fragmentation of the coal particles under combustion. Further Field Scanning Electron Microscopy and Back Dispersion Electron Energy Spectrum study elucidated the micro-configuration and components of the coal particles, as well as the morphological change of micro-configuration through the devolatilization.Our results showed that the expansion and fragmentation of coal particles during combustion mainly occurred at the devolatilization stage, and the temperature was between 400℃to 600℃. Regardless of the different sizes of coal particles, they all tended to break at the stage of devolatilization. It was even easier for coal particles to break if they contain high volatilize materials. During the combustion, small pieces fell off from the coal particles and induced minor crackles. These crackles later merged and expanded to form large crevasses which caused the final fragmentation of the coal particles. The fragmentation potential of certain coal samples during devolatilization can be determined by expansion co-efficiency and stress assays.Experimental results performed by our own rotating stove further validated the data derived from the Static Thermo-mechanical Analyse and High Temperature Microscopes. Our results provide analytical bases for the design of the boiler of fluidized bed power plant, and the choice of the coal sample.