Abstract
When mineral matters in coal transform during the reaction, the ash compositions as well as the particle size distribution vary. This phenomenon affects fundamental characteristics of ash deposition. In the experiment, three types of coal with the different melting temperature and ash content were burned under the condition of high-temperature air pulverized coal reaction. A water-cooled tube was inserted into the furnace to make the ash adhere. Particle size and composition distributions of ash particles in both reacting coal particles and depositing layer were analyzed, using a Computer Controlled Scanning Microscope (CCSEM). As a result, quantity of the ash deposition on the tube surface increases with a decrease of the melting temperature of coal ash. The growth rate for the coal with low ash-melting temperature became higher. For structure of the deposit layer, fine particles of size less than 3 mm mainly consisted of the initial layer for three types of coal, and the thickness was about 30 mm. Deposition of fine particulates of about 3 mm became a trigger of initial deposition at the stagnation point of tube even if the different types of coal were burned. This phenomenon was also simulated by a simple deposition model, which considered turbulence of flow field, thermophoresis force to the ash particles and so forth. The chemical compositions of ash particles in the reacting particles differed from those in the initial deposition layer. This suggests that the chemical compositions also contribute to the ash deposition phenomena.
