COAL PARTICLES AS DISCRETE ELEMENTS: THE ROLE OF COLLISIONS IN ENTRAINED-FLOW SLAGGING GASIFIERS

This study focuses on entrained-flow gasifiers operated in slagging mode where two main processes are realized: the conversion of coal into syn-gas and the separation of mineral ashes. To achieve high gasification efficiencies, flow configurations promoting the centrifugal motion of particles are adopted to enhance the separation of ashes that accumulate into a molten slag layer flowing down the reactor walls. The interaction of char particles upon impact with slag layer is an important topic, as it can determine the onset of a segregated phase close to slag layer with longer mean residence time and rich in still unconverted fuel, thus enhancing the overall gasifier's efficiency. With the help of results of DEM simulations for simplified configurations, with particles representative of coal at different burning levels (from solid unburned grains to fully molten ashes), the role of particle collisions is discussed. It is shown that the occurrence of desired segregation phenomena in proximity of the wall is possible for both unconverted (nonsticky char) and converted (sticky ash) particles. The effective flux of particles towards the wall slag layer appears strongly dependent on the initial particle-particle contact occurring where a dense phase develops, i.e. the injection region but also the region of first impact of particles with the walls, ruling the subsequent particle distribution pattern.