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Show In considering the general effect of particle size on ash behavior it can be seen that, quantitatively, the centrifugal gas flow can force wall impact of relatively large particles. This can occur in a time scale small relative to their combustion time scale, and result in deposition of their mineral (ash) content on the wall. On the other hand, smaller coal particles generally have a low ballistic parameter and combust in the gas flow. Their mineral content vaporizes or is entrained in the gas flow. To be more explicit in accounting for the observed differences in the levels of ash rejection and to direct improvements in combustor design, it was decided to examine the effects of particle size on ash rejection in a quantitative manner. This was accomplished through the application of hydrodynamic and coal combustion models to the case of the design and operation of the Polish 4 MW combustor. 2.0 EXPERIMENTAL RESULTS A cross-section drawing of the Polish Cyclone Combustor is shown in Figure 1. The inlet section to the cyclone is arranged as a scroll and the swirl blades are provided to distribute the air as uniformly as possible. The blades are mounted at 15° tilt. The air thus enters with both tangential and radial components. The coal injectors are arranged at 45° to the tangential direction and are mounted at about 75 percent of the combustor diameter, oriented in the plane of a radius vector. The combustor itself is inclined so that the slag tap is vertical to the floor. The coal particles when injected into cyclone burner are imparted with rotational momentum by the rotating gas in the burner and consequently, particles travel toward the wall. At the same time, the radial velocity of the particles is decreased due to the drag force between particles and gas. Smaller particles have a smaller inertia and hence travel relatively slow towards the wall.' Thus, depending upon the size, the particles may or may not reach the wall. The third important time scale, relates to particle burnout and ash vaporization rates. Figure 2 shows a schematic of the dynamic history of coal particle in the burner. The particles transported inertially to the wall complete burning and reject ash at the wall while those particles which -2- ^z7AVCO EVERETT |