OCR Text |
Show 0.2 - 0.4 lb air/lb CWS, and no fuel preheat. Although the properties of the coals affected the combustion results in minor and predictable ways (e.g., high volatile matter content contributes to good ignition stability), the overwhelming determinant of combustion performance was atomization quality. This can be understood in terms of the following proposed mechanism of CWS combustion (see Figure 8): 1) A single droplet of CWS containing many coal particles is created by the atomizer. 2) The droplet begins to dry from the outside, and the coal at the surface may begin to get tacky (especially for the high volatile bituminous coals used in this study). 3) There are many things that can happen at this point, the details of which depend on the coal, the furnace environment and possibly the CWS chemical additive package. For the CWS fuels tested in this study, the outcome is a single particle of approximately the same size as the original atomized droplet, consisting of all of the smaller coal particles "glued" together. It is this agglomerate which must be burned in the combustion process. 4) If all of the carbon is burned away, the particle becomes friable, and a fine fly ash can be obtained. At poor carbon converisons, however, the largest fly ash tends to be about the same size as the largest atomized droplets. WATER COAL ASH CONSTITUENTS INITIAL SURFACE DRIES DROPLET BURNS AS CARBON CONVERSION ASH ATOMIZED DROPLET AND MELTS SINGLE COAL PARTICLE CONSTITUENTS ARE LIBERATED Figure 8 Proposed CWS Combustion Mechanism -16- |