THE PROPERTIES AND THERMAL EFFECTS OF ASH DEPOSITS IN COAL-FIRED FURNACES

The physical and chemical character of fireside ash deposits depend on the processes by which deposits are formed and subsequent reactions w ithin the deposit and with furnace gases. The properties influencing h eat transfer, absorptivity for radiative transfer and thermal conducti vity for conductive transfer are shown from many measurements to depen d on this character. The literature data for the properties are review ed and are shown to depend principally on the physical ash character a nd whether the deposits have a particulate character or are sintered o r fused. Bounds for the range of properties and expected variations wi th temperature and deposit porosity and other physical properties are suggested and compared with those for pure oxides and salts. For the r adiative properties, theoretical predictions based on the optical prop erties are shown to predict trends with temperature and particle size for particulate ash and the observed transfer to higher emittance valu es for slags found at higher temperatures. The influence of the variat ion of these properties on radiative transfer is then quantified using mathematical models of furnaces.