OCR Text |
Show In these investigations, a distinction was made between particle arrival and deposition rates. The ratio of the two is termed the adhesion fraction and is usually expressed as the percentage of the arriving particles which "stick" to the surface. A value of 100 percent was assumed by some investigators (Rosner et al., 1979; Vermes, 1979; Decorso et al., 1979); however, a value less than this can be used based on the probabilities of particle adhesion (Cohn, 1982). Other investigators saw the need to consider both the adhesion and removal forces acting on deposited particles (Wenglarz, 1981; Menguturk et al., 1982; Vermes, 1979). An additional mechanism for particle adhesion has been stated by Wenglarz (1981) in his consideration of coal-fired Pressurized-Fluidized Bed Combustor (PFBC) power plant turbines. He commented that at inlet temperatures of less than 870 C (1600 F), particle attachment to surfaces may be due to weak van der Waal's forces with a minimum of glue, and at inlet temperatures greater than 885 C (1623 F), particle adhesion may be due to molten Na2S0^. With respect to fuel, he added that a Mg/V ratio of 3 to 1 in the fuel is preferable so that Mg-^Og (melting point 1205 C or 2200 F) can form. In this way, the highly corrosive ^2®b w""^ ^ow melting point can be combined with Mg so that the formation of molten glue deposits could be reduced and most of the corrosive deposition eliminated. Some typically found glue compounds of depositable particles, which have their origins in the fuel, have been noted by Whitlow, et al. (1982). 1.5.17 |