THEORETICAL AND EXPERIMENTAL STUDIES OF THE DEPOSITION OF NA2SO4 FROM SEEDED COMBUSTION GASES

The deposition of sodium sulfate from flames containing sodium and sulfur is regarded as one of the fundamental steps in the phenomenon of “hot corrosion” of turbine components. Recently, a local thermochemical equilibrium (LTCE) method of predicting condensation temperatures of sodium sulfate in flame environments was described. This paper presents results of an experimental study to test the validity of the theoretical dew point predictions and to provide the basis for developing a deposition rate theory. Experiments were run in a Mach 0.3 atmospheric pressure laboratory burner rig. Flames were doped with sea salt, Na2SO4, and NaCl, respectively. Deposits were collected on cylindical-platinum targets placed in the combustion products stream, and the deposition rate was studied as a function of collector temperature. Experimental deposition onset temperatures checked within experimental error with LTCE-predicted temperatures. A multicomponent mass transfer equation was developed to predict the rate of deposition of Na2SO4(c) via vapor transport at temperatures below the deposition onset temperature. The phenomena of species transport by simultaneous Fick diffusion, Soret (thermal) diffusion, convection, and turbulence are included, subject to the basic assumption that no reaction or phase change occur within the diffusion boundary layers. The present formulation is sufficiently general to include the transport of particles, provided they are small enough to be formally treated as heavy molecules. Agreement between maximum deposition rates predicted by this chemically frozen boundary layer (CFBL) theory and those obtained in the seeded laboratory burner experiments is good, but the predicted dependence on surface temperature exhibits plateau-like behavior not evident in the present experimental results. © 1979, The Electrochemical Society, Inc. All rights reserved.