A mass transfer model is developed that considers diffusive and chemical aspects of sodium sulfate formation and deposition on cooled blades of coal-fired gas turbines. The roles of gas phase condensation of sodium sulfate and multicomponent diffusion across a chemically frozen thin boundary layer are elaborated. A rational procedure is presented for correlating material wastage with laboratory weight gain data obtained by exposing alloy specimens pre-coated with a thin film of salt to SO2-SO3 in an oxygen environment. The sodium sulfate mass transfer model is used in conjunction with the correlation to project blade corrosion and lifetime as a function of gas turbine inlet temperature, blade cooling, and sodium and sulfur contaminant concentration.

A rich-quench-lean subscale turbine combustor has been used to expose specimens to the products of combustion from several beneficiated coal-water fuels. An analytical scheme is formulated to extract sticking coefficients from the measured weight gain data, particle size spectrum, and particle density and composition. The inferred sticking coefficients, appropriate for impaction on the pressure surface, range between 0.0003 and 0.11 and are strong functions of the gas and surface temperatures but rather insensitive to the impact angle. The implications of these results on coal-fired gas turbine operation are discussed.

f ( ) = average over flow cross-section (t) = binomial coefficient = approximate solution for indicated function, based on Eq.

A parametric study is conducted to elucidate the role of char, soot and ash particulates in determining the radiation properties of coal flames. The effects of combustion particulates are discussed in terms of the modification of the band structure of gas radiation to a luminous spectrum, introduction of scattering in radiation transport, particle size distribution, particle loading and particle composition. The results are interpreted as possible effects of coal beneficiation, coal micronization and flyash composition on heat transfer to the water walls of a coal furnace. I. INTRODUCTIONThe transfer of energy by iDfrared radiation from the flame to the waterwalls is a key process in utility steam generators using pulverized coal fuel.The major controlling factor in designing and operating a utility steam generator is the furnace exit temperature. This temperature determines whether ash deposits in the convection section will be molten and difficult to remove or flaky and easily controlled by soot blowing.Moreover, the need for attemperation of superheat steam and reheat steam has an impact on cycle efficiency and economics and is directly affected by the furnace exit temperature. This exit temperature is determined by the rate of fuel input, the burner design and by the radiative properties of the combustion gases and particulates. Thus, when utilities burn a coal different than that for which the furnace was designed, the unit must often be derated. Finally, the different radiative properties of the combustion products affect the furnace exit temperature and the heat transfer throughout the convective section.lt is generally agreed that the convective heat transfer is small compared to the transfer by radiation. The radiative transfer is due to both band emission from CO 2 and H20 and continuous emission from the various types of particles which occur in the flame. Existing evidence indicates that particulate contribution is dominant and therefore plays a key role in determining furnace exit temperature.Since the radiation characteristics of the entrained particles can be expected to be related to coal type and particle size, changes in the radiative heat transfer are a possible cause of the observed sensitivity of furnace performance to the coal being fired.The various types of particles entrained in the combustion gas can be classified as being carbonaceous (coal, char and soot) or noncarbonaceous/ inorganic (flyash). The carbonaceous particles are confined primarily to the firebox region whereas flyash may be the only type of particles remaining in the heat absorption region. The parameters determining particulate radiation are particle mass fraction and distribution in the flow field, particle size distribution, and the complex refractive index generally represented as n + ik where n and k are, respectively, the refractive index and the absorption The use of micronized (mass mean diameter smaller than I0 pm) and deeply beneficiated (ash and sulfur contents less than 1%) coal-based fuels being considered as...

A hybrid technique has been developed to solve three-dimensional spectral radiation transport equations for absorbing, emitting and anisotropically scattering media. An optimal mix of computational speed and accuracy is obtained OlS'fl_ilTIONOFTHISDOCUP4EP/T I$ UNLIIfIITI_ orr=,o_uc, the_