Abstract
Some trace metal compounds in the fuel tend to be enriched in the fine particulates. The fine particulates with the size of less than 1 m as well as hot metallic vapor with alkali metal compounds cause erosive and corrosive effects to blades of a gas turbine. Therefore, it is necessary to understand behaviors and mechanisms of fine particulates formation with alkali metal compounds during coal combustion. Combustion tests were conducted, using an electrically heated drop tube furnace to burn two types of coal with different Na and K concentrations. The burning particles were collected by a Low Pressure Impactor (LPI). As a result, the enrichment mechanism of Na was elucidated by the size distribution of Na concentration in the fine particulates collected in each stage of the LPI. For the fine particulates, the enrichment phenomena were controlled by an internal reaction of Na compounds vapor with fine ash particulates or nucleation, which depended on the coal type. For the relatively coarse particulates, on the other hand, the gas film diffusion controlled the enrichment of Na compounds into the ash particles with the chemical reactions of Na compounds vapor with the those ash particles.
