Some metal compounds in coal vaporize and form fumes during combustion. The fumes are generally exhausted through the flue gas. For coal-fired combined power generation systems such as pressurized fluidized bed combustion (PFBC), hot vapors may contact with the surfaces of gas-turbine blades. As this contact of the hot vapors with the surface has corrosive effect, it is necessary to control the formation of those fumes, which mainly contain alkali metal compounds. In this paper, the evolution behavior of alkali metal compounds, especially for sodium compounds, has been studied, using an electrically heated drop tube furnace with a low-pressure impactor. The main objective in this study is to elucidate the conditions and the possible mechanisms to form alkali metal compounds in particulate matter during combustion. Two types of coal with different sodium content were tested, where the coal conversion characteristics were established. Furthermore, the evolution and inclusion of sodium compounds into the sub-micron particles were studied in relation to the particle size distribution formed and sodium fraction distribution in the collected fine particulates. The study proved that the evolution and inclusion of sodium in the sub-micron particles depended on function of type of coal via its composition and the form by which sodium compounds existed in coal. The reaction-controlled mechanism and heterogeneous condensation via chemical reactions during combustion affected the inclusion of sodium in the sub-micron particles. In the coarse particles of above about 0.5 μm, reaction that formed those particles was mainly via gas film diffusion surrounding the particle.

This content is only available via PDF.
You do not currently have access to this content.