Ash deposits reduce heat transfer rates to furnace walls, superheater tube, and other heat transfer surfaces in coal and biomass fired power plants. The magnitude of this reduction largely depends on the thickness, thermal conductivity, and absorptivity of the deposits. Experiments to measure the thermal conductivity of fly ash deposits are conducted in the MFC.
The thermal conductivity of ash deposits depends more strongly on the deposit's physical structure than on its composition. The denser, more interconnected the deposit structure, the higher the thermal conductivity. Highly porous deposits of loose, unsintered particulate matter generally have low values of thermal conductivity. Solid, sintered deposits with higher densities have higher thermal conductivity values.
This dependence on structure makes in situ measurements particularly valuable, since it is difficult to remove deposits for laboratory analysis without modifying the structure. We have developed a technique to perform such in situ analyses, as illustrated below.