Application of coal ash in fluidized thermal beds

Thermal properties of soils are of great importance in view of the subsurface transmission of either heated fluids or high power currents. Fine-grained soils, in particular clays, pose a serious problem for conduction of heat due to very high thermal resistivity. As such, it becomes mandatory to devise a mechanism by which thermal resistivity of fine-grained soils may be reduced. An engineered backfill, with suitable thermal properties, is adopted frequently to reduce thermal resistivity of these soils. The potential of coal ash (i.e., in the form of either fly ash or lagoon ash) as a suitable backfill material, when mixed with cement, sand, and aggregates, has been explored by several researchers and is well established. However, with increasing amounts of lagoon ash being disposed of at thermal power plants, it is important to study its effectiveness as a fluidizing agent and its use in designing a proper fluidized thermal bed (FTB). Based on laboratory tests on different soils, generalized equations for estimating soil thermal resistivity have been developed in the recent past. These equations have been used for obtaining the optimum quantity of the lagoon ash for designing a fluidized thermal bed. Effect of moisture content and compaction density on thermal resistivity of different FTB compositions has also been studied.