Deposition characteristics of coal ash slurries at higher concentrations

High concentration slurry disposal system (HCSD) for transportation of coal ash to ash ponds from coal fired thermal power plants using pipelines has emerged as an economical and environmental friendly method. Coal Ash in slurry form is deposited in the ash pond and hence the deposition characteristics at higher concentrations (Cw >60% by weight) are very important. The settled solid profile in the ash pond at high concentrations is of great interest to the ash pond designers. The present study is an attempt to establish the relationship between the settled solid profile and the physical/rheological properties of coal ash slurry at high concentrations. The settled solid profile is experimentally measured in terms of cone angle for slurries of fly ash as well as mixture of fly ash (FA) and bottom ash (BA) in the ratio of 4:1 at high concentrations. The values of cone angle if the slurries are poured on either a pervious or impervious bed have also been measured. The results obtained from the experiments show that the cone angle depends on rheological properties like yield stress and Bingham plastic viscosity which in turn depend on various properties like solid concentration, particle size distribution etc. Also, cone angle for fly ash slurry is higher than that for the mixture of FA and BA slurry at any given concentration. Further, it was also observed from the experiments that cone angle is higher for pervious bed as compared to impervious bed for both types of slurries.