Effective Composition of High Concentration Fly Ash-Bottom Ash Mixture Slurry for Efficient Disposal Through Pipelines

Abstract

The composition of high concentration ash slurry requires careful selection of particle size distribution (PSD) to achieve the required rheological properties for efficient disposal through pipelines. In the present study, the maximum static settled concentration, CW-max, tests and rheological measurements were carried out for a total eighteen nos. of ash samples (nine nos. of fly ash samples and nine nos. of fly ash-bottom ash mixture samples) in the concentration range of 60 - 70 wt%. It was observed that the CW-max value reached maximum for the composition of mixture slurry consisting of fly ash and bottom ash with d50 as 6.4 mm and 144 mm respectively at a fixed blend ratio (weight ratio of fly ash to bottom ash) of 4:1. This was attributed to the packing effect and was correlated to the ratio of surface to surface separation for the coarse bottom ash particles, b, to the average fly ash particle size, d50-f , to achieve higher solids concentration. The rheological behaviour of the ash slurry samples were described by non-Newtonian power law model in the range of solids concentration studied. Also a substantial reduction in viscosity was observed for the same composition of mixture slurry sample which was attributed to the poly-dispersive characteristics of the ash particles. It was indicated that the slurry viscosity was very much influenced by particle size ratio (l = dlarge/dsmall ) and volume fraction of solids. The study revels that the blending of fly ash and bottom ash at a controlled PSD may be employed for preparation of high concentration ash mixture slurry for pipeline transport.

Keywords

• fly ash
• bottom ash
• maximum static settled concentration
• rheology
• maximum volume fraction