Dense ash slurry benefits reported
Fly ash and bottom ash generated by coal-fired power plants are generally transported hydraulically, pneumatically or by mechanical means to ash dumps, natural ash dams or artificial ash dams. The hydraulic transport of fly ash has traditionally been done in the form of dilute slurries, containing 10- to 30-percent solids by weight.
However, dilute slurry pumping has been questioned in view of: large quantities of contaminated water being recirculated; problems controlling scale buildup and wear; potential for leakage of ash water from dams and for ground water pollution; danger of ash dam wall failure; pollution of surrounding terrain by wind-born dust; high cost of large volume dam construction; and cost and difficulties associated with stabilizing and restoring the site.
Environmental constraints on ash disposal have limited the options available and increased costs in many countries. The problems are substantially eliminated by preparing ash slurry at high density for discharge onto a sloped disposal site where the deposit stabilizes, according to a recent report from EnviroTech Pumpsystems Netherlands b.v.
Highly concentrated, thick slurry runs out slowly over the disposal site after leaving the pipeline, and normally there is no water leakage. Abrasive wear is reduced because of laminar flow and low flow velocity, and dense slurries can be transported at low flow velocities in mild steel piping without much wear. High density disposal can offer several advances, such as: dense fly-ash slurries use significantly less water than dilute slurries; natural retention of slurry water in dense slurries often avoids the need for an ash dam water reclamation system and return water lines; the ash generally will dry out to form a fairly solid surface, unaffected by erosion and not prone to dusting in windy conditions; and energy saving for running pumps can be 50 percent or higher.
Piston diaphragm pump for fly-ash transportation in Australia.