Reliable pneumatic transport of coarse ash in dense-phase by optimally mixing with fine ash

Abstract

Fly ash generated in thermal power plants can vary widely in characteristics such as size, fine content, and bulk density. From a pneumatic conveying perspective, the ash can be either a dense- or dilute-phase material. Unfortunately, a common pneumatic conveying system cannot optimally cater for both dense- and dilute-phase. As a result, the installed systems are either over-designed (causing additional airflow, capital costs, excessive pipeline wear, etc.) or under-designed (causing pipeline blockage or very less tonnage). Based on a pilot plant study of conveying 10 blends of ash, 75% coarse ash and 25% fine ash create the optimal blend for dense phase conveying. A new bulk powder Froude number term (based on loose poured bulk density) and coarse-to-fine ratio have been used to represent reliable conveying criteria. For reliable dense-phase conveying, the ash mixture should have a bulk powder Froude number < 10 and a coarse-to-fine ratio > 10.