Flowability Of Moist Coal Combution Fly Ash

Abstract

In the combustion of coal the mineral contents remain as ash. The fine size fraction of the ash leaves the combustion zone with theoff-gas from which it is separated as fly ash. Depending on the physical and chemical properties these fly ashes can be utilized. Anessential parameter for the design and operation of transport equipment and storage facilities for fine grained materials is theirflowability. The moisture content of the material has considerable influence on the flowability because of the increasing influenceof the liquid bridges between the particles and the resulting capillary forces. In this study the influence of the moisture content onthe flow characteristics of a coal combustion fly ash was investigated. The fly ash sample was collected from the dust discharge ofthe electrostatic precipitator of a power plant using Polish hard coal as fuel. The mass median diameter of the fly ash was approximately20 μm. Microscopic images show that most of the particles are spheres. The flow properties of the fly ash were measuredusing a ring shear tester. The moisture content of the sample was adapted by addition of water. The dry fly ash was characterizedby very good flow properties, the flowability ffc was in the category ‘easy flowing’. Significant decrease in flowability was found atincreased moisture contents. Additionally, the bulk density of the fly ash was influenced by the moisture content. Thus, the flow--relevant parameters which have to be considered in design of transport and storage facilities of fine granular material worsenedwith increasing moisture content.