Experimental determination of the solid phase density of thermal power plant ash

Abstract

Recycling of ash and slag waste from thermal power plants is an important environmental and economic task. The widespread use of ash in construction is mainly hindered by the high content of unburned carbon. The fine granulometric composition of the ash makes most mechanical methods of recycling and flotation ineffective, and is the most effective, environmentally friendly, and cheapest method is hydraulic separation. It allows for the recovery of about 70% of construction raw materials, in which the carbon content is reduced to regulatory commercial values, from 20% in raw ash to 5–10%. A central element of hydraulic separation research is establishing the hydraulic characteristics of the fly ash, with a special focus on determining its actual density, considering that the ash includes more than 10 different mineral components that have also undergone high-temperature transformation. Theoretical determination of the solid phase density of a multi-component mixture does not yield a reliable result. This article examines methods for determining bulk, true, and actual density, experimental approaches to their measurement, and the impact of various factors on these parameters. Correct density determination underlies the calculation of hydraulic characteristics of ash suspensions, the speed of hydraulic flows, and the efficiency of extracting individual components by way of hydroclassification and hydroseparation. The purpose of the research is to refine the methodology and experimentally determine the density of the solid phase of fly ash in its natural state and ash classified by size -240+40 µm, -40+0 µm, using the sample of ash from Pridniprovska TPP. The results of this work are significant for engineering when creating new technologies, for hydraulic devices recycling ash aimed at minimizing environmental impact and optimizing the use of technogenic resources. It was found that the density of the solid phase of ash from the ash dump of Pridniprovska TPP varies from 1.783 g/cm³ to 2.3, averaging 2.0 g/cm³. Variations in density are related to the inhomogeneity of the chemical composition, the presence of closed cavities in the particles. Keywords: fly ash, ash and slag waste.