Management and Utilization of Fly Ash Containing High Free-Lime and Sulfur Trioxide Contents

Abstract

This study focuses on managing fly ashes with elevated free lime and sulfur trioxide contents, which are produced at a coal-fired power plant. Two techniques are employed for this purpose. The first technique involves pre-combustion, where correlations between coal and fly ash properties are established to estimate the properties of the resulting fly ash. Statistical analysis was performed on six years' worth of data on coal and fly ash properties provided by the power plant, including coal ash and fly ash analyses, to establish these correlations. These relationships not only help to produce fly ash with desired properties but also help to separate, collect, and manage the off-standard fly ash with undesired properties. The second technique is a post-combustion approach, specifically fly ash blending. An extensive experimental program was conducted to investigate the effects of blending high-free lime fly ash with low-free lime fly ash to be able to utilize the fly ash with high free lime content in the concrete industry. Three types of fly ashes were derived from 2 sources, and free lime was added up to increase the free lime content in these fly ashes. Subsequently, six blended fly ashes were prepared by mixing low and high-free lime fly ashes to evaluate their properties. Various tests, including water requirement, setting times, compressive strength, autoclave expansion, expansion due to alkali-aggregate reaction, and sulfate expansion, were conducted on the blended fly ash mixtures. When compared with the results of a previous study, the performance of the mixtures with the blended fly ashes fell between those of the mixtures containing high and low-free lime fly ashes. This finding indicates that the blending technique holds promise in addressing the issue of high-free lime fly ash effectively.