Paste technology – not just for mining anymore

Abstract

With recent changes in legislation in the United States the EPA (Environmental Protection Agency) has decreed that the disposal and storage of slurried Coal Combustion Residues (CCR) is no longer acceptable. The legislation applies to both legacy as well as active ponds. In addition, the Effluent Limit Guidelines (ELG) also dictates handling, transport and storage requirements for all process-affected water on site for coal fired power plants. These two significant regulatory changes in the industry are driving power companies towards alternate solutions for their waste management. While paste and thickened tailings technology has been widely used in mining applications around the world for more than 20 years it is relatively unknown in the power sector even though several paste plants have been designed, built and are operating. This paper will describe the issues facing the coal fired power plant industry and how paste and thickened ash is providing an alternative to thermal drying and landfilling options that currently exist. Specifically, test data will be shown that demonstrates the encapsulation of the minerals and metals of concern using paste. The paste recipe was developed to maximize the use of the Flue Gas Desulphurization (FGD) wastewater and other waste and wastewater streams produced in the facility along with the CCR materials available including fly ash and bottom ash. Case studies will also be presented from South Africa and the US, demonstrating the recipes and process design that can be implemented to solve both the CCR and ELG problems.