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Abstract
The coal industry is being subjected to increasing public scrutiny with regards to its effect on the environment and impact on public health and safety. Recently, disposal and storage of fine coal waste slurry has drawn considerable public attention. This article discusses the emerging paste thickening technology as a possible solution to the fine coal waste slurry disposal problem.
Paste-thickening studies were conducted on thickener underflow slurry from a central Appalachia preparation plant. Initial experiments were conducted with a laboratory scale T-Floc apparatus to optimize flocculant dosages to obtain maximum settling flux and underflow solids concentration. Results showed that the addition of anionic flocculant (400 g/t) to the slurry followed by cationic flocculant (100 g/t) provided the highest settling flux (3.85 tonnes/hr/m2) and solids concentration (35% by weight). Pilot-scale paste thickening tests were conducted using a Dorr-Oliver Eimco Deepcone™ thickener. The thickener concentrated the solids from 10% to 50% by weight using about 450 g/t of anionic and 150 g/t of cationic flocculants. The thickened paste had a yield stress of about 165 Pa that is sufficiently low to allow transport using a conventional positive displacement pump to a disposal area. The clarity of the overflow stream was similar to that currently obtained with a conventional thickener.
Funding for the project was provided by the Center for Advanced Separation Technology (CAST) and the Kentucky Science and Engineering Foundation (KSEF). Acknowledgments are made for the assistance provided by the Dorr-Oliver EIMCO, Arch Coal of W. Virginia, and Clean Soil and Energy Technologies. Mr. Roger Carter of Nalco Chemical Company provided flocculants and assistance in setting up the flocculation system at the plant site. Acknowledgement is also made of assistance provided by John Wiseman and Allen Howard of University of Kentucky Center for Applied Energy Research.