Completed Research
Investigation of Pyrite and Mineral Matter Reduction in a Selective Coal Agglomeration Process
Michael Vincent Ciocco, PhD, 1992
(Abstract: UMI Dissertation Publishing)
In selective agglomeration processes, fine coal/water slurries are contacted with light hydrocarbon in a high-shear agglomerator. Based on the hydrophobicity of the organic coal macerals, the light hydrocarbon selectively wets and bridges the clean coal particles to form agglomerates whereas the mineral matter, including pyrite, remains dispersed in the water phase. The major problem associated with selective agglomeration processes is poor pyrite-mineral matter removal. The objective of this research is to effectively liberate the mineral matter, particularly pyrite, from the feed coal by various grinding methods and to optimize the clean coal recovery and mineral matter as well as inorganic (pyritic and sulfate) sulfur removal using an advanced selective agglomeration process. Coal samples were wet and dry ground inside a sealed (inert atmosphere) chamber. Pyrite size and association analyses were carried out on the ground coal samples to assess the degree of inorganic sulfur liberation. A method was devised to estimate the fraction of inorganic sulfur liberated during grinding. A standardized agglomeration test procedure (using the light hydrocarbons, n-pentane and n-heptane) based on the reproducibility of the results of ash, total sulfur and inorganic sulfur reductions, and Btu recovery was established. The effects of surface modification reagents, pH, agglomeration time, agglomerant type, agglomerant to coal ratio, recovery sieve size, addition of a binder, particle size, and selective grinding with particle size classification on the performance of the agglomeration process were investigated. Statistical analysis of the results showed that increasing the agglomeration pH increased the ash and inorganic sulfur reduction for Upper Freeport coal and the inorganic sulfur reduction for Illinois #6 coal. Selective grinding with particle size classification was found to improve the ash and inorganic sulfur reductions for Illinois #6 coal. The energy recoveries for Illinois #6 and Wyodak coals were improved by using a smaller recovery sieve size, higher agglomerant to coal ratio, and addition of a binder. The effect of the agglomeration process on trace elements removal was also investigated. It was found that for the coals studied a majority of the trace elements were associated with the inorganic fraction.