Pilot-scale studies of sulfur and ash removal from coals by high gradient magnetic separation

This paper presents the results of pilot-scale studies of sulfur and ash removal from coal by high gradient magnetic separation (HGMS). Work was done on both the liquefied coal and the raw pulverized coal in water slurries. The effects of residence time, field intensity, packing material and density, slurry concentration and recycle on the grade and recovery of the wet separation of sulfur and ash from water slurries of Illinois No. 6 coal were quantitatively examined. The HGMS was effective in reducing the weight percent of total sulfur, ash, and inorganic sulfur by as high as 40, 35, and 80%, respectively; while achieving a maximum recovery of about 95%. The results have also provided the first experimental verification of the applicability of Bean's magnetic filtration model in quantitatively correlating the data obtained from the pilot-scale beneficiation of coal slurries by the HGMS. The successful verification of the model allows one to quantitatively identify the trade-off of operating parameters so as to optimize the magnetic removal of sulfur and ash. A pilot-scale HGMS system for the magnetic sedation of mineral residue from the liquefied coal has been designed and constructed. Typical results from preliminary experiments with the liquefied solvent refined coal (SRC) have been quite encouraging, indicating that the HGMS was effective in reducing the total sulfur and ash contents by as high as 70 and 76%, respectively. Finally, the liquefaction of the magnetically treated Kentucky No. 9/14 coal was studied and compared with that of the untreated coal. It was found that although the mineral matters which had been removed magnetically had a significant catalytic effect on the liquefaction behavior, the organic hydrodesulfurization remained practically the same for both the untreated and treated coals. This suggests that the magnetic removal of mineral matters prior to liquefaction may be advantageous for the SRC and other related liquefaction processes, in which the minimum hydrogenation is especially desired and the hydrodesulfurization is often limiting.