Oil agglomeration at low pH as a pretreatment for liquefaction of Wyoming (USA) subbituminous coal

摘要

Pulverized Wyoming subbituminous coal was beneficiated by low-pH oil agglomeration at CONSOL to prepare the coal for direct liquefaction. Conventional cleaning is not very effective in cleaning this coal; for example, conventional oil agglomeration only gives about 20% ash rejection. To improve ash rejection, the coal-water slurry was acidified to a pH of about 0.5. Oil agglomeration was effected with 33% (dry coal basis) of a coal-liquefaction recycle oil and high-shear mixing, producing agglomerates, which were separated from the rejected and dissolved inorganic matter by screening. The SO_3-free-ash content of the coal was reduced by 40% (from 5.5% to 3.3%, dry basis) and the organic recovery was nearly 100%. The alkaline elements that are potential scaling agents and catalyst poisons were selectively rejected from the coal. Iron, a potential liquefaction catalyst, was selectively retained with the coal. A 600 kg batch of coal-oil agglomerates was produced. The liquefaction performance of this material was compared to that of the raw coal in the Hydrocarbon Technologies Inc. (HTI) 1.5 kg/h continuous-flow bench-unit. The agglomerates handled well and improved solids separation performance. The coal conversion with agglomerates (98% MAF) was higher than that with the raw coal (95% MAF), and the product yields (56% C_4-343 °C distillate and 66% C_4-524 °C distillate, MAF basis) were excellent.