Agglomeration of low-rank coal as a pretreatment for direct coal liquefaction

Abstract

Laboratory experiments demonstrated that low-rank coals can be cleaned by agglomeration with distillate coal liquefaction recycle oils. Materials tested included a lignite, three subbituminous coals, a bituminous coal, two petroleum oils, and three coal liquefaction recycle oils. Ash rejections obtained were as high as ~ 50% for Texas lignite and 15–20% for two Wyoming subbituminous coals. A Montana subbituminous coal showed no ash rejection, though physical agglomeration occurred. Organic recoveries for the low-rank coal tests were always > 98%. All three liquefaction recycle distillates tested were effective agglomerating agents for low-rank coals. In the few cases tested, adjustment of the slurry pH to 2.0 or addition of cresylic acid to the slurry had beneficial effects for the lignite agglomeration. Selectively retained in the product ash were Fe (a potential liquefaction catalyst), Ti, Ca, and Mg, whereas Na was selectively rejected.