Processed bitumen pitch as an additive for marginal coking coals

Abstract

Pitch binders from various sources, including those derived from Canadian tar sands bitumen, conventional petroleum and coal tar were assessed on a comparative basis as additives for inert-maceral rich, partially oxidized, high-rank bituminous coals from western Canada. Results from dilatation tests and free-swelling indices indicated that the pitch obtained from thermally hydrocracked Athabasca bitumen was far superior to the pitch from the unprocessed feedstock, and gave the greatest improvement in the thermal rheological properties of the various coal/pitch mixtures tested. Thermal hydrocracking improved the quality of the unprocessed bitumen pitch, making it a suitable additive for high-rank bituminous coking coals. These findings were confirmed by pilot-scale coke-oven tests. Optical microscopic examinations of the semi-cokes indicated that the thermally hydrocracked Athabasca bitumen pitch had a distinct advantage over the other binders tested in being able to penetrate the cell cavities of semi-fusinite and fusinite. The ability of a pitch to penetrate pores within the coal macerals appears to be related in part to the size of the mesophase spherules formed during carbonization of the pitch.