Beneficiation of lignite by oil agglomeration as an integral part of coprocessing

Abstract

The low cost of Canadian low-rank coals makes them prime feedstocks for coprocessing with bitumens and heavy oils. Depending on the coal concentration in the feed slurry, the high ash level in some of these coals can cause operational problems as well as reduce the overall process efficiency and the net liquid product yield. To reduce the ash content in the feed slurry, oil agglomeration can be used for coal beneficiation (deashing) as an integral part of coprocessing technology. However, an optimum integrated approach requires the use of undiluted bitumen or heavy oil feedstocks as a bridging liquid. Also, low-rank coals as well as oxidized higher rank coals often possess a relatively hydrophilic surface. This makes the application of oil agglomeration extremely difficult. A novel method of beneficiating low-rank coals for coprocessing by oil agglomeration using a part of the feed bitumen for coprocessing has been conceived and developed. This method overcomes the hydrophilic surface problem of low-rank coals and allows the use of undiluted coprocessing feed oils as viscous as vacuum bottoms. Experimental results on the beneficiation of a Canadian lignite with vacuum bottoms are presented. The efficiency of the process was evaluated in terms of combustibles recovery and ash rejection. The agglomeration of Willowbunch lignite (ash content from 20 to 22 wt % on a mf basis) with Interprovincial Pipe Line (IPPL conventional crude) vacuum bottoms resulted in 51 to 97 wt % combustibles recovery and a corresponding 77 to 42 wt % ash rejection. The effects of vacuum bottoms concentration, operating temperature, and processing time on the beneficiation performance are discussed.