Mercury separation from fuel constituents in an ash-free coal manufacturing process

A novel process to produce ash-free coal, called Hyper-Coal (HPC), has been developed based on the coal liquefaction with organic solvent extraction. Seventy wt% of combustible contents can be extracted from raw coal via the dissolution in 1-methylnaphthalen at 633 K, reducing the ash and alkali contents to less than 1000 and 0.5 ppm, respectively. This process is also a promising approach to separate toxic trace elements from fuel constituent in coal before its combustion. Mercury is one of the toxic trace elements of growing concern, because mercury emission from a coal combustion process to the atmosphere has been becoming a serious problem in the coal use all over the world. Therefore, in this study, various intermediate products such as coal-organic solvent slurry were sampled from the HPC manufacturing process, and analyzed for mercury contents to investigate the mass balance and the distribution behavior of mercury in the process. As a result, it was found that a large portion of the mercury was separated from fuel constituents and recovered as a dissolved matter in the solvent. This dissolved mercury, however, built up in the total distribution behavior of mercury in the HPC manufacturing process again because the solvent was recycled for the coal extraction process without any cleanup treatment this time. Nevertheless, the mercury distributed into the HPC was lowered to be 20% or less of the total found in raw coal.