Assessment of the possibility of mercury removal from the organic and the mineral matter of hard coals in the process of thermal pretreatment

Abstract

One of the methods which enable a reduction of mercury emission from the energochemical coal conversion processes is the usage of low-mercury coal. The availability of such coals is limited. This necessitates the use of technological operations which allow for the removal of mercury from coal before its conversion (the precombustion methods). The effectiveness of these methods is strongly dependent on the mode of mercury occurrence in coal. It is common knowledge that mercury can occur in coal in both the organic and the mineral matter. Therefore, a universal method should allow for the removal of mercury from the mineral matter as well as from the organic matter of coal. The coal cleaning technologies currently used (dry and wet) enable the removal of only a portion of mercury occurring in the mineral matter of coal. In the case of the thermal pretreatment process, there is a conspicuous lack of knowledge concerning its effectiveness in terms of mercury removal from the organic and the mineral matter of coal. This issue was considered in the presented paper.To achieve the goal, samples of clean coals and rejects derived from the hard coal cleaning process were investigated in the thermal pretreatment process at the temperature of 300 °C. The examined clean coals were characterized by a relatively high content of the organic matter and a low content of the mineral matter. The rejects, by contrast, contained mainly the mineral matter.The thermal pretreatment process allowed for the removal of mercury from clean coals within the range from 13.0 to 45.2%. In the case of the rejects, the effectiveness of mercury removal was 33.3% and 34.5%. On this basis, it could be assumed that the thermal pretreatment process enables a partial mercury removal from both the organic and the mineral matter of hard coal.