Influence of dry coal deshaling by pneumatic vibrating FGX separator on steam gasification of coal

Abstract

Dry deshaling is a modern technique of enhancing coal quality and is considered more ecological and economical than traditional washing processes. Dry deshaling results in an increase in calorific value of coal, removal of ecotoxic elements and generation of usable by-products. At the same time, as a result of the deshaling, the components catalysing the gasification process are also removed. Therefore, the effect of this operation on gasification is uncertain. This study aimed to assess the effect of dry deshaling as performed by a pneumatic vibrating FGX separator on the steam gasification of coals. Two coals were subjected to dry deshaling with various efficiency of minerals removal (pre-improvement of coal quality, and deep enrichment to receive high-quality clean coal). Parents coals and corresponding clean coals were characterised and subjected to gasification measurements at 800, 900 and 1000 °C and the pressure of 1 MPa, using the thermovolumetric method based on an analysis of the composition of the resulting gas. The obtained results showed that reduction of ash content by dry deshaling was accompanied by an increase in carbon content, caloric value and change in ash composition (decreased content of SiO2 while increasing the content of numerous catalytically active oxides, such as Na2O, CaO, MgO and Fe2O3), and these changes were the greater, the deeper the deshaling was. Moreover, the deshaling operation positively affects the gasification process - formation rates of CO and H2 during char gasification, reactivity indicators, and yields of CO and H2 were improved. However, this positive effect was the more remarkable, the less ash was in the analysed sample. This indicates that the removal of minerals facilitated the access of the gasifying agent to the char surface, thus increasing the efficiency of the carbon-steam reaction. In turn, the effect of dry deshaling on calculated kinetic parameters was ambiguous, probably due to the complex mechanism of gasification reactions. Nevertheless, the obtained results show that FGX technology may be an attractive way of preparing coal for gasification. However, deep enrichment is necessary to substantially improve the steam gasification of coal.