Utilization of Estonian oil shale semicoke

Abstract

In thermal processing of oil shale in vertical retorts huge quantities of a solid waste — semicoke are formed. It has been shown that circulating fluidized bed combustion of semicoke could be a promising technology allowing utilization of its high residual energy potential. The main parameters of combustion process and the additional heat produced were calculated and verified by combustion tests in a fluidized bed device with a thermal capacity of 50 kW th. The experiments indicated that semicoke with low moisture content can be burnt directly in fluidized bed. For the combustion of semicoke with higher moisture content (over 10%) about 10% of oil shale must be added. In addition, possibilities for utilizing residual carbon present in semicoke by obtaining carbon-rich materials with further production, for example, activated carbon were discussed. A series of experiments accompanied by SEM and EDAX analysis was carried out in order to elucidate the distribution of carbon and mineral part in semicoke and to find possibilities for their separation and subsequent enrichment. Different separation methods — selective grinding and subsequent screening, pneumatic separation and triboelectroseparation method were analyzed. It was shown that due to close integration of mineral and organic part in semicoke, the separation of carbon-rich ingredients by these methods was not enough effective to obtain enriched products suitable for the production of activated carbon.