Simulation study of migration of hazardous trace elements in coal during gasification in entrained-flow gasifier

DONG He; XIE Qiang; TANG Yuegang; DANG Jiatao; WANG Xin

Abstract：Migration and partition of typical hazardous trace elements (TEs),including Hg,F,Be and U,in Ganhe coal during gasification in a lab-scale entrained-flow gasifier,has been investigated in the previous work.In this paper,process model of entrained-flow gasifier was studied and established based on the principle of minimizing Gibbs free energy with the aid of Factsage.In the light of thermal conversion procedure of fine coal particles,the coal gasification was interpreted as consisting of two stages including pyrolysis and gasification reaction,meanwhile,the carbon conversion modified coefficient was introduced to improve the accuracy of model.Then the process model was used to generate a simulation of modes of occurrence and possible release mechanism of TEs during entrained-flow coal gasification,and the simulated data were compared with the experimental data obtained from lab-scale gasification experiment mentioned above.The results show that good agreement has been attained between the simulated and experimental data.Besides,for Ganhe coal,under the reducing condition,mercury presents as Hg(g) and UO2 (s) is the dominant species of uranium,while fluorine and beryllium mostly present in gas phase in the form of HF(g) and Be(OH)2 (g),respectively.Thus,it could be concluded that mercury is a highly volatile element and its migration mainly depends on the elemental properties while the modes of occurrence in coal has little effect on it;fluorine and beryllium are semi-volatile elements,their migration is simultaneously affected by the modes of occurrence in coal and gasification parameters,in which high temperature enhances the release of TEs and reducing condition promotes the generation of the hydrides of TEs;uranium is a mostly non-volatile element and strongly influenced by its modes of occurrence in coal.