Experimental investigation on the evolution characteristics of anthracite-N and semi-coke reactivity under various O2/H2O pre-oxidation atmospheres

Abstract O2/H2O pre-oxidation could be regarded as a promising approach for clean and high efficiency utilization of high rank coals. A typical anthracite was employed for experimental clarification on anthracite-N evolution characteristics during O2/H2O pre-oxidation. The correlation among reaction atmosphere, nitrogen stripping efficiency and anthracite-N desorption characteristic was evaluated. The emission characteristics of nitrogen containing gaseous species and combustion reactivity of each pre-oxidized semi-coke were identified by utilizing XPS, TPD, Raman and TGA. Both O2 and H2O could synergistically accelerate the crack of large aromatic structures into small and reactive ones, leading to the migration of abundant nitrogen atoms initially located inside the aromatic structures to the edge during the O2/H2O pre-oxidation process. The decomposition of condensed aromatic systems would strengthen the reactivity of semi-coke particles. Nevertheless, excessive H2O (> 10 vol%) would generate massive •H which could penetrate into the matrix of anthracite particles, reducing the total amount of active structures on semi-coke surface. The results in this research indicated that an optimal reaction atmosphere (10 vol% O2 and 10 vol% H2O) was suggested for the anthracite O2/H2O pre-oxidation to realize the most effective regulation on anthracite-N emission pathway in the processes of both O2/H2O pre-oxidation and semi-coke combustion