Synergistic effects in rapid co-pyrolysis of semi-coke and coal at high temperature

Abstract

In this paper, semi-coke and bituminous coal were co-pyrolyzed at high temperatures by using an entrained flow reactor to investigate the synergies between semi-coke and coal on pore characteristics and fuel nitrogen conversion. The non-additive interaction between the two fuels on BET surface areas of mixture chars was observed. Less yields of NOx and its precursors during semi-coke pyrolysis demonstrated that char nitrogen, rather than volatile nitrogen, contributed to the more NOx emission. The inhibition on NO yields happened above 1100 °C, while the promotional effect worked below 1100 °C. The O/N ratio played a more significant role than H/N in NO yield below 1200 °C, while the influence of H/N was dominant above 1300 °C. The CH4 yield reached the peak at 1000 °C during co-pyrolysis, and was significantly improved due to interaction. The high temperature and co-pyrolysis were helpful to convert more fuel-N to N2 and reduce the yields of char-N, NOx, and its precursors. By contrast with the yields of gaseous products, the char nitrogen yield was hardly influenced by the synergistic effects. The release of nitrogen was slower than that of carbon below 1400 °C, which was opposite at 1500 °C. This work can provide reference for clean and efficient utilization of semi-coke.