NO release and reactivity of chars during combustion: The effect of devolatilization temperature and heating rate

The study has involved the investigation of the influence of pyrolysis heat treatment temperature (HTT) and heating rate on the reactivity and the release of char-N during temperature-programmed combustion (TPC) of a set of wire mesh reactor chars in a thermogravimetric analyzer-mass spectrometer system. The gas evolution profiles are bimodal and this indicates the presence of species of different reactivity. It was found that increasing pyrolysis temperature and heating rate both produced significant variation in the reactivity of the resultant chars with the former being more influential. This is apparent from the shift of peak positions and the change in the relative intensity of the low- and high-temperature peaks of CO, CO2, and NO evolution profiles. The differences in the CO2 and NO evolution profiles observed between the Gedling entrained flow reactor (EFR) and wire mesh reactor (WMR) chars of similar heat treatment temperatures may be explained by the different extents of pyrolysis experienced by the chars. However, chars produced in the WMR with pyrolysis temperatures up to 1200 degrees C show little variation in the char-N conversion to NO. This is believed to be due to the highly reactive nature of the chars which give rise to a high extent of reduction of the primary product NO formed during gasification leading to a low NO/char-N ratio. Heat treatment of the chars at lower heating rates and longer soak times to temperatures in the range 1100-1400 degrees C lead to reduced char reactivity and higher NO/char-N ratios under temperature-programmed combustion conditions. The results are consistent with the reduction of the primary oxidation product NO on the surface and in the pores of the char.