From O 2 / CO 2 to O 2 / H 2 O combustion : the effect of large 1 steam addition on anthracite ignition , burnout and 2 NO x formation 3 4

Steam-moderated combustion has been proposed to supress flue gas recycling in 12 oxy-fired units, but the influence of replacing CO2 by H2O has to be deeply studied. 13 In this paper, oxy-fuel combustion of anthracite with large steam addition has been 14 experimentally characterized, and main results are discussed as concerns the 15 influence upon the ignition temperature, the burnout and the NOx formation. The 16 tests have been carried out in an electrically-heated entrained flow reactor for a set 17 of O2/CO2 and O2/H2O/CO2 atmospheres, with steam addition up to 40 % vol. The 18 results show that ignition temperature diminishes when steam is added in low 19 rates (maximum decrease of 16 oC), but the trend is reversed for the higher steam 20 concentrations (maximum increase of 18 oC). The effect of steam addition on coal 21 burnout rates is more significant for the 21 % vol. O2 atmosphere, with a decrease 22 of 2.2–5.3 percentage points, and almost negligible for the 35 % vol. O2. An 23 outstanding reduction of NO specific emissions is detected when adding H2O, with 24 decrements ranging 28–45 % compared to the dry conditions. The transition from 25 O2/CO2 combustion to O2/H2O combustion barely affects the anthracite conversion 26 but significantly diminishes NOx formation rates. 27 28