Abstract Gasification reaction is not supposed to be omitted for pulverized coal MILD-oxy combustion regime, especially for the wet recycle (steam up to 40 vol%). This paper numerically investigates the individual effects of steam and oxygen on pulverized coal MILD-oxy combustion to have better understanding of char reaction behavior under this combustion mode. Results show that, the flame temperature affected by steam is because of thermal radiation, whereas that of O2 is because of chemical reactivity. The maximum value of the turbulent Damkohler number (Da,t) is within 0.25–1.9 for all cases, implying that the rate of chemical reaction is comparable with that of turbulent flow. For 30% O2 and 40% steam cases, gasification reaction accounts for up to ~62%. With a given O2 level, the reaction of char-H2O competes the active sites with char-O2 and char-CO2, whereas for a certain level of steam, a positive synergy exists between char-H2O and char-CO2. The effect of CO + H2O → CO2 + H2 on generating H2 becomes increasingly significant when O2 content is >21%, and easy to occur under low steam concentration. Increasing the O2 and steam is conducive for the decrease in overall char burnout rate. As the steam content increases, the reduction on char burnout rate is insignificant for 18% and 21% O2 cases, but it is serious for 24%–30% O2 cases.

中文翻译：

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粉煤 MILD-oxy 燃烧炭表面反应行为的 CFD 建模：氧气和蒸汽的影响

摘要 对于煤粉 MILD-oxy 燃烧制度，尤其是湿循环（蒸汽高达 40 vol%），不应省略气化反应。本文数值研究了蒸汽和氧气对煤粉 MILD-oxy 燃烧的单独影响，以更好地了解这种燃烧模式下的焦炭反应行为。结果表明，受蒸汽影响的火焰温度是由于热辐射，而O2的火焰温度是由于化学反应。在所有情况下，湍流 Damkohler 数 (Da,t) 的最大值都在 0.25-1.9 之间，这意味着化学反应速率与湍流相当。对于 30% O2 和 40% 蒸汽的情况，气化反应占高达~62%。在给定的 O2 水平下，char-H2O 的反应与 char-O2 和 char-CO2 竞争活性位点，而对于一定水平的蒸汽，char-H2O 和 char-CO2 之间存在正协同作用。当O2含量>21%时，CO+H2O→CO2+H2对生成H2的影响越来越显着，在低蒸汽浓度下容易发生。增加 O2 和蒸汽有利于降低整体烧焦率。随着蒸汽含量的增加，18%和21%的O2情况下烧焦率的降低不显着，但24%~30%的O2情况下则严重。增加 O2 和蒸汽有利于降低整体烧焦率。随着蒸汽含量的增加，18% 和 21% O2 情况下烧焦率的降低不显着，但在 24%~30% O2 情况下则严重。增加 O2 和蒸汽有利于降低整体烧焦率。随着蒸汽含量的增加，18% 和 21% O2 情况下烧焦率的降低不显着，但在 24%~30% O2 情况下则严重。