報告書番号

W99006

タイトル（和文）

火炉内における微粉炭燃焼場の数値シミュレーション（その1）k-ε2方程式モデルを用いた検討

タイトル（英文）

Numerical simulation of a pulverized coal combustion in a furnace

概要 （図表や脚注は「報告書全文」に掲載しております）

火炉内の旋回を伴う微粉炭燃焼場に対して三次元数値シミュレーションを適用し，実験値との比較を行なうことによって，数値シミュレーション結果の妥当性を検証した。また，石炭中の水分が微粉炭燃焼特性に及ぼす影響を検討した。その結果，以下の知見を得た。 (1)流れ場，温度場，濃度場の計算に対してはk-ε2方程式乱流モデルを，また，燃焼反応や輻射伝熱の計算に対しては適宜最適なモデルをそれぞれ用いた数値シミュレーションにより，火炉内の諸微粉炭燃焼特性量が有する傾向については十分予測可能である。また，計算値と実験値との差異は，k-ε乱流モデルの旋回流れ場に対する精度上の問題から，旋回が最も強いバーナ近傍領域において顕著になる。 (2)石炭中水分の増加に伴い，バーナ近傍領域における火炎温度およびNO濃度は減少し，O2濃度は増加する。また，未燃焼率は増加，NO転換率は減少する。

概要 （英文）

Coal is an important energy resource to cope with the future demand of electricity because its reserves are more abundant than that of other fossil fuels. In understanding the behaviors of the combustion quantities in a pulverized coal firing boiler and determining the optimal operating conditions, computational fluid dynamics (CFD) can provide an effective platform where a variety of coals and operating conditions can be tested at a relatively low cost. However, the reliability of the CFD for a coal combustion has not been elucidated enough yet because of the limit of the computational resources and the uncertainties of the some numerical models. The purpose of this study is, therefore, to apply the three-dimensional CFD using k-ε two-equation turbulence model to a pulverized coal (bituminous coal) combustion with swirl in a furnace, and to assess the validity of the resolutions. In addition, since in the near future low grade coals with high moisture content are considered to be utilized, the effects of moisture in coal on combustion quantities are investigated. The main result can be summarized as follows. (1) The predicted combustion quantities are in general agreement with the measurements. However, because of the low accuracy of the k-ε two-equation turbulence model in the swirl flows, the prominent differences in the distributions of the flame temperature and O2 and NO mole fractions are observed in the region near the burner where the swirl is strong. (2) With increasing the moisture content in coal, the flame temperature and O2 and NO mole fractions in the region near the burner decreases, increases, and decreases respectively, and the positions where the flame temperature and NO mole fraction show the maxima shift downward. Also, the moisture content causes the increase of the uncombustion fraction and the decrease of the conversion ratio to NO.The trends are similar to those given by previous measurements.

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