報告書番号

W00018

タイトル（和文）

亜瀝青炭燃焼時のNOx・灰中未燃分低減方法の検討（その２） -－ 二段燃焼用空気注入条件の影響評価 －-

タイトル（英文）

Investigation of Low NOx and Low Unburned Carbon Concentration Combustion on Pulverized Sub-bituminous Coal (Part. 2)- Influence of Injection Condition of Staged Combustion Air -

概要 （図表や脚注は「報告書全文」に掲載しております）

石炭燃焼量100kg/hの燃焼試験炉を用いて、亜瀝青炭燃焼時のNOx・灰中未燃分の排出特性に及ぼす二段燃焼用空気の注入条件の影響について検討した。その結果、二段燃焼用空気の注入位置を後流にすると、NOx濃度は低下し、その低減効果は飽和する傾向を示した。一方、その際の灰中未燃分濃度は注入位置が後流になるほど増加し、その傾向はバーナから約4ｍ離れた位置以降で特に顕著になった。また、二段燃焼率の増加に応じて、NOx濃度は低減したが、その低減効果は二段燃焼率30％以上で飽和する傾向を示した。一方、灰中未燃分濃度は、二段燃焼率が高くなると増加するものの、二段燃焼率20％と30％の条件ではほぼ同等となり、40％まで増加すると、急激に灰中未燃分が増加した。これより、亜瀝青炭に適した二段燃焼用空気の注入位置は、バーナから約4ｍ離れた箇所で、二段燃焼率は30％程度であることが明らかとなった。

概要 （英文）

At present, coal-fired power stations in Japan use mainly bituminous coal as fuel. Since coal consumption is increasing worldwide and bituminous coal will be in short supply in the near future, the low rank coal with lower calorific value will become an important fuel. Sub-bituminous coal, which contains more than 20% moisture, is looked to as a substitute fuel for bituminous coal, as the reserve is the most abundant among the low rank coal. We have already clarified that the emissions of NOx and unburned carbon in the fly ash enable to be reduced when the combustion air injection conditions of the burner adjusted effectively for sub-bituminous coal. However, those emissions are expected to be reduced still more. This report describes the influence of the two-stage combustion condition on the emission characteristics of NOx and unburned carbon in the fly ash of sub-bituminous coal combustion. This research was conducted using a pulverized coal combustion test furnace attached the CI-α burner. Main results are as follows.1. When the air injection point for two-stage combustion is settled downstream in the furnace, NOx concentration decreased at the exit of the furnace since the NOx reduction area before the injection point for two-stage combustion increased. The effect of NOx decrease became worse at a distance of 4m from the burner outlet. Then, the unburned carbon concentration in fly ash increased when the air injection point for two-stage combustion is settled downstream in the furnace. The tendency of increase of the unburned carbon concentration became much high at the distance of 4m from the burner outlet.2. When the ratio of the injection air for staged combustion increased at the distance of 4m of the injection point, NOx concentration at the exit of the furnace decreased. The effect of NOx decrease is saturated over 30% ratio of two stage combustion. The unburned carbon concentration in fly ash became high. The unburned carbon concentration in fly ash at the ratio of 20% of two-stage combustion was the almost same as the unburned carbon concentration at the ratio of 30%. When the ratio of the injection air for two-stage combustion was 40%, the unburned carbon concentration increased rapidly. As a result, the injection condition for two-stage combustion suited for sub-bituminous coal is that the injection point is the distance of 4m from the burner outlet and the injection ratio is 30% The injection point of two-stage combustion for sub-bituminous coal became later than the injection point for bituminous coal. 3. It was cleared that NOx concentration and the unburned carbon concentration were much lower when both the burner condition and the injection condition for two-stage combustion were suit for sub-bituminous coal, NOx concentration at the exit of the furnace was between 100ppm and 160ppm. The unburned carbon concentration was under 15%. These value were reduced as the same as the value of bituminous coal combustion.

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