報告書番号

W00017

タイトル（和文）

亜瀝青炭燃焼時のNOx・灰中未燃分排出特性 -－ 瀝青炭との混焼時の特性評価 －-

タイトル（英文）

Emission Characteristics of NOx and Unburned Carbon in the Fly Ash on Pulverized Combustion of Sub-bituminous Coal- Characteristic of Blending Combustion of Sub-bituminous Coal and Bituminous Coal -

概要 （図表や脚注は「報告書全文」に掲載しております）

石炭燃焼試験炉を用いて、瀝青炭燃焼時と同様のバーナ操作条件における亜瀝青炭と瀝青炭との混焼時のNOx・灰中未燃分排出特性を評価し、混炭時にこれらの排出量を抑制できるバーナ操作条件について検討を行った。混焼時のNOx排出量は、それぞれを単味燃焼した際のNOx排出量の中間となることが明らかとなった。一方、灰中未燃分濃度は、灰中未燃分濃度の低い瀝青炭と組み合わせても低減できず、未燃焼率はいずれの混炭率においても専焼時の値よりも高くなり、低い混炭率で極大値を示した。これは、亜瀝青炭に含まれる水分が蒸発する際の潜熱の影響により、火炎温度が低下することや、生成した水蒸気によってO2分圧が低くなるためと考えられる。２次空気の旋回強度を混炭率に応じて調整すると、着火の安定により灰中未燃分濃度が低減でき、また、二段燃焼用空気注入位置までの還元領域が広がるため、NOx排出量の低減も可能になった。

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 coals. Problems involving the utilization of the sub-bituminous coal are the low ignitability and combustion efficiency caused by the moisture in the coal. Control of NOx emission will also be necessary. Therefore, Sub-bituminous coal will be fired with bituminous coal for the moment. This report describes the emission characteristics of NOx and unburned carbon in the fly ash of sub-bituminous coal combustion blended with bituminous coal. This research was conducted using a pulverized coal combustion test furnace (coal combustion rate: 0.1 t/h) attached the CI-α burner. Furthermore, in order to optimize combustion conditions for sub-bituminous coal, we investigated the influence of the swirl force of secondary air on the emissions of NOx and unburned carbon in the fly ash. Main results are as follows.1. When the sub-bituminous coal is fired with bituminous coal, NOx emission at the exit of the furnace is moderate between that of bituminous coal combustion and that of sub-bituminous coal combustion.2. The unburned carbon concentration of the sub-bituminous coal combustion blended with bituminous coal is higher than that of the bituminous coal combustion. Then, combustion efficiency of blended coal is lower than that of each coal combustion and becomes the lowest when the blended ratio of sub-bituminous coal is about 25%. The reason of decrease of the combustion efficiency is considered that one is the decrease of the flame temperature because of the latent heat of moisture in the sub-bituminous coal and the other is the decrease of the oxygen concentration around the pulverized coal caused by the vaporized moisture.3. When the swirl force condition, meaning swirl vane angle of secondary air, is optimized for sub-bituminous coal, ignition condition improved and the consumption of oxygen is accelerated. The NOx reduction region before the air injection port for the two-stage combustion becomes wide. As a result, the emissions of both NOx and unburned carbon in the fly ash decrease. Furthermore, the reduction ratio of NOx and unburned carbon increase for higher blended of sub-bituminous coal.

報告者

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