報告書番号

W98002

タイトル（和文）

微粉炭燃焼特性に及ぼす石炭中水分の影響 --石炭燃焼炉を用いた高水分炭の燃焼特性評価--

タイトル（英文）

Influence of Moisture in Coal on Pulverized Coal Combustion Characteristics- Combustion Characteristics of High Moisture Content Coal Investigated by Coal Combustion Test Furnace -

概要 （図表や脚注は「報告書全文」に掲載しております）

本研究では、褐炭および亜瀝青炭を用い、水分が微粉炭燃焼特性に及ぼす影響について検討した。(1)石炭粉砕時に蒸発し微粉炭搬送用空気に含まれるガス状水分量が増加するとNOx生成は抑制される。微粉炭中の残存水分に対しては、水分量が少ない場合にNOx生成は抑制されるが、水分量が極端に多くなるとNOx生成量も増加した。灰中未燃分は、水分形態に関わらず水分の増加に伴い増大した。(2)水分が非常に多い褐炭は、火炎温度の低下と共にNOx生成が抑制され、NOx転換率は低水分炭に比べ若干低くなった。一方、亜瀝青炭程度の水分量では、火炎温度の低下および酸素消費の遅れは少なく、NOx転換率は高くなった。燃焼効率は、両炭種とも活性面の反応性が高く、低水分炭よりも高くなった。(3)褐炭は、二段燃焼時に十分な還元雰囲気が形成されず、NOx低減効果は低くなった。亜瀝青炭は、低い二段燃焼率でもNOx低減効果は大きいが、二段燃焼率が高くなると低減効果は飽和した。

概要 （英文）

The utilization of coal is promoted because the reserves of coal are more abundant than that of other fossil fuels whose depletion is imminent. As the demand for coal is likely to increase worldwide, it is hoped that low grade coals that has not yet been used in thermal power stations can be utilized to reduce the power generation cost by reducing the fuel cost. The types of coal that should be considered for use are low grade coals with a low calorific value and a high moisture content or high ash content.This report describes the influence of moisture on the combustion characteristics of pulverized coal with lignite coal (weight ratio of moisture content to supply amounts as dry ash free =1.5) and sub-bituminous coal (same ratio = 0.3).(1) The increase of moisture in primary air, which was vaporized from coal at the mill, caused the decrease of flame temperature and the delay of oxygen consumption and suppressed NOx formation. On the other hand, the change of NOx concentration showed the concave curve according as the moisture amount increased. It was considered that the increase of vaporization amount at the biginning of combustion suppressed the release of volatile matter from coal and the reduction of NOx at the rear of flame. The unburned carbon in fly ash enlarged irrespective of the moisture form according as the amount of moisture increased. The ratio of moisture vaporized from coal at the same amount of moisture supplied to the furnacewas higher, both concentrations of NOx and unburned carbon in fly ash were lower. (2) It was found that the NOx conversion ratio of lignite coal whose vaporized moisture and remained moisture in coal were too high was slightly lower than that of low moisture coal, because the flame temperature decreased and the NOx formation was suppressed. On the other hand, as the decrease of flame temperature and the delay of oxygen consumption were slight at the level of moisture content with sub-bituminous coal, the NOx conversion ratio of sub-bituminous coal was higher. It was considered that the NOx formation and reduction of sub-bituminous coal were different from that of low moisture coal, because of high reactivity after the evaporation of moisture, and so on. The ash content was low in addition to the high reactivity on both types of coal, the combustion efficiency of these types of coal are higher than those of low moisture coal. (3) The NOx reduction effect of lignite coal by the two staged combustion method was lower than that of low moisture content coal, because the formation of reduction atmosphere near the burner was insufficiency. Sub-bituminous coal had high NOx reduction effect on condition that the two staged combustion ratio was low, but the effect was saturated according as the two staged combustion ratio was high.

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