報告書番号

W99014

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１） -－バーナ操作条件の影響評価－-

タイトル（英文）

Study of Control NOx Emission and Unburned Carbon Concentration in Fly Ash on the Sub-bituminous Coal Combustion (Part.1)

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(燃焼量:0.1t/h)において、亜瀝青炭の中でも水分含有率が40％と高いワラ炭を用いて、燃焼火炎の特徴を明らかにすると共に、NOxと灰中未燃分の排出を抑制できるバーナ操作条件について検討を行った。瀝青炭を用いた場合と同様のバーナ操作条件で燃焼させた場合は着火が遅れると共に火炎が広がり、火炉から排出されるNOx・灰中未燃分が多く、その傾向は粉砕時に蒸発する水分が少なく微粉炭中に残存する水分が高い場合ほど顕著になることを把握した。バーナ操作条件の調整を行い、２次空気の旋回角度を弱めることにより、着火が安定し、NOxと灰中未燃分の排出量が同時に低減できることがわかった。さらに、１次空気の供給量を減少させると、NOxのより効率的な還元・分解の促進が図れ、火炉出口でのNOx濃度が一層低減でき、その効果は最も微粉炭中水分濃度の高い石炭のNOx低減において顕著であることを明らかにした。

概要 （英文）

At present, bituminous coal, whose calorific value is high and which is good for an environment, is used in thermal power stations in Japan. Since the demand for coal utilization is increasing worldwide and the cost of bituminous coal will be higher, low rank coal, whose calorific value is low, will be a major resource for thermal power plants in the near future. Sub-bituminous coal, the reserves of which is more abundant than that of other low rank coal, should be a fuel of great promise. Problems in the utilization of sub-bituminous coal include not only the worse of combustion efficiency but also the control of the NOx emission because of high moisture content in coal. In order to utilize the sub-bituminous coal for a coal fired power plant, it is necessary to reduce the NOx emission and unburned carbon concentration in fly ash. This report describes the combustion characteristics of sub-bituminous coal, moisture content of which is 40 %, and the influence of flow condition of CI-α burner on the NOx emission and unburned carbon concentration in the fly ash on the pulverized coal test furnace (coal combustion rate; 0.1 t/h).1) The ignition condition of sub-bituminous coal is worse because of high moisture content in coal, therefore, it is impossible to make the reduction flame after the burner outlet since the ignition of coal is delayed and the combustion flame diffuse when the combustion condition is adopted for the bituminous coal. It was found that the NOx emission at the exit of the furnace and unburned carbon concentration in fly ash became high with the increase of the inherent moisture in coal.2) When the swirl vane angle of secondary air is low, the ignition condition improves, the flame shape of the sub-bituminous coal becomes narrow and NOx concentration at the exit of furnace decreases. Furthermore, when the volume of primary air decreases to save the velocity of pulverized coal at the burner outlet, the flame grows stable and NOx reduction region before the air injection port for two stage combustion increase. As a result, it was found that the NOx concentration at the exit of furnace becomes much lower.3) When the swirl vane angle of secondary air was settled optimum position and the volume of primary air was controlled to save, both NOx emission at the exit of the furnace and unburned carbon concentration in fly ash decreased. The tendency of the decrease of the NOx emission became much higher on the high moisture content coal. It was obvious that the NOx reduction ratio was about 40 %.

報告者

キーワード