報告書番号

285017

タイトル（和文）

石炭燃焼時のサブミクロンばいじんの生成機構と抑制に関する調査

タイトル（英文）

THE FORMATION AND CONTROL OF SUBMICRON INORGANIC PARTICLES PRODUCED DURING PULVERIZED COAL COMBUSTION

概要 （図表や脚注は「報告書全文」に掲載しております）

本報告は，石炭中の灰分に起因するサブミクロンばいじんの生成機構について調査，検討し，併せて生成抑制の可能性について考察を加えたものである。１．微粉炭燃焼により生じるサブミクロン粒子は，揮発分に起因する気相析出型炭素（煤）と，灰分よりなるばいじんに分けられる。このうち後者はチャーが分割して燃焼することによる分裂生成と，チャー表面における灰分の還元，蒸発，外部への拡散，酸化を経る均質相核生成の二つの機構よりなる。２．均質相核生成によって生じた核粒子は衝突，融合によって急速に粒径を増し，炉内で０．１μｍ前後にまで成長する。３．サブミクロンばいじんの抑制には，分裂生成型のものについては，微小粒径の微粉炭の除去，均質相核生成によるものについては，チャー燃焼場の混合促進，あるいは燃焼温度を低下させ還元を抑制する方法が考えられる。

概要 （英文）

THE FORMATION MECHANISM AND THE CONTROL OF SUBMICRON INORGANIC PARTICLES ARE INVESTIGATED. THE SUBMICRON PARTICLES PRODUCED BY COAL COMBUSTION ARE THOSE OF SOOT, WHICH FORMED FROM UNBURNED VOLATILE MATTER, AND THOSE OF ASH TRANSFORMED FROM MINERAL MATTER CONTAINED IN COAL PARTICLES. THE LATTER ARE GENERATED THROUGH TWO KINDS OF PATHS, WHICH ARE THE BREAKING-UP FORMATION AND THE HOMOGENEOUS NUCLEATION. DURING CHAR COMBUSTION A CHAR PARTICLE BREAKS UP INTO SEVEVAL FRAGMENTS AND AFTER THEY BURN OUT ASH PARTICLES REMAIN. IN THIS MECHANISM MOST OF THE PARTICLES ARE GREATER THAN 0.3 MICRON M, BECAUSE THE AMOUNTOF SUBMICRON COAL PARTICLES IS VERY LITTLE. HOWEVER, THE LOCALLY REDUCING ATMOSPHERE EXISTS WITHIN A CHAR PARTICLES DURING COMBUSTION. SOME FRACTION OF REFRACTORY OXIDES ARE REDUCED TO VOLATILE SUBOXIDES OR ELEMENTS WHICH DIFFUSE AWAY FROM THE BURNING PARTICLE. ON ENCOUNTERING OXYGEN THESE SPECIES ARE REOXIDIZED TO PRODUCE A HIGH DEGREE OF SUPER SATURATION. THEN THE OXIDES HOMOGENEOUSLY NUCLEATE AND GROW RAPIDLY TO SUBMICRON PARTICLES BY COALESCENT COLLISION AND BY HETEROGENEOUS CONDENSATION. THEIR DIAMETERS ARE AROUND 0.1 MICRON M AND THEY ARE SOMETIMES CALLEDFUME WHICH MEANS SMALL SOLID PARTICLES CONDENSED FROM VAPOR. FOR THE CONTROL OF SUBMICRON INORGANIC PARTICLES THERE ARE SOME SUGGESTION FROM THIS RESEARCH. THAT IS, TO DECREASE THE PARTICLES WHICH COME FROM BROKEN-UP FRAGMENTS AND REMOVE THE VERY SMALL COAL PARTICLES, TO NARROW THE REDUCING ATMOSPHERE BY ACCELERATING MIXING OF THE CHAR COMBUSTION ZONE,AND TO DECREASE THE AMOUNT OF REDUCED FRACTION BY LOWERING THE COMBUSTION TEMPERATURE.

報告者

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