報告書番号

W97023

タイトル（和文）

石炭中灰分が微粉炭燃焼特性に及ぼす影響－石炭燃焼炉を用いた高灰分炭の特性評価－

タイトル（英文）

INFLUENCE OF ASH CONTENT ON PULVERIZED COAL COMBUSTION CHARACTERISTICS -COMBUSTION CHARACTERISTICS ON HIGH ASH 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）

本報告書では，高灰分炭燃焼時に石炭中灰分の含有量が微粉炭燃焼特性に及ぼす影響について以下のことを明らかにした。（１）高灰分炭の非二段燃焼時におけるＮＯｘ濃度は，灰分含有率が高くなるほど増大することが明らかになった。一方，高灰分炭燃焼時の灰中未燃分濃度としては低い値を示したが，未燃焼率は灰分含有率が増加するほど高くなった。（２）灰分含有率が高くなるに従い酸素の消費が遅れると共に，ＮＯｘの生成・分解が遅くなり，その結果，火炉出口でのＮＯｘ濃度が高くなった。高灰分になると，灰分によって奪われる熱量が多くなると共に，可燃分が灰分に覆われ易くなり，燃焼性が悪化するためと考えられる。（３）高灰分炭燃焼時には，二段燃焼によるＮＯｘ低減効果が弱まり，未燃焼率は増加することが明らかとなった。これは，酸素の消費が遅れることから，石炭の熱分解が抑制されると共にＮＯｘ還元領域が減少したことによると考えられる。

概要 （英文）

THE PROBLEMS OF HIGH-ASH COALS ARE BOTH THE AMOUNT OF ASH AND THE IGNITION OF PULVERIZED COAL. TO USE HIGH-ASH COALS IN CONVENTIONAL PULVERIZED COAL POWER PLANTS,IT IS NECESSARY TO UNDERSTAND THE EFFECT OF ASH ON COMBUSTION CHARACTERISTICS. THIS REPORT DESCRIBES THE COMBUSTION CHARACTERISTICS OF THREE HIGH-ASH COALS WITH THE SAME RATIO OF COMBUSTIBLE COMPONENTS AND VARIOUS ASH CONTENT (36,44 AND 53 WT.%) USING A PULVERIZED COAL COMBUSTION TEST FURNACE (0.1 T/H). (1)AT SINGLE-STAGE COMBUSTION,THE NOX CONCENTRATION ROSE AT THE FURNACE OUTLET WITH INCREASING ASH CONTENT. THE CONVERSION RATIO OF FUEL-BOND NITROGEN TO NOX WAS HIGHER THAN THAT OF THE BITUMINOUS COALS WITH SIMILARCOMBUSTIBLE COMPONENTS. ALTHOUGH THE CARBON CONTENT IN FLY ASH DECREASED BECOUSE THE AMOUNT OF ASH WAS HIGH,THE NON-COMBUSTION FRACTION WAS HIGHER THAN THAT OF BITUMINOUS COALS WITH A SIMILAR FUEL RATIO. (2) O2 AND NOX CONCENTRATIONS IN THE FURNACE SHOWED SOME DIFFERENCE BETWEEN COMBUSTION OF HIGH-ASH AND LOW-ASH COALS. AS ASH CONTENT INCREASED,THE FLAME BECAME DARK AND LONG,AND THE RATE OF O2 CONSUMPTION DECREASED. THEREFORE,THE RATE OF NOX FORMATION AND REDUCTION WAS DELAYED AND NOX CONCENTRATION ROSE AT THE FURNACE OUTLET. THE DECREASE IN COMBUSTION RATE IS PROBABLY DUE TO COVERAGE OF COMBUSTIBLE COMPONENTS BY ASH AND THE LARGESENSIBLE HEAT OF ASH. (3) ALTHOUGH TWO-STAGE COMBUSTION EFFECTIVELY DECREASED NOX AT THE FURNACE OUTLET,THE INCREASE OF NOX AS A FUNCTION OF ASH CONTENT WAS HIGHER THAN THAT OF SINGLE-STAGE COMBUSTION. THIS IS DUE TO THE DECREASE IN THE NOX-REDUCTION REGION UPSTREAM OF THE AIR INJECTION PORT BECOUSE THE COMBUSTION RATE BECAME MUCH LOWER FOR HIGH-ASH COAL AT TWO-STAGE COMBUSTION. THE NON-COMBUSTION FRACTION WAS HIGHER AT TWO-STAGE COMBUSTION THAN SINGLE-STAGE COMBUSTION. THE INCREASE IN THE NON-COMBUSTION FRACTION AS A FUNCTION OF ASH CONTENT WAS ALSO HIGHER AT TWO-STAGE COMBUSTION BECAUSE OF THE LARGE FALL IN COMBUSTION RATE.

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