Importance of maintaining an Oxidizing atmosphere at the Furnace Exit
Furnace slagging propensity is profoundly influenced by excess oxygen levels in the furnace.
To maintain an oxidizing environment, and prevent slagging, furnace oxygen levels should be uniform at 3.0% with no single point below 2.0% at the furnace exit. A reducing atmosphere (absence of oxygen), is conducive to slagging of furnace heat transfer surfaces because iron compounds in the coal undergo chemical changes which allow for a lower melting temperature of the coal ash. In areas of the furnace where there is adequate oxygen, pyrite (FeS2 ), is converted to Fe2O3 ( melting temperature of ~2900°F) and SO2. In reducing atmosphere, FeS2 can be converted to FeS ( that has a lower melting temperature of 2179°F-2190°F) and other ferric compounds of lesser oxidation that have lower melting temperatures. Ensuring the furnace exit is an Oxidizing atmosphere is also of critical importance in reducing Carbon in flyash, reducing formation of CO and prevention of coal-ash corrosion.