EXPANDED USE OF HIGH-SURFUR, LOW-FUSION COALS IN UTILITY BOILERS: EFFECT OF ADDITIVES

摘要

This paper reports on the ability of Mg(OH)_2 to control slagging at the Petersburg plant of Indianapolis Power and Light. This plant fires the 8.5-10 percent ash (ar), 20-25 percent Fe_2O_3 in ash, and 3-8 percent CaO in ash, 1050-1100 C Initial Deformation Temperature (reducing) Lynville Coal into a 440 MWe tangentially-fired boiler with plantent superheaters. This combination produces difficult slagging deposits on the north side of the boiler between the nose and the reheater. A slurry of Mg(OH)_2 was injected in the corners of the boiler above the burners. The injection of Mg(OH)_2 increased the MgO (oxidization product of Mg(OH)_2) in the deposits, reduced the Fe_2O_3 concentration in the south reheater deposit, and did not eliminate slagging, but did make the north side reheater deposit more friable. Use of x-ray mapping techniques shows that MgO enters the melt by direct infusion into the melt, ingestion into the melt, and partial infusion which coats the fly ash particles. The MgO is specifically ingested into FeO - AI_2O_3 - SiO_2 melt. There, MgO exchanges with FeO to form equivalent MgO- AI_2O_3 - SiO_2. The MgO compounds all have higher melting points than the corresponding FeO compounds. This paper used phase diagrams to estimate that the slagging problem at the Petersburg plant would be eliminated if the amount of MgO in the deposit were approximately doubled.