Alkali attack of coal gasifier refractory linings

Thermodynamic calculations are used to study the alkali reactions in coal gasifier atmospheres. The reactive alkali and sulfur species released from coal are first calculated at temperatures from 800 K to 1900 K and pressures from 1 atm to 100 atm. Four P-T diagrams are constructed for the stable alkali and/or alkali-sulfur species at differ-ent temperatures and pressures. Alkali vapors are generated by the reactions

Na₂CO₃_(s) + 2C_(s) = 2Na_(g) + 3CO_(g)

Na₂CO₃_(s) + H₂O_(g) + C_(s) = 2NaOH_(g) + 2CO_(g)

or

K₂CO₃_(s) + 2C_(s) = 2K_(g) + 3CO_(g)

K₂CO₃_(s) + H₂O_(g) + C_(s) = 2KOH_(g) + 2CO_(g)

The phases formed from alkali-cement, and alkali-sulfur-cement reaction are also predicted. For both 53% and 72% alumina cement, calcium aluminate (CaO•Al₂O₃) is decomposed by the reactions

CaO•Al₂O₃ + 2Na + 1/20₂ = Na₂O•Al₂O₃ + CaO

CaO•Al₂O₃ + 2K + 1/20₂ = K₂O•Al₂O₃ + CaO

or

CaO•Al₂O₃ + 2Na + l/2S₂ = Na₂0•Al₂O₃ + CaS

CaO•Al₂O₃ + 2K + 1/2S₂ = K₂•Al₂O₃ + CaS