Interaction of Refractories and Alkaline Containing Corrodants

An extensive literature review has been completed and thermodynamic modeling has been employed to analyze the reactions between black liquor (BL) and aluminosilicates to understand the corrosion mechanisms of candidate refractories for the black liquor gasification (BLG). Interactions of different refractory materials exposed to alkali-containing atmospheres are reviewed. Black liquor is a water solution of the non-Cellulose portion of the wood (mainly lignin) and the spent pulping chemicals (Na2CO3, K2CO3, and NA2S). FactSage thermodynamic modeling software was used to analyze the phases present in BL and to predict the interaction of BL with refractory compounds from the AL-Si-O system. The modeling included prediction of the phases formed under the operation conditions of a high temperature BLG process. Development of the new refractory materials for BLG application is a critical issue for implementation of this technology. At the operating temperature of the BLG, FactSagepredicted that the water would evaporate for them BL and that the organic portion of the BL would combust, leaving a black liquor smelt composed of sodium carbonate (70-75%), sodium sulfide (20-25%), and potassium carbonate (2-5%). Exposure of the aluminosilicates to this smelt leads to significant corrosion due to formation of expansive phases and , subsequently, cracking and spalling. Literature reports suggest that AZS refractories will be superior to silicates, zircon, and aluminosilicates for resistance to reaction from the alkali compounds, but these materials all undergo deleterious reactions. Other refractory ceramics such as fused spinel (altered only on the surface) and silicon nitride (dissolved in black liquor smelt) were also considered. Based on thermodynamic calculations, it appears that magnesia refractories will be stable in contact with black liquor smelt.