REFRACTORIES FOR BLACK LIQUOR GASIFICATION

gasification (BBLG). One particularly harsh application is linings for gasifiers used in the treatment of black liquor (BL). Black liquor is a water solution of the non-cellulose portion of the wood (mainly lignin) and the spent pulping chemicals (Na۲CO۳, K۲CO۳, and Na۲S). Development of new refractory materials for the black liquor gasification (BLG) application is a critical issue for implementation of this technology. FactSage® thermodynamic software was used to analyze the phases present in BL smelt and to predict the interaction of BL smelt with different refractory compounds. The modeling included prediction of the phases formed under the operating conditions of high temperature black liquor gasification (BLG) process. At the operating temperature of the BLG, FactSage® predicted that the water would evaporate from the BL and that the organic portion of BL would combust, leaving a black liquor smelt composed of sodium carbonate (۷۰-۷۵%), potassium carbonate (۲-۵%), and sodium sulfide (۲۰-۲۵%). Exposure of aluminosilicates to this smelt leads to significant corrosion due to formation of expansive phases with subsequent cracking and spalling. Oxides (ZrO۲, CeO۲, La۲O۳, Y۲O۳, Li۲O, MgO and CaO) were determined to be resistant to black liquor smelt but non-oxides (SiC and Si۳N۴) would oxidize and dissolve in the smelt. The other candidates such as MgAl۲O۴ and BaAl۲O۴ were resistant to sodium carbonate but not to potassium carbonate. LiAlO۲ was stable with both sodium carbonate and potassium carbonate. Candidate materials selected on the basis of the thermodynamic calculations are being tested by sessile drop test for corrosion resistance to molten black liquor smelt. Sessile drop testing has confirmed the thermodynamic predictions for Al۲O۳, CeO۲, MgO and CaO. Sessile drop testing showed that the thermodynamic predictions were incorrect for ZrO۲.

Keywords:

Black Liquor Gasification , Aluminosilicate , Oxide and Non-oxide Refractories.