Refractory Selection for High Temperature Black Liquor Gasification

A methodology has been established for the selection of materials for refractory linings in black liquor gasifiers that are to be employed by the pulp and paper industry. As a first step, a thermodynamic software package was used to determine that black liquor smelt was composed of a liquid solution of primarily Na2CO3 and Na2S under the operating conditions of the gasifier (950 degrees C, 1 atm). Next, the software was used to predict the interaction of the black liquor smelt with various ceramics such as aluminosilicates, single component oxides, and binary oxides that are candidates for the application. Finally, experiments were performed to verify or disprove the predictions. Using sessile drop testing, contact angles were determined for molten Na2CO3 on candidate refractory compounds. All of the candidate ceramics were wet by molten Na2CO3. Among the candidates, MgAl2O4 was found to have the highest contact angle (similar to 13 degrees). Post-mortem analysis was performed on sessile drop specimens using X-ray diffraction analysis and scanning electron microscopy with energy dispersive spectroscopy to determine if molten Na2CO3 had penetrated into or reacted with the ceramics. From the candidates, MgO and CeO2 were found to have the best resistance to attack, while MgAl2O4 was also found to be a promising candidate