EFFECT OF CRYSTALLINE PHASE-FORMATION ON COAL SLAG VISCOSITY

The Texaco Gasification Process employs a high temperature and pressur e slagging gasifier, in which the viscosity of the slag plays a key ro le in determining operating conditions. Empirical models are available in the literature and predict slag viscosity as a function of tempera ture and composition, However, these models are applicable only to hom ogeneous slags. The formation of crystalline phases during cooling can significantly change the viscosity, and the models often fail to pred ict correct slag viscosity behavior. The formation of crystalline phas es and its effect on slag viscosity were studied in four coal slags. T he four coals include SUFCo, Pittsburgh No. 8, and two Powell Mountain coals (A and B). Slag viscosity was measured at temperatures in the r ange of 1150-1500 degrees C under reducing atmosphere. The slag viscos ities of Sufco and Powell Mountain A (PMA) coals exhibited the behavio r of a glassy slag, of which the viscosity gradually increases as the temperature decreases. The other two, Pittsburgh No. 8 and Powell Moun tain B (PMB), showed the behavior of a crystalline slag with T-cv of 1 300 degrees C and 1430 degrees C, respectively. Crystalline phase anal ysis of the slag samples revealed that extensive network formation of dendrite spinels in Pittsburgh No. 8 and PMB caused a rapid increase i n the viscosity, while anorthites in SUFCo and large spinels and elong ated particles of corundum in PMA did not affect the slag viscosity as much.