Slag characterization for the development of new and improved service life materials in gasifiers using flexible carbon feedstock

In modern gasifiers, the carbon feedstock (coal, petcoke and/or biomass) is determined largely by carbon content, cost, availability, and environmental concerns. Ash impurities in the carbon feedstock vary widely in quantity and chemistry, impacting gasifier operation. Ash from mineral impurities in the feedstock liquefy at the elevated temperatures of gasification; impacting slag chemistry, viscosity, melting temperature, surface and interfacial tension - ultimately determining gasifier operating temperature and refractory service life. The slag itself experiences wide variations in the relative fraction and state of crystalline material (oxides, sulfides and metallic), non-crystalline (glass) material, or gas phases formed from feedstock ash. It is these variations that have a critical impact gasifier operation, determining slag fluidity along the walls and the chemical and physical stability (wear) of the refractory liner. In this paper, two aspects of joint research between NETL and CMU on slag and slag/refractory interactions will be discussed. The first area is researching phase formation in synthetic petcoke/coal slag (SiO ₂-Al₂O₃-Fe₂O₃-CaO-V ₂O₃) under simulated gasification conditions (1500°C and 10^-8 arm oxygen partial pressure). The second area focuses on interactions between coal and petcoke slags with commercial refractory currently used (high chrome oxide) or having the potential for use as a gasifier liner (high alumina). Refractory materials studied in the simulated gasifier environment were fired brick of the following compositions: 90wt%Cr ₂O₃-10wt%Al₂O₃ and 100wt%Al ₂O₃. Information from this research is being used to improve the performance of or to develop new refractory liner materials for gasifiers, and to understand mixed feedstock slag behavior under gasification conditions.