The kraft papermaking process, which is by far the predominant method used in North America, depends on recovery of the chemicals used in the digesting or pulping operation. Currently, the black liquor recovery boiler is the heart of this recovery process, but replacement of this boiler with a gasification system is being intensively studied. A switch to gasification can be justified based on capital investment, energy efficiency, and safety, but there are a number of significant obstacles to its successful development and implementation. Identification of suitable materials for the containment of the reaction and the reaction products is considered one of the most critical issues. There are currently two distinct gasification processes being actively developed; a low temperature process in which the alkali salts are kept below their melting point, and a high temperature process in which these compounds are handled in the molten state. Each process has unique materials requirements and issues that are described in this paper. In addition, results from recent studies of the compatibility of gasifier components with the respective environments are presented.
Keywords: corrosion, materials degradation, gasification, black liquor, alkali salts, hydrogen sulfide, fluidized bed, slagging gasifier